The objectives of this study were to compare the energy values of poultry by-product meal (PBM) as feed for adult beagle dogs using the direct, difference, and regression methods to examine dogs’ nitrogen metabolism, energy utilization, gaseous metabolism, and body health. Five groups of six 12-month-old female beagles with an average body weight of 9.67 ± 0.52 kg were tested in a 5×6 incomplete Latin square design, with six repetitions in each group. Five experimental diets were tested consisting of 100% PBM; three substitution diets containing either 15%, 30%, or 45% PBM (termed 15PBM, 30PBM, and 45PBM, respectively); and a basal diet (included 6.90% PBM). Each experimental period lasted for 10 days, comprising 4 days of dietary acclimation followed by 6 days of testing (including 3 day feeding period and 3 day fasting period), during which the heat production (HP) was determined and feces and urine were collected. Results showed that, in the feeding state, the nitrogen intake, urinary nitrogen, apparent nitrogen digestibility, retained nitrogen, and heat production (HP) increased significantly (P < 0.05) as the PBM level increased. The net protein utilization, biological value of protein, and total apparent digestibility of amino acids did not differ between the 30PBM and 45PBM diets (P > 0.05). The O2 consumption and CO2 production of beagles during the fasting period were not influenced by the PBM level (P > 0.05). The digestible energy and metabolizable energy values of the PBM estimated by the regression method were 20.16 MJ/kg and 18.18 MJ/kg dry matter (DM), respectively, and did not differ from those determined by the direct method (P > 0.05). The fecal dry matter percentages and fecal PBM scores were significantly higher in the PBM diet than in the difference method groups (P < 0.05). The direct method group had a significantly higher fecal score (4.63) than the other groups (P < 0.05), The fecal score of the 45PBM diet (3.50) was significantly higher than the 30PBM diet (2.90) (P < 0.05). In summary, the direct method and difference method of determining the effective energy value of PBM for beagles, produce significantly different results. Under the conditions of this test, the best proportion of PBM in beagle feed for optimum energy provision is 30%.

Methionine is the first or second limiting amino acid for ruminants, such as sika deer, and has a variety of biological functions such as antioxidant activity, immune response, and protein synthesis. This study aimed to investigate the effects of methionine supplementation on antler growth, serum biochemistry, rumen fermentation, and the bacterial community of sika deer during the antler-growing period. Twelve 4-year-old male sika deer were randomly assigned to three dietary groups supplemented with 0 g/day (n = 4, CON), 4.0 g/day (n = 4, LMet), and 6.0 g/day (n = 4, HMet) methionine. No significant difference (p > 0.05) was found in the production performance between the three groups, but antler weight was higher in both the LMet and HMet groups than in the CON group. Methionine supplementation significantly increased the serum glutathione peroxidase activity (p < 0.05). The serum immunoglobulin G level was significantly higher in the HMet group than in the other two groups (p < 0.05). No significant effect was found on the apparent amino acid digestibility of the three groups, but cysteine and methionine digestibility were higher in the LMet group. The serum hydroxylysine level was significantly lower in the LMet and HMet groups, whereas the serum lysine level was significantly lower in the HMet group compared with the CON group (p < 0.05). The LMet group had the highest but a nonsignificant total volatile fatty acid content and significantly higher microbial protein content in the rumen than the CON group (p < 0.05). The phyla Bacteroidetes, Firmicutes, and Proteobacteria were dominant in the rumen of the sika deer. The principal coordinate analysis (PCoA) and analysis of similarities (ANOSIM) results showed a significant change in the bacterial composition of the three groups (p < 0.05). The relative abundance of Prevotella and Rikenellaceae-RC9 was significantly higher in the LMet group compared with the CON group and CON and HMet groups, respectively. These results revealed that methionine supplementation improved the antioxidant activity and immune status, affecting amino acid metabolism and rumen microbial composition of the sika deer.