Farm Animal Metabolism and Nutrition

of the former is associated with increased
portal flux not only of non-essential amino
acids but also of ammonia, suggesting that
gastrointestinal tissue metabolism (cata-
bolism) of the amino acids is also increased
(van der Meulen et al., 1996). For ruminant
animals, the effect of increasing nitrogen

intake is more complex due to the moderat-

ing effect of the ruminal microflora in

influencing the flow of protein (principally

in the form of microbial protein) into the

duodenum. Figure 3.1 shows that the rela-

tionship between net portal flux of amino

acids and N intake is poor in comparison

Inter-organ Amino Acid Flux 53

Fig. 3.1.Relationships between nitrogen intake, portal-drained visceral
-amino nitrogen flux
(A: y= 20.429 + 0.136x, R^2 = 0.235) and portal-drained visceral NH 3 N flux (B: y = 12.96 + 0.594x,
R^2 = 0.772). From Seal and Reynolds (1993).