Dry-period seasonal effects on the subsequent lactation

Photoperiod and heat stress during the dry period influence subsequent lactation performance and health. To determine the effects of seasonal heat stress during the dry period on subsequent lactation performance, occurrence of health disorders during the first 80 DIM, and reproduction performance during the first 150 DIM, records of 2,613 multiparous cows under commercial conditions in Florida over 3 yr were analyzed. Seasons were COOL (December, January, and February) and HOT (June, July, and August). Traits analyzed were lactation number, 305-d milk production, calving interval, number of breedings, days open, and occurrence of postpartum health disorders such as digestive problems, mastitis, metritis, retained fetal membranes, and respiratory problems. Cows dry during HOT months had less milk yield in the subsequent lactation relative to COOL cows (10,351 vs. 10,902 kg; P < 0.01). Additionally, HOT cows had a greater incidence of mastitis (P < 0.01) and respiratory problems (P < 0.01) compared with COOL cows. Moreover, cows exposed to heat tended to have a greater incidence of retained fetal membrane (P < 0.06) compared with cows cooled while dry. Of interest, COOL cows had a greater incidence of postpartum digestive problems (P < 0.01). Additionally, cows dried during hot months had increased breeding number (P = 0.03), DIM to first breeding (P < 0.01), and DIM to pregnancy diagnosis (P < 0.01) in the subsequent lactation. Therefore, environmental-management strategies during the dry period may be needed to attain optimal lactation performance.