A comparison of 1- and 2-cell ova production by F2 50% Meishan versus F1 White line gilts.

The objective of this study was to compare recovery of pronuclear and 2-cell ova from F2 50% Meishan (MX) gilts versus F1 White line (L42) gilts. Sexually mature MX and L42 gilts were allocated across 2 treatments: Super (MX:n=9; L42:n=10) and Control (MX:n=6; L42:n=5) in a 2 x 2 factorial experiment. Allyl trenbolone (AT) was used to synchronize estrus in all gilts. Super gilts were given pregnant mare serum gonadotropin (PMSG: 1250 IU) at 24 h after AT withdrawal. Eighty-five hours after PMSG administration, all Super gilts received 750 IU of human chorionic gonadotropin (hCG). Super gilts which exhibited estrus within 24 h of hCG administration (MX-Super: n=6; L42-Super: n=5) and all Control gilts were bred naturally to Line 3 boars at 12 and 24 hours after the onset of estrus. Ova were recovered from Super gilts between 60 and 64 h after hCG and Control gilts at 48 h after the onset of estrus. All 1- and 2-cell ova were centrifuged at 15000 x g and observed using differential interference contrast microscopy. The mean ovulation rate was greater (P<0.05) for both MX-Super and L42-Super gilts in comparison to their respective Control groups. No differences were detected in the mean ovulation rate (P>0.38) or the mean number of 1- and 2-cell ova recovered (P>0.50) between MX-Super and L42-Super gilts. The proportion of 1- and 2-cell ova which exhibited visible pronuclei or nuclei was also similar among MX-SUPER and L42-SUPER gilts. This study demonstrates that MX gilts respond/perform comparably to L42 gilts with respect to estrus synchronization, superovulation, ova yield, and the ease of visibility of pronuclei or nuclei in the ova.

Testicular growth in boars of different genetic lines and its relationship to reproductive performance.

Testicular growth of 377 boars was compared by obtaining in situ measurements of testes width and length and excised tissue weights. Two experiments involved a line selected nine generations for ovulation rate (OR) and a control line (CL), and two experiments contained boars of the OR line and two other lines; WL, a Large White-Landrace cross, and a line founded by crossing lines OR and CL and selected six generations for increased average daily gain and decreased backfat (LG line). In situ testes measurements were similar for the OR and CL lines and were curvilinearly related to age. The LG line had smaller in situ measurements than the OR line (P less than .05) when both unadjusted means and means adjusted for body weight were compared. The OR line had 10.5% heavier testes than the CL line at 90.8 kg and a 9 to 15% advantage at 120, 141, 162 and 183 d of age. The OR line had more rapid testicular development from 120 to 183 d of age (P less than .05) than the CL line. The LG line had significantly lower excised testes weights (17 to 50% less), a lower percentage of tubules that showed active spermatogenesis and lower mean diameter of the seminiferous tubules (P less than .05) than the OR line. The relative differences between lines OR, CL and LG suggest that selection for lean growth rate has resulted in less rapid testicular development and increased age at puberty. The correlations of testes weights and in situ testes measurements taken at the time of castration were between .76 and .93. The correlations of testes width and testes length with epididymides weights were slightly lower, and correlations of body weight and testes weight ranged from .51 to .70. Mean diameter of the seminiferous tubules and percentage of tubules with active spermatogenesis were correlated with measurements of testes size (r = .50 to .61) and body weight at the time of castration (r = .29 to .36). Correlations of excised testes weights with number born in the boar's contemporary litter and ovulation rate of full sibs were uniformly positive. The correlations of measurements of testes size and backfat (r = -.09 to .20) suggest that the phenotypic relationship between testes growth and body composition is small. However, the response found in the LG line suggests a negative genetic relationship between lean growth rate and testicular growth rate.

Inheritance of teat number and its relationship to maternal traits in swine.

The relationship of teat number to seven measures of female reproduction was evaluated in the University of Nebraska Gene Pool population. Teat number was recorded for 7,513 pigs, ovulation rate for 2,794 gilts and litter size and weight at birth and weaning (42 days) for 789 gilts. Paternal half-sib and full-sib analyses were used to estimate heritabilities for each trait and to estimate the genetic and phenotypic correlations of teat number with the measures of reproduction. The direct response to selection for ovulation rate and the correlated response in teat number were also evaluated from the regressions of line differences (Select-Control) on generation number (10 generations of selection) and cumulative selection differential for ovulation rate. The paternal half-sib heritabililty for teat number was .32, and the paternal half-sib heritabilities for ovulation rate and the litter traits were similar to previous estimates from this population. Most of the genetic and phenotypic correlations with teat number were negative and all were nonsignificant. The realized heritability for ovulation rate was .46 +/- .10. The regression of response in teat number on generation number number was .08 +/- .03 (P < .10). An estimate of .44 was obtained for the realized genetic correlation of teat number with ovulation rate.