Piccioli-Cappelli F, Loor J J, Seal C J, Minuti A, Trevisi E
Istituto di Zootecnica, Facoltà di Scienze Agrarie, Alimentari e Ambientali, Università Cattolica del Sacro Cuore, 29122 Piacenza, Italy.
J Dairy Sci. 2014 Dec;97(12):7788-803. doi: 10.3168/jds.2014-8336. Epub 2014 Oct 29.
Diet composition defines the amount and type of nutrients absorbed by dairy cows. Endocrine-metabolic interactions can influence these parameters, and so nutrient availability for the mammary gland can significantly vary and affect milk yield and its composition. Six dairy cows in early and then late lactation received, for 28 d in a changeover design, 2 diets designed to provide, within the same stage of lactation, similar amounts of rumen fermentable material but either high starch plus sugar (HS) content or low starch plus sugar content (LS). All diets had similar dietary crude protein and calculated supply of essential amino acids. Dry matter intake within each stage of lactation was similar between groups. Milk yield was similar between groups in early lactation, whereas a higher milk yield was observed in late lactation when feeding HS. At the metabolic level, the main difference observed between the diets in both stages of lactation was lower blood glucose in cows fed LS. The lower glucose availability during consumption of LS caused substantial modifications in the circulating and postprandial pattern of metabolic hormones. Feeding LS versus HS resulted in an increase in the ratio of bovine somatotropin to insulin. This increased mobilization of lipid reserves resulted in higher blood concentrations of nonesterified fatty acids and β-hydroxybutyrate, which contributed to the higher milk fat content in both stages of lactation in the LS group. This greater recourse to body fat stores was confirmed by the greater loss of body weight during early lactation and the slower recovery of body weight in late lactation in cows fed LS. The lower insulin to glucagon ratio observed in cows fed LS in early and late lactation likely caused an increase in hepatic uptake and catabolism of amino acids, as confirmed by the higher blood urea concentrations. Despite the higher catabolism of amino acids in LS in early lactation, similar milk protein output was observed for both diets, suggesting similar availability of amino acids for peripheral tissue and mammary gland. The latter could be the result of sparing of amino acids at the gut level due to starch that escaped from the rumen, and to the balanced amino acid profile of digestible protein. This last aspect appears worthy of further research, with the aim to enhance the efficiency of protein metabolism of dairy cows, reducing environmental nitrogen pollution without affecting milk yield potential.
日粮组成决定了奶牛吸收的营养物质的数量和类型。内分泌 - 代谢相互作用会影响这些参数，因此乳腺可利用的营养物质会有显著差异，进而影响产奶量及其组成。六头处于泌乳早期和后期的奶牛，采用转换设计，在28天内分别采食两种日粮，这两种日粮在泌乳的同一阶段提供相似数量的瘤胃可发酵物质，但淀粉加糖含量高（HS）或淀粉加糖含量低（LS）。所有日粮的粗蛋白含量和必需氨基酸的计算供应量相似。泌乳各阶段内两组的干物质摄入量相似。泌乳早期两组的产奶量相似，而在泌乳后期饲喂HS时产奶量更高。在代谢水平上，泌乳两个阶段日粮之间观察到的主要差异是，饲喂LS的奶牛血糖较低。采食LS期间较低的葡萄糖可用性导致代谢激素的循环和餐后模式发生显著变化。与饲喂HS相比，饲喂LS导致牛生长激素与胰岛素的比值增加。这种脂质储备动员的增加导致血液中非酯化脂肪酸和β - 羟基丁酸浓度升高，这使得LS组在泌乳两个阶段的乳脂肪含量更高。饲喂LS的奶牛在泌乳早期体重损失更大，泌乳后期体重恢复较慢，这证实了它们更多地动用了体脂储备。泌乳早期和后期饲喂LS的奶牛胰岛素与胰高血糖素比值较低，这可能导致肝脏对氨基酸的摄取和分解代谢增加，血液尿素浓度较高证实了这一点。尽管泌乳早期LS组氨基酸分解代谢较高，但两种日粮的乳蛋白产量相似，这表明外周组织和乳腺的氨基酸可用性相似。后者可能是由于瘤胃未消化的淀粉在肠道水平上节省了氨基酸，以及可消化蛋白质的氨基酸谱平衡所致。最后这一点似乎值得进一步研究，目的是提高奶牛蛋白质代谢效率，减少环境氮污染，同时不影响产奶潜力。
