CONCENTRATE FEEDING LEVELS FOR UNIMPLANTED AND IMPLANTED FINISHING STEERS FED SILAGE

The effects of concentrate feeding level on intake and performance of unimplanted and implanted finishing Friesian steers (377 kg initial liveweight) fed good quality grass silage were studied. The feeding treatments imposed over 152 days were 1) silage only, 2) silage + 3 kg of concentrates/day, 3) silage + 6 kg of concentrates/day and 4) concentrates to appetite + 2.5 kg of silage/day. Each feeding treatment contained 10 unimplanted and 10 implanted (oestradiol/progesterone (Synovex-S) and trenbolone acetate (Finaplix) twice) steers with a pre-experimental slaughter group of 5 animals. Animals on Treatments 1, 2 and 3 were offered silage to appetite and the daily concentrate (barley 915, soybean meal 70 and minerals/vitamins 15 g per kg) allowance for those on Treatments 2 and 3 were given in two equal feeds. In-vivo digestibility of the feeds was obtained during the course of the experiment using three unimplanted and three implanted animals from each feeding treatment. The silage had good preservation quality (pH = 3.8). There was no effect of implantation on diet dry matter digestibility (DMD). DMD of diets 1, 2, 3 and 4 were 744, 759, 779 and 792 (SED 8.7) g per kg respectively. Silage and total DM intakes of unimplanted and implanted animals were 4.70 and 8.88 and 4.95 and 9.10 (SED 0.124 and 0.188) respectively. Silage and total DM intakes of animals fed diets 1, 2, 3 and 4 were 7.39 and 7.44, 6.20 and 8.65, 5.24 and 10.12 and 0.45 and 9.74 (SED 0.176 and 0.266) kg respectively. Implantation improved liveweight gains (kg per day) from 0.93 to 1.28 (SED 0.041) and carcass gains from 0.57 to 0.77 (SED 0.026). Daily liveweight gains of animals on Treatments 1, 2, 3 and 4 were 0.77, 1.03, 1.22 and 1.41 (SED 0.059) kg respectively. Corresponding daily carcass gains were 0.43, 0.62, 0.74, and 0.90 (SED 0.036) kg. Implantation decreased kidney plus channel fat weight, had no effect on carcass fat score but improved carcass conformation. Each increase in the level of concentrates fed up to 6 kg per head daily increased kidney plus channel fat weight, carcass fat and conformation scores. However, there was no difference between animals fed silage plus 6 kg of concentrates daily and those offered concentrates to appetite. Because carcass gain as a proportion of liveweight gain differed significantly between treatments carcass gain was considered the better indicator of performance. Carcass gain of unimplanted steers was three-quarters that for implanted animals on each feeding treatment.