The effects of dietary nonforage fiber sources on production responses of lactating dairy cattle have been well described, but interactions with other components of the diet have been less thoroughly explored. We investigated the effects of adding 2 commonly fed fat sources to a ration featuring high levels of nonforage fiber supplied by a corn milling by-product. Midlactation Holstein cows were blocked by parity, stratified by days in milk, and randomly assigned to 1 of 6 pens (12 cows/pen). Pens were randomly assigned to treatment sequences in a 3 × 3 Latin square design, where the treatments consisted of prilled saturated fat (SAT; Energy Booster 100, Milk Specialties Co., Dundee, IL), calcium salts of long-chain fatty acids (UNS; Megalac, Church and Dwight Co. Inc., Princeton, NJ), or no added dietary fat (control), with fat sources included to provide 1.2% added fat (dry matter basis). Treatment periods were 21 d; milk and feed samples were collected and milk yield and feed intake were recorded for the last 4 d of each period. Results were analyzed with mixed models with pen as the experimental unit, and orthogonal contrasts were employed to evaluate the overall effect of added fat and the effect of fat source. Dry matter intake and milk yield tended to increase with added fat. Protein content decreased with fat supplementation, to a greater degree for UNS than for SAT, but protein yield was not affected. Fat content, fat yield, and energy-corrected milk yield were not affected by treatment. Conversion of feed to milk tended to increase for UNS compared with SAT. Fat supplementation to diets high in nonforage fiber had effects that were similar to those reported for more traditional lactation diets, except for the dry matter intake response.

饮食中非饲用纤维来源对泌乳奶牛生产反应的影响已得到很好的描述，但与饮食中其他成分的相互作用尚未得到充分探讨。我们调查了将两种常用的脂肪来源添加到以玉米碾磨副产品提供的高水平非饲草纤维为特征的日粮中的效果。哺乳期荷斯坦奶牛被胎次封堵，在牛奶中按天分层，并随机分配给6头中的1头（每头12头奶牛）。笔以3×3拉丁方形设计随机分配给治疗顺序，其中的治疗包括小球状饱和脂肪（SAT； Energy Booster 100，Milk Specialties Co.，Dundee，IL），长链脂肪酸的钙盐（ UNS； Megalac，Church and Dwight Co. Inc.（新泽西州普林斯顿），或不添加饮食脂肪（对照），包括脂肪来源以提供1.2％的添加脂肪（以干物质计）。治疗时间为21天；收集牛奶和饲料样品，并记录每个时期的最后4天的牛奶产量和采食量。使用笔作为实验单位的混合模型分析结果，并采用正交对比评估添加的脂肪的总体效果和脂肪来源的效果。干物质摄入量和牛奶产量往往随脂肪的添加而增加。补充脂肪后蛋白质含量下降，UNS的程度比SAT更大，但蛋白质产量未受影响。脂肪含量，脂肪产量和能量校正的牛奶产量不受治疗的影响。与SAT相比，UNS的饲料转化为牛奶的趋势趋于增加。