Gregorini P, Clark C E F, Jago J G, Glassey C B, McLeod K L M, Romera A J
DairyNZ, Private Bag 3221, Hamilton, New Zealand.
J Dairy Sci. 2009 Sep;92(9):4572-80. doi: 10.3168/jds.2009-2322.
This study investigated the effect of restricting grazing time on circulating concentrations of ghrelin, nonesterified fatty acids (NEFA), and glucose before, and foraging behavior of dairy cows during, the first grazing session of the day (GS, 0800-1200 h). Forty-eight Holstein-Friesian cows (470 +/- 47 kg of BW; 35 +/- 9 d in milk) were strip-grazed on a perennial ryegrass pasture for either 4 h after each milking (2 x 4), 8 h between milkings (1 x 8), or the 24-h period excluding milking times (CTL). Cows were bled before the GS; plasma was analyzed for ghrelin and serum for glucose and NEFA. Herbage mass was measured pregrazing (0730 h), during and at the end of the GS (1200 h), and postgrazing (24 h after the first measurement). Herbage mass data were fitted to a model to estimate herbage disappearance rates. Herbage intake and bite mass were calculated using herbage mass disappearance and behavioral measurements. Bite rate, eating, searching, ruminating, and idling time were determined during the GS for each cow. No difference in glucose concentration was found between treatments. Concentrations of NEFA and ghrelin were the greatest for cows in the 1 x 8 treatment. Daily herbage intake did not differ between treatments; however, during the GS 1 x 8 had a greater herbage intake than 2 x 4 and CTL. Bite mass differed between treatments and throughout the GS. Bite mass was smallest for CTL during the first 60 min and greatest during the last 90 min, when cows in the 2 x 4 treatment had the smallest bite mass. Cows in 1 x 8 spent the longest time eating and the least time searching and ruminating. Eating time was greatest for 1 x 8 during the first 60 and last 90 min of the GS. Searching time only differed in the second 60 min, when it was the lowest for 1 x 8. Cows from all treatments did not ruminate during the first 120 min. Cows in CTL had the greatest rumination time during the last 90 min. The model fitted to represent dynamics of herbage mass disappearance presented differences in the fractional herbage disappearance rate. There was an interaction between treatment and time in herbage depletion rate. The results of this study present a fuller picture of foraging dynamics during the first 4 h of grazing and its potential relationship with physiological markers of hunger as affected by grazing management.
本研究调查了限制放牧时间对奶牛在一天中首次放牧时段（GS，08:00 - 12:00）前生长激素释放肽、非酯化脂肪酸（NEFA）和葡萄糖循环浓度的影响，以及放牧期间的采食行为。48头荷斯坦 - 弗里生奶牛（体重470±47千克；产奶35±9天）在多年生黑麦草牧场上进行条带放牧，挤奶后放牧4小时（2×4）、挤奶间隔放牧8小时（1×8）或排除挤奶时间的24小时（CTL）。在GS前采集奶牛血液；分析血浆中的生长激素释放肽以及血清中的葡萄糖和NEFA。在放牧前（07:30）、GS期间和结束时（12:00）以及放牧后（首次测量后24小时）测量牧草量。将牧草量数据拟合到一个模型中以估计牧草消失率。使用牧草量消失和行为测量数据计算牧草摄入量和咬食量。在GS期间测定每头奶牛的咬嚼率、采食、搜寻、反刍和空闲时间。各处理间葡萄糖浓度无差异。1×8处理的奶牛NEFA和生长激素释放肽浓度最高。各处理间每日牧草摄入量无差异；然而，在GS期间，1×8的牧草摄入量高于2×4和CTL。各处理间以及整个GS期间咬食量存在差异。CTL在最初60分钟内咬食量最小，在最后90分钟内最大，此时2×4处理的奶牛咬食量最小。1×8的奶牛采食时间最长，搜寻和反刍时间最短。在GS的最初60分钟和最后90分钟内，1×8的采食时间最长。仅在第二个60分钟内搜寻时间存在差异，此时1×8的搜寻时间最短。所有处理的奶牛在最初120分钟内均不反刍。CTL的奶牛在最后90分钟内反刍时间最长。用于表示牧草量消失动态的模型显示了牧草消失率分数的差异。牧草消耗率存在处理与时间的交互作用。本研究结果更全面地呈现了放牧前4小时的采食动态及其与受放牧管理影响的饥饿生理指标之间的潜在关系。
