Water is the nutrient required in greatest quantity by young animals accounting for 70-75% of a young animal’s body weight. It is often overlooked as an essential nutrient. Water is needed daily for the transport or nutrients, the excretion of waste products (urine and faeces), the digestion of feed, the maintenance of osmotic pressure, the lubrication of joints and eyes, the exchange of CO2 with oxygen in the lungs, and the regulation of body temperature – especially heat release by the lungs and urine. Bacteria in the rumen can only survive in a water environment. Most of the water that enters the rumen is from free water intake. Milk or milk replacer bypasses the rumen due to the esophageal groove that can be active until 12 weeks of age. The esophageal groove works to ensure that milk bypasses the rumen and goes directly into the abomasum (the true stomach). That process allows for milk to be digested and absorbed quickly. Water entering the rumen is a part of early rumen development. The water in milk or milk replacer cannot replace the necessity of fresh, clean water which should be offered daily to all animals. The intake of water stimulates starter intake (Kertz et al 1984) and promotes greater total feed intake (Thickett et al, 1981), which leads to improved performance and health (see Table 1). That being said, calves will often drink water because they are still hungry for milk – water does not provide calories!

Table 1 Summary of water trial results During periods of water loss, (e.g. scours or hot, humid weather) or water restriction (ice, dirty water, inadequate supply) dehydration will negatively affect feed intake and digestibility. Even mild dehydration (1-5% loss of body), with symptoms not visible to the human eye reduces metabolic efficiency and impairs the calf’s ability to regulate body heat (ear and leg extremities feel cool to the touch). As dehydration becomes more severe (9-11% of body weight), calves become depressed. When dehydration reaches 12-15% of body weight calves may die.

Table 2 Typical water intake for Holstein calves at 10-26 ^oC Water requirements change according to age and temperature (see Table 2). Once temperatures approach 32⁰C that requirement increases dramatically. It is necessary to maintain hydration and also cool the body – heat is generated through the constant process of metabolism and digestion in the calf. If enough water is not available to help cool the body, the animal will reduce their feed intake. An interesting fact is that calves seem to prefer warm water – intake was shown to be 47% higher compared to calves offered cool water (Huuskonen et al, 2011). There was no difference in health and growth parameters of calves offered warm versus cold water. Whether water is offered by pail or by nipple the total amount of water consumed does not seem to be affected (Hepola, 2008). When a calf is ill or scouring, water requirements will increase to maintain hydration and help heal the body. Furthermore, calves that consume water when they are healthy tend to have fewer days scouring and when they do scour the outbreak is less severe. Providing free-access water is a critical part of a successful feeding program for calves. It is a critical nutrient that ensures strong early development and helps maintain good health. Using water to ensure an optimal calf feeding program:

1. Fresh, clean water – drives starter intake, encourages rumen development.
2. Water is a separate nutrient – Water through milk or milk replacer is not enough, it is absorbed separately within the body and is designed to perform different functions.
3. Sanitation – clean all buckets and containers daily.  Check automatic systems regularly to ensure clean and adequate flow.