Effects of the straw inclusion in the diet of dairy calves on growth performance, rumen fermentation, and blood metabolites during pre- and post-weaning periods.

The aim of this study was to investigate the effects of the inclusion of chopped straw into a diet with pelleted starter feed on starter intake, growth performance, fermentation and blood metabolites of dairy calves during the pre- and post-weaning periods. Forty-four Holstein-Friesian female dairy calves were randomly assigned to four treatments: control (CON, starter without straw; n = 11), low straw (LS, starter feed containing 10% dry matter basis straw; n = 11), medium straw (MS, starter feed containing 15% dry matter basis straw; n = 11) and high straw (HS, starter feed containing 20% dry matter basis straw; n = 11). Starter intake and total dry matter intake were recorded daily, and bodyweight weekly until 84 days of age. The highest starter intake and total dry matter intake were noted in the LS and MS treatments during the post-weaning, and overall experiment periods. Also, the average daily gain was greater during the pre-weaning period for LS and MS than HS. Increasing chopped straw content in the starter feeds from 0% to 15% increased ruminal pH, especially at day 28, and molar concentration of acetate, and decreased concentrations of total volatile fatty acids and propionate throughout the trial. Concentrations of butyrate in the rumen were lower at day 28, and higher at day 56 and 84 in straw-supplemented calves compared to the CON treatment. Increasing chopped straw content in the starters feeds from 0% to 15% increased the total counts of bacteria and protozoa, but then this counts decreased with the content of 20% chopped straw. In conclusion, the inclusion of chopped triticale straw from 10% to 15% in the diet with pelleted starter feed can improve performance, and rumen fermentation in calves; however, increasing the dietary inclusion of straw to 20% can negatively affect growth performance.