Effects of caloric intake and infection on some aspects of protein metabolism in dogs.

In 3 separate trials a total of 48 purebred beagles were divided into 2 groups and fed a balanced diet supplying either 90-100 kcal./kg. body wt or 40-50 kcal./kg. body wt per day. The higher caloric intake resulted in an increase of 50-80 per cent of initial body wt after 5 or 6 weeks on the diet. The low-intake group lost about 10 per cent of initial body wt during the 6-week period. At the end of this period 12 dogs from each dietary group were exposed to distemper virus by intracerebral inoculation. In high-fed dogs the concentration of liver protein decreased significantly after inoculation. Of the free essential amino acids of the liver, threonine, valine and methionine decreased by day 3 post-inoculation as well as the ratio of the total essential to total non-essential (E/N) amino acids. Liver RNA was increased on day 3 and significantly lower on days 5 and 7. Cerebral RNA and DNA were lower on day 3, but showed no difference at day 5. In contrast to the results with high-fed dogs, the liver protein content of low-fed dogs increased as a result of infection. Infection also increased the levels of some of the essential amino acids by day 3 in this dietary group. Furthermore, the E/N ratio increased in the livers of this group after 3 days of infection. In general, changes in serum concentrations of the amino acids were not reflected by changes in liver concentrations. For infected dogs in this dietary group, liver RNA was lower on day 5 and higher on day 7 than in control animals. Cerebral DNA was lower on day 3 and higher on day 5 in infected dogs, whereas RNA was lower on both days. Cerebral protein content showed no change in either dietary group after infection. The physiological relationship between these chemical changes and the resistance of the host to infection is not completely understood. However, the present results suggest that the decreased resistance of high-fed dogs to infection is related in a complex way to changes in protein metabolism and hormone balance.