Influence of farm management and breed type on sow's conception-weaning interval and productivity in France

The number of piglets produced per sow per year has been calculated from the production performance results of French sow herds.The weaning-conception interval varies according to the season of farrowing: the average length is 15–20 days between October and June, and 26–30 days for the summer months. In addition, it is maximum between the first and the second litter and declines with the litter order. The interval is significantly smaller in crossbred females as compared to the two parental breeds used in France (Large White and Landrace) and this heterosis effect, appearing in spite of great differences in the size of the samples, has to be emphasized.The general average value for 142 333 litters ($\text{x}\text{= 22.4}\text{days}$) remains abnormally high although a very great number of the sows exhibit oestrus and are fertilized 5 days after weaning. However, even though 60% of the animals observed were pregnant 15 days after weaning 15% were fertilized between 22 and 40 days and 5% were not pregnant 3 months after weaning. A great effort must be made to develop efficient techniques for the detection of pregnancy and for culling non-fertilized animals in time. At present, mean age at weaning is 44 days (244 906 litters); it decreased from 60 days in 1967 to 38 days in 1973. It should be noted that weaning practised less than 10 days or more than 45 days after parturition disturbs the reproductive activity of the sow. Optimum weaning age, ensuring a minimum time lapse before fertilization of the sow, is between 21 and 35 days after farrowing.It may be concluded that control of reproduction, as well as reduction of the weaning age represent two means liable to increase the numerical productivity of French sow herds.