Department of Animal Science, University of California, Davis 95616.
Department of Land, Air and Water Resources, University of California, Davis 95616.
J Dairy Sci. 2019 Dec;102(12):11504-11522. doi: 10.3168/jds.2019-16543. Epub 2019 Oct 3.
Water is essential in livestock production systems. In typical dairy production systems, 90% of the total water used by a dairy farm is attributed to feed production. Theoretically, ration manipulation is a method to potentially reduce the irrigation water needed for feed crops without dramatically increasing diet costs. However, published quantitative studies on the relationship between feed production and water use that are integrated with linear programming models are scarce. The overall objective of this study was to develop an optimization framework that could achieve a balance between minimization of dietary costs and dietary irrigation water usage, and that could be used as a framework for future research and models for various livestock production systems. Weighted goal programming models were developed to minimize the dietary costs and irrigation water usage for a hypothetical cow under 8 different environmental scenarios. The environmental conditions used a 2 × 2 × 2 factorial design, including 2 atmospheric CO concentrations (400 and 550 ppm), 2 water years (dry and wet), and 2 irrigation methods (furrow and drip). A systematic weighting scheme was used to model the trade-off between minimizing diet cost and minimizing irrigation water use for feedstuffs. Each environmental condition generated a set of distinct diets, which each met the same nutrient requirements of the hypothetical cow but had a different water usage when the weighting scheme was changed from weighting minimum diet costs to minimum irrigation water usage. For water resource planning in areas of dairy production, this set of unique solutions provides the decision maker with different feeding options according to diet cost, water usage, and available feeds. As water was more constrained, dietary dry matter intake increased, concentrations of neutral detergent fiber, ether extract, and energy decreased, and the concentration of lignin increased because less nutritive but more water-saving feedstuffs were included in the diet. Mitigation costs of water usage were calculated from goal programming results and indicated that the potential value of water under water-limited conditions (e.g., in a drought region) was higher than that under water-sufficient conditions. However, a smaller increase in feed costs can initially significantly reduce water usage compared with that of a least-cost diet, which implies that the reduction of water usage through ration manipulation might be possible. This model serves as a framework for the study of irrigation water usage in dairy production and other livestock production systems and for decision-making processes involved in water resources planning in the broader area of animal production.
水是家畜生产系统的基本要素。在典型的奶牛生产系统中，奶牛场总用水量的 90%归因于饲料生产。从理论上讲，通过调整饲料配方，有可能在不显著增加饲料成本的情况下减少饲料作物所需的灌溉用水。然而，关于饲料生产与用水量之间关系的已发表的定量研究，与线性规划模型相结合的研究很少。本研究的总体目标是开发一个优化框架，在最小化日粮成本和日粮灌溉用水量之间取得平衡，并可作为未来各种家畜生产系统的研究和模型的框架。使用加权目标规划模型，在 8 种不同环境情景下，对假设奶牛的日粮成本和灌溉用水量进行最小化。环境条件采用 2×2×2 析因设计，包括 2 种大气 CO2浓度（400 和 550 ppm）、2 个水分年（干旱和湿润）和 2 种灌溉方法（沟灌和滴灌）。系统加权方案用于模拟最小化饲料成本和最小化灌溉用水之间的权衡。每种环境条件都会生成一组不同的日粮，这些日粮都满足假设奶牛的相同营养需求，但当加权方案从最小化日粮成本变为最小化灌溉用水量时，其灌溉用水量也会有所不同。对于奶牛生产区的水资源规划，这组独特的解决方案为决策者提供了根据日粮成本、用水量和可用饲料的不同喂养方案。随着水的约束越来越大，日粮干物质摄入量增加，中性洗涤纤维、乙醚提取物和能量的浓度降低，木质素的浓度增加，因为日粮中包含了更多的非营养但节水的饲料。通过目标规划结果计算了用水缓解成本，并表明在缺水条件下（例如在干旱地区）水的潜在价值高于在水充足条件下的价值。然而，与最低成本日粮相比，初始时饲料成本的较小增加就能显著减少用水量，这意味着通过调整饲料配方减少用水量是可能的。该模型为奶牛生产和其他家畜生产系统的灌溉用水研究以及动物生产更广泛领域的水资源规划中的决策过程提供了一个框架。
