风管射流缓解奶牛热应激作用机理与评估模型研究

我国南方夏季持续的高温高湿严重影响奶牛健康水平与生产性能。高温高湿下缓解奶牛热应激研究是畜禽养殖环境调控研究的热点与重点。作为一种高效畜禽舍环控措施，冷风机—纤维风管系统射流送风缓解奶牛热应激的机理研究较为薄弱。本项目以该系统最关键的风管射流为研究对象，通过对风管孔口射流场的数值模拟，揭示风管开孔关键参数（高度、孔径、排数）对射流动力学特性的影响规律；通过对风管射流下奶牛体表散热的数值模拟，探究不同射流初始参数（温度、相对湿度、速度）促进奶牛对流与蒸发散热效率的作用机理；通过开放式散栏饲养奶牛舍现场实验分析射流初始参数、舍内环境因子对奶牛行为、生理指标和生产性能的相关性，并构建射流下奶牛热环境评估模型。本研究旨在从射流动力学特性和奶牛体表散热特征角度深入解析风管射流对缓解奶牛热应激的作用机理，为我国南方开放式奶牛舍科学应用冷风机—纤维风管系统射流送风缓解奶牛热应激提供理论依据和技术基础。

The health status and production capacity of dairy cattle is greatly affected by the hot and humid climate in southern China during summertime. Studies related to the heat stress abatement for dairy cattle under such an extreme environment are hot and important. Cooling fan and perforated air ducting (PAD) system with air-jet into the animal occupied zone is an efficient way for the environment control inside livestock building, however, limited research on the mechanisms of heat stress abatement by the cooled air jet can be found. By means of numerical simulation on the air jet from the perforated duct, the relationships between the key parameters of the duct opening (height, diameter, and row number) and the dynamic characteristics of the air jet will be systematically studied. Meanwhile, with a verified cutaneous heat transfer model of dairy cow, the effects of the air jet key factors on the cutaneous convective heat transfer and evaporative heat transfer will be systematically revealed. Finally, field experiment in a natural ventilated and free stall dairy cattle barn will be carried out to find the relationships among the air jet key factors, the indoor environmental parameters, and the behaviour, physiological response, and production capacity of dairy cattle. With all the findings, an air jet specified and dairy cattle based thermal environmental evaluating model will be developed. The objective of this study is to uncover the mechanisms of PAD air-jet system on the heat stress abatement of dairy cattle considering both the characteristics of air-jet dynamic and cow’s cutaneous heat transfer. This study will provide the theoretical and technical basis of the accurate application of cooling fan and PAD system in the abatement of dairy cattle heat stress in southern China.