Over-estimating the contribution from late season grazing can result in cows failing to milk to expectations when they move on to winter diets.
This is the message from Trouw Nutrition GB ruminant manager Adam Clay. He says: “Faced with declining milk prices, farmers are looking to squeeze as much from grazing as possible.
“The problem is cows compensate for variable quality and quantity and reduced grazing intakes by losing body condition in the short-term.
“They then look to make this condition back up again when they move on to winter rations, to the detriment of milk production.”
He says the typical picture of milk production in the UK and GB is of declining output in late summer. There are several reasons for this associated with grazing quality and cow behaviour.
But production does not increase again until October/November, despite cows being on a general rising plane of nutrition from September onwards.
Mr Clay says the lag in production, despite increased feed rates, can be traced back to losses in body condition score (BCS) experienced in the late grazing season. He believes the primary cause of this is an over-estimation of the contribution from grazing in the second half of the grazing season.
“There is no doubt the quality of grazing will decline as the season progresses, although the actual rate will depend on how well the grass has been managed throughout the season and how well covers have been maintained.
“The biggest problem, however, is intakes. Quality can still be good, but cows just can not physically eat enough.”
Mr Clay says potential grazing dry matter intake falls from July onwards, largely as a result of reducing daylight hours, which limit the time cows will actively graze.
Based on Trouw Nutrition Grasswatch data, the average DMI reduction of grazing is 0.3kg/head/week from August until the end of the grazing season.
In May, cows consume about 13.6kgDM/day, but by August this will have dropped to closer to 12.2kgDM/day.
He says most farms do not see a significant drop in yields because, in response to the high protein content of grass, cows mobilise body condition to release energy, maintaining yields in the short-term. This gives a false impression of the value of grazing.
“This short-term loss of body condition to support immediate milk yields can explain the lag in production when cows come on to winter diets,” says Mr Clay. “They partition energy to re-gain condition, sacrificing milk yield.
“The impact seen in practice will depend on how much condition cows lose and how quickly they put it back on again (see table).”
Mr Clay says if a cow loses just half a condition score and recovers it over a three-month period, this will require the same energy as it takes to produce 1.9 litres per day over that period.
If she recovers the condition over two months, then yield will be reduced by 2.9 litres per day.
He stresses the problem can be much worse with fresh-calvers. An August-calver may lose 0.75BCS due to reduced contribution from grazing. Regaining this over three months will take 2.9 litres per day off peak production, and while she is regaining condition she will be far harder to get back in calf.
“Farmers should take steps to ensure cows enter winter in optimum body condition to avoid costly milk yield loss and ensure negative energy balance is not prejudicing fertility.
“Take time to measure growth rates so you know exactly what is in front of the cows and be realistic about intakes.
“Complement late season grazing carefully as this will be more cost-effective than trying to sort out problems as cows are housed.”
|Months of condition recovery|