Serum immunoglobulin levels in suckled beef calves: quantity or quality?

Ingestion and absorption of colostral immunoglobulins (Ig) continues to interest investigators seeking optimal health maintenance in newborn calves. Much of the attention has centred around peak Ig levels obtained in the serum of the calf in the immediate postpartum period. Reports generally link low levels to subsequent disease and one controlled study noted levels below 0.5 g/ dL resulted in poorer response to treatment (1). Contradictions exist and measurement of immunoglobulin levels has not always been a reliable predictor of morbidity and/or mortality (2,3,4,5). The question arises as to what mean levels are adequate and achievable realistically in suckled beef herds. Nutrition has been reported to affect colostrum and Ig yield (6), and seemed to be responsible for calf serum Ig differences noted between two ranches (7). A significant reduction in absorption of immunoglobulins was noted in calves born to Holstein heifers fed 66%, compared to a control group fed 1 15% of estimated NRC protein requirements during the last trimester of pregnancy (8). Would these calves be more "at risk" than those in the control group, when the result in this study indicated no significant differences in production ofcolostrum or Ig concentrations between groups? The unabsorbed immunoglobulins may have gone to boost local intestinal protection and thereby served an equally useful protective function. Differences have been noted between breeds on the same ranch (9,10), but heritability estimates within breeds have been conflicting (10,11) and there have been indications that selection for productive traits may influence serum Ig levels adversely (9,10). The reverse may also be true, but in any event there is probably a point beyond which efforts to increase mean levels of colostral or serum Ig levels by selection or management become impractical. In one large herd 48-h calf serum Ig levels reported by workers at this I nstitute were somewhat higher than most other published work, but were substantiated by another laboratory prior to publication (9). They indicated mean levels of4.56 g/ dL in calves from multiparous Shorthorn cows, and 2.54 g/ dL in primiparous dams' calves. Further evidence that Shorthorn calves in this herd consistently have serum Ig levels substantially above 1.5 g/ dL, first reported to be adequate in a farm situation in England (12), was provided recently. Serum samples were made available (Dr. H. Doornenbal, Agriculture Canada Research Station, Lacombe, Alberta) from calves involved in another experiment. Serum Ig levels were measured 12 to 24 h postpartum (Table 1) using the zinc sulphate turbidity test (ZST) (13). Turbidity was measured in a spectrophotometer (Unicam SP 1700 Ultraviolet Spectrophotometer, Pye-Unicam Ltd., England) and recorded as absorbance units at 498 nm. These units were converted into g/ dL gammaglobulin using the equation y = -6.649 + 33.99x, derived from a comparison of ZST and gammaglobulin levels in 48-h serum samples from calves in our own herd (A.D.R.I., Lethbridge) over a three-year period (Table II). The electrophoretic method used is described in detail elsewhere (14). Logan et al (15) showed that maximum levels of serum Ig are obtained 15 to 48 h postpartum, depending on Ig class. Small numbers of calves were used in the study, but it is generally agreed that maximum levels are reached by 24 to 48 h. Based on this information the levels in Table II are probably lower than they would have been had the blood samples been collected at 48 h. It is not unreasonable to assume, therefore, that similar levels also prevailed in the four years prior to measuring serum Ig. In spite ofthese apparently adequate levels and based on treatments, the incidence of undifferentiated neonatal diarrhea in those years was 62, 41, II and 39% respectively (unpublished). Recent reports (7,10) indicate that beef calves born without difficulty from dams receiving adequate nutrition may well have peak serum gammaglobulin levels equal to or greater