Macdonald K A, Verkerk G A, Thorrold B S, Pryce J E, Penno J W, McNaughton L R, Burton L J, Lancaster J A S, Williamson J H, Holmes C W
DairyNZ, Private Bag 3221, Hamilton, New Zealand 3240.
J Dairy Sci. 2008 Apr;91(4):1693-707. doi: 10.3168/jds.2007-0441.
This experiment compared Holstein-Friesian (HF) cows of New Zealand (NZ) origin representative of genetics present in the 1970s (NZ70; n = 45) and 1990s (NZ90; n = 60), and a group of HF cows of North American origin with 1990s genetics (NA90; n = 60), which were managed in grazing systems with a range of feeding allowances (4.5 to 7.0 t/cow per yr) over 3 yr. The NZ70 cows had the lowest Breeding Worth genetic index and the lowest breeding values for yields of fat, protein, and milk volume; the NZ90 and NA90 cows were selected to have similar breeding values for milk traits and were representative of cows of high genetic merit in the 1990s. The NZ90 cows had a higher milk protein concentration (3.71%) than either the NA90 (3.43%) or the NZ70 cows (3.41%), and a higher milk fat concentration (4.86%) than the NA90 cows (4.26%) with a level similar to the NZ70 cows (4.65%). The NZ90 cows produced significantly greater yields of fat, protein, and lactose than the NA90 and NZ70 cows. The NZ70 cows had the lowest mean annual body weight (473 kg) but the highest body condition score (BCS; 5.06). Days in milk were the same for the 2 NZ strains (286 d in milk), both of which were greater than the NA90 cows (252 d in milk). There was no genotype x environment interaction for combined milk fat and protein yield (milksolids), with NZ90 producing 52 kg/cow more than the NA90 at all feeding levels. The NZ70 strain had the highest seasonal average BCS (5.06), followed by the NZ90 (4.51) and the NA90 (4.13) strains on a 1 to 10 scale. Body condition score increased with higher feeding levels in the 2 NZ strains, but not in the NA strain. The first-parity cows commenced luteal activity 11 d later than older cows (parities 2 and 3), and the NA90 cows commenced luteal activity 4 and 10 d earlier than the NZ70 and NZ90 cows. Earlier estrus activity did not result in a higher in-calf rate. The NZ70 and NZ90 cows had similar in-calf rates (pregnancy diagnosed to 6 wk; 69%), which were higher than those achieved by NA90 cows (54%). Results showed that the NA90 strain used in this experiment was not suitable for traditional NZ grazing systems. Grazing systems need to be modified if the NA90 strain is to be successfully farmed in NZ. The data reported here show that the NA90 cows require large amounts of feed, but this will not prevent them from having a lower BCS than the NZ strains. Combined with poor reproductive performance, this means that NA90 cows are less productive than NZ HF in pasture-based seasonal calving systems with low levels of supplementation.
本实验比较了具有20世纪70年代遗传特征的新西兰（NZ）原产荷斯坦-弗里生（HF）奶牛（NZ70；n = 45）和20世纪90年代遗传特征的新西兰原产HF奶牛（NZ90；n = 60），以及一组具有20世纪90年代遗传特征的北美原产HF奶牛（NA90；n = 60），这些奶牛在放牧系统中饲养3年，给予不同的采食量（每年每头奶牛4.5至7.0吨）。NZ70奶牛的育种价值遗传指数最低，脂肪、蛋白质和产奶量的育种值也最低；NZ90和NA90奶牛被选来具有相似的产奶性状育种值，代表了20世纪90年代高遗传品质的奶牛。NZ90奶牛的乳蛋白浓度（3.71%）高于NA90奶牛（3.43%）和NZ70奶牛（3.41%），乳脂浓度（4.86%）高于NA90奶牛（4.26%），与NZ70奶牛（4.65%）相近。NZ90奶牛的脂肪、蛋白质和乳糖产量显著高于NA90和NZ70奶牛。NZ70奶牛的年均体重最低（473千克），但体况评分最高（BCS；5.06）。两个NZ品系的奶牛泌乳天数相同（286天），均多于NA90奶牛（252天）。乳脂和蛋白质总产量（乳固体）不存在基因型×环境互作，在所有采食量水平下，NZ90奶牛每头比NA90奶牛多产52千克。按1至10分制，NZ70品系的季节性平均BCS最高（5.06），其次是NZ90（4.51）和NA90（4.13）品系。两个NZ品系的体况评分随采食量增加而升高，但NA品系并非如此。头胎奶牛的黄体活动比经产奶牛（二胎和三胎）晚11天，NA90奶牛的黄体活动比NZ70和NZ90奶牛早4天和10天。较早的发情活动并未带来更高的受孕率。NZ70和NZ90奶牛的受孕率相似（妊娠诊断至6周时为69%），高于NA90奶牛（54%）。结果表明，本实验中使用的NA90品系不适合新西兰传统放牧系统。如果要在新西兰成功养殖NA90品系，放牧系统需要进行改良。此处报告的数据表明，NA90奶牛需要大量饲料，但这并不妨碍它们的体况评分低于NZ品系。再加上繁殖性能较差，这意味着在补饲水平较低的基于牧场的季节性产犊系统中，NA90奶牛的生产性能低于NZ HF奶牛。
