Abstract
Simple SummaryInformation about the real dominance status of an animal is important to prevent misinterpretations about the social structure in animal groups. Thus, “one fight, won more” must not be interpreted as being dominant. Here, significant dyads help to answer the question of whether one animal is definitely dominant over another, and to clearly evaluate the social hierarchy within a group of animals. In the present study, two calculation methods for the determination of significant dyads in pigs are proposed: on the pen level, i.e., taking all fights in the pen into account, and on the dyad level, i.e., each dyad is considered individually. In three mixing events (weaned piglets, fattening pigs, gilts) the impact of significant dyads on dominance indices was calculated. The number of significant dyads was low but the rank order between the two different methods remained stable. Comparing both of the proposed methods, limits should be calculated on pen level due to the higher flexibility. Thus, significant dyads can be also determined in pens with a low number of fights. Dominance indices are calculated by considering the differences between the number of won and lost fights. Whether these differences show a significant asymmetric outcome or not is neglected. Thus, two calculation methods for the limits of significant dyads are proposed using a sign test based on the differences in won and lost fights, considering all dyadic interactions in the pen (PEN: pen individual limits), and a sign test focusing on each individual dyad (DYAD: dyad individual limits). These were compared to the data set containing all dyadic interactions (ALL). Agonistic interactions in three mixing events were video recorded for two and a half days (weaned piglets) or one and a half days (fattening pigs, gilts). Dominance indices (DI) were calculated for all data sets. Pen/dyad individual limits revealed a small number of significant dyads (weaned piglets: 12.4%/8.8%; fattening pigs: 4.2%/0.6%; gilts: 3.6%/0.4%). Pen individual limits should be selected as they allow adaption of the limits according to the fighting frequency. Spearman rank correlation coefficients of the dominance indices between the data sets were always above 0.7, implying that the rank order remained relatively stable. Information about the impact of significant dyads on sociometric measures is important to prevent misinterpretations about the social structure in animal groups and should be considered in future studies.
Highlights
According to Makagon et al [1], the behavior of farm animals both influences and is influenced by the behavior of their pen mates, i.e., an individual’s interactions with others are dependent on the behavior of their pen mates and vice versa [2,3,4,5]
For fattening pigs and gilts, an even lower number of significant dyads with 4.2% and 3.6% for pen individual limits and 0.6% and 0.4% for dyad individual limits were obtained. These findings are in accordance with the average number of agonistic interactions per animal in the three observed age groups considering all dyadic interactions, i.e., weaned piglets, with 12.3 fights/animal fought significantly more compared to fattening pigs with
The results of the present study revealed with the high standard deviation for the number of different categories of dyadic interactions, that there is a huge variation in the behavioral patterns of each single animal group which has to be taken into account
Summary
According to Makagon et al [1], the behavior of farm animals both influences and is influenced by the behavior of their pen mates, i.e., an individual’s interactions with others are dependent on the behavior of their pen mates and vice versa [2,3,4,5]. Knowledge about the development and the spread of behavioral patterns within a group Animals 2019, 9, 344 tail biting) is important to understand the social mechanisms behind each behavioral pattern and allows the development, improvement and implementation of prevention and intervention strategies [1]. One example of these behavioral patterns is the establishment of a stable hierarchy within a group of animals after rehousing and mixing. There are various parameters that help to describe and analyze social relationships within a group of animals. First of all the level of the individual animal, followed by the level of pairwise relationships, the so-called dyads and lastly, the level of the whole group, with regard to all animals in each pen [7]
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