| Research reported in this thesis investigated effects of n-3 polyunsaturated fatty acid (LCPUFA) supplementation, litter birth weight phenotype, and their possible interactions, on reproductive performance of the gilt and sow and postnatal performance of the litter. In an initial study, LCPUFA supplementation to gilts from day 60 of gestation improved litter growth until the end of the nursery period, increased pre-weaning mortality, but did not affect subsequent reproductive performance of the dam. Consistent with the hypothesis that changes to the component traits affecting litter size (ovulation rate and embryonic survival) lead to intrauterine crowding (IUC) of embryos and intra-uterine growth restriction (IUGR) in a proportion of higher parity sows, data from an initial collaborative study confirmed that, compared to medium (MBW) or high (HBW) birth weight litters, low birth weight (LBW) litters had lighter placentae at term and stillborn pigs born showed benchmarks of IUGR such as a higher brain:liver weight ratio. LBW litters also had higher pre-weaning mortality and lower growth rates throughout the growth period and needed 9 more days to reach a fixed market weight than HBW litters. Carcass quality was similar between litter birth weight phenotypes. As litter birth weight phenotype was found to be repeatable within sows, and given the results from the initial gilt study, a second sow study was performed to investigate interactions between litter birth weight phenotype and LCPUFA supplementation to sows during the rebreeding period, gestation and lactation. Compared to untreated control sows, LCPUFA supplementation reduced litter size at birth and increased postnatal growth of medium/high birth weight (MHBW) but not LBW litters. After weaning, body weight was only improved by LCPUFA supplementation when no competition for food or space occurred, and had no effect on ADG, ADFI or feed efficiency. Carcass fat depth was higher and lean meat percentage lower, when sows were supplemented with LCPUFA. Overall, therefore, the economic benefits of LCPUFA supplementation are questionable. However, the swine industry should strive to find ways to decrease the number of LBW litters: Until this has been achieved, management strategies to deal with LBW litters are critical. |
