Duration of estrus in relation to reproduction results in pigs ou commercial farms

This research was conducted to determine factors that influence duration of estrus, AI strategy, and reproduction results between and within commercia l swine farms that use AI. Data from 15,186 sows and gilts on 55 farms for a period of 6.1 +/- 4.2 mo per farm were used in this study. The;average du ration of estrus was 48.4 +/- 1.0 h, ranging from 31 to 64 h, and was consi stent from month to month within a farm (repeatability of 86%). Differences in duration of estrus between farms accounted for 23% of the total variati on in duration of estrus. On most farms (n = 45), gilts showed a shorter (P < .05) duration of estrus than sows (40.8 +/- 1.1 h vs 48.5 +/- 1.0 h). Th e duration of first estrus after weaning was longer (P < .0001) compared wi th that of repeat-breeder sows (50.2 +/- 1.0 h vs 46.8 +/- 1.0 h). Duration of estrus decreased (P < .05) when interval from weaning to estrus increas ed from 4 to 6 d (56.0 +/- 1.2 h vc; 45.8 +/- 1.2 h). The regression of int erval from onset to estrus to first AI and interval from weaning to estrus varied between farms and ranged from -7.4 to +1.3 h/d; four farms had a pos itive relationship. Farrowing rate decreased (P < .05) from 89.7 +/- 2.7% t o 78.2 +/- 5.74 when the interval from weaning to estrus increased from 4 t o 10 d. The litter size decreased (P < .05) from 11.7 to 10.6 pigs when the interval from weaning to estrus increased from 4 to 7 d. Compared with a s ingle Al, double AT. in sows and gilts resulted in a 4.3 and 7.0% higher (P < .05) farrowing rate, respectively. When the first Al was performed after expected ovulation, reproduction results were lower than when AI was perfo rmed before or at expected ovulation in sows. Duration of estrus was not re lated to farrowing rate or litter size in individual pigs. Number of insemi nations per estrus, time of AI, and duration of estrus were correlated, whi ch made it difficult to assess which of these factors was primarily related to the farrowing rate or litter size. Knowledge of average duration of est rus on farms and of factors that influence the duration of estrus on commer cial farms can help to improve the efficiency of the AI strategy specific f or each farm.