Effects of mineral and vitamin supplementation on pregnancy rates in Nelore cattle submitted to FTAI programs with different reactivity scores

Abstract

A high-reactivity herd temperament reduces productivity and profitability in cattle farming. In Bos taurus indicus (Nellore) cattle, we hypothesized that a higher reactivity score is associated with a lower pregnancy rate, and that injectable supplementation with minerals (Cu, Zn, Mn, Se) and vitamins (A, E) would increase the pregnancy rate and reduce embryonic mortality in very reactive cows. Injectable supplement or control treatments were administered on days 25 and 10 before fixed-time artificial insemination (FTAI; Day 0 : day of FTAI). We selected 1722 cows 45 ± 7 days postpartum, with different behavioral reactivity levels, and a series of measures related to reproduction were measured. The cows were randomly grouped and received sc 1 mL/50 kg live weight of the supplement (n = 872) or placebo (n = 850), 25 and 10 days before the FTAI protocol (Day–25 and Day–10 respectively). On Day −10, devices containing 1 g progesterone were inserted into the vagina, and 2 mg estradiol benzoate was applied intramuscularly. On Day–2, the devices were removed and 530 µg of sodium d-cloprostenol, 300 IU of equine chorionic gonadotropin, and 1 mg of estradiol cypionate were applied. At 48 h after final injection, the cows were subjected to FTAI (Day 0). On Day - 25 (25 days before IATF), temperament was graded as 3 to 12 using composite reactivity score (RS), which evaluates movement and breathing while the animal is in the cattle chute, and their escape velocity, and was used to classify cows as calm (RS ≤ 4; n = 590), reactive (RS 5 to 8; n = 573), and very reactive (RS ≥ 9; n = 559). On Day 0, calm cows had a higher largest follicle diameter on the FTAI compared to reactive and very reactive (14.4 + 0.2 vs. 13.6 + 0.4 and 13.2 + 0.2 mm, respectively; P = 0.03). Interactions were observed, where supplemented cows compared to those no supplemented had higher pregnancy on Day 30 (P = 0.04; 60.00 vs. 54.10 % calm and 58.00 vs. 52.50 % very reactive) and Day 60 (P = 0.03; 58.70 vs. 47.90 % calm, 52.20 vs. 49.10 % reactive and 48.40 vs. 41.30 % very reactive) and reduced embryonic loss at 30 to 60 d (P = 0.04; 2.00 vs. 6.10 % calm, 4.20 vs. 8.40 % reactive and 9.60 vs. 11.20 % very reactive). Supplementation on Days–25 and–10 improved pregnancy rates and reduced embryonic in calm and very reactive cows.