Interactions between the associations of parity, lactation length, and weaning-to-conception interval with subsequent litter size in swine herds using early weaning.

Sixteen farms having an average lactation length between 14.9 and 18.9 days were selected based upon producers' willingness to keep records of production and lactation feed intake. Data contained 9162 subsequent litter-size records abstracted from computerized production information-system files and lactation feed-intake records. Two-way interactions between the associations of parity and lactation length, and parity and weaning-to-conception interval with subsequent litter size were found in the same statistical model. Subsequent litter size did not increase in parities 1 and 2 as lactation length increased--but subsequent litter size in sows of parities 3-6 increased. In only parity 1, sows with weaning-to-conception interval 6-12 days produced 0.5 fewer pigs at subsequent farrowing than those with weaning-to-conception interval 1-5 days. However, in multiparous sows, no difference in subsequent litter size was found between weaning-to-conception intervals 1-5 and 6-12 days.