EXTENT OF VARIABILITY IN NUTRIENT COMPOSITION WITHIN SELECTED BY-PRODUCT FEEDSTUFFS

The nutrient composition of nine by-product feedstuffs (BPF) was deter mined. BPF were selected based on economic importance to the dairy ind ustry, nutritional value, and availability. Three to nine different sa mples for each BPF were obtained throughout California. A total of 51 samples were collected: nine beet pulp (BP), eight rice bran (RE), sev en almond hulls (AH), four citrus pulp (CT), five bakery waste (BW), e ight wheat mill run (WMR), four brewers grains (BG), three distillery grains (DG), and three soy hulls (SH) samples. Chemical analyses measu red included dry matter, ash, crude protein (CP), fiber fractions, mac rominerals, and microminerals. The average chemical analyses determine d for each BPF were compared with average values reported by the Natio nal Research Council (NRC). Considerable variation within a given BPF was observed in the present study. For example, BP was found to contai n 18.81% acid detergent fiber (ADF) while the NRC reported an average composition of 25% ADF. The ether extract content of RE was found to b e 20.48% compared with 15.1% reported by NRC. Much of this variability was related to how the commodity was handled during or after processi ng. In the second part of this study, two theoretical diets were formu lated to calculate the effect of nutrient variability on diet composit ion. The BPF compositions of the two diets were 27% and 50% in Diet 1 and Diet 2, respectively. Specific byproducts sources of BP, RE, DG, a nd 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 con tent ranging from 14.30 to 15.20%. Similar changes to those observed f or CP were observed for the other chemical components. The effect of v ariability in by-product composition was more evident when evaluated o n a concentrate mix basis. Variability in the chemical component of BP F influenced the composition of both the total diet and the concentrat e mix, and the magnitude of effect depended upon the contribution of B PF to the total ration and the nutrient of interest.