Abstract
The objectives of this study were to examine the behavioral effects of providing limit-fed dairy heifers an increased amount of feed bunk space compared with recommended feed bunk allowance, and to determine if the effects of provision of extra bunk space would be comparable to those seen when limit-fed heifers are provided a low-nutritive feedstuff. Twelve Holstein dairy heifers (381.1±44.8 d of age, 417.3±47.9kg), divided into groups of 4, were exposed to each of 3 treatments using a 3×3 Latin square design with 7-d periods. The treatments were (1) 0.68m of feed bunk space/heifer (TMR-0.68), (2) 0.34m of feed bunk space/heifer (TMR-0.34), and (3) 0.34m of feed bunk space/heifer with an additional 0.34m of feed bunk space available for free-choice straw (TMR-S). The total mixed ration was fed once daily at a restricted level (1.83% of body weight) and contained (dry matter basis) 19.9% alfalfa/grass haylage, 20.1% corn silage, 49.6% high-moisture corn, and 10.4% protein supplement. Group dry matter intake (DMI) was recorded daily. Behavior at the feed bunk was recorded for the last 4 d of each treatment period. Due to the provision of straw, DMI was highest on the TMR-S treatment compared with the other treatments (9.4 vs. 7.8 kg/d). Heifers spent the most time feeding when on the TMR-S treatment (147.7 min/d), with no difference in feeding time between the limit-fed TMR treatments (64.5 min/d). Within the TMR-S treatment, feeding time on the straw was 76.9 min/d; thus, the rate of consumption of only the TMR was similar across all treatments. Unrewarded time at the feed bunk (when no feed was present) did not differ between treatments. Heifers did not differ in competitive behavior when on the limit-fed TMR treatments (13.1 displacements/heifer per day). However, while on the TMR-S treatment, heifers displaced each other more frequently (23.8 displacements/heifer per day) than while on the other 2 treatments. Overall, results suggest that neither increased feed bunk space nor provision of straw will reduce competition for, or slow consumption rates of, a limit-fed TMR. The provision of straw alongside a limit-fed TMR did increase DMI, which would contribute to further rumen fill, and allowed heifers to increase their time spent feeding throughout the day.
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