Learned Appetites for Calcium, Phosphorus, and Sodium in Sheep
Journal of Animal Science
American Society of Animal Science
Villalba, J. J., Provenza, F. D., & Hall, J. O. (2008). Learned appetites for calcium, phosphorus, and sodium in sheep. Journal of Animal Science, 86(3), 738-747. doi:10.2527/jas.2007-0189
If supplemental minerals are needed to promote optimal animal performance, what is the best way of providing them: free choice or in the diet? We hypothesized that herbivores discriminate among feeds containing Na, P, and Ca and modify their choices as a function of need. One group of lambs was fed a basal diet low in P and high in Ca (low P-high Ca), whereas another group was fed a basal diet high in P and low in Ca (high P-low Ca). After 73 d of exposure to the unbalanced diets, the lambs were conditioned by offering flavored grape pomace containing NaCl, CaCO3, or NaH2PO4. Preference for pomace + minerals was determined when all lambs were fed a basal diet of alfalfa pellets and barley grain (initial preference) and during 4 phases. Phases 1 and 2 occurred after 40 and 67 d of feeding the unbalanced basal diets, phase 3 occurred after conditioning with NaCl, CaCO3, or NaH2PO4, and phase 4 occurred 22 d after the groups were moved to 2 new (separate) locations so the animals in the different groups could not eat dirt, urine, or feces from the other pen. Preference for pomace did not differ between the groups during the initial preference tests (P = 0.62); both groups preferred NaCl > CaCO3 = NaH2PO4 (P < 0.001). As the study progressed, and lambs fed low P-high Ca had lower P and greater Ca concentrations in serum than lambs fed high P-low Ca (P < 0.001), the preference between groups diverged. In phase 2, lambs in high P-low Ca continued to prefer NaCl (P < 0.001), but lambs in low P-high Ca preferred NaH2PO4 (P < 0.05). After conditioning, both groups preferred NaCl = NaH2PO4 > CaCO3 (P < 0.01 to 0.11). After the groups were moved to different locations, lambs fed low P-high Ca showed the lowest concentration (3.7 mg/dL) of inorganic P in serum for all phases (P < 0.001), and they preferred NaH2PO4 > NaCl = CaCO3 (P < 0.001). In contrast, lambs in high P-low Ca avoided NaH2PO4 (P < 0.05). Lambs offered high P-low Ca showed a greater preference for CaCO3 (P = 0.12) and NaCl (P < 0.05) and a lower preference for NaH2PO4 compared with lambs fed low P-high Ca (P < 0.001). In summary, lambs discriminated among different flavored feeds containing NaCl, CaCO3, and NaH2PO4 and displayed preferences as a function of the mineral imbalance in their basal diets. Thus, it may be possible to feed Ca and P supplements free choice, such that individual animals within a group can manifest preferences based on their specific needs.