Grazing spring grass can help maximise milk from forage and reduce feed costs, but can be a challenge to the rumen, warns ForFarmers’ Bruce Forshaw.
“Spring grass is highly digestible, has low structural fibre, high protein levels, and variable levels of dry matter,” he says, advising producers against an abrupt approach to turnout. “Three weeks gives time for rumen microbes to adjust from the housed ration.”
Spring grass typically has protein levels around 24%, mostly in the form of rumen degradable protein (RDP) and a true digestible protein (TDP) of between 90% and 100%. “Rumen microbes will have problems utilising this protein, particularly if there isn’t enough fermentable energy available,” says Mr Forshaw. “Maize silage or a high starch concentrate can help soak up excess ammonia.”
Raised sugars from spring sunshine coupled with leafy green plants containing little fibre can challenge rumen function and cause sub-acute rumen acidosis.
A rumen pH below the optimum range of between 5.8 and 6.20 will affect milk constituents, feed conversion efficiency, fertility, and cause health issues.
Dry matter levels at grass can vary considerably from day to day depending on weather conditions, and can drop below 10% on wet days. Mr Forshaw recommends supplementing dry matter levels to maintain cow performance.
“Feeding the right forages and concentrates will help cows meet these challenges,” he says. “Concentrates formulated to even low crude protein levels can increase RDP, so feed concentrates based on TDP to protect the rumen and reduce waste.”
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