Towards Understanding Feeding Motivation and Management Factors Affecting Feeding Behaviour in Limit-Fed Dairy Heifers

The objective of this dissertation was to determine the feeding motivation of dairy heifers and to determine management factors that contribute to satiety in limit-fed dairy heifers. The first study of this dissertation determined the difference in behavioural patterns between limit-fed and ad libitum-fed dairy heifers so that we may understand how limit feeding diverges from normal behaviour. Limit-fed heifers were found to decrease time spent feeding, consume less DM, and increase their feeding rate across the day in comparison to ad libitum-fed heifers. Additionally, the diurnal patterns of ad libitum-fed heifers were much closer to normal behaviour as they consisted of several short, small meals distributed throughout the day. The next three studies examined the management factors of frequency of feed provision and feed bunk space and how these may impact the behaviour of heifers. Increased frequency of feed provision did result in more distribution of feeding activity throughout the day but also imposed feeding amounts that were likely insufficient to achieve satiety. Heifers fed once daily likely experienced satiety in the short term and did spend the most time feeding throughout the day but the diurnal patterns of these heifers did not allow for expression of normal foraging behaviour. Providing increased feed bunk space did not allow limit-fed heifers to spend more time feeding or impact competition within a pen whereas providing straw alongside of a nutrient-dense TMR did result in more normal diurnal patterns, albeit with an increase in competitive behaviour. There was no interaction found between feed bunk space and frequency of feed provision, indicating that limit-fed heifers must be provided with sufficient bunk space to feed simultaneously. Heifers provided with un-restricted bunk space did gain more and were more feed efficient and less variable in feeding time than heifers given restricted bunk space. Feeding once daily resulted in an increase in competition but also enabled heifers to gain well and to spend more time feeding each day. The remaining studies sought to quantify whether a preference for supplementary feed exists in limit-fed heifers and whether heifers will work, and to what extent, for this extra feed. The results indicated that heifers will consume similar amounts of supplementary long or short straw if provided to them alongside of a limit-fed TMR. The limit-fed heifers do, however, show a clear preference for long straw when offered the choice, suggesting that they find long straw to be more satisfactory for achieving rumen fill and/or meeting their behavioural foraging needs. Heifers were also found to work harder (push more weight), spend less time feeding and ruminating, and consume feed faster when provided a high-concentrate, limit-fed ration than when provided a high-forage, ad libitum-fed ration, suggesting that these animals are experiencing feelings of hunger and may not be physically or behaviourally satisfied. These findings indicate that there are clear behavioural differences between limit-fed and ad libitum-fed dairy heifers. Management factors, such as frequency of feed provision and feed bunk space, may be altered in such a way as to provide some benefit to the animals but are limited in their ability to normalize feeding behaviour and diurnal patterns. Provision of supplemental, long particle low-nutritive roughage (i.e. straw) aids much more in allowing limit-fed heifers to achieve satiety and is considered a desirable resource by the animals, as evidenced through their willingness to work for this supplemental feed.