Seasonal and management effects on fertility of the sow: a descriptive study

This study was undertaken to determine management and seasonal effects on f ertility in 1298 Finnish sow units over a 4-year period in 1992-1996. A mul tivariate analysis of the herd record data was undertaken to study the effe ct of various management factors on rebreeding rate. Factors found to have an effect were further subjected to time series plotting for seasonal effec ts. In addition, seasonal effects on the farrowing rate, age of gilts at fi rst mating and littersize as well as the 3-week litterweight were studied. Year and month caused the most significant variation in the rebreeding rate . Moreover, geographical area, herd and way of breeding (mating vs. artific ial insemination) were found to be significant determinants of rebreeding r ate. Dry sows loosely housed were more likely to be rebred than sows housed in individual stalls. Sows receiving roughage feed (hay, straw) or bedding (straw) were less likely to require rebreeding. A significant seasonal flu ctuation in farrowing rate was found with a nadir of 72.6% in August and a high of 80.9% in January. The average farrowing rate for the 4-year period was 77.7%. The age of gilts at first mating showed seasonal variation of 11 days (229.9 +/- 0.5 days in March and 241.4 +/- 0.5 days in November). In conclusion, this study indicates that group housing of dry sows increases t he risk of rebreeding. In group housed sows, rebreeding more often occurs a fter an irregular oestrus-to-oestrus interval in summer-autumn whereas a no t-in-pig seems to be a more common finding at late gestation in individuall y housed sows. (C) 1999 Elsevier Science B.V. All rights reserved.