Mixed annual forage species for growing lambs – average daily gain and rumen efficiency compared with a single species cereal

Context Annual forage crops are commonly used to provide high quality fodder for livestock in the south-east of Australia. While the agronomic benefits of some forage mixes such as cereals and peas have been studied, the animal production benefits of grazing mixtures of annual species forage crops compared with a single species cereal control have not been examined. Aims To determine average daily gain (ADG), rumen pH and volatile fatty acids (VFAs) when sheep grazed mixtures of annual fodder crops compared with a single species cereal control. Methods Eighty Border Leicester × Merino lambs (mean = 44.3 ± 0.55 kg) were allocated to one of four forage treatments (n = 20 per treatment) based on liveweight and fat score: a single species cereal control (wheat; C) or annual forage species mixes containing cereal (wheat, cereal rye) and brassica (canola, turnip, radish; C + B), cereal and legume (vetch, arrowleaf clover; C + L) or cereal, brassica and legume (C + B + L). Liveweight was assessed over a 42 day grazing period and rumen fluid parameters over 28 days. Key results Mean ADG from day 0–42 was higher for lambs grazing the C control (298.9 ± 9.7 g head−1 day−1) compared with the C + B (251.4 ± 9.7 g head−1 day−1) or C + L (240.0 ± 9.7 g head−1 day−1) mixes, but not the C + B + L mix (275.8 ± 9.7 g head−1 day−1). Rumen fluid pH was lower (P 0.001) for sheep grazing forage mixes containing brassica (C + B = 6.71 ± 0.07; C + B + L = 6.79 ± 0.07) compared with cereal alone (7.13 ± 0.07) or C + L (7.14 ± 0.07). Average daily gain was significantly (P 0.001) predicted by rumen pH and estimated methane (CH4) output (ADG = 58.1 × Rumen pH − 99.0 × CH4 + 236.4, r2 = 0.80, Root Mean Squared Error of Prediction = 16.9). Conclusions The higher ADG in the C and C + B + L compared with C + L forage treatments was related to higher dry matter on offer and lower estimated CH4 output. Further research should determine whether the lower pH observed when sheep grazed mixes containing brassica compared with cereals is associated with inefficient utilisation of energy from these forages. Implications Average daily gain can be similar for mixed forage species compared with cereal alone. Higher rumen pH and more efficient fermentation reducing CH4 may improve growth.