In at 10cm and out at 4cm has always been the grazing advice for livestock in Ireland, however these recommendations were established primarily for dairy systems and subsequently adopted by the beef side of the house.
While the key driver behind the majority of dairy farms is output per hectare, on the majority of beef farms where stocking rates are much lower, the performance of the individual animal is often as, if not more, important that output per hectare.
Beef systems research
Over the years, Teagasc Grange has carried out a number of trials looking at liveweight gains of beef cattle on differing pre- and post-grazing sward heights, as well as the subsequent effect this has on carcase weight and age at slaughter.
With age at slaughter coming more into focus in recent times with regard to reducing total greenhouse gas (GHG) emissions from beef systems, maximising liveweight gain from grazed grass can play a key role in reducing the average age at slaughter.
For every month slaughter age is reduced, it equates to a 250kgCO2e/head saving – around 3.6% of total GHG emissions per prime animal slaughtered in Ireland.
Pre-grazing yields
The first of two experiments looking at pre-grazing yields for beef systems was with suckler-bred yearling steers over the course of their entire second grazing season. One group enter pre-grazing yields of 1,500kgDM/ha (10cm pre-grazing sward height) while the second batch of bullocks were offered swards of 2,000kgDM/ha (12cm pre-grazing sward height).
There was one round of topping carried out to overcome grazing quality issues 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 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 1,500kgDM/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 1,500kgDM/ha group.
Interestingly, liveweight gains of both groups were similar up until August, when the performance of the high sward height group tailed off.
Post-grazing sward heights
Moving to post-grazing sward heights, in the first experiment two groups of beef-sired dairy-beef animals were grazed for an entire grazing season (mid-March to mid-October) to either a 3.5cm or a 5cm post-grazing sward height.
As may have been expected, the animals grazing to 3.5cm were lighter to the tune of 30kg compared to their 5cm compatriots at the end of the grazing season.
Suckler cows
A second experiment was carried out looking at either 4cm or 5.5cm post-grazing sward heights on suckler cows and calves over an entire grazing season. At housing time, cow body condition was poorer and calf liveweight was 8kg to 10kg lower for the group that grazed to the 4cm sward height.
Recent study
A more recent study looked at comparing post-grazing sward heights of 4cm and 6cm for spring-born, suckler-bred yearling bullocks over an entire grazing season and followed them through to beef out of the shed the following spring.
The experiment saw bullocks at grass for a 200-day grazing season receiving no supplementary concentrate. Following housing in early November, they received a diet of grass silage only plus minerals and vitamins and were slaughtered out of the shed at 24-months old.
At the end of the grazing season, the group that grazed to 6cm post-grazing sward height were 29kg heavier than the 4cm post-grazing sward height group. Following this through to slaughter, the heavier group at housing had a 15kg heavier carcase weight, meaning they held the advantage they had at housing.
Herbage digestibility measurements carried out throughout the grazing season reported no difference in the overall diet digestibility offered to stock and so it is assumed that the difference in liveweight was due to higher herbage intake.
Put simply, asking stock to graze to 4cm will restrict their intake somewhat, which will have a negative effect on performance.
In the post-grazing sward height trials, the pre-grazing heights were common to both groups. Grazing to 6cm versus 4cm resulted in a 15% reduction in the stock carrying capacity and the ground yielded 0.5t DM/ha less grass than that grazed to 4cm. Interestingly, there was no difference in the overall liveweight gain per hectare.
To reach the same carcase weight, the animals that grazed to 4cm would have needed another month in the finishing shed. This would incur further feed costs during an expensive feed period indoors and would have a negative impact on the overall carbon footprint of the system.
What this research shows is that there is a 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 animal growth.
The only caveat to this is that where stock are left too long in a paddock trying to hit a residual grazing height (e.g 4cm) this can have a negative effect on intake and therefore liveweight gain over the entire grazing period will be reduced.
The biggest learning to take from these studies is that getting grass allocation correct will have the biggest impact on grazing performance. In general, paddock sizes are too big on Irish beef farms for the number of stock grazing them. Ideally, stock should be moving to fresh grass every two days at least. Paddock size needs to suit the size of the grazing group and vice versa.
Increasing pre-grazing yields from 1,500kg DM/ha to 2,000kg DM/ha increased animal performance at pasture.Stock grazing 1,500kg DM/ha and 2,500kg DM/ha had a similar performance over first half of the grazing season. Performance dropped in the second half of the season for those on heavier covers.Bullocks grazing to 4cm post-grazing sward height versus 6cm were 29kg lighter at end of grazing season.Grazing to 4cm or lower has a negative effect on animal intake and therefore animal performance.
In at 10cm and out at 4cm has always been the grazing advice for livestock in Ireland, however these recommendations were established primarily for dairy systems and subsequently adopted by the beef side of the house.
While the key driver behind the majority of dairy farms is output per hectare, on the majority of beef farms where stocking rates are much lower, the performance of the individual animal is often as, if not more, important that output per hectare.
Beef systems research
Over the years, Teagasc Grange has carried out a number of trials looking at liveweight gains of beef cattle on differing pre- and post-grazing sward heights, as well as the subsequent effect this has on carcase weight and age at slaughter.
With age at slaughter coming more into focus in recent times with regard to reducing total greenhouse gas (GHG) emissions from beef systems, maximising liveweight gain from grazed grass can play a key role in reducing the average age at slaughter.
For every month slaughter age is reduced, it equates to a 250kgCO2e/head saving – around 3.6% of total GHG emissions per prime animal slaughtered in Ireland.
Pre-grazing yields
The first of two experiments looking at pre-grazing yields for beef systems was with suckler-bred yearling steers over the course of their entire second grazing season. One group enter pre-grazing yields of 1,500kgDM/ha (10cm pre-grazing sward height) while the second batch of bullocks were offered swards of 2,000kgDM/ha (12cm pre-grazing sward height).
There was one round of topping carried out to overcome grazing quality issues 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 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 1,500kgDM/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 1,500kgDM/ha group.
Interestingly, liveweight gains of both groups were similar up until August, when the performance of the high sward height group tailed off.
Post-grazing sward heights
Moving to post-grazing sward heights, in the first experiment two groups of beef-sired dairy-beef animals were grazed for an entire grazing season (mid-March to mid-October) to either a 3.5cm or a 5cm post-grazing sward height.
As may have been expected, the animals grazing to 3.5cm were lighter to the tune of 30kg compared to their 5cm compatriots at the end of the grazing season.
Suckler cows
A second experiment was carried out looking at either 4cm or 5.5cm post-grazing sward heights on suckler cows and calves over an entire grazing season. At housing time, cow body condition was poorer and calf liveweight was 8kg to 10kg lower for the group that grazed to the 4cm sward height.
Recent study
A more recent study looked at comparing post-grazing sward heights of 4cm and 6cm for spring-born, suckler-bred yearling bullocks over an entire grazing season and followed them through to beef out of the shed the following spring.
The experiment saw bullocks at grass for a 200-day grazing season receiving no supplementary concentrate. Following housing in early November, they received a diet of grass silage only plus minerals and vitamins and were slaughtered out of the shed at 24-months old.
At the end of the grazing season, the group that grazed to 6cm post-grazing sward height were 29kg heavier than the 4cm post-grazing sward height group. Following this through to slaughter, the heavier group at housing had a 15kg heavier carcase weight, meaning they held the advantage they had at housing.
Herbage digestibility measurements carried out throughout the grazing season reported no difference in the overall diet digestibility offered to stock and so it is assumed that the difference in liveweight was due to higher herbage intake.
Put simply, asking stock to graze to 4cm will restrict their intake somewhat, which will have a negative effect on performance.
In the post-grazing sward height trials, the pre-grazing heights were common to both groups. Grazing to 6cm versus 4cm resulted in a 15% reduction in the stock carrying capacity and the ground yielded 0.5t DM/ha less grass than that grazed to 4cm. Interestingly, there was no difference in the overall liveweight gain per hectare.
To reach the same carcase weight, the animals that grazed to 4cm would have needed another month in the finishing shed. This would incur further feed costs during an expensive feed period indoors and would have a negative impact on the overall carbon footprint of the system.
What this research shows is that there is a 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 animal growth.
The only caveat to this is that where stock are left too long in a paddock trying to hit a residual grazing height (e.g 4cm) this can have a negative effect on intake and therefore liveweight gain over the entire grazing period will be reduced.
The biggest learning to take from these studies is that getting grass allocation correct will have the biggest impact on grazing performance. In general, paddock sizes are too big on Irish beef farms for the number of stock grazing them. Ideally, stock should be moving to fresh grass every two days at least. Paddock size needs to suit the size of the grazing group and vice versa.
Increasing pre-grazing yields from 1,500kg DM/ha to 2,000kg DM/ha increased animal performance at pasture.Stock grazing 1,500kg DM/ha and 2,500kg DM/ha had a similar performance over first half of the grazing season. Performance dropped in the second half of the season for those on heavier covers.Bullocks grazing to 4cm post-grazing sward height versus 6cm were 29kg lighter at end of grazing season.Grazing to 4cm or lower has a negative effect on animal intake and therefore animal performance. 
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