The Effect of Exogenous Progesterone and Level of Feeding on Prenatal Survival in Gilts

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Abstract
Eighty-five gilts sired by two boars and weighing approximately 100 lb. were full-fed a growing ration until the second heat. All gilts were bred to fertile boars at the second estrus and one-half of them continued on the full-fed ration. The other gilts were fed a ration that contributed approximately 50% of the energy of the full-fed ration but equivalent quantities of protein vitamins and minerals on pasture. One-half of the gilts on each ration treatment were given 25 mg. of progesterone intramuscularly every other day from the third to the 25th day of gestation. One-third of each sub-group was slaughtered 25 days postbreeding, one-third 40 days after breeding and the remainder were allowed to farrow. The number of normal embryos, live pigs and percentage of embryonic survival were compared between ration and hormone treatments. Neither the ration used nor the hormone treatment had a significant influence on the number of embryos, live pigs or embryonic survival. However, the stage of gestation did have a significant influence on embryonic survival. At 25 days, 40 days and term, there were 11.8, 10.0 and 6.9 embryos or live pigs, respectively. The estimated survival rates at these same stages were 81.7, 76.1 and 50.6%, respectively. Therefore, 25 mg. of exogenous progesterone every other day during the first 25 days of gestation, and/or reducing the energy intake at breeding, did not reduce embryonic mortality. Gilts farrowed in January and February averaged 229±24 days of age and 246 ± 11 lb. at puberty. Gilts farrowed during April averaged 206 ± 33 days of age and weighed 214 ± 22 lb. at puberty. These differences for both age and weight at puberty due to season or climatic factors were statistically significant (P<0.01). Copyright © . .