High replacement rates for first- and second-parity sows have skewed current parity structures on many sow farms towards younger, less productive females, Dr. Billy Flowers of North Carolina State University told the recent Banff Pork Seminar. He said that as a result, herd productivity is being limited because females are culled before they reach their peak periods of reproductive efficiency.
Current research by Flowers and his team involves comparing conditions and management practices on two similar farms, one with high and one with low sow longevity. While the study is not complete, it has already revealed several factors which are thought to be related to the levels of sow longevity.
The comparison involves two, 2,400-head commercial sow farms that receive replacement gilts from the same gilt multiplication system, which eliminates any effect on longevity of management prior to delivery. “The definition being used for sow longevity is the proportion of sows that produce six litters,” Flowers said. “The high-longevity farm typically has 26 per cent of its sows reach their sixth parity, while only 12 per cent of sows produce six litters on the low-longevity farm.”
Although the results are preliminary, there are some interesting trends developing between the high and low sow longevity herds.
“After sows were rebred after their first lactation, the high-longevity farm still had 78 per cent of the gilts in production while the low-longevity farm only had 58 per cent,” Flowers said. “The majority of this difference appears to be related to the proportion of gilts and first-parity sows that were bred — 98 per cent of the gilts that were delivered to the high-longevity farm were bred and entered production compared with only 83 per cent of their contemporaries on the low-longevity farm.”
Farrowing rates for first-parity sows were comparable for both farms, he said. There was only a four per cent loss of sows from weaning to rebreeding on the high-longevity farm compared with a 12 per cent loss over the same time frame on the low-longevity farm. This trend continued during the rebreeding of sows after weaning their second litter.
“It appears that factors related to breeding in general and how sows are managed during lactation play significant roles in differences between the two farms in terms of sow longevity,” Flowers suggested.
Age of detection boars
One difference between the two farms that is likely related to differences in culling of young females is the age of boars used for estrus detection and how they are managed.
The high-longevity farm uses 14-month-old boars and collects them periodically after heat checks. In contrast, the low-longevity farm uses boars that are older than 24 months without ever collecting them,” Flowers said. “Boars on the high-longevity farm appear to have increased libido and both the sows and gilts show enhanced standing reflexes compared with the low-longevity farm. This, in turn produced higher mating quality scores.”
Bred females consistently show more intense initial standing reflexes and accept semen better on the high-longevity farm, Flowers said. Examination of the ovaries of gilts culled because they were never bred indicated that they did ovulate at some point but their estrus was not detected.
“Routine collection of boars used for detecting estrus appears to have a positive effect on behaviours associated with high levels of libido and stimulation of estrus behaviours in gilts and sows,” Flowers said.
Another difference between the two farms is that, on the high-longevity farm, a single person is responsible for breeding all the gilts and, after breeding, moving them to their gestation stalls. On the low-longevity farm, these tasks are performed by different members of the breeding barn staff. The researchers note that movement of gilts into gestation stalls takes less time on the high-longevity farm. A subsequent behavioural test, which measures a pig’s interaction with farm staff, showed that there were fewer, but longer, interactions between the person managing gilts on the high-longevity farm, indicating less fear.
“The significance of these observations remains to be determined; however, it is tempting to speculate that if they are representative of animals that are calm while being handled by workers, then this could have benefits not only in breeding, but during farrowing and lactation as well,” Flowers said.
Sows are assisted fairly aggressively during farrowing on the high-longevity farm compared with the low-longevity farm. “It is interesting to note that the high-longevity farm has fewer sows with a retained placenta or dead piglets and fewer sows that experience transient decreases in feed intake during the lactation period,” Flowers said. “It will be interesting to see if these trends continue. If they do, then it would be tempting to speculate that, in this production system, failure to assist sows leads to increases in retained piglets, which, in turn, could affect their feed intake temporarily later in lactation.”
Decreases in feed intake between five to seven days have been shown to change important physiological aspects associated with resumption of reproductive activity of sows after weaning, including their subsequent fertility, he notes.
As the study continues, and the sows move into later parities, it is expected that more differences in management that can be linked to longevity will emerge between the two farms.
“Hopefully, this information will provide a blueprint of sorts that production systems can use to develop their own management checklists for improving sow longevity,” Flowers said.
Bernie Peet is president of Pork Chain Consulting of Lacombe, Alberta, and editor of Western Hog Journal.