Large Litters and Piglet Quality
A Necessary Tradeoff?
Dinesh Thekkoot PhD
Litter size at birth has been considered one of the most important traits for evaluating sow prolificacy for the past few decades. Genetic selection for highly prolific sows has resulted in notable improvement in litter size at birth in pigs. But this hasn’t resulted in an equivalent increase in number weaned, as the preweaning piglet mortality also increased during this period. Individual piglet birth weight and birth weight variability within a litter are the two important factors that influence preweaning mortality in pigs.
Piglets with lower birth weight have an increased risk of becoming a stillborn piglet, and if born alive they can have a high pre-weaning mortality rate. Preweaning mortality has a curvilinear association with piglet birth weight. i.e. as birth weight increases, survival improves at a decreasing rate (Weigert et al. 2017). While pre-weaning piglet survival is a main concern to producers because of its direct impact on profitability, these low birth weight piglets usually have compromised production, such as decreased growth rate during growing and finishing phases. Rehfeldt and Khun (2006) reported that compared to the high birth weight littermates, the low birth weight piglets had a slower growth rate at finishing and were fatter at the time of slaughter. The study concluded that the muscle fiber growth in low birth weight piglets reached a plateau much earlier in life when compared to that of high birth weight piglets, and because of that, they redirected more amount of dietary energy towards body fat deposition. There are also chances for sending these lightweight piglets to alternative markets which might result in a reduced value. Thus producers can suffer significant economic loss because of low birth weight piglets.
Most producers would like to have sows with large litters, optimum birth weight, and uniform sized litter-mates. I.e. low litter birth weight variation. There are many advantages to such litters like (a) easy sow management during lactation (b) less pre-weaning and post-weaning mortality (c) better performance during the grow-finish period, etc. But in reality, we see wide variation in piglet birth weight. Studies have shown that at a phenotypic level, birth weight variation has a positive relationship with pre-weaning mortality. Birth weight variability is a lowly heritable trait with estimates ranging from 0.08 to 0.12 (Wang et al., 2016). Damgaard et al. (2003) reported that birth weight variation had a genetic correlation of 0.25 with the proportion of dead piglets, and -0.31 with the preweaning growth rate of piglets. All these results point to the fact that, it is not just the number of piglets born alive that needs to be increased, but the quality and uniformity of the litter.
At Genesus we routinely measure the piglet birth weight in all maternal lines. Measuring individual piglet birth weight and using that information in the selection process will help to address both the low birth weight and high within litter variability of birth weight. This along with the utilization of genomic selection will help to improve these traits which ultimately benefits Genesus customers by weaning larger litters having uniform piglets with high growth capacity, and thereby increasing the profitability.
Damgaard L H, Rydhmer L, Lovendahl P, Grandinson K. Genetic parameters for within-litter variation in piglet birth weight and change in within-litter variation during suckling. J Anim Sci. 2003;81(3):604–10
Rehfeldt, C. and Kuhn, G. (2006), Consequences of birth weight for postnatal growth performance and carcass quality in pigs as related to myogenesis, Journal of Animal Science, 84. 113-123.
Wang X, X. Liu, D. Deng, Mei Yu and X Li (2016). Genetic determinants of pig birth weight variability. BMC Genetics 17
Wiegert J. G., C. Garrison and M. T. Knauer (2007) Characterization of birth weight and colostrum intake on piglet survival and piglet quality. Journal of Animal Science, 95. 32-40
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