Abstract |
- Ninety-two spring-born and 76 fall-born steer and heifer calves
(Hereford and Angus x Hereford) averaging 188 and 255 kg, respectively,
were utilized in a 2x2 factorial arrangement of treatments to study
the effects of zeranol and monensin, alone and in combination, on
growth rate, feed efficiency and carcass characteristics. After
weaning, calves were stratified by weight for random allotment to
four treatments: 1) control (no monensin, no zeranol); 2) zeranol
alone; 3) monensin alone; and 4) zeranol-monensin combination.
Zeranol (36 mg) was implanted subcutaneously in the ear every 90
days and monensin (200 mg) was fed daily. The diet for both growing
periods consisted of hay free choice and a barley-biuret supplement.
The diet of both finishing periods (steers only) consisted of a full
feed of barley with limited hay intake and biuret for additional
protein. Results for the spring-born calves indicated treatments
3 and 4 increased ADG (P<.05) during the winter (196 days) while
feed efficiency for steers and heifers was improved by 8, 5; 24,
21; and 27, 11% on treatments 2, 3 and 4, respectively, as compared
to 1. Average daily gain for the summer grazing period (98 days) was increased (P<.05) by treatments 2 and 4. During the finishing
period (97 days), treatment 4 increased ADG (P<.05), while monensin
improved feed efficiency by 12%. Overall ADG (391 days) for steers
was increased 3, 7 and 16% on treatments 2, 3 and 4, respectively,
as compared to 1. During the growing period (111 days), fall-born
steers and heifers gained .68, .61; .86, .70; .82, .71; and .88,
.86 kg, respectively, on treatments 1, 2, 3 and 4. All treatments
increased gains (P<.05) over 1 with treatment 4 producing increased
gains (P<.05) with the heifers. During the 153-day finishing period
for treatments 1, 2, 3 and 4, gains were .85, .95, .92 and 1.01 kg,
respectively, with treatments 2 and 3 different (P<.05) from 1 and
treatment 4 different (P<.05) from 1 and 3. Again, monensin improved
feed efficiency by 12%. Overall ADG (264 days) for steers was
increased 13, 9 and 18% on treatments 2, 3 and 4, respectively, over
1. Carcass data for all steers indicated a one-third older maturity
score (P<.05) for steers receiving zeranol. Zeranol-implanted steers
also exhibited a tendency for a slight reduction in quality grade but
improved (2.1 vs. 2.3) yield grade. Either zeranol or monensin
produced an acceptable increase in gains, but the additive effect
exhibited by their combination provided additional and more consistent
gains during the growing and finishing periods.
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