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EFFECTS OF FEEDING LEVEL AND REARING METHOD ON SEXUAL DEVELOPMENT IN YANKASA SHEEP
Abstract:
The study examined the effects of feeding level and rearing method on sexual development in Yankasa sheep. Seventy-two animals with mean age and body weight of 145.3 +17.7 days and 10.1+2.6 kg respectively were used for the 4 months investigation. Animals were randomised in a 3×3 factorial design with feeding rate at 3 levels (low, medium and high) and rearing method at 3 levels (males alone, females alone and both males and females). Sixty-six animals survived to the end of the experiment, made up of 34 females 32 males. Traits investigated included, age, body weight and scrotal circumference at puberty, and changes in scrotal circumference in ram lambs; progesterone concentrations in ewe lambs, sexual activity and growth performance in both sexes. Feeding level and rearing method had highly significant (P<0.001 and P<0.01, respectively) effects on average daily gain (ADG) on experiment. The overall ADG (+ s.e.m.) was 77.8+3.0 g/day. Animals on the low, medium and high levels gained 66.8+5.49, 77.8+5.6 and 89.0+5.6 g/day respectively. As feeding level increases, there is a corresponding increase in live weight gain. Generally, males gained faster in weight than females. Males were sexually more active (26 out of 32) than females (3 out of 34). Mixed rearing produced animals that were sexually more active (13 out of 15) than males alone (13 out of 17). Sex and rearing method had highly significant (P<0.001 and P<0.01, respectively) effects on sexual activity. Progesterone concentrations in the Yankasa ewe lambs within 264 days of age was 0.57+0.04 ng/ml. Feeding level had a very highly significant (P<0.001) effect on progesterone concentrations, with the concentrations for low, medium and high levels of feeding as 0.43+0.05, 0.73+0.05 and 0.56+0.04 ng/ml, respectively. Although rearing method had no significant (P>0.05) effect on progesterone concentrations, mixed rearing showed relatively higher (0.61+0.04 ng/ml) concentrations than females alone (0.53+0.04 ng/ml). Generally, progesterone concentrations decreased with increase in the sampling date; implying probably that season of the year might have influenced progesterone concentrations in Yankasa sheep. For pubertal determination, the results showed that age, body weight and scrotal circumference at puberty in the ram lambs were 232.5+12.7 days, 18.3+0.4 kg and 22.7+3.1 cm respectively. The implication is that these animals are capable of breeding from this age. In the ewe lambs, serum progestrone profiles gave no clear indication of pubertal age. Feeding level and rearing method had no significant (P>0.05) effect on age and scrotal circumference at puberty in the ram lambs. However, feeding level showed a very highly significant (P<0.001) effect on body weight at puberty.
EFFECTS OF FEEDING LEVEL AND REARING METHOD ON SEXUAL DEVELOPMENT IN YANKASA SHEEP
