REPRODUCTIVE PERFORMANCE OF PREPUBERTAL DAIRY HEIFERS ON LOW OR HIGH β-CAROTENE DIETS
Twenty 5-mo-old heifers were assigned randomly to either a no-carotene or a carotene-supplemented grain ration (2–2.5 kg head−1 d−1) for a 10-mo trial to investigate the effect of β-carotene deficiency on pre and postpuberal reproductive performance. All heifers received, ad libitum, a low-carotene basal forage of corn silage, weathered hay and/or straw. Mean serum β-carotene and vitamin A were higher (P < 0.05) in the carotene-supplemented heifers. Beta-carotene supplementation improved (P < 0.05) overall average daily gain, but had no effect on mean age and body weight at puberty, estrous cycle length and services per conception. Mean serum concentrations of progesterone (P4) estradiol-17β, LH and FSH from prepuberty to day 17 of the first estrous cycle were not affected by β-carotene supplementation. Total P4 output during the estrous cycle did not differ between control and β-carotene-supplemented heifers. However, intensity of estrus was weaker (P < 0.01) and interval (h) from LH peak to ovulation was longer (P < 0.01) in the control (low-carotene) heifers. Key words: β-carotene, vitamin A, reproductive performance, prepubertal dairy heifers