Response of dairy cows to rumen neutralizers during an induction of ruminal acidosis

Abstract

A calcinated Mg source was developed to be a persistent rumen neutralizer (pHix-Up. Timab, France). We evaluated the propensity to ruminal acidosis of cows fed: 1) pHix-Up (PHP. 0.5% of DM), 2) sodium bicarbonate (BIC. 1% of DM), or 3) control (CTL). Fifteen Holstein cows (29.5 kg/d, 620 kg, 193 DIM) were individually fed a sequence of these 3 treatments in 5, 3 × 3 Latin squares, with 21-d periods. On d 17 of each period, feed was removed at 2100h and diet starch content was abruptly increased, on d 18 to 21, from 22.6 to 31.6% of DM by replacing citrus pulp with HMC. Data obtained over time was analyzed as repeated measures. Treatment means were compared by pairwise t-tests. Reticular pH mean (6.22 vs 6.28) and minimum (5.65 vs 5.81) were lower (P < 0.01, SEM = 0.05) and daily duration ≤ 6.2 (703 vs 573 min) was higher (P < 0.01, SEM = 78) on d 18 than d 19 to 21. The acetate to propionate ratio was 3.8 on d 17 and 2.7 on d 21 (P < 0.01, SEM = 0.1). Fecal pH was reduced during acidosis (P < 0.01) and was highest on PHP both before and during acidosis (P < 0.01). PHP tended (P ≤ 0.08) to increase mean pH (6.29 vs 6.24) and to reduce the duration of daily pH ≤ 6.2 (555 vs 653 min) and increased (P = 0.03) minimum pH (5.84 vs 5.72) relative to BIC. PHP also tended (P = 0.09) to increase minimum pH relative to CTL (5.75). Jugular blood pH, HCO3, and base excess were lower during than before acidosis (P ≤ 0.05) and CTL tended (P ≤ 0.09) to have lower blood HCO3 than BIC and PHP. Blood Mg concentration was highest on PHP (P < 0.01) and BIC tended (P = 0.08) to have higher Na concentration than PHP. Plasma D-lactate concentration did not differ (P ≥ 0.27). The DMI on d 18 to 21 was 23.7 kg/d on BIC and 22.1 kg/d on CTL (P = 0.02, SEM = 0.8). The increase in DMI induced by BIC was fast-acting and on d 21 both BIC and PHP had higher DMI than CTL (P ≤ 0.03). Milk yield and components and BW did not differ (P ≥ 0.15). Milk/DMI was lower (P = 0.04) on BIC than CTL. Treatments had no effect on daily milk fatty acid secretion and profile (P ≥ 0.13). Rumen neutralizers with Mg and Na improved blood buffering capacity and DMI during acidosis and PHP resulted in higher rumen pH than BIC.