Effect of rumen neutralizers on performance, digestibility, chewing behavior, and rumen fermentation of dairy cows

Abstract

Neutralizing pH feed additives might improve the performance of dairy cows through mechanisms related to the control of ruminal and systemic acidosis and a greater digestibility of the nutrients. A MgO calcinated source was developed to have high and persistent action on ruminal pH (pHix-Up, PHP). This experiment has evaluated the effect of sodium bicarbonate (BIC. 1% of DM) or PHP (0.5% of DM) addition in a basal diet (CTL) on dry matter intake, milk performance, milk fatty acids profile, digestibility of nutrients, rumen fermentative profile, ruminal and fecal pH, chewing behavior and venous acid-base balance. Fifteen Holstein cows (29.5 kg/d of milk and 193 ± 120 days in milk) formed 5 latin-squares 3 × 3 and received a sequence of the 3 treatments in periods of 21 days and 13 days of adaptation to the treatments. During the first 17 days of each period the cows were fed a 22.6% starch diet on a dry matter basis. At day 17, the feed was removed at 2200 h and a 31.6% starch diet was allowed ad libitum from days 18 to 21 and measurements were taken over time. The contrasts evaluated were: CTL vs PHP and BIC vs PHP. Before inducing acidosis, the dry matter intake (22.6 kg/d) and the milk production (27.5 kg/d) did not differ. PHP tended to increase the milk fat content (3.81%) in comparison to CTL (3.63%) and BIC (3.65%). PHP tended to increase the milk fat content of monounsaturated, unsaturated, stearic and oleic fatty acids and increased the daily secretion of monounsaturated, unsaturated and oleic. There was a tendency for increasing the total-tract ether extract to PHP in comparison with CTL (92.8 vs 91.5% of intake). During the acidosis induction the dry matter intake (22.9 kg/d) and the milk production (26.3 kg/d) also did not differ. BIC tended to increase the milk protein (3.36 vs 3.30%) and casein (2.63 vs 2.58%) content and increased the rumen microbial yield measured by the daily urine allantoin excretion. The blood pH, HCO3 - and base excess were lower during the acidosis induction. PHP increased the partial pressure of CO2 and tended to increase the concentration of bicarbonate ions and total CO2 in the blood in comparison to CTL. The rumen fluid acetate to propionate ratio was 3.8 before the acidosis and 2.7 during the acidosis and was not affected by the treatments. The fecal pH was lower during the acidosis and was higher for PHP before and during the acidosis. During the acidosis, PHP tended to increase the mean ruminal pH (6.29 vs 6.24), tended to decrease the duration of pH ≤ 6.2 (555 vs 653 min/d) and increased the minimum rumen pH (5.84 vs 5.72) in comparison to BIC. PHP also tended to increase the minimum rumen pH in comparison to CTL (5.75). The blood serum Mg concentration was higher for PHP and BIC tended to increase Na serum in comparison with PHP. Cows fed PHP before the acidosis tended to have lower meal (394 vs 408 min/d) and rumination time (460 vs 489 min/d and 73 vs 78 min/ruminal pH) than CTL. During the acidosis, PHP tended to reduce the eating (336 vs 353 min/d) and rumination time (19.4 vs 20.4 min/kg DM) in comparison to CTL. PHP suplemmentation to late lactation dairy cows with lower starch levels tended to increase the milk fat content and the milk fat secretion of unsaturated preformed fatty acids, the ether extract digestibility and the minimum ruminal pH. The neutralizing additives increased the buffering capacity of the blood during the acidosis and PHP induced a higher ruminal pH than BIC.