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Influence of Prenatal and Postnatal Fraternity Size on Reproduction in Swine^1,2,

University of Wisconsin, Madison 53706⁴

Abstract

Hypotheses of a negative association between fraternity size (size of litter in which an individual develops prior to birth or is reared following birth) and ovulation rate or litter size were tested by examining reproduction of females born or reared in varying prenatal and postnatal fraternities. Gilts were randomly assigned to develop prenatally and be reared postnatally in small or large fraternities. Dams of experimental animals were randomly assigned to one of two prenatal fraternity size treatments, either unilateral oviductal ligation (to bear a small prenatal litter) or no ligation (to bear a normal prenatal litter). Whereas this did result in differences (P < .01) in litter size at birth (small = 6.2 ± .4 vs large = 9.6 ± .9), there was considerable overlap in observed litter sizes between ligated and nonligated dams. Consequently, effects of prenatal fraternity size were examined by regression. Distinct differences in postnatal fraternity size were created by randomly assigning piglets to small (5 piglets) or large (10 piglets) postnatal fraternities within 24 h of birth. Differences in postnatal fraternity size were maintained through weaning at 3 wk (small = 4.9 ± .1 vs large = 9.4 ± .2). Weights at birth (regression of birth weight on prenatal fraternity size = –.07 ± .02, P < .01) and weaning (small = 6.09 ± .15 vs large = 5.46 ± .17 kg, P < .01) were heavier for gilts from small prenatal and postnatal fraternities, respectively, compared with gilts from large fraternities. Effects of prenatal and postnatal fraternity size on BW did not persist following weaning (P > .20). Both prenatal fraternity size (regression of fetus number on prenatal fraternity size = –.24 ± .11, P < .05) and postnatal fraternity size (small = 12.03 ± .58 vs large = 10.86 ± .68, P < .10) influenced number of fetuses at 30 d of gestation. Prenatal fraternity size also was negatively associated with ovulation rate (regression of ovulation rate on prenatal fraternity size = –.26 ± .13, P < .05). Differences in ovulation rate between postnatal fraternity classes followed the same pattern, but they were not significant. Neither prenatal nor postnatal fraternity size affected (P > .15) age at first estrus. No interactions of prenatal and postnatal fraternity size were observed for any of the traits examined (P > .15).

¹ Supported by the University of Wisconsin and Hatch Grant #1337.

² We acknowledge the technical assistance of S. Trace, A. Gerbitz, J. Critser, M. Hinshelwood, T. Block and M. Renk.

³ Current address and to whom reprint requests should be addressed: Dept. of Anim. Sci., Oklahoma State Univ., Stillwater 74078.

⁴ Dept. of Meat and Anim. Sci.