Learned appetites for calcium, phosphorus, and sodium in sheep

¹ Department of Forest, Range and Wildlife Sciences, Utah State University, Logan 84322-5230
² Department of Animal, Dairy and Veterinary Sciences, Utah State University, Logan 84322-5230

^* To whom correspondence should be addressed. E-mail: villalba{at}cc.usu.edu.

	Abstract

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, 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 groups were moved to 2 new (separate) locations so animals in different groups could not eat dirt, urine, and feces from the other pen. Preference for pomace did not differ between groups during 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 higher Ca concentrations in serum than lambs fed High P-Low-Ca (P < 0.001), 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 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; Figure 2). Lambs offered High P-Low Ca showed a greater preference for CaCO3 (P = 0.12) and NaCl (P < 0.05) and lower preference for NaH2PO4 than 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.

Key Words: calcium, learning, phosphorus, preference, sheep, sodium