Dangers of Spring Grass - Producers Get a Word of Warning
2011-04-20

With turnout just around the corner, SCA NuTec’s ruminant manager Philip Ingram warns producers to manage the switch from winter rations to spring grass.

Dr Philip Ingram, SCA Nutrition
ruminant product manager

“Grazed grass is a double edged sword,” says Dr Ingram. “It’s a cost-effective feed and offers many nutrients in abundance – lots of readily available energy and protein but little in the way of fibre to slow down the digestive process.”

Carbohydrates in lush spring grass are very rapidly digestible and so acids are produced at a much faster rate in the rumen than the digestive system can clear. This increased acid load in the rumen is commonly known as rumen acidosis.

Fibre in the diet is the animal’s natural means of buffering, or neutralising, this acid. This is because fibre is slowly digested and it also makes the cow chew which releases natural buffers in saliva that will neutralise acid. However, as spring grass is ‘lush’ with low levels of ‘non-mature’ fibre, this natural buffering effect is weak. Hence sometimes even a natural grass diet does not offer a normal balance of digestion and buffering.

Acidosis will reduce milk production and butterfat. Other effects are not as obvious initially but are potentially more damaging – lameness, poor fertility and general health problems.

A recent large scale study carried out by UCD, Ireland showed that 11% of spring calving herds had sub-acute acidosis (pH <5.5) and 42% were classified as marginal (pH 5.6 – 5.8). In fact, 80% were below the optimal pH range of 6.0 to 6.1 for digestion in the rumen. In one quarter of the herds studied, the prevalence of sub-acute acidosis was greater than 25%. This demonstrates that even in a ‘natural’ low concentrate grazing system acidosis presents a major threat.

“Producers should stage a gradual turnout. Turning cows out in early spring, even for a couple of hours per day, has been shown to increase milk production. This also allows the rumen time to adapt to spring grass - the acid absorption capacity of the rumen can increase when spring grass is gradually introduced. Buffer feeding of forages during the grazing season may also help to reduce acidosis, but this will also reduce grass utilisation.

“And producers shouldn’t ignore concentrate formulation. This needs changing at turnout to a ration. A winter ration that is high starch high protein can add to acidosis problems if fed at grass. The use of a buffering agent, such as SCA NuTec’s Equaliser, will help bolster the cow’s natural buffering ability. Equaliser incorporates a specific blend of buffering agents, providing a very powerful and long lasting buffer. It has consistently exceeded the buffering capacity of competitors during tests.”

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