Effect of drinking water temperature and potassium carbonate supplement on performance and physiological parameters of lactating cows under heat stress

This study was performed to evaluate the effects of water temperature and adding potassium carbonate supplement on growth performance, milk yield and composition, rectal temperature, respiratory rate, heart rate and some blood biochemicals of lactating cows during heat stress. Sixteen multiparous lactating Holstein cows (580±12 kg) were used in a change-over design with four treatments arranged in a 2×2 factorial experiment in 4 four-week periods (three weeks for treating followed by a week as gap). The treatments were two levels of drinking water temperature (chilled: 12°C and normal: 25°C), and two levels of potassium carbonate addition (0 and 0.96% of DM). Duration of the study was July to September with maximum and minimum ambient temperatures as 42 and 25 °C, respectively and overall temperature-humidity index value by 85.5. Feed intake of cows was measured daily. Blood samples were collected via tail vein at the final day of the periods. Rectal temperature, respiratory rate and heart rate were measured three times a period. Results showed that water temperature and potassium carbonate supplementation to diet had no significant effects on average daily gain, milk yield and composition, rectal temperature, respiratory rate, heart rate, blood urea nitrogen and ketene bodies levels of dairy cows during the experiment, but water temperature affected on feed intake where normal water caused an increase in feed intake of cows (P<0.05). Adding potassium supplement to diet had no significant effects on mentioned parameters but it decreased the respiration rate of cows (P<0.05). Generally, results showed that drinking water temperature did not affect on the physiological parameters but normal water can increase feed intake. Adding potassium supplement to diet only affected on the respiration rate of cows. The results of the study do not recommend the chilling of drinking water or adding potassium supplement to the diet of dairy cows under heat stress.