Hanigan M D, Palliser C C, Gregorini P
Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
J Dairy Sci. 2009 Oct;92(10):5043-56. doi: 10.3168/jds.2008-1922.
The model of R. L. Baldwin predicts various aspects of digestion and metabolism in the cow including nutrient partitioning between milk and body stores. However, prediction bias has been observed for body weight (BW) and body condition score (BCS) when diets of differing energy density are simulated over long periods. Originally, the model overpredicted BW loss in early lactation and gain in late lactation. This bias was reversed and limited to early lactation when a better representation of milk synthesis capacity was introduced into the model. It was hypothesized that a better representation of the effects of energy status on anabolic and catabolic hormones and a more complete representation of metabolic demands and growth associated with pregnancy would help in improving predictions of body tissue mobilization in early lactation. Providing independent glucose reference points and independent sensitivity scalars for the 3 hormones driven by glucose concentrations improved overall model precision. These improvements were primarily realized through reductions in prediction errors for blood glucose concentrations and BCS. In both cases, slope bias associated with the predictions was reduced, indicating that the changes in representation were beneficial although BCS bias was not completely removed. Milk component yields were predicted with slightly greater mean and slope bias. The addition of enhanced pregnancy calculations did not provide apparent additional benefit relative to model prediction errors. However, the data used for the assessments did not include observations from the last 60 d of gestation, where BW gain and metabolic demand associated with pregnancy would be expected to be greater. Improvements in BCS were not observed when the revised model was tested using an independent data set. Predictions of blood fatty acids, the rate of BCS and BW loss, and milk fat yields in early lactation were still inappropriate and require further work. The results could be caused by inaccurate early lactation intakes, the aggregated representation of blood fatty acids, or an inadequate representation of peripheral insulin resistance during early lactation.
R. L. 鲍德温模型预测奶牛消化和代谢的各个方面，包括牛奶与身体储备之间的营养分配。然而，当长期模拟不同能量密度的日粮时，观察到体重（BW）和体况评分（BCS）存在预测偏差。最初，该模型高估了泌乳早期的体重损失和泌乳后期的体重增加。当将更好的牛奶合成能力表示引入模型时，这种偏差得到了扭转，并且仅限于泌乳早期。据推测，更好地表示能量状态对合成代谢和分解代谢激素的影响，以及更完整地表示与妊娠相关的代谢需求和生长，将有助于改善对泌乳早期身体组织动员的预测。为受葡萄糖浓度驱动的3种激素提供独立的葡萄糖参考点和独立的敏感性标量，提高了整体模型精度。这些改进主要是通过降低血糖浓度和BCS的预测误差来实现的。在这两种情况下，与预测相关的斜率偏差都有所降低，这表明表示方式的改变是有益的，尽管BCS偏差并未完全消除。牛奶成分产量的预测平均偏差和斜率偏差略大。相对于模型预测误差，增加强化妊娠计算并没有提供明显的额外益处。然而，用于评估的数据不包括妊娠最后60天的观察结果，预计在这期间与妊娠相关的体重增加和代谢需求会更大。当使用独立数据集测试修订后的模型时，未观察到BCS的改善。泌乳早期血液脂肪酸、BCS和BW损失率以及乳脂产量的预测仍然不合适，并需要进一步研究。结果可能是由于泌乳早期摄入量不准确、血液脂肪酸的综合表示，或泌乳早期外周胰岛素抵抗表示不足所致。
