Department of Animal and Poultry Science, University of Guelph, Kemptville Campus, 830 Prescott Street, Kemptville, ON, Canada, K0G 1J0.
J Dairy Sci. 2011 Aug;94(8):4039-45. doi: 10.3168/jds.2011-4264.
The objectives of this study were to determine if feed sorting differs between primiparous (PP) and multiparous (MP) cows, if sorting changes from the period of peak lactation to peak dry matter intake (DMI), and whether feed sorting affects efficiency of production. Data on DMI, milk production, feed sorting (particle size of offered and refused feed), and energy status (plasma nonesterified fatty acid, β-hydroxybutyrate, insulin and glucose concentration) were collected on 30 PP and 30 MP lactating Holstein dairy cows, individually housed and fed in tie-stalls, during 3 wk (wk 2, 6, and 10) over 10 wk of a lactation study. Cows averaged 53, 81, and 109±10 d in milk (DIM) at the beginning of each of the 3 recording weeks. To determine sorting, feed samples were separated with a particle separator that had 3 screens (19, 8, and 1.18 mm) and a bottom pan, resulting in 4 fractions (long, medium, short, fine). Over the study period, MP cows consumed more DM and produced more milk than did the PP cows, but had similar efficiency of production (kg of milk/kg of DMI), and similar levels of plasma indicators of energy status. Across the study period, DMI increased, whereas milk yield decreased, resulting in decreased efficiency of milk production as cows moved further into lactation. All cows had higher nonesterified fatty acid and lower insulin concentrations in plasma at 53 DIM compared with at 81 and 109 DIM, suggesting they were mobilizing more body fat at that earlier stage of lactation. Across periods, all cows sorted against the longest ration particles, did not sort the medium ration particles, and sorted for fine ration particles; as a result, all cows consumed less neutral detergent fiber (NDF) and physically effective NDF (proportion of NDF retained on the 19- and 8-mm screens of the particle separator) than predicted. Greater selection against the longest ration particles was associated with greater efficiency of milk production; however, this sorting pattern also tended to be associated with lower milk fat percentage. The extent of the observed sorting against the longest, physically effective ration particles and for the finest ration particles was greater for PP cows than for MP cows across all 3 observation periods. Feed sorting remained consistent in cows across the DIM evaluated in this study and that this sorting behavior can affect the efficiency of milk production as well as milk fat percentage. Further, PP cows engage in more sorting of their ration than MP cows.
本研究的目的是确定初产（PP）和经产（MP）奶牛之间是否存在饲料分选差异，以及这种分选是否会从泌乳高峰期到干物质采食量（DMI）高峰期发生变化，以及饲料分选是否会影响生产效率。在一项泌乳研究的 10 周内，我们在 3 周（第 2、6 和 10 周）期间，分别对 30 头初产和 30 头经产荷斯坦泌乳奶牛进行了 DMI、产奶量、饲料分选（提供和拒绝的饲料的粒径）和能量状态（血浆非酯化脂肪酸、β-羟丁酸、胰岛素和血糖浓度）的数据收集。在每个记录周的开始时，奶牛的泌乳天数（DIM）平均为 53、81 和 109±10d。为了确定分选，使用具有 3 个筛网（19、8 和 1.18mm）和底部锅的颗粒分离器将饲料样品分开，得到 4 个部分（长、中、短、细）。在整个研究期间，MP 奶牛的 DM 摄入量和产奶量均高于 PP 奶牛，但生产效率（每公斤 DMI 的产奶量）和血浆能量状态指标水平相似。在整个研究期间，DMI 增加，而产奶量减少，导致随着奶牛进入泌乳后期，产奶效率降低。与 81 和 109DIM 相比，所有奶牛在 53DIM 时血浆中非酯化脂肪酸浓度较高，胰岛素浓度较低，表明它们在泌乳早期阶段更多地动员体脂。在整个时期，所有奶牛对最长的日粮颗粒进行了分选，对中等日粮颗粒没有进行分选，对细颗粒日粮进行了分选；因此，所有奶牛的中性洗涤纤维（NDF）和物理有效 NDF（颗粒分离器 19 和 8mm 筛网保留的 NDF 比例）的摄入量均低于预测值。对最长日粮颗粒的选择程度与产奶效率的提高有关；然而，这种分选模式也往往与较低的乳脂百分比有关。在所有 3 个观察期内，PP 奶牛对最长、物理有效日粮颗粒和最细日粮颗粒的观察分选程度大于 MP 奶牛。在本研究中评估的 DIM 范围内，奶牛的饲料分选保持一致，这种分选行为会影响产奶效率和乳脂百分比。此外，PP 奶牛比 MP 奶牛更倾向于对其日粮进行分选。
