Observations on reproduction in a pedigree herd of Large White pigs

Abstract

1. The information analysed in this report is taken from records of the Compton herd of Large White pigs over a period of about 4 years. 2. Length of gestation period: close concentration about the mean of 114·17 days; no apparent relationship between litter size and extremely long or short gestation period. There was no difference in the average duration of pregnancy as between old and young sows, nor was there any evidence of a characteristic tendency to long or short pregnancies in individuals. The incidence of stillbirths appears to be independent of the length of the gestation period. 3. The number of pigs born, alive or dead, ranged from 3 to 24, the average being 13·12. The average number of pigs born alive was 12·4 and the average number weaned was 8·1. 4. The average number of pigs born rose with successive pregnancies to a maximum of more than 15 in the 6th and 7th litter and declined thereafter. The average number born alive reached a maximum of more than 14 in the 5th litter and declined thereafter, the decline being less marked among pigs born alive than among all pigs including stillbirths, apparently because embryonic mortality (before parturition) bears more heavily on the litters of older sows, whereas the incidence of stillbirths is not related to age (or to the ordinal number of the litter). 5. The incidence of stillbirths was studied in relation to litter size, the data being compared with similar data recorded elsewhere. The proportion of stillbirths was higher among female piglets than among males. The reverse was true in litters of less than average size, and the possible significance of this difference between smaller and larger litters is discussed. 6. The foetal sex ratio appears to bear no relation to the ordinal number of the litter or to its size. 7. The reasons for discard of sows which have been culled during the period under review have been recorded and are briefly discussed.