Short communication: A milk replacer aversion model in calves to test flavour-masking effects

Abstract

This study aimed to evaluate the availability of two sensory additives (SAs) to masque non-palatable ingredients commonly present in milk replacers (MRs). Both SAs were based on a synergistic mixture of non-nutritive flavouring substances with four taste categories (sweet, umami, sour, and salty); the only difference between them was the inclusion of polyols, which were not included in SA2. Two experiments were conducted for this purpose. In Experiment 1, an MR aversion model was developed using 24 Holstein male calves (7 ± 0.9 d of age and 43.3 ± 1.39 kg of body weight [BW]). In the first two weeks of the study, calves were fed increasing amounts of MRs until the animals were able to consume 8 L/d at 15% dry matter (DM) concentration for two feedings per day. Thereafter, MR aversion was induced in half of the calves by adding a mixture of bitter taste feed additives (Bittermix) from days 14 to 22 of the study (aversion week). The daily MR intake and eating rate were recorded from the two previous days of the challenge and during the aversion week. In Experiment 2, the same model was used with 37 Holstein male calves (6 ± 0.9 d of age and 40.2 ± 1.40 kg of BW). Owing to health issues in this experiment, the aversion week was postponed at 38.5 ± 1.12 d of age until the animals were able to consume at least 90% of 8 L/d at 12.5% DM concentration. The aversion test was performed as follows: no supplementation (CTRL), Bittermix at 30 g/kg of dry MR (BM), BM plus SA1 at 2 g/kg of dry MR (SA1), and BM plus SA2 at 2 g/kg of dry MR (SA2). Data were analysed with a generalised mixed model that accounts for the fixed effects of MR supplementation, the meals during the aversion week, the interaction of the MR supplementation and meals, and a calf as a random effect. In the aversion test of Experiment 1, calves that were fed Bittermix showed an increase in the incidence and amount of MR refusals (P < 0.05) compared with CTRL calves. In Experiment 2, the incidence of refusal and time devoted to consuming MR were similar in all treatments. However, the eating rates were greater (P < 0.01) in CTRL and SA2 than in BM and SA1. Adding a mixture of bitter tasting feed additives in the MR changed the feed intake parameters of the calves. The addition of a specific sensory additive, namely, SA2, reversed the negative effects caused by the bitter products.