Summary
A survey of parasites in sheep sent for slaughter at the Fletcher International abattoir at Narrikup, on the south coast of Western Australia was conducted from September 2002 to January 2003. Faecal samples were taken each day from 6 lines of sheep selected at random, except that preference for sampling was given to lines showing evidence of scouring (diarrhoea). A total of approximately 4400 sheep from 367 lines from locations throughout WA were sampled (244 adult sheep, 10 hogget and 133 lamb), with scouring in 10% of lines.
A mail questionnaire of production factors sent to the sheep vendors attracted a high response rate. The study results are considered generally applicable to the WA sheep meat industry. The results indicate that sheep worms are an unrecognised burden on prime lamb production in WA, and that most producers had not taken effective worm control measures in lambs. Mean worm egg counts in lambs exceeded 1500 eggs per gram (epg), and in over 40% of lines, counts were above levels usually considered warranting drenching. Even allowing for a faecal concentration effect, these results suggest substantial losses in productivity. In adult sheep, counts were lower (mean 486 epg), but in 13%, counts were greater than 1000 epg.
The factors associated with scouring were more difficult to elucidate, largely because the number of cases was relatively low. However, although not statistically significant, high worm burdens remain the most likely cause in lambs. In adult sheep, scouring is also considered due to worms through the larval hypersensitivity syndrome. The association of Giardia and Cryptosporidium with scouring in adult sheep may be of relevance.
The worm burdens in slaughter sheep was surprising given the level of control typically used in wool enterprises, especially during the spring and summer period. Effective worm control in prime lambs should not prove difficult and would include worm egg count monitoring, pasture management and drench treatments. The mail survey indicated significantly lower worm burdens in lambs drenched in the 2 months prior to consignment. Pasture movements also aided worm control.
The survey also produced new information regarding protozoal infections in sheep at slaughter, and illustrated the value of molecular techniques in maximising sensitivity. Using PCR detection, Giardia infections in lambs were found in 45% of lines, and Cryptosporidium in 26%. Infection rates in adult lines were only one-third those of lambs, but were associated with scouring, whereas there was no such relationship in lambs. A number of Giardia genotypes were detected, including a livestock genotype and the potentially zoonotic group A (although no implications for Australian abattoir products are evident).
The most common Cryptosporidium genotypes identified were the cervid type and the novel bovine B genotype, although little is known of their prevalence or zoonotic potential. The identification of C.andersoni is the first report of this species in Australia and the first report in sheep. These findings indicate the need to communicate to sheep meat producers the importance of effective nematode control practices. Should these results also prove to apply to the industry outside WA, an extension campaign would provide a significant national productivity benefit.
