Composition of Colostrum from Dairy Heifers Exposed to High Air Temperatures During Late Pregnancy and the Early Postpartum Period

¹ Istituto di Zootecnia, Università della Tuscia, Viterbo 01100, Italy

This study examined the effects of heat stress on composition of colostrum from primiparous cows during late pregnancy and the early postpartum period. Two groups of 6 Holstein heifers were utilized. During the last 3 wk of pregnancy and during the first 36 h after calving, one group was exposed to thermal comfort (temperature-humidity index = 65); the other group was exposed to high air temperatures (temperature-humidity index = 82 from 0900 to 2000 h and temperature-humidity index = 76 from 2100 to 0800 h). Heifers under heat stress had higher rectal temperatures and respiratory rates; lower plasma tri-iodothyronine and glucose; higher plasma nonesterified fatty acids and ß-hydroxybutyrate; lower intakes of dry matter, net energy for lactation, and crude protein; higher water intakes; and lower body condition scores. The decline of plasma immunoglobulins (Ig) over the final 2 wk of pregnancy was less pronounced for heifers under heat stress. For the first four milkings, colostrum of cows exposed to high air temperatures had lower mean concentrations of IgG and IgA; lower mean percentages of total protein, casein, lactalbumin, fat, and lactose; lower contents (grams per liter) of short- and medium-chain fatty acids; lower energy; lower titratable acidity; and higher pH. Thus, high air temperatures during late pregnancy and the early postpartum period markedly affected the composition of colostrum from primiparous dairy cows.

Key Words: dairy cows • heat stress • colostrum composition

Submitted on March 18, 1996
Accepted on August 8, 1996

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