Date Published: March 7, 2018
Publisher: Public Library of Science
Author(s): Jennifer M. C. Van Os, Erin M. Mintline, Trevor J. DeVries, Cassandra B. Tucker, Juan J. Loor.
Domestic cattle (Bos taurus taurus) are adapted to digest high-roughage diets, but in confinement they are commonly fed low-roughage, high-energy diets. This practice may leave cattle with an unfulfilled need to consume forage. A way to quantify motivation is to require animals to work to access a resource. Using this method, we evaluated cattle motivation to obtain forage when fed high- or low-roughage diets during and 30 d before the study. Individual heifers were fed Sudan grass (Sorghum × drummondii) hay (high roughage, n = 6) or a diet with 12% forage (as fed, low roughage, n = 6) in an open feed trough. In a second trough, 200 g/d of Sudan grass hay were fed behind a push gate, to which additional weight was added daily until heifers no longer pushed. We predicted heifers would push heavier weights, show a shorter latency, and spend more time pushing the gate when fed a low- vs. high-roughage diet. Indeed, heifers fed a low-roughage diet pushed the gate immediately after hay delivery (1.7 min) and much sooner than those fed a high-roughage diet (75.7 min). On the day before they no longer pushed the gate, latency for heifers in the low-roughage treatment remained only 3.2 min after hay delivery. The suddenness with which they ceased pushing the next day suggests they were unable to move heavier weights to express their motivation. This may explain why maximum weight pushed and time spent pushing the gate did not differ between treatments. The gate pushing by heifers with unrestricted hay access is the first demonstration by cattle of contrafreeloading: performing work to obtain a resource that is simultaneously available for free. In conclusion, consuming forage is important to cattle and is affected by both their primary diet and an internal motivation to work to obtain feed.
Domestic cattle (Bos taurus taurus) are ruminants adapted to digest diets high in roughage. The repertoire of natural feeding behavior in cattle includes appetitive components related to foraging (searching for and investigating feed) and consummatory aspects such as chewing and ruminating. In extensive rangeland or pasture settings, cattle spend a large portion of the day grazing (7–13 h/d) and ruminating (5–10 h/d) . In contrast, in some intensive production systems (i.e., pre-weaned dairy heifers, veal calves, and feedlots), cattle are commonly fed low-roughage, high-energy diets based on grain concentrates. For example, 48% of US feedlot cattle in the finishing phase are fed diets with >75% concentrate on a dry-matter (DM) basis . Such diets, in theory, allow cattle to efficiently meet their nutrient requirements, but may have adverse effects on other aspects of physiology and behavior.
This study provides evidence that confined cattle are motivated to obtain supplemental forage, particularly when fed a high-energy diet with only 12% forage (as fed). Immediately after feed delivery, individually housed cattle fed a low-roughage diet pushed the gate to obtain hay before consuming their primary diet the majority of the time, and they worked to obtain forage much sooner than those fed a high-roughage diet. Contrary to our predictions for the other measures of motivation, however, heifers in both treatments pushed similar maximum weights and showed comparable gate use and hay consumption from this trough. The considerable gate use by heifers in the high-roughage treatment is the first demonstration by cattle of contrafreeloading, wherein animals expend effort to obtain a resource even when it is otherwise freely available .
Individually indoor-housed cattle are motivated to obtain supplemental forage, particularly when fed a low-roughage, high-concentrate diet. Whereas cattle fed a high-roughage diet did not use the gate until over an hour after feed delivery, those fed a low-roughage diet worked to obtain hay immediately after its delivery and did so before consuming any of their primary diet the majority of the time. Regardless of their primary diet, cattle pushed nearly half of their bodyweight to access a small portion of hay. The use of the gate by heifers with free access to hay is the first demonstration of contrafreeloading in cattle. In conclusion, consuming roughage is important to domestic cattle, and this desire is affected by both their primary diet and an internal motivation to work to obtain feed.