Physiological and pathological effects of feeding high levels of magnesium to steers

• Published in: Journal of animal science Vol. 68; no. 12; p. 4400
• Main Authors: Chester-Jones, H. (Univ. of Minnesota, Southern Exp. Sta., Waseca), Fontenot, J.P, Veit, H.P
• Format: Journal Article
• Language: English
• Published: United States 01.12.1990
• Subjects: ABSORCION; ABSORPTION; Absorption - drug effects; ANIMAL HEALTH; Animals; BEEF CATTLE; BLOOD; Body Weight - drug effects; BOEUF; BOVIN DE BOUCHERIE; BUEY; BULLOCKS; Calcium, Dietary - metabolism; Cattle; Cattle Diseases - chemically induced; Diarrhea - chemically induced; Diarrhea - veterinary; DIGESTIBILIDAD; DIGESTIBILITE; DIGESTIBILITY; Digestion - drug effects; Eating - drug effects; GANADO DE CARNE; Hydrogen-Ion Concentration; MAGNESIO; MAGNESIUM; Magnesium - metabolism; Magnesium Oxide - adverse effects; Male; MINERAL ABSORPTION; Osmolar Concentration; PATHOLOGIE; PATHOLOGY; PATOLOGIA; Phosphorus - metabolism; Rumen - anatomy & histology; Rumen - drug effects; SANG; SANGRE; SANIDAD ANIMAL; SANTE ANIMALE; Sodium - metabolism; TOXICIDAD; TOXICITE; TOXICITY
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/1990.68124400x

The effects of feeding high levels of Mg were evaluated in a 130-d study with 24 steers. Six steers were allotted to each of four diets supplemented with MgO to attain .3, 1.4, 2.5 or 4.7% Mg, DM basis. Chromic oxide was used as digesta marker; fecal grab samples were collected once daily during nine consecutive 10-d periods. Steers fed 2.5 and 4.7% Mg refused some feed during the study, so their respective dietary Mg intakes were 2.4 and 3.7% (DM basis). Severe diarrhea and a lethargic appearance were observed in steers fed the two higher Mg levels. Fecal DM and apparent DM digestibility decreased linearly (P less than .01) with increased dietary Mg. Apparent Mg absorption (g/d) increased linearly (P les than .01) and apparent Ca and P absorption (g/d) decreased linearly (P less than .01) with addition of Mg to the diet. Increasing dietary Mg linearly elevated blood serum and erythrocyte Mg (P less than .01; P less than .05, respectively) and serum inorganic P (P less than .05) and linearly decreased serum Ca (P less than .01). Magnesium concentration in liver, kidney, skeletal muscle and rib-bone and P in skeletal muscle all increased linearly (P less than .05) with dietary Mg. Increasing dietary Mg in the steers caused a progressive degeneration of the stratified squamous epithelium of rumen papillae. A progressively more serious Mg toxicosis condition developed over time in steers fed diets containing 2.4 and 4.7% Mg.