Heat stress can be devastating as it affects production, reproduction, the immune system and the general wellbeing of the animal. In the last couple of years we have seen an increase in the number of days per year when cows suffered because of hot days. This is expected to worsen with climate change. Therefore, dairy farmers must be prepared to manage heat stress and introduce precautionary measures. In this context it is useful to estimate the economic losses incurred, which was the topic of the study of Dr F.C. Ferreira and colleagues in the United States (US). They published the results in the Journal of Dairy Science, Volume 99 of 2016, page 9931 to 9941, under the title: Economic feasibility of cooling dry cows across the United States.
Heat stress during the dry period reduces milk yield in the subsequent lactation. The question posed by the authors was whether cooling of dry cows has merit. More specifically, their objectives were to quantify the economic losses due to heat stress if dry cows are not cooled and to evaluate the economic feasibility if dry cows are to be cooled. Weather data from the National Oceanic and Atmospheric Administration were used to calculate the number of heat stress days for each of the 50 US states. A heat stress day was declared when the daily average temperature-humidity index was equal or more than 68. The number of dairy cows in each state in 2015 was obtained from the USDA-National Agricultural Statistics Service. For the purpose of the study it was assumed that 15% of the cows were dry at any time, that a 60 day dry period was used and that the calving interval was 400 days.
It was interesting that only cows in their second or more lactation periods benefitted from cooling during the previous dry period. Milk yield decreased by about 5 kg in the subsequent lactation if the cow experienced heat stress during the dry period. The value of milk minus feed cost was calculated as $0.33 per kg of milk. The investment analysis included purchases of fans and soakers and use of water and electricity. Investment in a dry cow barn was considered separately. The authors indicated that the average US dairy cow would experience 96 (26% of the year) heat stress days and loses 447 kg of milk in the subsequent lactation if not cooled when dry. Annual losses would be $810 million if dry cows in the US were not cooled ($87 per cow per year). For the top three milk-producing states (California, Wisconsin, New York), and Florida and Texas, the average milk losses in the subsequent lactation were 522, 349, 387, 1197 and 904 kg and the reduced profit per cow per year would be $101, $68, $75, $233 and $176, respectively. The average benefit-cost ratio and payback periods of cooling dry cows in the US were 3.15 and 0.27 years (dry cow barn already present) and 1.45 and 5.68 years (if investing in a dry cow barn).
In conclusion, the results showed that cooling of dry cows was profitable for 89% of the cows in the US when building a new barn is required and very profitable when construction of a dry cow barn is not required. Since other benefits of cooling, such as increased health and more productive offspring, were not considered in the investigation, an investment in cooling of dry cows where feasible should be positive since, compared to the US, South Africa experiences even more heat stress days.