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.

No abstract

The anaemia produced by Haemonchus contortus was characterized by a marked reduction in haemoglobin concentration and packed cell volume, accompanied by a marked rise in the concentration of potassium in the erythrocytes [Ke+] and a fall in the concentration of sodium [Nae+]; total [Ke+ + Nae+] remained steady. Infection was associated with reduced food intake and a lowered concentration of plasma protein, but plasma potassium and sodium remained constant. During the first 10 weeks of the experiment both the infected and the control sheep developed an anaemia of unknown aetiology, characterized by raised [Ke+], [Nae+], and [Ke+ + Nae+] values, and plasma protein concentrations.The evidence presented seems to suggest that sheep of haemoglobin type A may harbour fewer worms than sheep with haemoglobin type AB following infection with H. contortus.

In December 1970 and in January, February, March, April, May and September 1971 separate plots of sown pasture, each 0.1 ha, were contaminated by grazing sheep infected with gastrointestinal nematodes. In succeeding months each plot was grazed by worm-free tracer lambs for 2 weeks; the lambs were then withdrawn and held for 2 weeks in pens before slaughter for total differential worm counts. Observations on each plot continued for 12 months; the numbers of worms found in the tracer lambs indicated the seasonal occurrence of nematode larvae on pasture. For Haemonchus contortus, larval availability from deposition was rapid in summer and slow in autumn, maximum inhibition at the fourth larval stage occurring in larvae picked up in the winter months. Ostertagia spp. presented a marked contrast, with curtailed development in summer and contamination in autumn producing high levels of infection on pasture in late winter and early spring when inhibition was at maximum levels. Of the other species studied, intestinal Trichostrongylus spp, showed a similar pattern of development to H. contortus in summer, but as with Ostertagia spp. autumn contamination could produce infection peaks in late winter and spring. Inhibition at the fourth larval stage was not a characteristic of intestinal Trichostrongylus spp. For T. axei autumn and winter conditions favoured development, and peak infestations occurred in spring and coincided with maximum inhibition. Nematodirus spp. developed mainly in summer and most inhibition occurred at this time. Spring (September) contamination with Nematodirus spp. did not result in detectable levels of infection. For all other species spring contamination was rapidly translated to pasture and the infection was comparatively short-lived. All species were capable of overwintering on pasture and with the possible exception of T. axei a persistence of infection of at least 12 months was demonstrated. For Ostertagia spp. the importance of late summer and autumn contamination in its epizootiology and control in a summer rainfall region has been confirmed.

Two experiments are reported. In experiment 1, light infections with the intestinal nematode Trichostrongylus colubriformis reduced wool growth of sheep by 42 per cent compared with pair-fed controls. There was no significant difference in wool growth between those sheep given a cystine supplement as an intraperitoneal pellet and those given a daily intra-duodenal injection of cystine, although cystine was poorly absorbed from the peritoneal cavity. In experiment 2, fifteen sheep were fed a maintenance ration and their wool growth rates defined. When six of the sheep were given a daily intra-duodenal drip containing 2 g cysteine hydrochloride, and six sheep were given the same drip intravenously, their wool growth rate increased by a mean of 33 per cent compared with the wool growth of the three untreated sheep, irrespective of the route of administration of the cysteine. Three sheep in each group of six were then lightly infected with Trichostrongylus colubriformis and the wool production of all sheep was measured in the presence and absence of the daily cysteine supplement via the two routes. The infection depressed wool growth, but did not influence the wool growth response to either route of cysteine supplementation. It was concluded that the reduced wool growth induced by trichostrongylosis could not be attributed to malabsorption of cysteine. Evidence was obtained that sheep resistant to Trichostrongylus colubriformis produced less wool when subjected to a larval challenge.

The use of increase in teat length for bioassay of oestrogens in sheep has been investigated. In wethers injected intramuscularly with stilboestrol dipropionate the best precision was obtained by measurement of the increase 9 days after the beginning of oestrogen administration. The range of doses over which the log dose-response relationship was linear was rather narrow (4–16 µg stilboestrol dipropionate per day). Applied in the field, the technique provides a means of assessing the effective intake of oestrogens by grazing sheep. Marked seasonal fluctuations in the oestrogen intake of wethers grazing a red clover pasture were recorded; the lowest level was in May and peaks occurred in August and December–February.

No abstract

Wool growth rates of grazing sheep that were resistant to infection with the intestinal nematode Trichostrongylus colubriformis were measured in the presence and absence of a larval challenge. In one experiment, resistant sheep exposed to a moderate level of larval challenge grew 11 per cent less wool than unchallenged resistant sheep grazing the same paddock. A second experiment confirmed the previous results but showed that the magnitude of this wool growth depression did not depend on the severity of the challenge