Responses in ovulation rate, embryonal survival, and litter traits in swine to 14 generations of selection to increase litter size.

Abstract

Eleven generations of selection for increased index of ovulation rate and embryonal survival rate, followed by three generations of selection for litter size, were practiced. Laparotomy was used to count corpora lutea and fetuses at 50 d of gestation. High-indexing gilts, approximately 30%, were farrowed. Sons of dams in the upper 10% of the distribution were selected. Selection from Generations 12 to 14 was for increased number of fully formed pigs; replacements were from the largest 25% of the litters. A randomly selected control line was maintained. Responses at Generation 11 were approximately 7.4 ova and 3.8 fetuses at 50 d of gestation (P < .01) and 2.3 fully formed pigs (P < .01) and 1.1 live pigs at birth (P < .05). Responses at Generation 14 were three fully formed pigs (P < .01) and 1.4 live pigs (P < .05) per litter. Number of pigs weaned declined (P < .05) in the index line. Total litter weight weaned did not change significantly. Ovulation rate and number of fetuses had positive genetic correlations with number of stillborn pigs per litter. Significantly greater rate of inbreeding and increased litter size at 50 d of gestation in the select line may have contributed to greater fetal losses in late gestation, greater number of stillborn pigs, and lighter pigs at birth, leading to lower preweaning viability. Heritabilities of traits were between 8 and 25%. Genetic improvement programs should emphasize live-born pigs and perhaps weight of live-born pigs because of undesirable genetic relationships of ovulation rate and number of fetuses with numbers of stillborn and mummified pigs and because birth weight decreased as litter size increased.

Estimation of genetic trends from 1977 to 1998 for farrowing characteristics in the French Large White breed using frozen semen

“…A similar degradation of piglet survival was observed over the last years in French pig herds (see the large-scale study of Le Cozler et al (2002)) and in several other experimental studies (review of Blasco et al, 1995;Johnson et al, 1999). This unfavourable trend is generally considered as a response to selection for the number born in total.…”

“…Vallet, 2000) resulted in higher losses in late gestation. Conversely, Johnson et al (1999) did not obtain any deterioration of late foetal survival in a line selected for increased litter size. Intrauterine crowding may be accentuated by the higher growth potential of G98 foetuses (Canario et al, 2007).…”

“…It is not only due to a scale effect, as G98 first-parity piglets had a higher probability of stillbirth than G77 piglets, albeit litter size was similar in both groups. Johnson et al (1999) suggested that it might be mediated through a negative effect on birth weight. Lighter piglets would be less developed at birth, in association with problems in tissue differentiation and growth (Klemcke et al, 1993) and would have a higher probability of stillbirth.…”

“…Previous results have shown that the use of a proper selection criterion such as the number born alive (Johnson et al, 1999;Canario et al, 2006b) or the maternal component of probability of stillbirth (Leenhouwers et al, 2003) instead of total number born, should prevent further degradation of farrowing mortality. Our results give some insight into the mechanisms associated with this increased mortality and into the traits that may be important to consider when defining future breeding goals.…”

A whole genome scan to detect quantitative trait loci for gestation length and sow maternal ability related traits in a White Duroc × Erhualian F2 resource population

“…Producers can supervise the farrowing and treat sows at the appropriate time to induce farrowing and give assistance to sows and piglets to reduce piglet mortality during the perinatal periods (Holyoake et al, 1995). The selection for increased litter size brings problems with increasing piglet mortality and decreasing piglet growth (Johnson et al, 1999). Sows are required for good maternal ability to take care of their litters, because maternal effects are more important than any other single factor in determining early offspring growth and survival (Lee et al, 1991).…”