Use of digital infrared thermal imaging to assess feed efficiency in Angus bulls1

Feed intake, ADG, and feed efficiency were measured for 84 d on 277 yearling Angus bulls, from 60 to 81 bulls each year, for 4 yr. Digital infrared thermal images of areas of the left ribs, with hair or with hair removed by clippers, were recorded for each bull. The bulls were housed in groups of 12 and were individually fed once daily a TMR of corn silage and supplement. Initial BW was 273 ± 42 kg, daily DMI was 7.83 ± 0.99 kg of DM/d, ADG was 1.53 ± 0.23 kg/d, and G:F was 0.196 ± 0.027. Residual feed intake ranged from −2.17 to 3.07 kg/d, with a SD of 0.55. Residual feed intake was positively correlated (P < 0.05) with DMI (0.49) and negatively correlated with G:F (-0.50) but was not correlated with any temperature measures. Daily DMI was correlated (P < 0.05) with the SD of temperature of clipped (r = -0.15) and unclipped rib area (r = −0.55), and the temperature difference in clipped and unclipped rib areas (r = -0.28). Temperature of clipped rib area (0.16 ≤ r ≤ 0.33), and clipped - unclipped rib area temperature difference (r = -0.28) were correlated (P < 0.05) with ADG. Within clipped or unclipped rib areas, minimum, maximum, and mean temperatures were positively correlated with each other (0.34 ≤ r ≤ 0.93) and negatively correlated with SD (-0.20 < r < -0.63). Thermal imaging may be useful in characterizing intake and gain in group-fed beef cattle.