Index Selection for Components of Litter Size in Swine: Response to Five Generations of Selection

Abstract

Selection for an index of ovulation rate (OR) and embryo (fetal) survival rate (ES) to 50 d of gestation (I = 10.6 x OR + 72.6 x ES) was practiced for five generations in a line that was a composite population of the Large White and Landrace breeds of swine. A control line sampled from the same population was selected randomly and mated. Ovulation rate and number of fetuses (FETS) were measured by laparotomy and ES was calculated as FETS/OR. The select line averaged 43 litters by 18 sires and the control line averaged 42 litters by 15 sires per generation. Each generation, all females available in the select line (average of 147) were mated and laparotomized, but only selected females were farrowed. One-half of the females underwent laparotomy in the control line. Inbreeding coefficients at generation five averaged 5.34% for the select line and 4.59% for the control line. Regressions of the difference between means of the lines on generation number were .57 ± .11 for OR, -.013 ± .0096 for ES, .20 ± .20 for FETS and 5.10 ± 1.76 for I. Realized heritability for I was .30 ± .09. Heritabilities estimated by regression of daughter on dam were .17 ± .07 for OR, .18 ± .09 for ES and .08 ± .10 for FETS, and the genetic correlation between OR and ES was estimated to be -.56 ± .24. The increase in number of pigs per litter at birth was .19 ± .14 per generation. INDEX SELECTION FOR COMPONENTS OF LITTER SIZE IN SWINE: RESPONSE TO FIVE

Animal model estimation of genetic parameters and response to selection for litter size and weight, growth, and backfat in closed seedstock populations of large white and Landrace swine2

“…The genetic change in litter size obtained with Model 3 was approximately .12% of the mean, .012 pigs&, similar to values reported by Kaplon et al (1991b) and Southwood and Kennedy (1991). When selection was applied only to litter size or t o traits related to litter size, such as ovulation rate and embryonic survival, larger changes in litter size have been reported (Neal et al, 1989;Lamberson et al, 1991).…”

Genetic variability of age and weight at puberty, ovulation rate and embryo survival in gilts and relations with production traits

“…Conversely, the value obtained for weight at puberty is larger than most literature estimates (Young et al, 1978;Hutchens et al, 1981 (Neal et al, 1989) and with estimates obtained in mice and rabbits (Clutter et al, 1990;Blasco et al, 1993b (Young et al, 1977), 50 days of gestation (Neal et al, 1989) or at birth (Young et al, 1978) is observed. This may be due to differences in the populations studied, but may also indicate that uterine competition tends to increase throughout gestation.…”

Estimation of genetic and phenotypic parameters for sow productivity traits in South African Large White pigs

“…Also, there may be a negative correlation among some of the component traits, resulting in a low heritability. Some authors observed greater response in litter size after selecting for litter components (Neal & Johnson, 1986;Neal et al, 1989;Bennett & Leymaster, 1990). Haley & Lee (1992) concluded that genetic variation in ovulation rate is largely responsible for the genetic variation in number of live pigs born, with no contribution from genetic variation in prenatal survival.…”