Animal & Grassland Research and Innovation Centre, Teagasc, Moorepark, Fermoy, Co. Cork, Ireland.
Animal. 2013 Aug;7(8):1390-400. doi: 10.1017/S1751731113000451. Epub 2013 Mar 27.
Grazing pastures to low post-grazing sward heights (PGSH) is a strategy to maximise the quantity of grazed grass in the diet of dairy cows within temperate grass-based systems. Within Irish spring-calving systems, it was hypothesised that grazing swards to very low PGSH would increase herbage availability during early lactation but would reduce dairy cow performance, the effect of which would persist in subsequent lactation performance when compared with cows grazing to a higher PGSH. Seventy-two Holstein-Friesian dairy cows (mean calving date, 12 February) were randomly assigned post-calving across two PGSH treatments (n = 36): 2.7 cm (severe; S1) and 3.5 cm (moderate; M1), which were applied from 10 February to 18 April (period 1; P1). This was followed by a carryover period (period 2; P2) during which cows were randomly reassigned within their P1 treatment across two further PGSH (n = 18): 3.5 cm (severe, SS and MS) and 4.5 cm (moderate, SM and MM) until 30 October. Decreasing PGSH from 3.5 to 2.7 cm significantly decreased milk (-2.3 kg/cow per day), protein (-95 g/day), fat (-143 g/day) and lactose (-109 g/day) yields, milk protein (-1.2 g/kg) and fat (-2.2 g/kg) concentrations and grass dry matter intake (GDMI; -1.7 kg dry matter/cow per day). The severe PGSH was associated with a lower bodyweight (BW) at the end of P1. There was no carryover effect of P1 PGSH on subsequent milk or milk solids yields in P2, but PGSH had a significant carryover effect on milk fat and lactose concentrations. Animals severely restricted at pasture in early spring had a higher BW and slightly higher body condition score in later lactation when compared with M1 animals. During P2, increasing PGSH from 3.5 to 4.5 cm increased milk and milk solids yield as a result of greater GDMI and resulted in higher mean BW and end BW. This study indicates that following a 10-week period of feed restriction, subsequent dairy cow cumulative milk production is unaffected. However, the substantial loss in milk solid yield that occurred during the period of restriction is not recovered.
放牧至低后茬高度（PGSH）是一种在温带草地系统中使奶牛日粮中采食的牧草数量最大化的策略。在爱尔兰春季产犊系统中，假设放牧至非常低的 PGSH 会增加早期泌乳期的牧草供应，但会降低奶牛的生产性能，与放牧至较高 PGSH 的奶牛相比，这种影响会持续到后续泌乳性能中。72 头荷斯坦弗里森奶牛（平均产犊日期为 2 月 12 日）在产后被随机分配到两个 PGSH 处理组（n = 36）：2.7 厘米（严重；S1）和 3.5 厘米（中度；M1），从 2 月 10 日到 4 月 18 日（第 1 期；P1）实施。这之后是一个持续时间（第 2 期；P2），在此期间，奶牛在其 P1 处理内被随机重新分配到另外两个 PGSH 中（n = 18）：3.5 厘米（严重，SS 和 MS）和 4.5 厘米（中度，SM 和 MM），直到 10 月 30 日。将 PGSH 从 3.5 厘米降低到 2.7 厘米显著降低了牛奶（每天每头减少 2.3 公斤）、蛋白质（每天减少 95 克）、脂肪（每天减少 143 克）和乳糖（每天减少 109 克）的产量、牛奶蛋白质（每天每头减少 1.2 克/公斤）和脂肪（每天每头减少 2.2 克/公斤）的浓度和牧草干物质采食量（每天每头减少 1.7 公斤干物质）。严重的 PGSH 与 P1 结束时的体重（BW）较低有关。P1 PGSH 对 P2 后续牛奶或牛奶固体产量没有持续影响，但 PGSH 对牛奶脂肪和乳糖浓度有显著的持续影响。与 M1 动物相比，早春时在牧场上受到严重限制的动物在后期泌乳期的体重和体况评分略高。在 P2 期间，将 PGSH 从 3.5 厘米增加到 4.5 厘米会由于更高的 GDMI 而增加牛奶和牛奶固体的产量，并导致平均 BW 和终 BW 增加。这项研究表明，在经历了 10 周的饲料限制后，奶牛的累积产奶量不受影响。然而，限制期间发生的大量牛奶固体产量损失并未恢复。
