Departamento de Producción Animal y Salud de los Sistemas Productivos (IPAV), Facultad de Veterinaria, Universidad de la República, San José, 801000, Uruguay.
Programa de Producción de Leche, Instituto Nacional de Investigación Agropecuaria (INIA), Colonia, 70002, Uruguay.
J Dairy Sci. 2023 Sep;106(9):6060-6079. doi: 10.3168/jds.2022-22743. Epub 2023 Jul 18.
The aim of this study was to evaluate the inclusion of alfalfa grazing during 8 h continuous or partitioned in 2 separated sessions of 4 h after each milking, on nutrient intake, digestibility, ruminal fermentation, feeding behavior, milk production, milk composition, and milk fatty acid profile, in late-lactation cows fed a partial mixed ration (PMR). Twelve dairy cows (193 ± 83 d in milk, 584 ± 71 kg of body weight) were housed in individual outdoor pens and assigned to treatments according to a 3 × 3 Latin square design replicated 4 times. The treatments were as follows: (1) control (T0), cows were fed a total mixed ration (TMR) provided ad libitum 20.0% crude protein (CP), 32.2% neutral detergent fiber (NDF); (2) fed a diet combining a PMR which had the same ingredient composition as the TMR (60% of ad libitum intake) + 1 session of 8 h of pasture (T8), continuous grazing alfalfa (Medicago sativa; 20.6% CP, 35.8% NDF) after the p.m. milking; and (3) PMR (60% of ad libitum intake) + 2 daily sessions of 4 h of access to pasture after each milking (T4+4). The experiment lasted 57 d and was divided into 3 periods of 19 d each. The first 12 d of each period was used for diet adaptation, and the last 7 d was used for data collection. No differences among treatments were observed for any of the productive variables, feeding efficiency, or purine derivatives excretion. Cows in T0 had greater intake and apparent digestibility of dry matter, organic matter, and nonfibrous carbohydrates compared with T4+4 and T8. Compared with T0, alfalfa grazing increased the concentration of C18:1 trans-11 and decreased those of C16:0 and C17:0 in milk fat. Cows in T4+4 consumed 1.1 more kg DM/d of alfalfa and N provided by alfalfa in the diet was 3 percentage points higher compared with T8 cows (266 vs. 229 g/d, respectively). In addition, T4+4 cows had a greater daily range of ruminal pH than T8 (0.73 vs. 0.93), and the highest concentrations of NH-N were recorded during the a.m. grazing session while in T8 cows it occurred during the night. In conclusion, including 8 h of alfalfa grazing in T8 and T4+4 treatments allowed the substitution between 35.8 and 38.7% of the total dry matter intake (DMI) of a PMR (with a similar CP concentration to alfalfa) for pasture, maintaining milk solids production and increasing the C18:1 trans-11 of milk fat compared with a TMR in mid late-lactation cows. In an herbage plus PMR diet, splitting the 1 continuous grazing session of 8 h into 2 sessions of 4 h increased the proportion of energy and N provided by alfalfa pasture and reduced PMR intake, without modifying the total nutrient intake or productive performance of cows.
本研究旨在评估在泌乳后期奶牛的部分混合日粮（PMR）中，连续 8 小时或在每次挤奶后分为 2 次，每次 4 小时进行紫花苜蓿放牧，对养分摄入、消化率、瘤胃发酵、采食行为、产奶量、乳成分和乳脂肪酸组成的影响。12 头奶牛（泌乳 193 ± 83 天，体重 584 ± 71 公斤）被安置在单独的户外围栏中，并根据 3 × 3 拉丁方设计重复 4 次进行分组。处理方法如下：（1）对照组（T0），奶牛自由采食总混合日粮（TMR），粗蛋白（CP）含量 20.0%，中性洗涤纤维（NDF）含量 32.2%；（2）采食组合日粮，其中包含与 TMR 相同成分组成的 PMR（60%自由采食）+ 1 次 8 小时的放牧（T8），在下午挤奶后连续放牧紫花苜蓿（Medicago sativa；CP 20.6%，NDF 35.8%）；（3）PMR（60%自由采食）+ 2 次每日 4 小时的放牧（T4+4），在每次挤奶后进行。试验持续 57 天，分为 3 个 19 天的周期。每个周期的前 12 天用于适应日粮，最后 7 天用于数据收集。与 T0 相比，T4+4 和 T8 组的奶牛产奶量、饲料效率或嘌呤衍生物排泄没有差异。与 T0 相比，T0 组奶牛的干物质、有机物和非纤维碳水化合物的摄入量和表观消化率更高。与 T0 相比，苜蓿放牧增加了乳脂中 C18:1 反式-11 的浓度，降低了 C16:0 和 C17:0 的浓度。与 T8 组相比，T4+4 组奶牛每天多消耗 1.1 公斤 DM 的紫花苜蓿，且紫花苜蓿在日粮中的氮提供量高出 3 个百分点（分别为 266 克/天和 229 克/天）。此外，与 T8 组相比，T4+4 组奶牛的瘤胃 pH 日变化范围更大（0.73 比 0.93），且在 T8 组奶牛中，最高的 NH-N 浓度出现在夜间挤奶期间，而在 T4+4 组奶牛中则出现在上午放牧期间。总之，在 T8 和 T4+4 处理中，包含 8 小时的紫花苜蓿放牧，允许用紫花苜蓿（CP 浓度与 PMR 相似）替代 PMR 总干物质摄入量（DMI）的 35.8%至 38.7%，维持乳固体产量，并增加乳脂中 C18:1 反式-11 的含量，与泌乳后期奶牛的 TMR 相比。在粗饲料+PMR 日粮中，将连续 8 小时的 1 次放牧分为 2 次 4 小时的放牧，可以增加紫花苜蓿牧场提供的能量和氮的比例，减少 PMR 的摄入量，而不改变奶牛的总养分摄入量或生产性能。
