Variation among regeon and season in energy balance of grazing haifers.

高羊茅放牧草地光能固定效率的季节变化被查在1986- 1987年3月下旬至10月下旬的整个生长季中，入射太阳能的0.78%（分别为3017 GJ/10a和2843 GJ/10a）固定在牧草中，0.76%被放牧的荷斯坦小母牛消耗，0.021%保留在小母牛体内。在植物和动物生长的各个阶段，能量转换效率值均以春季放牧季最高，夏季放牧季最低，牧草供能（HA）、基于禁食代谢的放牧强度（GI）和牧草能量消耗（HCE）之间的关系可用下列方程表示：春、秋季HCE=12.3GI-49.2GI^2/HA-0.709（R^2=0.94）夏季HCE=-3.58GI+46.7GI^2/HA+3.43（R^2=0.69）这里的HA是HCE和每个放牧期结束时剩余未吃的可利用牧草量之和。根据ARC（1980）的方法计算了禁食代谢，认为与气温呈负相关的HCE和IVDMD的季节变化是引起放牧辅助植物次级生产光能转化效率季节变化的主要原因。

Seasonal changes in efficiency of solar energy fixed on grazed pasture of tallfescue (Festuca arundinacea Schreb.) was investigated. Threughout growing season from late March until late October in 1986-1987,0.78% of incident solar energy (3017 GJ/10a and 2843 GJ/10a, respectively) was fixed in herbage available, 0.76% was consumed by grazing Holstein heifers and 0.021% was retained in heifers'body. At every step of energy conversion in plant and animal growth, the values of efficiencies were highest in spring grazing season and lowest in summer grazing season.Relation among herbage energy supply (HA), grazing intensity (GI) based on fasting metabolism, and consumed herbage energy (HCE) was expressed as followsing equations :in spring and autumn HCE=12.3GI-49.2GI^2/HA-0.709 (R^2=0.94)in summer HCE=-3.58GI+46.7GI^2/HA+3.43 (R^2=0.69)Here, the HA is the sum of HCE and the amount of residual herbage available left uneaten at the end of each grazing peirod. Fasting metabolism was calculated by ARC (1980)'s method.These seasonal variation in both HCE and IVDMD,which were relating negatively with air temperature, were regarded to be a main cause of the seasonal change in solar energy conversion efficiency for secondary production of grazing helfers.