Absorption of magnesium by the young steer

Area of Science:

• Animal Nutrition
• Ruminant Physiology
• Mineral Metabolism

Background:

• Magnesium (Mg) is an essential mineral for ruminant health.
• Dietary Mg absorption can be influenced by various factors, including diet composition and rumen environment.
• Understanding Mg absorption dynamics is crucial for preventing deficiencies in grazing and feedlot cattle.

Purpose of the Study:

• To quantify net magnesium absorption in steers fed different diets.
• To investigate the influence of rumen conditions on magnesium absorption.
• To determine the site of magnesium absorption in the gastrointestinal tract of steers.

Main Methods:

• Rumen and duodenal cannulated steers were used.
• Diets included pasture, dried grass, and flaked maize with or without hay.
• Magnesium absorption was assessed using inert markers (cerium-144 or chromic oxide) and analyzing duodenal digesta.
• Rumen fluid composition (pH, Na:K ratio) was monitored.
• Ileal cannulation was used in a subsequent experiment to assess Mg absorption beyond the duodenum.

Main Results:

• Net Mg absorption varied from near zero on pasture to 0.2-0.5 for flaked maize.
• Mg absorption efficiency correlated positively with rumen Na:K ratio and negatively with rumen pH.
• Little net Mg change was observed between the duodenum and ileum, suggesting limited post-duodenal absorption.
• Initial Mg absorption in the rumen appeared negligible in the first few hours post-dosing.

Conclusions:

• Dietary factors significantly impact net Mg absorption in steers.
• Rumen environment plays a critical role in modulating Mg uptake.
• The primary site of net Mg absorption in steers appears to be anterior to the duodenum, with limited absorption occurring further down the digestive tract.