Muñoz C, Letelier P A, Ungerfeld E M, Morales J M, Hube S, Pérez-Prieto L A
Instituto de Investigaciones Agropecuarias, INIA Remehue, Casilla 24-O, Osorno 5290000, Chile.
Escuela de Medicina Veterinaria, Facultad de Ciencias Silvoagropecuarias, Universidad Mayor, Camino La Pirámide N°5750, Huechuraba, Santiago 8580745, Chile.
J Dairy Sci. 2016 Oct;99(10):7945-7955. doi: 10.3168/jds.2016-10919. Epub 2016 Aug 4.
Few studies have examined the effects of fresh forage quality on enteric methane (CH4) emissions of dairy cows under grazing conditions. The aim of the current study was to evaluate the effects of 2 contrasting forage qualities induced by different pregrazing herbage masses in late spring on enteric CH4 emissions and milk production of grazing dairy cows. The experiment was conducted as a crossover design with 24 lactating Holstein Friesian dairy cows randomly assigned to 1 of 2 treatments in 2 experimental periods. Each period had a duration of 3wk (2wk for diet adaptation and 1wk for measurements), and the interval between them was 2wk. Treatments consisted of 2 target pregrazing herbage masses [2,200 and 5,000kg of dry matter (DM)/ha above 3cm], generated by different regrowth periods, corresponding to low (LHM) and high (HHM) herbage mass treatments, respectively. Daily herbage allowance (Lolium perenne) for both treatments was 20kg of DM per cow measured above 3cm. Enteric CH4 emissions were individually determined during the last week of each period using the sulfur hexafluoride tracer technique. Daily herbage intakes by individual cows during the CH4 measurement weeks were estimated using the n-alkanes technique. During the CH4 measurement weeks, milk yield and body mass were determined twice daily, whereas milk composition was determined once in the week. The LHM pasture had a higher crude protein concentration, lower neutral detergent fiber and acid detergent fiber concentrations, and higher in vitro digestibility, with a lower proportion of ryegrass pseudostems, than the HHM pasture. Cows offered the LHM pasture had greater herbage (+13%) and total DM (+12%) intakes, increased milk (+13%) and energy-corrected milk (+11%) yields, and tendencies toward higher milk protein (+4.5%) and higher milk urea nitrogen (+15%) concentrations than their counterparts offered the HHM pasture. No differences were found between treatments in total daily CH4 production. However, the LHM treatment reduced enteric CH4 emissions per unit of milk yield (-11%) and enteric CH4 energy as a percentage of ingested gross energy (-9%) and tended to reduce CH4 per unit of dry matter intake (-8.2%) and energy-corrected milk yield (-10%) compared with the HHM treatment. The results from this study suggest that a grazing management that favors better quality pasture, as was the case of the LHM pasture in late spring compared with the HHM pasture, increases milk production of grazing dairy cows and reduces enteric CH4 emissions per unit of milk produced, constituting a viable CH4 mitigation strategy.
很少有研究考察过放牧条件下新鲜牧草质量对奶牛肠道甲烷（CH4）排放的影响。本研究的目的是评估晚春时节不同放牧前牧草量所导致的两种截然不同的牧草质量对放牧奶牛肠道CH4排放和产奶量的影响。试验采用交叉设计，24头泌乳期的荷斯坦弗里生奶牛在两个试验期内随机分配到两种处理中的一种。每个时期持续3周（2周用于日粮适应，1周用于测量），两个时期之间的间隔为2周。处理包括通过不同的再生期产生的两种目标放牧前牧草量[高于3厘米的干物质（DM）分别为2200和5000千克/公顷]，分别对应低牧草量（LHM）和高牧草量（HHM）处理。两种处理的每日牧草供应量（多年生黑麦草）均为每头奶牛高于3厘米处测量的20千克DM。在每个时期的最后一周使用六氟化硫示踪技术分别测定肠道CH4排放。在CH4测量周期间，使用正构烷烃技术估算每头奶牛的每日牧草摄入量。在CH4测量周期间，每天测定两次产奶量和体重，而每周测定一次牛奶成分。与HHM牧场相比，LHM牧场的粗蛋白浓度较高，中性洗涤纤维和酸性洗涤纤维浓度较低，体外消化率较高，黑麦草假茎比例较低。采食LHM牧场的奶牛比采食HHM牧场的奶牛有更高的牧草摄入量（+13%）和总DM摄入量（+12%），产奶量（+13%）和能量校正奶量（+11%）增加，并且牛奶蛋白（+4.5%）和牛奶尿素氮（+15%）浓度有升高的趋势。在每日总CH4产量方面，处理之间未发现差异。然而，与HHM处理相比，LHM处理降低了每单位产奶量的肠道CH4排放（-11%）以及肠道CH4能量占摄入总能的百分比（-9%），并且有降低每单位干物质摄入量的CH4排放（-8.2%）和能量校正奶量的CH4排放（-10%）的趋势。本研究结果表明，与HHM牧场相比，像晚春时节的LHM牧场那样有利于质量更好的牧场的放牧管理，可提高放牧奶牛的产奶量，并降低每单位产奶量的肠道CH4排放，构成一种可行的CH4减排策略。
