No abstract

No abstract

No abstract

Forty-eight multiparous Holstein cows were blocked according to month of parturition, age, and previous milk yield and arranged in a randomized complete block design to evaluate the effect of a naturally occurring sodium sesquicarbonate on DMI, milk yield, milk composition, milk value, and systemic acid-base status. Cows were assigned at parturition to diets containing sorghum silage, alfalfa hay, concentrate, and 0 or 1% naturally occurring sodium sesquicarbonate (DM basis); cows were fed these diets for 308 d postpartum. Blood was collected every 4 wk via jugular venipuncture for analysis of pH, HCO3, partial pressure of O2, and partial pressure of CO2. Sesquicarbonate exhibited alkalogenic properties by increasing blood HCO3, partial pressure of CO2, and total CO2 for the 308-d lactation. Buffer tended to increase DMI and increased milk protein throughout lactation. During 0 to 56 d postpartum, sodium sesquicarbonate did not affect milk yield or composition. In midlactation (56 to 252 d postpartum), buffer increased milk protein content only. During 252 to 308 d postpartum, milk fat and protein contents increased with buffer supplementation. Hence, the value of milk yielded daily was similar for all cows. Effects of dietary buffer on all variables were more pronounced during late lactation.

Four ruminally cannulated, lactating Holstein cows were assigned to a 4 x 4 Latin square to monitor the effects of intraruminal NaHCO3 infusion on changes in the rumen environment. Sodium bicarbonate (110 g), dissolved in 3.8 L of water, was infused twice daily at a constant rate for 2 h starting at 0, 2, or 4 h postfeeding. All cows had access to their diet containing sorghum silage and concentrate in a 35:65 ration (DM basis) for 45 min twice daily. Ruminal fluid was collected at feeding and every 30 min postfeeding for 12 h on the last day of each 7-d period. Dry matter intake was lower for buffer infusion at 2 to 4 h than for water-infused control but was not affected by the other NaHCO3 infusions. Although total milk yield was not affected, milk fat percentage and fat yield tended to be lower for the NaHCO3 treatments. Compared with the water infusion, the NaHCO3 infusion from 2 to 4 h postfeeding most effectively prevented the postfeeding increase in ruminal free proton concentration. Additionally, volume of ruminal liquid was increased for the NaHCO3 infusions from 0 to 2 h and 4 to 6 h; ruminal liquid turnover time was increased for the NaHCO3 infusion at 4 to 6 h, but ruminal kinetics otherwise were not affected by NaHCO3. Although infusion of NaHCO3 from 2 to 4 h prevented severe alterations in ruminal acid-base status, it did not increase total VFA concentration or the acetate:propionate ratio. Although total VFA concentrations were not affected by NaHCO3 infusion, acetate:propionate ratio was higher for the NaHCO3 infusion from 0 to 2 h than for the control. Based upon alterations in ruminal acid-base status, exogenous buffer ideally should be provided to the rumen from 2 to 4 h postfeeding; however, our results indicate that the effectiveness of this regimen might be improved if buffer is combined with a rapidly released or unprotected dietary buffer.