Protein and energy relationships in dairy cattle. 2. Lactating cows.
Nitrogen requirements of lactating cows were calculated by means of statistical relationships established for nitrogen excretion in faeces and urine, for nitrogen balance, and for nitrogen flow in proximal duodenum and terminal ileum. The data used for elaboration of the relationships came from simultaneous measurements of nitrogen and energy balances. It appears that an increase in dietary nitrogen solubility augments total nitrogen and apparently digestible nitrogen requirements of the animals because of higher urinary nitrogen losses. This effect can be off-set by an increased metabolizable energy intake. High proportions of concentrates in the diets cause a shift in nitrogen excretion from faeces to urine. Requirements of intestinal absorbed nitrogen and its conversion into milk protein are dependant of dietary nitrogen solubility and metabolizable energy concentration, while they are favourably influenced by energy supply. Crude protein concentration is not an adequate way for expressing optimal protein supply in lactating cows because it may vary between 11.2% and 20.0% according to dietary characteristics for the same animal.
Teller
E
E
Catholic University of Louvain, Faculty of Agriculture Science, Department of Nutritional Biochemistry, Louvain-la-Neuve, Belgium.
Godeau
J M
JM
D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004044:Dietary Proteins / Q000378:metabolism*; D004386:Duodenum / Q000378:metabolism; D004734:Energy Metabolism; D005260:Female; D007082:Ileum / Q000378:metabolism; D007774:Lactation / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D011247:Pregnancy; D012044:Regression Analysis
D004044:Dietary Proteins; D009584:Nitrogen