The authors of ‘Comparison of veterinary drugs and veterinary homeopathy: part 1 and 2’, respond

International audienc

The influence of experience on contest assessment strategies

Abstract Animal contest behaviour has been widely studied, yet major knowledge gaps remain concerning the information-gathering and decision-making processes used during encounters. The mutual assessment strategy, where the individual assesses its own fighting ability (Resource Holding Potential, RHP) and compares it to that of its opponent, is least understood. We hypothesise that individuals need experience of agonistic encounters to become proficient at mutual assessment. Pigs (Sus scrofa, n = 316) were contested twice. In between contests, animals did or did not (control) receive intense fighting experience. A substantial proportion of the contests reached an outcome with a clear winner without fighting. Non-escalation was highest in RHP asymmetric dyads of the second contest, irrespective of experience. In contest 1 (no experience) and in contest 2 for the experienced animals, costs increased with loser RHP and where unaffected by winner RHP, suggesting a self-assessment strategy. In contest 2 control dyads, which only had experience of one prior contest, a negative relation between winner RHP and costs suggested mutual assessment during the pre-escalation phase but not during escalated aggression. This reveals that a brief and relatively mild experience can be beneficial in the development of mutual assessment whereas profound experience may result in adoption of a self-assessment strategy

Complex contests and the influence of aggressiveness in pigs

Animal contests vary greatly in behavioural tactics used and intensity reached, with some encounters resolved without physical contact while others escalate to damaging fighting. However, the reasons for such variation remains to be fully explained. Aggressiveness, in terms of a personality trait, offers a potentially important source of variation that has typically been overlooked. Therefore, we studied how aggressiveness as a personality trait influenced escalation between contestants matched for resource-holding potential (RHP), using detailed observations of the contest behaviour, contest dynamics and escalation levels. We predicted that winner and loser behaviour would differ depending on personality. This was tested by examining 52 dyadic contests between pigs, Sus scrofa. Aggressiveness was assayed in resident–intruder tests prior to the contest. Contests were then staged between pigs matched for RHP in terms of body weight but differing in their aggressiveness. In 27% of the contests a winner emerged without escalated physical fighting, demonstrating that a fight is not a prerequisite between RHP-matched contestants. However, the duration of contests with or without fighting was the same. In contests without a fight, opponents spent more time on mutual investigation and noncontact displays such as parallel walking, which suggests that ritualized display may facilitate assessment and decision making. Winners low in aggressiveness invested more time in opponent investigation and display and showed substantially less aggression towards the loser after its retreat compared to aggressive winners. Aggressiveness influenced contest dynamics but did not predict the level of escalation. Prominent behavioural differences were found for the interaction between personality and outcome and we therefore recommend including this interaction in models where personality is considered. Analyses based on contest duration only would miss many of the subtleties shown here and we therefore encourage more detailed analyses of animal contests, irrespective of the level of contest escalation

Lateralization influences contest behaviour in domestic pigs

Cerebral lateralization, i.e. hemispheric asymmetries in structure and function, relates in many species to a preference to attack from their left. Lateralization increases cognitive capacity, enabling the simultaneous processing of multiple sources of information. Therefore, lateralization may constitute a component of fighting ability (Resource Holding Potential), and /or influence the efficiency of information-gathering during a contest. We hypothesized that lateralization will affect contest outcome and duration, with an advantage for more strongly lateralized individuals. In 52 dyadic contests between weight-matched pigs (Sus scrofa; n=104; 10 wk age), the direction of orientation towards the opponent was scan sampled every 10s. Laterality indexes (LI) were calculated for the direction and strength of lateralization. Up to 12.5% of the individuals showed significant lateralization towards either the right or left but lateralization was absent at the population level. In line with our hypothesis, animals showing strong lateralization (irrespective of direction) had a shorter contest duration than animals showing weak lateralization. Winners did not differ from losers in their strength or direction of lateralization. Overall the results suggest that cerebral lateralization may aid in conflict resolution, but does not directly contribute to fighting ability, and will be of value in the study of animal contests

Sociable swine : indirect genetic effects on growth rate and their effect on behaviour and production of pigs in different environments

Social interactions between pigs can influence their health, welfare, and productivity. The effects of social interactions on individuals are partly genetic, and this genetic effect is known as an Indirect Genetic Effect. IGEs are thus the heritable effects of an individual on the trait values of its social partners, e.g. group mates. Previous research has identified IGE for production traits, which suggests that selection for IGE may contribute to selection response. However, validation through selection experiments is required. The objectives of this thesis were a) to determine the consequences of selection for ‘IGE on growth rate’ (IGEg) for production traits and behaviour of pigs, and b) to study possible mechanisms underlying IGEg in pigs. First, the relationship between pig behaviour and growth rate was studied in several trials. This showed that oral manipulative behaviours directed at pen mates, such as tail- and ear biting and chewing, can reduce growth rate of the victims, whereas receiving social nosing may enhance growth rate. Second, a one-generation selection experiment was conducted in pigs. Sires (n= 24) and dams (n= 64) were selected to create a high vs. low contrast for IGEg in the offspring (n= 480). The contrast was 14 g average daily gain (ADG). Offspring were studied in a 2×2 arrangement with IGEg (high vs. low) and housing conditions (conventional vs. enriched with straw bedding) to examine genotype × environment (GxE) interactions. Selection did not alter production traits, including ADG. Behaviour showed consistent changes, whereby high IGEg pigs showed less biting behaviour towards group mates and objects. High and low IGEg pigs did not differ in aggression or body lesions during 24-h regrouping with unfamiliar pigs. They did, however, differ in aggression towards their own group members when they were reunited after the temporary regrouping test. In combination with other tests and observations, this might indicate that high IGEg pigs are less fearful or less stress sensitive than low IGEg pigs. There were no G×E interactions, but enrichment had a positive effect on behaviour which was additive to that of selection. Despite the lack of response in ADG, genetic selection for IGEg and enriched housing conditions improved the behaviour and welfare of pigs.</p

Trade-offs between proximity and physical contact during group integration in pigs (Sus scrofa domesticus)

During behavioural trade-offs, individuals have to decide whether to express a behaviour which may lead to a reward or potential costs when engaging in a risky situation. Social integration forces animals to make such trade-offs. We hypothesized that animals predominantly demonstrate non-tactile behaviour and hence less tactile behaviour in a high-risk context such as during social integration, while using tactile behaviour more than non-tactile in less risky situations such as under social stability. Pigs (Sus scrofa domesticus) typically are in close physical contact to each other, but physical contact also relates to increased aggression. We investigated 18 groups (142 pigs) across different phases of social stability, thereby observing snout proximity and snout contact. Additionally, aggression (reflecting costs) and growth performance (reflecting benefits) were measured. Data were analysed using mixed models while accounting for group stability. Snout proximity was indeed most frequent during social instability and reduced as stability increased, while snout contact remained more constant. The high occurrence of snout proximity during social instability suggests conflict avoidance and thus risk aversion. Animals that showed more frequent snout proximity grew slower, while initiators and recipients of frequent snout contact had a better growth performance. The causality of these effects cannot be ascertained but it is possible that slower growing, and thus weaker individuals may have made a behavioural trade-off by choosing proximity rather than contact during social instability. The results further emphasize the importance of distinguishing between nuances in behaviour

An estimation of the financial consequences of reducing pig aggression

Animal welfare scientists have accumulated knowledge and developed interventions to improve livestock welfare, but these are poorly adopted in commercial practice. Animal welfare interventions are rarely tested for economic viability and this limits their uptake. This study employs Stochastic Partial Budgeting (SPB) to determine the viability of animal welfare improvements. Aggression between pigs is used as an example because there is a large literature base from which to draw interventions, and the problem has persisted for decades without resolution. Costs and benefits of three interventions to control aggression (pre-weaning socialisation, synthetic maternal pheromones and large social groups) were estimated by reviewing the academic and industry literature and by conducting a survey of sixteen pig farmers. The net effects were compared to farmers' willingness to pay (WTP) for interventions to reduce aggression as identified by recent research. Results are consistent with prior research which indicates that improving animal welfare generally comes at a cost to producers. Nevertheless, pre-weaning socialisation resulted in a neutral or positive net effect 38% of the time and should be central to campaigns promoting the control of aggression in the industry. Exposing pigs to synthetic maternal pheromones did not improve profitability but the net costs were small and within the realms of WTP for a sub-group of farmers with animal welfare goals. The net costs of converting existing buildings in order to house pigs in large social groups were beyond the realms of farmers' WTP. The approach adopted in this study, of combining SPB with WTP from the sector, should be extended to other animal welfare issues