Drinking warm water in a cold environment impairs growth performance and alters the gastrointestinal microbiota in growing calves

This study aimed to investigate the effects of drinking water temperature on growth performance and gastrointestinal microbiota in growing calves. Forty-five weaned male calves were randomly divided into three treatment groups (n = 15 per group). The groups were provided with drinking water at different temperatures: 5-10 °C (FC), 20-25 °C (FM), or 35-40 °C (FW). The experiment lasted for 30 days, during which all calves were housed in individual hutches. Body weight and jugular blood samples were collected on days 0, 15, and 30; body measurements were taken on days 0 and 30. On day 30, rumen fluid and faecal samples were collected for 16S rRNA gene sequencing of the V3-V4 regions. Calves in the FW group showed significantly higher water intake and diarrhoea frequency, along with significantly lower average daily gain (ADG), compared to the other groups. During the first 15 days, the ADG for the FM and FW groups was significantly lower than that of the FC group. Additionally, the FM and FW group maintained higher faecal scores throughout the experimental period. Rumen microbial analysis revealed a higher abundance of the potentially pathogenic genus Pseudoscardovia in the FW group compared to the FC group. In a cold winter environment, providing drinking water at 35-40 °C reduced growth performance, elevated faecal scores, and increased the abundance of harmful microorganisms in the gastrointestinal tract of growing calves.