Relationship of severity of subacute ruminal acidosis to rumen fermentation, chewing activities, sorting behavior, and milk production in lactating dairy cows fed a high-grain diet

Mar 12, 2014Journal of dairy science

How moderate digestive acid imbalance relates to fermentation, chewing, feed sorting, and milk production in dairy cows on a high-grain diet

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Abstract

Minimum ruminal pH values in lactating dairy cows fed a high-grain diet ranged from 5.16 to 6.04.

The acidosis index, which measures the severity of subacute ruminal acidosis (SARA), varied significantly among cows, ranging from 0.0 to 10.9 pH · min/kg of dry matter intake.
Cows classified as tolerant to high-grain diets had a lower acidosis index (0.04 ± 0.61 pH · min/kg) compared to those classified as susceptible (7.67 ± 0.75 pH · min/kg).
Despite differences in SARA severity, total volatile fatty acid concentration and profile were similar between tolerant and susceptible groups.
Tolerant cows exhibited less sorting behavior against long particles compared to susceptible cows (sorting index=87.6 vs. 97.9).
Tolerant cows had a shorter total chewing time (35.8 min/kg of dry matter intake) compared to susceptible cows (45.1 min/kg of dry matter intake).
Milk urea nitrogen concentration was higher in tolerant cows (12.8 mg/dL) than in susceptible cows (8.6 mg/dL), potentially indicating different fermentation processes in the rumen.

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The objectives of the current study were to evaluate the variation in severity of subacute ruminal acidosis (SARA) among lactating dairy cows fed a high-grain diet and to determine factors characterizing animals that are tolerant to high-grain diets. Sixteen ruminally cannulated late-lactating dairy cows (days in milk=282 ± 33.8; body weight=601 ± 75.9 kg) were fed a high-grain diet consisting of 35% forage and 65% concentrate mix. After 17 d of diet adaptation, chewing activities were monitored for a 24-h period and ruminal pH was measured every 30s for 72 h. Acidosis index, defined as the severity of SARA (area of pH <5.8) divided by dry matter intake (DMI), was determined for individual animals to assess the severity of SARA normalized for a feed intake level. Although all cows were fed the same diet, minimum pH values ranged from 5.16 to 6.04, and the acidosis index ranged from 0.0 to 10.9 pH · min/kg of DMI. Six cows with the lowest acidosis index (0.04 ± 0.61 pH · min/kg) and 4 with the highest acidosis index (7.67 ± 0.75 pH · min/kg) were classified as animals that were tolerant and susceptible to the high-grain diet, respectively. Total volatile fatty acid concentration and volatile fatty acid profile were not different between the groups. Susceptible animals sorted against long particles, whereas tolerant animals did not (sorting index=87.6 vs. 97.9, respectively). However, the tolerant cows had shorter total chewing time (35.8 vs. 45.1 min/kg of DMI). In addition, although DMI, milk yield, and milk component yields did not differ between the groups, milk urea nitrogen concentration was higher for tolerant cows compared with susceptible cows (12.8 vs. 8.6 mg/dL), which is possibly attributed to less organic matter fermentation in the rumen of tolerant cows. These results suggest that a substantial variation exists in the severity of SARA among lactating dairy cows fed the same high-grain diet, and that cows tolerant to the high-grain diet might be characterized by less sorting behavior but less chewing time, and higher milk urea nitrogen concentration.

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Relationship of severity of subacute ruminal acidosis to rumen fermentation, chewing activities, sorting behavior, and milk production in lactating dairy cows fed a high-grain diet

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