16 The Business of Canadian Hog Farming Better Pork | August 2024 BALANCING LITTER SIZE mean piglet birth weight are likely to prove disappointing since variation in piglet birth weight within litters has a much greater influence on piglet mortality than mean piglet birth weight per se. Variation in birth weight within litters certainly does not decrease as mean birth weight is improved and so the problem of smaller piglets competing within litters with larger littermates for sucking positions and for nutrition remains. It is this very competitive situation which prevails within litters for nutrition which puts the smaller piglet at such a distinct disadvantage relative to its larger littermate.” Although PWM and birth weight are not strongly associated genetically, there is still a low genetic correlation between birth weight and survival. Birth weight is also genetically associated with other important traits such as weaning weight and later growth rate. As mentioned above, variation in birth weight is more strongly associated genetically with piglet survival. Therefore, Hypor's breeding program includes both mean and variation in birth weight traits along with a runt piglet trait (< 800 g) in the maternal objective as auxiliary traits to the primary traits of total born and piglet survival. Our goal is to increase individual birth weight, reduce variation in birth weight, and reduce the number of runt piglets. Producers may be tempted to increase average piglet birth weight through management interventions, mimicking selection for mean birth weight. However, to our knowledge, no large reductions in PWM have been observed with an intervention such as bump feeding late in gestation. Several studies have shown bump feeding will only increase birth weight in first parity sows. This is analogous to the low genetic correlation between these traits; adding a small amount to every piglet does little to eliminate the problem of competition from larger litter mates. Producers would be better off focusing their time, money, and energy on other factors known to reduce PWM directly. These include reducing drafts and altering ventilation, checking heat lamps/mats, and CaCl before farrowing, and more frequent feedings to reduce stillborns. Teat count Finally, we cannot avoid discussing another limiting factor in weaning pigs: Teat counts. Hypor has put considerable pressure on functional teat counts for many years (Figure 3). Gilts need to start with enough teats as we know sows lose functional teats as they age and throughout a lactation. Wiegert and Knauer have shown that piglet survival can be as low as 75 per cent for sows with 14 or fewer teats, while sows with 17 teats can on average wean 90 per cent of their piglets. Genetics or management? Feedback from producers indicate that many of them attribute initial litter size (e.g. total born) to their genetic supplier along with birth weight, while PWM is viewed as something that can be changed with management. While there are many interventions producers can implement to improve both total born and PWM, both are under considerable genetic control and therefore can be selected in a balanced breeding program. Although heritability estimates are low (often below 0.15), genetic progress is cumulative and should be in the economically desired direction (i.e. weaned pigs). In conclusion The economic value for total born or live born piglets is $0. Only weaned pigs should have an economic value in combination with wean-to-finish traits. For producers to wean more pigs, their genetic supplier must put enough emphasis on piglet survival traits directly and not indirectly through either selection for initial litter size or individual piglet birth weight. Hypor has been directly selecting for piglet survival for many years to increase the number of pigs weaned. Not only is this important for the health of the piglets we care for, but it also has a direct impact on the sustainability of the entire industry. BP Figure 3. Hypor’s bar chart showing the proportion of each teat count over time (2003 to 2023). AUSTIN PUTZ Austin Putz is a geneticist with Hypor in the United States. He is based in Iowa. Courtesy of Hypor
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