A panting score index for sheep
When exposed to hot conditions, heat dissipation via an increase in respiration rate (RR) is an important thermoregulatory mechanism for sheep. However, evaluating RR under field conditions is difficult. In cattle, a viable alternative has been to assess panting score (PS); therefore, the objective of this study was to evaluate the relationship between RR and PS to determine if a PS index can be used to evaluate heat load in sheep. One hundred and forty-four Merino wethers (44.02 ± 0.32 kg) were used within a climate-controlled study. The study was replicated twice over 29 days, where each replicate consisted of two treatments: (1) thermoneutral (TN) and (2) hot (HOT). Ambient temperature (TA) and relative humidity (RH) were maintained between 18 and 20 °C and 60 and 70% respectively for the TN treatment. For the HOT treatment, heat load increased steadily over the 29 days. Minimum TA was 22.5 °C and maximum was 38.5 °C, while RH decreased (60 to 30%) as TA increased in the HOT treatment. A comprehensive PS classification was developed by enhancing the current sheep PS index and aligning the descriptors with the current PS index utilized in beef cattle studies. Respiration rate and PS were obtained for each animal at 3-h intervals between 0800 h and 1700 h daily. These data were used to determine the mean RR for each PS, across the study and within the TN and HOT treatments. The relationship between PS and RR was evaluated using a Pearson’s correlation coefficient. Data were also analyzed using a general linear model to determine the impact of PS, posture and animal identification (animal ID) on RR within each PS. Unsurprisingly, RR increased as PS increased, and PS, 0 and RR, 2.5 were 30.7 ± 0.59 and 246.8 ± 12.20 bpm respectively. There was a strong relationship between RR and PS (r = 0.71; P < 0.0001). As RR increased, sheep were more likely to be observed standing (P < 0.001). Mean PS of sheep within the HOT treatment (1.49 ± 0.02) were greater (P = 0.0085) when compared to the TN (1.17 ± 0.02) sheep. Individual animal ID accounted for approximately 7–37% of the variation observed for RR across PS, indicating that animal ID and climatic conditions were influencing RR and PS. These results suggest that the comprehensive PS index described here can be used as a visual appraisal of the heat load status of sheep.
KeywordsHeat stress Sheep Thermal comfort Panting score Respiratory dynamics Respiration rate
The authors would like to thank Allan Lisle for his assistance with statistical analysis. The authors also wish to acknowledge Jarrod C. Lees for his valuable comments and suggestions on improving this manuscript. The authors also wish to acknowledge and offer thanks Meat and Livestock Australia Pty Ltd. for providing the plates used within Fig. 1.
Funding for this study was provided by Meat and Livestock Australia Pty Ltd., North Sydney, NSW, Australia, LiveCorp, North Sydney, NSW, Australia and the Australian Federal Government, Canberra, ACT, Australia.
Compliance and ethical standards
This study was conducted with the approval of The University of Queensland (UQ) animal ethics committee (SAFS/178/13/MLA).
- Bligh J (1985) Temperature regulation. In: Yousef MK (ed) Stress physiology in livestock, vol I. CRC Press Inc., Baco Raton, Florida, pp 75–96Google Scholar
- Department of Agriculture Fisheries and Forestry. 2011. Australian standards for the export of livestock (version 2.3) 2011 and the Australian Positoin Statement of the Export of Livestock, Australian Government: http://www.agriculture.gov.au/. Accessed 18 May 2016
- Lees, A. M. 2016. Biological responses of feedlot cattle to heat load (PhD Thesis). The University of Queensland, School of Agriculture and Food SciencesGoogle Scholar
- McCarthy M 2005. Pilot monitoring of shipboard environmental conditions and animal performance. MLA Final Report LIVE.223. Meat and Livestock Australia, North Sydney, NSW, AustraliaGoogle Scholar
- Stockman CA (2006) The physiological and behavioural responses of sheep exposed to heat load within intensive sheep industries. Murdoch University, Perth, WA. AustraliaGoogle Scholar
- Young BA, Hall AB (1993) Heat load in cattle in the Australian environment. In: Coombes R (ed) Australian Beef. Morescope Publishing, Melbourne, AustraliaGoogle Scholar
- Young BA, Hall AB, Goodwin PJ, Gaughan JB (1997) Identifying excessive heat load. In: Bottcher RW, Hoff SJ (eds) Livestock environment V, proceedings of the fifth international symposium. American Society of Agricultural Engineers St. Joseph, MI, USA, pp 572–576Google Scholar