Simple SummaryThis study aims to explore whether drinking heated water is able to increase the performance of yak calves. We collected and analyzed data from a two-month experiment on yak calves. The results show that compared with drinking cold water, drinking heated water significantly improved the apparent total tract digestibility (ATTD) and ruminal fermentation function. In addition, we found that heated water significantly improved the immune function of the body through serum indexes, and the nutrients in the blood were significantly increased compared with cold water. Furthermore, the serum hormones were also changed by heated water, with higher levels of hormones related to growth. Overall, drinking heated water in the cold season could increase the performance of yak calves in terms of better ATTD, ruminal function and immunity.AbstractThis study was conducted to investigate the effects of heated water intake on the growth performance, serum biochemical indexes, apparent total tract digestibility (ATTD) of nutrients and ruminal fermentation function of yak calves in winter. A total of 24 yaks (59.09 ± 3.181 kg) were randomly selected and divided into a cold water (fluctuated with the temperature of test sites at 0–10 °C) group (CW) (58.58 ± 3.592 kg) and a heated water (20 °C) group (HW) (59.61 ± 2.772 kg). After 2 months of the experiment, body weight, serum biochemical indexes, ruminal fermentation characteristics and ATTD were measured. The results showed that drinking heated water increased (p< 0.05) the total weight gain and average daily gain of yaks compared with those drinking cold water. Heated water increased (p< 0.05) the levels of immune globulin M, interleukin-6, triiodothyronine, tetraiodothyronine and growth hormone compared with cold water. In addition, yaks drinking heated water showed higher (p< 0.05) ATTD of crude protein and ether extract, as well as increased (p< 0.05) content of total protein, albumin and urea nitrogen in serum than those drinking cold water. Compared with cold water, heated water showed increased (p< 0.05) total volatile fatty acids, acetic acid and propionic acid, and a reduced (p< 0.05) acetic acid to propionic acid ratio (p< 0.05). In conclusion, drinking heated water at 20 °C could improve performance via increasing nutrient digestibility and ruminal fermentation function in yak calves.