By Lorna MacPherson, dairy consultant SAC Consulting

During the summer months there are always reminders in the farming press regarding the potential risks of heat stress in dairy cows and what can be done to mitigate this. However the effect of warmer weather should also be considered on the pre-weaned dairy calf.

Usually when it comes to discussing environmental temperature and calf performance it is the cold winter temperatures that tends to be the focus, as a calf under three weeks of age has a lower critical temperature of 15˚C. This means that below this temperature, extra energy is required to maintain body temperature, with less energy available for growth and immunity.

Calves have an upper critical temperature of 25˚C and while we have had very few days this year in Scotland with temperatures close to this, as the weather warms up, effects on calves should be considered, particularly with reference to water intake.

At temperatures over 25˚C, calves will experience heat stress and respond by eating less starter feed and increasing water intake. Other behavioural signs include panting, sweating and more time spent standing in an attempt to dissipate heat from the body.

It is unlikely that healthy calves will refuse milk so increasing milk volume or concentrate of milk powder allows energy intake to be increased to help meet increased maintenance requirements and maintain growth.

The Red Tractor Assurance Scheme standards for dairy state that calves must have unrestricted access to clean drinking water at all times from birth. However, it is still not uncommon to find units where calves do not have access to water for the first seven to 10 days of life while housed in individual pens.

It is often assumed that calves receive sufficient water through milk or milk replacer. However, milk bypasses the rumen via the oesophageal groove and is digested in the abomasum. The rumen also requires water to help develop the beneficial bacteria and thereby enhance rumen development and function, further strengthening the case for water to be provided from day one in warm conditions.

Water is an essential nutrient for calves, even in the first few days of life. A new-born Holstein heifer calf is made up of 80% water and this only reduces to around 70% at 40 days of age. For those calves that are not offered water immediately from birth, they are more likely to suffer from lack of fluids which in turn will reduce growth performance and suppress the immune system, making them more susceptible to disease.

Recent research published in the Journal of Dairy Science looked at the effect of water provision on feed and water intake, growth performance, health status and nutrient digestibility in Holstein heifers calves. The study was carried out at the Dairy Research and Teaching Unit at Iowa State University. The USDA reported in 2016 that US dairy farmers wait on average 17 days before offering drinking water to new-born dairy calves. This study compared calves offered ad-lib water from birth to those offered water from day 17 onwards.

The calves offered water from birth drank on average 0.75kg water/day during the first 16 days. There was also an increase in consumption with temperature in both groups of calves, with an average increase of 0.068kg/day for ˚C increase in temperature. This means the average increase in water requirement for a calf going from 10˚C to 20˚C is an extra 0.68kg/day. The increment during weaning when milk was reduced by 67% doubled to 0.141kg per 1˚C, highlighting the importance of sufficient water provision when weaning calves during warm conditions.

Overall, the study showed that while both groups of calves had similar starter feed intake, the calves offered water from birth drank more milk, were heavier at weaning, showed higher digestibility of nutrients (fibre) and better feed conversion efficiency compared to calves that had delayed access to water after birth. This suggests that water provision from birth is important to maximise growth potential and that warmer weather strengthens the argument for water provision from day one to those producers currently not providing this.

Reference: Wickramasinghe, H. K. J. P., Kramer, A. J. and Appuhamy, J. A. D. R. N., 2019. Drinking water intake of newborn dairy calves and its effects on feed intake, growth performance, health status and nutrient digestibility. Journal of Dairy Science, 102: 377-387.