This study evaluated the effects of particle size (PS)and dietary level of alfalfa hay (AH) on rumen fermentationparameters, blood metabolites, eating behavior,and growth performance in dairy calves during transitionfrom liquid to solid feed. Sixty newborn dairycalves (41 ± 2.5, kg of body weight) were used in a 2× 2 factorial arrangement with the factors dietary AHlevel (medium, 12.5%, or high, 25%, on DM basis) andPS (fine = 1 mm or medium = 3 mm, as geometricmeans) of AH. Hence, the dietary treatments were (1)medium level of AH with fine PS (M-FPS), (2) mediumlevel of AH with medium PS (M-MPS), (3) high levelof AH with fine PS (H-FPS), and (4) high level of AHwith medium PS (H-MPS). Particle size of AH did notaffect total DMI (TDMI) during the preweaning period,although TDMI was greater for calves fed MPS than inthose fed FPS during the postweaning and overall periods.Calves fed MPS spent more time eating solid feedand ruminating and less time on nonnutritive oral behaviorscompared with FPS calves. The dietary level ofAH did not affect behavioral parameters. Average dailygain of calves was not affected by dietary treatmentbefore weaning. During the postweaning and overall periods,average daily gain was greater in calves fed MPSthan in those fed FPS at the 25% AH level, but thiseffect was absent with 12.5% AH. Furthermore, the rumenpH values on d 35 and 70 of the study were greaterfor MPS than for FPS, regardless of the dietary level ofAH. Effects of AH level, PS, and their interaction didnot affect blood glucose concentrations in developingcalves. These results indicate that feed intake, feedingbehavior, rumen fermentation parameters, and bloodβ-hydroxybutyrate concentration may be affected byrations differing in forage PS; thus, providing calveswith MPS can improve calf performance and reducetheir nonnutritive oral behaviors.
