Department of Primary Industries, Ellinbank Victoria 3821, Australia.
J Dairy Sci. 2010 Apr;93(4):1401-11. doi: 10.3168/jds.2009-2727.
Extending the lactation length of dairy cows beyond the traditional 10 mo toward lactations of up to 22 mo has attracted interest in the pasture-based seasonal dairying systems of Australia and New Zealand as a way of alleviating the need for cows to conceive during peak lactation, such as is required to maintain seasonally concentrated calving systems. Lactation lengths longer than 10 mo instead provide cows with more time to cycle and conceive after parturition and may therefore be more suitable systems for high-producing Holstein-Friesian cows. Before recommending such systems there is a need to evaluate the effects of long lactations on the suitability of milk for manufacture of high-quality dairy products. In the current experiment, the composition of milk from cows entering the second half of a 22-mo lactation was examined in detail and compared with that from cows undergoing a traditional 10-mo lactation. On 2 occasions, coagulation properties were measured using low amplitude strain oscillation rheometry, and Cheddar cheese was made in 250-L pilot-scale vats. Results showed that milk from extended lactations had higher concentrations of fat and protein than cows undergoing 10-mo lactations under similar management conditions and at the same time of year. The ratio of casein to true protein was not affected by lactation length and neither were the proportions of individual caseins. The increase in milk solids during extended lactations translated into a more rapid rate of coagulation and ultimately a firmer curd on one of the two occasions. Milk from extended lactations yielded more cheese per 100 kg of milk, and there were few differences in the composition or organoleptic properties of the cheese. These data are the first to show that pasture-based dairy industries could embrace the use of extended lactations without compromising the core business of producing high-quality dairy products.
将奶牛的泌乳期从传统的 10 个月延长至长达 22 个月，这在澳大利亚和新西兰的牧场季节性奶牛养殖系统中引起了关注，因为这是一种缓解奶牛在泌乳高峰期怀孕需求的方法，例如为了维持季节性集中产犊系统。超过 10 个月的泌乳期可以让奶牛在分娩后有更多的时间循环和怀孕，因此可能更适合高产荷斯坦-弗里森奶牛。在推荐此类系统之前，需要评估长泌乳期对牛奶适合制造高质量乳制品的影响。在当前的实验中，详细检查了进入 22 个月泌乳期后半段的奶牛的牛奶成分，并将其与经历传统 10 个月泌乳期的奶牛的牛奶成分进行了比较。在两次试验中，使用低振幅应变振荡流变仪测量了凝固特性，并在 250 升中试罐中制作了切达干酪。结果表明，在相似的管理条件下，在同一时间，延长泌乳期的牛奶中的脂肪和蛋白质浓度高于经历 10 个月泌乳期的奶牛。酪蛋白与真蛋白的比例不受泌乳期长度的影响，个别酪蛋白的比例也不受影响。延长泌乳期导致牛奶固体增加，从而导致凝固速度更快，最终在两次试验中的一次形成更坚硬的凝乳。延长泌乳期的牛奶每 100 公斤牛奶产量更多的奶酪，并且奶酪的成分或感官特性几乎没有差异。这些数据首次表明，基于牧场的乳制品行业可以采用延长泌乳期，而不会影响生产高质量乳制品的核心业务。
