Estimation of genetic and environmental risk factors associated with pre-weaning mortality in piglets using generalized linear mixed models

Risk factors and variance components of pre-weaning mortality were estimate d using generalized linear mixed models. Data were from 12 727 piglets born alive from 1338 litters recorded at the pig breeding farm of the Universit y of Kiel from 1989 to 1994. Deviances due to risk factors were estimated b y generalized linear model and their odds-ratios by generalized linear mixe d model both with binomial errors and a logistic link. Variance components of sire, dam and litter were estimated using a legit or probit link functio n as well as a linear model for which estimates were transformed to the und erlying continuous scale. Highest increase in deviance, indicating the risk factor, which accounts for the greatest amount of unexplained variation of pre-weaning mortality tons obtained after exclusion of individual birth we ight (1206) from the model, followed by year-season (217), parity-farrowing age or interval (58), genotype of piglets (56), sex (39), total number of piglets born (18) and gestation length (16). Substitution of individual bir th weight successively by average piglet birth weight per litter lifter bir th weight and standard deviation of birth weight within litter resulted in models with substantially lower explained variation of pre-weaning mortalit y Odds of pre-weaning mortality was 1.5 times higher for males than for fem ales and 2.0 times higher in piglets from German Landrace dams than from La rge White dams. Odds increased to the fifth parity by 2.2 times the odds of the first parity or increased for the age group of darns between 850 and 9 49 days by 2.3 times the odds of the age group with less than 350 days. Whe n the continuous risk factors of individual birth weight, average piglet bi rth weight and litter birth weight decreased or standard deviation of birth weight within litter increased by one standard deviation from the mean, th e odds ratios increased by 6.0, 1.6, 0.8 and 0.4, respectively. Piglets wit h individual birth weights of 1.8, 1.5, 1.2 and 1.0 kg showed a rapid incre ase in odds ratios of pre-weaning mortality of 1.4, 2.7, 7.0 and 16.1, resp ectively, relative to piglets with 2.1 kg. Estimates of direct heritability for pre-weaning mortality on the linear observed, transformed underlying, logit and probit scale were 0.02, 0.06, 0.07 and 0.07, respectively. Low es timates of heritability for pre-weaning mortality, even on the underlying c ontinuous scale, suggested low potential for improvement by selection. Ther efore, selection for individual birth weight phenotypically closely associa ted with pre-weaning mortality was recommended to improve survival of pigle ts during the nursing period.