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.
Highlights
Heat stress affects the health and productivity of dairy cows negatively
An increased concentration of urea during exposure to heat stress was found with significantly higher concentration in obese cows (p
During exposure to heat stress, they significantly increase rectal temperature, their respiratory tract quickly gets weak in the thermoregulatory process, and they significantly decrease the amount and quality of produced milk as compared to normal and thin cows
Summary
Heat stress affects the health and productivity of dairy cows negatively. Homeothermic animals have a thermoneutral zone in which energy expenditure to Abbreviations: 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.maintain normal body temperature is minimal, constant and independent of environmental temperature (Youself, 1987). Heat stress affects the health and productivity of dairy cows negatively. Homeothermic animals have a thermoneutral zone in which energy expenditure to Abbreviations: 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. The most sensitive cattle category to high ambient temperature are lactating dairy cows because they produce much more heat than non-lactating ones (Blackshaw and Blackshaw, 1994). Cattle housed in a climatic chamber and exposed to 23 days of heat stress revealed that complete recovery of feed intake was obtained only after 10 days at thermoneutrality. Respiration rates returned to normal level, while rectal temperature undershot, possibly indicating adaptation to heat stress (Williams et al, 2009).
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