When using the daily excretion of PD to calculate the amount of exogenous purine absorbed by the animal, we need to correct for the contribution from the PD of endogenous origin. In sheep, when we take into account the amount of exogenous purines utilized by the animal, the net endogenous contribution (i.e. the endogenous loss minus exogenous purines utilizad) is reduced. Therefore,as the amount of exogenous microbial available to the animal increases the net endogenous contribution decreases to practically Zero (fig.2).the respons curve of PD excretion ve purine absorbed is not linear as shown in the work of Chen et al. 1900 and Balcells et al. 1992. In cattle, since the exogenous puries are not available for utilization by the animal, the purine loss must be replaced by de novo synthesis from amino acids. As a result, there is always a net endogenous contribution to the total excretion in urine (fig.2). the response curve of PD. Two equations proposed by this laboratory based on data available so far will be discussed in a later section. The studies of Balcells et al.(1991,1992) also derived a similar equation for sheep and confirmed the general model for cattle. However, more work is still needed to assess whether all parameters adopted in the equations will apply to all situations.
When using the daily excretion of PD to calculate the amount of exogenous purine absorbed by the animal, we need to correct for the contribution from the PD of endogenous origin. In sheep, when we take into account the amount of exogenous purines utilized by the animal, the net endogenous contribution (i.e. the endogenous loss minus exogenous purines utilizad) is reduced. Therefore,as the amount of exogenous microbial available to the animal increases the net endogenous contribution decreases to practically Zero (fig.2).the respons curve of PD excretion ve purine absorbed is not linear as shown in the work of Chen et al. 1900 and Balcells et al. 1992. In cattle, since the exogenous puries are not available for utilization by the animal, the purine loss must be replaced by de novo synthesis from amino acids. As a result, there is always a net endogenous contribution to the total excretion in urine (fig.2). the response curve of PD. Two equations proposed by this laboratory based on data available so far will be discussed in a later section. The studies of Balcells et al.(1991,1992) also derived a similar equation for sheep and confirmed the general model for cattle. However, more work is still needed to assess whether all parameters adopted in the equations will apply to all situations.
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