A meta-analysis of the potential effect of forage provisionon growth performance and rumen fermentationof dairy calves was conducted using published datafrom the literature (1998–2016). Meta-regression wasused to evaluate the effects of different forage levels,forage sources, forage offering methods, physical formsof starter, and grain sources on the heterogeneity ofthe results. We considered 27 studies that reported theeffects of forage provision to dairy calves. Estimatedeffect sizes of forage were calculated on starter feedintake, average daily gain (ADG), feed efficiency (FE),body weight (BW), and rumen fermentation parameters.Intake of starter feed, ADG, BW, ruminal pH,and rumen molar proportion of acetate increased whensupplementing forage but FE decreased. Heterogeneity(the amount of variation among studies) was significantfor intake of starter feed, ADG, FE, final BW, andrumen fermentation parameters. Improving overallstarter feed intake was greater in calves offered alfalfahay compared with those offered other types of forages.During the milk feeding and overall periods, improvingADG was greater for calves fed a high level of forage(>10% in dry matter) compared with those fed a lowlevel of forage (≤10% in dry matter) diets. The advantagesreported in weight gain at a high level of foragecould be due to increased gut fill. Improving overallADG was lower for calves offered forages with texturedstarter feed compared with ground starter feed. Themeta-regression analysis revealed that changes associatedwith forage provision affect FE differently for variousforage sources and forage offering methods duringthe milk-feeding period. Forage sources also modulatedthe effect of feeding forage on ruminal pH during themilk-feeding period. In conclusion, forage has the potentialto affect starter feed intake and performance ofdairy calves, but its effects depend on source, level, andmethod of forage feeding and physical form of starterfeed independently of grain sources inc
