Benefits of barley straw as a forage for dairy calves before and after weaning.

The aim of this study was to assess the potential consequences on calf intake, performance, behavior, ruminal microbiome, and ruminal epithelium development of combining the inclusion of chopped barley straw and alfalfa hay during the pre- and post-weaning periods keeping concentrate to forage ratio constant among dietary treatments. Forty-five Holstein calves (44 ± 5.7 kg of BW and 3 ± 1.5 d of age) individually penned were blocked by body weight (BW) and randomly assigned to a common pellet concentrate fed ad libitum along with one of following forage feeding strategies: barley straw before and after weaning (SS), barley straw before and alfalfa hay after weaning (SA), or alfalfa hay before and after weaning (AA). All calves received the same milk replacer regimen. Forage was supplied in a separated bucket at the rate of 7.5% (preweaning) and 15% (postweaning) of total solid feed intake of the previous day. Feed intake and BW were recorded daily and weekly, respectively. Rumen samples were obtained via a stomach tube at 53, 66, and 87 d and were composite in 3 samples of 5 animals each for subsequent rumen microbiome analysis. A rumen epithelium sample was taken by endoscopy at 90 d to assess gene expression of occludin, claudin-4, NHE1, NHE3, MCT1, MCT4, IL6, and TGFß1. Data were analyzed with a mixed-effects model accounting for the fixed-effects of block, forage, week of study, and their interaction, and calf as a random effect. The type of forage fed did not affect concentrate feed, forage, or total DM intake before weaning. However, SA and AA calves consumed less concentrate feed and SA calves grew at a lower rate after weaning than SS calves. Expression of the gene coding for MCT1 in the rumen epithelium was greatest in SS among treatments. Rumen microbiome did not differ among treatments, while the relative abundance of Acidaminococcus and Selenomas genera increased, while Alloprevotella, Bifidobaterium, Olsenella and Succiclasticum genera decreased with age. In conclusion, feeding barley straw before and after weaning was more effective than feeding alfalfa hay in promoting concentrate feed intake after weaning and fostering an increase in the expression of MCT1 in the rumen epithelium.