Davis M E, Rutledge J J, Cundiff L V, Hauser E R
J Anim Sci. 1983 Oct;57(4):832-51. doi: 10.2527/jas1983.574832x.
Weights and individual feed consumption collected on 160 beef, dairy and beef X dairy dams and their progeny were used to estimate several measures of lifetime cow efficiency. Dams were fed either a high or a low energy diet. Efficiency was expressed as the ratio of outputs to inputs. Outputs included progeny weaning weights plus cow salvage weight, and inputs were progeny creep feed consumption plus the dam's lifetime feed consumption. In the first approach, life cycle cow efficiency was estimated by expressing weight output as a ratio to feed inputs when weights and feed consumptions were weighted by their probabilities; probabilities were a function of age distribution and percentage calf crop in a theoretical herd consisting of 100 cows and 20 yearling replacement heifers. In the second approach, actual lifetime cow efficiency was estimated by expressing weight outputs as a ratio to feed inputs when all components were weighted equally. Both approaches included efficiency estimates calculated with and without cow salvage value. Dams receiving low energy diets generally had lifetime efficiencies equal or superior to those fed high energy diets in spite of older ages at calving. Dams on the high energy diet had greater salvage value, but did not wean calves of sufficient additional size to offset their own increased metabolizable energy (ME) intake. Dam breeds and breed crosses of smaller size tended to be more efficient than those of large size, demonstrating the effectiveness of mating small dams to large sire breeds for improving cow efficiency. Breeds calving at later ages were less efficient. Efficiency ratios improved as number of progeny weaned increased.
收集了160头肉牛、奶牛以及肉牛与奶牛杂交母牛及其后代的体重和个体采食量，用于估算母牛一生效率的若干指标。母牛被饲喂高能量或低能量日粮。效率以产出与投入的比率来表示。产出包括后代断奶体重加上母牛的残值体重，投入则是后代早期补饲采食量加上母牛一生的采食量。在第一种方法中，当体重和采食量按其概率加权时，通过将体重产出表示为饲料投入的比率来估算生命周期母牛效率；概率是年龄分布以及由100头母牛和20头一岁龄后备母牛组成的理论牛群中犊牛出生率的函数。在第二种方法中，当所有成分均等加权时，通过将体重产出表示为饲料投入的比率来估算实际的一生母牛效率。两种方法都包括有和没有母牛残值时计算的效率估计值。尽管产犊时年龄较大，但接受低能量日粮的母牛一生效率通常等于或优于接受高能量日粮的母牛。接受高能量日粮的母牛有更高的残值，但所产犊牛额外增加的体重不足以抵消其自身增加的可代谢能量（ME）摄入量。体型较小的母牛品种及其杂交品种往往比体型较大的更高效，这表明将小型母牛与大型公牛品种交配对于提高母牛效率是有效的。产犊较晚的品种效率较低。随着断奶后代数量的增加，效率比率提高。
