Animal Health

Know your fodder: feed testing facts

By Dairy News

(By Dr Gemma Chuck, APiAM Animal Health)

THIS SEASON there is the potential for a fodder supply shortage across Australia’s dairy regions.

In times of low pasture supply, it is essential to carefully plan what the likely feed requirements will be for your herd and actively manage the quality, supply and price risks of the bought-in feed.

This helps ensure the nutritional needs of the herd are met while reducing the risk of adverse feeding events, such as ruminal acidosis, exposure to mycotoxins and chemical residues.

Why should I feed test?

The quality of a feed can be highly variable and is influenced by a range of management and seasonal factors. However, the only way to know the absolute nutritional value of your home-grown or bought-in feed is to feed test a sample of the feed.

The information from a feed test can help indicate how much an animal is likely to consume and how this will affect her growth or milk production.

This may impact important management decisions, such as how to effectively utilise the feed and if any additional supplements are required.

The results also help quantify the dry matter of the ration and if there is any opportunity to use alternative, less costly fodder.

What feed samples do I need?

Core samples of your hay or silage can be obtained and tested for nutritional value. Numerous samples should be taken from bales or the feed face (if using pit silage).

Silage sampling should be delayed for 6 to 12 weeks to ensure complete fermentation. Well-preserved silage will ferment in 6 weeks, but fermentation will proceed more slowly if the preservation is less efficient.

It is ideal to also weigh a representative proportion of round or square bales to enable optimal interpretation of the feed test results. It is recommended to contact your veterinarian or nutritional adviser to discuss feed testing options of your herd.

When submitting feed samples for analysis it is important that the samples are representative of the feed the herd will consume and processed according to the laboratory’s requirements.

Interpreting a Feed Test Result

Interpretation of the results of a feed test can be summarised as follows:

Description

Interpretation

Acid detergent fibre (ADF; per cent of DM)

Measures the plant components (fibre) that are the least digestible, including cellulose and lignin. As ADF increases digestibility decreases, so forages with high ADF are typically lower in energy.

Dry Matter Digestibility (DMD; per cent)

Measures the amount of a feed removed after passing through the cow’s digestive system. The higher the digestibility, the better the feed quality.

Metabolisable Energy (ME; MJ/kg DM)

Estimates the amount of energy in a feed available to the animal to perform normal physiological functions. The higher the ME the better the quality of feed. ME is estimated from digestibility. For high levels of production, the energy content of the diet should be above 11 MJ ME/kg dry matter. Examples include:•

  • Concentrate feeds: ~11–13 per cent
  • Hay: ~9–10 per cent
  • Silage: ~9–11 per cent

Description

Interpretation

Sample

Gives details of the sample sent to the lab.

Moisture

Measures the weight before and after drying to give moisture percentage.

Dry Matter (DM; per cent)

The percentage of the residual feed after removing the water content. Examples include:

  • Concentrate feeds: ~90% DM
  • Hay: ~85-90% DM
  • Pit silage: ~30-35% DM (Less than this may result in poor fermentation)
  • Baled silage: ~35-45% (Less than this may result in very heavy bales with poor fermentation. More than 45% DM will result in inadequate fermentation due to poor compaction.)

Crude protein (CP; per cent of DM)

Gives an estimate of the protein content in a sample. In good silage, there should be only a small difference in the quality of the silage compared to the original pasture. Examples include:

  • Concentrate feeds: ~10-50%, depending on type
  • Hay: ~9-20%, depending on type
  • Grass silage: ~16-17%

Neutral detergent fibre (NDF; per cent of DM)

Measures the amount of fibre that consists of various components (hemicellulose, cellulose and lignin). The amount of NDF is negatively associated with the cow’s dry matter intake — the higher the NDF the less a cow can eat. High-quality silage will have an NDF of 50 per cent or less. Hay can range from ~40 per cent (lucerne hay) to 60 per cent (grass hay) NDF.

-Source: Dairy Australia

- Dr Gemma Chuck is an advisor with apiam animal health