Behavioural and genetic investigation of fighting ability in Valdostana breed

Fighting ability is a well-known attitude in Valdostana cattle (i.e., Aosta Chestnut and Aosta Black Pied cattle), due to the strong belligerency that cows exhibit at pasture, when unfamiliar animals met and new hierarchies for the access to resource have to be established. This peculiar attitude revives during the traditional tournaments of Batailles de Reines, annually performed by cows in the Aosta Valley. Annual competition consists of 20 eliminatory tournaments and a final challenge, where only the two autochthonous breeds are allowed to take part in the battles. Using data coming from the battles, fighting ability has been investigated aiming to assess both the behavioural and genetic aspects. Four steps have been followed, aiming to look at fighting ability under different but complementary point of views and to shed light on different concerns. At first, data from 4 tournaments undertaken in 2009 have been video recorded and analysed (i.e., a total of 168 fights) in order to depict both the dynamics of agonistic interaction among cows and what factors may affect the shape and the outcome of a conflict. A suitable phenotypic score for fighting ability (i.e., Placement score) was developed in a second study using data from 6 years of battles (i.e., 2001-2006, approximately 16,000 records belonging to about 6,000 cows). This in order to build a genetic model able to investigate the variance components of fighting ability and to quantify genetic parameters. Additionally (i.e., third study), the analyses included the incidence of conspecifics in the genetic estimates of fighting ability, considering the introduction of the opponent either within the phenotype itself or directly in the model as indirect genetic effect (IGEs). As alternative analysis, the contribution of conspecifics has been retained directly into the phenotype, implementing the previous score into a Competitive Placement Score, thus applied into analogous genetic models. As further step, the effect of another force (i.e., inbreeding) and its relationship with the genetic values for fighting ability has been investigated in Aosta Chestnut and Aosta Black Pied cattle. Population data coming from the entire pedigree, as well as all available information on 9 years of battles (i.e., about 24,000 records of over 8,200 participants) permitted to assign individual inbreeding coefficients to cows. Thus, the incidence of inbreeding into genetic models for fighting ability was studied, as well the possible relation among genetic merits and inbreeding. Results obtained from this study indicate that fighting battles among cows seem to follow the typical dynamic of an escalated contest, with a cumulative assessment of the two contenders. Moreover, age, weight, and, most of all, prior experiences of the previous battles play a role in determining the outline and the intensity of the conflict. In addition, the genetic component of fighting ability results of main importance in affecting the outcome of the encounters. As well, weight, age, herd and tournament revealed as significant factor in the investigation of phenotypic variance, and, together with a direct additive and a permanent environmental, they have allowed the estimates of “non zero” genetic parameters. Heritability of fighting ability showed a level of about 0.08 when evaluated using a classical quantitative model, whereas the introduction of indirect genetic effects drove heritability estimates to levels of approximately 0.11. Moreover, including indirect genetic components showed a better general model fitting, whereas classical quantitative models taking into account of the opponent within the score exhibited the worst fitting. Reasoning on the different variance components that can be accounted into the model (i.e., either direct or indirect and due to conspecifics, as well as related to the permanent environment), models that included the opponent only as genetic effect have provided better estimates. Including the kinship as classes of inbreeding coefficient within the genetic models, heritability estimates undergo some small variations under classical quantitative models (i.e., +0.02) whereas models with IGEs did not experienced any shift due to inbreeding. However, the genetic values for fighting ability resulted as reduced in correspondence to increasing levels of inbreeding, as shown by the negative slope of the linear regression analysis performed on lineages of fighting cows with increasing inbreeding levels. As well as inbreeding shows a positive trend over years due to selection, it is interesting to note that, despite the incidence of inbreeding depression and a lack in planned selective programs, also fighting ability reveal a positive increase in mean breeding values (about 2-3% of gain/year). Thus, models including indirect genetic effects are the most appropriate tool in investigating social traits, and the study of fighting ability in Valdostana cattle may provide some interesting suggestions for the analysis of social traits in the area of animal breeding.