Effects of an injectable mineral supplement on physiological responses and milk production of heat-stressed Holstein cows

ABSTRACT

Summer heat stress in northwest Mexico compromises the physiological thermoregulation capacity and productive performance of lactating Holstein cows, and supplementation of minerals appears to reduce the adverse impact of heat stress in cattle. The objective herein was to evaluate the effects of an injectable mineral supplement containing phosphorus, selenium, potassium, magnesium, and copper on physiological responses, milk production, and milk composition of Holstein cows exposed to heat stress. Sixteen cows were blocked by parity and assigned to one of two treatments (n = 8) using a randomized complete block design: 1) control cows and 2) mineral-treated cows. All cows were exposed to environmental heat stress conditions (i.e., temperature-humidity index = 79.4 ± 4.3 units). No study variable was affected (P ≥ 0.20) by the treatment x sampling day interaction. While the mineral supplement did not affect any physiological variable in the afternoon, this treatment decreased breaths per min (P = 0.01) and most body surface temperatures (P ≤ 0.06; head, shoulder, leg, right-flank, and udder) in the morning. There was no effect (P = 0.37) of the mineral supplementation on milk yield but increased (P ≤ 0.03) the percentages of solids non-fat, protein, lactose, and density in the milk. In conclusion, Holstein cows' physiological thermoregulation and milk composition experiencing summer heat stress were improved by applying an injectable mineral supplement.(AU)