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Fread, Emily Morgan

Animal and Veterinary Sciences

2023

M.S.

Heat stress negatively impacts dry dairy cows in subtropical climates, but impacts in moderate climates are unknown. The objective of this thesis was to determine if dry cows and their calves in Northern NY and VT are impacted by episodic heat stress and varying levels of heat exposure. Another aim of this study was to determine farmers' knowledge of heat stress, heat abatement use, and the need for future research.Chapter 2 describes a study conducted on a Northern NY farm, where dry cows were housed in moderate heat abatement, meaning fans over a bedded pack or free stalls. Surprisingly, cows had higher reticular temperature and rumination time on hot days. Although not reflected in body temperature or rumination data, these cows were heat-stressed as they stood longer on hot days to dissipate heat. Cows who experienced high amounts of heat stress during the dry period (DP) had a shorter gestation length. Cows who experienced low amounts of heat stress during the DP tended to have higher-quality colostrum than those with moderate heat stress. Cows who experienced high amounts of heat stress during the late DP had lower 21-day milk production. Calves were not statistically affected by in-utero episodic heat stress for the measured variables. Chapter 3 describes a study conducted on a Northern VT farm, where dry cows were housed on pasture for their early DP and on a bedded pack with access to an outdoor sandlot for their late DP. Similar to the study conducted in Chapter 2, this study indicated that cows ruminated longer on hot days. Unlike in Chapter 2, cows only had higher reticular temperature on hot days when housed on pasture, not when they had the option of shade access of the barn. Cows who experienced high amounts of heat stress during the late dry period tended to have greater weight loss from dry off to calving. Eight farmers with varying farm sizes and heat abatement use were interviewed regarding their opinions of heat stress and usage of heat abatement, as described in Chapter 4. Overall, all farmers felt their cows were negatively impacted by heat stress, and most had implemented heat abatement strategies on their farms. A prevalent theme of many interviews was farmers' hesitancy to install sprinklers as a form of heat abatement due to concerns about animal health and water availability. These studies indicate that dry cows are negatively impacted by episodic heat stress in the Northeast, so heat abatement should be provided during the DP. Farmers in the area believe heat stress negatively affects their cattle and have observed positive impacts of providing heat abatement for their animals.