Abstract:
Feeding highly fermentable carbohydrate-rich diets to dairy cows is universally practised to achieve the energy intake needed to support higher levels of milk production. However, this dietary regimen can reduce rumen pH, and thereby adversely impact rumen fermentation, milk production and composition. Lithothamnium (Lith), calcified remains of a marine algae, is an alternative buffering agent to negate these effects and may provide advantages over sodium bicarbonate (NaHCO3) due to its slower rumen dissolution rate. Whilst past research has only considered effects on pH, this study looks at new in-vitro methodologies such as the buffer value index (BVI) and buffering capacity (BC) have been developed to simulate the rumen environment and how different buffers will react over different incubation intervals. Furthermore, an in vivo 4 x 4 Latin square design experiment, spanning a total length of 92 days was carried out with 4 lactating dairy cows. Four treatment diets were formulated, each differing by the type of buffer included, namely; Control, NaHCO3, Lith A, Lith B. the following parameters were recorded; milk production parameters, feed intake and digestiblity, animal health, ruminal pH parameters. Sodium bicarbonate and Lith A as buffer sources aided in significantly increasing the dry matter and crude protein digestibility. Increased DMI for the control diet may have contributed towards increased milk yields. It may be speculated that lowered SCC for Lith B may be attributed to the effect of the exogenous buffer to aid in udder health and improve cow immunity. Significant differences between Lith B and NaHCO3 were observed for mean pH, with Lith B exhibiting a lower ruminal pH and increased time spent below pH 5.8 in the rumen. This low pH contradicted previous studies that claim lowered milk fat under such ruminal conditions, whilst the milk fat in this study was numerically higher for Lith B. Increased butyrate content for cows fed Lith A versus the control may aid in explaining milk fat numerical differences between the control diet and Lith A. Although buffers do in turn help to alleviate low pH problems in the rumen, however, alternative strategies which investigate fermentation pathway control may be more successful in combating bouts of SARA in the long-term.
