Guanidinoacetic acid and betaine supplementation have positive effects on growth performance, nutrient digestion and rumen fermentation in Angus bulls

This study evaluated the influences of guanidinoacetic acid (GAA) and betaine (BT) on growth performance, nutrient digestion and ruminal fermentation in bulls. Forty-four Angus bulls were blocked by live body weight and then randomly divided into four groups in a 2 × 2 factorial design. Betaine of 0 or 0.6 g/kg dry matter (DM) was added to diets containing 0 or 0.6 g/kg DM GAA, respectively. The experiment included a 20 day period for adaptation and a 60 day period for data collection. Average daily gain and feed efficiency were increased by GAA or BT but no further increase was observed for supplementing BT and GAA together than for addition with BT or GAA alone. Supplementary GAA or BT did not influence DM intake but increased apparent digestibility of DM, organic matter (OM), crude protein (CP) and acid detergent fibre (ADF). Digestibility of neutral detergent fibre (NDF) was increased by GAA inclusion but was unaltered with BT provision. Ruminal pH reduced but total volatile fatty acids and ammonia nitrogen elevated with dietary inclusion of GAA or BT. Rumen short chain fatty acids percentages and fermentation pattern were not influenced by GAA. Dietary inclusion of BT increased molar proportions of acetate, valerate, isobutyrate and isovalerate as well as the ratio of acetate to propionate. Rumen populations of Ruminococcus flavefaciens and Fibrobacter succinogenes increased with addition of GAA or BT and the increase was greater when BT was added in diets with GAA compared to diets without GAA. Addition of GAA or BT increased activities of cellobiase, xylanase, α-amylase and protease and populations of total bacteria, cellulolytic bacteria and Ruminobacter amylophilus but did not affect Prevotella ruminicola. Addition of BT increased carboxymethyl-cellulase and pectinase activities and total fungi population. Blood creatine content was increased by GAA or BT and was greater for addition of GAA and BT together than for GAA or BT addition alone. Serum contents of glucose, folate, arginine and methionine were unchanged but total protein increased with GAA or BT provision. Blood homocysteine content was unaffected by GAA but decreased with BT supplementation. The data showed that GAA or BT addition improved growth performance and feed efficiency but supplementing GAA and BT together did not further increase the performance of bulls when compared with GAA or BT inclusion alone.