Mix and Match: Grouping Cows According to Aggressiveness can Reduce Herd Stress

Herds of dairy cows include dominant and submissive individuals. Most of you can identify your herd's boss cow, and though serious brawls are not that common, mild aggressive interaction such as head butting and pushing, as well as non-aggressive, perhaps submissive behavior such as grooming, are visible on an on-going basis. Clearly cows are social beings that interact with each other.

It would be reasonable to expect that a peaceful "society of cows" with minimal disturbances results in the greatest comfort, production and health. As decision-maker for your herd, your management impacts on how the society functions. Yet there is very little research-based information, to help us develop management strategies to improve the social condition of the herd.

Researcher C.J.C. Phillips and M. I. Rind, in Great Britain are two of several "cow sociologists" working toward a clearer understanding of interactions among cows. Two of their recent studies published in the Journal of Dairy Science (Vol. 84 pg. 2424-2429 and Vol. 85 pg. 51-59) may help us begin to understand cows a little better.

In one study, 66 cows were observed for three hours daily for one month, and assigned a "dominance value" based on the number of aggressive interactions which they won or lost. Results showed that in general, big framed cows were more dominant and older cows ranked higher than younger cows. Dominant cows were the first in the parlour for milking. On pasture, they ate faster, but were not necessarily the first to start grazing. Dominant cows also produced slightly more milk than lower ranked individuals.

On the assumption that the submissive cows were stressed by the presence of the dominant animals, the herd was divided so the dominant half was grazed and housed separately from the submissive half. After the split, all cows spent more time lying down -45 minutes per cow per day, suggesting less stressful group dynamics.

Milk production and feeding behavior depended on whether or not hay was fed, but overall, milk yield for dominant cows was unchanged. Submissive cows produced 0.5 litres more milk when separated from dominant herd mates, and all cows gained more weight.

The other study involved separate established groups of 24 second and later lactation cows and 24 first calf heifers. To see how cattle responded to mixing, a new group was formed using eight of the heifers and eight of the cows. During the first week after mixing, milk production went down three per cent, and after six weeks, it remained one per cent lower than the other two groups. The amount of aggressive behavior in the mixed group was not much greater. However cows in the other groups spent 50 minutes more per day grazing and ruminating. All cows in the mixed group spent less time lying down. It appears that in newly established groups submissive cows are busy watching for the boss cow and the boss cow is busy showing she is in charge, and no one has time to eat, rest or make milk.

In this study, production decreased only three per cent. Producers often report much greater drops, perhaps because ration changes at the time disrupt the cow's metabolism, or because housing conditions or crowding intensify the interactions between animals. Most studies support moving several cows at once. In one trial introducing two to 14 per cent new cows into a group had similar effects on the group's production. This suggests mixing cows less frequently in greater numbers is less stressful than adding one new cow at a time.

Generally, any factor that changes group dynamics can be disruptive and can cause decreased production. For example, the disruption, reduced rest and lower feed intake caused by an aggressive cow in heat in a free-stall barn is obvious in many of our own time-lapse videos taped in Ontario barns. Such cows should be taken out to reduce the risk of injury from mounting activity.

Social pressure can also be severe for a newly lame cow, especially if she falls from a dominant position to a lower ranking. Temporary separate housing can do much to promote healing and avoid the disruption in social order as well.

In the first study, cows responded with weight gain and increased resting when researchers reduced the range of social dominance. Setting up separate pastures for first calf heifers and older cows, as was done in the research, is clearly uneconomical since the response was small. When other management considerations make grouping necessary, it may be worthwhile to group by "dominance".

For example in the freestall system, milking cows should not be away from feed for more than two to three hours daily. To achieve this, groups should be no bigger than what the parlour can milk in one hour. A 240-cow herd with a two-by-10 parlour, milking 80 cows per hour should have three groups of 80 cows.

High and low production groups for older cows are likely the first priority. Should the third group be medium producers? The British studies show each move disrupts the social order and it's doubtful that further gains from ration changes will make up for it. A single group of first heifers at all stages of lactation more sense.

Having this group avoids stressful mixing of new, low-ranking heifers with the boss cows. It also narrows dominance range in all milking groups. Heifers require extra feed for growth, and have flat lactation curves so there are nutritional benefits as well. Since they are generally smaller than mature cows, a separate group and different freestall sizes will keep all cows cleaner.

When it comes to balancing group size with cow numbers, the work of Phillips and Rind also proves helpful. If you need a few cows for the heifer group, they report you can find lower ranking submissive cows at the end of the older cows when they go through the parlour. Aggressive heifers, suitable for filling in a mature cow group will be the first in line when the heifers are milked.

While most of you don't milk in three groups, understanding and relating to the social order of your cows is worthwhile no matter what herd's size. Peace and harmony has benefits for cows and their owners no matter how big or small the community of cows.

By Jack Rodenburg - Dairy Production Systems Program Lead/OMAFRA
This article appeared in the January 2003 Ruminations column of the Ontario Milk Producer magazine.