Pasture and sugar levels – managing risk – especially during frosts
Understanding how grass grows, and the effects of seasonal changes on the fluctuating levels of sugars, is very important for owners of horses and ponies that are pre-disposed to laminitis/or are sugar sensitive.
The key points of how grass grows are below – (from the Laminitis website).
- Green plants create sugar through the process of photosynthesis.
carbon dioxide + water + sunlight = sugar + oxygen
- Plants use the sugar for growth and reproduction - this process is called respiration.
glucose + oxygen = carbon dioxide + water + energy for growth/respiration
- When sugar production from photosynthesis is greater than the sugar required for growth/reproduction, the excess sugar is stored as fructan or starch (carbohydrates) for later use.
- Plants respire all the time, in darkness and in light, but only photosynthesize in light.
- Increased light leads to increased photosynthesis (up to a point).
- No light/darkness: respiration rate is higher than photosynthesis (there is no photosynthesis without light).
- Dim light: photosynthesis at same rate of respiration.
- Bright light: photosynthesis rate is higher than rate of respiration.
Under normal circumstances, when the temperature is above 5°C, grass undergoes sugar accumulation during the day, (higher on sunny days). The sugar levels will be highest at the end of a sunny day. These accumulated sugars are then used up overnight as the grass grows and sugar levels are lowest by 5 AM. This is one reason why it is better to turn your horse out at night onto pasture and then stable or yard during the day as the grass is accumulating sugar faster than it can use it for growth during the daytime. There are however some exceptions to this, and these are, when the grass is struggling to grow during drier seasons (under stress), and the temperature is too low for the grass to grow (frosty conditions).
These environmental conditions result in heightened sugar levels, as they are stored in the plant ready for when the grass can grow.
KEY IMPORTANCE
- As we begin to see frosts, grass hardly grows (respires) when temperatures are below 5°C.
- The levels of sugars build up in the plant, concentrating the amount available to your horse or pony as he grazes and increasing the risk for sugar-sensitive or laminitis-prone equines.
The solution:
The risk of elevated sugars will remain if there is cold frosty weather with bright sunny days, and especially where the temperature does not rise above 5°C. Only once the temperature rises consistently above 5°C it will be sufficient for the plant to respire (grow and use up stored sugars), and on cloudy days will the sugar levels be lower (and safer) to graze.
If you are removing your horse from pasture over a risk period (or to reduce the effect of exposure to sugar levels in grass for shorter periods during a day), opting to replace some of your horses fibre with Fiber Protect, Fiber Ezy or Fiber Lucerne is a great way to mitigate the risk associated with frost-affected pasture.
Soaking of hay is also an option to remove sugars from it, however it is less reliable way to remove a consistent amount of sugar and it changes the microbiome of the forage to be less desirable for gut health, not to mention the loss of some nutrients (Daniels et.al 2020).
Quality fibre sources such as Fiber Protect and Fiber Lucerne followed by Fiber Ezy, contain the lowest soluble starch and sugars in a fibre source that you can provide your horse or pony with.
Fiber Protect and Fiber Lucerne have approximately 1.5-3% per Kg of DM (even less % as fed), and Fiber Ezy is slightly higher at approximately 4% Kg of DM. This forages are routinely tested at this level by an independent laboratory.
The Laminitis Society recommends that horses with conditions exacerbated by high sugar levels consume forage fibre with soluble starch and sugar levels no higher than 10% to 12%/Kg DM – unfortunately many forage fibre sources such as grasses and dried hays exceed this level.
Fiber Protect, Fiber Lucerne and Fiber Ezy are all great forage choices if low sugar and starch is required in the diet of the Equine.
TAKE HOME MESSAGE:
- Prevent or limit access to grass during and after sunny frosty weather until the weather changes to milder nights and overcast days
- Feed analysed hay or fibre sources with sugar and starch levels below 10% Kg DM
- It is not the frost itself that is the risk, it is the weather conditions that cause the frost, so do not allow horses to graze once the frost has melted with the sun - wait until the grass has been able to respire and use up some of its sugar.
