Modeling the Adequacy of Dietary Fiber in Dairy Cows Based on the Responses of Ruminal pH and Milk Fat Production to Composition of the Diet

Abstract

The main objective of this study was to develop practical models to assess and predict the adequacy of dietary fiber in high-yielding dairy cows. We used quantitative methods to analyze relevant research data and critically evaluate and determine the responses of ruminal pH and production performance to different variables including physical, chemical, and starch-degrading characteristics of the diet. Further, extensive data were used to model the magnitude of ruminal pH fluctuations and determine the threshold for the development of subacute ruminal acidosis (SARA). Results of this study showed that to minimize the risk of SARA, the following events should be avoided: 1) a daily mean ruminal pH lower than 6.16, and 2) a time period in which ruminal pH is <5.8 for more than 5.24 h/d. As the content of physically effective neutral detergent fiber (peNDF) or the ratio between peNDF and rumen-degradable starch from grains in the diet increased up to 31.2 +/- 1.6% [dry matter (DM) basis] or 1.45 +/- 0.22, respectively, so did the daily mean ruminal pH, for which a asymptotic plateau was reached at a pH of 6.20 to 6.27. This study also showed that digestibility of fiber in the total tract depends on ruminal pH and outflow rate of digesta from reticulorumen; thereby both variables explained 62% of the variation of fiber digestibility. Feeding diets with peNDF content up to 31.9 +/- 1.97% (DM basis) slightly decreased DM intake and actual milk yield; however, 3.5% fat-corrected milk and milk fat yield were increased, resulting in greater milk energy efficiency. In conclusion, a level of about 30 to 33% peNDF in the diet may be considered generally optimal for minimizing the risk of SARA without impairing important production responses in high-yielding dairy cows. In terms of improvement of the accuracy to assessing dietary fiber adequacy, it is suggested that the content of peNDF required to stabilize ruminal pH and maintain milk fat content without compromising milk energy efficiency can be arranged based on grain or starch sources included in the diet, on feed intake level, and on days in milk of the cows.

Palm kernel expeller increases milk fat content when fed to grazing dairy cows

“…The combination of increased NDF levels and decreased fibre degradability of summer pasture as opposed to spring pasture and the high NDF content of PKE may induce a positive milk fat content response. This is supported by Zebeli et al (2008), who stated that NDF intake (physical effective form) enhances milk fat content. The objective of this study was to compare the effects on milk production, milk composition, and ruminal fermentation end-products from partially replacing maize with increasing levels of PKE in concentrates fed to Jersey cows grazing kikuyu-based pasture during summer.…”

Effect of palm kernel expeller as supplementation on production performance of Jersey cows grazing kikuyu-ryegrass pasture

“…Physical effective NDF is strongly associated with milk fat yield and ruminal pH, as was demonstrated by Zebeli et al (2008). An increase in milk fat content was expected for cows fed the LP and HP treatments due to the high NDF levels of these concentrates, 188 and 295 g/kg DM, respectively.…”

Ochratoxin A in Ruminants–A Review on Its Degradation by Gut Microbes and Effects on Animals

“…Ruminal pH generally continues to decline 4–6 hours after feeding [117,118]. Total duration of pH drop below certain thresholds are considered to be most significant for the effects of pH changes [119]. Since protozoa limit being washed out from the rumen actively by attaching to larger particles, a reduction of such structures to attach and therefore to limit outflow may be a constraint for the protozoa population, too.…”