Milk fat depression is a well-known challenge in the dairy industry. Understanding the mode of action and different factors influencing milk fat depression will help both farmer and nutritionist in their attempt to minimize the drop in milk fat yield in dairy cows. In these 12 interesting facts, the main focus is on the effect of rumen pH on milk fat depression.

  1. Different factors influence milk fat depression (MFD). This includes rumen pH, unsaturated fatty acids (UFA) and digesta passage rate (Jenkins et al., 2020).
  2. Grazing cows fed predominantly rye-grass pasture are potentially at risk of developing low rumen pH (O’Grady et al., 2007).
  3. High-quality pastures may have low effective NDF and high sugar content. Therefore, mean daily ruminal pH values of 5.6 to 6.5 have been reported in dairy cows fed high-quality pasture (Bargo & Muller, 2005).
  4. A survey assessed rumen fluid, animal health status, milk production data and pasture composition. A total of 144 cows between 80 and 150 days in milk were sampled on 12 farms. 11% of cows were classified as affected with acute rumen acidosis (pH < 5.5), 42% experienced sub-acute rumen acidosis (pH 5.6 – 5.8) and 47% were normal (pH > 5.8) (O’Grady et al., 2008).
  5. Supplementing pasture-based Holstein dairy cows with a mixture of Acid Buf and Marine MgO significantly increased 4% fat corrected milk (FCM) and milk fat yield (Rafferty et al., 2019).
  6. Supplementing pasture-based Jersey cows with Acid Buf significantly increased 4% FCM (Van Dyk et al., 2015).
  7. Reduction in rumen pH may decrease digestion in the rumen (Mulligan et al., 2002).
  8. Reduction in rumen pH may reduce the production of acetate and butyrate (Bauman et al., 2001).
  9. Lower rumen pH may result in increased propionate levels. This potentially can increase circulating insulin levels, resulting in increased uptake of acetate and butyrate by the adipose tissue (Bauman et al., 2001).
  10. Acetate and butyrate are fatty acids used by the mammary gland to synthesize short-chain fatty acids (C4 – C10), which are then used to synthesize butterfat molecules (triacylglycerol) (Koch & Lascano, 2018). Reduction in acetate and butyrate may, therefore, decrease production of butterfat molecules.
  11. There is a strong correlation (P< 0.001) between rumen pH and milk fat %. A decrease in rumen pH may result in a reduction in milk fat % (Allen, 1997).
  12. Feeding lower degradable maize (7-hour starch = 66.5%) based diet after cows experienced MFD, resulted in better production performance, compared to feeding higher degradable corn (7-hour starch = 87.8%) based diet (Koch et al., 2019).


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