SELENIUM SUPPLEMENT
FOR PASTURE
Tall fescue and quackgrass paddocks of 1,5-acre were grazed by five
pregnant heifers. The heifers were rotated from one-half paddock to the
other each 28 days. The paddocks were fertilized with ammonium sulfate
at 80 pounds of N per acre and flood irrigated as necessary. The heifers
were placed on pasture on May 5 and removed on October 22. A mineral
supplement (Table 20) was supplied to each paddock at the rate of 2
ounces per head per day. Sodium selenite was added to the mineral
supplement at 200 and 400 parts per million (ppm) selenium. Each grass
by selenium treatment was replicated twice in a completely random design.
The selenium and mineral intake for each paddock is listed in
Table 21. The mineral intake of heifers on tall fescue decreased as
selenium content on the mineral increased. The mineral intake on quackgrass was not affected by mineral selenium content. Only three groups
consumed the 2 ounces of mineral offered. Nine other groups consumed
as little as 1 ounce of mineral.
Heifers on quackgrass pastures demonstrated a linear rise in whole
blood selenium from 0.2 to 0.4 ppm as a result of selenium supplement.
The tall fescue group increased from 0.2 to 0.27 ppm in the blood and
remained level thereafter (Table 22). The weight gain of heifers on
quackgrass increased by 0.3 pounds per day as a result of selenium
supplement both early and late in the grazing season. Selenium had no
effect on weight gain on tall fescue early in the season. In the late
part of the grazing season, selenium supplement and tall fescue groups
gained 0.2 pounds less than tall fescue with no selenium (Table 23).
27
The perloline and pyrrolizidine alkaloids of tall fescue are known
to increase in content in the latter part of the grazing season. These
alkaloids have been shown to affect digestibility and performance through
effects on the gastro-intestinal tract of cattle. These data indicate
inhibition of selenium supplement utilization by some factor in tall fescue. It seems reasonable that the seasonal factor in tall fescue may be
an alkaloid or alkaloids which develop in the late grazing season.
Table 20. Hi-Phos, Hi-Copper Mineral Supplement for Klamath, Oregon Area
Guaranteed Analsis
Ash
Calcium (CA)
Calcium (CA)
Phosphorus (P)
Magnesium (g)
Iron (FE)
Cobalt
Manganese (Mn)
Copper (CU)
Zinc (ZN)
Iodine (I)
Salt (NaCL)
Salt (NaCL)
Vitamin A
Vitamin D3
(Max.)
(Min.)
(Max.)
(Min.)
(Min.)
(Min.)
(Min.)
(Min.)
(Min.)
(Min.)
(Min.)
(Min.)
(Min.)
(Min.)
(Min.)
65.000%
8.000%
9.000%
13.000%
0.015%
0.250%
0.004%
0.080%
0.500%
0.400%
0.000%
4.500%
5.500%
20,000 USP Units/Lb
5,000 USP Units/Lb
28
Table 21. The selenium and mineral intake of pregnant heifers grazing
Tall fescue (TF) and quackgrass (QG) pastures, 1980
Mineral Intake
QG
TF
--oz/hd/day-
Se Intake
TF
QG
- mg/hd/day
Se
(ppm)
Rep.
0
1
2
0
0
0
0
2.1
2.0
1.4
1.4
X
0
0
2.1
1.4
1
2
12.9
8.6
15.9
9.8
2.0
1.5
1.4
0.9
x
10.7
12.9
1.8
1.2
1
2
21.2
9.3
31.8
28.7
1.9
0.8
1.4
1.3
3:
15.2
30.2
1.2
1.4
13.0
21.6
1.7
1.3
200
400
Overall mean
Table 22. The whole blood selenium of pregnant heifers grazing Tall
fescue (TF) and quackgrass (QG) pastures, 1980
Se
(PPm)
Pasture
7 May
2 July
(PPm)
27 Sept.
0
TF
QG
0.21
0.18
0.12
0.12
0.09
0.05
200
TF
QG
0.20
0.21
0.25
0.22
0.26
0.28
400
TF
QG
0.20
0.19
0.26
0.30
0.27
0.39
LSD
P(F)
CV
0.02 ppm Se
0.01%
18.4%
29
Table 23. The 84-day weight gain of pregnant heifers grazing Tall
fescue (TF) and quackgrass (QG) pastures, 1980
May-July
TF
QG
August-October
QG
Se
(ppm)
TF
0
145.6
144.7
99.5
69.7
200
157.0
168.2
80.7
95.1
400
143.2
159.4
84.7
92.0
LSD
32.5
51.7
SD
13.3
21.1
CV
11.2
17.4
lb/head
30