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Nitrogen Retention in Pigs during the Estrous Cycle or Pregnancy and after Hysterectomy or Ovariectomy¹

Iowa State University,³ Ames 50010

Abstract

Gilts representing various stages of pregnancy, the estrous cycle and after hysterectomy or ovariectomy were used to evaluate protein anabolism as determined by nitrogen balance. The cumulative increase in body weight during gestation was greater than that found in each of the other experimental groups, but when the weights for the conceptuses were eliminated, the increases in body weight were similar for all treatments (37 vs. 38 kg).

Nitrogen retention was low (e.g., 3 g/day) during the first 15 to 20 days of pregnancy and continued to increase (e.g., 7 to 10 g/day). Although nitrogen retention continued to increase during later stages of gestation, it increased only slightly or declined in cycling, hysterectomized or ovariectomized gilts, which resulted in a quadratic response. Over all collection periods, nitrogen retention was not significantly different between groups. Hysterectomized gilts excreted larger volumes of urine and also had increased total urinary nitrogen.

The weights and areas of the ham and loin muscles were unaffected by the reproductive stage, but there was less backfat in the pregnant animals than in any of the other groups. Ham muscles from the pregnant gilts had significantly less protein than did the intact-nonpregnant, hysterectomized or ovariectomized animals. Water content in the ham was greater during pregnancy than that found during the estrous cycle. Intramuscular fat of the ham was similar among all treatments.

It seems that corpora lutea contributed little to protein anabolism in the gilt, but pregnancy reduced the amount of protein in muscular tissue. This suggests that protein mobilized from the dam was used in the development of the conceptuses.

¹ Journal Paper No. J-7149 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Projects 1325 and 1712. This work was supported, in part, by Grant HD-00184-05 from the National Institute of Child Health and Human Development, National Institutes of Health. We thank Dr. V. C. Speer and Dr. R. C. Ewan for the use of laboratory facilities and Dr. D. F. Cox for assistance with statistical analyses of the data.

² Present address: Haynes Milling Co. Inc., Portland, Indiana 47371.

³ Department of Animal Science.