Effect of level of nutrition on onset of puberty and conception rates of zebu heifers.

Sixty zebu heifers were divided into three equal groups and reared on isocaloric diets but on different levels of protein. The protein levels were 19.17% (high), 13.37% (medium; NRC recommendations) and 8.3% (low). All animals were examined weekly per rectum for the presence of follicles and corpora lutea and also checked daily for standing heat. The presence of a mature corpus luteum was considered to indicate the attainment of puberty. Body weight and pelvic dimensions were taken at biweekly intervals. Intact bulls were introduced to heifers after they reached puberty and once they reached 200 kg live weight. Pregnancy diagnosis was carried out at 60, 90 and 120 days following introduction of bulls. Mean age at puberty for heifers in the high protein group (570.4 days), medium protein group (640.8 days) and low protein group (704.2 days) differed significantly (P<0.05). body weight at puberty for heifers in the high, medium and low protein groups was 207.1, 187.0 and 161.7 kg, respectively (P<0.05). Pelvic size at puberty was not influenced by the nutritional level. Conception rates of heifers in the three groups were influenced by level of nutrition. Pregnancy rates for the high protein group (58.8%), medium protein group (27.8%), and low protein group (16.7%) by 90-day post-breeding period were significantly different (P<0.05), but body weight at conception between the groups did not differ significantly. The results show that increasing the protein level in the diet is a means of improving the reproductive performance of zebu cattle.