Fifty-five microsatellite markers were scored in an F2 population of pigs (n = 114 females) developed at the University of Nebraska. The population was produced by crossing a line previously selected for 10 generations using an index of ovulation rate and embryonal survival and a line selected at random. The lines were from a common base population and differed by 6.7 ovulations and 3.1 fetuses at 50 d of gestation. Ovulation rate and number of fully formed and mummified pigs were recorded for each female. Data were analyzed with regression models that included random animal effects. Likelihood-ratio tests were used to test for quantitative trait loci (QTL) effects by deviating the log-likelihood for the full model that included additive and dominance QTL effects from the log-likelihood for the reduced model that did not contain QTL effects. A QTL for ovulation rate was found on chromosome 8 (P < .001) with an additive effect of 3.07 ovulations. Other evidence of potential QTL affecting ovulation rate was found on chromosomes 4 (P < .10), 13, and 15 (P < .05). Effects on chromosomes 4, 13 and 15 were not significant for fan experiment-wise threshold value of P < .001. No significant QTL for litter size or number of mummified pigs were found. Additional data are needed to confirm the location and the effect of QTL found for ovulation rate before markers associated with them can be used in marker-assisted selection.

Selection for predicted weight of testes at 150 d of age (PWT) was practiced for 10 generations to determine the effect on reproductive and growth traits in swine. .14 mm per generation in boars and .16 k .14 mm in gilts. Negative genetic trends occurred in age a t puberty in both lines, but the difference between lines was not significant. At Generation 10, ovulation rate was .76 k .43 eggs more for gilts of the TS line than for C gilts. Genetic correlations of PWT with other traits are presented. Heritability of PWT was moderately high and its phenotypic variance was large; therefore, a high rate of response of 5.5% per generation occurred. Selection for PWT was not effective in decreasing age at puberty or increasing ovulation rate of daughters.

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Body, testis, and epididymis weights were recorded and homogenization-resistant sperm nuclei were counted to determine daily sperm production and the number of sperm stored within the cauda epididymis (CAUDASP) in 145 boars of a control line (C) and 128 boars of a line selected for increased predicted weight of testis (TS) at 150 d of age. Random samples of boars were evaluated at five ages between 70 and 450 d in Generation 8 and 15 ages between 70 and 296 d in Generation 9. Data were analyzed using an animal model that included the fixed effect of line and the linear, quadratic, and cubic effects of age. Variance components were estimated using a DFREML algorithm. Boars of the TS and C line did not differ in body weight (P > .05) in Generation 8. In Generation 9, boars of line TS were heavier between 118 and 198 d of age (P < .001); thereafter, body weights of the lines were similar (P > .05). The increase in organ weights for the testes and epididymides between 70 and 160 d of age were greater (P < .01) for boars of line TS in each generation, and differences between the lines in testis weights established around puberty were maintained at 450 d of age. Daily sperm production and CAUDASP increased more rapidly at younger ages and plateaued at greater values (P < .05) in boars of line TS. At ages less than 200 d, boars of line TS produced more sperm per gram of parenchyma than control boars.(ABSTRACT TRUNCATED AT 250 WORDS)