Effects of hunger level and tube diameter on the feeding behavior of teat-fed dairy calves

Behavioral changes caused by variation in hunger have a great potential in health monitoring in dairy cattle. The present experiment used 48 Danish Holstein bull calves with a median age of 33 d. We examined the effect of different levels of hunger (reduced, in which calves were fed 1.5L of milk via esophageal tube before feeding; increased, in which calves were fed half milk ration at the previous feeding, or control, in which calves were fed normal ration at the previous feeding) on feeding behavior of calves fed via different tube diameters (6.0, 3.0, or 1.5mm). Behavior observed during a 40-min period after morning milk feeding on d 7, 9, and 11 of testing is reported. No significant interactions between tube diameter and hunger level on behavior were found. Reduced tube diameter led to increased latency to empty the teat bucket, increased duration of nutritive sucking, and decreased duration of nonnutritive sucking for calves fed via 1.5-mm tubes compared with calves in the 2 other treatments. The duration of nonnutritive sucking increased with increasing level of hunger. Furthermore, calves with reduced hunger showed a lower frequency of butting than calves at the 2 other hunger levels. The present results show that only a rather high reduction in tube diameter led to reduced drinking rate. Neither reduced nor increased hunger levels led to changes in drinking rate, but calves showed reduced nonnutritive sucking and butting when they were less hungry and increased nonnutritive sucking and butting when hunger was increased. The results suggest that nonnutritive sucking is a more sensitive indicator than drinking rate of changes in feeding motivation. Consequently, reduction in nonnutritive sucking might be a new candidate in the search for behavioral indicators of disease in dairy calves.