THE VOLUNTARY INTAKE OF DIETS DIFFERING IN DIGESTIBLE ENERGY CONCENTRATION AND FORM OF HAY

One hundred sixty steer calves were allotted to 10 groups and fed diets with hay to concentrate ratios of 77:23, 68:32, 59:41, 49:51, and 40:60. At each ratio, one group received long (baled) hay and one group received cubed hay. The steers were marketed as they reached 475 kg liveweight. There were interactions between form of hay and hay to concentrate ratios for feed and digestible energy (DE) intake per day and digestible energy intake per unit metabolic weight (DE/W0.75). The DE/W0.75 of diets containing long hay increased as the proportion of concentrate was increased from 23 to 41% then levelled off when concentrate was increased above this level. With the cubed hay diets, DE/W0.75 declined as proportion of concentrate in the diet increased from 23 to 41% then increased rapidly as the proportion was increased to 60%. The feed to gain and DE to gain ratios declined as the percent concentrate in the diet increased for both long and cubed hay diets. The rate of gain increased as the proportion of hay in the diet was decreased for diets containing hay or cubed hay. Carcass backfat thickness increased as the proportion of hay in the diet decreased. Steers fed long hay had thicker backfat than those fed cubed hay. Key words: Voluntary intake, beef, hay to grain ratio