Estimating Supplemental Concentrate Needs

Use this Supplemental Concentrate Needs Calculator to calculate the amount of a given supplement to meet requirements of metabolizable energy (ME) and metabolizable protein (MP) for different types of goats consuming various basal dietary forages. Enter the data into the table and then click the Calculate Supplemental Concentrate Needs button. The results will be displayed in the table at the bottom of the page.

Goats are raised in many different types of production systems; but, feeding components can be grossly categorized into two types: 1) basal forage plus supplemental concentrate (BFSC) and 2) totally mixed diet or ration (TMR). Most meat, cashmere, and Angora production systems entail the first type of feeding system, with greatest prevalence of TMR for dairy production systems.

With BFSC, concentrate is supplemented to provide needed energy and protein not supplied by basal forage alone. Therefore, to determine the composition and feeding level of supplemental concentrate, it is necessary to know energy and protein characteristics of forage, as an estimate of forage intake is needed also.

Feed tags for supplements typically list the CP concentration. Likewise, the CP concentration in basal forage can be determined by a commercial laboratory, or perhaps this can be estimated based on past levels in similar forage. For simplicity, the CP concentration in forage along with an assumed factor for converting CP to metabolizable protein (MP; MP concentrate (%) = 64.0 + (0.16 × rumen undegraded protein concentration, % of total CP) will be used.

A number of measurements are necessary to most accurately determine the rumen undegraded protein concentration (UIP) in forages and supplemental concentrates. However, as noted for calculation of MP requirements, knowledge of the general type of feedstuff can allow an adequate estimate of the UIP concentration for most practical purposes. For example, many fresh forage diets would probably have a UIP concentration of 20% (on a total CP basis), which means that 80% of the CP is degraded in the rumen. Dried forages would have a slightly higher UIP level (e.g., 30% for grasses). In general, as the dietary level of concentrate increases, the UIP level increases. Since not a large number of feedstuff UIP concentrations have been determined with goats, below is a table with UIP levels for cattle (Preston, 2000) that can be used until more values determined with goats become available. Typically, feed tags list the major ingredients, which then can be used along with the table below, to derive a reasonable estimate of the UIP concentration. However, default UIP values of 20% for the basal forage and 40% for the supplemental concentrate have been used in the input box below.

Click to show/hide table.

To estimate the need for supplemental concentrate, an estimate of forage intake is needed. The feed intake calculators can be used for this, unless there is already knowledge of how much of a particular type of forage is consumed by class of goat of interest. The next factor to be considered is potential associative effects. An associative effect can be defined as a response, such as in total feed intake, digestibility, performance, etc., when mixtures of feedstuffs are consumed that are not as would be expected based on consumption of the feedstuffs alone. Associative effects can be positive or negative. That is, in some instances feed intake, for example, might be greater or less than expected. An example of a positive associative effect is when a very low protein forage (e.g., 4 or 5% CP in weathered and(or) mature prairie hay) is fed and a high-protein supplemental concentrate (e.g., soybean meal) is given, resulting in an increase in forage intake. An example of a negative associative effect is when a moderate to low digestibility forage (e.g., TDN concentration of 40-50% is supplemented with a moderate to high level (e.g., 0.75-2.0% BW) of concentrate high in cereal grains like corn. In this case, the supplemental concentrate elicits a decrease in forage intake, or there is ‘substitution' of concentrate for forage.

There has not been a great deal of research on associative effects with goats compared with cattle or sheep. Thus, it is not possible to use a well accepted method of addressing the issue. Nonetheless, because associative effects are known to occur in goats, a simple system being used in another project of the Institute will be employed until further information is available.

When the supplemental concentrate level is at least 0.5% BW (DM basis), the following formula is suggested to address negative effects on forage intake of supplementation with high energy feedstuffs.

SUBN = -1 * ((-0.0007 - (0.2491 × DMIBWS) + (0.7641 × DMIBWS2) - (0.2006 × DMIBWS3)) - ((55 - DIGF) × 0.04))

SUBN = change (negative or a decrease) in forage intake, expressed as a fraction of supplement intake (for example, if supplement is given at 1% BW (DM basis), and SUB is -0.6, then hay intake is decreased by 0.6% BW.
DMIBWS = supplement intake as % BW (DM basis)
DMIBWS2 = DMISBW squared
DIGF = digestibility of forage

DIGF can be calculated from ME concentration as: DIGF = (ME concentration, MJ/kg + 1.8749) / 0.1867.

For forages < 6% CP (DM basis) and supplements 15% or greater in CP concentration (DM basis), and a supplemental concentrate less than 0.5% BW (DM basis), the following formula is suggested to address the positive associative effect of high-CP supplements on intake of low-protein forages.

SUBP = (1.0398 - (0.2323 × DMIBWS) - (0.7047 × DMIBWS2) + (0.3757 × DMIBWS3)) - ((6 - PTCPF) × 0.05)

SUBP = change (positive or an increase) in forage DM intake expressed as a fraction of supplement intake (for example, if supplement is given at 0.25% BW (DM basis), and SUB is 0.6, then hay intake is increased by 0.15% BW.

DMIBWS = supplement intake as % BW (DM basis)
DMIBWS2 = DMIBWS squared
PTCPF = % CP in forage or basal diet

In most practical supplementation settings, associative effects will be minor and not worth considering. However, they will be considered here when sgnificant, perhaps resulting in change in projected forage intake and need for supplemental concentrate.

In some settings MP or CP will be relatively more limiting than energy. However, goats appear relatively more efficient in recycling nitrogen than cattle or sheep, which suggests that the likelihood of MP being more limiting than ME is at least slightly less for goats. Also, it is important to note that with low-quality forage, both ME and ME may be limiting, and frequently supplemental concentrate given to correct a ME deficiency will be more than adequate to also correct for a MP shortfall. Nonetheless, this should be tested, with use of whichever estimate of supplemental concentrate used (i.e., based on ME vs MP) that is greater. The corresponding estimate of forage intake is employed as well.

If the combination of the particular animal forage, and supplemental concentrate conditions results in an unrealistically high proportion of concentrate in the diet, then a change in one of these three factors is warranted. For example, perhaps the forage is simply too low in quality whatever the supplemental concentrate for relatively high animal requirements for ME and(or) MP. Or, a supplemental concentrate with a much higher level of ME and(or) MP could be warranted.

In this regard, this calculator also displays the concentrations of MP and CP in the supplement necessary to exactly meet the need when the amount of supplement is being based on ME. Likewise, the optimal ME concentration in the supplement is listed when the supplement amount was determined by the MP requirement. If no value is listed in a box then supplemental concentration was based on this factor (ME or MP) or, forage alone without supplemental concentrate satisfied the requirement.

In addition to calculation of MP intake, the requirement for and intake of rumen degraded intake protein (DIP) are estimated. In most instances, however, because MP intake is determined as the sum of microbial protein and feed protein passing from the rumen intact, when MP intake is adequate so too will intake of DIP be.

To estimate the dietary ME concentration of the basal forage as well as supplemental concentrate, often feed tags list the Total Digestible Nutrient (TDN) concentration. Likewise, most commercial feed laboratories estimate the TDN concentration based on analyses, such as for crude protein (CP) and various fiber fractions.

As an example of this calculator, the following conditions can be used.

Parameter Value
Age Mature
BW (kg) 50
ADG (g/d) 0
Me: Biotype Indigenous
Gender Female
Forage MEC (MJ/kg) 8
MP: Forage CP (%) 5.5
Concentrate TDN (%) 80
Concentrate CP (%) 20
Forage UIP (% CP) 20
Concentrate UIP (% CP) 40

The feed intake calculator with optional adjustments should be used. With 5.5% CP in the basal forage, the amount of supplement is based on MP rather than ME. Total ME intake is 8.03 MJ, which is slightly greater than the requirement of 7.95 MJ. Hence, the optional ME concentration in the supplement is 11.00 MJ, slightly less than the assumed concentration of 12.08 MJ/kg. Very importantly, since the basal forage had a CP concentration of 5.5% (less than 6%) and the supplement CP level was above 15% (i.e., 20%), the supplement had a positive associative effect on basal forage intake (initial projected intake of 1.62% BW without supplementation compared with 1.79% BW when the supplement was given).

Conversely, with a basal forage CP concentration of 7%, the amount of supplement is based on ME rather than MP. MP intake now is slightly greater than the requirement (i.e., 55.24 vs 43.11 g). This results in optimal MP and CP concentrations in the supplement markedly less than assumed. This example brings out the importance of knowing forage composition in order to design appropriate supplementation strategies.

The ME concentration can be calculated with these simple formulas:
ME (MJ/kg) = TDN (%) × 0.15104 and
ME (Mcal/kg) = TDN (%) × 0.0361.

Enter concentrate TDN (%)
ME (MJ/kg)
ME (Mcal/kg)
Enter forage TDN (%)

1. Choose class of goat growing
2. Enter body weight (kg)
3. Enter average daily gain (g/day)
4. Enter ME requirement (MJ)

or use

5. Enter MP requirement (g)

or use

6. Enter estimate of intake of forage without supplementation (% BW)

or use

(maintenance energy based on body weight alone)

(adjusted maintenance energy)

Enter forage ME concentration (MJ/kg DM)
You can use the forage TDN calculator above and the ME concentration will be entered automatically.
Enter supplemental concentrate ME concentration (MJ/kg DM)
You can use the concentrate TDN calculator above and the ME concentration will be entered automatically.
9. Enter CP concentration in forage (%)
10. Enter CP concentration in supplemental concentrate (%)
11. Enter UIP concentration in forage (% of total CP)
12. Enter UIP concentration in supplemental concentrate (% of total CP)
13. Enter forage % DM (default is 90%)
14. Enter supplemental concentrate % DM (default is 90%)
To convert from English to metric system,
enter your values here.
They will be automatically entered into the table to the left.


Final estimate of total DM intake, which is that based on ME or MP, dependent upon the greater estimate of supplemental concentrate intake (kg):
Total DM intake (% BW):
Final estimate of supplemental concentrate DM intake, based on ME or MP (whichever is greater) (kg):
Supplemental concentrate DM intake (% BW):
As fed supplemental concentrate intake (kg):
As fed supplemental concentrate intake (% body weight):
Forage DM intake (kg):
Forage DM intake (% BW):
As fed forage intake (kg):
As fed forage intake (% body weight):
As fed total intake (kg):
As fed total intake (% body weight):
Supplemental concentrate DM intake (% total diet):
Forage DM intake (% total diet):
ME from forage (MJ):
ME from concentrate (MJ):
Total ME intake (MJ):
MP from forage (g):
MP from concentrate (g):
Total MP intake (g):
DIP requirement (g):
DIP from the diet (g):
Optimal supplemental concentrate ME concentration when the amount of supplement needed to meet the MP requirement was greater than that for ME (MJ/kg DM):
Optimal supplemental concentrate TDN concentration when the amount of supplement needed to meet the ME requirement was greater than that for MP (% DM):
Optimal supplemental concentrate MP concentration when the amount of supplement needed to meet the ME requirement was greater than that for MP (% DM):
Optimal supplemental concentrate CP concentration when the amount of supplement needed to meet the ME requirement was greater than that for MP (% DM):

Sources used in this calculation method are:

Luo, J., A. L. Goetsch, T. Sahlu, I. V. Nsahlai, Z. B. Johnson, J. E. Moore, M. L. Galyean, F. N. Owens, and C. L. Ferrell. 2003. Prediction of metabolizable energy requirements for maintenance and gain of preweaning, growing, and mature goats. Small Ruminant Research 53:231-252.

NRC. 2000. Nutrient Requirements of Beef Cattle, 2000 Update. National Academy Press, Washington, DC.

Nsahlai, I. V., A. L. Goetsch, J. Luo, Z. B. Johnson, J. E. Moore, T. Sahlu, C. L. Ferrell, M. L. Galyean, and F. N. Owens. 2004. Metabolizable energy requirements of lactating goats. Small Ruminant Research 53:253-273.

Sahlu, T., A. L. Goetsch, J. Luo, I. V. Nsahlai, J. E. Moore, M. L. Galyean, F. N. Owens, C. L. Ferrell, and Z. B. Johnson. 2004. Nutrient requirements of goats: developed equations, other considerations and future research to improve them. Small Ruminant Research 53:191-219.

UIP concentrations were derived from:

Preston, R. L. 2000. Typical composition of feeds for cattle and sheep. In: Beef 36(10), 10-20. Intertec Publ. Co. Overland Parks, KS.

For substitution and stimulation calculations, the following were some of the sources reviewed:

Horn, G. W., and F. T. McCollum, III. 1987. Energy supplementation of grazing ruminants. In: M. B. Judkins (Editor) Grazing Livestock Nutrition Conference. pp 125-136. University of Wyoming, Laramie.

McCollum, F. T., III, and G. W. Horn. 1990. Protein supplementation of grazing livestock: A review. Prof. Anim. Sci. 6(2):1-16.

Moore, J. E., M. H. Brant, W. E. Kunkle, and D. I. Hopkins. 1998. Effects of supplementation on voluntary forage intake, diet digestibility, and animal performance. J. Anim. Sci. 77(Suppl. 2):122-135.