A New Zealand study¹⁹ was undertaken to demonstrate that an effective drench, Startect, when used on a property with existing drench resistance, can help to manage drench resistance and maximise sheep productivity.

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STUDY DESIGN

The NZ study commenced in March, and finished in September. Ten farmlets had approximately 30 lambs on each farmlet. The replicated design provided a high level of statistical accuracy. Stocking rate remained consistent on each farmlet throughout the study.
Five farmlets used Startect, and the ineffective drench, albendazole (ABZ) was used on the remaining five farmlets. Lambs were all drenched following the manufacturer recommended dose rates at monthly intervals (preventive drenching). All lambs were retained on the property for the duration of the study.
Worms established previously on the study site were known to be resistant to BZ (white) drenches. They were mixed resistant infections, composed of Trichostrongylus, Teladorsagia and Nematodirus.

Faecal Egg Count Reduction Tests (FECRT) were completed after every treatment (Fig 1).
Startect remained highly effective against all worm species throughout the study, >99%.
FECRT of the last two ABZ treatments demonstrated efficacies of 48.4% and 40.9% for Trichostrongylus and Teladorsagia, respectively.
The 28-day retreatment interval in all likelihood over-exaggerated the actual level of resistance to ABZ; drench resistant worms would have continually accumulated in the stock each month as drenching and FECRT were undertaken at monthly intervals.

Fig 1: Mean faecal egg counts (FEC) from lambs treated with STARTECT or albendazole over the duration of the study.

Body condition scores were significantly higher for the Startect lambs while dag scores were significantly higher in ABZ treated lambs (Fig 2 and 3). During the latter two to three months of the study FEC and body condition scores were in the ranges that suggested the lambs were affected sub-clinically by parasitism.

Fig 2: Mean values for production and parasite factors for lambs treated with STARTECT or albendazole at monthly intervals.

Fig 3: STARTECT treated lambs compared to those treated with an ineffective drench.

STARTECT treated lambs at the third drench.

Albendazole treated lambs at the third drench.

Both treatment groups started the study at equal average liveweights (29kg). Lambs in both groups grew throughout the study (Fig 4).
Liveweight changes between Startect treated and ineffectively treated lambs were significantly different after the second drench.
Differences between the groups remained significant thereafter.
Startect treated lambs grew an average 9kg more across the study (Fig 4).
This translated into 4.7kg carcass weight, almost 1kg improved growth per month.

Fig 4: Cumulative liveweight of lambs treated with STARTECT or albendazole at monthly intervals over the time of the study.

Lambs given Startect reached a target draft liveweight of 38kg earlier than those treated with the ineffective ABZ (Fig 5).
By the third drench, 55% of Startect v 29% of ABZ drenched lambs had reached target.
Before the fourth drench, 99% of Startect treated lambs were at or over 38kg, but only 77% of ABZ lambs were 38kg.
At the end of the study, almost 10% of ABZ drenched lambs had not reached the 38kg target.
Under these study conditions, farmers using Startect could expect to sell lambs earlier. This would improve farm profitability creating a cash flow earlier; plus, finishing lambs earlier also means saving labour, time and drench costs with fewer treatments required.

Fig 5: Percentage of lambs reaching target draft weight of 38kg.