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US Department of Agriculture, Clay Center, NE 68933
Abstract
Four-hundred and ten Duroc, Hampshire, Yorkshire and Landrace x Large White (L x LW) reciprocal-cross gilts were reared in confinement (C) or nonconfinement (NC) during either a winter (October to April) or summer (April to October) season. Within each season, gilts were assigned to experiment in two groups according to age (winter, period 1 and 2; summer, period 3 and 4). At 2.5 months of age, littermate gilts were allotted by weight to C or NC pens, with 16 to 18 gilts/pen. Confinement pens were located in an enclosed building, and measured 3.7 x 4.6 m with a 2.1 x 4.6 m slatted floor area. Dirt lot NC pens were 29.3 x 9.8 m with 3.7 x 4.3 m steel shelters. Gilts were checked once daily for estrus beginning at 4.8 months of age. Weekly blood samples were collected from noncyclic gilts (5.5 to 9 months of age) for serum progesterone analysis, and reproductive tracts of gilts noncyclic at 9 months of age were examined by laparoscopy. C rearing reduced by 12% the average percentage of gilts showing regular estrous cycles (cyclic gilts) from 5 to 9 months of age, and 71.3% of C-reared gilts and 85.2% of NC-reared gilts were cyclic at 9 months of age. The percentage of cyclic gilts at 9 months tended to be higher (P<.25) during the winter (October to April) than during the summer (April to October) season (81.3 vs 75.2%). In the summer, the percentage of gilts cyclic at 9 months was higher (P<.005) in period 3 than in period 4 (84.7 vs 65.6%). Season of sexual maturation influenced both C and NC gilts. The percentage of cyclic gilts was highest for L x LW, intermediate for LW x L and Hampshire and lowest for Yorkshire and Duroc gilts (96.5, 81.9, 81.3, 71.1 and 60.3%, respectively). At 9 months of age, 99 gilts were noncyclic. Of these, 14 had stopped showing estrus and ovulation, 33 were prepuberal and 52 were behavioral anestrus. Breed, housing and season influenced the percentages of prepuberal and behaviorally anestrous gilts.
1 Cooperation of the Nebraska Agr. Exp. Sta., Univ. of Nebraska, Lincoln, is acknowledged. Research supported in part by USDA Cooperative State Research Service grant 701-15-42, USDA, SEA-AR, Dept. of Anim. Sci., Nebraska Agr. Exp. Sta., Lincoln, and Roman L. Hruska US Meat Animal Research Center, Clay Center, NE.
2 The author expresses his appreciation to the swine operations personnel for care of the experimental animals, to Toni Tolles for data compilation and laboratory analysis, to Marilyn Bierman for assistance in manuscript preparation and to J. J. Ford for critical evaluation of this experiment.
3 SEA-AR, Roman L. Hruska US Meat Animal Research Center.
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