Teagasc has recently released some interesting results regarding the grazing efficiency of certain perennial ryegrass varieties – from the Department of Agriculture, Food and the Marine (DAFM) 2016 recommended list.
Grazing efficiency refers to how well grass swards are grazed by the animals. Grass varieties with good grazing efficiency are grazed to a low post-grazing sward height (PostGSH) and varieties with poor grazing efficiency are grazed to a high and uneven PostGSH.
The purpose of the study was to identify which perennial ryegrass varieties had the most superior grazing efficiency and identify which varieties were most suitable for grazing.
In 2016, 30 perennial ryegrass varieties were chosen and sown. Over the course of the next two years, the plots were grazed (19 times) with the pre and post-grazing swards examined and results recorded.
The plots were grazed when they reached a target pre-grazing cover of 1,400kg DM/ha and the cows were removed when a PostGSH of 4cm was achieved.
Results
Residual grazed height vs. grazed herbage yield
Over the course of two years, the relationship between the residual grazed height (varietal grazing efficiency) and the grazed herbage yield of the varieties was examined.
Varieties with negative residual grazed height (left hand side of the graph) are indicative of varieties with high grazing efficiency; such as AberGain and AstonEnergy – which are both tetraploid varieties.
Varieties with positive residual grazed height (right hand side of the graph) are indicative of varieties with low grazing efficiency and may require ‘topping’ during the grazing season period.
Organic matter digestibility (OMD) vs. post-grazing sward height
Additionally, over the two years, the relationship between the varieties OMD and the post-grazing residual were examined.
The data clearly shows that the cows grazed varieties with a higher OMD content which achieved lower post grazing sward heights.
Tetraploids have higher OMD content so achieved lower post grazing sward heights.
Live leaf content vs, post-grazing sward height (cm)
Finally, the relationship between the proportion of live leaf in the grass variety and the post-grazing residual were examined.
From the data you can see that cows prefer to graze varieties with a higher leaf content, achieving lower post-grazing residuals. This may be due to the high palatability of the grass or how the grass variety presented itself for grazing.
Conclusion
In conclusion, each study shows that tetraploid grass varieties are the leading varieties for achieving the most superior grazing efficiency and so the lowest post-grazing sward heights.
However, huge variability exists amongst the tetraploid varieties in terms of residual grazed height, OM content and live leaf content.
These results also show the importance of farmers picking a good grazing variety when picking a variety for a grazed sward and how farmers should strive to achieve a tetraploid content of at least 50% in a new reseed.