J.I. Leenhouwers

Genetic aspects of piglet survival

Amongst all fully formed piglets at the end of gestation, piglet survival until weaning (PS) is on average 81%. Selection for fast lean growth and increased litter size tends to decrease piglet survivability. Estimated heritabilities for PS and its component traits are generally low, on average around 0.04. Despite this, selection for improved survival is possible since the genetic variance for the trait is substantial. Genetic analyses indicated significant genetic correlations between PS on one side and litter size, gestation length, within-litter variation in birth weight, feed intake, gain, and backfat on the other. Genetic correlation of PS with birth weight, however, was low. Selection on birth weight as an indirect way to improve PS is doubtful. Genetic differences between piglets in survivability will be reflected in differences in body composition rather than in differences in birth weight. Experimental work on litters with high versus low genetic merit for PS, results of various selection experiments and experimental work with Meishan pigs support these findings.

Progress of farrowing and early postnatal pig behavior in relation to genetic merit for pig survival.

The objective of this study was to investigate whether pigs with different genetic merit for survival differed in birth weight, progress of farrowing, early postnatal behavior, or rectal temperature within 24 h after birth. On a nucleus farm in Rio Verde, Brazil, information was collected on 280 pigs, originating from 25 litters with known estimated breeding values for pig survival (EBVps). Litters were selected in such a way that a continuous range of EBVps with a maximum genetic contrast was achieved. Birth weight was recorded for all pigs. Indicators for progress of farrowing were birth intervals and duration of farrowing. Behavioral indicators of pig vitality were time until first upright standing (FUS), time until first udder contact (FUC), time until first teat in mouth (FTM), and time until first colostrum uptake (FCU). Rectal temperature was measured within 24 h after birth. Farrowing survival and early postnatal survival (within 3 d after farrowing) were registered. Farrowing survival and early postnatal survival both increased with increasing EBVps (farrowing survival: P = 0.007; early postnatal survival: P = 0.027). Birth weight decreased with increasing EBVps (P = 0.01). Birth intervals tended to increase with increasing EBVps (P = 0.10) and duration of farrowing was not related to EBVps. Time until first teat in mouth increased with increasing EBVps (P = 0.05), but the other behavioral indicators of pig vitality were not related to EBVps. Rectal temperature within 24 h after birth was not related to EBVps. Pigs with a higher genetic merit for survival have a lower birth weight but nevertheless have an increased farrowing survival and early postnatal survival. Their increased survival cannot be explained by differences in progress of farrowing, early postnatal behavior, or rectal temperature within 24 h after birth.