Effects of substituting grain with forage or nonforage fiber source on growth performance, rumen fermentation, and chewing activity of dairy calves

• Adding low level of beet pulp (BP) or alfalfa hay (AH) to calf starter was studied.
• Feeding AH increased ruminal pH and ruminating time but failed to improve performance.
• Supplementing starter with BP at 100 g/kg enhanced preweaning intake and daily gain.
• Increasing BP to 200 g/kg had no negative effect on performance.

The optimum level of fiber source supplementation in calf starter is beneficial for promoting rumen development and growth performance of young calves. This study evaluated the effects of replacing grain sources (mainly barley) with forage [alfalfa hay (AH)] or nonforage [beet pulp (BP)] fiber source on rumen parameters [pH, and short chain fatty acid (SCFA)], blood metabolites [glucose, and β-hydroxybutyrate (BHBA)], chewing activity (ruminating, eating, and total chewing), intake, and growth in pre- and postweaning dairy calves. Fifty-two male Holstein calves with 4 d of age and 41.7 ± 3.3 kg body weight (BW) were randomly assigned to 4 treatments. The 4 starters were formulated with similar crude protein [CP, 190 g/kg dry matter (DM)] and metabolizable energy ‎value [(ME), 13.3 MJ/kg DM], but different in fiber sources and levels. Treatments were a basal starter with no fiber source [CON, 141 g neutral detergent fiber (NDF)/kg DM], or with 100 g AH/kg DM (AH-100, 171 g NDF/kg DM), 100 g BP/kg DM (BP-100, 171 g NDF/kg DM)‎, and 200 g BP/kg DM (BP-200, 199 g NDF/kg DM). All the calves were offered 5 L of milk/d from d 3–45, and 2.5 L/d from d 46 until weaning on d 50. The study finished when calves were 70 d old. Compared with CON calves, calves in the AH-100 treatment tended to consume less starter feed, and exhibited significantly lower average daily gains (ADG), BW, and some structural growth measurements in overall period, calves in the BP-100 treatment tended to consume more starter, and had greater ADG, BW, and blood glucose in the pre-weaning period. Growth and feed intake were not affected during the postweaning period or with increasing the level of BP in the diet. Dietary treatment did not alter significantly total SCFA concentration or SCFA proportions on d 35. However, rumen molar proportion of acetate increased and that of butyrate decreased in calves fed either of fiber sources on d 70. Moreover, molar proportion of propionate and acetate to propionate ratio decreased in calves fed either the BP-100 or the BP-200 on d 70. Rumen pH, and eating and ruminating time were greater for calves receiving the AH-100 diet than those receiving the CON diet. Feeding either level of BP had no effect on chewing activity but tended to increase rumen pH during the preweaning period. No significant effect of AH supplementation was observed on ‎BHBA although a decreasing trend was observed by supplementation of BP at the post-weaning period. In summary, chewing time, and rumen acetate and pH increased, but daily gain decreased as a result of supplementing 100 g AH/kg DM in the starter feed. Added NDF from BP source did not affect chewing activity but tended to increase preweaning rumen pH and growth performance (100 g BP/kg DM), and had no effect on theses parameters in the postweaning period.