ChileanJAR

The experiment was carried out at the Humán Research Station (INIA, Los Angeles). Seventy eight European Hoistein steers (23-month-old; 420 kg inicial uve weight-L.V/.) were used during 104 winter days in 1977, to evaluate the effect of the addition of hay and urea to rations basad on wet sugar beet pulp (ad libitum) + rapeseed meal. Five leveis of red dover hay (X₁ = 0.00; 0.25; 0.50; 1.00 and 1.50 kg/100 kg L.W.) and five levels of substitution of rapessed meal by urea (X₂ = 0;25; 50; 75 and 100%) were included; a central composite design, with 4 extra treatments to include the test, was employed, having 13 treatments with 6 animal-replications. Results were analyzed as surface responses. Adjusting equations for daily gain, protein conversion efficiency, and estimated energy con- version efficiency are given. Wet beet pulp + 100% urea showed the lowest gain (0.10 kg/steer/day). Daily gain was 1.0 kg for 25% rapeseed meal substitution + 1.0 kg hay/100 kg L.W. Considering only the leve) of hay, protein conversion efficiency was better with 0.50 and 1.00 kg hay/100 kg L.W. lndependently tothe hay level, the most efficient rations were with 25% urea. One kilogram of hay and 500/o urea, showed the best protein conversion efficiency. The highest estimated energy conversion efficiency was obtained with 1.00 kg hay/100 kg L.W./day + 50% urea. Maximum output (1.044 kg L.W./animal/day) was reached with 1.03 kg of hay/100 kgJL.W. + 41.7% rapeseed meal substitution. Maximum profit was given by 0.946 kg hay/100 kg L.W. + 36,1% rapeseed meal substitution, with a daily gain of 1.04 kg and a net income of $45.03/steer/day. A sensitivity analysis showed that a 23.89% increase in the price of beef allows a 1.48% and a 1.92% increase in the use of hay and urea, respectively.