Effects of replacing barley grain with corn grain on performance, rumen and blood parameters in dairy cows fed...

Different grain sources in the diet have shown varying effects on performance of dairy cows. Also, the variability in response to different starch sources is influenced by the type of forage used. This study investigates the combined effects of two forage (alfalfa hay vs. corn silage) and grain (barley vs. corn) sources on dry matter intake (DMI), feed efficiency, milk production and composition, apparent nutrient digestibility, blood metabolites, and ruminal metabolism of dairy cows. Eight second-parity early lactation Holstein cows (63 ± 5 d in milk) were used in a replicated 4 × 4 Latin square with a 2 × 2 factorial design. Diets were iso-energetic and iso-nitrogenous and were based on either corn (CG) or barley (BG) grains, and corn silage (CS) or alfalfa hay (AH). Diets with CS had more long (108 vs. 68 g/kg DM) and medium particles (369 vs. 331 g/kg DM), and thus, longer mean particle size (5.4 vs. 4.6 mm) compared to diets with AH. Cows fed BG had less DMI and lower actual and energy-corrected milk (ECM) yield than CG-fed cows. The total tract digestibility of starch (952 vs. 987 g/kg) and crude protein (CP) (687 vs. 743 g/kg) were lower in CG cows than cows fed BG. Additionally, cows fed CG tended to have lower ruminal propionate concentrations than those fed BG, suggesting differences in ruminal fermentability between BG and CG. Milk fat content (30.6 vs. 29.2 g/kg) and ECM production (42.6 vs. 40.7 kg/d) tended to be greater in cows fed diets containing AH rather than CS. Furthermore, despite similar nutrient digestibility and total volatile fatty acid production, AH-fed cows had a higher ruminal acetate-to-propionate ratio compared to those fed CS. Replacement of BG with CG improved performance by increasing DMI; however, the expected positive effects of substituting CS with AH in BG-based diets may be obscured by the impact of differences in forage particle size (PS). These results indicated that inclusion of CG might be an optimum choice for modulating ruminal condition and enhancing performance compared to BG during early lactation.