Conditioned feeding responses in sheep to flavoured foods associated with sulphur doses

A study was conducted to determine whether sheep form conditioned flavour a versions (CFAs) or preferences (CFPs) for food flavours associated, respect ively, with excessive or appropriate concentrations of sulphur (S) and also whether the rate of formation and strength of CFAs and CFPs are dependent on the animal's initial S status or the level of administration of S. In ex periment 1, 48 mature ewes were conditioned to associate a new food contain ing a novel flavour with an infusion of S delivered intra-ruminally, or the same food containing another novel flavour with an infusion of distilled w ater. The same flavours were then used in experiment 2. At the end of each conditioning period, the relative preference for the two flavoured foods wa s determined by measuring the amount of each food ingested during a two-cho ice, 20-min preference test. Experiment 1 consisted of two phases. In phase 1 each conditioning period lasted for 5 days and was repeated four times, whereas in phase 2 the conditioning period lasted for 8 days and was repeat ed three times. In experiment 1 the sheep were initially in an S-adequate s tate. In experiment 2, the sheep were re-randomized to treatments and start ed in an S-depleted state. The conditioning periods also lasted for 8 days and were repeated three times. There was no evidence to support the hypothesis that sheep develop CFAs or CFPs to food flavours associated with S doses in phase 1 of experiment I. I n phase 2, however, sheep formed CFAs towards the food with the flavour the y had come to associate with administration of high levels of S. Repeated e xposure to the flavour associated with high levels of S led to stronger ave rsions and there was an interaction between the S dose level and conditioni ng periods, indicating that the rate of development of these CFAs was highe st for the highest S dose levels. The differences between results of phase 1 and 2 were probably due to the different numbers of reinforcements and di fferent intervals between specific flavour/dose associations. In experiment 2 there was no evidence for the development of CFPs or CFAs t o food flavours associated with S doses. The apparent indifference of the s heep to S was probably due to their responding more to their previous exper ience of the food flavours than to their S status. Spearman rank correlatio ns on flavour preferences indicated that conditioned flavour responses form ed in experiment 1 persisted in individual sheep when they were allocated a t random into their new treatments in experiment 2 and influenced or masked the formation of new associations. This demonstration of 'carry-over' effe cts highlights the importance of considering an animal's previous experienc e of flavours and their associations with post-ingestive consequences when coming to conclusions concerning current development of CFAs and CFPs. Thes e results may also have more general implications for feeding studies in an imals that are randomized into treatment groups without regard to their pre vious feeding experiences.