Effects of Vitamin A Supplementation on Reproductive Function and Estrus Synchronization Response of Kamphaeng Saen Heifers Raised under Restrictive Feeding

During the dry season in tropical areas, green pastures are limited. Heifers or cows fed primarily hay or rice straw are at risk of insufficient ß-carotene (provitamin A). Vitamin A (VitA) is crucial for reproductive functions. This study investigated the influence of VitA supplementation on the reproductive performance of Kamphaeng Saen beef heifers raised under restrictive feeding (n = 18; body condition score [BCS] = 3.5) over 48 days. The animals were equally divided into two groups: 1) the control group (fed a basal diet) and 2) the VitA group (fed the basal diet plus 100,000 IU of VitA per head per day). After 28 days of VitA supplementation, all heifers underwent estrus synchronization protocol. Reproductive tract and ovarian components were examined using ultrasonography to evaluate the size of the cervix, uterine horn, ovaries, follicles, and corpus luteum (CL) on Days 13 and 20 of the estrus synchronization protocol. Blood samples were collected to assess VitA and progesterone concentrations in serum. The results indicated that heifers supplemented with VitA tended to have more compact CL (P = 0.06). However, VitA did not significantly improve overall reproductive tract components or blood parameters between the control and VitA groups (P > 0.05). These findings suggest that VitA supplementation can enhance CL quality with short-term supplementation, but long-term VitA supplementation requires further investigation.