48
THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
EFFECTS OF C L I M A T I C F A C T O R S O N L I V E S T O C K
F. R. E D W A R D S
Georgia Agricultural Experiment Station
Climatic factors include those environmental influences, such as temperature, humidity, atmospheric ionization, light 'and other forms of radiation, which in the final analysis are the result of solar radiations on the
earth, its waters, and its atmosphere. The climatic differences from the
equator to the poles are due chiefly to the amount of solar radiation received throughout the year and at different times during the year. Seasonal changes in climate are due to the inclination of the earth's axis
from an angle perpendicular to its plane of rotation around the sun.
These climatic factors and seasonal changes are generally quite dependable in their constancy for any one place on the earth's surface. Studies
by C. G. Abbott of the Smithsonian Institution have shown that solar
radiations may vary as much as 10 per cent but such extreme variations
are seldom reflected more than fractionally by such climatic factors as
temperature, due to the equalizing effects of atmosphere, winds, bodies
of water, and latent heat.
It is generally understood that influences affecting animals may be
classed as either hereditary or environmental. Leaving out the relative
weights of these two classes we can safely say that both are of fundamental importance. Since climatic factors obviously belong in the class
of environmental influences we will not consider the hereditary influences here. An analysis shows that climatic factors are not exceeded in
fundamental importance, according to the definition given above, by
any other environmental influences when we consider both the direct
and the indirect effects. This does not except even such essentially important influences as feed and water, for these in turn are dependent
on climatic factors.
Due to the more or less definite zoning of climates and to the relative
constancy of climatic conditions at almost any given place it is easy to
understand that biological species and sub-species would evolve to suit
the special climatic conditions under which they have long existed.
That this is true is shown by the remarkable adaptations seen under
different climatic conditions. The palm and the orchid have evolved
under a tropical climate and are adapted to such conditions while the
spruce and the reindeer moss have been evolved to suit the colder
climates under which they have developed for countless generations.
In the animal kingdom we find that most species, especially the warmblooded animals, are more adaptable to climatic variations than are
THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
49
plants. This is due to their controlled body temperature, power of locomotion, intelligence, and other qualities.
However, even among mammals one finds frequent and striking evidence that much evolution has taken place to adapt them to their
climatic habitat. The humped zebu and the water buffalo of coastal
Bengal, for example, have evolved to meet climatic conditions far different from those in Tibet, only 400 miles away, under which their bovine
cousin, the yak, has developed. The amount, nature, and extent of the
hair covering, for conserving body heat and for protecting against sunlight, is one of the most obvious means for adaptation to climatic factors
but we find that there are scores of other ways by which an animal may
be adapted to meet the various climatic influences. In recent years some
information has been obtained on the part played by various endocrines
in this. W e know, for instance, that metabolism, so important in adaptation to climate, is controlled by endocrine substances.
It is possible not only for animals to evolve over a long period by
various more or less permanent body changes to meet certain climatic
conditions but it is also possible for temporary climatic changes to effect
animals and bring about passing changes in body functions. Some of
the functions that apparently may be influenced temporarily by climatic
factors are the breeding cycle, lactation, digestion, metabolism, growth,
fattening, hair growth and shedding, and endocrine activities.
The importance of climatic factors in livestock production has not
been fully recognized, it seems, when judged by the attention given by
research workers. Perhaps this may be attributed in part to the fact that
most livestock research has been carried on in a limited area of the
earth's surface, chiefly under temperate climatic conditions, where improved livestock production has reached its highest development. Under
these conditions the animals are generally well adapted to the climate,
so the importance of these factors is probably not as obvious as is the
case under conditions to which the animals are less well adapted. It is
understandable, therefore, that most of the attention of research workers
has been given in the past to such problems as feeding and nutrition
and that the effects of climatic factors on animals have been left largely
to the zoologists and other workers in the more basic branches of the
biological sciences. W e believe that increasing attention will be paid to
this in the future by research men in the field of animal husbandry. Recent developments in the practical control of certain environmental
factors, such as "air-conditioning", should stimulate research along this
50
THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
line with domestic animals, particularly dairy cattle, as well as with
man.
A statistical study, now in progress at the Georgia Experiment Station, has brought out some interesting indications on the effects of season
of breeding on the butterfat producing capacity of the resulting individual. This study is based on all herd book and registe r of merit records
of the American Jersey Cattle Club for the 23 year period starting
with the establishment of the register of merit in 1903. The figures presented here are based on the complete records as indicated above for two
states, Georgia and Maine. These two states were chosen as being suit,
able for a comparison of this kind not only by reason of their contracting
latitudes but also because both are located on the eastern seaboard and
have oceanic types of climate and it was felt that both had enough
production records to be significant.
In this study all register of merit records for the two states were
listed according to the time of year when the cow was born. In this
the year was divided into 24 approximately equal divisions so that each
of the 12 months were split in two parts, as nearly equal as possible. In the
graphical presentation of the data the birth dates are changed to conception dates inasmuch as it is believed that the conception date (or breeding
date) is of more practical use to the farmer or dairyman than is the
birth date which is after all dependent on the date of breeding. Also
it would seem probable that the conception date has a more direct influence on the producing ability of the resulting individual than has the
birth date. In figuring the conception or breeding date from the birth
date 281 days were deducted from the median date for the period involved; this is based on the average gestation period for cattle.
All production records were figured to a 365 day equivalent and
for a mature cow (5 years old) standard. In order to simplify the
weightings given to cows of the different producing capacities all
qualifying for the register of merit were divided into classes on a mature
cow 365 day test basis. Those with less than 500 pounds butterfat were
given a weighting of one point, those above this but not qualifying
for medals were weighted two points, and those having medals were
weighted three points. It was necessary to correct the figures obtained
from the above for the 24 different divisions of the year in order to
eliminate the influence of uneven birth rates through the year. This
required a tabulation of all animals recorded in the hem books for the
two states during the 23 year period. The results obtained in the study
are presented in the accompanying table.
T H E A M E R I C A N S O C I E T Y OF A N I M A L P R O D U C T I O N
Birth Date
(by half
months)
Birth Distribution
(percentage of 12
months total) x
Month, half
Georgia
%
Weighted Produc.
Figures, Uncor,
rected for Birth
Distribution
(percentage of 12
months total) xx
Maine
%
Georgia
%
51
Weighted Produc.
Figures, Corrected
for Birth Distribution (percentage
of 12 months
total)
Maine
%
Georgia
%
Maine
%
Jan., first ........ 4.631
3.764
4.721
3.308
4.248
3.662
Jan., last ........ 4.478
3.716
5.150
4.812
4.792
5.396
4.771
Feb., first ........ 4.587
3.940
3.004
4.511
2.729
Feb., last ........ 4.302
3.267
3.863
3.120
3.742
3.980
Mar., first ........ 5.114
4.116
3.433
4.012
2.797
4.062
Mar., last........ 5.553
4.709
6.009
4.012
4.509
3.550
Apr., first ........ 5.421
4.660
3.433
3.566
2.639
3.182
Apr., last ........ 5.202
4.036
6.009
2.526
4.813
2.608
May, first........ 5.641
3.700
3.863
31418
2.854
3.850
May, last ........ 5.004
3.491
4.721
2.229
3.931
2.661
June, first........ 4.741
3.091 -
2.575
2.377
2.263
3.204
June, last ........ 3.841
3.635
3.433
1.932
3.724
2.215
July, first........ 3,578
3.331
3.433
4.606
3.998
5.762
July, last ........ 3.139
3.443
3.863
3.715
5.128
4.496
5.111
Aug., first........ 3.753
4.725
3.433
5.795
3.812
Aug., last ........ 3.270
4.965
3.433
6.092
4.375
5.113
Sept., first........ 3.995
5.365
1.288
6.092
1.343
4.732
Sept., last ........ 2.722
5.093
6.867
4.7r
10.~13
3.891
Oct., first....... 2.963
5.109
3.863
5.943
5.432
4.847
Oct,, last ........ 3.248
4.949
6.867
5.052
8.809
4.254
Nov., first........ 3.205
4.404
4.721
4.903
6.138
4.639
Nov., last ........ 3.358
4.228
3.004
4.458
3.728
4.394
Dec., first........ 3.863
3.892
5.150
3.418
5.556
3.659
Dec., last ........ 4.412
4.372
3.863
5.0~2
3.648
4.815
x from herd record books,
xx from register of merit.
T h e figures in t h e table give t h e p e r c e n t a g e o f t h e e n t i r e 12 m o n t h s
total f o r each h a l f m o n t h . I n o r d e r to s m o o t h o u t irregularities in t h e
c o r r e c t e d p r o d u c t i o n figures a
m o v i n g average w a s used f o r m a k i n g t h e
g r a p h i c a l p r e s e n t a t i o n . I n o b t a i n i n g this m o v i n g average full value w a s
given to t h e m a i n figure a n d h a l f value to t h e t w o a d j a c e n t figures. T h e
c h a r t s h o w s t h e d e v i a t i o n f r o m t h e composite average.
52
THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
~+3.0
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-2.0
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RELATION OF C O N C E P T I O N D A T E T O B U T T E R F A T P R O D U C T I V I T Y
OF JERSEY C O W S I N GEORGIA A N D M A I N E
Deviation from average part of annual production of periodic parts
(moving averages in per cent by semi-monthly periods).
It is seen from the table and chart that the chances for a cow having
high butterfat producing capacity are better if she was conceived during
December or January in Georgia and from October to May in Maine.
These seasons are those of cool temperatures in both cases and the figures
appear to indicate that conception occurring during the cool season
has a tendency to increase the butterfat producing capacity of the resuiting individual. The chart reflects quite accurately the short summers
in Maine and the short winters in Georgia. The midwinter decline in
Maine, from December to March, inclusive, is attributed to the fact
that dairy cattle there, especially purebreds of high quality, are usually
warmly housed during this time. This is not generally true in Georgia
where winter temperatures are mild. The late fall and early spring
upturns in Maine are due, it is believed, to the effects of cool weather
when the cattle are out doors. It has not been possible to eli,ninate the
effects of all other variables than temperature in a study of this kind but
these other variables appear to be compensating to a large extent and the
THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
53
figures presented are believed to have significance. A careful study of the
results seems to indicate that the differences are due more to direct effects
of climatic factors than to seasonal nutritional differences in pastures and
feeds.
If the season of conception has an influence on the butterfat producing capacity of a cow the question arises as to what this can be attributed. One theoretical explanation that has been offered is that under
wild or feral conditions cattle breed at a more or less definite season of
the year, as do many wild animals. Under domestication cattle have
gotten away from this seasonal breeding, as has man and other domesticated animals. The theory is that even though cattle have quit their
old seasonal breeding habits they are still best'adapted for breeding at
that time of the year and produce stroriger calves with more vitality
when bred at that "natural" breeding season. This supposed increase i n
vitality, constitution, and strength is offered as an explanation for the
indicated higher butterfat producing capacity. Possibly it might be
found that a clearer explanation would be found in the effects of temperature and other climatic factors on the secretion of some of the
endocrines connected with reproduction.
The l~trge body of figures involved in this study have not permitted
consideration of more than two states at this time but it is planned to
add other selected states to the study later when opportunity presents.