Estimation of the Productive Energy Content of Corn Germ Meal Based on a Growth Assay in Wean-to-Finish Pigs.

Two wean-to-finish growth studies were carried out to determine the productive energy (PE) of CGM by correcting ME estimates for caloric efficiency relative to a control (reference diet). Both studies used a RCBD and evaluated CGM inclusion level (0, 12.5, and 25% in Study 1; 0, 10, 20, 30, and 40% in Study 2). The CGM was from a single source; the chemical composition averaged across both studies was: DM, 88.4%; CP, 23.8%; Crude Fat, 2.4%; NDF, 37.1%; ADF, 11.6%; Ash, 2.7. A total of 1,020 (10 replicates) and 2,380 (14 replicates) barrows and gilts were used in Study 1 and 2, respectively, housed in groups of 34 (Study 1 single-sex; Study 2 mixed-sex). Start and end BW were from 6.6 ± 0.54 and 6.4 ± 0.56 to 127.1 ± 1.71 and 133.3 ± 1.62 kg, for Study 1 and 2, respectively. An 8-phase dietary program was used with diets formulated to be isocaloric (by using supplemental fat), to a constant standard ileal digestible lysine to energy ratio within phase, and meet or exceed nutrient requirements proposed by NRC (2012). The corn-soybean meal-based control diet (0% CGM) was used as the reference diet to compare with the CGM diets to estimate PE. Caloric efficiency (calories consumed per unit of weight gain) was calculated for each treatment using the feed:gain ratio. For Study 1, the CGM ME value used to formulate diets, based on published values and previous unpublished research, was 3,037 kcal/kg. The pen of pigs was the experimental unit; data were analyzed using PROC MIXED of SAS; the model accounted for the effects of CGM level and block. Increasing CGM level increased feed-gain linearly (P < 0.05; 2.34, 2.38, and 2.42 kg/kg for 0, 12.5, and 25.0% CGM diets, respectively; SEM 0.023) which gave an estimate of productive ME for CGM of 2,604 kcal/kg. For Study 2, CGM diets were formulated using this ME value (adjusted for the chemical composition of the batch of CGM used). Increasing CGM inclusion level increased feed:gain linearly (P < 0.05; 2.46, 2.49, 2.49, 2.51, and 2.55 kg/kg for 0, 10, 20, 30, and 40% CGM diets, respectively; SEM 0.018) and this resulted in an estimate productive ME of CGM of 2,462 kcal/kg. These results suggest considerable variation in CGM PE estimated from growth studies. Further research is needed to define appropriate methodology to determine PE and validate the energy content of CGM.