LAUSR

We determined whether sheep discriminate among mineral supplements containing P and Mg and if they modify their selection as a function of need. During 3 consecutive days, 40 lambs under a basal diet of alfalfa pellets and barley grain were offered 4-way choices among= (1) MgO-powder form (MgO-82% Mg), (2)MgO-coarse form (C-MgO-82% Mg), (3) Magnesium Phosphate (Bolifor® Mag33-33% Mg, 2.7% P), and (4)Magnesium Phosphate (Bolifor® MGP-25% Mg, 15% P), and 2-way choices between MGP and each of the other minerals, and between MgO and C-MgO (Baseline). Subsequently, lambs were randomly assigned to 4 groups (10 lambs/group) and fed rations such that the levels of Mg and P were low (LMg-LP), adequate (NMg-NP), low in Mg and adequate in P (LMg-NP), or adequate in Mg and low in P (NMg-LP). After 29 d, groups received again the described choices (post-deficiency). Intake and preference indexes during choice tests were analyzed as a split-plot design with lambs nested within group and day as the repeated measure. During Baseline, lambs ate and preferred Mag33 > C-MgO = MGP > MgO (P < 0.05). This pattern remained during post-deficiency, but lambs in LMg showed the greatest preference for Mag33 (P < 0.05). All lambs preferred C-MgO over MgO or MGP (P < 0.05), but lambs in LMg-NP showed the greatest preference for C-MgO (P < 0.05) and the lowest preference for MGP (P < 0.05). Serum concentrations of P (7.1 to 8.4±0.2 mg/dL) and Mg (3.0 to 3.9±0.1 mg/dL) increased after post-deficiency tests relative to Baseline (P < 0.05). Lambs discriminated among different mineral sources and the physical form of MgO influenced preference. Groups in low Mg diets favored sources of Mg with no or low concentration of P, and when P was adequate (LMg-NP), they reduced their preference for the source with the greatest concentration of P (MGP).