Serum complement activity of protein-energy malnourished beef cows.

Beef heifers were fed protein- or energy-deficient rations (or both) for approximately the last 5 months of pregnancy. Serum samples were periodically collected and were analyzed for amounts of total complement (C) hemolytic activity. After being fed the rations for approximately 2 months, heifers given low-energy rations had significantly lower (P < 0.01) amounts of C than did those fed adequate energy rations, This decrease in C was observed regardless of the amount of dietary protein, although low protein intake seemed to exaggerate the effect of low energy consumption. Reduced protein in the rations had no effect on C titers when caloric intake was adequate. Also, the depressive effect of low dietary energy on C values was no longer apparent after approximately 4 months of feeding the rations. Amounts of C dropped by 20 to 40 U for all groups at or near the time of parturition. The C values averaged over all test dates were significantly lower (P < 0.05) for those heifers given low energy in their rations as compared with values for heifers fed adequate energy rations (146.9 vs 160.8 U).