Executive Summary
- Transition feeding is essential when turning cows out to grass to protect rumen health and maintain milk production.
- Spring grass is highly digestible and can contain 18–25% crude protein, but it has less fibre than winter silage.
- Cows should be introduced to grazing gradually over 10–14 days, beginning with short grazing periods of 2–3 hours per day.
- Continuing silage buffer feeding helps stabilise rumen function while cows adapt to fresh pasture.
- Early spring grazing increases the risk of grass tetany, so magnesium supplementation of around 20–30g per cow per day is often recommended.
- Maintaining dry matter intake is critical, as fresh pasture contains around 80% water and cows may temporarily reduce intake during transition.
- Lactating dairy cows typically require 60–100 litres of water per day, so reliable water supply in grazing paddocks is essential.
- Monitoring milk yield, manure consistency and cow mobility during the first 2–3 weeks after turnout helps identify any feeding adjustments needed.
Each spring, dairy farmers across the UK prepare for one of the most important nutritional changes in the production year: transition feeding when turning cows out to grass.
Moving from a silage-based diet to fresh pasture offers major cost advantages. Grazed grass remains one of the cheapest sources of energy available to dairy farms. However, introducing it too quickly can disrupt rumen function, reduce milk yield and increase health risks.
A carefully managed feeding transition allows cows to adapt gradually to grazing while maintaining stable intake and production. For many farms managing herds of around 200 cows, this short adjustment period can influence herd performance for the rest of the grazing season.
Why the Transition to Grass Requires Careful Management
Spring grass is nutritionally very different from the conserved forage cows consume during winter housing.
Once soil temperatures rise above 5–6°C, pasture growth accelerates rapidly. Early-season grass often contains 18–25% crude protein alongside high levels of rapidly fermentable sugars.
This makes grass an extremely valuable feed source, but it also creates a sudden dietary shift.
Compared with winter silage, spring grass generally contains:
- Less structural fibre
- Higher sugar content
- Greater moisture levels
If cows move directly from winter rations to unrestricted grazing, rumen microbes may not adapt quickly enough to the new diet.
This imbalance can reduce rumen pH and increase the risk of subacute ruminal acidosis (SARA). In dairy herds, SARA is linked to reduced feed intake, milk yield losses and increased lameness.
Managing the dietary transition carefully helps maintain rumen stability and protects production.
How to Transition Feed Cows When Turning Them Out to Grass
The most successful grazing systems introduce cows to pasture gradually rather than allowing full-day access immediately.
Many farms begin turnout with two to three hours of grazing per day, typically after morning milking. Grazing time is then increased gradually over 10–14 days as cows adapt to fresh forage.
During this period, continuing to feed silage is strongly recommended.
Providing conserved forage alongside grazing is commonly referred to as buffer feeding. The fibre in silage helps maintain rumen function while cows adjust to the higher digestibility of spring grass.
Buffer feeding is particularly important for high-yielding cows. In early lactation, dairy cows may require 200–250 megajoules of metabolisable energy per day. Grass alone may not consistently provide this level of energy during early spring.
Managing Magnesium and Mineral Balance
One of the most significant nutritional risks during early grazing is grass tetany, also known as hypomagnesaemia.
Rapidly growing spring grass can contain high potassium levels, particularly where fertiliser has been applied. Elevated potassium interferes with magnesium absorption in the rumen.
Cold weather, wet conditions and low fibre intake can further increase the risk.
To prevent deficiency, many dairy nutritionists recommend supplementing magnesium during early turnout. Typical supplementation levels are 20–30 grams of magnesium per cow per day.
Magnesium can be provided through mineral blends, concentrate feeds or mineral buckets depending on the farm’s feeding system.
Maintaining adequate magnesium intake during the transition period significantly reduces the risk of metabolic disorders.
Maintaining Dry Matter Intake
Dry matter intake often fluctuates during the early stages of grazing.
Fresh pasture typically contains around 80% water, meaning cows must consume a larger volume of forage to meet their energy requirements.
If intake falls during this period, milk production can decline quickly. Poorly managed transitions sometimes lead to temporary milk losses of 1–2 litres per cow per day.
Maintaining consistent feeding routines helps stabilise intake. Continuing silage feeding after milking, avoiding abrupt ration changes and ensuring cows have constant access to clean water all support a smoother transition.
Water availability is particularly important. Lactating dairy cows may consume 60–100 litres of water per day, depending on milk yield and weather conditions.
Supporting Cow Health During the Transition
Nutrition is only one factor influencing how cows adapt to grazing.
During the grazing season, cows typically walk longer distances between housing, pasture and milking facilities. On many farms this can amount to several kilometres each day.
Cows entering the grazing period with mobility problems may struggle to maintain adequate grazing time. Reduced grazing time directly affects dry matter intake and milk yield.
Housing comfort during the final weeks before turnout therefore plays an important role in grazing preparation.
Dairy cows naturally lie down for 12–14 hours each day. Adequate rest supports rumination and hoof health, both of which contribute to stable feed intake.
Comfortable cubicles and supportive lying surfaces such as cow mats or mattresses help ensure cows enter the grazing season in good physical condition.
Monitoring Cows During the First Weeks of Grazing
The first two to three weeks after turnout are often the most important period for monitoring herd performance.
Changes in milk yield, manure consistency or cow mobility can indicate that the feeding transition needs adjustment.
Farmers should monitor:
- Grazing behaviour
- Milk production
- Manure consistency
- Mobility and walking behaviour
Small adjustments to grazing hours, buffer feeding or mineral supplementation during this period can prevent larger problems later in the season.
Quick Transition Checklist
Before turning cows fully out to grass:
- Introduce grazing gradually over 10–14 days
- Continue silage buffer feeding
- Provide 20–30g magnesium per cow per day
- Ensure access to 60–100 litres of water per cow daily
- Monitor milk yield and manure consistency
These steps help stabilise rumen function and support a smooth transition to grazing.
A Smooth Feeding Transition Supports the Whole Grazing Season
Spring grass offers dairy farms one of the most cost-effective feeding opportunities available.
However, the transition from winter housing to pasture must be handled carefully. Gradual grazing introduction, continued fibre intake and appropriate mineral supplementation all help maintain rumen stability and protect milk production.
A well-managed transition feeding strategy when turning cows out to grass ensures cows adapt smoothly to grazing and make the most of the spring grass supply.
Frequently Asked Questions
When should dairy cows be turned out to grass in the UK?
Most farms begin turnout once soil temperatures exceed 5–6°C and grass height reaches around 8–10 cm. Ground conditions should also be suitable to avoid poaching.
How long should cows graze when first turned out?
Cows are typically introduced to grazing gradually, starting with 2–3 hours per day and increasing turnout time over 10–14 days.
Do cows still need silage when grazing in spring?
Yes. Buffer feeding with silage during the transition period helps maintain fibre intake and stabilise rumen function.
How much water do grazing dairy cows drink?
Lactating dairy cows typically consume 60–100 litres of water per day, depending on milk yield and weather conditions.