A Review of the Causes of Reproductive Failure in Swine

Abstract

SUMMARY Environmental and hereditary factors which are known to affect reproduction in swine are summarized. Losses in terms of eliminated breeding stock are considerable. It is estimated that 20–25 per cent of gilts and 12–14 per cent of sows may be eliminated due to infertility (non-pregnant, anoestrous, genital defects). Piglet mortality from parturition to weaning amounts to no less than 1:5–25 per cent. The average litter size is influenced by parity, age of sperms, ovulated eggs and maternal environmental factors. Conception rates are highly influenced by the number of natural matings or artificial inseminations per oestrous period. Anoestrus or silent heat is one of the foremost single restraining factors for the full utilization of the reproductive capacity of pigs. Prolonged anoestrous periods occur particularly in sows after their first farrowing. Continuous high plane feeding (protein as well as energy) after the lactation period and until mating must be considered of paramount importance for heat manifestation in breeding sows. The “flushing” technique seems to show correlation between the feeding level and the ovulation rate in pigs. Certain minerals and vitamins, particularly manganese and vitamin A, are essential for normal reproduction in sows and gilts. Hormonal control of oestrus with gonadotrophins is used extensively in some countries but hormonal treatments of highly selected breeding stock is not advisable. At present synchronization of heat in pig populations needs further elucidation before this technique can be recommended as a routine procedure in the field. Strictly venereal diseases are not known to occur in pigs. Some infections (Brucella suis and certain Leptospira species) are widespread causes of abortion and stillbirth. Also viral agents (hog cholera, pseudorabies, SMEDI viruses) are known to cause foetal death in pigs. Different bacteria may cause sporadic abortion, stillbirth and less severe cases of endometritis (streptococci, Staphylococcus aureus, Salmonella sp., Escherichia coli a.o.). Malformations of the genital organs occur rather frequently in gilts and sows. Between normal breeding boars some degree of variation exists within their fecundation rate (approximately 10 per cent). Nearly 40–50 per cent of breeding boars are eliminated at an early age due to infertility (impotentia coeundi, poor semen quality). The productive efficiency of boars used for A.I. is three times that of boars used for natural matings. The total production costs of piglets produced by A.I. is about one-half the costs for production of piglets by natural mating. Therefore expansion of A.I. may be expected in the future and underlines the importance of controlling inherited abnormalities (malformations, chromosomal abnormalities, etc.). Some defects (atresia ani, congenital spinal cord and vertebral anomalies, myoclonia congenita and dermatosis vegetans) may occur with a frequency which necessitates immediate replacement of the boar.