Relying too much on cheap cereals to make up the energy shortfall from poor first cut silage could prove costly with compromised milk yields and health problems.
Cereal prices have fallen this year to about £100/t and some farmers may be tempted to feed more wheat or barley.
“There is plenty of low energy silage around in the north west, with D values of 62-64. This was the result of wet weather delaying cutting, causing grass to be over mature grass at cutting,” says independent nutritionist John Long.
There will be temptations to overfeed cereals resulting in excess starch, but he warns that going too far risks acidosis.
“Starch wise, I aim to keep starch levels at 15-17% and no higher. You sometimes see some rations approaching 20%, but with wet, high-lactic acid silages, the cow’s rumen is starting to get too acidic.”
“I had one client who began feeding wholecrop wheat and started to see things go wrong with loose dung consistency and rumination was being affected. The wholecrop had a high starch content of 30%, rather than the usual 25% pushing the ration to 18% starch.
One way to get energy into the ration without adding to starch and acid levels is by adding rumen protected fats.
“Protected fats do have a role in getting energy into rations. For example, I had a client with one good clamp at 69D and poor clamp 63D and he wanted to take the 375g of fat out, but that equated to two litres of milk.”
Richard Kirkland of Volac highlights that fat contains two-and-a-half times the energy concentration of cereals, therefore, takes up less space in the total dry matter intake.
“This allows higher fibre levels to be maintained to reduce acidosis risk, while increasing energy supply.”
But while many farmers view fat simply as an energy source, it also plays other unique roles in animals, says Dr Kirkland.
Cows have an essential requirement for fat. “Just like a cow needs sugar and protein, it is the same for fat.”
US guidelines are that rations for high-yielding cows should contain 6-8% fat. “Or put another way, the amount going in should be similar to that being produced in milk.”
A typical diet based on forage and cereal will have 3.5% fat (DM basis), he says.
A shortfall in overall energy supply is the number one factor affecting fertility. A further important factor is having sufficient fat in the diet, as the key fertility hormone, progesterone, is produced from fat.
Cows with low levels of progesterone are less likely to maintain pregnancies. “Research in Ireland reported that 25% of cows that don’t get pregnant is due to insufficient progesterone.”
However, it is not just promoting the supply of cholesterol, as some fats promote the development of eggs at ovulation.
“Yes you will see health benefits and fertility when feeding fats, says Mr Long. “Just cereals and starch, you will get cycling, but conception rates will suffer. Losing cow condition is the key benefit of fat.
Including 300g of rumen protected fat costs less than one litre of milk, but a big benefit of fat is keeping condition on cows and higher conception rates.
Therefore, Mr Long recommends aiming for 15% starch and 250-500g rumen protected fat.
However, Dr Kirkland warns against replacing too much cereal with fat. “Don’t just double fat at expense of starch. Too low a starch level can lead to low milk protein.
The type of fat is crucial, as some forms can severely impair milk fat production.
Brewers’ grains can contain 10% fat and distillers’ grains are maybe nearer 15% fat. While they contribute to energy intake, they contain unsaturated fatty acids and feeding high levels can depress milk fat.
This is because the oil coats the fibre in the rumen and disrupts fibre digestion. This in turn leads to a reduction in the volatile fatty acids used in milk fat production.
Some fats can also directly inhibit milk fat production in the udder and researchers are only starting to understand this process, he says. This highlights the value of evaluating the type of fat in the ration.
One way to reduce this risk is to feed rumen protected fats, says Dr Kirkland. This helps minimise the impact on the rumen.
“There are a lot of good wholecrop silages this year with many starches about 30%.”