Effect of retinol palmitate on ovulation rate and embryo quality in superovulated cattle

Abstract

We evaluated the influence of administration of retinol palmitate (Vitamin A) on ovulation rate and embryo quality in 48 beef cows superovulated with 2 different doses of FSH. Synchronization of estrus was accomplished by giving 2 injections of prostaglandin F 2α (PGF) 11 d apart. Multiple ovulation was induced by giving a total of either 32.5 mg or 27 mg of FSH over 4 d beginning on the 8th to 10th d post estrus. Within FSH dose, cows received either 1 million IU of Vitamin A (im) in corn oil or an equivalent volume of corn oil alone on the 1st d of FSH injections. Embryos were recovered nonsurgically and evaluated 7 d post estrus. Ovulation rate was estimated on the day of embryo recovery by use of transrectal ultrasonography and actual counts of corpora lutea were made on ovaries taken at slaughter following embryo recovery. The FSH response rate (percentage of cows with multiple ovulations) for all cows was 65.9% and was not affected by FSH dose or Vitamin A. Cows with less than 20 ovulations had a higher percentage of total embryos recovered (59.6 vs 35.8%; P = 0.002), and more of those embryos were transferable (36.2 vs 14.3%; P = 0.005) compared to cows with more than 20 ovulations. The dose of FSH did not affect embryo quality or the total number of embryos recovered, but the lower dosage resulted in more ovulations per cow (26.7 vs 18.0; P = 0.03). Vitamin A did not affect ovulation rate or total embryos recovered, but it increased the mean number of high quality (Grades 1 and 2; 4.25 vs 1.86; P = 0.01) and total transferable embryos (Grades 1, 2 and 3; 5.87 vs 3.13; P = 0.04). The mean number of blastocysts was greater for Vitamin A-treated cows (2.25 vs .73; P = 0.02). Means for nontransferable embryos were not different between FSH dose or Vitamin A treatment groups. These findings suggest that 1) ovulation rates above 20 per cow do not yield gains in total or transferable embryos, and 2) Vitamin A may improve embryo quality without affecting ovulation rate in superovulated cattle.