The combination of β-carotene and vitamins improve the pregnancy rate at first fixed-time artificial insemination in grazing beef cows

The aim of this experiment was to evaluate the effects of feeding the combination of β-carotene and vitamins (ADE and biotin) on reproductive performance of grazing beef cows. A total of 430 suckled multiparous Nellore cows (Bos indicus, initial body weigh = 417 ± 58 kg) were used in a randomized block design. At the beginning of the trial (30 days before fixed-time artificial insemination - FTAI) animals were assigned according to calving date, body condition score (BCS) and blocked according to blood β-carotene concentration. Treatments were: Control (mineral supplement: no β-carotene and vitamins) and Treated (combination of 500 mg β-carotene, 70,000 IU Vit. A, 10,000 IU Vit. D3, 500 mg Vit. E and 10 mg biotin/cow/day into the mineral supplement). Animals were synchronized using estradiol/progesterone (E2/P4) based protocol. Pregnancy rate was evaluated 30 days after FTAI and 30 days after the end of breeding season. No difference in the cyclicity rate [presence of corpus luteum (CL); P = 0.31] before FTAI synchronization protocol on day 11 was observed. The percentage of cows in estrus between P4 device removal and FTAI did not differ between groups at first (P = 0.39) and second FTAI (P = 0.18). The combination of β-carotene and vitamins into the mineral supplement increased the pregnancy rate at first FTAI: Control: 57.6% (125/217) vs. Treated: 66.7% (142/213; P = 0.04) but not at second FTAI: Control: 55.4% (51/92) vs. Treated: 50.7% (36/71; P = 0.52) and to the natural mating: Control: 46.3% (19/41) vs. Treated: 31.4% (11/35; P = 0.07) or at the end of breeding season Control: 89.9% (195/217) vs. Treated: 88.7% (189/213; P = 0.77). In the non-pregnant cows, the occurrence of CL did not differ between groups at first (P = 0.93) and second (P = 0.89) pregnancy diagnostics. Treated cows had greater embryo thoracic width at second pregnancy diagnostic compared to Control cows (P = 0.003). Positive correlations were observed between the pregnancy rate at first FTAI (day 30) and BCS at day 11 (P = 0.05), largest follicle at day 2 (P = 0.01), and blood β-carotene concentration on day -11 (P = 0.06) of FTAI protocol. Including the combination of β-carotene, vitamins ADE and biotin into mineral supplement for grazing beef cows increases the conception rate at first FTAI and can be a tool to optimize the reproductive performance.