| Summary: | Two trials were conducted to determine the effect of hour of weaning on endocrine changes, weaning-to-estrus interval (WEI), and rebreeding performance of sows. A total of 84 Cotswold sows of mixed parity were used in a completely randomized design. Sows were maintained in a cycle of 9h light: 15h dark from day 105 of gestation. After an 18-day lactation sows were weaned at either 0800h (AM; immediately after lights-on) or 1645h (PM; immediately before lights-off). Eighteen sows were fitted with indwelling ear-vein catheters on the day before weaning. Sera, from blood samples taken at 30-minute intervals from the day of weaning to the second day of standing estrus, were analyzed for luteinizing hormone (LH), estradiol, and progesterone. All sows were monitored for WEI, synchronization of post-weaning estrus, pregnancy, and subsequent farrowing performance. Sows were naturally inseminated on the first day of estrus followed by AI at approximately 10 and 24h. (Abstract shortened by UMI.)
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