Gregorini P, Eirin M, Refi R, Ursino M, Ansin O E, Gunter S A
Southwest Research and Extensions Center, Division of Agriculture, University of Arkansas, Hope 71801, USA.
J Anim Sci. 2006 Jul;84(7):1943-50. doi: 10.2527/jas.2005-537.
The timing of grazing bouts (GB) determines how cattle allot time to meet their nutritional needs. Net photosynthesis and evapotranspirational losses increase herbage nonstructural carbohydrate and DM concentrations, which may lead to longer and more intense GB at dusk. Hence, linking the grazing pattern, plant phenology, and herbage allocation time emerges as an option to manipulate the GB and nutrient intake. The objectives of this work were to analyze grazing behavior and performance of beef heifers when herbage allocation was at 0700 each morning (MHA) or at 1500 each afternoon (AHA). Two pairs of experiments were conducted during the winter and spring examining behavior and performance. Measurements were grazing, rumination, and idling times during daylight hours, and their patterns, as well as bite rate, ADG, change in BCS, and daily herbage DMI. In the behavioral experiments, 8 heifers strip-grazed annual ryegrass (Lolium multiflorum Lam.). The grazing, rumination, and idling times as well as bite rate were measured and also analyzed per time of day. In the performance experiments, 48 beef heifers strip-grazed annual ryegrass in 2 groups according to treatments. Daily DMI, ADG, and changes in BCS were analyzed. The AHA increased daily idling time (P < 0.01) and decreased grazing time (P < 0.01). The AHA concentrated grazing time in the evening, when bite rate was greater (P < 0.01). The daylight rumination time varied by time of day (P < 0.01), but total daylight rumination time did not differ (P = 0.11). With AHA, rumination time and idling time were concentrated in the morning and afternoon. In the performance experiment during the winter, there was a treatment x week effect (P < 0.01) for ADG and change in BCS. Beginning in wk 4, heifers in AHA gained 150 g of BW and 0.0145 points of BCS more than those in MHA (P < 0.05) per day. In the spring, AHA increased ADG by 549 g and 0.0145 points of BCS more than those in MHA (P < 0.05) per day during the entire 6 wk. The herbage DMI (kg/d) did not differ in winter (AHA, 5.0 vs. MHA, 4.5) or spring (AHA, 5.6 vs. MHA, 5.0). These results suggest that timing of herbage allocation alters grazing, rumination, and idling patterns; AHA leads to longer and more intense GB when herbage has greater quality, which improves cattle performance.
放牧时段（GB）的时间安排决定了牛如何分配时间以满足其营养需求。净光合作用和蒸散损失会增加牧草的非结构性碳水化合物和干物质浓度，这可能导致在黄昏时出现更长且更密集的放牧时段。因此，将放牧模式、植物物候和牧草分配时间联系起来成为一种控制放牧时段和营养摄入的选择。本研究的目的是分析当每天早上0700（早饲组，MHA）或每天下午1500（午饲组，AHA）进行牧草分配时，肉用小母牛的放牧行为和生产性能。在冬季和春季进行了两组实验，以研究行为和生产性能。测量了白天的放牧、反刍和空闲时间及其模式，以及采食量、平均日增重（ADG）、体况评分（BCS）变化和每日牧草干物质采食量（DMI）。在行为实验中，8头小母牛对一年生黑麦草（多花黑麦草，Lolium multiflorum Lam.）进行条带放牧。测量并分析了放牧、反刍和空闲时间以及采食量在一天中不同时间的情况。在生产性能实验中，48头肉用小母牛根据处理分为2组，对一年生黑麦草进行条带放牧。分析了每日DMI、ADG和BCS的变化。午饲组增加了每日空闲时间（P < 0.01），并减少了放牧时间（P < 0.01）。午饲组将放牧时间集中在晚上，此时采食量更大（P < 0.01）。白天反刍时间随时间变化（P < 0.01），但白天总反刍时间无差异（P = 0.11）。采用午饲组时，反刍时间和空闲时间集中在上午和下午。在冬季的生产性能实验中，ADG和BCS变化存在处理×周效应（P < 0.01）。从第4周开始，午饲组的小母牛每天比早饲组多增重150 g体重，BCS增加0.0145分（P < 0.05）。在春季，整个6周期间，午饲组比早饲组每天ADG多增加549 g，BCS增加0.0145分（P < 0.05）。冬季（午饲组，5.0 vs. 早饲组，4.5）和春季（午饲组，5.6 vs. 早饲组，5.0）的牧草DMI（kg/d）无差异。这些结果表明，牧草分配时间改变了放牧、反刍和空闲模式；当牧草质量更高时，午饲组会导致更长且更密集的放牧时段，从而提高牛的生产性能。
