Variation in the risk of developing sub-acute ruminal acidosis in lactating dairy cows

• Author / Creator

  Gao, Xiaosheng

• Sub-acute ruminal acidosis (SARA) is a common metabolic disorder in high-producing dairy herds. Diet formulation strategies can be implemented to decrease the incidence of SARA, but some cows in a herd may still experience SARA. The overall objectives of this research were to evaluate if variation exists in the risk of developing SARA among lactating dairy cows and to determine factors associated with this variation. In study 1, as expected, variation was detected in the risk of developing SARA among lactating dairy cows when they were fed the same high-grain diet. Cows with lower risk of SARA (LS) sorted to a less extent but also had less chewing time compared with cows with higher risk of SARA (HS). In addition, higher milk urea nitrogen (MUN) concentration was found for LS cows compared with HS cows. Therefore, in study 2, it was further evaluated if MUN and milk fat content could be used as non-invasive indicators to identify cows with higher or lower risk of SARA. Results showed that minimum and mean rumen pH was higher, and duration of rumen pH below 5.8 was shorter for cows identified presumably with lower risk of SARA compared with ones identified presumably with higher risk. In study 3, other factors that might potentially relate to the variation in the risk of SARA among lactating cows were evaluated. Results showed that the microbial enzymatic activity for carbohydrate digestion in the rumen was not different between LS and HS cows. In addition, no difference was found in volatile fatty acid (VFA) absorption rate between LS and HS cows. But differences in relative mRNA abundance of genes involved in VFA metabolism in rumen epithelium among cows might be related to the variation in the risk of SARA. In addition, in study 3, it was found that HS cows identified in mid-lactation consistently had lower rumen pH in late-lactation than LS cows. Feeding different types of carbohydrates may have a different effect on VFA absorption rate, which may play an important role in affecting the risk of SARA. Therefore, in study 4, effects of increasing dietary non-fibre carbohydrate content with starch, sucrose or lactose on VFA absorption, rumen fermentation, and milk production of mid-lactating dairy cows were evaluated. It was found that feeding high disaccharide diets to lactating dairy cows increased dry matter intake, milk fat and protein yields, and energy corrected milk yields compared with a high starch diet even though rumen pH was lower for cows fed high disaccharide diets. But, not as expected, the treatment effects on rumen pH could not be attributed to VFA absorption rate. In summary, substantial variation exists in the risk of developing SARA among lactating dairy cows fed the same high-grain diet. This variation may not be caused by chewing activity, microbial enzymatic activities and VFA absorption rate, but it may be associated with differences in sorting behaviour and expression of genes involved in VFA metabolism in rumen epithelium among the cows.

• Subjects / Keywords

  • Milk urea nitrogen
  • Milk fat
  • Volatile fatty acid absorption
  • Rumen digestibility
  • Sub-acute ruminal acidosis
  • Sorting behaviour
  • Chewing activity

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3ZS2KJ5V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.