The effects of dietary acid detergent fibre content on the performance of finishing lambs

This study investigated the effects of incremental increases in acid detergent fibre (ADF) content on the nutrient digestibility and performance of South African Mutton Merino wether lambs fed low-fibre finishing diets. Four dietary treatments were formulated with similar nutritional compositions, but with ADF concentrations of 46.8, 59.3, 63.8, and 79.9 g/kg dry matter. The digestibility study was conducted over seven days, while the production study was conducted over 67 days, after which the lambs were slaughtered. Significant differences between treatment means were declared at a 5% probability level. A high ADF concentration (79.9 g/kg) increased the finishing diet’s neutral detergent fibre and ADF digestibility. None of the other nutrients or dry matter digestibility values were affected by the change in ADF concentration. However, a low ADF concentration (46.8 g/kg) resulted in a significantly lower (more efficient) lamb feed conversion ratio, and less metabolisable energy was used for live weight gain. Carcass characteristics were unaffected by the dietary treatments. In conclusion, lamb performance was positively affected by a low ADF content in low-fibre finishing diets with a similar neutral detergent fibre content. More research is required to evaluate the effects of different ADF concentrations in high-fibre diets on nutrient digestibility and the performance of wether lambs. Submitted 20 November 2024; Accepted 23 January 2025; Published March 2025 ------------------------------------------------------------------- Significance of research to South African science The article contributes significantly to South African science by addressing feed efficiency in the country’s sheep production systems. Conducted at the University of the Free State, the study evaluates how varying levels of acid detergent fibre (ADF) in low-fibre finishing diets affect nutrient digestibility and lamb performance. Given the growing use of feedlot systems in South Africa's mutton industry, this research provides locally relevant data on optimising dietary fibre to enhance growth efficiency without compromising carcass quality. Its findings support the use of lower ADF content for improved feed conversion, offering practical implications for more cost-effective and sustainable lamb finishing practices in the region.