=37but _ hope someone e_se that is working in ,_hisfie_d can°
Dr o Lush, go ahead.
_n the plant wor_d, they do know some marvelous series of' multiple o_AeAesamong the
seif_s_er_ity genes° Wherever you have se!f-steriIHy of' such a nature that a poARengrain car_
rying a g_ven gene cannot grow down the stySe of a plant that has .that same gene in e_ther _ocus,
you must have c_t_east three genes to keep the system going o NaturaA seAect_on favors the rarest
gene of the seHes o You m_ght ca_ _hot extreme overdom_nonce, because onAy the heterozygotes
can be formed _n the first place. And _hen each hete_ozygate can be poA_inc_tedonAy by pollen
carrying some aR_ele which is different from the two in the plcmt itse_fo _ think they know up to
forty different al_e_es _n some of _hase ser_eso Now thr_t _sso extreme o case because the homo_
zygotes can't even exist that _ wonder whether _t con foirAy be calAed overdominanceo At any
ra,te_ there _s that body of knowledge about heterosis and muAt_p_e a_ieteso
Sweet Clover _sst_ll another case°
Dro Lerner, you scare me, _m afraid we°re going to end up by breeding these birds from
the test tube° _°ve been watching a_ this antigen group dea_ going a_ongo _m not a very good
laboratory technician°
-__-e-_her
am _.........................
----1
Dr o Lush, _ went to _ake this opportunity to thank you° _t h_s been very good° _ think we
a_ got a _ot out of it. We°_ a_l take a break for 15 minutes at this time° We al_ heard Dr.
D_ckersonOs _ntroduct_on this morning so _m not going to repeat his h_storyo We have assigned
to Dr o Dickerson "The Advantages and Disadvantages of Progeny Testing o" We thought long and
hard to make up that one° _ think it is only fair to se,_ how he handles _to Go oheod_ Dr°
Dickerson o
-.,_ , _/,_ _:_o
_t seems to me that this meeting today, _n itself, _s a good e×amp_e of heterozygote
superiority or overdom_nonce or whatever you want to ca_ it_ because we college professors
ere _ong on pencils and cho_k_ but short on experimental
data° You f'e_[ows have _o_sof ch_ckenso You should have lots of data° Maybe if we ge_ together more often there w_ be a _ittle
hybrid vigor _n _ea.rn_nghow to breed poultry more effective_yo _s it a_ right to embark that
far _nto your topic, Dr o Lush ?
Progeny testing h_s es Hs chief advantage increased accurc_cy in eva_uating individuals°
We a_l recognize that_ end it has cflreody been mentioned that when you average the performonce of a I_.rge numbe_ of" progeny from an _ndiv_dua_ _ the environmento_ influences which
d_ffer between indiv_dua_ progeny tend to be cancelled out° Hence, progeny tesHng e_minates
some of the nongenet_c sources of error _n eva_uat_ng individuals depending upon the adequacy
of the test° This has _ong been recognized,
but _t _s the chief advantage of progeny testing,
neverthe_esso A[so_ eva_uafing an animal on the b_s_s of progeny performance tends to e_imi.=
note error from nonaddifive gene _ction_ the kind of gene action Dr o Lush was ta_king about°
The effects of dominance end gene interaction may make _n _nd_vidua_s performance d_ffer
from its average transmitting obi_ityo Another p_us factor for progeny testing that m_ght be
mentioned before we get into det_s_
_s that some of the newer methods of deliberately
selecting for maximum cross peHormance between particular strains require progeny testing as the
only too_ or bas_s of se_ect_on which w_l take you where you went to gOo
Same of the disadvantages of progeny testing will net be new to you either. The main one
_s the sharply reduced intensity of selection that _spossible on the 'basis of progeny tests° This
comes about _rst, because we can only progeny test a very _mited number of _nd_viduals compared to the tota_ number produced° _f we are going to save any of those tested for further use
on the bas_sof their superior progeny performance,
we must save a fairly _arge proportion of
the whole number tested, because we.hove a relatively sma_ group of tested birds from which
-38ta select_ Morta!_ty among breeding birds further reduces opportunity for seAection based on
progeny test,depending on how adequately management is able to control mortality
among
breeders° _n addition to the higher mortaAity among the birds that have been p_ogeny tested,
there _s the reduced fertility
of' tested maAes and the Jower AeveRof egg production of tested
females which limit reproduction af _he progeny tested b_rds as compared to the cockerel and
pulRet breeders° A_ of those things tend to make the amount of se_ect_on that con be based on
progeny testing sma_ compared to the intensi_y of selection that can be practiced on the basis
af _nd_v_dual or family perforrr_nce among pulAets and cockerel breeders..
That, to me, summarizes the c_dvantages and disadvantages of progeny testing°
However,
we do need to consider the system of breeding foAIowedo RfweBre to determine how much emphases should be g_ven to progeny testing in _he breeding program, we can consider by cont_,ast,
two different systems of breeding° One is the closed flock system of breeding, _n which you have
a s_ngle homogeneous popuAation, a s_rain of purebred pouAtry or a standard-bred strain of pouitry_ The other system of' breeding _sone in which the breeder is selecting directly for improved
performance of a cross between two d_fferent strains° Of course, the ro_e of progeny testing wil_
be qu_te d_fferent in the two ceses_
think it _sfair to say that the optimum use of progeny testing for se_ect_on within c_osed
f_ocks depends, in part, on the leve_ of performance af the breeder°s _lock_ _n a flock where
se_ect_on based on _ndividua_ and family performance with _itfle emphasis on p_ogeny testing
has been practiced for many generations, perhaps fifteen or twenty yea.rs, and a relatively high
leve_ of performance has been achieved,
the rate of further _mprovement from that kind of selection may be s_ghto Under such conditions,
relatively heavy use of progeny tested birds wou_d be
ind_catedo The obiective ' _n the case of overdom_nance, _s to get a c_oser approach _o the optimum equilibrium
gene frequency° _n the case of intermediate optimum type of Bnher_tance._
you're se_ectlng to _,ncrease the proportBon of the gametes produced by the breeders that are in
the _ntermediate cc_tego_y_
_f by contras_ a breeder is _n the early stages of a breedBng program to establish a new
strain, s_art_ng with e_ther unimproved stock or w_th stock that _s (_ mi×.ture of many dBfferent
strc_ns, then A think the emphasis on progeny testing general_y should be kept rather _ight.and
the emphasis on _ndividual and family performance relatively heavy_ Here we could ignore for
some time the effects of dominance and gene _nterc_ction that we have been discussing, and the
optimum proportion of breeders selected on the bas_s of a fu_ year_s family performance and a
part year progeny test wou_d be relatively
_OWo_ th_nk perhaps _ use the b_ackboard a _itfle
bBt here to i_us_rate what _m after°
We're ta_k_ng about a c_osed f_ock system of breeding, a flock in which some progress _s
being made from _ndividual and family se_ect_ano What is the optimum proportion of tested
breeders to use as compared _o pu_et and cockere_ breeders ? Pu_et breeders wou_d be selected
after three or four months production on the bas_saf part year famB_y and _ndividua_ performance.
_n selecting cockerels for egg production you would have to rely on the part year performance of
their s_sterso The tested b_rds _hat _Bm ta_king about in thls example would be the year_ng hens
that have a full=year _ndiv_dual and family egg production and c_part-year progeny test° These
year_ing hens are birds that were used as pu_e_- breeders. C)n the basis of their full year family
and individua_ performance and their p(_rt year progeny test_ you°re going to pBck a portion of
those b_rds that were used as pu_et breeders _ast year to use again as year_ng breeders this year°
have had an admonition from the chairman to keep thBs simp_eo Joe said that everything
had been f_ne up to now° Dr o Lush, you can fee_ very good about that° But Joe is apprehensive
about the future° _ ta_d him that perhaps _ should be, too, but 0 wasn't going to wor_y about ira.
_39_
,
We w_lA make a rough chart showing a_ong the bottom the proportion of the matlngs that
a:re with males selected on the basis of progeny test, in th_s cc_sethe percent say of ten tested
maAeS,o On the s_de we have expected yearly progress, the measure of your expectation of genetic improvement for each unit of time. _m not going to put in the numerical figures along
here because they are expressed _n terms of the s'_andard deviation of genotypes and that would
not be good at alA, would _t? But we will put in some definite proportions of tested maAes,
ranging from 0% to 50% ° Suppose we are housing approximately
ten puARetsfrom each female
breeder used, or fuA_=.sibfamiA_es of ten b_rds each. The next thing we_ve got to decide _s the
number of roofings per mOrea Suppose that the number of dams per maAe _sa_so ten, and that
we house roughly a ]000 puA_ets each year. Out of a hundred female breeders, mated to ten
mcfles, we will house, roughAy, ten puARetsfrom each femaAe breeder used° That, by the way,
is about the number of pu_ets you might expect to house per breede_ w_th a normal hatching
season, at lec_st w_th us° Now, suppose we examine progress to be expected from select_Ono Bf
we use only pulRet breeders_ we w_Rl choose one hundred breeders out of the thousand housed.
Using ten _ema_es to each ma_e means that we will be picking ten ma_es out of 1000_ _f we
raised al_ our ma_eSo But perhaps ten out o_ 200 would be more _ke_y if we keep to housing
age something _ike an average of _o ma_es from each _u_=s_b fami_yo The _'irst point on the
curve of expected c_nnua_impravemen_ _sfor use of a_l pullets and cockere_ breeders° At this
nextr point here, we're _s_ng nine young ma_es each year and we're keeping _he best one o_ the
nine we tested _as_ryear to be used again and expected _mprovement goes up a _itt_e b_to When
20% o_: the ma_es are ye_r_ng tested birds, selection wou_d be two out of e_ght_ 30% would be
selecting three o_t of seven_ 40% wou_d be selecfing _o_r out o£ six_ 50% would be selecting
f_ve out of five° _ th_nk you see why the proportion _o be mated to tested ma_es can't go too
high° You soon get to a po_nt where you can practice no se_ect_on whatever on the basis of the
progeny _est, where you are keeping all the moles that were tested to be used the second year.
So actua_ progress expected from use of 50% year_ng tested mc_es is that expected from select_
ing only _ive ma_es ou_ of the 200 or so on the basis of' a part year family perforrr_nce,
_nd
using a_ f_ve of them far two years _n a row. Now you could immediately
raise the question,
why use as many as ten b_rds _'Ore_ch young ma_e tested ? That is a perfectly va_id obiection
because you could test your young ma_es on perhaps three to five b_rds each° _'hot wou_d give
you a _arger number of tested ma_es from which to pick those to be used as yeorl_ng tested
breeders and you could perhaps use your year_ing tested breeders on ¢_smany as twenty or twentyfive birds_ That, of.course, wou_d increase the opportunity of selecting on the basis of progeny
test. The only drawback _s that _f _nstead of using ten birds per young mcfle, you use five, it
means that you c_regoing to need twenty instead of ten young ma_es to test° You can°t select
twenty mo_es that are ius_ as good as.the best ten, can you ? _t means you save twice as many
young males. Therefore, this curve w_l start at a _ower point cmd it only catches up over here
some p_ace. By the way, you probably have a_ready been struck with how f_ot=topped th_s curve
is, how _itfle d_fference _t makes what proportion of tested ma_es we use. This is perfectly true
if we consider only the average effects of genes. What happens as you move out this way, as
far as males are concerned, _s that the more tested ma_es you use, the sma_er and more select
the group of young ma_es you progeny test, and therefore, the greater _he superiority of the
young mc_es selected. The _arger the proportion of the tested ma_es you have _o keep_ the _ess
the selection among the tested ma_es and therefore, the sma_er the advantage from basing
selection on progeny test. _n either family performance _or young ma_es or progeny test performance _or tested males, the larger proportions you have to keep, the smaller the difference
_sgoing to be between _he overage merit of those kept and the who_e group that they were
chosen from° _t _s a matter of balancing one against the other in deciding where the optimum
_40_
wouAd l_eo It looks as though, at least _n the early stages of a C_osed flock breeding program,
that one would not be iustified in using more than ten to twenty percent of seRected tested males°
Efa larger proportion of tested m_les is used, you are practicing
too A_tfle selection among the
tested maAes in p_cking the ones that you are going to use over agaln_ and you lose the advantage.
Perhaps we should consider further the valldlty of assuming that breedlng males are selected
from 200 cockerels each year° Changing this number from 150 to 250 would not af'fect the _ntensity of young merle se_ectlon very much, because 10/]50 and 10/250 are both rather intense seAections. _f selection of young males is to be based on part year family performance,
then the
cuAling from ]000 to 200 that you do on the range or even earAier wiAI have to be based upon in=
formation that came aAong after you had aAready produced these chicks, or on the hatchability
or earRy mortality of the family,
before any egg production data is availabAe. Th_s early cuAl_ng
couRd be s_ilA greater° Of course, if' you cut down numbers of cockereRs too mvch, then you are
limiting the room that you have to select when the part-year egg production comes along° In
the many attempts we have made to decide how much relative a_'tention the different traits
should hc_ve in seAect_on index, egg production really wags the dog° _n other words, it is difficurt to iust_fy heavy emphas_s on hc_tchabil_ty or early mortcflity and sti_ keep in m_nd the relative economic importance of the characters,.
am r:o't sure _ understand that _igure of 200 males when you only have 100 families from
which to select?
We h_ve 100 fc_mi_ie$ and we have assumed more or _essarbitrarily
that we will keep more
than a couple hundred maces unti_ the part=year family egg production is obtained.
You are only going on _ami_y egg production average and you are selecting ten out of a
hundred each time ?
But _ could save two out of each {'ami_yo Might even s_ve three.
Well_ that wou_d s.til_ be out of a hundred. Tha_ would be seven out of one hundred,
ten out o_ two hundred°
'
not
We_,. two ma_es from each o_ the _ive best _am_es is 5/100 fami_es or ]0/200 cockerels,
the proportions are the same° Before _ _eave th_s ma_e picture _nd before _ _eave this curve of
expected progress, _ should say thc_t if by any chance your breeding program is at a point where
family Se_ect_on or part yec_r family performance is not tc_k_ngyou anywhere_ then it may very
we_ be advisable to _ncrease the number of young males tested and reduce the number of matings in which each young ma_e is involved° Th_s is for the purpose of having a bigger selection
d_fferent_a_ when you come to pick your tested males from among those testedo For example,
_f _ want to test 18 cockerels w_th 5 females each and keep one to use on the 20% of the breeders the fo_low_ng year, this increases the selection different_a_ because only one out of eighteen
tested mc_es _s selected _nstead of one out of nine. The reason that would not be advisable, _f
you were really making appreciable progress from family selection,
is because one can't pick
e_ghteen males that _re iust as good as the best nine young ma_eSo _ntensity of select_on of
young ma_es is reduced by testing too many, i_ the family selection is doing any good° Are
there any questions you wan_"to raise about the general approach ?
don't see that° What if you took two males _rom one family,
what wou_d be the d_ffer_
ence ? How do you know that one ma_e is better than the other before you _est them ?
You don'to You are selecting on part-year family performc_nce o
Why shouldn't H happen tha_ one family is better than another ? Why not use five males
out of one family? Why shouldn't you use that?
The only obiection wou_d be the possible effect on inbreeding° _s there still a question on
that ?
Unless _ didn't
hear you right,
you sa_d it would be harder to select eighteen good
-41
possibiA_fies than nine ? _ don°t see why it wouRdo Taking eighteen moles out of 200 or whatever
number you have ava_ob_e_ you get eighteen iust as good as the best n_ne.
The point _s, that you could do that if you hove saved pAenty of young males until three
or four months along after housing in most of the families,
and if you wished to save moles from
the same number of families whether nine or elghteen were selected_ But you may be a I_ttle
cc_gey about feeding large numbers of males that Aong, as most department heads are° Consequenfly, then you may have only one or two males from the fam_Aies that turn out to be your
best ones. What you say would be true only if you knew during the summer what family you were
golng to want two or three or four mares from _n January° But foresight is seldom that good and
will be willing to bet w_th any of you that you can't p_ck e_ghteen young ma_es, year after year,
from the same size flock that would be iust as good as if you only hod to p_ck nine. _sthat still
not clear ?
_f you ore picking them so_ely on family _nher_tance, you haven't got 200 families ?
You hove 100 fam_lles, that's right_
So, if seRection is soReAyon familles,
your denominators are on the number of families
you hove ?
Well, we have 100 families.
You could keep two from each of the top four families. You
would be saving then 4% of your top families,
which wouJd be _n effect e_ght out of 200,
wouAdn't _t?
All right, whet a was starting to emphasize here was that if the se_ect_on of young birds on
the basis of part year fomiAy performance was no _onger h_ghJy effective,
then you might very
_ogicol_y test _orger numbers of young mo_es. Th_s wou_d sh_ft your emphasis more _argely to
select_on on the bas_sof p_ogeny test. Yeor_ng moles then could be used on as many females as
he could handle_ maybe twenty, by using twenty bird pens. Moving up to 20% here wou_d mean
that you could test sixteen ma_es out of which you would need to keep only one to use on twenty
breeders the f'o_low_ng year. You would be using 80% of your birds to test sixteen young males
and you would be mating the remaining 20% to the best one out of the s_xteen tested the pre=
vious year° Emphas_s on progeny tested sires depends a great dea_, _t seems to me, on how far
you ore in your breeding program_ whether you are still on the up-grade so far as effectiveness
of family and _nd_v_duol selection _sconcerned, or whether you have gotten to a po_nt where
the pickings are becoming pretty sigma _n the latter case, _ th_nk there are good reasons for
sh_fting over to a much heavier emphas_s on the use of.progeny tested b_rdso Under the over_
dominance p_cture, you wou_d be pu_ing c_oser to the optimum or the equilibrium
gene Frequency, which is the best that you could achieve _n a closed flock system of breeding. Under
an _ntermed_ate optimum s_tuat_on, you wou_d be favoring individuals that were homozygous
for intermediate gametes° _ won't go _nto th_s in great deta_l_ but there are reasons _n favor of
progeny test_ngo _f you ore at a point where ep_static variation accounts for a _arge portion of
the genetic variability,
you may make _ittle progress. You can, nevertheless, _ncrease the
proportion of breeders that produce _ntermediate gametes to a greater extent by select_on on
progeny test than by selecting on _ndividua_ or family performance.
Now, _ guess 0 can leave the same curve up there for the effect of using tested female
breeders on expected progress, if we substitute proportion of tested females for proportion of
tested ma_es.
By tested female in th_s case, you s_mply mean one that has ten pullets w_th part=year
egg production records and one whose family has o fu_ egg production record_ as contrasted
with the pullet case where you°re got iust a part-year family performance and the b_rd°s own
port=year record. Otturns out that progress, when we use a_ young ma_es but use varied pro_
portions of tested females, coincides almost _dentico_y with the curve _°ve shown a_ready for
-42
maAeSo Rnothe_ words, there _,sa s_ght a.dvc_ntage in using a sma_ proportion of tested females Q
_t _sn_t great_ but there is a _it_e a,nd the optimum, depending on how much attention you pay
to the _nflect_on of_th_s curve wouAd vary be_,een 10 and 25% of oAder yearling birds_ Now if
you use optimum proportions _nd_cated of both tested males and fema_es_ then this curve ralses
up a _ttRe b_t up here_ one supplements another° So as far as _ am able to ca_cuRate_ and we
must recognize thait these c_re calculations based on heritab_i_y and how much env_ronmentaA
error _s averaged ou_ by having progenies of a g_ven size_ etCo_ the optimum proportion of tested
breeders within the det_'in_ions Mhave used here would vary somewhere in this 10 to 25°/'orange.
You have to recognize that _f your level of performance _s h_gh and I_tfle progress _sbeing ob_
tanned from family selection, then _h_ proportion of tested b_rds _ndoubtedly should be higher
than 10 to 25%° But _ga_n you can_ " go too far in th_s direction before you cut off your nose to
spite your face° You are _sing so many tested breeders that you can't practice any se_ect_on in
choosing them_ Now you cc_n bring up variations in which you use some other flock to test large
numbers of young cockere_s, but that is a _tfle d_fferent, because you still have to use those
birds _o test young m_,_es_ _ _rh_nk_in the _ong run, it doesn't come out much differently
than i_f
you consider all the birds you are working with as one flock° Any questions ?
How do yo_J_rrive a_ the selection of the 200 cockerels that you are going to raise ? Are.
they _rom a_ fam_es or are _hey from the most selected s_ster families ?
Well_ in o_r own c_osed flock breeding work, we set up a selection _ndex which takes into
accoun_ ha_ch_bil_ty _f the fam_ly_ the early mor_c_lHy of the fam_ly_ the egg production of the
famlly_ and the adult mortality of the _am_yo We weigh those th_ngs according to their relative
economic importance as nec_r_s we can arrive at _t and according to haw highly heritable _he
various tra_ts are to the best in_ormat_on availab_e_ Of course_ the males are culled from _000
to 200 before the part_yec_r egg production
ava_ab_eo
and adult mortality
part of the family
index is
Then you pick your mc_es from the fami_es that have the best _nde× ? _n the spring you
save these cocke_e_ ch_cks_ _,sthat what" you mean ? Or do you raise ]000 cockerel chicks_ too?
No o We raise a_ cockerels to twelve weeks in the c_osed _ockso By that t_me, the full
year f_mi_y performc_nce on their parents is avai_ab_e_ and you c_n do some cu_ing on the basis
of parent performance and on the basis of v_abi_ity, hatchabi_ty,
and grow_rh rate up to twelve
weeks of the cockere_s own fc_mi_y_ But s_nce egg production swings such a heavy hand in the
ma_e se_ect_en that you actually wc_nt to make, you can°t ' cu_ too severely at twelve weeks°
You canOt el_m_nc_te ma_es from too many families or you may wffsh you hadn_to You may find
that you don°t have any ma_es from families that you wau_d _ffke to hc_ve_ _n practice_ we have
kept ma_es frorr, abou_ _wo_thirds of the best fam_eSo When we _hffnk a family w_l_ do excepfiona_y wel[_ we may keep two or three ma_es a_ twelve weeks of age from that family.
But
any select_on for egg production at _his t_me must be on the basis of the dam_s and s_re_sfami_ieSo Egg production records on the parent's families w_ll have been completed by this t_meo
When do you complete those p_ren_s egg production records ?
_t a_l depends upon what you cal_ your fu_l year egg production° We use performance to
abou_ 450 days of age, which ends in June and Ju_y, in our flocks.
Your year is not c_year ?
Our year _s not _ year., no, because we have _o be able to empty those houses and have
them ready for the new pu_etSo
Don_ you mean to say that _nformat_on on the hatchab_ty
of eggs from the dam is
available when the progeny are twelve weeks of age?
You wou_d have to wa_t awhile after the hatching season in order to summarize the full
season's hatchab_!ity
on the dam° _f' much cu_l_ng was done at hatching
time,
it would have to
-43_
be on the basis of the family or _nd_v_duai performance of the parents° Presumably the parents
were already selected on th_s basis° Further culA_ng C_thatching would only restrict the.opportunity for selection on the basis of _nformat_on on the new generation°
Did I understand you correcHy to say that the t_me would come when you would eliminate
or reduce the amount of seRection pressure based on indXv_dual performance ? Is that right? In
any system of breeding, would you eRiminate consideration of the individual?
No, not at a_ but you may reduce it somewhat° Bf you test a _arger number of young
males in order to have more choice among tested ma_es, that may reduce progress if you are
really making any progress from selection on the basis of part®year family performance,
because
it means that you are practicing
less _ntense selection in picking the young males to be tested.
However, if that early curling on the bas_sof individual and famiAy performance isn't doing you
much good anyway, then it wouldn°t hurt you ta go ahead and test more young males. It amounts
to a I_ttle less intensity of cuAA_ngof young males for the purpose of putting more emphasis on
select_on based on progeny test°
am thlnk_ng, maybe _ d_dn't put myquestion acros,So Bam thinking of the physical fitness of the bird, over and above theoreti'_.a! consideratr_ons.
Well, _ am assuming that you Can pick e_ghteen cockerels that WOUld not be greatly
different than nine out of 200 in physicah fitness. There is some question as to how much emphases should be placed on the appearance an'd growth rate, etco of the male anyway, provided
he is healthy and strong enough to I_veo
You are speaking of production flocks ?
am ta_king about phenotype of you,ng males° _s that what you are referring to ?
This same se_ec__on wou_d apply to meat strains as well as to production strains ?
_t doesn't matter whether you are ta_k_ng about a meat strain or an egg stra_no If your
F_ock has reached a po_nt where ind_v_dua_ and family selection _s no _onger effective,
then
progeny test selection _s _ike_y _c_be more important .than ind_vidua_ performance selection.
As long as you are sti_ getting _nywhere from indiv_dua_ performance and family average,
progeny testing doesn't deserve a very b_g p)ace _n your breeding program°
Now, let me ask th_s question° _f these conclusions are based on a _im_ted number of
mat_ngs, then wou_d they apply _f the number ofindiv_dua_ ma_e mat_ngs were greatly _ncreased ? Could you.go on indefinitely, as Far as _nd_vidual .Family se_ect_on _s concerned ?
As long as you are making geod progress°
Wel_, assuming that ?
On that assumption these curves wou_d apply pre_'ty we_l _ far as optimum proportions
of tested mcfles and femc_e breeders. WSat yeu are really trying to do is to keep to genetic
_mprovement from selection among tested males that takes pk_ce _n one year_s tlme the same
as _t is from the selection theft you make among young ma_eSo Suppose the total length of this
arrow represents the d_fference between the average for al_ young ma_es, for all hundred families, and the mean performance of those families from Which yol_ keep young males to be
tested° This _s the young males mated in test pens° S_nce we can p_ck among our young males
only eight or ten out of 200, 5% or _ess, we can expect quite a large difference in the family
performance _evel for the young makes chosen, compared to all young ma_es We might have
kept° But s_nce it _s based on part-year performance and o.n family performance of only ten
birds, only a portion of that.total reach is actua!_y generic, The restof it is either environmenta_ error _n evaluating the family or St _sdue _o n_cking of various types. Now when you
come to select among the n_ne tested males, .that were chosen originally from 200 cockerels,
you need to save at least one out of the nine° One out of nine _s 1_% but keeping nine out of
200 is 4 1/2% ° therefore_ we get a bigger selection d_fferentia_ or bigger apparent advantage
-44_
in plck_ng our young males, but less of it is generic. _n picking the best tested males among
the nine that were tested, a larger proportion of the apparent superiority is genetic, but since
we have to keep one out of those nine, we cannot have as big a selection differential°
In considering the optimum proporHons of young and old males to be used, the real genetic superiority from selection should be the same in _he selection among tested males as it was the previous
year in selecting the nine to be tested from the 200 cockerels° In other words, the two have to
be in balance when you are at the opHmum proportion of tested and untested males° If you test
only six cockerels, _t means that 40% of the females can be mated to tested males and at least
two males out of those six tested will be needed to mate with those 40° Then you have reduced
the amount of culling based on progeny test to keeping only the best third, and if a few males
happen to die, you may end up with only the best half or best _o-thirdso
Which means that you
are not practicing much selection on the basis of progeny testing and all you are doing apparently is treading water as far as selecHon among old males is concerngdo
I want to ask you w_th reference to this curve of expected annual improvement,
in terms
of percent, what is the dlfference between using an optimum number and using no tested males ?
Well, compared with using only young males and females, uslng the optimum proporHon
of both males and females, it wouAd be an increase of not more than five or six percent.
It seems to me you are doing an awful lot of talking about something that isn't very
significant _
Well, sir, you know they assigned th_s topic to me and if _ don't do anything but show
you that there isn't a whole lot to be gained by progeny testing, where you have individual and
family performance as an alternative,
maybe it will be worthwhileo
Now that we are over on that subiect , perhaps I had better bring up what _ had on my
mind.
OoKo
I wonder about the practical value of using old progeny tested cocks, anyway ? There
are a lot of us who have made up a few pens of old cock birds and find that two or three of
them donat come through wlth any chickens anyway and that immediately
throws out one
breeding pen and you donat get any offspring from them° Rt certainly doesn't help your business
any° That throws your theoretical proportions all out of k_lter. Isn't it iust as well to pick your
best young cockerels from your best families ?
It all depends where you are on the curve of progress from selection on individual and
family performance° K guess my time is up°
Do you have some more you want to cover ?
Well, I_ll just make a general statement w_th regard to this other type of breeding where
you are deliberately
selecHng for performance of strain crosses° There, of course, you have to
base your selecHon on progeny testing° You have no alternative.
You are selecting one strain
to match another° Somehow or other, these problems of old males dying and not being fertile
keeps right on belng a factor, but you need to use the progeny test anyway° Justification
for
resorting to selection for maximum performance of strain crosses, of course, rests on the importance of this heterozygote advantage or overdominance we were talking about this morning
and other types of gene interaction in the genetic variability
that you have to deal with° That
is why it is so important that we learn more about iust what kind of gene action and interaction
we are dealing with° The effects of both inbreeding and crossbreeding indicates that the degree
of heterozygosity does exert a maior influence on important performance characters, such as
hatchability,
mortality,
and egg production° But we certainly need some critical breedingexperiments before the relative importance of dominance compared to gene interaction can be
determined° Present evidence, it seems to me, indicates that both are _mportant and that the
-45rate of improvement from long continued selection within closed flocks may become negligible even though the estimates of herltabillty
continue to be positive.
In some work that Mr.
Krueger is doing, we have been looking hard to find evidence for negative genetic correlations
between the components of egg production and between growth rate and egg production,
largely
without success. Genetic correlations seem to be more positive than negative so far, but we are
still looking for negative relationships that may help explain the sometimes discouraging lack of
results from selection.
Under these conditions, deliberate selection for maximum cross performance between complimentary
strains seems to offer proi'nlse of significant further improvement.
And, as I believe Dr. Lush mentioned this morning, you need t he cumulative effects from recurrent cycles of selection to efficiently
obtain crosses that are anywhere near the potential
maximum; because the range in performance of crosses within any one generation is very small
compared with the potential range. I was going to say just a few words here about different
methods of progeny testing for maximum cross performance.
I might just run through these and
if there are any questions about them, we can drop back. The expected effectiveness of this
reciprocal recurrent selection between two non-inbred populations,
that Dr. Lush mentioned
earlier, can be compared with that From recurrent selection for cross performance with a highly inbred tester line, somewhat as follows: Many of these points Comstock made in his original
publication.
And others, of course, Fred Hull has made in his various publications.
Are we
clear on what the two methods are ? You have non-inbred A selected to cross well with noninbred B. You are practicing selection within this "A" strain, both among females and males.
on the basis of progeny tests of those birds in matings with individuals of strain B, and the reverse. The Other system is one where you use an inbred "A" and select non-lnbred population
"B" to fit it. Those are the two systems that we are contrasting.
Both of them involve progenytest selection.
The first thing that comes to your mind in comparing these two systems, of
course, is that if the tester line is highly inbred, you aren't going to be changing it much.
if
the tester llne A were homozygous, you would not be changing it at all, and all of your selection would have to be done over here in non-inbred strain B. So, you would be practicing only
half as much selection, with an inbred tester, as you would in fitting two non-inbred strains to
each other.
In the latter case, you are selecting on both sides. In the first case, you are selecting on the one side only.
These two systems are alike in the potential limits of cross performance, so _r as dominance is concerned,: but the use of a highly inbred tester here would be
more likely to limit the ultimate cross performance if partial dominance or-gene interaction
were important.
You could have loci at which partial dominance was the rule in the genetic
effect on total performance_ and this inbred line A tester could carry some genes that could not
be compensated for no matter what you had in strain B. These two systems will be similar in the
inltlal cross performance except that it _should be easier to select the B stock from the many
stocks that you might be able to start wlth_ to fit a particular inbred line than it would be to
select the B stock that would match a non-lnbred A stock.
In Bell's experiment with Drosophila, fortunately or unfortunately,
in comparing these two systems it happened that in selecting the non-lnbred stock to fit a particular inbred line, the cross started at a higher level
than in the experimental selection between two non-inbred stocks and maintained that advantage throughout the period of selection,
l_ow this may have been purely an accident, presumably it was. In trying to repeat the experiment,
he is attempting to start these two systems at
the same base, as far as cross performance is concerned.
It seems to me it would be easier to
pick the strain that would fit the highly inbred tester initially.
If heterozygote advantage is
highly important and the population is anywhere near this plateau we are talking about in response to ordinary selection, or in other words, if gene Frequencies are anywhere near a stable
equilibrium,
the imporvement in cross performance per cycle during the early stages of
-46_
recurrent selection wc_uld be expected to be Far greater w_th a homozygous tester than with two
non-inbred strains. The reasons for that are not easy to go into briefly° S_mply, when gene frequency in the tester stock "A" is at equilibrium
at a given _ocus, progeny testing b_rds over
here with that strain will give you no d_scr_mination bet_ween big "A" and little "a" gene at a
given locus in strc_in B o Hence, progeny test select_on won°t c(_rry you anywhere if gene frequencies are at an equilibrium
level _n the tester Iffneo The further away one of your tester
strains _s from equilibrium
gone frequencies, the greater the effectiveness of progeny test selectlon on the other side. An inbred strain ho,s e_ther agene frequency of zero, or one, if it is
completely homozygouso This mec_ns that there will be mcximum dffscrim_nat_on between the
gametes of males tested in strain B when m_ted with inbred s_rain A, rsnd you get much less
effective discrlminatlon
_f your tester is a non=inbred papulatlOno nn the early stages, selecting
a non=inbred stock to fit a high!y inbred tester could m(_ke more progress per cycle than recip=
rocal selection between two non=_nbred stocks° Progress expected from selection between two
non©inbred population increases as the d_Ference _n gene frequency between the two strains becomes larger. And it would f_nc_ly catch up wi_h homozygou_ tester selection when differences
in frequency per locus approached something like 0°5° From what _ have sa_d, _ think you can
see a possible reason, at lea.st, why a part_r_lly inbred tester_ _whlch is _bout all we might be
able to actually use at th_s stage of the game _n poultry), would have some advantage over a
non=inbred strain of poultry for one side of a reclprocal selection scheme° Now, _n any system
I_ke th_s, you have a given number of Females _n one strain _hat can be used for testing young
males in the other strain° fit may be _arge, or _t may be smc_ll, depending on the scale of your
operation but you'll h_ve a certain number of females revised in each strain each year that can
be test-mated w_th mc_les From _he o_her populatBon. And c_galn in thBs situation, there is an
optimum number of matlngs _c_use for each young male tested° Suppose we chart the expected
genetic superiority of the tested males _h_t _re s_ved from c_given number that are tested°
Suppose we have ]00 fem,_les _vcsilable far testing m(_les,, ius_ as an arbitrary number° Bt m_ght
be half that or twice the_, depending upon the sc(_e of your particulc_r operatBon, but if you
have 100 females to be used for _estBng mc_es,, how moony ma_es should you test on those, in
order to have maximum superio_'i_y of i_he best two tested m_es For use in reproducing this B
IBne ? Each year we are going to _est so many m_es out of which we are going to plck two to
use in reproducBng _ha_ B line, let's say° Well, we could h(_ve shown all the possible number
of matlngs per cockerel but we wi_ iust tc_ke up _o ten° _f we had as many as ten birds used
for each male tested, we could only _es_ten m_es out of which we would have to p_ck two
to reproduce the strain the fo_low_ng year.. _f we usecl only one female to test e(_ch male, we
could test 100 males ou_ of whBch to pBck tw_ bu_ if we use only one bird to test ec_ch male,
we would have a very inaccurate _es_of the m(_le,_ wouldn't we ? You would only have one
mating, w_th ten pullets housed per mcs_ing, from w'hBch to evaluate each maleo We have used
two mat_ngs, w_h twenty test c_oss pu_Bets housed ou_ aF each male tested, so the curve goes
something I_ke this with an optimum somewhere between three c_ndflve matBngs per cockerel,
for the expected superiorBty of the t_wobest ma_es picked ou_ of the tota_ number tested. That
would mean that BFyou used three femoles to test each young male, you would be testing 33
young males and p_cking two out o_ those° Bf you used f_ve pulle_s for each, _hat would be
testing 20 young males ou_ c_fwhich you would pick two to reproduce one° Bf you go out beyond
this_ you are not increasBng accuracy very much° We could draw sBm_lar curves showBng that
accuracy goes up at an ever decreasing rate, whereas the intensity of the selection, _the proportion saved, in other words), is coming down° What you _re after _s the point at which the
gaBn from more accurate evaluation of the male by having more matlngs ceases to cancel the
reduction _n the amount of culling that can be done on the bas_s of progeny test among the
-47tested males _
Are you assuming ten daughters for o female ?
Yes, in this case° Changing that number plus or minus 'five would not change the conclusion very much° The main point is s_mply that there is an optimum number of matings per
male and it _snot terribly high° ! think all of you hove been very k_ndo Maybe I had better let
you talk for a while°
I am going to toke another advantage of my position. I am going to give the poultry
breeders the first crack at Dr o Dickerson. I believe that if ! get the ponel members up here, we
are going to run over on time. _ think that the breeders have many questions they would llke to
throw at us o Mr o Hannah, you have the opportunlty to ask the first question°
I would like to artificially
select and use ten daughters out of a possible thirty. How are
you golng to evaluate the family from which they came ? You are using only one-thlrd,
you are
throwing away two-thirds,
how are you going to know what you have ?
There is a mlsconception here some place° In the progeny testing that I am talking about
there will be no culling among the progeny until the end of the laying year° What are you
referrlng to ?
To this number of females to be tested from a given hen, you said that. you had one hundred tester line females to be used in testing males of this B strain° Where do you get the onethird? You said you would use ten females, but that wouldn't make any difference whether
you used five or fifteen. If you do any selection at all out of the females, aren't you influenclng to a certaln extent the evaluatlon of the family?
Yes, I think I see what you mean° [ assumed when I said flve, that you only house five
pullets from each dam tested, either the first five pullets from each dam or all pullet progeny
in a matlng period or hatching perlod short enough so you would only get five pullets from one
matlng_ I wasn°t implying any selection of the progeny of each hen.
Would you do any selection at oil, artificially
?
No. Selectlon in this program _s entirely based on progeny test. The progeny are crossbred birds. There is no polnt in culling them. You aren°t golng to use them as breeders anyway.
What you are going to use as breeders ore the best of these hundred pullets that you test-cross,
and the best of the males_ whatever the number may be, that you test®cross° We are not going
to do anything with the test cross progeny except use them for evaluation of thelr parents.
The number of progeny per mating then would be a minimum of ten°
Well, you would have to decide how many chicks you were going to hatch, how long a
hatchlng season you were going to have in thes'e test-cross matingso
If ten is a minimum,
is anything above that more deslrable ?
Well, the reason n picked ten is because that is about the slze of a full-sib family that
you get from o slngle dam in a hatching season of two months° Isn't that somewhere near
correct ?
Isn't less than ten o good test ?
Well, practlcal[y,
_ expect you had better stick pretty close to ten. If you reduce that
number, it means that you must use some more females of the tester llne for testing males,
if you have fewer pullets produced by each female of the tester line. I would say that you
would probably want to keep the number of females of the tester line that you needed to use
in matlngs down within reason° Of course there is nothing holy about this number of 100. In
actual practice you might much rather try selecting between three or four different pairs of
lines with smaller number involved in each case than putting all of your hopes on this one
particular combination of B strain wlth Co
_48 ®
What is a partially inbred line? What _s an inbred?
A partially
inbred line is the kind that you have and everybody else has. You don't want
to run inbreedlng up so high that you have a strain that is impossible to work with and, on the
other hand, you ought to have enough inbreedlng to give you a little hand-hold for effectiveness
of progeny-test selection° That isn't a very good answer, is it ? What do you want me to say,
25o/o? O° K ot 25%°
Why can°t you sib=test in reclprocal recurrent selection ? You said you must progeny test.
Well, you could select brothers of males that had a favorable progeny test. Is that what
you mean ? That again is a matter of degrees. Here you are selecting A and B, over here two
different breeds°
i am selecting males adaptable in their ability to cross but ! am doing it on sib testing
basis because I am doing it entirely on January hatched stock, and my test is from June until
November.
I am not clear on what sort of slb testing you have in mind.
Well, egg production and mortalltyo
You are basing your selection on birds that are A x B ?
Yes
o
•You want to know if strain A crosses well with B and you are making
between the two ?
Yes.
some test matings
What can that do except to evaluate the parents of the cross ?
Well, ! make my selecHon on a sib test, all January hatched, egg production June to
November and I believe from the brothers of the best sisters sib tested. I mate up ten brothers
wlth their sisters°
In other words, you have a full=sib family in the A line here. You use a portion of those
birds in test cross maHngs and _f they do well, you can go back and breed from their full sisters
in the A lineo
No,I switch my cockerels° ! have four hatches of A with B matings and then I switch my
cockerels and have four hatches pure A, from the same cockerels.
Oh, all right° In other words, in the same season you are test crossing males and reproduce from them.
! take four hatches _n January, ! take four hatches in late February or March of pure A.
Then you have to practice your selection among the progeny of these within strain matings after you find out how the test crosses behave, for the individual and other members of
the same family° That is all right, provided you feel that you can afford to reproduce from
birds and then cull maybe two=thlrds of the progeny after you flnd out which parents you
should have used.
That°s the niece test, rather than a s_b-test, isn°t it ?
I think the plan has mer_to In fact this past year, we did that same thing. We reproduced
from young males at the same time that we were test crossing them° If the young male's testcross progeny turn out-well, we will keep his wlthln-Iine
progeny. If they don't, we'll discard
them. However, _t does mean that you will have to raise more wlthin-line
progeny in order to
be able to cull.
You talk about a short term test. Which months do you mean ? Do you mean Dr. Lerner's
September to June period ?
Oh, in our particular case, we house pullets at twenty-two weeks and take production to
approximately
300 days of age, which would be about one hundred forty-six days, a little less
than five months from houslng at a standard age. That might differ with somebody else _ but it
_49_
constitutes part-year
and females tested°
egg production
of test_cross progeny_ for use in selectlng
the better males
! believe that by putting your hatchlng date forward to early January on the short term
testing that you do your test from June to November , which _ believe makes your sib testing
four times more severer from June to November with no lighting and contains 70% production
in October and November, than if you are dolng Dr. Lerner_s way of sib testing from September
through January° I mean by bringing your hatching date forward two months, you can make your
test four times as severe for your short term test_ngo It is four times more severe a test because
you have that resistance to molt of pullets that come in to lay in May and June and lay 70% in
October and November without I_ghtso
Well, with pullets you would not be bothered much with that molto
Before we go on w_th that, ! would like to have the breeders and geneticists have another
opportunity to ask some more questions of Dr° D_ckersono "
What e×peHence has he had in holding these tested males over for breeding abillty during
the year ?
Rather sad l I th_nk we had some management problems to consldero When these young
males were put in the breeding housef it had some older birds _n _t. In our particular case, we
were reproducing from young males and older females in some cases_ We found that those young
males seemed to die off quite read_lyo We thlnk, or we hope, that a different management
procedure where we used only young cockerels and pullets in one breeding house and older males
and older birds in another may help, but _t was serious° If it kept on belng as serious as it has
been w_th us, we would have to go entirely to the method that th_s gentleman brought up of reproduclng from the same young males wh_le we have them allve, and at the same time we are
test-crossing them° We would have some test_cross matlngs and some w_thin-llne
matings within
the same pen, or at least in the same hatching season.° Then we would do our culling among
their progeny rather than using the best better-tested males over again the next year. We hope
we can lick this tested-male mortality to a greater extent than at present so that we will have
some opportunlty to select between tested males themselves o When most of them die,. you reproduce from what you have left, and the amount of selection based on progeny performance
may be slight°
With regard to progeny testing, fi know from my former vlslts to breeders, every breeder
I know is so discouraged that he uses very few males over the next year°
It is very serlous.
You w_ll be surprised how young cockerels will stand up for their own rights if you put
them in a week sooner than your old b_rdso
Putting the two together, put the cockerels _n a week sooner and let them become accustomed and let them become "boss'_ and then add your old males°
Our trouble is not from old males and young males fighting together° We use slngle_male
mating pens°
But I say, put the young males in the room f_rst and let them become accustomed to _t
and then the old ones are newcomers_ It will make quite a I_tfle difference on the scraping°
You are talking fighting between males, that is not our problem o
If it is holding them over, we used to put them out in alfalfa fields and timber, etc._
and the smaller room you put males to hold them, either young or old, the less males are going
to Ioseo This is our experience°
You mean that if you keep them in small individual wire cages, for example, you feel
llke there w_ll be less loss.
No,
in a room,
_n confinement°
There are a much larger percentage of them get by than
_50 i
where they are turned out on range°
On this problem of keeping over old males, we had that unfortunate experience of carrying through a male in the summer and ready to use them in a speclal mating the next breeding season, and you find that he is ster_leo We learned that if we keep our males with hens on
a year round basls, they have no sterility at allo We were able to use them continuously and
we are using males four or five or s_x years old.
Our difficulty
on mortality comes during the same season these young males were used
for mating° When we pull them out of the mating pens in order to use the second ser_es on those
same pens, the ones that are pulled out we have been putting in laying pens and they have already been in contact w_th some older breeders_ They not only die out themselves but they
spread respiratory infections, etCo, to the laylng houses. I am taking down my hair unneces_
sarily, Rthink. You people don_t have those klnd of problems.
Now, Rbelieve we have one more questlon.
If you were interested in making the greatest possible gain each generation and considering the fact that you have considerable losses from males, infertile,
etc., what would you say
is the optlmum number of females per pen per mole ?
mam not sure I get the g_st of the questlono You say, _f you were bothered by heavy mortality among tested males ?
Considering that ?
Considerlng that, what is the optimum number of matings per male ?You are thinking
that in order to have any room for selection left, if you are golng to lose a lot ot: the tested
males, that you should test a larger number w_th any given limitation,
as far as total number
of females is concerned ? Yes, that is right. You tend to move back on thls diagram that I have
here, as far as proportions, instead of staying up around five, you might move back towards
three or four mat_ngs per maleo
Well,let's
assume that all the males liveo How many females per male would you say
was optimum ?
That is where the three to five came in o
You say _hree to five ?
That°s rlghto _t is c_fairly flat _op curve in that range from three to five° Bnother words,
what you gain in accuracy by going from three to five, you just about lose in the room for
selection among the males left o
You are assuming, though, that you only have one hundred females° Say if you could
use as many females as you wanted to, is there some advantage then in putting more than five
females to the male ? That is the case of most commercial
breeders. Well, we are not limited
to one hundred females, normally it is closer to four or five hundred.
In a reciprocal selectlon program?
Yes, you are talking about reciprocal selectiono
If you have four or five hundred females _n these strains that are being selected to fit the
test, remember you have _'oselect replacements for those next year so that just because you
have a bigger population of females w_th which to test males, it doesn°t mean you can change
thls optimum too much. You have to save more males to reproduce the straln w_th next year.
ket°s switch then to the other type and when you are not just standard progeny testing,
you are not worrylng about thc_to Wouldn't it be some advantage then to putting more females
per male ?
If you do that, you are going to test fewer males.
Well, I know, in our set-up, we have fifty pedigreed pens we are going to fill up wlth
females, why not put twenty in instead of five ? That's my point. That way we could use
selection on the female side with respect to egg quality,
that line.
egg weight
and hatchabillty,
along
Well, if you are going to pu_ twenty in instead of five, it means that you are going to
use four times as many female breeders.
Welve got them, that's a fact.
You might better increase the number of pens and test more males, as far as the genetics
of the situation is concerned° When you put twenty or twenty_five birds in to test single males,
it means that you are definitely restricting the total number of males that you can test with a
given number of females. The more you restrict the number of males tested, the less cholce
you have in plcklng the best tested male out of those, so there is an optimum,
there.
_f, in closed flock selection, you are going over then to almost entirely selection of
young males on the basls of family performance,
then you have an _ncentive to use as few
young males as you can in order to have the maxlmum selection pressure between these familles and _t would be w_se to go toward higher numbers of mafings per male.
You mean the main difference would be to llmit the number of females we should use
in our breeding pens? If we are trapping a thousand birds, we want to use four hundred of them
to fill up our breeding pens or only two hundred?
Noo You are saying that you wouldn't use any tested males, or hardRy any?
Hardly any°
In that case, as far as the males are concerned, your whole obiective is to use as choice
a bunch of young males as you can° Therefore, you want to use as few young males as you can
and sill0 not run your inbreeding up too fast°
We use about twenty and cu_ them down pretty heavily as we go along.
How about using full-brothers
of the best _ested males ? Rsthat fairly accurate ?
Well, there is a correlation of 0°50 between full brothers, you are just Sosing half of
your opportunity to seaect.
Bt would be some heKp _n the fSock mating, wouldnit it?
Thls concludes Dr. Dickerson_s portion of the program and R'm sure we all enioyed it
_ver¥
much°
We will have a two hour break Z_
until
this evenlng°s
meeting.
•.
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-_ ....
_. ..........
_.
Even though _t"_S_u-n_daymorning, it 0sstill an anformal meet0ng. You can take off
your coats, if you want too You can put your feet on the seat in front of you if the occupant
doesn't obiect.
We have had Dr° Lerner°s pedigree and performance record. I won't repeat that again
this morning° We certalnSy are famillar wlth his work because we discussed it quite a bit
yesterday° His subiect , here again an assignment "C_rcumstances that _ncrease and Decrease
the Effectiveness of Selection."
_ w_l_ now turn _he meeting over to-Dro Lerner.
Mr. Chairman, _ am very g_ad to hear tha_ you have already had your $50 worth so
you won't expect any more from me. _ hope tha_ holds true for the rest of you. When this
topic was first assigned to me, _ thought it sounded very attractive but the more I looked at
the rifle, the less _ knew wha_ _ was expected to talk abou_o My predecessors on the program
actually dealt w_h two somewhat speclf_c aspects, and apparently _ was expected to cover
something much more general, s_nce bo_h of the topics dealt with yesterday are _n a way
circumstances or conditions that affect efficiency of se_ectlOno So, _ think thebest way to
introduce the subject is perhaps to go over in a very general way some of the points that have
occurred to me _n connection w_th _he genera_ rifle leaving the details and some of the num_
erous other c_rcumstances that may arise that have not occurred _n my tabulation to the discussion by the panel and by the flOOr o