Abstract.

Heat stress has a detrimental effect on the health and production performance of dairy cow. To alleviate the heat stress, sprinkle cooling system is widely used in the dairy barns in Eastern and Southern China, where is characterized by a hot and humid climate in summer. Due to a lack of systemic design and study, the cooling effect usually could not reach the targeted goals and the animals suffer a severe stress. In order to improve the system performance, this study was conducted to test the effect of spraying interval (SI) and water temperature (WT) on alleviating the heat stress of dairy cows. Based on the parity, day in milk, and milk yield, 48 Chinese Holstein dairy cows were assigned into four groups with different treatments: Thermal insulation a (TIa), Thermal insulation b (TIb), Non thermal insulation a (NTIa) and Non thermal insulation b (NTIb). In period 1, a 4-min SI was used for TIa and NTIa, and a 6-min SI was used for (TIb) and (NTIb). After a 3-day transition, the 4-min SI was exchanged with the 6-min one. The results showed that spraying water temperature of TI groups was 2.8 ºC lower. The rectal temperature of TIa group cows was about 0.2 ºC lower than that of cows in the other three treatments, and its vulva temperature was lower as well. Respiration rates of the cows in TIb and NTIb groups were 79.5 and 92.8 per min, respectively, and the TIb group was significantly lower. Comparing NTI group, the Blood serum potassium of the TIa group was much higher (PTI = 0.003). Blood serum calcium contents of dairy cows in the TI groups were decreased (PTI = 0.036). Cortisol in cows of TIa group was higher than that of TIb and NTIb groups (P = 0.039). TI group had a lower growth hormone (GH) than NTI group (P = 0.049). This research shows the cooling effect of the spraying system could be improved by adding thermal insulation on the water tank and decreasing the SI, which does not greatly alter concentrations of metabolic hormones in lactating dairy cows.

Measurement, Sampling and Laboratory Analysis

Blood serum sodium and potassium were determined by a flame photometer (Singh et al., 2012). Blood serum calcium was measured by Hitachi automatic biochemistry analyzer (Hitachi High-Tech, Tokyo, JP). Cortisol, growth hormone (GH), triiodothyronine, and thyroxine were tested with the kits supplied by Beijing North Institute of Biotechnology. Epinephrine and norepinephrine were measured by using kits from Wuhan ColorfulGene Biological Technology Co., LTD.