Learned aversion towards oxalic acid-containing foods by goats: does rumen adaptation to oxalic acid influence diet choice?

The ability of goats to learn to avoid flavored alfalfa hay enriched with oxalic acid was investigated in an indoor choice experiment. In addition, the influence of rumen adaptation to oxalic acid on the strength of avoidance behavior was studied. The experiment consisted of four nine-day conditioning periods during which 24 goats were fed hay with or without added oxalic acid for two-day bouts in sequence. Sensory differences between the hays were emphasized by incorporating artificial flavors (fenugreek vs. apple). Half the goats were adapted to oxalic acid by daily oral administration of 0.6 mmol/kg live wt/day of free oxalic acid, which successfully generated an active oxalic acid-degrading rumen microbial population. At the end of each conditioning period, short-term preference for the hay diets was measured in 20-min choice trials. Plasma calcium concentrations were measured during each conditioning period as an indicator of the physiological effect of oxalic acid ingestion. Animals showed a chronic mild hypocalcemia (initial baseline values were 115 mg Ca/dl plasma vs. 89 mg Ca/dl plasma for the mean of the rest of the samplings during the conditioning phase). Preference for the oxalic acid-containing and the control diets was similar prior to conditioning. During conditioning, preference for the oxalic acid-containing diet was diminished (e.g., preference ratios during third conditioning period averaged 0.30 for oxalic acid-containing diets and 0.70 for control diets; P < 0.05). In preference tests carried out one, three, and five weeks after the last conditioning period, preference progressively returned to preconditioning levels. The rumen adaptation treatment did not result in different behavioral responses to the oxalic acid-containing foods. In this experiment goats learned to avoid a mildly aversive agent present in their food when given the opportunity to associate the sensory properties of the food with its physiological effects. Prior physiological adaptation to the aversive compound did not influence the behavioral response.