Effect of roughage-to-concentrate ratios combined with different preserved tropical forages on the productive performance of feedlot lambs

Abstract This study proposes to investigate the production performance of lambs fed diets containing different roughage sources and formulated with different roughage-to-concentrate ratios (R:C). A total of 108 castrated male Santa Ines lambs aged 3 to 6 months, at an average body weight of 26.1 kg ± 5.6 kg were used. The experiment was set up as a randomized block design with a 2 × 3 factorial arrangement represented by two R:C ratios (400:600 or 600:400 g/kg, dry matter basis) and two roughage sources [transvala grass (Digitaria decumbens Stent cv. Transvala) hay or sorghum (Sorghum bicolor) silage], or a combination of the two sources. Six diets were tested, namely, Diet 1 – 400 g/kg hay +600 g/kg concentrate; Diet 2 – 400 g/kg silage +600 g/kg concentrate; Diet 3 – 200 g/kg hay +200 g/kg silage +600 g/kg concentrate; Diet 4 – 600 g/kg hay +400 g/kg concentrate; Diet 5 – 600 g/kg silage +400 g/kg concentrate; and Diet 6 – 300 g/kg hay +300 g/kg silage +400 g/kg concentrate. The concentrate was composed of ground corn, soybean meal, urea and a mineral mixture. The diets with the lower R:C ratio (400:600 g/kg DM) provided the highest intakes of dry matter and other nutritional components as well as increased animal performance and carcass yield parameters. Better feed efficiency was observed in the lambs fed the silage-containing diets. In conclusion, the tested roughage sources can be used in lamb diets, and the roughage level of 400 g/kg DM maximizes feed efficiency in lambs. When using hay in the diet formulation, higher weight gain rates are achieved with a R:C ratio of 400:600 g/kg; for diets formulated with silage, in turn, the recommended R:C ratio for increased weight gain is 600:400 g/kg. Thus, depending on the availability of roughage, the producer may choose one of the sources and associate it with the most adequate proportion of concentrate to maximize the performance of feedlot lambs.