Reynolds C K, Humphries D J, Kirton P, Kindermann M, Duval S, Steinberg W
School of Agriculture, Policy and Development, University of Reading, PO Box 237, Earley Gate, Reading, RG6 6AR, United Kingdom.
School of Agriculture, Policy and Development, University of Reading, PO Box 237, Earley Gate, Reading, RG6 6AR, United Kingdom.
J Dairy Sci. 2014;97(6):3777-89. doi: 10.3168/jds.2013-7397. Epub 2014 Apr 3.
The objective was to measure effects of 3-nitrooxypropanol (3 NP) on methane production of lactating dairy cows and any associated changes in digestion and energy and N metabolism. Six Holstein-Friesian dairy cows in mid-lactation were fed twice daily a total mixed ration with maize silage as the primary forage source. Cows received 1 of 3 treatments using an experimental design based on two 3 × 3 Latin squares with 5-wk periods. Treatments were a control placebo or 500 or 2,500 mg/d of 3 NP delivered directly into the rumen, via the rumen fistula, in equal doses before each feeding. Measurements of methane production and energy and N balance were obtained during wk 5 of each period using respiration calorimeters and digestion trials. Measurements of rumen pH (48 h) and postprandial volatile fatty acid and ammonia concentrations were made at the end of wk 4. Daily methane production was reduced by 3 NP, but the effects were not dose dependent (reductions of 6.6 and 9.8% for 500 and 2,500 mg/d, respectively). Dosing 3 NP had a transitory inhibitory effect on methane production, which may have been due to the product leaving the rumen in liquid outflow or through absorption or metabolism. Changes in rumen concentrations of volatile fatty acids indicated that the pattern of rumen fermentation was affected by both doses of the product, with a decrease in acetate:propionate ratio observed, but that acetate production was inhibited by the higher dose. Dry matter, organic matter, acid detergent fiber, N, and energy digestibility were reduced at the higher dose of the product. The decrease in digestible energy supply was not completely countered by the decrease in methane excretion such that metabolizable energy supply, metabolizable energy concentration of the diet, and net energy balance (milk plus tissue energy) were reduced by the highest dose of 3 NP. Similarly, the decrease in N digestibility at the higher dose of the product was associated with a decrease in body N balance that was not observed for the lower dose. Milk yield and milk fat concentration and fatty acid composition were not affected but milk protein concentration was greater for the higher dose of 3 NP. Twice-daily rumen dosing of 3 NP reduced methane production by lactating dairy cows, but the dose of 2,500 mg/d reduced rumen acetate concentration, diet digestibility, and energy supply. Further research is warranted to determine the optimal dose and delivery method of the product.
本研究旨在测定3-硝基氧丙醇（3-NP）对泌乳奶牛甲烷产生量的影响，以及对消化、能量和氮代谢的相关变化。选用6头处于泌乳中期的荷斯坦-弗里生奶牛，每天分两次投喂以玉米青贮为主要粗饲料来源的全混合日粮。采用基于两个3×3拉丁方、为期5周的试验设计，奶牛接受3种处理中的1种。处理方式为对照安慰剂，或通过瘤胃瘘管，在每次喂食前等量直接向瘤胃内注入500或2500毫克/天的3-NP。在每个周期的第5周，使用呼吸测热计和消化试验测定甲烷产生量、能量和氮平衡。在第4周结束时测量瘤胃pH值（48小时）以及餐后挥发性脂肪酸和氨浓度。3-NP可降低每日甲烷产生量，但效果不呈剂量依赖性（500和2500毫克/天的剂量分别降低了6.6%和9.8%）。投喂3-NP对甲烷产生有短暂抑制作用，这可能是由于该产品通过液体流出、吸收或代谢离开瘤胃所致。瘤胃挥发性脂肪酸浓度的变化表明，两种剂量的产品均影响瘤胃发酵模式，观察到乙酸盐：丙酸盐比例降低，但高剂量抑制了乙酸盐的产生。产品高剂量时，干物质、有机物质、酸性洗涤纤维、氮和能量消化率降低。可消化能量供应的减少并未完全被甲烷排泄的减少所抵消，因此，3-NP最高剂量降低了代谢能供应、日粮代谢能浓度和净能量平衡（牛奶加组织能量）。同样，产品高剂量时氮消化率的降低与机体氮平衡的减少有关，低剂量时未观察到这种情况。牛奶产量、乳脂浓度和脂肪酸组成未受影响，但3-NP高剂量时乳蛋白浓度更高。每天向瘤胃投喂两次3-NP可降低泌乳奶牛的甲烷产生量，但2500毫克/天的剂量降低了瘤胃乙酸盐浓度、日粮消化率和能量供应。有必要进一步研究以确定该产品的最佳剂量和投喂方式。
