Effect of calcium hydroxide or urea treatment of barley straw on intake and digestibility in sheep

Abstract

Three experiments were undertaken with 7 to 8-month-old Suffolk cross Mule lambs weighing 35 kg (Experiment 1) and 29 kg (Experiments 2 and 3). Rations of restricted concentrates (176 g dry matter (DM)/day, Experiment 1; 142 g DM/day, Experiments 2 and 3), and ad libitum straw (Experiments 1 and 2) or restricted straw (Experiment 3) were fed over 35 days per experiment to measure intake (10 days) (Experiments 1 and 2) and digestibility (8 days faeces collection). Chopped straw was mixed with Ca(OH) 2 and/or urea dissolved in 0.8 1 water/kg straw. Treated straw (500 g DM/kg) was stored (56 days at 9.4°C in Experiment 1; 60 days at 9.6°C in Experiments 2 and 3) in sealed polythene bags before feeding. In Experiment 1 with 8 lambs/treatment, daily intakes of digestible straw organic matter per kg live weight (g DOM/kg W day −1) were: untreated straw, 5.7; 30 g urea/kg straw DM, 5.8; 30 g urea and 30 g Ca(OH) 2/kg straw DM, 6.9; 30 g urea and 60 g Ca (OH) 2, 8.7; 60 g urea and 60 g Ca (OH) 2, 9.4. In Experiment 2, using 48 lambs, straw intakes were higher. Intakes of g DOM/kg W day −1 were: untreated, 8.0; 60 g Ca(OH) 2, 11.2; 15 g urea and 60 g Ca(OH) 2, 12.2; 30 g urea and 60 g Ca(OH) 2, 13.7. In Experiment 3, using 12 lambs/treatment, with straw intakes at 13.7 g organic matter (OM)/kg W day −1, straw OM digestibilities (g/kg) were: untreated, 485; 60 g Ca(OH) 2, 575; 15 g urea and 60 g Ca (OH) 2, 585. No mold was encountered in any treated straws. Treatment with 30 g urea and 60 g Ca (OH) 2 was considered optimum as it maximised intake of digestible straw. An unexpected finding was that urea hydrolysis during storage was reduced in the presence of Ca (OH) 2.