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Summary The object of this study has been to describe a type of social organization existing within a herd of dairy cattle, and to explore the effects of this organization on the behaviour of the individuals. Some of the ramifications of the organizational patterns are explored in an effort to trace the development of the organization. A rather detailed description of the physical plant and management routines at the station where these studies were conducted is presented in the first section of the dissertation, so that the reader who is unfamiliar with dairy herd practices may better understand the ensuing discussion. Aggressive behaviour patterns of the individual are also described in detail so as to afford the reader a clearer understanding of the role of the individual in the group. Such behaviour apparently follows a definite sequence, each phase of which is discussed in detail. The various links in the chain of aggression are termed: the approach , the threat , the physical contact , and the ensuing victory or defeat. The approach may be active or passive; while passive approach merely describes the chance meeting of two cows engaged in random wandering, active approach implies purposeful behaviour on the part of one or both of the animals. Direct physical contact between two animals involves either butting or actual fighting. Butting is defined as when one animal uses its forehead to direct a blow at another without any retaliatory action on the part of the struck animal. On the other hand, fights occur when the struck cow strikes back. Commonly, a fight consists of a series of encounters; the actual encounters do not last for more than about a minute at a time and invariably end with one animal taking flight. The interval between encounters may vary from a few seconds to five minutes, with “displacement grazing” being the major activity between encounters. Actually, most contesting actions observed did not progress further than the threat stage, although these contests are considered just as decisive as if they had progressed through the fight phase. Each group in the herd was observed for at least one hour a week during the course of this study. During the observational period, careful notes were kept of each animal involved in a contest, and the outcome of the, contest was recorded. Close to 5,000 individual contests were recorded and were plotted on a large master chart. The pattern of wins and losses clearly indicated that the herd was organized in a straight-line peck-order very much like that previously described by workers in the field of domestic fowl. The dominance order was compared to the ages, weight and production records of the animals. A highly significant relationship obtained between rank and age and also between rank and weight, but the relationship between rank and milk production was inconclusive. The correlation between rank and the failure to complete a full lactation period was of a low order of significance and therefore not considered further. In an effort to separate age and weight from seniority, two completely strange cows were introduced into a group of fourteen animals from the experimental herd. After the new group had stabilized, the dominance order was again plotted and it was found that the two introduced cows were very much “out of line” with respect to age and weight. Later, when the two strange cows were introduced to two high ranking animals from the experimental herd, the group of four set up a rather elaborate circular type of dominance order. This particular order did not show any relationship to age or weight, although it was markedly affected by the previously established relationships within the pairs of animals. Hence, it is concluded from these results that although age and weight are closely allied to the social scale pattern in the herd, they are probably not causally related. The data are suggestive that in normal herd management, seniority, as depicted by age or weight, is of primary importance in the determination of rank position. The socal position of each animal is probably determined at three to six months of age, when she first encounters large, group living conditions. |
