Effect of Time of Birth on Fall- Born Beef Calf Rectal Temperature and Metabolites in First 72 Hours of Life

We hypothesized that fall calves born during the warmest part of day would have increased body temperatures resulting in poor metabolic and hydration status. Thus, our objective was to determine effects of time of birth on neonatal calf rectal temperature, energy and protein metabolites, and electrolytes. Jugular blood samples and rectal temperatures were obtained from fall-born crossbred beef calves (yr 1: n = 23; yr 2: n = 27) at 0, 6, 12, 24, 48, and 72 h of age, where 0 h samples were obtained between standing and suckling. Calves were categorized into three 8-h periods based on time of birth to represent differing ambient temperatures and sunlight exposure: morning (0400 to 1159 h; n = 17), afternoon (1200 to 1959 h; n = 26), and night (2000 to 0359 h; n = 7). Data were analyzed with effects of time of birth category, sampling hour, their interaction, and year in the model. Sampling hour was considered a repeated effect. The interaction of time period and sampling hour affected (P < 0.001) rectal temperature, serum sodium, and serum chloride, and tended to affect (P = 0.07) blood urea nitrogen. At 0 h, afternoon-born calves had greater (P ≤ 0.02) rectal temperature than morning and night. Afternoon and morning calves had greater (P ≤ 0.006) rectal temperature than night at 6 h. At 12 h, morning calves had greater (P = 0.003) rectal temperature than afternoon. Rectal temperature of morning-born calves at 24 h was lower (P < 0.001) than afternoon and tended to be lower (P = 0.07) than night. Afternoon and night calves had greater (P ≤ 0.003) rectal temperatures than morning calves at 48 h. At 72 h, afternoon calves had greater (P ≤ 0.001) rectal temperature than morning. Blood urea nitrogen tended to be greater (P = 0.07) for night calves than morning at 0 h. Serum sodium at 12 h was greater (P ≤ 0.001) in morning compared with afternoon and night calves. Serum chloride of morning calves tended to be greater (P = 0.07) than afternoon at 12 h. At 48 h, serum chloride was greater (P = 0.02) for afternoon than morning. Although rectal temperature was affected by time of birth, there were no major differences in calf metabolites or electrolytes, suggesting that time of birth and rectal temperature do not have major effects on neonatal calf metabolic or hydration status.