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Last week, we outlined some of the recent research work carried out at Teagasc Grange in relation to post-grazing sward heights. This week, we take a look at pre-grazing sward heights.
Two experiments have looked at this in recent years. The first with suckler-bred yearling steers over the course of their second grazing season.
One group enter pre-grazing yields of 1,500kg DM/ha (10cm pre-grazing sward height), while the second batch of bullocks were offered swards with 2,000kg DM/ha (12cm pre-grazing sward height).
In this first trial, there was one round of topping carried out to overcome stemmy grass appearance mid-summer.
By housing in November, the group that grazed the heavier covers were 14kg heavier than those that entered the lower grass covers.
Digestibility samples
Digestibility samples of the grass that were taken throughout the season reported similar levels of digestibility, so the heavier weight was attributed to higher grass intake.
The second study went a step further and compared 1,500kg DM/ha (10cm) pre-grazing sward heights with 2,500kg DM/ha (14cm) pre-grazing sward heights.
In this trial, there was no topping carried out on any pasture throughout the season.
At the end of the grazing season, those grazing the heavier covers were 16kg lighter than the 1,500kg DM/ha group.
Interestingly, liveweight gains of both groups were similar up until August, when the performance of the high sward height group tailed off.
What it shows is that there is a fairly large tolerance of grass pre-grazing yield for beef systems, provided quality is good.
This means that grazing heavier covers in the first half of the season will not have a negative effect on growth.
The only caveat to this, which was apparent from last week’s post-grazing sward height trials, is that where stock are left too long in a paddock trying to hit a residual grazing height (eg 4cm), this can have a negative effect on intake and therefore liveweight gain over the entire grazing period.
The biggest learning to take from these studies is that getting grass allocation right will have the biggest impact on your grazing performance.
It means having stock moving to fresh grass every two days at least. Paddock sizes need to suit the size of the grazing group and vice versa.
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