Effects of plane of nutrition, confinement system, and forage preservation on supplemental mineral intake and content of minerals in the blood of pregnant beef cows

Jugular blood samples were taken in four periods: autumn, early winter, midwinter, and spring in each of 2 consecutive years from 108 Shorthorn cows that were assigned to one of three housing systems (In, In–Out, or Out), one of three levels of feeding (ad libitum, 75% of ad libitum, or 50% of ad libitum), and one of two forages (hay or grass silage). Blood samples for each group on each bleeding date were analyzed for Ca, P, Mg, Mn, and Cu. The planned reduction in feed intake in the first three periods resulted in a consistent increase in the voluntary consumption of the mineral supplement. Plasma inorganic P levels parallelled the intake of the mineral supplement. Plasma Ca levels appeared unrelated to either feed or supplemental mineral intake. Plasma Mg concentrations were significantly (P