Litter productivity at first and second parity by gilts mated at different weights at first or second estrus

Graduation date: 1983Purebred Yorkshire gilts with weights ranging from 70 to 105\ud kilograms were moved from a total-confinement rearing unit to a\ud total-confinement brood stock unit where approximately ten gilts\ud per pen were mixed to provide new penmates. Each gilt was thus\ud exposed to an unfamiliar environment and to foreign penmates along\ud with continuous area presence of boars and adults sows. Each day,\ud gilts were moved from their pens and checked for estrus by direct\ud boar contact for at least 20 minutes per day. By random allotment\ud within weight groups, gilts were designated to be mated at first or\ud second heat. Gilts which did not reach puberty within 42 days after\ud allotment were removed from the study. After mating, all gilts were\ud managed alike during gestation and lactation. Once gilts were mated,\ud production data were obtained for two parities.\ud Thirty-four gilts in each mating group farrowed first-parity\ud litters; 79 percent of gilts mated at first estrus and 76 percent of those mated at second estrus mated within 30 days postweaning of\ud first litter for production of a second litter. Conception rates\ud were 81.5 and 80.7 percent, respectively.\ud There were no significant differences (P > .05) between gilts\ud from the two groups for age or weight on experiment, age or weight\ud at breeding, weight at 110 days of gestation at first or at second\ud parity, or in weight at weaning of first-parity litters, weight loss\ud during first lactation, weaning-to-estrus interval, or in conception\ud percentage following first lactation.\ud At both first and second parity, number of pigs per litter,\ud total litter weight, and average pig weight at birth, 21 and 42 days\ud of age were not significantly different (P > .05) between gilts\ud initially mated at first versus second estrus. Gilts from the two\ud groups produced significantly more pigs (P < .05) at second parity\ud than at first parity. Correlation coefficients for litter\ud productivity traits between first and second parity were low and\ud not significant within either mating group. No significant\ud correlation (P > .05) existed for first-parity lactation weight\ud loss or litter productivity traits between dams which did or did not\ud come in heat within 30 days postweaning.\ud On test, weight had no significant association with days to\ud mating within either group. Breeding weight of gilts for\ud first-parity litters was not significantly associated with any\ud first-parity litter trait. The only significant correlations\ud between breeding weight of gilts initially bred at first estrus\ud were with number of pigs at 42 days (r = 0.36, P < .06) at second parity, and total second-parity litter weight at birth (r = 0.38,\ud P < .05). There was no association between breeding weight of\ud those bred at second estrus and second-parity litter traits.\ud Weight loss during first lactation as not significantly associated\ud with days to postweaning estrus for either group, or with litter\ud size at birth at second parity. Weight at 110 days of first-parity\ud gestation of gilts from either of the two groups had no effect on\ud second-parity litter traits except for a significant correlation\ud with number of pigs at 42 days for those initially bred on first\ud estrus (r = 0.32, P < .10).\ud For gilts bred at first estrus, dam's weight at weaning of\ud first-parity litters had significant correlation at second parity\ud with number of pigs at 21 days (r = 0.30, P < .10) and at weaning\ud (r = 0.42, P < .05), and with total litter weight at weaning\ud (r = 0.42, P < .05) at second parity. For first-parity gilts bred\ud at second estrus, weight at weaning of first-parity litters had\ud significant correlation at second parity with number of pigs weaned\ud (r = -0.39, P < .06); total litter weight at 21 days of age\ud (r = -0.32, P < .10) and with total litter weight at weaning\ud (r = -0.34, P < .10).\ud Association of weight with litter productivity tended to be\ud small; when significant, they tended to be positive for dams\ud initially mated at first estrus and negative for those initially\ud mated at second estrus. Correlations between litter productivity\ud traits at first and second parity were not significant for either\ud mating group. Although litter productivity differences between the two mating\ud groups were not statistically significant, they are in general\ud agreement with findings reported in the literature of increased\ud productivity due to delayed mating versus mating at pubertal estrus