Teagasc, Moorepark Dairy Production Research Centre, Fermoy, Co. Cork, Ireland.
J Dairy Sci. 2010 Sep;93(9):4318-31. doi: 10.3168/jds.2009-2686.
The primary objective of the study was to quantify the effect of genetic improvement using the Irish total merit index (Economic Breeding Index) on dry matter intake and feed efficiency across lactation and to quantify the variation in performance among alternative definitions of feed efficiency. Three genotypes of Holstein-Friesian dairy cattle were established from within the Moorepark dairy research herd: 1) low Economic Breeding Index North American Holstein-Friesian representative of the Irish national average dairy cow, 2) high genetic merit North American Holstein-Friesian, and 3) high genetic merit New Zealand Holstein-Friesian. Animals from within each genotype were randomly allocated to 1 of 2 possible intensive pasture-based feed systems: 1) the Moorepark pasture system (2.64 cows/ha and 500 kg of concentrate supplement per cow per lactation) and 2) a high output per hectare pasture system (2.85 cows/ha and 1,200 kg of concentrate supplement per cow per lactation). A total of 128 and 140 spring-calving dairy cows were used during the years 2007 and 2008, respectively. Each group had an individual farmlet of 17 paddocks, and all groups were managed similarly throughout the study. The effects of genotype, feed system, and the interaction between genotype and feed system on dry matter intake, milk production, body weight, body condition score, and different definitions of feed efficiency were studied using mixed models with factorial arrangements of genotypes and feed systems accounting for the repeated cow records across years. No significant genotype-by-feed-system interactions were observed for any of the variables measured. Results showed that aggressive selection using the Irish Economic Breeding Index had no effect on dry matter intake across lactation when managed on intensive pasture-based systems of milk production, although the ranking of genotypes for feed efficiency differed depending on the definition of feed efficiency used. Performance of animals grouped on alternative definitions of feed efficiency showed that conventional definitions such as feed conversion efficiency or residual feed intake may be inappropriate measures of efficiency for lactating dairy cows. An alternative definition, residual solids production, is proposed. This definition of feed efficiency identifies animals that produce greater volumes of milk solids at similar levels of feed intake without excessive body tissue mobilization and with improved fertility performance. The results also suggest that although there are differences in feed efficiency between strains of Holstein-Friesian, there is also variation within genotypes so that improvements in feed efficiency can be realized if the appropriate definition of feed efficiency is incorporated into breeding programs.
本研究的主要目的是量化使用爱尔兰总效益指数（经济育种指数）对泌乳期干物质采食量和饲料效率的遗传改良效果，并量化替代饲料效率定义之间的性能差异。从摩尔帕克奶牛研究群体中建立了 3 种荷斯坦-弗里生奶牛基因型：1）低经济育种指数的北美荷斯坦-弗里生，代表爱尔兰全国平均奶牛，2）高遗传优势的北美荷斯坦-弗里生，和 3）高遗传优势的新西兰荷斯坦-弗里生。每个基因型的动物都被随机分配到 2 种可能的密集牧场饲料系统之一：1）摩尔帕克牧场系统（每头奶牛 2.64 公顷和 500 公斤浓缩饲料补充剂）和 2）高公顷产量牧场系统（每头奶牛 2.85 公顷和 1200 公斤浓缩饲料补充剂）。2007 年和 2008 年分别使用了 128 头和 140 头春季产奶牛。每个组都有一个 17 个围场的独立农场，整个研究期间所有组都以类似的方式管理。使用混合模型研究基因型、饲料系统以及基因型和饲料系统之间的相互作用对干物质采食量、牛奶产量、体重、身体状况评分和不同饲料效率定义的影响，其中混合模型的事实安排考虑了奶牛在多年间的重复记录。对于所测量的任何变量，都没有观察到基因型与饲料系统之间的显著相互作用。结果表明，在集约牧场牛奶生产系统中，使用爱尔兰经济育种指数进行积极选择对泌乳期的干物质采食量没有影响，尽管不同基因型的饲料效率排名取决于所使用的饲料效率定义。根据替代饲料效率定义分组的动物的表现表明，常规定义，如饲料转化率或剩余饲料摄入量，可能不是泌乳奶牛效率的适当衡量标准。提出了替代定义，即剩余固体产量。这种饲料效率定义可以识别出在类似采食量水平下产生更多牛奶固体量而不会过度动员身体组织并具有改善繁殖性能的动物。结果还表明，尽管荷斯坦-弗里生的品种之间存在饲料效率差异，但基因型内也存在差异，因此如果将适当的饲料效率定义纳入育种计划，就可以实现饲料效率的提高。
