Parasitism and production in weaner sheep grazing alternately with cattle

Abstract

Three systems for the post-weaning management of Merino wethers were compared over two years. In all systems, the sheep were given two anthelmintic treatments with levamisole per year; at weaning in January, and in July. In the first system (SC) the same paddock was used as a weaning paddock each year in succession. In the second system (SC 6) sheep and cattle grazed the paddock alternately for 6- month periods from January and July; the third system (SC 12) comprised sheep and cattle grazing alternately for 12-month periods from July of each year. Compared with the SC treatment, weaners from the SC 6 treatment had significantly lower faecal egg counts and lower burdens of Haemonchus contortus, Trichostrongylm axei, Trichostrongylus colubriformis and Nematodirus spp. They had significantly higher numbers of Cooperia oncophora and similar numbers of Ostertagia circumcincta. SC 6 sheep made greater liveweight gains, produced heavier fleeces, and suffered lower mortalities than their SC counterparts. Results for the SC 12 system were usually intermediate. In a third year, the SC 12 system was modified to include a monthly treatment with levamisole. The liveweight gains, egg counts and mortalities of the monthly treatment sheep did not differ significantly from those of the SC 6 sheep. Both systems were superior to the SC treatment in controlling nematode infections in weaner sheep. There were no significant effects of any treatment on liveweight gains of cattle, although outbreaks of ostertagiosis occurred in the third year in two of the four replicates of the SC system.

Effect of cattle grazing strategies and pasture species on internal parasites of sheep

“…which according to Steel et al (1984) could reduce nematode burdens in lambs, faecal egg counts in ewes and lambs, and adult nematode populations in lambs, were similar between sheep-only and sheep-and-cattle systems. This result is contrary to the findings of Barger & Southcott (1978) who found faecal egg counts and worm populations in wethers were lower when grazing was interchanged with cattle at six-monthly intervals compared with a set stocked sheep system. These differences may be caused by the presence of different nematode genera.…”

“…Steel et al (1982) showed that, compared with Trichostrongylus, considerably higher infections of Ostertagia can be tolerated before animal production is affected, and Haemonchus contortus is recognised as being considerably more pathogenic than either of them. That Barger & Southcott's (1978) lambs were set stocked on the sheep system but rotationally grazed on the sheep and cattle system may have also contributed to differences between their systems, as it has been conjectured that, compared with rotational grazing, set stocking increases nematode intake of lambs. It should be noted that faecal worm egg counts in excess of 1100 epg from lambs, as occurred in the present study, are considerably higher than is generally recommended before anthelmintic intervention.…”

“…These differences may be caused by the presence of different nematode genera. Barger & Southcott's (1978) experiment was conducted in New South Wales, Australia, where Haemonchus contortus was a major cause of the high (50%) lamb mortality rate on the sheep system. Haemonchus contortus represented c. 1% of larvae on pasture in the present experiment.…”

“…The integration of animal hosts with differing nematode susceptibilities may be one such option, as alternating sheep and cattle grazing has been shown by Barger & Southcott (1978) to reduce nematode burdens in sheep.…”

Sheep and goat nematode resistance to anthelmintics: pro and cons among breeding management factors

“…The concept presents a spatial and temporal component when digestive-tract nematodes are considered: the part of the population in refugia corresponds to the free-living stages, located on pastures and not submitted to the anthelmintic treatment given to the hosts. Free-living stages represent more than 90% of the total population of gastro-intestinal nematodes of ruminants [2]. L4 larvae, encysted in the abomasum, are not considered in refugia since they are easily eliminated by a double dose of benzimidazoles [14].…”