Physically effective fiber alters feed intake and feeding behavior in growing dairy heifers

Abstract

The physicochemical characteristics of feeds offered to ruminants influence nutrient availability for metabolism and directly affect animal performance. In growing dairy heifers, this may compromise the allometric development of body tissues and the mammary gland. Our objective was to evaluate the effect of physically effective fiber content in the diet on feed intake, water consumption, and feeding behavior of feedlot dairy heifers. Twelve crossbred heifers (Holstein X Gir), with an average body weight of 131 ± 55 kg and 12 ± 2 months of age, were assigned to four groups in a 4 x 4 triple Latin square design. Treatments consisted of four total mixed rations (TMR) containing 517, 537, 557, and 577 g/kg of neutral detergent fiber (NDF) on a dry matter (DM) basis. Feed refusal was collected, water intake was estimated, and feeding behavior was recorded through direct observation over four 72- hours periods per animal (totaling 288 hours). A negative linear effect of increasing NDF content was observed on DM intake (P = 0.01), water intake (P = 0.03), and body weight (P = 0.008). feeding time increased linearly with the highest NDF level (average: 7 h 25 min/day), while rumination and idling times showed no significant differences (P > 0.05). In summary, higher fiber levels in the diet of feedlot dairy heifers limit the physiological digestive, promoting changes in feeding behavior with greater feed selection at the bunk.