PSVIII-A-7 - Effects of new forage barley and oat varieties on silage fermentation characteristics, and feed intake, milk production and composition, and N balance in dairy cows

Abstract: Forages are the foundation of dairy cow diets and typically comprise 50% of the dietary dry matter and ≥40% of the total NE_L intake. New forage barley (CDC Renegade; designated RENE) and forage oat (CDC Arborg; ARBO) varieties are available for feeding dairy cows in western Canada. The objectives were to determine the ensiling characteristics of RENE and ARBO and to compare the effects of feeding them as the major forage source on feed intake, milk yield and composition, ruminal pH, and nitrogen (N) balance in dairy cows. Eight multiparous Holstein cows (82 ± 12 days-in-milk at the beginning of the study) were used in a 4 × 4 Latin square design study with 14 d of dietary adaptation and 7 d of data and sample collection. Cows in one Latin square were ruminally-cannulated to determine dietary effects on ruminal pH and N balance. The four diets tested contained RENE, ARBO, Conlon (CONL), and Rosser (ROSS) silages as the major source of forage, with ROSS and CONL being included for comparison as they are commonly-used barley varieties in western Canada. Silage fermentation characteristics were largely similar for the four forages, except for total short-chain fatty acid concentrations which tended (P = 0.08) to be greater for RENE and ROSS when compared to CONL and ARBO. Silage starch contents were greater (P < 0.01) for CONL and ROSS when compared to RENE and ARBO, which were similar. Silage aNDFom contents were greater (P < 0.01) for RENE and ARBO when compared to CONL and ROSS, which were similar. Dry matter intake (mean = 34.3 kg/d) and milk yield (mean = 48.6 kg/d) were unaffected by treatment (P ≥ 0.42). Milk fat content was greater (P = 0.03) for cows fed RENE compared to those fed CONL, with that of cows fed ROSS and ARBO being intermediate and not different to RENE and CONL. Milk fat yield was greater (P = 0.02) for cows fed RENE compared to those fed ROSS, with that of cows fed CONL and ARBO being intermediate and not different to RENE and ROSS. Intake of N, urinary and fecal excretion of N, total N excretion, milk N, and apparent N balance were unaffected by diet (P ≥ 0.21). Mean ruminal pH was greater (P = 0.02) in cows fed ARBO compared to those fed ROSS, with that of cows fed CONL and RENE being intermediate and not different to CONL and RENE. Our results show that the new forage varieties, RENE and ARBO, can support similar levels of milk yield compared to forage varieties such as CONL and ROSS.