Effects of positive reinforcement training for heifers on responses to a subcutaneous injection.

Cattle are subjected to routine procedures that require restraint and close contact to humans, which are both potentially aversive to the animal. Positive reinforcement training techniques may affect how animals perceive and respond to these procedures. The objectives of the current study were to describe a positive reinforcement regimen used to train cattle to stand still for a sham injection, and to assess the effects of this training on the responses to an actual injection. Eight "agency" heifers were trained, over an average of 85 ± 4.6 sessions, with positive reinforcement (i.e., animals received a grain reinforcer for desired behaviors) to enter a headlock, and they were habituated with counterconditioning and desensitization to a sham injection (i.e., animals were gradually exposed to the sensation of the sham injection, paired with access to grain). The headlock remained open at all times to allow heifers to leave. Eight "habituation" heifers were exposed to the treatment area and headlock for an equal number of sessions and duration as agency heifers, and 7 "naïve" heifers were provided no exposure to the treatment area. Once agency heifers tolerated the sham injection, all animals received a 1-mL subcutaneous injection of 0.9% NaCl while in the head lock (habituation and naïve heifers were locked in but agency heifers were free to withdraw). Immediate responses to the injection, starting with tenting of the skin, were video recorded and summarized as a reactivity score, which included the number of steps, head tosses, and backing-up movements; we also recorded the latency to approach the treatment area and headlock for 3 d after the injection. Of the agency heifers, 5 remained standing for the actual injection, whereas 3 heifers moved out of the headlock for a brief period (1, 3, and 5 s, respectively). Habituation heifers had a higher reactivity score [17.5 (10.5-28); median (IQR)] than agency [6 (2-13.5)] and naïve heifers [6 (5-7)]. Averaged over the 3 d after injection, agency heifers showed lower latencies to come to the treatment area [8.7 (7.2-24.2) s] than did habituation [50.5 (28-60) s] and naïve [53.7 (18-60) s] heifers. Agency heifers voluntarily entered the headlock within 1.3 (1-1.5) s but, with one exception, none of the other heifers did so within the allowed 15 s. These results indicate that dairy heifers can be trained with positive reinforcement and counterconditioning to voluntarily accept a painful procedure, and that training can reduce avoidance behaviors during and after the procedure.