Relationship between sporidesmin-induced liver injury and serum activity of gamma-glutamyltransferase in Romney lambs sired by facial eczema-resistant or control rams

Abstract

AIM: To test whether long-term selection for resistance to facial eczema (FE) influences the relationship between liver injury score (LIS) and serum activity of gamma-glutamyltransferase (GGT) in sporidesmin-dosed sheep.

METHODS: Two groups of Romney lambs were generated for this study in 1999, out of an unselected group of ewes and sired by either selected FE-resistant (R) line (n=74 lambs) or unselected Control (C) line (n=119 lambs) rams from the Ruakura Research Centre long-term FE-selection experiment. The lambs were given a single oral dose of sporidesmin, sampled for determination of serum GGT activity 3 weeks later, and lambs that had serum GGT activity >55 IU/l (reactors) were humanely killed and assessed for LIS post mortem, 6 weeks after dosing. A second round of dosing was applied to the non-reactors, followed as above by analysis of serum GGT activity and assessment of LIS post mortem (both reactors and non-reactors).

RESULTS: There was a significant linear relationship between LIS and log_eGGT, which did not differ between the 2 sire lines (LIS= -2.96 (SE 0.38) + 0.89 (SE 0.07) × log_e GGT, R²=0.54, p<0.001).

CONCLUSIONS: Serum GGT is a valid indicator of LIS in lambs by sires selected for different levels of susceptibility to FE. The log_eGGT-LIS relationship has not changed as a result of genetic selection for resistance to FE.

KEY WORDS:

• Sheep
• facial eczema
• sporidesmin
• liver injury
• GGT
• breeding