EFFECT OF BUFFERING DAIRY COW DIETS ON RUMEN FERMENTATION AND PRODUCTION

High yielding dairy cows receive substantial amounts of concentrates containing a high proportion of starch in their diets. Starch ferments quickly in the rumen resulting in a drop in pH and if not controlled, sub-acute acidosis. This results in impaired fermentation, discomfort and reduced milk production. One way of controlling the condition is to add buffers to the diet. Buffers, however, differ in their capacity to uphold pH and therefore the authors decided to compare different buffers available in South Africa.

In the study, six ruminally cannulated Holstein cows were used to evaluate the effect of two dietary buffers on rumen pH, milk production, milk composition, and rumen fermentation parameters. A high concentrate TMR diet, formulated to potentially result in sub-acute acidosis, was formulated to construct three dietary treatments in which calcareous marine algae (calcified remains of the seaweed Lithothamnium calcareum) was compared with limestone (control) and sodium bicarbonate plus limestone. The treatment diets contained either 0.4% of dietary dry matter (DM) as Acid Buf, which is a calcified marine algae product (AB treatment), or 0.8% of dietary DM as sodium bicarbonate and 0.37% as limestone (BC treatment), or 0.35% of dietary DM as limestone as control (CON treatment). Cows were randomly allocated to treatments according to a double 3 × 3 Latin square (cross-over) design, with three treatments and three periods. The total experimental period was 66 days during which each cow received each treatment for a period of 15 days before the data collection period of 7 days. Rumen fluid was collected to determine volatile fatty acids, lactic acid and ammonia concentrations. Rumen pH was monitored every 10 minutes for two consecutive days with a portable data logging system fitted with in-dwelling electrodes. Milk samples were analyzed for solids and mineral contents.

The effect of treatment on rumen acidity was clearly visible, especially in the period from midday to midnight when rumen pH dropped below 5.5 for a longer period of time (13 hours) in CON than in BC (8.7 hours) and AB (4 hour). Daily milk, 4% fat-corrected milk, and milk yield per kg feed DM differed among treatments, with AB the highest, followed by BC and CON. Both buffers increased milk fat content. However, treatment had no effect on milk protein content, but protein yield was increased in AB because of the higher milk yield. Total rumen volatile fatty acids and acetate concentrations were higher and propionate was lower in AB than in CON. The molar proportion of acetate was higher in AB than in CON, but that of propionate was lower in both buffer treatments than in CON. The acetate:propionate ratio was therefore increased in the AB and BC compared with CON. A higher ratio is favourable to milk fat development. Lactic acid concentration was higher in CON than in the buffer treatments, but treatment had no effect on rumen ammonia concentrations.

The results convincingly showed that buffer inclusion in high concentrate diets for lactating dairy cows had a positive effect on milk production and milk fat content. Calcareous marine algae, at a level of 0.4% of dietary DM (which equates to about 90 g per cow per day), had a more pronounced effect on rumen pH, milk production, milk fat and efficiency of feed conversion into milk than the conventional sodium bicarbonate at a level of 0.8% of dietary DM (which equates to about 180 g per cow per day).

Reference:

C.W. Cruywagen, S. Taylor, M.M. Beya & T. Calitz, 2015. The effect of buffering dairy cow diets with limestone, calcareous marine algae, or sodium bicarbonate on ruminal pH profiles, production responses, and rumen fermentation. J Dairy Sci. 98, 5506-5514.