Abstract

The aim of this study was to determine the effects of body condition score to metabolic acclimation in heat stressed Holstein cows. Body condition of cows had no effect on any of the tested parameters during the thermal neutral period, exceptfor the percentage of protein in milk. Heat stress has been demonstrated to have animpact on all the selected parameters, and has been found to be the cause ofdecreased milk production and quality, increased rectal temperature and respiration rate, decreased glucose, non esterified fatty acids (NEFA) and cholesterol concentration, increased urea and bilirubin concentration, and loss of subcutaneous fat. Obese cows (BCS>4) had less ability of acclimation to heat stress as compared to normal and thin cows (significantly lower production and milk quality, and significantly higher rectal temperature and respiration level in relation to theother groups of cows). Obese cows showed a significantly higher concentration ofNEFA and significantly lower glucose during exposure to heat stress. The steady increase in NEFA concentrations and decrease of backfat thickness suggested thatfat was used for energy purposes, which significantly increased the heat balanceand led to poor acclimation to heat stress in obese cows. Cows with high body condition were at higher risk of developing liver failure and lipidosis (reduced cholesterol and elevated bilirubin concentration) during heat stress, which could be linked with increased concentrations of fatty acids in the blood. This was found with an increased concentration of urea during exposure to heat stress, with significantlyhigher concentration in obese cows. Using the fat for energy purposes depends onthe sensitivity to insulin, which increases during heat stress. Obese cows arenaturally less sensitive to insulin and more prone to lipolysis. However, these signsshould be the focus of future research.

Key words: Body condition score, heat stress, metabolic status, cow.

Abbreviation

THI, Temperature-humidity index of heat stress load; BCS, body condition score; NEFA, non esterified fatty acids; BHB, beta hydroxy butirate;NEBAL, negative energy balance; NEM, nett energy for maintenance.