Considerations for long acting parasite control in ewes pre-lamb
Words: Zoetis
When it comes to managing internal parasites in sheep, especially during the critical pre-lambing period, farmers have several anthelmintic options.
In ideal conditions, ewes should enter pre-lamb at Body Condition Score (BCS) 3 with adequate feed and not require a drench. But if conditions are not ideal, a long-acting treatment may benefit some ewes.
Two options are Cydectin® Long-Acting Injection for Sheep and anthelmintic capsules.
Extended Protection
Both products are long-acting. Capsules provide an average of 100 days (85–115) protection against all susceptible parasites.
Cydectin Long-Acting Injection offers:
Up to 112 days of persistent activity against Teladorsagia circumcincta
Up to 91 days for Haemonchus contortus (barber’s pole worm)
Up to 42 days against Trichostrongylus colubriformis
This extended duration protects at-risk ewes—those that are multiple bearing, in poor condition, under feed stress, or hoggets—from larval challenge when they need it most.
Single Active vs Combination
Cydectin LA is highly effective against all major internal parasites. It contains moxidectin, the most potent of the macrocyclic lactone (ML) family. It can kill parasites resistant to other MLs, including abamectin (up to a point).
The high concentration of moxidectin (reaching 25ppb compared to ~8ppb in Cydectin Injection for Cattle and Sheep¹ ²) ensures parasites get maximum exposure to the active ingredient, delivering an improved upfront kill and longer persistent efficacy.
By contrast, capsules—though in combination—expose parasites to a much lower larvicidal dose of actives over a longer period of time.
Trace Elements
Capsules provide additional cobalt (for vitamin B12 production) and selenium, supporting ewe and lamb health where deficiencies exist.
Cydectin LA contains no minerals. However, with both products, ewes still require a pre-lamb clostridial vaccination, and these minerals are available in some vaccine options.
Dosage
Many ewes are 75–80 kg at mating. By pre-lamb treatment time, twin-bearing ewes may be 15 kg heavier.
With Cydectin LA, ewes can be dosed to a higher or lower weight, saving money on drench or avoiding under-dosing. It also has a wide margin of safety when used as recommended.
Capsules are a fixed dose for ewes 40–80 kg. Heavier ewes will require two capsules.
Withholding Periods
Capsules have a meat withholding of 128–133 days. If feed is tight, treated ewes that lose lambs or are culled must remain on-farm consuming valuable feed.
By contrast, Cydectin LA has a withholding period of 91 days, allowing these ewes to be sent to slaughter up to six weeks earlier.
Production Trial Results
A comparative study³ was conducted using Cydectin LA and capsules, with an untreated control group, in poor condition twin-bearing ewes.
No significant difference was found in ewe weight, BCS, or lamb weight at weaning between the two treatments.
Both treatment groups were significantly heavier (3 kg) than untreated controls.
A higher proportion of ewes reached BCS 3, and lambs were on average 2.6 kg heavier.
Choosing the Right Option
When deciding between Cydectin Long-Acting Injection and capsules, farmers and their advisors should consider:
Specific flock needs
Labour availability
Local parasite challenges
The best option pre-lamb is to have well-fed ewes in good condition, which generally precludes the need for any anthelmintic control.
If anthelmintics are required, Cydectin LA offers a convenient, flexible, high-concentration option with proven efficacy and safety.
Zoetis New Zealand Limited. Tel: 0800 963 847 | www.zoetis.co.nz
Cydectin is a registered trademark of Zoetis. ACVM No. A9926
References
Alvinerie, M. et al. The pharmacokinetics of moxidectin after oral and subcutaneous administration to sheep. Vet. Research, 1998
Murphy, A.W, Holm-Martin, M. Evaluation of the efficacy and protection period of a 2% moxidectin long-acting injection for sheep under field conditions in NZ and Australia. Proceedings WAAVP, 2004
Bingham C. et al. Comparison of two long-acting pre-lambing anthelmintic treatments on the productivity of ewes in low body condition. NZVJ, 2017