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An Analysis of the Dependency Structure between a Gilt's Prebreeding and Reproductive Traits. I. Phenotypic and Genetic Correlations¹

Oklahoma Agricultural Experiment Station, Stillwater 74074 and and U.S. Department of Agriculture, El Reno 73036

Abstract

This study involved the records of 339 purebred Duroc, Hampshire and Yorkshire gilts and 192 two-breed cross gilts resulting from matings among the three breeds. The primary purpose of this paper was to investigate the relationship of prebreeding traits, including the growth of the gilt and her littermates, with subsequent measures of reproduction. Heritabilities were estimated for several traits and in general the estimates were somewhat higher than most estimates in the literature. Genetically, all measures of growth were favorably and moderately to highly correlated to ovulation rate, with the relationship being stronger for traits measured late in growth as compared to traits measured early in growth. The only traits that had large genetic correlations with number of corpora lutea per embryo were birth weight (r_g=–.90) and weaning weight (r_g=–.91).

None of the phenotypic correlations between prebreeding traits and reproductive traits were large and only eight of the 68 correlations were significant. Gilts which grew faster, were younger at 100 kg, were heavier at breeding and had more days from 100 kg to breeding also had higher ovulation rates. Gilts which were heavier and older at breeding and had more days from 100 kg to breeding also had more embryos.

A stepwise regression procedure was used to find the "best" model to predict ovulation rate (CL), number of embryos (EMB), embryo per corpora lutea (E/CL) and corpora lutea per embryo (CL/E). The "best" model accounted for only 15%, 18%, 9% and 6% of the variation in CL, EMB, E/CL and CL/E, respectively.

¹ Journal Article 3153 of the Agricultural Experiment Station, Oklahoma State University, Stillwater. Research conducted by the Department of Animal Science and Industry (Project 1444) in cooperation with die U.S.D.A., Agricultural Research Service, Southern Region.

² Present address: U. S. Meat Animal Research Center, Clay Center, NE 68933.

³ Department of Animal Sciences and Industry, Oklahoma State University, Stillwater 74074.

⁴ Department of Animal Science, University of Nebraska, Lincoln 68583.

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