PSVIII-8 The impact of foliar fungicide application on barley silage fermentation characteristics and performance of lactating dairy cows

Forages are an important component in dairy cow diets and barley silage is the primary forage source in western Canada and parts of the USA. Foliar fungal diseases can infect barley, thereby causing leaf damage and a loss of yield and quality. The objectives were to determine the effects of foliar fungicide application on two barley forage varieties, one resistant (CDC Fraser) and the other susceptible (Claymore) to foliar fungal disease, on silage ensiling characteristics and feed intake, milk production and composition, ruminal pH, and nitrogen (N) balance in dairy cows. Multiparous Holstein cows [n = 12; mean (ays in milk (DIM) = 40 ± 17; mean body weight (BW) = 720 ± 26 kg] at the start of the experiment) were used in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of dietary treatments. Experimental periods were 25 d, with 18 d of dietary adaptation and 7 d of sample and data collection. Test diets were: 1) fungicide-treated Claymore silage (CF); 2) untreated Claymore silage (CNF); 3) fungicide-treated CDC Fraser silage (FF); and 4) untreated CDC Fraser silage (FNF) as the major source of forage. Forage yields were 1.86 (FNF), 1.46 (CNF), 1.17 (FF), and 1.35 (CF) t dry matter (DM)/ha, likely reflective of the low rainfall during the growing season. Experimental silages were similar in crude protein (mean = 14.0%; DM basis), ammonia (mean = 1.95%), and total volatile fatty acid (mean = 9.25%) concentrations. CDC Fraser silage had greater lactic acid concentration (P < 0.001) but decreased pH (P = 0.01) and acetic acid concentration (P < 0.01) than Claymore silage. Silage aNDF contents (DM %) were similar in FF and FNF, but greater in CNF than CF (interaction; P < 0.05). Without fungicide application, barley variety had no effect on silage starch content (DM %), whereas with fungicide application, Claymore had a greater silage starch content than CDC Fraser (interaction; P < 0.05). Dry matter intake, milk yield, and milk composition were unaffected by diet (P > 0.05). Total tract nutrient digestibility was unaffected by diet (P > 0.05). Intake of N, and urinary and fecal N excretion, total N excretion, milk N, and apparent N balance (expressed as g/d or % of N intake) were unaffected by diet (P > 0.05). Ruminal short-chain fatty acid (SCFA) concentrations and pH were unaffected by diet (P > 0.05); however, total SCFA concentration was similar in CF and CNF but was greater in FNF than FF (interaction; P < 0.05). Valerate concent