Turnout will introduce the long awaited opportunity to slash costs by making milk from grass and cutting out bought-in feeds, but in reality there are other issues to consider.
Veterinary nutritionist Debby Brown says it is important to consider grass quality.
“We are just recovering from a winter which broke the 500mm rain barrier – the second wettest on record. As such some grazing swards will have suffered from waterlogging while in many areas grass is quite simply wet.
“The warm winter may have encouraged growth, but the wet soil is slow to fully warm up and in many cases swards will be short of energy.
“To find out how much milk you can realistically take from grazed grass, analyse your swards pre-turnout.”
Dr Brown says the analysis is likely to return with grass dry matter (DM) content anywhere from 14-20 per cent DM which, in feed value terms, is a massive range.
“For example, you can expect to realise just maintenance plus five litres with grazed grass analysing at 14 per cent DM, compared to 13.8 litres from top quality swards analysing at 20 per cent DM.”
Considering the range of variations, Dr Brown says it is going to be crucial to know the quality and quantity of feed you are turning the cows on to in order to maintain targets – both yield, constituent value and fertility.
“If grass is in energy deficit then it will be necessary to feed a buffer.” (See table).
Dr Brown says it generally takes about three weeks for bugs in the rumen to adapt to the significant diet change at turnout, so this change should be managed gradually.
“A few hours of on/off grazing allows the herd to graze in what may be suboptimal conditions and adjust to grazing slowly.”
She also says the challenge to the rumen will increase as the proportion of grass in the diet increases.
“Grass can also be high in crude protein and have low levels of neutral detergent fibre, plus potentially high or variable sugars. All of this places cows at risk of sub-acute rumen acidosis, which has a negative impact on cows’ performance and fertility.”
|Fresh grass DM (per cent)||14||16||18||20|
|Grass silage buffer: 10.5MJ/kg DM, 13 per cent CP, 30 per cent DM||2.5kg||2kg||1.5kg||1kg|
|Maize silage buffer: 11.0 MJ/kg DM, 8 per cent CP, 30 per cent DM||3kg||2.5kg||1.7kg||1kg|