1.2. Milk feeding in dairy calves
Traditionally, dairy calf milk feeding systems have been based on daily feeding rates of 8–10% of body weight (BW) [9]. This feeding regime is highly restrictive compared to ad libitum feeding. Research has shown that calves allowed ad libitum access to milk from artificial teats drink 8–10 l [10]. Calves allowed to suckle drink up to 12–15 l of milk per day at 2–4 weeks of age [11] and [12] (Grøndahl, unpublished). Khan et al. [13] recommend to feed dairy calves the equivalent of 20% of BW per day based on a comprehensive literature review. This recommendation is more in line with the natural milk intake level of dairy calves. The Norwegian milk feeding recommendations were also recently increased from 6 to 8 l per day [14].
Until 3–4 weeks of age, restrictive milk feeding can result in the calves being unable to meet their daily energy requirements [15], leading to chronic hunger [16]. One way of feeding the calf more milk is to introduce an additional meal. This increases the workload for farmers without automated milk feeders and is therefore often undesirable. Another way is to increase the meal size. Fear of exceeding the abomasal capacity causing milk to enter the rumen, however, is a major reason to limit the meal size.