Effects of cold environment and intake level on the energetic efficiency of feedlot steers.

The effects of cold climatic conditions on energy partitioning were investigated with 49 Hereford-type steers fed an all-concentrate, barley-based diet in a 2 x 3 factorial comparative slaughter trial. Steers (seven per treatment) were kept either indoors or outdoors (n = 2) and fed at 50, 65, or 80 g of DM/kg of BW.75 (n = 3) for up to 106 d. Mean temperatures were 16.9 +/- 2.7 degrees C and -7.6 +/- 6.8 degrees C in indoor and outdoor locations, respectively. Steers housed indoors grew 49% faster (P less than .001) and had 51% better gain: feed ratios (P less than .05) than those kept outdoors. Outdoor steers retained 65% less (P less than .001) energy. Estimated fasting heat production in the outdoor steers was 18% higher (P less than .01) and efficiency of ME use for maintenance 14% lower (P less than .01) than in the indoor steers, which resulted in an estimated increase of 41% in the ME requirements for maintenance in the outdoor steers. The NEg content of the diet was decreased from 1.29 Mcal/kg in the indoor steers to .76 Mcal/kg in the outdoor steers. Outdoor steers deposited 21% of their energy as protein, whereas indoor steers deposited only 14% of their energy as protein, which could explain the low NEg value of the diet in the cold environment. It was concluded that the main factors contributing to reduced energetic efficiency in the cold were an increased maintenance requirement and a greater proportion of the dietary energy retained as protein.