The Combination of ß-Carotene and Vitamins Improves the Pregnancy Rate at Fixed Time Artificial Insemination (FTAI) in Grazing Beef Cows

This experiment was conducted in a commercial beef farm located in Rio Brilhante, MS, Brazil during the spring/summer breeding season (September to October 2016). A total of 430 suckled multiparous beef cows (Nelore; Bos indicus, 417.2 ± 57.9 kg) were used. Cows were maintained on 4 paddocks of Brachiaria brizantha with ad libitum access to water. At the beginning of the trial (30 d before the first timed-AI) animals were assigned according to calving date, stratified by BCS (mean of 2.5 ± 0.5, 1 to 5 scale) and ß-carotene blood concentration (mean of 4.2 ± 1.8 mg/L), and randomly assigned to treatments: Control (mineral supplement: no ß-carotene nor vitamins) and Treated (combination of 500 mg ß-carotene, 70000 IU Vit. A, 10000 IU Vit. D3, 500 mg Vit. E and 10 mg biotin/cow/d in the mineral supplement). The mineral supplement (8% Na; 30% TDN; 35% CP; 22.5% NPN) was daily offered to the animals in collective feeders at amount of 200 g/cow/d. The ß-carotene, vitamins and minerals used were from DSM^® Produtos Nutricionais Brasil SA. Cows were rotated through the paddocks every 8 d to avoid effects related with pasture amount and quality. Animals were synchronized using an estradiol/progesterone-based timed-AI protocol: d 0, insertion of the progesterone device and 2.0 mg of estradiol benzoate i.m.; d 9, treatment with 0.15 mg of PGF2α analogue (D-cloprostenol), 300 IU eCG and 1.0-mg estradiol cypionate i.m. and the intravaginal progesterone device was removed; d 11, FTAI. Blood samples were collected at the beginning of the experiment and at the moment of the FTAI. Serum ß-carotene was quantified using portable photometer (iCheck^®; BioAnalyt, GmbH, Teltow, Germany). Data were analyzed using the GLIMMIX 9.3 procedure of SAS. The conception rate at FTAI was greater (P=0.04) in cows supplemented with ß-carotene and vitamins (66.6%; 142/213) than control group (57.6%; 125/217). The blood ß-carotene concentration at the beginning of the experiment was 4.2±1.7 mg/L for the control group and 4.3 ± 2.0 ng/mL for the ß-carotene and vitamins group (P>0.05). At FTAI the blood ß-carotene concentration was 5.1 ± 1.5 mg/L for the control group and 4.8 ± 1.5 mg/L for treated cows (P>0.05). In conclusion, despite no difference in blood ß-carotene concentration, feeding grazing beef cows with the combination of ß-carotene and vitamins A, D, E, and biotin in the mineral supplement increased conception rate to timed-AI by 15.6%.