Effect of forage source included in total mixed ration on intake, sorting and feeding behavior of growing heifers fed high-concentrate diets

The objective of this experiment was to compare the effects of using 2 different forage sources on intake and sorting and feeding behavior in growing heifers fed a high-concentrate diet offered as a total mixed ration (TMR). Eight Simmental heifers (initial BW of 148.1 +/- 4.83 kg) were used in a crossover design experiment. Treatment diets were a TMR with either barley straw (BS) or alfalfa hay (AH) as forage source. Diets were offered on an ad libitum basis, with a forage to concentrate ratio of 8 to 92. The experiment was performed in two 28-d periods, with 3 wk of diet adaptation and 1 wk of sampling in each period. Heifers were weighed before feeding on 2 consecutive days at the beginning and the end of the experiment, and in the sampling week. Feed and refusal samples were collected daily in the sampling week for DM determination and chemical analysis. Particle size separation was performed using the 3-screen Penn State Particle Separator. Dry matter digestibility was estimated using acid-insoluble ash as internal marker. Feeding behavior was recorded using an automated feeding system. Sorting behavior was measured with the intake of different particle size. Dry matter intake was greater (P < 0.05) in heifers fed BS (6.7 kg/d) than AH (5.8 kg/d) when these animals faced TMR for first time in period 1, but DMI did not differ between diets in period 2 when they were accustomed to the method of feeding. Apparent DM digestibility did not differ between diets (62.7 and 64.3% for BS and AH, respectively). Heifers fed BS sorted in both periods against long particle size (P < 0.01) and against medium particle size in period 2 (P < 0.01), a behavior that did not appear in heifers fed AH. Heifers sorted for short particle size in both diets in period 1, this behavior being maintained in period 2 for heifers fed BS, while it disappeared in heifers fed AH. This sorting behavior preferentially shown in heifers fed BS resulted in a tendency (P = 0.06) for greater length of each meal and a longer feeding time (P = 0.02). In conclusion, at 8% of incorporation, forage source affected intake in only 1 of the 2 experimental periods. Heifers fed BS showed a sorting behavior with preferential consumption for concentrate in the TMR, feeding time being greater in BS than in AH. In contrast, heifers fed AH sorted for short particle size when faced for the first time with a new method of feeding, this sorting behavior disappearing once heifers had got familiar with it.