Effect of Age and Dietary Magnesium on Voluntary Feed Intake and Plasma Magnesium in Ruminants

The effects of calcium and sodium loading on organic matter digestibility and mineral absorption in sheep. 2. Absorption of minerals

“…Loading an extruded concentrates with Ca (5 times the ARC requirement) lowered Mg digestibility (27%) in the forestomachs in comparison with the control (55%) and sodium (44%) groups (P<0.05). Chicco et al (1973), Ben Ghedalia et al (1982) and McDowell (1992) also observed lower Mg absorption in sheep loaded with Ca, indicating on important role of the forestomachs in Mg absorption and the marginal role of the small intestine. The increase in Ca intake with the ration from 5 (group I) to 19 g/d (group II) increased the Ca flow throughout the duodenum and ileum and the digestibility of Ca in the forestomachs (P<0.05), while at the same time reducing its digestibility in the small intestine.…”

“…As the concentration of these elements in the diet rises, their specific antagonisms in terms of absorption and tissue distribution of other minerals becomes increasingly evident (Chicco et al, 1973;Bartley, 1976;NRC, 1980;Shiga and Harii, 1987;Alfaro et al, 1988). Antagonism between elements can lead to a deficit of many elements, especially those that normally occur in feeds at near-minimum levels (Underwood, 1977;Alfaro et al, 1988;Tucker et al, 1988).…”

Magnesium

“…High levels of dietary P or Ca adversely affect Mg absorption. Chicco et al (1973) found that fecal Mg excretion is increased and serum Mg decreased by feeding high Ca and P levels to sheep. Magnesium and Ca may compete for the same absorption sites along the small intestine (Alcock and Macintyre, 1962).…”

“…Suboptimal performance can be related to a decline in cellulose digestion. Studies with lambs and steers suggest that feed intake and cellulose digestion decline faster than does serum Mg when Mg-free diets are fed (Chicco et al, 1973;Emery, 1976).…”

The effects of calcium and sodium loading on organic matter digestibility and mineral absorption in sheep 3. Changes in the Ca, Mg, Zn and Cu concentrations in rumen fluid

“…Both approaches, fertilization and treatment, can lead in consequence to overloading of macroelements in both ruminants and other animals. Macroelement overdosing in the ruminant diet can disorder absorption, flow rate in the gastrointestinal tract and metabolism of minerals and other dietary components (Chicco et al, 1973;Underwood, 1977;NRC, 1980;Ben-Ghedalia et al, 1982;Alfaro et al, 1988). Sodium overloading increases saliva excretion (Bartley, 1976), changes the Na:K ratio in saliva (Chiy and Phillips, 1993), affects Mg absorption (Fontenot et al, 1973) and increases water requirements (Evans, 1981).…”