Keep watch for nutritional stress

To establish whether nutritional stress is an issue for your herd, a good starting point is to know how much you are feeding.

This may be an obvious statement, but without this vital piece of information, making assessments of nutrition becomes more difficult.

As an example of potential ration imbalances, I visited a farm that had suffered a 2-litre milk drop after switching from first- to second-cut grass silage. This is the equivalent of 10.6 MJ less energy output.

Example ration imbalances

First-cut grass silage was consumed at 54kg freshweight (FW), second cut was consumed at only 32.5kg FW. A simple solution, therefore, would be to feed more. However, the difference was explained when we measured the dry matter (DM).

First cut was 24% DM compared with 40% for second cut. When the calculation was done (FW x DM%) the results were both about 13kg. Pushing for more silage consumption would therefore lead to wastage of a valuable commodity, especially this winter, so we had to look at other ways to increase the energy.

By how much? Feed Conversion Efficiency (FCE) of milk production indicates how efficiently feed is turned into milk. It can be estimated by dividing 4% Fat Corrected Milk (4%FCM in kg) by Dry Matter Intake (DMI in kg). A modest value is 1.35, but what’s yours? Some can get to more than 1.5.

In this example, we were 10.6MJ down on output, so we are 14.3MJ (10.6MJ x 1.35) down on intake, based on the same efficiency. The challenge is to decide how to get that into a cow, which involves using trusted advisers and remembering to keep an eye on the protein content of the ration.

Energy deficiency

So how might this show up in your cows apart from a drop in yield? Another effect is reduced milk protein. A change from 3.2% to 3.05% means a reduction of only 42g of yield in a 27-litre cow. However, a protein regularly below 3% is a cause for concern and an often-quoted reason is the dilution effect of high yields. However, unless your average is more than 35 litres, the cause needs investigating.

Energy Deficiency Symptoms

A common effect you might encounter is fewer cows seen bulling. Normally, a three-week block results in 40-60% of eligible cows being served (eligible being calved 60 days onwards). This is the submission rate and one should aim towards the higher end (60%). A dip in the submission rate may be an effect of low energy.

When it comes to pregnancy diagnosis time, nearly 80% of those presented should be in-calf. Below this may point to heat detection as a problem, which can be heavily influenced by low energy.

Do you know these figures? If you milk record, your vet can quickly and easily produce these figures for you. If you don’t, then it’s time to sit down and work it out – these are critical management figures.

Vet visit findings

Disease can be precipitated by nutritional stress. Any case of conditions such as cystic ovaries, endometritis or non-cycling is unacceptable; but in practice we have a tolerance level for these and other conditions.

A figure of 5-10% is quoted, but there is great variation so it is useful to know actual numbers.

From a nutritional point of view, a cow losing body condition before calving, or having sub-clinical milk fever, causes a chain reaction, meaning your cow is at a great risk. However, there are other causes of endometritis to be considered.

What’s it worth?

• Delaying conception by up to a month (conceiving from 80-110 days after calving) can cost up to £3 a day from lost income.
• For a delay of five months, you’re missing out on £8 a day.
• As time goes on to a seven- month delay, it gets to the point where a 10,000-litre cow has no value other than as a cull. It would have been cheaper to invest in a heifer.

Keeping an eye on nutritional stress

• Measure what you are feeding
• Measure key management figures such as submission rate
• Monitor what diseases you have on farm that could be worsened by nutritional stress
• Act constructively to solve the problem

Vet viewpoint is written by members of the XL Vets group.

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