Harnstoff und Allantoin in der Milch von Kühen während und nach Verfütterung zu hoher und zu niedriger Proteinmengen

Nonprotein nitrogen and protein distribution in the milk of cows

The NPN content of milk represents only 5 to 6% of the total N in milk. However, the significance of this milk N fraction to energy and N metabolism in the dairy cow has not been well characterized. The single largest contributor to the NPN fraction of milk NPN is urea. Urea equilibrates in body water, and blood urea is the primary source of milk urea. The urea in milk can be derived from at least two sources: the end product of digestion and amino acid catabolism. Blood urea N was positively associated with intakes of ruminally degradable and undegradable protein and negatively associated with intake of net energy. Consequently, it might be possible to develop a system to evaluate the dietary protein and energy status of the lactating dairy cow employing milk urea in conjunction with milk true protein.

[Allantoin excretion of wethers in variations of raw protein and energy administration]

216 values of urinary allantoin excretion were received from 8 digestibility trials, which included 48 rations with different protein and energy content. Thus relations between allantoin excretion and food intake and ration composition, respectively, could be evaluated. Additionally variations in N balance were measured, since there is a close relation to allantoin metabolism. Fecal N excretion was elevated with increasing energy intake, but varied only slightly with modified N supply. Urinary N excretion and also N retention increased with higher N intake. On the other hand urinary N losses were reduced with increasing energy supply and part of the saved nitrogen was deposed into the body. There was a distinct increase in allantoin excretion with raised protein intake, when N supply ranged generally low. But with a daily supply of crude protein above 60 to 70 g there was no significant further response in allantoin excretion. Allantoin excretion increased linearly with higher energy supply. Several restrictions for conclusions on the extent of microbial protein production in the digestive tract estimated out of measured allantoin values were discussed.