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Effect of litter size on piglet birth weight and birth weight as an indicator of pig quality
Swine maternal line selection programs place large emphasis on litter size. Increasing litter size improves sow production efficiency, but can reduce piglet birth weight. Piglet birth weight is associated with survivability and growth rate. Increasing litter size while maintaining or improving pig quality would maximize production efficiency and profitability for a commercial swine operation. The objective of this study was to determine the effect of litter size on birth weight and the effect of birth weight on growth rate and survivability. All fully-formed pigs, including stillborns (n=7896), from 459 Duroc and 248 Yorkshire litters born January to May 2013 at a single farm in Nebraska were weighed at birth. The average birth weight was 1.40 kg for Durocs and 1.21 kg for Yorkshires. Selected pigs were put on-test at 79.6 (± 4.9) days and taken off-test at 151.1 (± 23.8) days. Using a model with breed and sex as fixed effects, a random litter effect, and birth weight and age as covariates a 1 kg increase in birth weight was associated with a 3.54 kg (P=0.03) increase in on-test weight. Using a similar model for off-test weight, there was a 10.72 kg (P=0.03) increase in off-test weight for a 1 kg increase in birth weight. The relationship between total born and piglet birth weight was estimated using a model with fixed effects of breed and sex, a random litter effect, and a covariate for total born. For every 1 pig increase in total born, birth weight was reduced by 0.03 kg (P=0.05). A generalized linear model with fixed effects for sex and breed, a random litter effect, and a covariate for birth weight was used to analyze survival to weaning. Pigs weighing greater than 1.5 kg had at least a 90% chance of survival to weaning, and Yorkshire pigs had a higher chance of survival compared to Durocs. Recognizing the relationship between birth weight and litter size as well as later performance will allow swine genetic companies to focus on maintaining pig quality when selecting for increased litter size. Determining the genetic correlations between birth weight, litter size, growth rate, and survivability would be important if birth weight were to be incorporated into a swine breeding program.
Keywords:
birth weight, litter size, swine