The objectives of this study were to monitor the physiological events associated with decreasing liveweight in Bos indicusheifers and to determine the characteristics which best predicted the onset of nutritional anoestrus. Eleven post-pubertal Brahman heifers received a diet resulting in a liveweight loss of 0.7 kg/day. Changes in ovarian morphology were monitored using daily transrectal ultrasonography. Liveweight was recorded twice weekly. Heifers became anoestrus after 98 ± 9 days, following a decrease in liveweight of 68.6 ± 4.9 kg, equivalent to 21.5 ± 1.5% of initial weight. At this time, maximum diameters of ovulatory follicles and corpora lutea (CL) had decreased by 16.7 ± 3.9% and 23.7 ± 3.1%, respectively. Onset of anoestrus was best predicted by liveweight and maximum diameter of CL when expressed as proportions of initial liveweight and size of CL. The percentage decreases in liveweight and maximum diameter of CL to give a 50% probability of anoestrus were 21.0% (95% confidence interval = (17.7, 27.4)) and 23.0% (16.7, 37.0), respectively.
Proceedings of the New Zealand Society of Animal Production, Volume 56, , 381, 1996
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