Climate change impacts shifting landscape of the dairy industry in Hawai‘i

Contributed by Mandeep Adhikari:

Future projections indicated that air temperature would increase 1.3 to 1.8 °C by mid-century and 1.6 to 3.2 °C by the end-century (Zhang et al., 2016; Elison Timm, 2017) at the Dairy Farms (“OK Dairy” and “UP Dairy”) in Hawaii. The agriculture and livestock industries, particularly the dairy subsector in Hawai`i, is vulnerable to climate changes as higher temperatures and less rainfall will have adverse effects on cattle. This article highlights how additional heat stress and forage scarcity due to elevated temperature and reduced rainfall challenge animals’ production and health, forage growth, and ranch management. This work has been published in the journal of Translational Animal Science ( ).

To assess the risk of heat stress on cattle production, monthly Temperature Humidity Index (THIs) were calculated for both locations using the average monthly temperature and humidity data between 1920 and 2019. Results showed that the THI ranged from 64.6 to 70.1 at the “OK Dairy” site, while it ranged from 67.8 to 73.5 at the “UP Dairy” site. The four summer months (June to September) at the “OK Dairy” site were not conducive for high-producing dairy cattle (THI > 68). However, the THIs at the “OK Dairy” site never reached 72 (the critical threshold for low-producing cattle) and mostly remained within the range of 67 to 70, indicating favorable conditions for low-producing dairy cattle throughout the year. The high-producing dairy cows in the “UP Dairy” site were exposed to mild (THI > 68) to moderate (THI > 72) heat stress continuously (14 to 24 h) for several months (April to November). During these periods, THI hardly drops below 68, and therefore the dairy cows in the “UP Dairy” site experience more heat stress in absence of nighttime recovery than in the “OK Dairy” site. Therefore, High milk producing dairy cattle are vulnerable to heat stress at both locations particularly during hottest four months of the calendar year (Jun -Sep).

Figure 5 -Temperature–humidity index and wind speed across 24 h during the summer season (June to September) using the average data of recent 20 years (2000 to 2020). The dotted horizontal line with the green color above indicates the optimal heat stress threshold for high-lactating dairy cattle. The line with the red color indicates the warning threshold for suffering from heat stress for low-lactating cattle. At the red line, high-lactating cattle suffer even more than low-lactating cattle. The dotted horizontal line with black color indicates the effective wind speed that maintains homeostasis in cattle.

Rainfall at the “OK Dairy” site is expected to increase over time, while the “UP Dairy” site can be even dryer by the mid-century and the end-century. Empirical results for future forage production indicated that the monthly forage production in the “OK Dairy” site is projected to increase by 6% to 8% by mid-century and 13% to 19% by the end-century. Whereas, the forage production in the “UP Dairy” site is projected to decrease 5% to 8% by mid-century and 10% to 11% by the end-century. These projections revealed that the “UP Dairy” site suffers more from forage scarcity, making ranching activities even more difficult in the future unless irrigation is possible. In contrast, “OK Dairy” sites can be even more productive with abundant grass growth in the future.

Figure 6 – Projected percentage change in forage production at the “OK Dairy” and the “UP Dairy” site by the mid-century and end-century.

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