Vitamin A is essential for reproduction, mainly through the maintenance and development of epithelial and other body tissues. It is also involved in the secretion of specific uterine proteins necessary to maintain pregnancy.
Research at universities and commercial units indicates that sows may need supplemental vitamin A at levels above NRC requirements for optimum reproductive performance. Sows receiving one million IU of vitamin A, injected intramuscularly at weaning, averaged up to half a pig more in the subsequent litter than unsupplemented sows.
In studies at a commercial operation in Texas, sows that previously had small litters showed a greater response to vitamin A injections than sows that normally had larger litters. Older sows, with a greater number of parities, also showed a greater response to vitamin A injections than younger sows.
In a Washington State University study (Brief and Chew, 1985), sows injected with vitamin A and (or) beta-carotene had less embryonic mortality and more live pigs per litter at birth and weaning, as well as heavier litter weights at weaning than controls (Figures 2 and3). The treatments in this study were as follows:
- Deficient: fed 2,100 IU vitamin A per head daily in ration.
- Pooled data from animals fed 12,300 IU vitamin A and (or) 32.6 mg beta-carotene per head daily in ration.
- Pooled data from animals injected with 12,300 IU vitamin A and (or) 32.6 mg beta-carotene per head daily intramuscularly.