A statistical study of the effect of excessive feeding of calcium and phosphorus supplements on the blood calcium and phosphorus of dairy cows

A statistical study of the effects of the feeding of large amounts of calcium and phosphorus supplements on the level of these minerals in the blood of dairy cows was made on the basis of 274 blood samples collected from 15 herds. The effects of four presumably independent variables, the actual amount of either calcium or phosphorus in the ration, milk yield, stage of lactation and the Ca/P ratio of the ration, were investigated simultaneously. When the level of calcium in the blood (x1) was considered as the dependent variable, it showed a possibly significant correlation only to two of the above mentioned independent variables, e.g., to Ca/P ratio (x2) and milk yield (x3). The coefficients of partial correlation obtained were r12,3 = + 0.3766 and r13,2 = + 0.1545 and that of multiple correlation r1(23) = 0.3966. These correlations can be expressed quantitatively with the following equation: x1 = 4.88 + 0.427 · x2 + 0.0373 · x3, where x1 = the amount of calcium in blood in mg. per 100 ml, x2 = the Ca/P ratio of the ration and x3 = kilograms of milk produced per day. When the effect on the level of inorganic phosphorus in mg. per 100 ml. of blood (x1) was investigated similarly, again only two of the variables studied, e.g., the actual amount of phosphorus (g. per day) in the ration (x2) and the milk yield (x3) appeared to be effective. The coefficients of partial and multiple correlations obtained were r12,3 = + 0.4861, r13,2 = - 0.1447 and r1(23) = 0.4892. This effect expressed as a linear function, is given by the following equation: x1 = 3.59 + 0.0142 · x2 - 0.0304 · x3. When the cations Na+, K+,and Ca++, and the anions CL- and HPO4-- were determined separately in the blood, the total amount of cations expressed in chemical equivalents exceeded the total equivalent amount of inorganic anions to an amount that was about twice the equivalent amount of the bicarbonate alkali reserve of the blood. The total cation excess varied independenly of the Ca/P ratio of the ration, but the latter showed a negative correlation to the bicarbonate alkali reserve, probably due to an increasing amount of organic acids in the blood. No effect on the pH of either blood of feces was noticed. It is concluded that an excessive amount of phosphate may be conducive to maintaining a high blood inorganic phosphate level. Similarly, a high Ca/P ratio of the ration or an excessive amount of calcium carbonate in the feed, along with proper rumen fermentation, may be conducive to maintaining a high calcium content in the blood of high producing dairy cows.