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Phosphorus appetite in sheep: Dissociating taste from postingestive effects^1,2

J. J. Villalba^*,3, F. D. Provenza^*, J. O. Hall and C. Peterson^*

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

³ Corresponding author: villalba{at}cc.usu.edu

We hypothesized that lambs discriminate the postingestive effects of P and associate those effects with feed flavor to modify feed choices. Three predictions were tested based on this hypothesis: 1) lambs will modify preference for arbitrary flavors eaten during intraruminal infusions of NaH₂PO₄, 2) changes in preferences are more specific than changes in osmotic load induced by salts of Na; and 3) preference for P is inversely related to the concentration of inorganic P in blood. Thirty lambs were depleted of P by the offer of a P-deficient diet, allocated to 3 groups (10 lambs/group), and conditioned during 3 periods as follows: During conditioning period 1, lambs in each of 3 groups ate a poorly nutritious feed (grape pomace), flavored differently for each group, while water was infused into the rumen. During conditioning periods 2 and 3, lambs again ate grape pomace, with 2 new flavors now paired with infusion of an aqueous solution (126 mmol) of NaCl (conditioning period 2) or NaH₂PO₄ (conditioning period 3), rather than with water. After conditioning, all lambs were offered a choice of the 3 flavors during preference tests immediately after conditioning (period 1) and every 3 wk thereafter (periods 2, 3, and 4). During period 1, when serum inorganic P levels were greatest, lambs preferred flavors paired with water > NaCl > NaH₂PO₄ (P < 0.05). During periods 2 and 3, as inorganic P concentrations decreased in serum, lambs preferred flavors paired with NaH₂PO₄ > NaCl (period 2, P = 0.10; period 3, P = 0.05). Lambs preferred flavors paired with water > NaH₂PO₄ in period 2 (P < 0.001), but those differences disappeared in periods 3 and 4 (P > 0.05). During period 4, lambs preferred flavors paired with NaCl > NaH₂PO₄ (P < 0.10). The estimate of the slope for the linear relationship between intake of flavors paired with NaH₂PO₄ and serum inorganic P was negative (P < 0.0001), whereas estimates of the slopes for the relationships between intake of flavors paired with NaCl or water and serum inorganic P were not different from 0. Thus, preference for P was inversely related to the concentration of serum inorganic P. Our results suggest lambs discriminated among the postingestive effects of NaH₂PO₄, NaCl, and water and associated those effects with specific flavors. Lambs avoided flavors paired with NaH₂PO₄ during periods of P replenishment, and they increased preference for those flavors during periods of P need.

Key Words: choice • feed preference • intake • phosphorus • postingestive learning • sheep

This article has been cited by other articles:

				J. J. Villalba, F. D. Provenza, and J. O. Hall Learned appetites for calcium, phosphorus, and sodium in sheep J Anim Sci, March 1, 2008; 86(3): 738 - 747. [Abstract] [Full Text] [PDF]