Relationship between infrared thermography measures and feed efficiency in New Zealand sheep

Abstract Text:

A data set to investigate genetic parameters for feed efficiency in New Zealand maternal sheep is being collected.  As measurement of this trait is expensive, route to market for breeders will be through genomic selection.  Another potential way to enable breeders to select for this difficult to measure trait, combined with genomics will be through predictor traits.  Using custom built electronic feeding stations, individual feed intake was collected on 197 ewe lambs born in September 2014 with the 6-week feed intake trial taking place June-August 2015.  Residual Feed Intake (RFI; MJ/day) was determined using a prediction model that included mid-point body weight (kg^0.75) and average daily gain.   Infrared thermography measures were investigated as a potential indicator trait with images collected at two time points.   A thermal video captured the left side of the head, and back of the ear (approximate distance of 0.5 m), using an infrared camera (ThermaCamS60, FLIR, Systems AB, Dandoryd, Sweden).  Four head sub-regions were identified and maximal and average temperature calculated for the eye, bridge of the nose, muzzle and middle of the back of the ear.  To identify potential regions of influence a sub-set of images from 30 individuals were interpreted representing the six most extreme RFI animals (three high RFI; three low RFI), and also individuals with extreme RFI values from four sires identified as the producers of the most extreme RFI progeny (two high RFI sires; two low RFI sires).   The difference in RFI was significant (P < 0.001) between the extreme groups (-1.5 ± 0.28 MJ/day vs +1.6 ± 0.29 MJ/day).  Within a time point, the average temperature measurements for the four different positions were significantly correlated (all P < 0.01). Between time points, back of the ear measurements showed the highest correlation (r=0.7; P < 0.001) and the greatest mean temperature difference between groups at each measurement point.  At the first time point, the estimated average ear temperature of the lowest RFI animals was 26.7 ± 0.67 °C vs 29.2 ± 0.69 °C for the highest RFI animals (P = 0.015), with corresponding values at the second time point of 27.2 ± 0.55 °C vs 29.5 ± 0.59 °C (P = 0.011).  These results provide evidence of a relationship between thermal images and feed efficiency in maternal growing sheep that will be investigated further as a potential indicator trait for selection in industry. 

Keywords: Indirect, Phenotyping, Selection