Will it Pay to Supplement Cows at Grass Year?

With current high feed prices will dairy farmers be justified in feeding concentrates at grass this season? NWF technical manager Tom Hough considers the options.

While welcoming the return of realistic milk prices, many dairy farmers will be concerned at the impact of higher feed prices on margins and will be looking to cut back on supplementary feed rates. The key word to bear in mind is supplementary.

Where compound feeds, straights or buffers are fed as supplements to address dietary deficiencies in forage supply then the economic case is sound and supplements can be justified. However, where they are a direct substitute for grass at moderate milk yields then the reverse is true. The skill is in correctly assessing both the true value of available grass and the nutrient requirements of your herd through lactation and throughout the grass growing season.

Before looking forward to this year it is wise to look back at last, to see if there are any lessons to be learnt and to ensure mistakes are not made again. Understanding the value of grass is fundamental. AFBI Hillsborough showed that correctly supplementing cows at grass with compound improves DMI and yield. Equally where grass is over-estimated and supplements cut back too far, cows risk losing excess condition and will struggle as a result of being underfed in the late summer.

Milk yield from grazing is primarily a function of grass intakes not just nutrient content of the grass per se. Grass energy levels are remarkably constant over the growing season but dry matter yields vary significantly.

The graph shows the average yield per cow per day available from grazed grass on a monthly basis for the last three years using data collected by the Frank Wright milk from grazed grass system. It emphasises the importance of knowing how much grass is in front of the cows.

Take June as an example. In 2005 grazing would support M+24 litres per day while in 2006 this had dropped to M+15. If the assumption was made that the grass in ‘06 was as good as ’05 then cows would have been underfed. Equally, underestimating the value of grass in ’05 would have resulted in potentially expensive overfeeding.

Once you have a good idea of grass available, choices for supplementation becomes a more straightforward decision. If a cow’s energy requirements exceed the potential in grazing then supplementary feed will pay and the decision then becomes one of which supplement to use to provide the energy required.

One of the big issues with spring grass is that the nutrient supply is out of balance with what the cow, or more importantly the rumen requires. Young grass is high in degradable protein, sugars, polyunsaturated fat, and low in fibre.

Problems associated with nutrient imbalance include elevated milk urea levels, low butterfat’s, rumen upset (SARA) and excess condition score loss. Selecting the correct supplement for your individual needs is therefore key to ensure you get maximum benefit from your grass, as after all, when managed correctly it is the most cost effective feed on your farm.

To help assess whether cows are failing to meet dietary energy requirements, keep a careful eye on body condition score. Mid and late lactation cows should be putting on condition, but unless you monitor and record it monthly using the NWF BCS monitor you will not know if they have lost too much or are putting too much on, both will have a detrimental effect on cow health, fertility and your bank balance.

Dry cow management in particular often takes a downward turn due to lack of diet control. A lot of cows were underfed in late summer in both of the last two years which saw herds struggle for performance well into winter. Condition score monitoring is probably the best tool for assessing dry cow nutrition.

The other key reason to supplement cows is to ensure adequate mineral intakes are achieved. Moving from controlled, mineralised winter diets, to a grazed grass system can result in a large drop in mineral intakes. This is especially true with later lactation cows who will be challenged to maximise grazed grass intakes.

A failure to supply adequate minerals can predispose cows to a range of conditions including higher cell counts and increased incidence of lameness.

As an example, a housed cow producing 25 litres and being fed 5kg of a typical compound would require an additional 75g per day of a standard mineral. The same cow out at grass and receiving no compound will need 125g of mineral supplement.

Overall decisions on supplementation should be taken with a long term view, encompassing yield, milk quality, health and fertility. Short term gains from reduced supplementary inputs may well be out-weighed by longer term losses.

While dairy farmers are right to challenge all costs on the farm, an over-zealous approach to reducing feed rates at grass could cost more than it saves. By accurately assessing grass availability and targeting supplements it will still be possible to make healthy margins this spring and prepare the herd for the challenges of next winter.