Effects of Dietary Neutral Detergent Fiber on Intakes of Dry Matter and Net Energy by Dairy and Beef Cattle: Analysis of Published Data

Meta-analysis was applied to evaluate the relationships between dietary NDF and voluntary intakes of DM and net energy by cattle from 2 databases. The databases were configured from literature publications for dairy (18 experiments) and beef cattle (11 experiments) in which dietary NDF concentration varied as a result of changes in proportions of forage and concentrate, and NDF was not contributed from by-product feeds. In dairy cattle, the relationship with dietary NDF (% of DM) was studied for DMI (% of animal BW and kg/d per animal), NEl intake above maintenance (kcal/kg of BW0.75), NEl intake above maintenance relative to DMI (Mcal/kg of DMI), and milk fat content (%), whereas for beef cattle, relationships were evaluated with DMI (% of animal BW and kg/d per animal), NEg intake (kcal/kg of BW0.75), and NEg intake relative to DMI (Mcal/ kg of DMI). Variables were weighted for different pooled SE of treatment DMI (or milk fat) means across trials. Initial models were fit to account for random slope and intercept terms to yield trial-adjusted data, and trial-adjusted dependent variables were regressed on dietary NDF. In dairy cattle, for dietary NDF concentrations ranging from 22.5 to 45.8%, DMI (% of BW and kg DM/d per animal) decreased (r2 = 0.595 and 0.672, respectively) with increasing NDF. The NEl intake above maintenance decreased (r2 = 0.815) more markedly than DMI; however, milk fat increased linearly (r2 = 0.617) with increasing NDF. In beef cattle, dietary NDF (range = 7.5 to 35.3%) was positively related to DMI (r2 = 0.954 for % of BW and 0.965 for kg DM/d per animal) and NEg intake (kcal/kg of BW0.75, r2 = 0.859), but differences in NDF did not account for variation in NEg intake per unit of DMI (r2 = 0.001). Total NDF concentration of diets should be an effectivebasis of exchanging fiber sources in feedlot diets to achieve equal DMI, and small increases in dietary NDF in feedlot diets might increase NEg intake without major changes in feed efficiency. Conversely, with dairy cattle, total DM and NEL intakes decreased with increasing dietary NDF. Increased NDF resulted in greater percentages of milk fat, which would need to be balanced with potentially lower milk production associated with decreased NEl intake.