Susceptibility to facial eczema in lambs sired by East Friesian, Romney Control, and Romney facial eczema resistant rams

Ten East Friesian (EF), eight Romney Control (RC). and two Romney Facial Ec zema Resistant (RR) rams were mated with Romney (R) ewes to generate EF x R , RC x R, and RR x R lambs. These lambs were compared for their susceptibil ity to an oral challenge with sporidesmin, the toxin causing facial eczema. All lambs of 16.0 kg or above (average weight 21.3 kg) were dosed after we aning with sporidesmin (0.14 mg kg(-1) liveweight) at an average age of 83 days. Resistance or susceptibility was assessed by taking a blood sample 21 days after challenge, and measuring serum gamma-glutamyltransferase (GGT), an enzyme whose concentration is elevated after the liver injury resulting from a toxic challenge. In total, 289 animals were challenged (96, 119, an d 74, respectively, for sire strains EF, RC, and RR). Percentages of non-re actors with GGT concentrations below a threshold value indicative of subcli nical facial eczema (< 56 i.u. l(-1)) were 62, 37, and 57 for sire strains EF, RC, and RR, respectively. The EF and RR sire strains had lower log, GGT than the RC sire strain (significant when tested against the residual mean square but not against the sire term), but the difference between EF and R R was not significant. Large differences among sire groups within sire stra in were found, as expected. The non-reactors (n = 145) were re-dosed with a higher concentration of sporidesmin (0.15 mg kg(-1) liveweight). Blood was collected again 21 days later and GGT concentrations measured. Percentages of second-round non-reactors, relative to numbers receiving the first dose were 14, 6, and 7, for sire strains EF, RC, and RR, respectively, but ther e were significantly more clinical cases in EF-sired than RC- or RR-sired a nimals (P < 0.05). Overall, these results showed that lambs sired by EF and RR rams had similar levels of resistance to facial eczema according to GGT measurements, whilst lambs sired by RC rams were less resistant. A differe nt ranking resulted from comparing the clinical incidence only.