Moving to a grass-based diet is a nutritional challenge for dairy cows and shouldn’t be rushed. ForFarmers Product Manager, Bruce Forshaw, outlines his advice on how to make the transition as seamless as possible.
Farmers are often keen to get their cows out onto grass as soon as possible to maximise milk from forage and reduce feed costs. However it can be a challenge to the rumen, warns Bruce Forshaw.
“Spring grass is highly digestible, has low structural fibre, high crude protein levels and variable levels of dry matter, so can pose some challenges.”
He advises against an abrupt approach to turning out. “Take your time moving cows onto spring grazing. Three weeks gives time for the rumen microbes to adjust from the housed diet, as well as giving ground conditions more time to improve; particularly important this year after all the wet weather.”
Spring grass typically has protein levels of about 25%, in the form of rumen degradable protein (RDP). “The rumen microbes will have problems utilising this protein, particularly if there isn’t enough fermentable energy available,” he explains. “This RDP is then broken down to ammonia in the rumen, passes through the rumen wall into the blood stream and is converted to urea in the liver. This in turn can have a negative impact on milk production, cow fertility and foot health.”
Spring sunshine which raises sugars alongside leafy green plants that don’t have much fibre can challenge rumen function and lead to Sub-acute Rumen Acidosis (SARA). “Look out for changes in milk constituents and cow behaviour that may indicate early signs of SARA. Lower fibre levels in the rumen also mean you don’t get the scratch factor which produces the saliva that helps regulate rumen pH.”
Low pH (below the optimum range of 5.8 to 6.2) in the rumen will affect milk constituents, feed conversion efficiency and fertility, as well as causing a range of health issues.
“SARA is one of those things that can fly under the radar for a while, but can have a substantial financial impact on a herd,” Bruce stresses.
DM levels at grass can vary dramatically from day to day, depending on weather conditions, dropping to below 10% on really wet days. “Don’t overestimate the cow’s DM intakes and supplement dry matter levels to ensure cow performance is not compromised.
“In fact, make sure cows get the right forages and concentrates at turnout to help them meet these challenges. There are a range of options you can use,” says Bruce.
“Use a concentrate with a lower protein level. Concentrates formulated to even low crude protein can increase RDP so use more modern concentrate based on True Digestible Protein to protect the rumen and reduce wastage.
“See what the cows are telling you about their diet. Are 65% or more lying down ruminating three hours after milking? Check rumen fill at this point too. Also check dung consistency. Loose dung with undigested fibre is a sign of poor rumen health and may indicate SARA in the herd.”
Grazed grass is low in magnesium and levels can drop further after fertiliser application. Cows are at higher risk of milk fever on early spring grass, particularly during cold, wet weather. As ruminants can’t store magnesium it’s important to ensure that daily requirements are met to avoid grass staggers or lower performance.
Remember that clinical signs are just the tip of the iceberg – the effects could be costing money across the herd in poor performance and other health issues.
Generally, the earlier cattle are out the better, as this is when spring grass is at its highest quality. However, this will be delayed during or after wet weather as poaching will be a risk.
Bruce explains: “Wet weather can cause a variety of physical, biological and chemical changes within the soil – all of which can affect soil structure. Although many of these changes will start to reverse once the soil begins to dry out, it is important to assess soil structure on any fields before grazing or travelling with machinery.”
As more extremes in weather occur, and increasingly frequent wet spells, assessing the sward and soil will be critical in getting grazing and silage leys back into maximum production, he explains.
Grass is the cheapest feed on the farm so making the most of it is vital, concludes Bruce. “Taking these simple steps will ensure that transition goes smoothly and doesn’t cost cow performance or health.”
Cows need an average of five litres of water for every litre of milk produced. Bruce says: “Providing enough water is an essential nutritional requirement, and cows shouldn’t have to walk more than 200 metres to access a supply.
“Other infrastructure is of course important too. Make sure you walk your fields well in advance to check that cow tracks, gates and fences are in good condition.”
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