Sorting is the term given to the selective behaviour of cows, or any stock, when offered mixed feeds. Sorting is that frustrating ‘nosing’ behaviour which creates nest shapes in the feed, and pushes it away from the feed fence. Usually cows sort for the concentrate portion of the ration, but they may be sorting against unpalatable feeds, or even looking for fibre if they have eaten too much concentrate previously. Irrespective of the motive, sorting causes unbalanced nutrient intake. This is proven to result in reduced efficiency of feed conversion through reduced rumen balance, and so financial loss. Another unseen problem with sorting is that it reduces feed intakes as cows eat slower due to all that messing around at the feed fence.
Recent publicity of techniques such as ‘compact TMR’ (where lots of water is added to the concentrate and the TMR extensively mixed) have brought the issue of sorting back into conversations. The moisture level of a TMR mix is often highlighted as key to sorting but is this right? And what other factors are important? With so many factors at play in each farm situation it is often difficult to be sure what works or doesn’t – this is where the research on the subject is really useful to provide scientific guidance rather than just assumption and opinion! So what does the science say?
Particle size – researchers have found that when particles of over 19mm are sorted against these cows have lower rumen pH and butterfat. At a group level the effect of this has been measured at 0.9L milk/day for every 2% of the fibre sorted, which is very significant. This makes sense that cows miss the fibre when they do not eat it, but think about how many cows are fed long fibre (bigger than a 5 pence piece) to improve rumen health! Fibre is only effective when they eat it, otherwise the heifers, shy and lame cows have to eat it later in the day. It may be a little counter-intuitive but chopping forages shorter gets more fibre into cows, both through a reduced ability to sort against these longer pieces; and a general increase in forage intake as they can physically eat more of it.
Dry Matter content – like the assumption that long fibre is good for cows, there is an assumption that a wetter mix is more difficult to sort. It figures that the concentrate will stick to the forage making it harder to separate. This assumption has been proven true for very dry rations based on dry forages for example a TMR based on hay. But we don’t see these in the UK, and for silage based TMR in the range we normally see them (40-50%DM) then adding water has actually increased sorting in some studies. Further the addition of water to these already moist rations resulted in decreased intakes, and increased risk of feed heating. So according to the science in most of our South West TMR rations adding water is a pretty questionable idea. Molasses is more beneficial, it adds to stickiness and palatability without the ‘fill’ effect of lots of water.
What else can we do? – Management factors. Twice a day feeding has been shown to reduce sorting, yet is often practically difficult on farm. It has also been shown to increase dry matter intake, an added bonus where it is possible. Palatability is also under our control. Good forage making and avoiding spoiled feeds in the mix will reduce unpleasant tastes cows try to avoid. Similarly with concentrates some raw materials are more palatable than others and FeedCo choose these for our feeds for this reason. As mentioned above cows will sort for the fibre particles when the diet is unhealthy causing low rumen pH. Accurate rations with the right balance of fast fermenting carbohydrate to fibre are important and should not be underestimated.
For some reason we can be tempted to blame the cows when they are sorting, like they are spoilt children caught raiding the biscuit tin! Our challenge is to prevent them doing it rather than helplessly blaming them, and I hope this may have helped inform good decisions.