Growth performance, nutrient digestibility, ruminal fermentation, and rumen development of calves during transition from liquid to solid feed: Effects of physical form of starter feed and forage provision

Fifty-two 4-d-old male Holstein dairy calves (41.3 ± 0.41 kg of BW) were used in a completely randomized design to evaluate the effects of physical form of starter feed on intake, nutrient digestibility, ruminal fermentation, structural growth, and rumen development. At d 4 of age, individually housed calves were randomly allocated (n = 13 per treatment) to 1 of 4 dietary treatments: 1) ground starter feed (Ground; mean particle size of 0.72 mm diameter), 2) textured starter feed including steam flaked corn and barley grains (Textured; mean particle size of 3.61 mm diameter), 3) pelleted starter feed (Pelleted; mean particle size of 4.53 mm diameter), and 4) ground starter feed with 10% chopped alfalfa hay (Ground + AH; mean particle size of 1.02 mm diameter). Calves received 4.0 L/d of pasteurized milk from d 1 to 46 of study and 1.0 L/d from d 47 to 49. Weaning occurred at the end of d 50 and the study lasted for 70 d. During the study (d 1-70), total dry matter (DM) and starter feed intakes, and final BW were greater for calves fed Ground + AH compared with those fed Ground and Pelleted starter feeds. Compared with Pelleted group, calves fed Textured starter feed had greater total DM and starter feed intakes, and final BW with no difference between Ground and Pelleted groups. Feeding Ground + AH starter feed increased average daily gain compared with other groups through the entire of trial. Similarly, feed efficiency was increased and tended to increase in Ground + AH as compared with the Ground and Pelleted groups as well as the Textured group, respectively. Fecal score and skeletal growth measurements were not affected by the dietary treatments. Calves fed Ground + AH starter feed spent more time rumination and had greater rumen pH at d 70 compared with calves fed other starter feeds with no difference in values at d 35. Ruminal NH3N concentration was not different between Ground + AH and Textured groups but was greater for both groups compared with Ground and Pelleted groups. At d 70, total volatile fatty acids concentration and the molar proportion of propionate were greater for calves fed Pelleted- vs. Ground + AH starter feed with no difference across other groups. Empty viscera weights including reticulorumen, omasum, and abomasum were not different between Ground + AH and Textured groups; but Ground + AH starter feed increased viscera weights as compared with the Ground and Pelleted starter feeds which was substantiated with both greater rumen wall thickness and muscularization. Overall, Ground + AH starter feed was able to maintain rumen pH at least by induction of greater time spending rumination and promoted growth performance of calves and also influenced morphometric attributes of the rumen wall which substantiated the effect of alfalfa hay supplementation on macroscopic and microscopic appearances by decreasing plaque formation and increasing muscularization, respectively. These benefits, however, were small when Textured starter feed was provided.