Numerous climatic indices have been utilized to predict the effect of hot, and cold, climatic conditions on animal production and welfare. To date, the dairy industry has relied extensively on the Temperature Humidity Index (THI) to predict adverse climatic conditions; however, neither solar radiation nor air movement is accounted for in the THI equation. The Dairy Heat Load Index (DHLI) was initially developed as an alternative climate index. In its current format, the DHLI does not account for the effects of heat load mitigation strategies, such as shade, which decreases the negative effects of hot climatic conditions on lactating cows. Therefore, this experiment aimed to determine the effectiveness of the DHLI as a predictor of heat load responses in both shaded and unshaded cows, as compared with the THI. Forty lactating Holstein Friesian (n = 40) cows were selected and paired based on live weight, milk yield, and days in milk. One cow from each pair was randomly allocated to one of two treatments: shaded (n = 20) or unshaded (n = 20). Cows were given 7 days to acclimate prior to the commencement of data collection. After 28 days, cows were transitioned into the alternate treatment in a crossover design and given 7 days to acclimate prior to data collection. Behavioral observations (0800, 1200, 1400, and 1800 h daily), daily milk yield (kg), milk composition (various days), and vaginal temperature (T_VAG, °C; 5 pairs/week, over a 4-week rotation) were recorded. Overall, data from this experiment indicated that the DHLI was a better predictor of standing and feeding behaviors in unshaded cows and drinking behaviors in shaded cows. Conversely, the THI was a better predictor of standing behavior and shade usage in shaded cows. Furthermore, the THI was a better predictor of mean panting score (MPS) in shaded cows, whereas the DHLI performed better in unshaded cows. Additionally the DHLI was a better predictor of T_VAG in these cows. Finally, when evaluating the 7-day average of each climatic index, the DHLI was a better predictor of change in milk yield. Incorporation of additional animal and management factors is required if the DHLI is to become an effective heat load management tool.

许多气候指数已被用来预测炎热和寒冷气候条件对动物生产和福利的影响。迄今为止，乳制品行业广泛依赖温湿度指数 ( THI ) 来预测不利的气候条件；然而，在THI方程中既没有考虑太阳辐射也没有考虑空气运动。乳制品热负荷指数 ( DHLI ) 最初​​是作为替代气候指数开发的。在目前的格式中，DHLI没有考虑减轻热负荷策略的影响，例如遮荫，它可以减少炎热气候条件对泌乳奶牛的负面影响。因此，本实验旨在确定DHLI的有效性与THI相比，作为阴影和无阴影奶牛热负荷反应的预测因子。 根据活重、产奶量和产奶天数，选择并配对 40 头泌乳荷斯坦弗里西亚 ( n = 40) 奶牛。每对中的一头奶牛被随机分配到两种处理中的一种：阴影（n  = 20）或无阴影（ n  = 20）。在开始数据收集之前，让奶牛适应 7 天。28 天后，奶牛在交叉设计中过渡到替代治疗，并在数据收集前给予 7 天适应环境。行为观察（每天 0800、1200、1400 和 1800 小时）、每日产奶量 (kg)、牛奶成分（不同天数）和阴道温度 ( T _VAG, °C; 5 对/周，在 4 周的轮换中）被记录下来。总体而言，该实验的数据表明，DHLI可以更好地预测无遮蔽奶牛的站立和采食行为以及遮蔽奶牛的饮水行为。相反，THI可以更好地预测遮荫奶牛的站立行为和遮荫使用情况。此外，THI是阴影奶牛平均喘气分数 (MPS) 的更好预测指标，而DHLI在无阴影奶牛中表现更好。此外，DHLI是这些奶牛中T _VAG的更好预测指标。最后，在评估每个气候指数的 7 天平均值时，DHLI是牛奶产量变化的更好预测指标。如果DHLI要成为有效的热负荷管理工具，则需要结合额外的动物和管理因素。