The use of ammonium sulphate as an acidiogenic agent in bone meal licks to improve the phosphorus status in cattle

Abstract

Sixteen Bonsmara calves ( 4 males, 12 females) were blocked according to sex and randomly assigned to 2 groups of 8 each. They were offered licks containing bone meal and salt (control) and bone meal and ammonium sulphate at 1.25, 2.5, 5, 10, 15, and 18% (treatment) to evaluate the effect of dietary anions on blood, bone and faecal P, Ca and Mg for a period of 6 weeks. Calves were also fed ad lib a roughage containing 50% Medicago Sativa and 50% Cencrus Ciliaris. Blood, bone and faecal samples were taken on the same day to prevent variation between sampling periods and mineral contents. Bone, blood and faecal P concentrations were significantly (P<0.05) higher in the anionic treatment group in most weeks of the experiment compared to the control group. Bone P concentration was significantly (P<0.05) increased in the anion treatment group at every sampling period, not only compared with control animals, but also compared to other treatment concentrations of ammonium sulphate, indicating that the ammonium sulphate was able to improve the P content of bone at each of the 6 concentrations used in the lick. A relationship existed between bone and blood Ca where there was resorption from bone with increased blood and faecal Ca and decrease in bone Ca. The response of bone Ca and P was in opposite directions in most weeks of supplementation. When bone Ca increased bone P decreased and when bone Ca decreased bone P increased and this indicate independent absorption and resorption of Ca and P into and out of bone and a wide Ca:P ratio varying from 1.5:1 to 5:1. Faecal P concentration was significantly (P< 0.05) increased in the faeces of the treatment animals at all sampling periods except when ammonium sulphate was added at 2.5% and 15%. The mean concentration of P in the blood was significantly (P<0.01) higher in the calves on the anionic diet compared with the calves on the control diet and the bone thickness was significantly (P<0.05) greater in the calves fed the anionic diet compared with those fed the control diet. It should also be noted that the bone thickness followed bone P and not bone Ca. Bone Mg was diet. It should also be noted that the bone thickness followed bone P and not bone Ca. Bone Mg was unpredictable when compared to the other two mineral parameters. Bone Mg fluctuated, and it was difficult to build a relationship between bone Mg, Ca and P. When bone Ca increased, bone Mg also increased but only at 1.25% NH4S04 and 5% NH4S04. It was only at 2.5% NH4S04 that bone Ca decreased with a decrease in bone Mg. At the 10%, 15% and 18% NH4S04 level of supplementation these two minerals responded in opposite directions. Results from this research indicate that the addition of anions, in the form of NH4S04 has a beneficial effect in increasing bone P; and because of simultaneous increases in blood, bone and faecal P when ammonium sulphate was added to the lick at 1.25 and 18%, also has a P sparing effect for animals grazing a P-deficient veld.