Indicators of Feed Quality

The balance of the indicators listed below will determine the quality of feed for dairying. If analyses shows values outside the normal ranges it might be advisable to supplement. Note that indicators apply to the whole diet consumed.

CRUDE PROTEIN (CP) (%DM)

A minimum of 15% is required to maintain milk production in lactating cows. Growth can be achieved with 10-14% CP, with better results at the high end of the range.

Maintenance requirement is about 7% CP, so values lower than 7% will cause a CP deficiency. Note that maize silage normally has a low CP%, barely enough to provide maintenance requirement, so it should be regarded predominantly as an energy supplement.

SOLUBLE SUGARS AND STARCH (%DM)

SSS supplies the rumen microbes with energy for their synthetic activities. The normal range for pasture is 10-15%. If SSS is less than 10% rumen microbial fermentation is likely to be reduced with negative effects on digestion. Maize silage should be in the range 30-40% SSS. The normal range for Pasture silage is 2-7% SSS.

FIBRE (Acid detergent [ADF] and neutral detergent [NDF] fibres) (%DM)

ADF and NDF are both measures of difficult-to-digest plant cell wall carbohydrates. Generally the lower the fibre the better, but not below 20% ADF or 30% NDF, because some fibre is needed to stimulate rumen activity. Normal ranges are:

                                                                                                ADF                                         NDF

                                Good quality                                  20-35                                     30-45

                                Average quality                               35-50                                   45-70

                                Poor quality                                      >50                                        >70

FAT (CRUDE FAT [Lipid]) (%DM)

The normal range in pasture based dies is 2.5-4.5%. Too much fat (>7%) can interfere with ribre digestion and cause diarrhea.

ELEMENTS (%DM)

The following concentrations of major elements should meet animal requirements. Lower values are likely to limit animal performance.

                                Na           0.12                                         Ca            0.44

                                K*            0.58                                        P              0.32

                                Mg           0.19                                        S              0.18

*K concentration >5% are undesirable and would reduce Mg availability, leading to a need to supplement with Mg.

IN VITRO ORGANIC MATTER DIGESTIBILITY (OMD) (%DM)

OMD estimates the total nutrients apparently digested by the animal. It is measure in the labratory (in vitro) and calibrated against animal measurements (in vivo). Normal ranges are:

                                Poor quality                           <55

                                Average quality                                 55-70

                                Good quality                         >70

NB           Instrument calibration is based on actual feeding trials of a sample feed source. Maize silage cannot be used as a sole feed source; as such we are unable to provide a result for In vito organic matter Digestibility.

METABOLISABLE ENERGY (ME) (MJ/kg DM)

ME is a measure of the energy that is available to the animal for maintenance, growth and milk and wool production. ME is calculated using a well-established equation. Normal ranges are:

                                Poor quality                           <8

                                Average quality                                 8-10

                                Good quality                    10-12

                                Excellent quality               >12

SILAGES (Additional quality indicators)

Silage is a fermentation product and the chemical composition will reflect this. Some RFC is converted to organic acids (especially lactic) that preserve the silage and some protein is degraded to ammonia. The following indicators are used, in addition to those given above to assess silage quality.

pH. Well fermented pasture and maize silages made in a pit or stack should have a pH <4.5 and legume based silages should be <5. Wrapped silages are usually of a higher DM% and their pH should be <5. Values higher than these indicate a poor primary fermentation or subsequent spoilage.

Ammonia (NH3-N) (% total N). NH3-N concentration reflects the degree to which dietary protein has been degraded during silage fermentation. NH3-N should be less that 5% for maize silages and <10% for pasture silages. Values higher than these indicate excessive wastage and probably loss of quality.

Lactic acid (%DM). A high lactic acid content is desirable: >6-8% for wet silages (>65% moisture) and >3-4% for wilted silages (<55% moisture. Lower values indicate poor quality.

Volatile fatty acids (%DM). Acetic acid should be <2%, propionic acid <1% and butyric acid <0.1%. If concentrations are higher than these values poor fermentation of spoilage is indicated.

Information kindy supplied by FeedTECH, AgResearch Nutrition & Behaviour

Indicators of Feed Quality

Maize Silage feed analysis