Kerry Houlahan, PhD, Geneticist, Genesus Inc.
A recent summary for the USA showed that from 1993 to 2022 litter size has increased 1.1%/year which equates to 3.15 pigs per litter or a 37.9% increase (Langemeier 2023). Increasing litter size leads to the increase in preweaning mortality (Knap et al., 2023). The MetaFarms Sow Production Index Q4 2021 is comprised of 415 farms from the USA, Canada and Australia, and estimates preweaning mortality to be 14%, or approximately 2 piglets per litter. With increased litter size, there is also a need to increase the number of functional teats. Functional teats can have many definitions, ranging from the ability to express milk, to being able to raise a viable piglet. Nevertheless, ensuring there are enough teats to provide sufficient colostrum and milk to these ever-growing litter sizes is of great importance.
When considering the number of teats on a sow, location of these teats is a consistent topic of discussion. It has been suggested that the quality of colostrum and milk decreases as the anatomical position of the teats becomes more posterior (McBride et al., 1965; Lannom and Flowers, 2018; Knol et al., 2022). In line with this, others suggest that teats in front of the naval will, on average, produce better than those behind the naval. With that in mind, we conducted a pilot study to determine the genetic relationship of teat location (in front or behind the navel) with traits of economic importance as it relates to piglet survival. These traits included preweaning mortality, number weaned and litter weaning weight. Data for this pilot study included teat number and location for 46,703 Landrace and 56,340 Yorkshire gilts collected from two herds, and weaning traits on 17,168 Landrace and 15,929 Yorkshire sows from six herds. A total of 5,653 Landrace and 5,333 Yorkshire had data for all traits. All data was collected from January 1, 2012, to May 1, 2023.
Table 1: Heritability (standard error) on the diagonal and genetic correlations (standard error) above the diagonal of teat location and total number of teats for Landrace and Yorkshire
Results of this pilot study show that teat number and placement are highly heritable (0.43 to 0.61). This means there is genetic potential to select for teat placement, in addition to selecting for an increase in the total number of teats. The results of this study agree with previously reported heritability estimates, though in some cases the results of this study are slightly higher than previously reported (McKay and Rahnefeld 1990; Lundeheim et al 2013; Towers 2016). Based on the genetic correlations, increasing the total number of teats will also increase the number of teats in front and behind the navel, with similar results observed in McKay and Rahnefeld 1990. The results of our study also show that increasing the number of teats in front of the navel will decrease the number behind the navel, and vice versa.
Table 2: Genetic correlations (standard error) between teat placement and traits related to piglet survival for Landrace and Yorkshire.
Teat location appeared to impact number weaned and litter weaning weight more compared to pre-weaning mortality. In both breeds the number of teats ahead of the navel had the most favourable correlation with litter weaning weight. For number weaned the results suggest that having more teats overall, and more teats behind the navel could be favourable. Preweaning mortality results suggest that simply increasing the total number of teats may have a larger impact than the placement of the teats.
Planned future work includes investigating genetic correlations of functional teats and functional teat placement with piglet survival. This work aims to provide the most profitable maternal genetics through the incorporation of novel traits into the Genesus breeding program, ultimately benefiting Genesus customers.
Knol, E.F. et al. 2022. J. Anim. Sci. 100(6); skac190, https://doi.org/10.1093/jas/skac190
Langemeier, M. 2023. Farmdoc Daily (13):19. https://farmdocdaily.illinois.edu/2023/02/long-term-trends-in-pigs-per-litter-2.html
Lannom, K.E. and Flowers, W.L. 2018. National Hog Farmer. https://www.nationalhogfarmer.com/hog-health/teat-location-impacts-colostrum-and-milk-composition-and-piglet-growth
Lundeheim et al. 2013. Acta Agriculturae Scandinavica, Section A — Animal Science, 63(3): 121-125. https://doi.org/10.1080/09064702.2013.841749
McBride, G. et al. 1965. Anim. Prod. 7: 67–74. https://doi.org/10.1017/S0003356100022297
McKay, R.M and Rahnefeld, G.W. 1990. Can. J. Anim. Sci. 70:425-430. https://doi.org/10.4141/cjas90-054
Towers, L. 2016. The Pig Site. https://www.thepigsite.com/articles/genetics-of-teat-number-in-swine