Grass growth increasing, milk protein % dropping

This week, there is a running theme of high pre grazing covers and suppressed protein %.

Farms that have been walked weekly and surpluses removed have maintained milk production with excellent protein levels. This is owing to maximum energy intake by the grazing animals on high quality covers. Protein % is an indicator of the cows energy levels – sudden drop in protein % indicates a reduction in energy intake, e.g. after heavy rainfall or when cows graze excessive pre grazing covers (>1600kgs/ha).

As discussed last week, the natural process of the grass plant in sending up a seed head means that the increased stem content has further reduced the energy in these higher covers. Speeding up the grazing round to 18-20 days, (achieved by removing surplus paddocks) and a target cover/lu of 150-170 will result in grazing lower covers with reduced stem content. The following rotation will then be largely stem free. All of the above will increase the energy content of the grass and thereby increase protein %. The one point you must be careful of is the level of surplus grass we remove from the platform, it is for this reason that I give a range in cover/lu targets above (150 or 170).

On farms where surpluses are removed by mowing, the regrowths in these paddocks will take approx 28-30 days before a PGC of 1500 is back on them. As we now need to be on an 18-20 day rotation, these paddocks will not be back in this round which will increase the demand/ha. Ensure you do not increase the demand/ha too much (>80), potentially resulting in a deficit in 10 days time.

E.g. on a farm today, the cover/lu was 200kgs. In our decisions, we reduced this to 170kgs with surplus paddocks removed as bales at the next opportunity, the farmer had pre mowed two paddocks last week. This will reduce growth rates slightly and so 170kg/cow was low enough to reduce the pre grazing covers and ensure we will have sufficient grass in 10 days. If there was no pre mowing done on this farm, we could have easily reduced cover/lu to 150kgs.

The main point – walk farm, go through your figures, establish what your cover/cow is and come up with a grazing plan for the week ahead. Taking out surpluses without this information is guess work and usually results in more surpluses arising in 7 days time as you didn’t take out enough. To increase protein, grass quality must be excellent – increasing meal levels might get you an extra pen/calendar at Christmas but it certainly won’t do anything for the cows energy demands, as grass is making up the greatest proportion of the diet.


A reduction in butterfat levels at this time of the year is not due to insufficient fibre, but an increased lipid content in the grass; this reduces fermentation which in turn affects rumen acetate production, the building block for milk fat synthesis. Farmers feeding a dairy nut high in maize meal should replace the maize with other energy sources such as sugar beet/soya hulls as maize is rapidly degradable in the rumen and can further suppress acetate production. Grass will always have sufficient fibre with an NDF content of >35%.

Cathal McAleer is a grassland consultant working with individual farmers and facilitating discussion groups throughout Ireland.

087 160 2491 / 0044 7749 531679 [email protected]