Author : Grazyne Tresoldi
Publisher :
ISBN 13 : 9780438628489
Total Pages : pages
Book Rating : 4.6/5 (284 download)
Book Synopsis Mitigating Heat Stress in Lactating Dairy Cows by : Grazyne Tresoldi
Download or read book Mitigating Heat Stress in Lactating Dairy Cows written by Grazyne Tresoldi and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The US dairy industry loses millions of dollars every year due to problems associated with high heat load such as reduced milk production and cattle mortality. Although dairy farmers provide their cattle with heat abatement resources (shade, sprayed water, fans), economic losses associated with heat load indicate a problem is ongoing in the US dairy industry, suggesting the strategies used are not effectively cooling the cows. In fact, little is known about how heat abatement resources are provided in commercial situations (i.e., quantity and quality), nor their effectiveness. Thus, identifying dairy cattle experiencing high heat load and adopting appropriate mitigation strategies can lead to improvements in animal welfare and profitability. In addition to finding more effective heat abatement strategies for cattle, changes in weather patterns have raised concerns about the use of potable water in agriculture. In the US, 75% of the large dairies use sprayed water to relieve heat load during summer. The widespread use of water indicates that there are opportunities to improve the efficiency of water use and cow cooling. Aspects of spray management (i.e., flow rate, temperature threshold the spray is activated and timing) can affect the quantity of water used; however, their effects of cooling effectiveness are variable. For example, using higher flow rates increases water use but that does not necessarily translate into more cooling. Manipulating timing has a potential to affect water use and cooling effectiveness – as it is connected to how the spray cools the cows. The objectives of this dissertation were to describe the provision of heat abatement resources as well as behavioral and physiological responses to heat load in commercial dairies, and to evaluate the cooling effectiveness of different spray strategies. In Chapter 1, I investigated the accuracy of sampling strategies to measure responses to heat load in lactating cows during the warmest part of the day. In this study, I found that behavioral and physiological responses can be sampled as often as every 30 min without compromising the accuracy of results. In Chapter 2, I describe the diversity of provision of heat abatement resources and cattle responses to heat load on 10 commercial dairy farms in CA. The results of this assessment indicated that some CA dairies were doing well while others faced challenges. Respiration rates, for example, could be as low as 65 to as high as 95 breaths/min and were positively related to inactivity. In addition, the quantity of water used to spray cows ranged from 0 to 25.6 liters/h per cow and it was a product of different flow rates, spray timing and cow:nozzle ratio. Chapters 3 to 5 evaluate the effects of different spray timing strategies on cow cooling. First, I tested the effects of time on and off, thus, strategies varying in quantity of water use, in restrained cattle. Next, I evaluated the combined effects of different flow rates and timing (using the same water volume) on behavior, physiology and production in cows housed in a freestall barn. Spraying cows for longer (Chapter 3 and 4) or reducing time off (Chapter 4), thus, using more water, reduced heat load more effectively in cattle than strategies that required less water (2.5 vs. 64 L of water per application, Chapter 3; 20 vs. 33 L of water/h per cow, Chapter 4). When spraying cows the same quantity of water, timing did not affect cooling effectiveness (Chapter 4 and 5). On the other hand, using a higher flow rate (22 vs. 33 L of water/h per cow), tended to improve cow cooling and milk production. However, these differences were small and their biological relevance is unclear, especially in this situation, where all cows were relatively cool. My dissertation has provided insight into heat abatement in dairy cattle: methodology to study it, the range of provision on commercial farms and new information about how spray management affects dairy cattle behavior and physiology. Happily, I have identified clear ways to mitigate heat load in arid, hot conditions, but the challenge about how to reduce water use, while still ensuring that cows are cool, remains.
