Abstract

Neonatal ruminants are born hypoglobulinemic, and therefore are at risk for infection.^2,5 Neonates are considered to be immune competent, but several weeks are required for them to build an adequate immune response to an infectious agent. These animals therefore rely exclusively on passive immunity for the first few weeks of life.³ Single radial immunodiffusion (SRID), a quantitative method that utilizes anti-sera to measure the concentration of IgG, is considered the gold standard for determining IgG status. Several semiquantitative methods, such as refractometry, colorimetry, glutaraldehyde coagulation, and sodium sulfite precipitation provide estimates (via subjective evaluation of a turbidity reaction) of immunoglobulin concentration. Recently, the efficacy of using gamma glutamyl-transferase (GGT) activity in neonatal serum to predict IgG concentration has been explored.^1,3,4,6 In neonates that have suckled and absorbed colostrum, serum activity of GGT is 60 to 160 times higher than in the normal adult. Serum GGT activity has been shown to be an effective indicator of passive transfer in calves and lambs, but not in alpaca or llama crias.^1,4,6 The goal of this retrospective study was to compare GGT activity and estimates of immunoglobulin levels in neonatal serum from six species of exotic ruminants: bongo (Tragelaphus euryceros isaaci), Java banteng (Bos javanicus), Addra gazelle (Gazella dama ruficollis), slender-horned gazelle (G. leptoceros), bontebok (Damaliscus dorcas dorcas), and reticulated giraffe (Giraffa camelopardis reticulata). In addition, a commercial bovine SRID kit (Veterinary Medical Research and Development Inc., 115 NW State Street, Pullman, WA 99163 USA) was tested using banked serum from five of the six species (serum from neonatal bontebok was not available). Only the bongo and banteng serum produced readable results with the bovine SRID kit reagent. For these species, correlations were performed for IgG and GGT, total protein and glutaraldehyde time. Using normal values from the domestic cattle literature, neonates were grouped into two categories, normal and failure of passive transfer (FPT), on the basis of IgG concentration. An IgG of 1600 mg/dl or greater was considered normal, and below that was considered to indicate partial or complete FPT. Sensitivity and specificity of a cutoff value of 90 IU/L for GGT were calculated. Sensitivity and specificity were also calculated using a total protein value of < 6.0 mg/dl for banteng and < 5.0 mg/dl for bongo. For the remaining species, total protein was used as an estimate of immunoglobulin concentration. A level below 5.0 mg/dl was considered to indicate partial or complete FPT. Correlations between GGT and total protein and glutaraldehyde time were performed. Modified (assuming unequal variances) student t-tests were used to compare means of GGT activities for normal neonates and FPT neonates, but for these animals normal or FPT were determined solely on the basis of total protein. Modified student t-tests were used to compare means of GGT activities for normal neonates and FPT neonates (Table 1).

In banteng and bongo, GGT was useful for diagnosing FPT in neonates, but because the SRID kits are inexpensive and readily available tests that provide quantitative measures of IgG, this methodology is recommended for these species. Results from the bontebok and gazelle species were difficult to interpret. Although GGT levels correlated with other measures of IgG levels, no one test seemed able to accurately predict FPT. Further research on these species is warranted; a quantitative measure of IgG would be a most helpful development. GGT levels may be useful for diagnosing FPT in giraffes, but again, further research is warranted. It is not clear if the GGT activity measured in neonatal giraffes is of maternal origin or the result of liver dysfunction in the neonate.

Table 1. GGT activity (IU/L).

a. Indicates value significantly different from normal neonate at P < 0.05.

References

1.  Johnston NA, SM Parish, JW Tyler, CB Tillman. 1997. Evaluation of serum GGT activity as a predictor of passive transfer in crias. J. Am. Vet. Med. Assoc. 211 (9): 1165-66.

2.  Parish S.. 1996. Ruminant immunodeficiency disease: failure of passive transfer. In: Smith, B.P.(ed.) Large Animal Internal Medicine. St Louis: Mosby, Pp. 1857-60.

3.  Parish SM, JW Tyler, TE Besser, CC Gay, D Krytenberg. 1997. Prediction of serum IgG concentration in Holstein calves using serum GGT activity. J. Vet. Int. Med.11(6): 344-47.

4.  Perino LJ, RL Sutherland, NE Woollen. 1993. Serum GGT activity and protein concentration at birth and after suckling in calves with adequate and inadequate passive transfer of IgG. Am. J. Vet. Res. 54 (1):56-9.

5.  Tennant B, BH Baldwin, RK Braun, NL Norcross, M Sandholm. 1979. Use of the glutaraldehyde coagulation test for detection of hypogammaglobulinemia in neonatal calves. J. Am. Vet. Med. Assoc. 174 (8): 848-53.

6.  Tessman RK, JW Tyler, SM Parish, DL Johnson RG Gant, HA Grasseschi. 1997. Use of age and serum GGT activity to assess passive transfer status in lambs. J. Am. Vet. Med. Assoc. 211 (9): 1163-64.