The horse's body contains approximately 0.05 % magnesium, 60 % of which is found in the skeleton. Magnesium is an activator for many enzymes and is required for normal muscle function. Normal absorption of magnesium is 40-60 %. During the calculation of magnesium requirements a value for absorption of 40 % is assumed (NRC 1989).
Maintenance. Mg (g/d) = 0.015*BW
Growth: between 0.85 and 1.25 g of Mg are deposited per kg of body weight gain; NRC assumes 1.25 g in their calculation.
Mg (g/d) = 0.015*BW + 1.25*DWG
Magnesium requirement for growth with training:
Mg (g/d) =(0.015*BW+1.25*DWG)* (DE for exercised / DE for unexercised)
Pregnancy: The requirement for magnesium during the last 3 months of pregnancy increases by 0.3 mg/kg BW.
Months 9 - 11: Mg (g/d) = 2.0 * DE (MJ)
Lactation. The magnesium concentration in mare's milk during early lactation is approximately 90 mg/kg and declines to 45 mg/kg in late lactation. The absorption of magnesium is assumed to be 40 %.
1st - 2nd month:
Mare 200 kg: Mg (g/d) =0.015*BW + (0.04*BW*0.09) /0.4
Mare above 300 kg: Mg (g/d) =0.015*BW + (0.03*BW*0.09) /0.4
3rd month - weaning:
Mare 200 kg: Mg (g/d) =0.015*BW + (0.03*BW*0.045)/ 0.4
Mare above 300 kg: Mg (g/d) =0.015*BW + (0.02*BW*0.045)/ 0.4
Work: Mg (g/d)= 1.92 * DE (MJ)