Infrared thermography (IRT) was tested for predicting heat production in Nellore and Angus young bulls. A total of 32 animals with initial body weight (BW) of 380.6 ± 6.1 kg were housed in individual stalls. Eight animals of each breed were fed ad libitum with a whole shell corn (WSC) diet (85% whole shell corn and 15% of a pellet based on soybean meal) or a silage/concentrate (SC) diet (30% silage and 70% concentrate based on corn and soybean meal). After 50 experimental days, skin and eyeball temperatures were obtained by infrared thermal images (Fluke Ti 55ft, Fluke Corporation) and the pictures were analyzed using the software SmartView 3.0. The daily intake was measured and a metabolic trial was conducted with total collection of feces and urine to estimate the metabolizable energy intake (MEI). With 90 d of growth, the cattle were slaughtered. The retained energy (RE) was calculated using comparative slaughter technique. Heat production (HP) was calculated as the difference between MEI and RE. The data were analyzed using the GLM and REG procedures of SAS adopting significance level of 0.05. Angus cattle show greater daily MEI, daily HP and body temperatures than Nellore (Table 1). SC diets show greater MEI and HP, but similar eye and skin temperatures. We found a moderate correlation (P < 0.05) between daily HP and maximum (r = 0.46) and average skin (r = 0.47) and maximum (r = 0.44) and average eyeball (r = 0.40) temperatures. We concluded that IRT technique has a potential to be used to evaluate HP in cattle. Table 1. Metabolizable energy intake (Mcal/d), heat production (Mcal/d), and maximum and average temperatures of skin and eyeball (°C) of Nellore and Angus bulls fed whole shell corn (WSC) or a silage/concentrate (SC) diets

Item	Nellore			Angus		SEM	P-value
SC	WSC	SC	WSC	Breed	Diet	Breed × Diet
ME intake	26.3c	21.1d		38.1a	32.7b	1.8	<0.0001	0.006	NS
Heat production	21.6bc	17.2c		31.2a	26.0b	1.6	<0.0001	0.006	NS
Temperature
Maximum skin	35.9b	36.4b		36.8a	36.6a	0.2	0.0118	NS	NS
Average skin	34.6b	35.1b		35.6a	35.7a	0.2	0.0015	NS	NS
Maximum eye	36.6b	36.8b		37.2a	37.1a	0.2	0.0184	NS	NS
Average eye	34.8b	35.3b		35.5a	35.5a	0.2	0.0328	NS	NS