Effects of dietary moisture content and forage source on performance, nutrient digestibility, and rumen fermentation...

This study investigated the effects of TMR moisture content and forage source on feed intake, growth performance, nutrient digestibility, rumen fermentation, and blood metabolites in Holstein calves. Forty-eight calves (24 males, 24 females; initial BW: 39.8 ± 2.18 kg) were used in a 2 × 2 factorial arrangement of treatment with the factors being moisture content of TMR (10% or 50%) and forage source (alfalfa hay [AH] or wheat straw [WS]). Calves were randomly assigned to one of the 4 treatments, including (1) a TMR containing WS with 10% (WS10) or (2) 50% (WS50) moisture content, and TMR diet containing (3) AH with 10% (AH10) or (4) 50% (AH50) moisture content. Calves were weaned on d 65 and remained in the study until d 80. All calves had free access to drinking water and the diet all the time. The experimental diets contained 20.1% CP, and the geometric mean particle sizes for AH and WS were 7.43 and 9.33 mm, respectively. Each calf was fed 4 L/d of milk from d 3 to 15 and 7 L/d from d 16 to 58. Weaning was conducted gradually from d 59 to 65 by reducing milk allowance by 0.5 L per meal per day. Except for calves fed AH50, the distribution of particle size in feed refusals was substantially different from that of experimental diets. There was an interaction effect between dietary forage type and moisture content regarding the overall DMI, TMR intake, and ME intake. Calves fed AH50 had higher overall DMI (1.55 kg/d) and TMR intake (1.02 kg/d) than other groups. No significant interaction was detected between TMR moisture content and forage source concerning growth performance, ADG, feed efficiency, and ruminal fermentation parameters. Calves fed AH showed higher NDF digestibility compared with those offered WS. Regardless of forage type, adding moisture increased DM and OM digestibility, and ruminal ammonia-N. Total volatile fatty acid (TVFA) and molar proportion of acetate increased at postweaning, with significant increases for TVFA and a tendency for acetate overall. Blood metabolite profiles were generally unaffected by TMR moisture content, except for blood urea nitrogen concentration on d 80 and alanine aminotransferase concentration on d 60, both of which were higher in calves fed the TMR with 50% moisture. Calves fed the diet containing AH showed higher BHB than those fed WS on d 60. These results showed that adding moisture to the TMR containing AH can improve feed intake, energy consumption, and rumen fermentation in dairy calves.