Interpreting feed analyses

We have been asked by many farmers over my years of clinical practice to explain and interpret feed analyses of varying products.

Here we will focus on pasture and silage ...

Dry matter (DM)

DM is the part of a foodstuff or other substance which would remain if all its water content was removed. It is not normally considered a problem, though may negatively impact on total DM intake at very low levels (<10%). Pasture can fall to these low levels in spring and autumn. Silage is best if it is in the range 30-40%. Accuracy is vital in calculating feed costs, supplements fed and quality of pasture consumed.

Organic Matter (OM)

OM describes the amount of useable material in a feed per kgDM. The higher the figure the better. Pasture is usually between 870-910 g/kgDM. Maize silage is often higher, up to 960 g/kgDM, which may indicate why it performs so well in many diets.

Crude Protein (CP)

CP describes the crude protein content of a feed. The diet should ideally be between 170-200 g/kgDM. Pastures usually range from 120-380 g/kgDM. Rapidly growing pasture is likely to be 240-380 g/kgDM; slow growing summer grass is 120-180 g/kg DM. During spring and autumn, we often require low protein supplements (e.g. maize silage) and in summer high protein supplements (e.g. turnips).

Undegraded Protein (UDP)

Bypass Protein – this is the portion of crude protein that bypasses the rumen and is absorbed in the small intestine. Often not tested for, but we would prefer UDP to be 25-35% of crude protein. It is often expensive to procure supplements of UDP.

Rumen Degraded Protein (RDP)

RDP is the balance of crude protein that is broken down in the rumen. This usually includes a proportion of non-protein nitrogen (NPN). The NPN is increased in pasture with the use of nitrogen fertilisers, is often not able to be utilised and needs to be cleared from the rumen and excreted.

Acid Detergent Fibre (ADF)

ADF describes the proportion of fibre content in a feed with regard to its cellulose and lignin. The diet should ideally be between 200-250 g/kgDM. Rapidly growing grass is likely to be 160-240 g/kgDM. Slow growing summer pasture is likely to be 250-320 g/kgDM. During spring and autumn, we often require high fibre supplements (e.g. maize and pasture silage, hay), and in summer low to medium fibre supplements (e.g. turnips and some grains). Feed quality is often inversely related to dietary ADF levels.

Neutral Detergent Fibre (NDF)

NDF is the portion of fibre content in the feed with regard to cellulose, hemicellulose and lignin. The diet should ideally be between 320-400 g/kgDM. Pastures are likely to be 260-520 g/kgDM but in spring and autumn 260-380 g/kgDM and in summer 400-520 g/kgDM. Dry matter intake is often inversely related to NDF levels.

Soluble Carbohydrate (SolCHO)

These are simple sugars. The diet should ideally be between 250-350 g/kgDM. Pasture usually have low levels in the range of 50-150 g/kgDM. Sunshine lifts these levels around 0.5% per hour during the course of a sunny day. Maize silage and many grains have higher levels of soluble carbohydrates.

Pectin

This is a form of fibre that has similar dietary characteristics to SolCHO. Ryegrass usually has levels of 1.0-3.0% and clovers 6.0-8.0%.

Metabolisable Energy (ME)

ME is the quantity of energy in megajoules (MJ) that is available for animal nutrition. Most feed range from 6.0-14 MJ ME/kgDM. Pastures usually range from 9.0-12.5 MJ ME/kgDM. During summer we often require high energy supplements (e.g. turnips, some by-products, grains).

Digestibility (DOMD – Digestible organic matter in dry matter)

Describes the proportion of organic matter in a feed that can be digested by an animal. It is inversely related to the fibre content (ADF) in that feed. DOMD is giving the most reliable prediction of energy content.

pH (Acid-base content)

This is normally only present on reports of silages (pasture and maize silage). The pH should be 4.5 or less if the ensiling process has been successful. If the pH is 5 or higher there is a possibility that many disease-causing bacteria will survive (eg. Listeria spp, Salmonella spp, Tuberculosis and mastitis causing bacteria.)

Calcium (Ca)

Calcium is primarily required for milk synthesis, bones, teeth, blood clotting and muscle contraction. The diet should ideally be between 6.0 and 8.0g/kgDM and be near the upper end of the range for peak milk production. Pastures usually range from 4.0-6.0 g/kgDM and are often near the lower end of this range in early spring.

Phosphorus (P)

Phosphorus is primarily required for milk synthesis, bones, teeth and energy metabolism. The diet should ideally be between 4.0-5.0g/kgDM. Pastures usually fall within this range.

Potassium (K)

Potassium is primarily required for electrolyte balance, enzymes, muscles and nerves. The diet should ideally be between 10.0-12.0 g/kgDM, though pastures usually range from 30.0-55.0 g/kgDM. Most supplements have levels well below these figures and improve this imbalance in the diet. High levels of dietary K interfere with Ca, Mg and Na uptake.

Sulphur (S)

Sulphur is primarily required for rumen metabolism of protein and for cartilage and tendons. The diet should ideally be between 2.0-3.0 g/kgDM. Pastures usually range from 3.0-5.0 g/kgDM. Some forage such as maize silage are very low in S (<1.0 g/kgDM).

Magnesium(Mg)

Magnesium is primarily required for enzymes and bones. The diet should ideally be between 2.0-3.0 g/kgDM. Pastures usually range from 1.5-3.0 g/kgDM, and are often near the lower end of this range in early spring. Some forages such as maize silage are normally low in Mg(<1.5g/kgDM).

Sodium (Na)

Sodium is primarily required for acid-base balance (DCAD), muscles and nerves. Diet should be ideally between 1.8-2.5 g/kgDM. Pastures usually range from 1.0-3.0 g/kgDM, and are often near the lower end of this range in early spring. Some forages such as maize silage are normally low in Na (< 1.0 g/kgDM).

Chloride (Cl)

Chloride is primarily required for DCAD, osmotic pressure post calving and hydrochloric acid production in the abomasum. This is of particular importance in the dry cow diets to initiate calcium mobilisation.

Checking the range of these elements will help you when viewing your pasture and supplement reports. If you have any queries, please contact your local veterinarian.

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