Effect of initial time of forage supply on growth and rumen development in preweaning calves

To determine the effects of the initial timing of forage supply on growth, ruminal fermentation parameters and rumen development in preweaning calves, 18 7-day-old Holstein calves of 42 +/- 3 kg were randomly divided into three treatment groups. The dietary treatments were (1) milk and commercial starter diet (MS) control, (2) milk and starter diet supplemented with oat hay at 2 weeks (MSO2), and (3) milk and starter diet supplemented with oat hay at 6 weeks (MSO6). Starter feed and oat hay were provided ad libitum, and 2 L of milk was provided twice daily. Samples were collected at 64 days of age. Supplementing with hay increased the dry-matter intake; P < 0.05). The height, body length, heart girth and cannon bone circumference were similar among the three treatments (P > 0.05). The concentrations of serum glucose (P = 0.07) and -hydroxybutyric acid; P < 0.05) were lower in the MSO6 group than in the MS and MSO2 groups. Rumination time was longer, and time spent on non-nutritive oral behaviour (such as e.g. licking surfaces, tongue rolling, wood-shaving consumption) was lower for hay-supplemented calves than for the control (P < 0.05). Although ruminal pH of hay-supplemented calves was significantly higher than that of the control, total rumen fluid volatile fatty acid concentrations were not significantly different among treatments. Calves in the MSO2 group had a smaller ratio of empty weight to slaughter weight (P < 0.05) and a larger total digestive tract weight (P < 0.05); the empty gastrointestinal tract weights were similar among the three treatments, suggesting that MSO2 calf weight gain may have resulted from intestinal chyme accumulation. Compared with the control, hay-supplemented calves had reduced rumen papilla width and epithelium thickness (P < 0.05), and no discernable plaque formation. Hay supplementation in the diet of preweaning calves improved the overall dry-matter intake, improved rumination, reduced non-nutritive oral behaviours, improved rumen pH, and ensured healthy rumen development; furthermore, productivity and rumen development were better in calves supplemented with hay from the second week.