Impact of Forage Inclusion Rate in a Dry Total Mixed Ration on the Behavior and Growth of Growing Dairy Cattle
The objective of this study was to determine the impact of forage inclusion rate in a dry TMR on behavior and growth of young dairy cattle. Ten Holstein bull calves (90.5 ± 2.4 d of age, weighing 136.0 ± 12.3 kg) were assigned to 1 of 2 treatments, a TMR containing (DM basis) either: 1) 85% concentrate and 15% chopped straw for 10 wk (wk 1-10); or 2) 85% concentrate and 15% chopped straw for 5 wk (wk 1-5), then 70% concentrate and 30% chopped straw for 5 wk (wk 6-10). After 10 wk, all animals were transitioned to a TMR containing (DM basis) 42.3% corn silage and 57.7% haylage for 2 wk (wk 11-12). DMI was recorded daily and BW was recorded 2x/wk. Feeding behavior was scored from digital video recordings 3 d/wk. Samples of TMR and orts were taken for particle separation 3 d/wk. Sorting was calculated as: actual intake of each particle fraction expressed as a % of its predicted intake. Data were averaged by week and analyzed in a repeated measures mixed effect model. DMI (5.5±3.3 kg/d), ADG (1.7±0.1 kg/d), feed efficiency (3.5±1.4 kg DM/kg gain), and eating time (151.9±8.8 min/d) were similar between treatments during wk 1-5. Calves on the 70% diet ate less DM (5.5 vs 7.4 kg/d; SE=0.4; P=0.006), grew slower (1.3 vs 1.6 kg/d; SE=0.08; P=0.02), sorted more against long forage particles (62.8 vs 103.8 %; SE=6.3; P=0.01), and spent a greater duration of time feeding (194.9 vs 102.6 min/d; SE=12.5; P=0.001) during wk 6-10. A treatment×hour interaction (P<0.001) in the analysis of feeding patterns indicated that this difference in feeding time occurred only during the first 8 h after feed delivery. Despite no differences in DMI (5.2 kg/d) or ADG (1.1 kg/d) in wk 11-12, there was a carryover effect on behavior. In wk 11-12, a treatment×hour interaction was detected (P=0.03); calves previously-fed the 70% diet continued to spend more time feeding immediately after feed delivery. Interestingly, during wk 11-12 those calves did not sort for or against long particles (103.6%), while the calves previously-fed the 85% ration sorted for (107.0%) those particles. These results show that feeding a dry TMR to weaned calves can promote high growth rates and efficiency. Further, altering forage content of such a TMR may have an impact on the expression and persistence of feeding behavior patterns.
Keywords: feeding behavior, forage concentration, straw