Positive Influence of Rectal Temperature at Fixed Timed Artificial Insemination on Pregnancy Outcome in Beef Cattle

The aim of these studies was to determine the effect of rectal temperature at fixed timed artificial insemination (FTAI) on pregnancy outcomes in cattle. To accomplish the objective, regression analyses were performed utilizing Bos taurus and Bos indicus cattle. Rectal temperature of Bos taurus cattle at FTAI (n = 427) ranged from 37.8 to 41.8 ⁰C (39.5± 0.6 °C) and positively influenced pregnancy outcome (P = 0.006). Each 1 ⁰C increase in rectal temperature increased pregnancy odds 1.63 times (95% Confidence Interval (CI): 1.16 to 2.31). At FTAI, 42.39% of animals were hyperthermic (> 39.5 °C); probability for pregnancy (P = 0.02) and calving (P = 0.03) was higher in these animals. Animals that exhibited estrus activity had greater probability for pregnancy (P = 0.05; Odds Ratio (OR): 1.70, 95% CI: 1.01 to 2.86) and calving (P = 0.006; OR: 2.41, 95% CI: 1.30 to 4.48). Minimum (min) and maximum (max) ambient temperature and average max ambient temperature 3 d before FTAI were also influential on pregnancy and calving outcomes. Estrus activity occurring after CIDR (controlled internal drug release) removal but before FTAI was positively associated with higher rectal temperatures at FTAI (P = 0.02). Other factors influencing rectal temperature at FTAI were parity (P = 0.006) and min ambient temperature (P = 0.08) on day of FTAI. Within Bos indicus cattle, rectal temperature ranged from 37.0 to 40.9 ⁰C (39.6 ± 0.5; n = 1,278) and was positively associated with pregnancy outcome (P = 0.0001). Each 1 ⁰C increase in rectal temperature at the time of AI increased pregnancy odds 1.93 times (95% CI: 1.42 to 2.60). At FTAI, 60.64% of animals were hyperthermic (> 39.5 °C); probability of pregnancy was higher in this subset of animals (P = 0.01). Estrotect patch (P < 0.05) and body condition (P < 0.0001) scores were also influential. Estrotect patch score > 2 had a higher probability for pregnancy (P= 0.02) as did body condition scores > 2.75 (P < 0.0001). Higher rectal temperature at FTAI was associated with body condition scores > 2.75 (P = 0.02). Per each 1 kg increase in body weight rectal temperature at FTAI was lower by 0.00087 ⁰C (P = 0.006). Independent of cattle species, higher rectal temperature was positively associated with pregnancy and calving outcomes.