Learned behaviours lead to bone ingestion by phosphorus-deficient cattle

Abstract

Grazing cattle deficient in phosphorus (P) often seek out and chew bones, apparently to obtain dietary P. To investigate this phenomenon heifers naïve to P deficiency were either fed a P-deficient diet (LowP) or grazed P-adequate pasture (AdeqP), and preference tests examined their attraction to weathered bones or a control of wood. During Phase 1 (Days 1–145), the LowP heifers developed severe P deficiency and pica, but demonstrated little attraction to weathered bones. During Phase 2 (Days 146–155), heifers were allowed to interact with and to chew a variety of weathered bones. After this experience LowP heifers were more attracted to bones during Phase 3 (Days 156–166) than during Phase 1 (P < 0.05), and more attracted than AdeqP heifers during either phase. Subsequently, in Phase 4 (Days 167–171), LowP heifers were more attracted than AdeqP heifers (P < 0.01) to weathered bones than to a control of wood, and in Phase 5 (Days 172–176) to bones with more extended weathering. During Phase 6 (Days 177–182), attraction was reduced when bones were placed inside a cloth bag. The olfactory constituents from weathered bones were dominated by aliphatic aldehydes and ketones, consistent with long-chain fatty acid breakdown. It was concluded that attraction of P-deficient cattle to seek and ingest bones is primarily a learned response. Smell, taste and visual appearance all appear to be important cues for attraction. Pica is likely important in causing P-deficient cattle to investigate unusual materials, including bones, resulting in cattle learning by making an association between bone chewing and P ingestion.