The effects of feed restriction and realimentation on the growth and reproductive function of Bokoloji bulls

A group of Bokoloji bulls (n = 36), consisting of 18 young bulls (12 to 18 mo old) and 18 old bulls (24 to 30 mo old) were used to study the effects of feed restriction and realimentation on reproductive function. The bulls were placed either on a low (L), medium (M) or high (H) plane of nutrition during the 3 treatment periods. At the low and medium feeding levels, the animals received approximately 25 and 45%, respectively, of the intake of the bulls on the high plane diet. All the bulls were fed a low (L) plane of nutrition for 90 d in the first treatment period. The 3 treatments were designated as LL, LM and LH for the mid-period, and as LLH, LMH and LHH for the final period, according to the prescribed level of feeding. Body measurements and scrotal circumference were taken for all bulls before slaughter. A total of 18 bulls was slaughtered at the end of the mid-period, while the remaining 18 bulls were slaughtered at the end of the final period. Testicular weights as well as gonadal and epididymal sperm reserves were determined. At the end of the mid period, the bulls on a high plane of nutrition had significantly (P < 0.05) higher live weights and chest girths than bulls on the medium and low planes of nutrition. Gonadal sperm/spermatid reserves of 5.2 X 10(9) and epididymal sperm reserves of 2.4 X 10(9) in bulls on the high plane of nutrition were significantly (P < 0.05) higher than the sperm reserves for the bulls on either the low or the medium plane of nutrition. At the end of the final period, no significant differences existed among the LHH, LMH and LLH treatments in liveweight, chest girth, scrotal circumference and sperm reserves (P > 0.05). It is concluded that bulls which have undergone feed restriction for 90 d are capable of regaining their body growth and reproductive function if such bulls are placed on an adequate plane of nutrition.