Control of pig reproduction in a breeding programme.

Important improvements in the management of sows have been made over the past 20 years in Europe and the U.S.A. Nevertheless, annual productivity varied between 15 and 25 piglets weaned per sow per year in France for 1983. Reasons for such a difference in productivity have been analysed quantitatively. Marked differences exist between herds in the genotype of pig used and in the age of puberty. Transportation acts as a stress stimulus and stimulates puberty attainment. However, there is variability in the occurrence of oestrus amongst different purchased batches of pigs. Recent endocrine results led to four phases in sexual maturation of gilts being distinguished (perinatal, infancy, activation and resting) and permitted a better understanding of the variation in the onset of puberty. After a lactation of 3 weeks or more, about 25% of primiparous sows did not return to oestrus within 1 week of weaning. Fertility of these sows with a delayed oestrus was 10% lower than in sows having a normal oestrus after weaning. The past 3 decades of research on control of ovulation have yielded positive results. However, there is no satisfactory method for the induction of puberty. One method used to regulate the oestrous cycle in gilts is treatment with a progestagen. This method is still available commercially in France. The close synchronization obtained with a progestagen treatment has led to the use of AI at fixed days (Days 6 and 7) in crossbred gilts but not for purebred gilts. Some environmental factors (e.g. male stimulation, age of gilts at treatment, diet and month of AI) have been analysed to evaluate their effects on farrowing rate and litter size. After weaning, a short treatment with a progestagen (20 mg/day) tends to improve the synchronization of oestrus (3-9 days), especially in primiparous sows. Farrowing rate and litter size are similar in treated sows and control sows. However, this technique does not permit fixed-time AI without detection of oestrus. Diagnosis of pregnancy was successful with ultrasound scanning. This technique can be performed 20 days after insemination if the sow is tied up during the examination and at 22 days if the sow is restrained in a retention box. From 22 days after mating, errors made for positive and negative diagnoses were less than 5%. These techniques contribute to a better control of reproduction in different management systems.