In a 2 stage surveillance project we monitored worm egg counts (WEC) in 18 herds of undrenched weaner cattle, determined the main worm types present in those herds with more than 100 eggs per gram of faeces (epg), conducted faecal egg count reduction trials (FECRT) in 6 of the herds and measured the growth response to suppressive drenching compared to normal commercial practice in 6 of these herds. Weaner WECs were below 125 epg in two thirds of the herds monitored and ranged from 10 to 360 epg. The major worm egg type present was Cooperia followed by Ostertagia.
The FECRT detected one herd with levamisole (Lev) resistant Cooperia. In 2 of 2 herds where a half dose ivermectin (IVM) was tested, there was less than a 95% reduction in WEC compared to controls perhaps suggesting early onset of resistance to macrocyclic lactone (ML) drenches. Finally, in 4 of the 6 herds monitored, weaner heifers treated to suppress worms with a long acting injectable moxidectin (Mox) drench, grew significantly faster over the 3 winter months following weaning compared to the balance of the mob which were treated with the producers usual drench. These heifers will be monitored till they are 2 years of age to determine the profitability of alternate worm control practices.
Gastrointestinal worms are the second biggest health cost facing southern beef producers at around $40 million pa (Sackett et al 2006). Locally, beef cattle production has increased in recent years to be the most important animal enterprise in terms of DSEs in the Central Tablelands of NSW.
Current drenching recommendations made by Meat and Livestock Australia for our district appear to be based on one report conducted in the 1970s (Smeal, 1981). He found considerable benefits in growth by suppressing Ostertagia with regular benzimidazole (BZ) treatments compared to undrenched controls.
While there is little evidence of resistance to the main 3 drench classes in Australian cattle worm populations, it has been reported in New Zealand (Rhodes, 2006) in Cooperia and Ostertagia. Given the high frequency of drenching in the high rainfall region of NSW, as identified in our 2007 project, we think it of value to conduct further FECRTs in herds with high levels of WEC in young cattle.
In a pilot targeted surveillance project investigation in 2007 (Eppleston and Watt, 2007), we surveyed the parasite management practices in local beef herds, monitored 16 representative herds for evidence of parasitism in 1-year old heifers and tested the efficacy of the 3 drench classes in 2 herds. In brief we found most producers drenched young cattle often, with a high reliance on ML drenches. We also found that yearling WECs were generally low (<200 epg), but plasma pepsinogen levels were elevated in the majority of herds, indicating abomasal wall damage from worm larvae. Although limited, this data showed no correlation between these two objective measures of worm burden. In addition we found no evidence of resistance to the 3 drench classes.
In the project reported here which we conducted in 2008, we report further data on the level of WECs at weaning, drench resistance testing in local beef herds and extended previous observations to the impact of internal parasites on the health and growth of weaner beef heifers.
Herds from 2 groups of beef producers at Rydal and Lyndhurst used in our 1st project were used in a 2 stage trial. Eighteen producers from across these groups collected faecal samples for screening for WECs.
Stage 1 - assessing worm burdens and drench efficacy at weaning
We collected 2 bulk faecal samples (5 animals per sample) from undrenched cattle around weaning from 18 herds and these were used to screen for WECs. The WECs were conducted at the Orange DPI Veterinary Laboratory and those herds with more than 100 epg at the initial screening were used to conduct FECRTs and determine worms present by larval culture.
As per our protocol (Appendix 1), at the FECRT drench the weaners were randomly divided into groups of 12 animals (one group per drench tested plus a control group) for use in the FECRT. The drenches evaluated were LEV and BZ, both administered orally, and an IVM injected subcutaneously. In 2 herds a half dose IVM was also administered with the aim of detecting early onset of IVM resistance. An undrenched control group was also identified. Individual faecal samples were collected 14 days later and tested at OAI. We used the standard definition of resistance to a drench class i.e. when there was less than a 95% reduction in WEC in the drenched group compared to undrenched control group (Colas et al 2006).
Stage 2 - The impact of worms on growth of young cattle
Six owners of herds from within the 18 screened volunteered to supply their herds for growth monitoring. Within 12 weeks of weaning in these herds, we weighed at least 100 heifers. Every fifth heifer was treated with a long acting ML injectable drench (Cydectin, Fort Dodge) to continuously suppress worms (treated group). The same heifers were retreated every 90 days (it has a 90 day protection claim for Ostertagia, and 120 days for Haemonchus and 21 days for Cooperia).The remainder of the heifer cohort was treated with the owners' usual drenching program (control group - Table 2). The heifers NLIS tag was used for recording purposes allowing us to sample the same heifers at each visit.
Each property was visited at 3-monthly intervals as outlined in Table 1, and this will continue until 23 months of age (6 herd visits). At each visit all trial heifers were weighed and 10 'treated' and 10 'control' heifers had faeces collected for individual WECs and pooled fluke egg counts (5 per pool from 'controls' only).
Table 1. Scheduled dates and ages of trial cattle at each farm visit to carry out weighing and suppressive drenching.
Blood was collected from 5 treated and 5 control heifers and was used to determine serum pepsinogen, liver fluke ELISA, and glutathione peroxidase levels.
Growth rate responses to drench treatment were analysed by analysis of variance using a generalised linear model with MiniTab software.
Stage 1 Worm populations in undrenched weaner cattle.
In total we tested 18 mobs of weaner cattle prior to their first drench. The WEC ranged from 10 to 360 eggs per gram (epg) of faeces (Figure 1).
We collected larval culture results from 6 herds and the proportion of each worm type is presented in Figure 2. Overall, the percentage of Cooperia, Ostertagia, Trichostrongylus, Oesophagostomum and Haemonchus eggs was 54%, 24%, 3%, 10% and 9% respectively.
We conducted a total of 6 FECRTs (2 in 2007 and 4 in 2008). The results expressed as the percentage reduction in WEC of the drenched group compared to the undrenched control group are presented in Table 2. In addition the WEC measured during the initial herd screening prior to the FECRT control is presented for comparison purposes.
Table 2. Efficacy of drenches in reducing worm egg count in 6 herds as determined by FECRT.
Stage 2 Details of the management and drench schedules for the 6 herds monitored in this trial are presented in Table 3.
Table 3. Management schedule for Stage 2 monitor herds
To date data has been collected from the visit at weaning and 3 months later. These weights were converted to average daily gain across the 90 days between weightings and these are presented for the 2 drench treatment groups in Table 4 and graphically in Figure 3. There was no significant interaction between herd and drench treatment on growth. However both herd and drench treatment had significant effects (P<0.01).
Table 4. Impact on growth (kg/day) of suppressive drenching compared to the owners 'control' treatment in monitor heifers.
The WECs and pepsinogen levels for each herd at the weaning visit and 3 months later are presented in Table 5. The worm species present in treated and control heifers are presented for 4 herds in Table 6. When analysed by logistic regression there was a significantly higher proportion of Cooperia (P<0.05) and a lower proportion of Ostertagia (P<0.001) eggs in the drenched group compared to the undrenched controls.
Table 5. Worm egg counts and pepsinogen levels at weaning and 3 months post weaning (pw) in treated and farmer control heifers.
Table 6. Larval culture in treated and control heifers 3 months after treatment.
Summary data on liver fluke and selenium (glutathione peroxidise) levels is presented in Table 7.
Table 7. Liver fluke and selenium monitoring in 6 central tablelands beef herds
WECs are the method of choice when monitoring worms in sheep flocks, but in cattle objectively monitoring worm burdens even in young animals is difficult given currently available tools. As a result providing advice to beef producers on when to drench is challenging.
In this study, we measured WECs in undrenched weaner heifers at a time before immunity had fully developed and egg output could be expected to be more reliable measure of worm burden than in older animals. WECs were low (less than 125 epg) in two-thirds of the mobs tested, but in the remaining herds, counts were as high as 350 epg suggesting a reasonable level of worm challenge by weaning or soon after. However larval culture of these mobs indicated that often these eggs were from the less pathogenic, more fecund Cooperia, rather than Ostertagia.
It is interesting to note that in Stage 2 of the trial where plasma pepsinogen levels were measured in most herds, 6/40 (15%) heifers had pepsinogen levels over 7.5 U/L at the weaning visit and 14/30 (47%) in controls vs. 3/15 (20%) for drenched heifers 3 months after weaning. Ostertagia antibodies are being measured using an experimental procedure but results are not yet available.
Using the FECRT protocol developed for this trial we observed only 2 drench groups where the WEC reduction (<95%) suggested that drenches may have been ineffective. In herd BC the BZ drench produced a 93% reduction in WEC; however the low egg count in the controls means that this should be treated with caution. In herd PT the levamisole drench reduced the WEC by 72% suggesting resistance in this worm population. While the ivermectin drenches at full dose were all effective, in the 2 herds where we included a half dose group the results suggest the early development of resistance to ML drenches.
The growth stage of this trial has not yet been completed but it is clear from WEC and pepsinogen data, that suppressive drenching both decreased the total worm burden and skewed the population away from the pathogenic Ostertagia species to the likely less pathogenic Cooperia species. This resulted in improved growth rates in 4 of the 6 herds monitored during the 3 winter months after weaning compared to drenching practices commonly used in some commercial beef herds in the Tablelands of NSW. More complete analysis will need to wait until the heifers have been monitored through to at least their first joining.
The difference between herds in post weaning winter growth is marked and reflects the different supplementary feeding practices of the producers. A suggested benchmark for joining weight is around 300 kg and it may be that the control animals will still reach this target over subsequent spring/summer growth periods using cheaper pasture feed. Economic analysis will be carried out to determine the value of winter feeding of weaners on the cost of production and hence profitability.
We thank NSW DPI for supplying funds to commence these investigations. Ben Kidd and Stephen Burman from Fort Dodge kindly supplied the suppressive drench and assisted with development of the trial protocol, farm visits and data collection.
CT RLPB Protocol for conducting cattle FECRTs