Physiological, health, lactation, and reproductive traits of cooled dairy cows classified as having high or low core body temperature during the dry period1.

Primary objectives of this study were to compare concentrations of pregnancy-associated glycoprotein (PAG) before calving, prolactin (PRL) after calving, and energy balance indicators before and after calving in cooled cows classified as having high (HT) or low (LT) core body temperature (CBT) during the dry period. Secondary objectives were to investigate associations between dry-period CBT and likelihood of cows developing health disorders, and compare health, productive and reproductive traits of HT and LT cows. Dry Holstein cows (n = 260) with 250 to 260 d of gestation from three herds were enrolled in the study during summer. Cows were provided evaporative cooling during the dry and lactating period. The vaginal temperature was recorded in 5-min intervals during 7 consecutive days and cows were classified as HT or LT. Blood samples were collected weekly from enrollment until 14 ± 3 d in milk (DIM). Additional blood samples were collected within 12 h postpartum from a subgroup of cows (n = 25) to determine PRL concentration. Cows were monitored for health disorders, productive, and reproductive performance until 13 wk of the subsequent lactation. High temperature cows had shorter (P < 0.01) gestation length (273.9 ± 0.9 vs. 278.2 ± 0.9 d) and greater (P < 0.01) incidence of twinning (19.7 vs. 4.2%) than LT cows. Cows classified as HT had greater (P = 0.02) PAG concentration (134.1 ± 4.9 vs. 117.4 ± 4.9 ng/mL), but postpartum PRL concentration did not (P = 0.55) differ between HT and LT cows. Primiparous HT cows had greater (P = 0.05) prepartum nonesterified fatty acids concentration (135, 95% CI = 102 to 178 vs. 104, 95% CI = 75 to 144 mmol/dL) than primiparous LT cows, but no differences (P = 0.72) were observed between CBT group in multiparous cows. The concentration of β-hydroxybutyrate was greater (P = 0.04) for LT compared with HT cows at 7 ± 3 DIM. The quadratic effect of CBT tended (P = 0.09) to be associated with risk of health disorders within 60 DIM. Milk yield tended (P = 0.10) to be greater for LT compared with HT cows (49.3 ± 1.9 vs. 46.2 ± 1.6 kg). Pregnancy per AI at first service did not (P = 0.64) differ between HT and LT cows. In conclusion, HT cows have distinct concentrations of PAG in late gestation and energy balance indicators during the transition period. In addition, CBT assessment during the dry period may be a useful tool to identify cows expected to have impaired health and milk yield in the subsequent lactation.