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.

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, equations to predict associative effects between basal forages and supplemental feedstuffs for goats were developed based on survey of goat nutrition studies to improve diet formulation with the Langston University Interactive Nutrient Calculation system.

A literature survey of goat nutrition studies with ad libitum forage intake with or without supplementation was conducted, resulting in a database with 135 treatment mean observations, representing measures from 503 animals and derived from 26 publications. The database was divided into three datasets based on forage CP concentration (Low: < 6%, Moderate: 6 – 10%, and High: > 10%). The datasets were used to develop equations addressing positive and negative associative effects. Change in forage ME intake relative to metabolic BW (MEIMBWFOR; kJ/kg BW0.75) due to supplementation was predicted based on potential variables of supplement ME intake also scaled to metabolic BW (MEIMBWSUP; kJ/kg BW0.75), forage OM digestibility (OMDIGFOR; %), CP concentration (PTCPFOR; %), and NDF concentration (PTNDFFOR; % DM), supplement CP concentration (PTCPSUP; %) and ME concentration (MECSUP; MJ/kg), and quadratic functions of these variables (MEIMBWSUP2, OMDIGFOR2, PTCPFOR2, PTNDFFOR2, PTCPSUP2, and MECSUP2). Model development for each dataset was conducted by two analytical methods, stepwise regression and the Least Absolute Shrinkage Selection Operator (LASSO). Equations employing both methods were developed, with stepwise regression accounting for greatest variation:

Low:
MEIMBWFOR = -1859 + (1.13 * MEIMBWSUP) - (0.00284 * MEIMBWSUP2) + (63.8 * OMDIGFOR) - (0.433 * OMDIGFOR2) - (1.62 * MECSUP2) + (10.0 * PTCPSUP) - (0.0282 * PTCPSUP2)

Moderate:
MEIMBWFOR = 1732 - (0.579 * MEIMBWSUP) + (40.9 * PTCPFOR) - (62.4 * OMDIGFOR) + (0.601 * OMDIGFOR2)

High:
MEIMBWFOR = 563 - (0.00191 * MEIMBWSUP2)

Similar variables were selected with both analytical methods for each dataset, but variables selected differed among datasets. Although goodness of fit measures were relatively high for each dataset, they ranked Low > Moderate > High, suggesting greatest robustness for Low and complexity in influencing factors for High. In conclusion, equations to predict associative effects between basal forages and supplements consumed by goats developed for basal forage with low, moderate, and high CP concentrations should be useful in diet formulation.

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.

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.

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:

Tsukahara, Y., Puchala, R., Goetsch, A.L., 2020. Predicting feedstuff associative effects in goats. J. Anim. Sci. 98 (Suppl. 4), 454. https://doi.org/10.1093/jas/skaa278.790.

Dolebo, A.T., Puchala, R., Gipson, T.A., Dawson, L.J., Sahlu, T., Goetsch, A.L., 2017. Evaluation of a method to predict negative feedstuff associative effects in meat goats consuming diets with different forage sources and levels of concentrate. J. Appl. Anim. Res. 45, 470-479. https://doi:org/10.1080/09712119.2016.1217867

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.