Relationship of ocular and rectal temperatures to indicators of stress in mature horses
Rectal temperature has commonly been used as an indicator of health in many species of livestock including horses. However, collection of a rectal temperature can be difficult and stressful on the animal. New technology, such as thermal imaging cameras, have recently become more prevalent and have been used to collect the body temperature of animals at other, less invasive sites including the ocular globe. The objective of this research was to determine the relationship between rectal temperature and ocular temperature and to evaluate the efficacy of these measurements as indicators of the stress level of horses. To accomplish this, ocular temperature (OT), rectal temperature (RT), neutrophil count, lymphocyte count, heart rate (HR), and respiration rate (RR) were recorded before and during an immune challenge, using a novel vaccination, of 30 mature horses (413 to 551 kgs and 5-10 yrs). Neutrophil to lymphocyte ratio (N:L) has been shown to be a good indicator of systemic inflammation and overall stress in an animal and was used as the primary indicator of stress in this study. To determine the relationship between temperatures and among indicators of stress the PROC CORR procedure of SAS was utilized. The relationship between OT and RT was found to have a weak correlation (r=0.37; P<0.01), illustrating that the OT is not a good substitute for traditional RT measurements. Additionally, OT had very little relationship with N:L (r=-0.01; P=0.94), HR (r=0.19; P=0.31), or RR (r=0.17; P=0.38). While still very weak, RT had stronger relationships than OT with N:L (r=-0.11; P=0.40) and RR (r=0.26; P=0.17) and a similar correlation to HR (r=0.19; P=0.31). Of all the non-invasive measurements (OT, HR, and RR), RR had the strongest correlation to N:L as an indicator of systemic stress, (r=-0.24; P=0.21). While OT is less invasive than RT, a direct measurement of OT is not a reliable predictor of RT in an animal. Still, it may hold some value to livestock and wildlife producers due to its ease of measurement, but without further investigation into the relationship of OT and indicators of stress, its utility remains limited.
Ocular temperature, rectal temperature, stress