Bachman K C, Hayen M J, Morse D, Wilcox C J
Dairy Science Department, University of Florida, Gainesville 32611.
J Dairy Sci. 1988 Apr;71(4):925-31. doi: 10.3168/jds.S0022-0302(88)79638-1.
During 12 mo, 1818 milk samples were collected from Holsteins and Jerseys (n = 261) to evaluate effects of advancing lactation and pregnancy on milk fat hydrolysis. Aliquots, cooled immediately and stored 48 h at 4 degrees C, were analyzed for free fatty acid content. Holsteins had higher acid degree values than Jerseys (.90 vs. .62). No difference in values was detected between alternate a.m. (.74) and p.m. (.76) sampling times. Repeatability of acid degree values from lactation to lactation was low (.22). Days in milk, days pregnant, and milk yield had curvilinear effects on acid degree values, whereas SCC effects were linear. Estimated acid degree value at 335 d in milk (average dry-off) was lowered from .80 to .63 when adjusted for days pregnant and to .48 when adjusted also for milk yield. These responses agree with the increased acid degree values associated with two late lactation events: increasing day pregnant and decreasing milk yield. Estrogen secreted by the developing fetal-placental unit could mediate changes in milk composition that promote milk fat hydrolysis.
在12个月期间，从荷斯坦奶牛和泽西奶牛（n = 261）采集了1818份乳样，以评估泌乳进展和怀孕对乳脂肪水解的影响。将立即冷却并在4℃下储存48小时的等分试样分析游离脂肪酸含量。荷斯坦奶牛的酸度值高于泽西奶牛（0.90对0.62）。在上午（0.74）和下午（0.76）交替采样时间之间未检测到值的差异。从一个泌乳期到另一个泌乳期酸度值的重复性较低（0.22）。产奶天数、怀孕天数和产奶量对酸度值有曲线影响，而体细胞数的影响是线性的。当根据怀孕天数进行调整时，估计在产奶335天（平均干奶期）时的酸度值从0.80降至0.63，当同时根据产奶量进行调整时降至0.48。这些反应与两个泌乳后期事件相关的酸度值增加一致：怀孕天数增加和产奶量减少。发育中的胎儿-胎盘单位分泌的雌激素可能介导促进乳脂肪水解的乳成分变化。
