Into the Comfort Zone: Understanding Swine Thermal Preference

Lindsey Allison Robbins, Purdue University

Abstract

Exposure to thermal stress can negatively impact an animals’ overall welfare, resulting in decreased body condition, lower reproductive success, and in severe cases, mortality. Heat stress occurs when temperatures exceed an animal’s thermoneutral zone, effecting an animal’s production efficiency and overall well-being. The swine industry has prioritized efficient production and as a result has gained rapid improvements in lean growth and increased litter sizes. Unfortunately, modern swine are unable to cope with the negative effects of heat stress as they are unable to sweat, have a small lung capacity for respiration to be effective at heat dissipation, and have increased lean mass with improve growth rates. On the other hand, temperatures that fall below the thermoneutral zone are not usually an issue for swine. This is, in part, due to housing environments being able to maintain warmer temperatures and the animal’s reduced surface area to mass ratio making them efficient at heat conservation and cold tolerant. However, piglets are still susceptible to cold temperatures. From a stable temperature of 39°C in the uterus, piglets are born into an environment that is significantly colder and are unable to thermoregulate for the first 72 hours after birth. Because of this, they can suffer from hypothermia quickly. In addition, piglets lack brown adipose tissue, an essential tissue that aids in non-shivering thermogenesis, resulting in lowered resistance to cold environments. Thus, it is crucial to understand the preferred temperatures of swine to create recommendations on when to initiate mitigation strategies to combat the negative effects of thermal stress. However, this is further complicated given that temperature preference can be altered by various factors. Thermal preference differs with age, pregnancy, social context, early life experiences, and behavior, making it exceptionally difficult to classify an animal’s thermoneutral zone. Therefore, the central hypothesis of this dissertation was that thermal preference of swine would be impacted by various factors including early life thermal stress, social aggregation, and reproductive stage. The objective of chapter 2 was to determine if past thermal experiences altered thermal preference in pigs. To test this, piglets were first exposed to one of three early life thermal treatments between 7 to 9 days of age: thermoneutral (25°C with a heating lamp), cold stress (25°C without a heating lamp), and heat stress (cycling 32 to 38°C). At weaning (~20 days of age) pigs were split into groups of 4 same sex and early life thermal treatment and thermal preference was assessed later in life (~15 to 56 days of age) using a thermocline. Pigs differed in thermal preference across different early life thermal treatments. Early life cold stressed pigs preferred warmer temperatures (+ 2.2°C) compared to their thermoneutral exposed counterparts. However, early life heat stressed pigs did not differ in thermal preference compared to both early life cold and thermoneutral exposed counterparts. These results suggest early life cold stress influences thermal preference later in life. Unrelated to the main objective of this project, early life thermoneutral pigs demonstrated a cooler thermal preference (23.2 to 25.2°C) than recommended guidelines set forth by the Guide for the Care and Use of Agricultural Animals in Research and Teaching (referred to the Ag Guidefrom hereon) of 26 to 32°C for piglets between 3 to 15 kg.

Degree

Ph.D.

Advisors

Gaskill, Purdue University.

Subject Area

Zoology|Animal sciences|Physiology|Atmospheric sciences|Thermodynamics

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