The Influence of the Physical Form of the Diet on Fluid Dynamics and Mineral Content of Rumen Fluid in Lactating Cows Fed 12 Times Daily

Abstract

The effect of the physical form of the diet on liquid metabolism, osmotic pressure, and the macromineral concentrations in the rumen fluid was investigated in a study with 3 lactating cows. Two 3x3 Latin square blocks were used, with 3 physical forms of rations, made by adding different amounts of long straw (LS), 4%, 10%, and 20%. All rations consisted of pelleted feed and barley straw fed in either a long or in a ground and pelleted physical form. The rations were fed restrictively every second hour day and night throughout the experiment. Energy, organic nutrients and macrominerals were supplied in amounts corresponding to Danish Standards for cows yielding 24 kg 4% FCM. Increasing the content of LS from 4% to 20% resulted in significant linear increase in the outflow of liquid from the rumen (p<0.002), liquid dilution rate (p<0.02), saliva secretion (p<0.002), and concentration of sodium in the liquid phase of the rumen fluid (p<0.02). Water intake (p<0.02), the osmotic pressure in the rumen fluid phase, and the concentrations of Ca (p<0.004), P (p<0.001), Mg (p<0.001), K (p<0.001), and the Na/K (p<0.03) in the rumen fluid phase decreased linearly.

Key Words:

• straw
• rumen fluid dynamics
• calcium
• phosphorus
• magnesium
• sodium
• potassium
• chloride
• sodium/potassium
• saliva
• osmotic pressure