Optimum grazing stocking rate in mid-season

Best practice grazing management over the summer months is to maintain pre-grazing herbage mass between 1,300 and 1,500kg dry matter (DM)/ha (8 and 10cm), and target a post-grazing sward height of 4-4.5cm.

Grazing conditions have been difficult this spring; therefore, grass quality on a lot of farms needs correction. In order to correct/maintain grass quality through June, July, and August, there must be some scope in the grazing system to allow for surplus paddocks to be taken as bales to ensure quality regrowth.

Many farmers say they ‘dread the sight of bales’, and tighten cows onto higher stocking rates to avoid these surpluses. However, this often leads to cows being forced into heavy covers and being short of grass intake over the summer.

It is better to have some flexibility in the system. This flexibility will be determined by the herd demand throughout this period, which is dictated on a lot of farms by the decision on how much land is closed up for second-cut silage on the grazing platform.

Table 1 shows the daily grass demand per hectare at different stocking rates. The target grass allowance in this example is to maximise herd performance from grazed grass, and would typically mean a daily grass allowance of 18kg DM per cow. When you look at typical average growth rates across this period, they range from 50-65kg DM/ha/day.

Table 1: Daily herd demand at different stocking rates

Setting herd demand above this will increase pre-grazing yields, reduce grass quality, reduce animal performance, and increase concentrate fed, thus, increasing the overall cost structure. As a rule of thumb, farms that grow 12t DM/ha annually should stock the farm at 3LU/ha during this period, while farms that grow 14t DM/ha annually should stock the farm at 3.5LU/ha. This will allow approximately 20% of the grazing area to be taken as surplus during this 10-week period (June 1-August 15).

Farms that have experienced reduced growth rates due to drought conditions over the last number of seasons should set demand based on average growth rates over a five-year period, make provisions for adequate silage stocks from other land sources rather than overstocking the grazing area, and target to have second-cut silage crops made by July 15. As far as the 'dreaded bales' are concerned, running these stocking rates will usually result in about two surplus bales per hectare from the grazing block, or 100 bales for an average size herd. That’s not a major issue considering the potential benefits to grass quality and cow performance.

This article first appeared in the June Teagasc Dairy Advisory newsletter.