1698
Effect of reducing dietary starch on intake, lactation performance, and ruminal parameters of dairy cows: A meta-analysis
A meta-analysis was conducted to determine the effect of feeding reduced-starch diets on intake, lactation performance, and ruminal parameters of dairy cows from a data set comprising 131 treatments means from 56 peer-reviewed trials from 1993 to 2014. Reduction in dietary starch was achieved by partially replacing cereal grains with non-forage fiber sources, forages, or sugars. Dependent variables were calculated as the difference between observations on the higher starch (% of DM) diet and observations on the reduced-starch diet(s) within trial. The higher starch concentration was used as a covariate within trial when P ≤ 0.15. Data were analyzed using Proc Mixed of SAS with treatment as a Fixed effect and trial as a Random effect. Dietary CP and NDF contents (% of DM) were (mean ± SD) 17.8 ± 2.3 and 31.8 ± 5.5%, respectively, across all trials. The higher starch diet and reduced-starch diets contained (mean ± SD) 28.9 ± 5.0% and 21.5 ± 4.8% starch, respectively, across all trials. Dry matter intake was 24.3 ± 2.6 kg/d across all trials, and decreased 0.1 kg/d per %-unit (DM basis) decrease in dietary starch content (P < 0.001). Milk yield (kg/d) decreased 0.2 kg/d per %-unit decrease in dietary starch content (P < 0.001). Fat- and energy-corrected milk followed a similar pattern (P < 0.001). Feeding reduced-starch diets decreased milk fat (7 g/d), protein (9 g/d), and lactose (12 g/d) yields per %-unit decrease in dietary starch (P < 0.001). Milk fat concentration was unaffected by reduced dietary starch (P = 0.60), whereas milk protein (0.005 %) and lactose (0.004 %) concentrations were decreased per %-unit decrease in dietary starch (P ≤ 0.01). There was a trend for lower feed conversion (kg milk / kg DMI) on reduced-starch diets (P = 0.06). Total ruminal VFA concentrations were decreased 0.4 mM per %-unit decrease in dietary starch (P = 0.03), however, ruminal acetate and butyrate (mol/100 mol) concentrations (P ≥ 0.41) were unaffected. There was a trend for a decrease of 0.09 mol/100 mol for ruminal propionate concentration on reduced-starch diets (P = 0.09), and rumen acetate: propionate ratio was increased (P = 0.03) on reduced-starch diets. Rumen ammonia (mg/dL) and pH (P ≥ 0.32) were unaffected by reducing dietary starch content. Dry matter intake, milk, and component yields were decreased for dairy cows when fed reduced-starch diets.
Keywords:
dairy cow, lactation, starch