The Teagasc pasture profit index (PPI) is a perennial ryegrass variety selection tool.
Varieties which have higher agronomic performance for grass traits are rewarded with higher economic values.
The traits include seasonal herbage yield, quality, silage and persistency all of which affect paddock performance and are measured by the Department of Agriculture, Food and the Marine recommended list trials.
On-farm variety evaluations in the past eight years have highlighted certain differences in grazing utilisation of some grass varieties.
These grazing difficulties create additional grassland management challenges and lead to disappointing paddock performance.
Grassland farmers want an indication of a variety’s ability to be grazed prior to sowing.
To date, farmers have had no feedback prior to sowing a variety on whether it’s good, average or poor in its grazing performance. This knowledge gap has led to variety grazing evaluations and now the incorporation of a grazing utilisation trait in the PPI.
This is one of the major traits linking the plant to the animal that has been omitted from evaluation programmes up to now. From 2021, a provisional grazing utilisation trait is included as part of the PPI using the utilisation star rating.
Utilisation star rating
The utilisation trait is measured from variety grazing evaluation studies conducted at Teagasc Moorepark. Variety plots are grazed by cows on a rotational grazing basis as used on Irish farms.
Grazing performance of varieties is measured using residual grazed height. The residual grazed height of a variety is the difference between observed post-grazing sward height (measured with a rising plate meter) and its predicted post-grazing sward height.
Predicted post-grazing sward height is calculated based on the pre-grazing sward height of a variety.
Where a variety’s observed post-grazing sward height is greater than its predicted height, the resulting residual grazed height is positive which is indicative of poorer grazing efficiency, ie the variety was grazed to a higher post-grazing sward height than expected. If a variety’s observed post-grazing sward height is lower than is predicted, the resulting residual grazed height is negative, indicative of better grazing performance (ie better cleanout).
The residual grazed height performance of each variety is used to determine the additional herbage utilised by a variety over the grazing season. This additional/reduced herbage is multiplied by 4c/kg to determine the utilisation economic value of each variety.
The utilisation potential of varieties is expressed as a star rating. Table 1 displays the corresponding range in utilisation values for each star rating. Varieties with a higher star rating for utilisation are better grazed by cattle.
Varieties are evaluated by the Department of Agriculture to ensure they meet a minimum performance standard. Varieties that are not recommended listed should not be sown on farms.
The number of varieties sown within mixtures should be limited to three or four to ensure that superior varieties are allowed to express their performance advantage.
Mixtures containing many varieties dilute the performance of superior varieties which may subsequently lead to disappointing swards. Farmers don’t want poor return on their reseeding investment and the effect of poor graze-outs is evident in the following rotations with declines in digestibility and productivity of those swards.
Variety selection decisions in the past were based on ploidy and heading date characterisations of varieties as these factors tended to give predictable results in how they behave. Variation between varieties of the same ploidy for many traits does occur.
In the current recommended list, tetraploid varieties have performed very well and this success has seen more tetraploid inclusion in swards. This trend is likely to continue.
Research from Teagasc investigating the effect of heading date range on mixture performance in rotational grazing systems found that wide heading date range within mixtures did not affect the digestibility or grazing efficiency of the sward.
Intensive grazing of swards before excessive seed head production occurred, limited the heading date influence in these studies. For silage swards, heading date range should be kept to a minimum and be no more than six days between varieties.
The planned field use should dictate variety selection. Paddocks that are located on the milking platform are unlikely to be used for silage and therefore the silage index doesn’t have to be emphasised.
Traits of importance for rotationally grazed paddocks include spring and autumn herbage production, quality and grass utilisation.
For fields destined for intensive silage production, use the silage sub-index (>€25) to identify the highest yielding varieties for those systems.
Farmers wanting to select varieties for some grazing and silage production should be guided towards varieties that exhibit high performance in silage production (>€20) and utilisation. It is worth noting, that some intermediate heading varieties have good graze out.
– Aidan Brennan
The addition of stars to the PPI is a nice new feature. In my view, farmers who are picking varieties which are primarily going to be used for grazing need to be looking at the stars as much as the other individual grazing related traits such as yield and quality.
It is very easy to work your way down the PPI picking varieties with at least four or five stars that have a high PPI.
Varieties with low stars are less suited to grazing mixtures. They have low utilisation scores for a reason – cows don’t like grazing them.