The following was written by WormCheck in 2019 but remains relevant in the Victorian Eastern Region.

Keep your paddocks clean by regularly collecting the manure and removing it from the areas grazed by alpacas. Also regular worm counts helps you to identify whether your alpacas have a internal parasite issue. There are many sites that conduct worm counts, WormCheck is just one of them. Alpacas share the same worms as sheep and goats, so cross grazing with horses/donkeys is beneficial.

HOW LONG DO WORMS SURVIVE ON YOUR PASTURE? Hint: it’s longer than you think.

The lifecycle of many gastrointestinal parasites of livestock and horses (in particular, those of the Strongyle family) is such that a vast majority of the worm’s life may be spent on pasture. After eggs are shed in the manure, the eggs will develop and hatch into larvae. These larvae will then further develop, going through stages known as moults. Eggs will hatch into L1 (stage one larvae), which will moult to L2 (stage two larvae), and then a further moult into L3 (stage 3 larvae). It is at the L3 stage where livestock will ingest the larvae, which once inside a host animal moult again into L4 before maturing into adults.
The time it takes for eggs to hatch and develop into infective L3 depends on environmental conditions. For the majority of horse strongyle worms, in normal conditions (10-25oC) worms will go from egg to L3 in 2-3 weeks. In optimal conditions (25-33oC) this happens in as little as 4 days. In colder conditions (6-10oC) it may take several weeks to a few months. Below 6oC no development will occur, however eggs will not die unless the temperatures are below freezing for a considerable amount of time.
Once larvae have developed to L3 stage they can survive living on your pasture for months. In cooler weather (0-25oC) larvae from both horse and cattle/sheep worms will happily survive on your pasture for up to nine months. The only way to kill larvae on pasture is when the weather becomes hot and dry – temperatures above 35oC may be enough to dry out and kill larvae. However, if manure remains in patties/mounds, they may retain enough moisture for L3 to survive. Paddocks that have been cut for hay over summer can be thought of as almost worm-free (stress the almost here as larvae are harder to kill than cockroaches).
This all means that over winter/spring, when your pastures are damp and green, harrowing paddocks will only spread infective larvae around, further contaminating your pasture. Collecting the manure off your pasture is a better option, and composting it to kill eggs and larvae. If harrowing is part of your pasture management, before putting the animals back on, graze first with another animal (e.g. rotate between cattle/horses) as ruminants (cattle/sheep/goats) cannot be infected with horse worms and vice versa.

So maybe have another think about what you might define as a ‘clean’ paddock, and plan your worming to when it best suits the environmental conditions (stay tuned, there will be another post on this).

Nielsen, M. K., Kaplan, R. M., Thamsborg, S. M., Monrad, J., & Olsen, S. N. (2007). Climatic influences on development and survival of free-living stages of equine strongyles: implications for worm control strategies and managing anthelmintic resistance. The Veterinary Journal, 174(1), 23-32.
Eysker, M., Jansen, J., & Mirck, M. H. (1986). Control of strongylosis in horses by alternate grazing of horses and sheep and some other aspects of the epidemiology of strongylidae infections. Veterinary parasitology, 19(1-2), 103-115.
Nielsen, M. K., L. Mittel, A. Grice, M. Erskine, E. Graves, W. Vaala, R. C. Tully, D. D. French, R. Bowman, and R. M. Kaplan. “AAEP parasite control guidelines.” AAEP Parasite Control Subcommittee of the AAEP Infectious Disease Committee (2013).
Durie, P., Parasitic gastro-enteritis of cattle: The distribution and survival of infective strongyle on pasture. Australian Journal of Agricultural Research, 1961. 12(6): p. 1200-1211.

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