Abstracts Category : Other

Response of Dairy Cows to Dietary Starch Concentrations: Performance, Nutrient Digestion, and Gas Emissions

by Juan Isidro Sanchez-Duarte

Three studies and a meta-analysis were conducted to determine the performance, nutrient digestion, and gas emissions of dairy cows fed diets with different starch concentrations (19 to 27% of DM). Study 1 evaluated the effects of reducing corn grain starch with non-forage fiber sources (NFFS, soybean hulls and beet pulp) in diets of soybean meal (SBM) or canola meal (CM). In study 1, reducing starch from 27 to 20% with soybean hulls and beet pulp had a negative effect on dry matter intake (DMI), milk yield and energy-corrected milk (ECM), regardless of the crude protein (CP) source. Those effects were explained by a low dry matter (DM) and organic matter (OM) digestibility in cows fed 19% starch. Study 2 explored through a meta-analysis the effects of reducing cereal grain starch with NFFS on the performance, nutrient digestion, and rumen fermentation of dairy cows. The meta-analysis indicated that when dietary starch intake increased from 1 to 9 kg/d, DMI responded quadratically, but milk yield, milk protein concentration, and milk lactose yield increased positively. Milk fat concentration however decreased linearly as starch intake increased in the cows. As dietary starch intake increased in the cows, the concentration of total volatile fatty acids (VFA) and acetate decreased linearly, but propionate, acetate to propionate ratio, isobutyrate, isovalerate, and valerate increased linearly. Increasing starch intake affected quadratically the DM digestibility, linearly CP digestibility, and negatively neutral detergent fiber (NDF) digestibility. Therefore, reducing cereal grains starch with NFFS has a negative effect on dairy cows performance. Studies 3 and 4 evaluated the effects of diets with conventional (CONV) and Brown midrib (BMR) corn silage with two starch concentrations (19 vs. 25% of DM) on performance and gas emissions, respectively. In study 3, cows fed BMR diets tended to have higher DMI than cows fed CONV corn silage diets. Cows fed BMR-25% had the greatest milk yield and ECM, but cows in BMR-19% produced the same amount of milk and ECM than cows with CONV corn silage in any starch concentration. These effects were explained by the increased digestibility of DM, OM, and CP in response to diets with 25% starch and the increased DMI with BMR corn silage. In study 4, diets did not affect DMI, milk yield, ECM, milk composition, nutrient digestion, and emissions of CH4, NH3, and CO2. However, cows fed BMR corn silage and 25% starch produced less CH4 and CO2 per kg of DM, OM, and starch digested than cows in CONV corn silage with any starch concentration, but cows fed 25% starch produced more NH3 and CO2 per kg of NDF digested. Overall, reducing starch with increasing NFFS has a negative effect on dairy cow performance and nutrient digestion, but including BMR corn silage improved those effects by increasing nutrient digestion. The combination of BMR corn silage and high starch diets have the potential to reduce gas emissions per kilogram of nutrient digested in lactating dairy cows. Advisors/Committee Members: Alvaro Garcia.