Fifty-six Holstein-Friesian cows were used in a randomized complete block design to test the effects of supplemental energy from protein (PT) and fat (FT) on lactation performance and nutrient digestibility in a 2 × 2 factorial arrangement. During the control period, cows were adapted for 28 d to a basal total mixed ration consisting of 34% grass silage, 33% corn silage, 5% grass hay, and 28% concentrate on a dry matter (DM) basis. Experimental rations were fed for 28 d immediately following the control period and consisted of (1) low protein, low fat (LP/LF), (2) high protein, low fat (HP/LF), (3) low protein, high fat (LP/HF), or (4) high protein and high fat (HP/HF). To obtain the HP and HF diets, intake of the basal ration was restricted and supplemented isoenergetically (net energy basis) with 2.0 kg/d of rumen-protected protein (soybean + rapeseed, 50:50 mixture on DM basis) and 0.68 kg/d of hydrogenated palm fatty acids (FA) on a DM basis. Milk production and composition, nutrient intake, and apparent digestibility were measured during the final 7 d of the control and experimental periods. No interaction was found between PT and FT on milk production and composition. Yields of milk, fat- and protein-corrected milk, and lactose increased in response to PT and FT and lactose concentration was unaffected by treatment. Milk protein concentration and yield increased in response to PT, and protein yield tended to increase in response to FT. Milk fat concentration and yield increased in response to FT and were unaffected by PT. Milk urea concentration increased and nitrogen efficiency decreased in response to PT. Feed and nitrogen efficiency were highest on the LP/HF diet and both parameters increased in response to FT, whereas milk urea concentration was not affected by FT. Energy from fat increased the concentration and yield of ≥16-carbon FA in milk and decreased the concentration of FA synthesized de novo, but had no effect on their yield. Concentration and yield of de novo-synthesized FA increased in response to PT. Concentration and yield of polyunsaturated FA increased and decreased in response to PT and FT, respectively. Apparent total-tract digestibility of crude fat decreased in response to PT, and FT increased crude protein digestibility. Energy supplementation through rumen-inert hydrogenated palm FA appears to be an efficient feeding strategy to stimulate milk production with regard to feed and nitrogen efficiency compared with supplementing an isoenergetic level of rumen-protected protein.

在随机完整区组设计中，使用56头荷斯坦-弗里斯兰奶牛，以2×2因子排列方式测试蛋白质（PT）和脂肪（FT）的补充能量对泌乳性能和营养物质消化率的影响。在对照期间，将母牛适应基础总混合日粮28天包括34％的草料青贮饲料，33％的玉米青贮料，5％的草料干草和28％的干物质（DM）精矿。在控制期之后立即饲喂28 d的实验定量饲料，其中包括（1）低蛋白，低脂（LP / LF），（2）高蛋白，低脂（HP / LF），（3）低蛋白，高脂脂肪（LP / HF），或（4）高蛋白和高脂肪（HP / HF）。要获得HP和HF饮食，必须限制基础饮食的摄入，并以等能量的方式（以净能量为基础）补充2.0 kg / d的瘤胃保护蛋白（大豆+油菜籽，以DM为基础的50:50混合物）和0.68 kg / d基于DM的氢化棕榈脂肪酸（FA）。牛奶的产量和成分，营养摄入量，在对照和实验期的最后7天内测量了表观消化率。PT和FT之间在牛奶产量和成分上未发现相互作用。牛奶，经脂肪和蛋白质校正的牛奶以及乳糖的产量随PT和FT的增加而增加，乳糖浓度不受处理的影响。乳蛋白浓度和产量随着PT的增加而增加，而蛋白产量则随着FT的增加而增加。牛奶脂肪浓度和产量随FT的增加而增加，不受PT的影响。牛奶尿素PT会增加浓度，降低氮效率。LP / HF日粮的饲料和氮效率最高，并且两个参数均响应FT而增加，而牛奶尿素浓度不受FT影响。脂肪中的能量增加了牛奶中≥16碳FA的浓度和产量，降低了从头合成的FA的浓度，但对它们的产量没有影响。从头合成的FA的浓度和产率随PT的增加而增加。多不饱和FA的浓度和产率分别响应于PT和FT而增加和降低。PT引起的粗脂肪表观总消化率降低，FT引起的粗脂肪消化率降低蛋白质消化率。与补充瘤胃保护蛋白的等能量水平相比，通过瘤胃惰性氢化棕榈FA补充能量似乎是刺激饲料和氮效率的乳汁生产的有效喂养策略。