Parasitic gastroenteritis in calves during their firstseason at grass: The potential for a performance-based targeted selective anthelmintic treatment programme

Q Science (General);S Agriculture (General);SF600 Veterinary Medicine

Jackson, Abigail ; Ellis, Kathryn

University:University of Glasgow

关键词: Parasitic Gastroenteritis, Targeted Selective Anthelmintic Treatment, TST, FSG, Organic;   

Others  :  http://theses.gla.ac.uk/4290/1/2013Jacksonphd.pdf

来源: University of Glasgow

【 摘 要 】

The work described in this thesis was designed to investigate the current impact of parasitic gastroenteritis on organic and conventional dairy farms in first season grazing youngstock in Scotland, and to elucidate a marker of significant parasite challenge within individual calves, in order to target these calves with an anthelmintic treatment. It was felt particularly that any recommendations should be practical and easily implemented on-farm, and optimise anthelmintic usage, with regard to animal health, welfare and performance on both organic and conventional farms.There is world-wide recognition that nematode parasite infections are one of the greatest causes of lost productivity of grazing livestock. In the UK, the single most important cause of parasitic gastroenteritis in cattle is infection with the abomasal nematode, Ostertagia ostertagi, although concomitant infection with the less pathogenic intestinal nematode, Cooperia oncophora is common. Often, non-organic (conventional) producers use anthelmintic treatment programmes that prevent disease or treat all animals in a group without necessarily considering the basic epidemiological information needed for an optimal strategic control. Organic producers are encouraged to avoid this approach, thus it may be hypothesised that organic livestock harbour higher parasite burdens compared to livestock in conventional systems. However, little information is available on current UK organic dairy anthelmintic use and subsequent parasite challenge to youngstock. This thesis aimed to investigate current management practices on three Scottish organic farms compared to three Scottish conventional farms and examine different ways of assessing parasite challenge (including novel markers) with a view to the implementation of a targeted selective treatment (TST) programme.Liveweight gain assessment by means of weigh-bands as a tool to investigate the effect of parasitism on the host was also examined. In year one of the study, the six farms were visited on four occasions throughout the grazing season where fifteen first season grazers on each farm had their liveweight measured (weigh-band or weigh-scale), a faecal egg count (FEC) recorded and plasma pepsinogen, plasma fructosamine and Ostertagia ostertagi antibody concentrations measured.Knowledge of the epidemiology and pathophysiology of gastrointestinal nematode infestation has led to the identification of parasitic biomarkers for use either as a diagnostic tool or for providing a threshold for anthelmintic treatment. Faecal egg counts (FEC) are the most widely used parameter, both clinically and in studies on gastrointestinal nematode infections of ruminants, because of their relative convenience and low cost. Organic producers are encouraged to use faecal egg counts in order to direct anthelmintic treatment to calves, or groups of calves, that have counts of 200 eggs per gram or more (Soil Association, 2010). The recent launch of COWS (Control of Worms Sustainably in Cattle) in May 2010 - an initiative to prevent widespread anthelmintic resistance and to use anthelmintics appropriately in cattle in the UK - has also seen conventional farmers encouraged to use faecal egg counts in the same manner as their organic counterparts (Taylor, 2010i). None of the biomarkers, including FEC, investigated in the study reflected liveweight gain adequately to use in a targeted selective anthelmintic treatment programme. An ideal biomarker would give indication of calves that would most benefit from anthelmintic treatment before liveweight gain was affected.The biomarkers in this study indicated presence of gastrointestinal parasitism but could not target the animals that had poor liveweight gains. The emphasis on FEC in advice to farmers regarding the need for anthelmintic treatment requires re-evaluation. The data from year one showed that the conventionally farmed first season grazers (FSG) had significantly higher liveweight gains than the organically farmed calves. Anthelmintic treatment was applied to the organic calves in the study when the calves were known to be harbouring gastrointestinal parasite infection from positive faecal egg counts. The organically farmed first season grazers in this study had high gastrointestinal parasite challenge, indicated by parasite-based markers such as FEC and plasma pepsinogen concentration. The conventional producers in this study exposed FSG to 652% more days of anthelmintic than the organic producers and gained superior liveweight gains over the grazing season. Essentially, the organic producers fulfilled the ethos of organic production, reducing anthelmintic usage and showing necessity of anthelmintic treatment. However, subclinical and clinical parasitic gastroenteritis reduces animal welfare, the essence of the organic ethos. The organic industry needs to investigate whether there is a superior alternative to FEC that still promotes the organic ethos and reduces subclinical and clinical parasitic gastroenteritis.The possibility of using liveweight gain as a marker for anthelmintic treatment was investigated. An accurate assessment of liveweight is necessary if calf liveweight gain is to be calculated accurately and used as a threshold for anthelmintic treatment. Cattle weigh-scales are expensive and often not available on farm, particularly where youngstock may be grazing at pasture and gathered in the field for handling. With this in mind, cattle weigh-bands, which measure heart girth and relate this to liveweight, have been devised and used in practice in order to estimate cattle liveweight. Realistically, if a liveweight gain threshold were to be recommended for use on farms in the UK, the weigh-band must estimate liveweight and hence liveweight gain accurately. Given that many farmers do not possess weigh-scales on farm, use of heart-girth measurements to estimate liveweight gain is the best option available to farmers currently. Year two involved the implementation of a targeted selective anthelmintic treatment (TST) programme on two organic farms and one conventional farm; all were previously involved in the year one study. Anthelmintic treatment was applied only to FSG calves growing at <0.75kg/day at two points in the grazing season. Organic Farm 1 (O1) and Organic Farm 2 (O2) increased the liveweight gain of the FSG in year two by 50% and 44% respectively. Farm O2 exposed the FSG to 1160% more days of anthelmintic than in 2009; however, approximately 10% of the group were left untreated. Conventional FSG showed reduced liveweight gain from the previous year by 19%. However, respiratory disease was present on-farm also and may have confounded findings. Applying a performance-based targeted anthelmintic regime treatment in the field is possible and using it on farms where anthelmintic treatment was already minimal, such as organic farms, increased liveweight gain in first season grazers without significantly increasing anthelmintic treatment. Applying a TST regime to a conventional farm where previously a suppressive anthelmintic treatment had been applied may have reduced liveweight gain in the first season grazers (FSG) but maintained it at an acceptable level. The acceptance by farmers of TST strategies, and their implementation, may require a high level of input and education to the farming community.