ASSOCIATIONS BETWEEN LITTER SIZE AND SPECIFIC SOW-LEVEL MANAGEMENT FACTORS IN ONTARIO SWINE

This retrospective study examined associations between sow-level management factors and litter size in a target population of Ontario swine farms that used computerized recording systems between 1987 and 1991. The data were from 112 herds with 66 525 individual sow records. The average litter sizes were ten pigs (SD = 2.7) for primiparous sows and 11.4 pigs (SD = 3.1) for multiparous sows, respectively. The total born litter size (including pigs born alive, stillborn and mummified) was regressed on the sow-level variables of interest, Multiple regression models were built using a backward elimination approach and variables significant at P<0.05 were retained. There was a curvilinear relationship between litter size and parity; the largest litters were from sows in parities three through ten. Natural matings resulted in one more pig per litter than artificial insemination. Lactation lengths of 27-32 days and 33-40 days resulted in progressively larger litter sizes in subsequent farrowings than shorter lactation lengths. Litter size was highest at weaning-to-concepti on intervals of up to 4 days, decreased daily from 5 to 7 days, at which point it reached a plateau, until Day 11 when it increased again. The sow's current litter size was positively associated with her previous litter size. The model explained only 18% of the variation in litter size. As the age of the gilt at first conception increased, the litter size increased.