On Farm B, the number of pigs born alive was similar for sows receiving increased fortification (9.8) and controls (9.9) regardless of parity. The researchers point out, however, that 90 percent of the sows on Farm B were between parities 3 and 5; thus, an inadequate number of sows in parities 1, 2 and 6 may explain the lack of similar results in early and late parities.
The researchers indicated the response variation by parity on Farm A is particularly interesting. Typically, the productive curve of a sow when measured by pigs born alive is somewhat bell-shaped. Numbers increase in parities one and two, plateau between parities three and five, and begin to decrease with parity six. It has been widely suggested that reproductive efficiency is less than optimal during early parities because the reproductive axis is still developing, and also during later parities because the aging process reduces reproductive performance.
The mechanisms responsible for this pattern are not fully known, but Flowers and Spears note that changes in ovulation rate and embryonic survival are often suggested as the reasons. Possibly the increased supplementation of vitamins during these early and late parities resulted in more liveborn pigs by enhancing the development of the reproductive axis in young, growing gilts and sows, and by delaying age-related changes in the reproductive system of older sows.
On Farm B, the 9.8 percent increase in farrowing rate was a consistent observation in each of the four replicates. The researchers note that the reason for this increase is not readily apparent, but they point out that the sows receiving increased supplementation had a higher percentage of litters with four pigs or less than controls. (There was also a higher percentage with more than 15 pigs per litter.) Because it normally takes four or five pigs to maintain pregnancy, the researchers point out that such small litters should not have occurred.
However, they hypothesize that the increased vitamin supplementation altered the physiological processes involved in maternal recognition and implantation in the pig to sustain pregnancies with such small numbers. The fact that no litter of less than four total pigs born was observed in the control sows provides support for this speculation, but the researchers note that more research is required.
Whatever the mechanism, the North Carolina researchers note these results demonstrate that increased vitamin supplementation during post-weaning and early gestation improved farrowing rate and number of pigs born alive in commercial swine operations tested.
- Flowers, W.L., and J.W. Spears. 1996. Effect of vitamin supplementation during breeding on sow reproductive performance. North Carolina State University (report).
- Lindemann, M.D. 1993. Supplemental folic acid: a requirement for optimizing swine reproduction. J. Anim. Sci. 71:239.