Abstract
One hundred and forty-four steers of predominantly Angus breeding were used to compare the effects of three housing units (conventional semi-enclosed manure pack, semi-enclosed slatted floor and enclosed–insulated slatted floor) and two diets (high moisture corn and corn silage) on the performance, energy metabolism and carcass composition of steers finished for 88 days in the summer. No diet × housing unit interaction on response criteria was observed. The mean temperature in the enclosed unit (24.6 C) was more than 3 C greater than in other units. Mean relative humidities in each slatted floor unit were 74% whereas it was 70% in the conventional unit. The enclosed–insulated unit may have been insufficiently ventilated. Steers in this unit ate less (P 0.05) dry matter per day (6.78 kg) than those in the semi-enclosed slatted floor unit (7.64 kg) and in the conventional unit (7.66 kg). Different effects of housing unit on gain reflected differences in feed intake. Carcass characteristics of cattle from each housing unit were similar (P 0.05). Efficiency of utilization of metabolizable energy (ME) for maintenance and gain expressed as energy retention (ER) adjusted to equal ME intake was greater (P 0.05) for cattle in the semi-enclosed slatted floor unit (5.17 Mcal/day) than in the insulated–enclosed unit (4.36 Mcal/day). ER adjusted to equal ME intake for steers in the conventional unit was 4.76 Mcals/day. Serum tetra-iodothyronine (T4) levels were similar (P 0.05) for cattle in all housing units, but were depressed in all cattle during a period of the warmest weather. Corn-fed steers ate significantly less dry matter and had significantly greater gain and feed efficiency than silage-fed steers. Backfat thickness was greater (P 0.05) for corn-fed versus silage-fed steers but this difference disappeared when values were adjusted to equal carcass weight.