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

• Published in: Journal of animal science Vol. 77; no. 3; pp. 541 - 557
• Main Authors: Johnson, R.K, Nielsen, M.K, Casey, D.S
• Format: Journal Article
• Language: English
• Published: Savoy, IL Am Soc Animal Sci 01-03-1999; American Society of Animal Science; Oxford University Press
• Subjects: animal breeding; Animal Husbandry; Animal productions; Animal reproduction; Animals; artificial selection; Biological and medical sciences; breeding value; Classical genetics, quantitative genetics, hybrids; corpus luteum; embryogenesis; Embryos; Female; Fetal Death; fetus; Fundamental and applied biological sciences. Psychology; genetic improvement; Genetics of eukaryotes. Biological and molecular evolution; heritability; Hogs; litter size; Litter Size - genetics; litter traits; litter weight; Male; Mortality; Ovulation; ovulation rate; Phenotype; selection criteria; selection program; Selection, Genetic; swine; Swine - embryology; Swine - genetics; Swine - physiology; Terrestrial animal productions; Vertebrata; Vertebrates; weaning; Genetic selection; Embryo; Mortality; Artificial selection; Genetic parameter; Ovulation; Pig; Vertebrata; Litter size; Mammalia; Artiodactyla; Animal production; Ungulata
• ISSN: 0021-8812; 1525-3163; 0021-8812
• DOI: 10.2527/1999.773541x

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 improvements programs should emphasize live-born pigs because of undesirable genetic relationships of ovulation rate and number of fetuses with number of stillborn and mummified pigs and because birth weight decreased as litter size increased.