Hugh Chester-Jones After helping our nursery dairy calves survive a tough winter at the Southern Research and Outreach Center (SROC) in Waseca, we are looking forward to the spring and summer months and need to address changes in our calf management strategies. In our SROC calf work, it has been more challenging to maintain good calf growth and health in the summer than in the winter months.
Factors contributing to calf performance challenges:
High ambient temperature and humidity – This can result in reduced calf starter intake and higher incidence of infections. The Upper Critical Temperature (UCT) for calves has been shown to be 78Â°F or greater. The potential for heat stress occurs when combining temperature with high relative humidity expressed as temperature humidity index (THI). A THI of 72 or greater can cause calves discomfort. In such situations, calf panting and sweating do not compensate for this stress and calf energy needs will increase which must be supported by adequate nutrition. In addition, as calves attempt to maintain body temperature in the summer months increased respiration and sweating results in water losses which have to be replaced. As environmental temperature increases, water intake increases accordingly.
Access to water and effects of feed supply – These are important factors. Research has indicated that the amount of water needed by nursery calves depends not only on the environmental conditions but also on the incidence of scours and the amount of milk/milk replacer and starter intake. Water intake is closely related to starter intake which in turn drives rumen development. However, water intake may increase independent of starter intake when temperature is above the UCT for calves. Research has shown the amount of liquid in milk replacer also affects amount of water consumed. Water temperature can also affect water intake.
Other stressor factors that affect calf performance include management of the housing environment (individual and group-fed calves; clean uncontaminated water offered; ensure water buckets and facilities are clean), exposure to direct sunlight, less than adequate ventilation, and fly population control. In addition, calves born from heat-stressed dams will often have light birth weight, depressed intake and compromised immune function with the potential for rapid dehydration.
How do pre-weaned calves respond to milk and starter feeding without additional water offered? - In a study by Kertz et al. (1984), calves were offered ad libitum (free choice) or no water when fed 4.2 pounds of milk replacer (11.4% solids) twice daily for 3 weeks and once daily in week 4 prior to weaning. There were no differences in daily gain for the first 3 weeks but greater gain in week 4, and 38% overall for calves offered ad libitum water. Starter intake was higher for calves fed ad libitum water from week 2 onwards with the largest differences in weeks 3 and 4. No effect of water intake on scours incidence was observed. The authors emphasized the importance of ad libitum water to support good starter intake and growth.