Effect of Diet Neutral Detergent Fibre Content on Dry Matter Intake, Nutrient Digestibility, Growth Efficiency and Carcass Characteristics of Finishing South African Mutton Merino Wether Lambs

A study was conducted to investigate the effect of incrementally decreasing the diet neutral detergent fibre (NDF) content on dry matter (DM) intake, nutrient digestibility, growth efficiency and carcass characteristics of finishing South African Mutton Merino wether lambs. Five isonitrogenous dietary treatments were formulated, differing in fibre and NDF contents, with the NDF content in descending order. Treatments contained 379 (CON), 314 (NDF1), 251 (NDF2), 192 (NDF3) and 143 (NDF4) gram NDF/kg DM, respectively. The digestibility study was conducted over a period of 7 days, whereas the production study was conducted for 61 days. Diet DM, organic matter (OM), non-structural carbohydrate (NSC), CP, NDF, acid detergent fibre (ADF) digestibility, as well as metabolisable energy (ME) content, were highest in diets with the lowest NDF content (NDF4 treatment). Diet DM intake was however the lowest for treatment NDF4. An increase in lamb feed conversion ratio (FCR: all treatments compared to CON) and ME utilised/kg live weight gain (NDF2 and NDF3 compared to CON: lower values) were also evident for increasing treatment NDF content. A low dietary NDF content also positively affected most of the carcass characteristics. The advantage of feeding a highly digestible and low-NDF diet seems to have had the desired effect on the growth efficiency and carcass quality of South African Merino wether lambs. The observed increase in fibre (ADF and NDF) digestibility as NDF (lucerne hay) inclusion decreased, contrasts the reports of previously concluded studies and requires further investigation.