Delamaire E, Guinard-Flament J
Unité Mixte de Recherches INRA/Agrocampus Rennes Production du Lait, 33590 Saint-Gilles, France.
J Dairy Sci. 2006 Jun;89(6):2007-16. doi: 10.3168/jds.S0022-0302(06)72268-8.
Increasing the milking interval decreases milk yield and modifies milk composition. To gain a clearer understanding of the regulation of milk yield and composition, a study was conducted to establish the response curves of nutrient extraction by the mammary gland and mammary epithelial permeability in response to increasing milking intervals. Four multiparous lactating dairy cows were milked at 8-, 12-, 16-, or 24-h intervals over a period of 7 d using a Latin square design. Between the 8- and 24-h milking intervals, milk yield and milk protein levels fell curvilinearly from 38.2 to 29.2 kg/d and from 1,086 to 827 g/d, respectively. Milk fat yield decreased linearly from 1,475 to 1,235 g/d. Indicators of the opening of tight junctions increased linearly with increasing milking intervals: milk BSA increased from 148 to 207 mg/L and plasma lactose increased from 22.9 to 32.0 mg/L. The mammary gland's ability to extract nutrients decreased with increasing milking intervals. Extraction rates of glucose, beta-hydroxybutyrate, and total glycerol decreased significantly (from 27.2 to 23.3%, from 42.3 to 34.4%, from 36.6 to 30.8% between 8- and 24-h milking intervals, respectively), and not significantly for alpha-amino nitrogen (from 23.2 to 20.0%). The extraction rate of acetate remained constant. Moreover, the extraction of milk fat precursors appeared to be less regulated than those of the precursors of milk protein and lactose, which could partly explain why milk yield and milk protein yield decreased more than milk fat yield. The arteriovenous differences of beta-hydroxybutyrate and total glycerol remained constant, whereas those of glucose decreased significantly from 0.98 to 0.87 +/- 0.05 mmol/L and not significantly from 0.74 to 0.64 +/- 0.12 mmol/L for alpha-amino nitrogen. As a result, the mammary gland's ability to extract nutrients appears to be downregulated explaining partly the decrease in daily milk yield observed in response to increased milking intervals.
延长挤奶间隔会降低产奶量并改变牛奶成分。为了更清楚地了解产奶量和成分的调节机制，开展了一项研究，以确定乳腺营养物质摄取和乳腺上皮通透性随挤奶间隔延长的反应曲线。选用4头经产泌乳奶牛，采用拉丁方设计，在7天内分别按8小时、12小时、16小时或24小时的间隔进行挤奶。在8小时至24小时的挤奶间隔期间，产奶量和牛奶蛋白水平呈曲线下降，分别从38.2千克/天降至29.2千克/天，从1086克/天降至827克/天。乳脂产量从1475克/天线性下降至1235克/天。紧密连接开放的指标随挤奶间隔延长呈线性增加：牛奶中的牛血清白蛋白从148毫克/升增加至- 207毫克/升，血浆乳糖从22.9毫克/升增加至32.0毫克/升。乳腺摄取营养物质的能力随挤奶间隔延长而下降。葡萄糖、β-羟基丁酸和总甘油的摄取率显著下降（在8小时至24小时的挤奶间隔期间，分别从27.2%降至23.3%、从42.3%降至34.4%、从36.6%降至30.8%），而α-氨基氮的摄取率下降不显著（从23.2%降至20.0%）。乙酸盐的摄取率保持不变。此外，乳脂前体的摄取似乎比乳蛋白和乳糖前体的摄取受调控程度更低，这可能部分解释了产奶量和乳蛋白产量的下降幅度为何大于乳脂产量。β-羟基丁酸和总甘油的动静脉差值保持不变，而葡萄糖的动静脉差值显著下降，从0.98降至0.87±0.05毫摩尔/升，α-氨基氮的动静脉差值下降不显著，从0.74降至0.64±0.12毫摩尔/升。因此，乳腺摄取营养物质的能力似乎受到下调，这部分解释了随着挤奶间隔延长观察到的日产奶量下降现象。
