Nutrient utilization, ruminal fermentation, microbial nitrogen flow, microbial abundances, and methane emissions in...

The effects of replacing 50% of cereals-based concentrate with feed blocks (FB) including wastes of tomato fruits (diet ACT), wastes of cucumber fruits (diet ACC), or barley grain (diet ACB) on nutrient use, ruminal fermentation, microbial N flow to the duodenum, methane emissions, and abundances of total bacteria and methanogen were studied in goats. Four adult, dry, nonpregnant, rumen-fistulated Granadina goats (32.1 ± 5.52 kg BW) were used and 4 diets were studied in 4 trials by using a 4 × 4 Latin square experimental design. Diets consisted of alfalfa hay plus concentrate in a 1:1 ratio (AC) or 1:0.5 plus FB including wastes of ACT, ACC, or ACB. In each trial, goats were randomly assigned to 1 of the diets. Intake of each FB including ACT, ACC, and ACB were 203 ± 73, 179 ± 39, and 144 ± 68 g·animal(-1)·d(-1), respectively. The ACT and ACC diets did not (P > 0.05) compromise digestible and metabolizable energy, but reduced N retention by up to 29% (P = 0.03). Cucumber-based FB decreased the purine bases (PB):N ratio (P = 0.02) in total bacterial pellets isolated from the rumen content. Tomato-based FB decreased purine derivatives urinary excretion (P = 0.04) and microbial N flow (P = 0.03) without affecting the efficiency of synthesis but decreased methane emission by 28% (P < 0.001) compared with the other diets. Tomato and cucumber-based FB resulted in greater (P < 0.001) rumen VFA concentration and molar proportions of propionate and butyrate (P ≤ 0.02) than AC and ACB diets. No effect (P = 0.07) of diet on total bacteria abundance was observed whereas the abundance of methanogens increased (P = 0.01) with wastes-based FB. Our study suggests that ACC-based FB could replace one-half of the amount of concentrate in goat diet without compromising rumen fermentation and nutrient and energy use and without increasing methane emissions. Blocks including ACT showed an antimethanogenic effect but reduced microbial N flow to the duodenum. Further research is needed to improve both N and energy use of diets including ACT- and ACC-based FB.