Parity and Body Condition Score Drive Summer Fertility in Sows
Depending on the dynamics of your production system, consistent weaned pig output can be a large economic driver. Seasonality in reproduction can impair our ability to maintain constant reproductive output. Sows that lactate during warm summer months may have poorer subsequent litter sizes and farrowing rates when compared with sows that lactate during non-summer months.
Past research suggests heat stress impacts subsequent farrowing rate more than subsequent litter size. Our team recently evaluated the impact of parity and prefarrow sow body condition in a hot environment on subsequent farrowing rates.
We collected data on 1,866 sows at a 3,600-sow commercial farm in eastern North Carolina from May to August 2021. The farm had a history of experiencing more seasonality in reproduction than the other farms within the production system. Traits recorded included the percentage of sows conceiving by seven days after weaning (includes sows culled for no heat), the percentage of sows farrowing a subsequent litter, sow caliper score prefarrow, sow caliper score at weaning and sow caliper lactation loss.
As you can see in Figure 1, as perhaps expected, first litter sows lost more body condition than multiparous sows as they are, on average, not able to consume as much lactation feed.
Figure 1. Impact of parity and prefarrow sow body condition score on lactation body condition loss during periods of heat stress. P1 = gilt litters; P2+ = multiparous sows; Sow caliper <12 = “thin”, 12 to 15 = “ideal”, >15 = fat; Sow caliper loss – a one-unit change is equivalent to 1/3 of a body condition score change (1 to 5 scale).
Again, as may be expected, Figure 2 shows first litter sows were less likely to conceive by seven days after weaning relative to multiparous sows. However, there was an interaction between parity and prefarrow sow body condition. First-litter females were more likely to conceive by seven days after weaning if they had more body condition prior to farrowing.
Similarly, Schenkel and fellow researchers reported in 2010 that heavier body condition in first-litter sows resulted in greater subsequent reproduction in a tropical region in Brazil. Yet, this was not the case for multiparous sows. Prefarrow sow body condition did not appear to greatly impact the percentage of sows conceiving by seven days after weaning in multiparous sows. Our findings in multiparous sows does not support the belief that greater lactation condition loss impairs subsequent reproduction. Further validation is needed.
Figure 2. Impact of parity and prefarrow body condition score on the % of sow conceiving within 7 days of weaning during periods of heat stress. P1 = gilt litters; P2+ = multiparous sows.
As you can see in Figure 3, a similar percentage of first-litter females ultimately farrowed a subsequent litter when compared to multiparous sows. But the first-litter females accumulated more costly nonproductive days in doing so. Within first parity females, there did appear to be a trend for lower herd retention for “thin” gilts.
In summary, this study suggests this commercial farm should farrow gilts that are just into the “fat” range on the Knauer sow caliper scale. In the U.S., gilts are commonly bred at this condition score if bred between 300 and 330 pounds. The participating farm likely needs to identify “thin” gilts in late gestation and adjust feeding levels accordingly. Going forward, our team will continue to evaluate ideal sow body condition in relation to productivity and profitability in modern genetic lines.
Figure 3. Impact of parity and prefarrow body condition score, during periods of heat stress, on the % of sows farrowing a subsequent litter. P1 = gilt litters; P2+ = multiparous sows.
References:
Bryan, M. R., C. E. Hostetler, and M. T. Knauer. 2013. Industry productivity analysis – Seasonality in sow farm traits. J. Anim. Sci. 91(Suppl. 2):94.
Knauer, M. T. and M. T. See. 2007 (Abstr.). Genetic relationships between swine maternal traits in different seasons. J. Anim. Sci. 85(Suppl. 2):19.
Knauer, M. T., and D. J. Baitinger. 2015. The sow body condition caliper. Appl. Eng. Agric. 31:175-178.
Schenkel, A. C., M. L. Bernardi, F. P. Bortolozzo, & I. Wentz. 2010. Body reserve mobilization during lactation in first parity sows and its effect on second litter size. Livestock Sci. 132: 165-172.
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