Physiological responses and pregnancy rate of black and white Holstein heifers during hot and cold seasons in a desert region

Abstract

Our aim was to compare certain physiological traits and pregnancy rates in dairy heifers classified by coat color during summer and winter months in a Sonoran Desert region. Sixty Holstein heifers were randomly selected (age and weight of 13.1 ± 0.82 months and 382 ± 5.3 kg) and divided by season (i.e., winter and summer) and hair coat color (i.e., black and white). There were 28 summer heifers (13 black/15 white) and 32 in winter (18 black/14 white). Respiratory frequency (RF) was determined visually, and body surface temperatures (BSTs) of several anatomic regions were collected using thermography at 06:00 and 15:00 h every 3rd day. Furthermore, three blood samples were collected from each heifer in each season to determine hematological profiles and serum analytes (i.e., electrolytes, metabolites, hormones). Reproductive variables were pregnancy rate and services per pregnancy. Ambient temperatures ranged from 25 to 49 ◦C in summer and 3 to 28 ◦C in winter. In summer and winter, RF and most BST were higher (p < 0.05) in black heifers in the morning, while only head, right flank, and loin were higher (p < 0.05) in the afternoon. Cortisol and progesterone concentrations were higher (p < 0.01) in summer, while thyroid hormones were higher (p < 0.05) in winter. Glucose, triglycerides, cholesterol, urea, and sodium were higher (p < 0.05) in winter. Reproductive traits were unaffected by season or coat color. Although there were some differences in physiological variables and some biochemical parameters by season and coat color, these alterations were not enough to modify reproductive responses of Holstein heifers