What is the impact of neutral detergent fibre digestibility on productive performance of beef cattle fed tropical forages?

Our objective was to quantify the relationship between total neutral detergent fibre (NDF) digestibility and nutritional and productive characteristics in cattle fed tropical forages using a meta-analytical approach. The dataset used to develop this work was compiled from 24 experiments carried out with beef cattle in Brazil, published between 2005 and 2020, and totalising 115 treatment means. All the experiments were carried out using change-over designs and included a control treatment (i.e., only forage). There was a linear and positive relationship (P < 0.01) between total NDF digestibility and voluntary forage intake. We estimated a 0.17 g/kg body weight increase in forage intake for each percentage point (i.e., 0.01 g/g) of improvement in NDF digestibility. On average, increasing total NDF digestibility caused a linear improvement (P < 0.01) in rumen microbial nitrogen production (NMIC) and in dietary digested organic matter (DOM). The total NDF digestibility was linear and positively associated with nitrogen balance (NB, P < 0.01). However, the increment in NB as a response to total NDF digestibility was more prominent as dietary NDF decreased (P < 0.01). In summary, we concluded that increasing NDF digestibility in cattle fed tropical forage-based diets improves the voluntary forage intake and the supply of energy and metabolisable protein. This simultaneous effect causes an increase in the animal's nitrogen accretion and weight gain, but this effect will be more prominent as the dietary content of neutral detergent fibre decreases.