Reproductive performance of weaned sows after single fixed-time artificial insemination under a tropical climate: Influences of season and insemination technique.

We evaluated the reproductive performance of sows after single fixed-time AI under a tropical climate and investigated the influences of season and insemination technique on the efficacy of single fixed-time AI. After weaning, the sows were divided into CONTROL (n = 212) and FIXED-TIME (n = 212) groups. Sows in the CONTROL group were inseminated at 12 and 36 h after the onset of oestrus, while sows in the FIXED-TIME group were administered 10 μg of GnRH at 72 h after weaning and were inseminated 32 h later. Reproductive performance parameters, including total born, born alive, mummified foetuses and stillborn piglets per litter, piglet birth weight, variation of piglet birth weight within litter, regular return-to-oestrus and farrowing rate, were compared between the two groups. Season was classified into two groups: cool (n = 170) and hot (n = 254), and insemination technique was classified into two groups: conventional AI (n = 171) and intra-uterine insemination (IUI) with a reduced number of spermatozoa (n = 253). On average, regular return-to-oestrus (3.3 vs. 5.6%, P > 0.05) and farrowing rates (92.8 vs. 88.1%, P > 0.05) did not differ between CONTROL and FIXED-TIME groups. However, the total born and born alive piglets per litter in the FIXED-TIME were lower than in the CONTROL group (12.0 vs. 12.8 piglets/litter; P = 0.030 and 11.3 vs. 12.2 piglets/litter, P = 0.007). Interestingly, the number of total born piglets in the FIXED-TIME group was lower than in the CONTROL group only in the sows inseminated in the hot season (11.7 ± 0.32 and 12.9 ± 0.31, respectively, P = 0.005). Piglet birth weight, variation of piglet birth weight within litter, number of piglets at weaning and body weight of piglets at weaning did not differ between groups, irrespective of the season (P > 0.05). The total number of piglets born per litter in the FIXED-TIME group was lower than that in the CONTROL group in sows inseminated via IUI (11.7 ± 0.32 and 12.9 ± 0.32, respectively, P = 0.013), but not in sows inseminated using conventional AI (12.7 ± 0.42 and 12.5 ± 0.41, respectively, P = 0.772). Single fixed-time AI could be successfully performed in sows under a tropical climate, with a promising reproductive performance. However, a decreased litter size at birth after single fixed-time AI was observed when insemination was performed in the hot season. Moreover, single fixed-time AI using IUI with a reduced number of spermatozoa also decreased litter size at birth.