Extent of variability in nutrient composition within selected by-product feedstuffs

The nutrient composition of nine by-product feedstuffs (BPF) was determined. BPF were selected based on economic importance to the dairy industry, nutritional value, and availability. Three to nine different samples for each BPF were obtained throughout California. A total of 51 samples were collected: nine beet pulp (BP), eight rice bran (RB), seven almond hulls (AH), four citrus pulp (CT), five bakery waste (BW), eight wheat mill run (WMR), four brewers grains (BG), three distillery grains (DG), and three soy hulls (SH) samples. Chemical analyses measured included dry matter, ash, crude protein (CP), fiber fractions, macrominerals, and microminerals. The average chemical analyses determined for each BPF were compared with average values reported by the National Research Council (NRC). Considerable variation within a given BPF was observed in the present study. For example, BP was found to contain 18.81% acid detergent fiber (ADF) while the NRC reported an average composition of 25% ADF. The ether extract content of RB was found to be 20.48% compared with 15.1% reported by NRC. Much of this variability was related to how the commodity was handled during or after processing. In the second part of this study, two theoretical diets were formulated to calculate the effect of nutrient variability on diet composition. The BPF compositions of the two diets were 27% and 50% in Diet 1 and Diet 2, respectively. Specific by-products sources of BP, RB, DG, and SH were compared with the NRC diet composition used in the initial diet formulation. As the proportion of BPF in the diet was increased (Diet 2) nutrient composition of the diet was more variable with CP content ranging from 14.30 to 15.20%. Similar changes to those observed for CP were observed for the other chemical components. The effect of variability in by-product composition was more evident when evaluated on a concentrate mix basis. Variability in the chemical component of BPF influenced the composition of both the total diet and the concentrate mix, and the magnitude of effect depended upon the contribution of BPF to the total ration and the nutrient of interest.