Rumen acidosis is a metabolic disorder of ruminants, characterized by a severe drop in rumen pH. This is due to an accumulation of acids, especially lactic acid in the rumen. Lactic acid is one of the strongest acids with a major effect on rumen pH. A low and / or fluctuating rumen pH can have a severe impact on the productivity and health of dairy cattle, especially during the early lactation period. Rumen acidosis can, for example, occur during the rapid change from a low concentrate to a high concentrate diet. Megasphaera elsdenii (Me) is a lactate-utilizing micro-organism that converts the lactic acid that is produced from the fermentation of starch in the rumen, to propionic acid. Based on the ability of Me to convert lactic acid to propionic acid, a study was conducted to determine the effect of dosing live sources of Me on the level of rumen acidosis, general health and productivity. Sixty high-producing multiparous dairy cows were used in a randomized complete block design experiment. Cows were blocked according to milk production during the previous lactation and, thereafter, randomly allocated, within each block, to one of the following treatments: <ol> <li> 60% concentrate TMR;</li> <li> 60% concentrate TMR with Me dosing;</li> <li> 70% concentrate TMR;</li> <li> 70% concentrate TMR with Me dosing.</li></ol> The experimental period was 60 days and cows were dosed on day 2, 10 and 20 post-partum. Cows were housed in a semi-intensive housing unit equipped with Calan gates for determining individual feed intake. Daily milk production and dry matter intake were measured, as well as body mass and body condition score. Milk was analyzed for fat, protein, lactose and MUN; rumen fluid for pH, volatile fatty acids and lactic acid; faecal samples for pH and starch and feed refusal samples for nutrient components. In addition the health statuses of the cows were also monitored. In general the results did not show a clear advantage of dosing Me, regardless of the level of concentrate. Dry matter intake, milk production, milk composition, feed efficiency, body mass and body condition score were not affected by treatment (P > 0.05). Contrary to expectation, treatment did not affect rumen pH, rumen lactic acid or volatile fatty acid concentrations (P > 0.05). Faecal pH, however, was higher and the starch content lower in cows dosed with Me (P < 0.05) suggesting a positive effect on rumen fermentation and more efficient total tract starch fermentation. Furthermore only two cows were culled from the dosed group, compare to eleven from the control group, suggesting a positive influence of Me on the general health of stress, early lactation cows. Further research is needed to better quantify the potential role of Me in preventing SARA.
Dissertation (MSc(Agric))--University of Pretoria, 2008.