Comparison of plasma FSH concentration in boars and gilts from lines selected for ovulation rate and embryonal survival, and litter size and estimation of (co)variance components for FSH and ovulation rate
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The objective of this research was to determine whether plasma concentration of FSH was genetically correlated with ovulation rate and thus was a useful trait for indirect selection. Blood samples were collected from 619 animals from five lines of pigs. Line I was selected for increased index of ovulation rate and embryonal survival, and Line C was its randomly selected control. Pigs sampled from Lines I and C were from generations 12 and 13. Pigs from three additional lines that were derived from eighth-generation pigs of Lines I and C also were used. These lines were Line C2, a randomly selected control derived from Line C, Line COL, derived from Line C, and Line IOL, derived from Line I; each of these lines was selected an additional five generations for increased ovulation rate and increased litter size. A single blood sample was collected from each pig between 46 to 63 (d 58), 86 to 98 (d 90), 110 to 133 (d 124), and 147 to 153 (d 150) d of age. The heritability of ovulation rate was .28 and heritabilities of plasma concentration of FSH at d 58, 90, 124, and 150 were .41, .25, .12, and 0, respectively. Genetic correlations between ovulation rate and d-58, d-90, and d- 124 plasma concentration of FSH were .31, .23, and 0, respectively. Line I gilts had greater estimated breeding values for plasma concentration of FSH at d 58 and 90 than Line C gilts (P < .01). Line COL gilts had greater estimated breeding values for plasma concentration of FSH at d 58 than Line C2 gilts (P < .01). Line I boars had greater estimated breeding values for plasma concentration of FSH at d 90 than Line C boars (P < .05). Even though genetic correlations were low, selection for increased plasma concentration of FSH was estimated to be 93% as effective in changing ovulation rate as direct selection because selection for FSH can be practiced in both sexes. Thus, selection for increased plasma concentration of FSH seems to be a practical method for increasing ovulation rate in pig breeding programs without using laparoscopy.