Valadares Filho S C, Broderick G A, Valadares R F, Clayton M K
Universidade Federal de Viçosa, MG, Brazil.
J Dairy Sci. 2000 Jan;83(1):106-14. doi: 10.3168/jds.S0022-0302(00)74861-2.
Twenty-four multiparous lactating Holstein cows were blocked by days in milk and assigned to treatment sequences in a replicated 4x4 Latin square with 21-d periods. The four diets, formulated from alfalfa silage plus a concentrate mix based on ground high moisture ear corn, contained [dry matter (DM) basis]: 1) 20% concentrate, 80% alfalfa silage (24% nonfiber carbohydrates; NFC), 2) 35% concentrate, 65% alfalfa silage (30% NFC), 3) 50% concentrate, 50% alfalfa silage (37% NFC), or 4) 65% concentrate, 35% alfalfa silage (43% NFC). Soybean meal and urea were added to make diets isonitrogenous with equal nonprotein N (43% of total N). Intake of DM and milk yield indicated that adaptation was complete within 7 d of changing the diets within the Latin square. There were linear increases in apparent digestibility of DM and organic matter, and a linear decrease in neutral detergent fiber (NDF) digestibility with increasing dietary NFC. Solutions of significant quadratic equations yielded estimated maxima for intake of DM, organic matter, digestible organic matter, and NDF at, respectively, 37, 38, 43, and 27% dietary NFC. There were linear increases in yields of milk, protein, lactose, and solids not fat with increasing dietary NFC. Feed efficiency (milk/DM intake) yielded a quadratic response with a minimum at 27% dietary NFC. Maxima for milk fat content, fat yield, and fat-corrected milk yield were estimated to occur at, respectively, 30, 34 and 38% dietary NFC. In this short-term trial, maximal DM intake and fat-corrected milk yield indicated that the optimum concentrate for cows fed high moisture ear corn plus alfalfa silage as the only forage was equivalent to 37 to 38% dietary NFC; however, yields of milk, protein and solids not fat were still increasing at 65% dietary concentrate (43% NFC).
24头经产泌乳荷斯坦奶牛按产奶天数进行分组，并被分配到一个重复的4×4拉丁方试验设计中，每个试验期为21天。这四种日粮由苜蓿青贮料加上以高水分玉米芯为基础的精料混合料配制而成，其干物质（DM）含量分别为：1）20%精料，80%苜蓿青贮料（非纤维碳水化合物含量为24%；NFC）；2）35%精料，65%苜蓿青贮料（NFC含量为30%）；3）50%精料，50%苜蓿青贮料（NFC含量为37%）；4）65%精料，35%苜蓿青贮料（NFC含量为43%）。添加豆粕和尿素以使日粮粗蛋白含量相等且非蛋白氮含量相同（占总氮的43%）。干物质采食量和产奶量表明，在拉丁方内更换日粮7天内适应期结束。随着日粮NFC含量增加，干物质和有机物的表观消化率呈线性增加，中性洗涤纤维（NDF）消化率呈线性下降。显著二次方程的解表明，日粮NFC含量分别为37%、38%、43%和27%时，干物质、有机物、可消化有机物和NDF采食量的估计最大值出现。随着日粮NFC含量增加，牛奶、蛋白质、乳糖和非脂固形物产量呈线性增加。饲料效率（奶产量/干物质采食量）呈二次反应，日粮NFC含量为27%时最低。估计日粮NFC含量分别为30%、34%和38%时，乳脂含量、乳脂产量和校正乳产量达到最大值。在这个短期试验中，最大干物质采食量和校正乳产量表明，以高水分玉米芯加苜蓿青贮料作为唯一粗饲料饲养奶牛时，最佳精料含量相当于日粮NFC的37%至38%；然而，日粮精料含量为65%（NFC含量为43%）时，牛奶、蛋白质和非脂固形物产量仍在增加。
