Bajramaj D L, Curtis R V, Kim J J M, Corredig M, Doelman J, Wright T C, Osborne V R, Cant J P
Department of Animal Biosciences, University of Guelph, Ontario, N1G 2W1 Canada.
Department of Food Science, University of Guelph, Ontario, N1G 2W1 Canada.
J Dairy Sci. 2017 Aug;100(8):6139-6150. doi: 10.3168/jds.2016-12380. Epub 2017 Jun 7.
The objective of this study was to determine if the addition of glycerol to the diet of dairy cows would stimulate milk protein yield in the same manner as the addition of corn grain. Twelve multiparous lactating dairy cows at 81 ± 5 d in milk were subjected to 3 dietary treatments in a replicated 3 × 3 Latin square design for 28-d periods. The diets were a 70% forage diet considered the basal diet, the basal diet with 19% ground and high-moisture corn replacing forages, and the basal diet with 15% refined glycerol and 4% added protein supplements to be isocaloric and isonitrogenous with the corn diet. Cows were milked twice a day and samples were collected on the last 7 d of each period for compositional analysis. Within each period, blood samples were collected on d 26 and 27, and mammary tissue was collected by biopsy on d 28 for Western blot analysis. Dry matter intake increased from 23.7 kg/d on the basal diet to 25.8 kg/d on the corn diet and 27.2 kg/d on the glycerol diet. Dry matter intake tended to be higher with glycerol than corn. Milk production increased from 39.2 kg/d on the basal diet to 43.8 kg/d on the corn diet and 44.2 kg/d on the glycerol diet. However, milk yield did not differ between corn and glycerol diets. Milk lactose yields were higher on the corn and glycerol diets than the basal diet. Milk fat yield significantly decreased on the glycerol diet compared with the basal diet and tended to decrease in comparison with the corn diet. Mean milk fat globule size was reduced by glycerol feeding. Milk protein yield increased 197 g/d with addition of corn to the basal diet and 263 g/d with addition of glycerol, and the glycerol effect was larger than the corn effect. The dietary treatments had no effects on plasma glucose concentration, but plasma acetate levels decreased 27% on the glycerol diet. Amino acid concentrations were not affected by dietary treatments, except for branched-chain amino acids, which decreased 22% on the glycerol diet compared with the corn diet. The decreases in plasma acetate and branched-chain amino acid concentrations with glycerol and the larger effects of glycerol than corn on milk protein and fat yields suggest that glycerol is more glucogenic for cows than corn grain.
本研究的目的是确定在奶牛日粮中添加甘油是否会像添加玉米谷物一样刺激乳蛋白产量。选用12头处于泌乳期81±5天的经产奶牛，采用重复3×3拉丁方设计，进行3种日粮处理，为期28天。日粮分别为：70%粗饲料日粮作为基础日粮；基础日粮中用19%的粉碎高水分玉米替代粗饲料；基础日粮中添加15%精制甘油和4%蛋白质补充剂，使其与玉米日粮等热量、等氮。奶牛每天挤奶两次，在每个时期的最后7天采集样本进行成分分析。在每个时期内，于第26天和第27天采集血样，并在第28天通过活检采集乳腺组织用于蛋白质印迹分析。基础日粮组的干物质摄入量为23.7千克/天，玉米日粮组为25.8千克/天，甘油日粮组为27.2千克/天。甘油组的干物质摄入量往往高于玉米组。基础日粮组的产奶量为39.2千克/天，玉米日粮组为43.8千克/天，甘油日粮组为44.2千克/天。然而，玉米日粮组和甘油日粮组的产奶量没有差异。玉米日粮组和甘油日粮组的乳糖产量高于基础日粮组。与基础日粮组相比，甘油日粮组的乳脂肪产量显著降低，与玉米日粮组相比有降低趋势。饲喂甘油会使乳脂肪球平均大小减小。基础日粮中添加玉米后乳蛋白产量增加197克/天，添加甘油后增加263克/天，甘油的效果大于玉米。日粮处理对血浆葡萄糖浓度没有影响，但甘油日粮组的血浆乙酸水平降低了27%。日粮处理对氨基酸浓度没有影响，但支链氨基酸除外，与玉米日粮组相比，甘油日粮组的支链氨基酸浓度降低了22%。甘油使血浆乙酸和支链氨基酸浓度降低，且甘油对乳蛋白和乳脂肪产量的影响大于玉米，这表明甘油对奶牛的生糖作用比玉米谷物更强。
