In vitro evaluation of Lithothamnium calcareum algae on the gas production and dry matter degradability

Lithothamnium calcareum is an algae rich in calcium carbonate and magnesium. Assumed that the calcareous algae have tamponade power in ruminant diets, the replacement of sodium bicarbonate buffer on cattle diets by an alternative renewable is interesting. With the aim of evaluate the influence on degradability and gas production of two granulometry of the algae, polder (PCBp) and slow (BCBs). The work was done using the in vitro technique gas production, described by Theodorou et al. (1994). After that, BCB40 (40%BCBp + 60%BCBs), BCB50 (50%BCBp + 50%BCBs), BCB60 (60%BCBp + 40%BCBs). A treatment with sodium bicarbonate (BIC) was used as positive control and another without adding any additive as negative control (CON). Eight Holstein cows with rumen cannula were used as donors of rumen content. In each bottle were added 1g of substrate (50% concentrate and 50% forage). Eight Holstein cows with rumen cannula were used as donors of inocule. In each bottle were added 1g of substrate (50% concentrate : 50% forage). The bottles were incubated at 39 ?C for 24h and 72h. At the end of the incubation time were estimated the accumulated gas production and degradability of dry matter. The experimental design used was randomised blocks with four blocks. Each block being an inoculum, with five treatments and two replicates. The statistical analyses were performed using SAS 9.2, the average test used was Tukey at the 5% significance level. No statistical differences were observed between treatments with algae. Differences were found only in treatments with algae when compared the others treatments. About 69% of substrate was degraded in the presence of BIC, while about 64% with the presence of BCB. When no tamponade was added, just 30% of DM was deteriorated. This low degradability can be explained by the rapid lowering of pH which inhibited strongly the microbial action, thus, producing less gas. In contrast, the addition of BIC favoured the action of the microorganisms, but also promoted a high gas production. Although BIC treatment has greater degradation than others, the treatments with algae had better energy efficiency due to the lower relation between de amount in ml of gas produced per weight in grams of dry matter degraded.