Calcium and Phosphorus Requirements

Calcium (Ca) and phosphorus (P) requirements of goats are based on recommendations of NRC (2007). These requirements and calculations are described below, with abbreviations, assumptions, and units defined first.

Abbreviations, assumptions, and units

  • DMI = dry matter intake (kg)
  • ADG = average daily gain (g)
  • BIRWT = birth weight per kid (kg)
  • LS = litter size (number of kids)
  • MY = milk yield (kg)
  • Assumed Ca absorption of 45%
  • Assumed ration of fetus to birth weight of 85%
  • CaMAINT = Ca requirement for maintenance (g)
  • CaADG = Ca requirement for ADG (g)
  • CaLACT = Ca requirement for lactation (g)
  • CaPREG = Ca requirement for pregnancy (g)
  • CaTOT = Total Ca requirement (g)
  • Assumed P absorption of 65%
  • Assumed ratio of fetus to birth weight of 83.3%
  • PMAINT = P requirement for maintenance (g)
  • PADG = P requirement for ADG (g)
  • PLACT = P requirement for lactation (g)
  • PPREG = P requirement for pregnancy (g)
  • PTOT = Total Ca requirement (g)
  • Ca requirements
    • CaMAINT (g) = (0.228 + (0.623 * DMI)) / 0.45
    • CaADG (g) = (11 * ADG / 1000) / 0.45
    • CaLACT (g) = (1.4 * MY) / 0.45
    • CaPREG (g) = ((0.23 * LS * BIRWT * 0.87) / 0.45
    • CaTOT (g) = CaMAINT + CaADG + CaLACT + CaPREG
  • P requirements
    • PMAINT (g) = (0.081 + (0.88 * DMI)) / 0.65
    • PADG (g) = (6.5 * ADG / 1000) / 0.65
    • PLACT (g) = (1 * MY) / 0.65
    • PPREG (g) = ((0.132 * LS * BIRWT * 0.833) / 0.65

For some users, however, it may be common and desirable to base the Ca requirement on the level of dietary P and vice versa, if the ratio of Ca:P is less or grater than desired. Therefore, the user can also specify a set Ca:P ratio for a listing of requirements based on this alternative method.

Because the maintenance Ca and P requirements are based on DMI, estimating DMI is the primary step in determining the requirements. DMI estimates can be directly entered, or feed intake calculators can be used. It should be noted, however, that equations to predict DMI for pregnant animals were not addressed by Luo et al. (2004) or Sahlu et al. (2004). Nonetheless, some adjustments of DMI by goats in late gestation are included based on a limited amount of data.

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

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


Choose class of goat

growing mature
lactating Angora
2. Enter preferred Calcium:Phosphorus ratio
(Default is 2:1)
3. Enter body weight (kg)
4. Enter average daily gain (g/day)
Enter ME concentration of diet (MJ/kg DM)
You can use the TDN calculator above and the ME concentration will be entered automatically.
6. Enter CP concentration in diet (%)
Lactating goats require additional calcium and phosphorus for milk production.

Enter daily milk yield (kg)


Choose breed-type of goat to predict milk yield

Meat Dairy Angora

You may edit predicted milk yield, if you feel this value is incorrect.

  1. input litter size  
  2. Enter week of lactation  
  3. input age of doe at kidding  
  1. input breed  
  2. input parity  
  3. input week of lactation  
  4. input litter size  
Pregnant goats require additional calcium and phosphorus for pregnancy.

Enter litter size and average birth weight (kg)


Estimate birth weight by using breed averages

litter size:

birth wt:

day of pregnancy:

9. Enter estimate of DM intake (% BW)


Choose class of goat for FI calculator
(should be same as in #1)

growing mature
lactating Angora

(maintenance energy based on body weight alone)

(adjusted maintenance energy)

To convert from English to metric system,
enter your values here.
They will be automatically entered into the table to the left.


Calcium requirement for maintenance (g):
Calcium requirement for gain (g):
Calcium requirement for lactation (g):
Calcium requirement for pregnancy (g):
Total Calcium requirement (g):
Phosphorus requirement for maintenance (g):
Phosphorus requirement for gain (g):
Phosphorus requirement for lactation (g):
Phosphorus requirement for pregnancy (g):
Total Phosphorus requirement (g):
Calcium:Phosphorus ratio:
Additional Calcium added to balance preferred ratio or to 2:1 ratio (g):
Additional Phosphorus added to balance preferred ratio or to 2:1 ratio (g):

Sources used in this calculation method are:

Luo, J., A. L. Goetsch, I. V. Nsahlai, J. E. Moore, M. L. Galyean, Z. B. Johnson, T. Sahlu, C. L. Ferrell, C. L., and F. N. Owens. 2004. Prediction of voluntary feed intake by lactating, Angora, growing and mature goats. Small Rum. Res. 53:357-378.

NRC. 2007. Nutrient Requirements of Small Ruminants. National Academy Press. Washington, DC.

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. Energy and protein requirements of goats: developed equations, other considerations, and future research to improve them. Small Rum. Res. 53:191-220.