Validation of animal and laboratory methods in digestibility research
Brian J. Kerr
Experimentation in research explores new ideas and helps gain new knowledge which includes treatment observations, laboratory analyses, statistical analyses, and interpretation of the data. The use of appropriate methodology plays an important role in high quality research as it helps yield accurate, reliable and repeatable data. The same components can be analyzed by multiple methods due to the accumulation of approved methods. In this thesis two methodologies have evaluated to make suggestions based on time, budget, and resource availability. Currently there are several accepted methods for the drying of animal excreta; however some methods have been reported to negatively impact the nutrient composition more than other methods. Therefore, one objective of this thesis was to evaluate nutrient and energy losses due to drying method on feces, urine, and poultry excreta. Twelve individually penned growing pigs were fed one of three diets and 16 pens of 10 growing broilers were fed one of four diets that differed in nutrient composition. Feces, urine, and excreta that varied in nutrient composition were collected after 7 d of diet adaptation. Samples were dried using one of four methods: UD-undried, FD-freeze dried, OD55-oven dried at 55yC for 48 h, or OD100-oven dried at 100yC for 48 h, after which DM, GE, N, C, and S were determined. There were no differences among drying methods except FD excreta had a greater S concentration than OD (P < 0.10). Covariates are auxiliary variables used in the statistical covariance analysis to limit variation for accurately calculating the least squares means.
Digestibility research has shown limited use of covariates because the benefits are unknown. Therefore, the second objective of this thesis was to determine an appropriate covariate for digestibility experiments to limit variation that may affect treatment observations. Seventy two barrows were randomly assigned to one of three dietary treatments for Phase-1 (P1; 14 d). On d-14, pigs were randomly reassigned to one of the three diets within initial dietary treatment for Phase-2 (P2; 14 d). Fecal and blood samples were collected on d-10 or d-14 of P1 and d-14 P2. Fecal samples were dried and analyzed for C, ether extract, GE, N, NDF, P, and S. Plasma samples were analyzed for plasma urea nitrogen and triglycerides. When P1 criterion was used as a covariate for P2 data, it was significant for C, ether extract, GE, NDF, N, S, and plasma urea nitrogen (P < 0.10). In conclusion, the data indicate that if initial diets are known, one must balance subsequent treatments for the initial diet because of potential diet by diet interactions. If the initial diets are not known, then an initial criterion would be effective in reducing the variation associated with subsequently obtain data, and should be considered as a covariate in future nutrition research. Therefore, the methods utilized and processed are important for yielding accurate and precise data.