The effects of free-choice provision of wheat straw with different particle size on ruminal fermentation, blood metabolites and nutrients digestibility of Holstein dairy calves

This study was performed to assess the effects of offering wheat straw as free choice with different particle sizes on ruminal fermentation, blood metabolites and nutrients digestibility of Holstein dairy calves. Individually housed calves (n = 40, BW = 43.8 ±3.2 kg) were used in a completely randomized design and divided to four different treatments consisting of: 1) starter feed without wheat straw supplementation (control; CON), 2) starter feed + wheat straw with 1mm geometrical mean particle length (GMPL, Fine), 3) starter feed + wheat straw with 4mm GMPL (Medium), and 4) starter feed + wheat straw with 7mm GMPL (Long). Calves entered the trial on d 15, weaned on d 56 and the study ended on d 90 of age. After morning feeding, the ruminal pH were increased by offering forage only at 8 h on d 35 and 4 and 8 h on d 90 (P = 0.05). The total short chain fatty acids concentration (SCFAs), molar proportion of acetate and propionate were similar across treatments, however, the molar proportion of butyrate increased (P = 0.04) in forage supplemented calves compared with CON calves. Regardless of forage particle size, dry matter and crude protein digestibilities were increased in forage supplemented calves compared with CON calves (P = 0.05). Moreover, no differences were found for different geometrical mean particle length of WS. Overall, free-choice provision of wheat straw enhanced ruminal pH, apparent nutrient digestibility, and rumen development indicators (BHBA) in Holstein dairy calves.