Effects of spring- versus fall-calving on perinatal nutrient availability and neonatal vigor in beef cattle.

To determine the effect of calving season on perinatal nutrient availability and neonatal beef calf vigor, data were collected from 4 spring- (average calving date: February 14; n = 203 total) and 4 fall- (average calving date: September 20; n = 179 total) calving experiments. Time to stand was determined as minutes from birth to standing for 5 s. After birth, calf weight and size (length, heart and abdominal girth, and cannon circumference) were recorded. Jugular blood samples and rectal temperatures were obtained at 0, 6, 12, and 24 h postnatally in 6 experiments and at 48 h postnatally in Exp. 2 to 8. Data were analyzed with fixed effects of season (single point) or season, hour, and their interaction (over time, using repeated measures). Experiment was a random effect; calf sex was included when P ≤ 0.25. Within calving season, correlations were determined between calf size, vigor, and 48-h serum total protein. Fall-born calves tended to have lighter ( P = 0.09) birth weight and faster ( P = 0.05) time to stand than spring-born calves. Season did not affect ( P ≥ 0.18) gestation length, other calf size measures, or 48-h serum total protein. Fall-born calves had greater ( P ≤ 0.003) rectal temperature at 0, 24, and 48 h postnatal. Spring-born calves had greater ( P ≤ 0.009) circulating glucose at 0 h, serum non-esterified fatty acids at 0 and 6 h, and plasma triglycerides at 0, 6, 12, and 48 h. Fall-born calves had greater ( P ≤ 0.03) sodium from 6 to 48 h and magnesium from 0 to 24 h of age. Phosphorus was greater ( P ≤ 0.02) at 6 and 12 h of age in spring-born calves. Spring-born calves had greater ( P ≤ 0.04) aspartate aminotransferase at 12 and 24 h and creatine kinase at 0 and 12 h of age. Fall-born calves had greater ( P ≤ 0.03) albumin, calcium, and chloride, had lower ( P ≤ 0.03) bicarbonate and direct bilirubin, and tended to have greater ( P = 0.10) anion gap (all main effects of calving season). Calf birth weight had a weak positive relationship ( P ≤ 0.03) with 48-h serum total protein and time to stand in fall-born, but not spring-born, calves. Overall, fetal growth was restricted and neonatal dehydration was increased by warm conditions for fall-born calves, but vigor and metabolism were negatively affected by cold conditions in spring-born calves. These data suggest that calving season influences perinatal nutrient availability, which may impact the transition of beef calves to postnatal life.