Do sheep and cattle care for their immediate neighbours? They do when they are left on their own because they want to rejoin them. But once together they hardly show respect. There is a clear social strata created by age, size and the presence of horns and there must be numerous other factors that determine the place of any particular individual animal in the social ranking.
But there are interacting factors that confuse any analysis. These mostly involve efficiency. A good example is ewes in winter. Without question four-tooth ewes perform better when run on their own. They are still a growing animal going into winter. On their own they scan better, maintain condition better and have a greater lambing outcome. But in flocks of less than about 4000 ewes, to have the four-tooths out really compromises the efficiency and effectiveness of a winter rotation. In my opinion having too many mobs is one of the most common causes of running out of winter feed. The challenge is to be able to work out the relative benefits of them being on their own against the costs of being in less control.
The question of the ideal ewe mob size is one I’m commonly asked. What confuses the response is the variation in performance outcomes are influenced by so many factors that to say more than 2000 is not ideal is just not possible.
I see high-performing flocks that run 4000-plus ewe mobs in rotation over winter at stocking rates the same as other farmers run 2000 in a mob. To be high-performing they must be meeting the feeding objectives but it could be, for example frequency of shifts or terrain that could be the difference as to why it works on some farms and not others. Rather than focus on how big mobs are I always look first at how well the feeding objectives can be met. To do this usually requires well-planned winter feed allocations. To achieve these often relies on moderating the number of mobs so as to adequately ration the feed. Reducing the number of mobs always increases the number in each mob. Of course, when feed is short the reflex response is to reduce the number of mobs.
The number of bulls in a mob is probably the easiest situation to ascertain a certain number is best. Yearling bulls in spring in mobs of 50 can be unpleasant to watch, that is if they are in a rotational system. Bulls a year older are even more unpleasant to watch. The performance cost of too many bulls is easier to see than in other stocking systems and the balance between the size of mobs and the efficiency of pasture management is easier to work out.
But in other young cattle systems it is much murkier. In some contract grazing systems the heifer mobs are kept according to their origin so the mob sizes can be quite different. Obviously the break sizes and maybe the shift frequency could be adjusted but even so there is a perception that bigger mobs do not perform as well.
I recently looked at two grazing enterprises that are part of a bigger beef and sheep system. In both there were four mobs on one farm and seven on another where the heifer mobs were of significantly different sizes. There was absolutely no clear association between mob size and growth rates. The biggest mob was 160 and smallest 65.
But the potential growth rates of these heifers when they are arrive has already been hugely influenced by their background. Genetics aside, their colostral intake, the amount of milk they got before weaning, their weaning weight, growth rates up to weaning and for the May arrivals, the weight they arrive at will all have an influence. Of course, those May arrivals bring with them a summer experience that could affect their subsequent growth.
So mob size probably ends up being a minor player as long as enough feed – quantity and quality – is being provided. Once again the effect of feeding levels probably transcends all other factors.
