Effects of calcium propionate on rumen fermentation, urinary excretion of purine derivatives and feed digestibility in steers

SUMMARY The objective of the current study was to evaluate the effects of calcium propionate supplementation on rumen fermentation, urinary excretion of purine derivatives (PD) and feed digestibility in the total gastrointestinal tract of steers. Eight ruminally cannulated Simmental steers (462±14 kg) were used in a replicated 4×4 Latin square arrangement of treatments with experimental periods of 21 days. The treatments were: control (without calcium propionate), LCaP (calcium propionate – low), MCaP (calcium propionate – medium) and HCaP (calcium propionate – high) with 100, 200 and 300 g calcium propionate per steer per day. Diet consisted of 0·60 maize stover and 0·40 concentrate (dry matter (DM) basis). DM intake (average 9 kg/day) was restricted to a maximum of 0·90 of ad libitum intake. Ruminal pH (range of 6·7–6·5) linearly ( P <0·003) and quadratically ( P <0·005) decreased, and total volatile fatty acid (VFA) concentration (range of 64·4–67·1 m m ) tended ( P <0·087) to increase linearly with rising calcium propionate supplementation. Ratio of acetate to propionate fell linearly ( P <0·006) and quadratically ( P <0·008) from 3·5 to 2·6 as calcium propionate supplementation increased due to the additional propionate supplementation. In situ ruminal neutral detergent fibre (NDF) degradation of maize stover and crude protein (CP) degradability of concentrate mix were improved with increasing concentration of calcium propionate. Urinary excretion of PD was linearly ( P <0·032) and quadratically ( P <0·048) increased with greater calcium propionate supplementation (72, 74, 77 and 76 mmol/day for control, LCaP, MCaP and HCaP, respectively). Similarly, digestibilities of organic matter (OM), NDF and CP in the total tract were also linearly and quadratically improved with increasing calcium propionate. The results indicate that the calcium propionate supplementation potentially improves rumen fermentation and feed digestion in beef cattle. It is speculated that calcium propionate stimulates the digestive microorganisms or enzymes in a dose-dependent manner. In the experimental conditions of the current trial, the optimum calcium propionate dose was about 200 g calcium propionate per steer per day.