Using chemical treatments, especially spray-on products, is critical in preventing infestations by inhibiting the development of larvae.
Using chemical treatments, especially spray-on products, is critical in preventing infestations by inhibiting the development of larvae.
Content brought to you by PGG Wrightson
Heading into the busy summer months on farm, The Country has partnered with PGG Wrightson’s animal production technical team for a three-part series of practical advice for dairy, sheep, and beef farmers across New Zealand.
Hosted by Rowena Duncum, the second episode addresses flystrike – right from what makes sheep attractive to flies, through to how to spot affected animals, plus prevention and treatments methods.
In it, Duncum is joined by Andrew Dowling, a technical expert for animal health and nutrition as part of PGG Wrightson’s Animal Production Technical Team.
Dowling grew up on a Central Otago sheep farm – where weekends and school holidays meant shearing not skiing – before graduating with a Bachelor of Veterinary Science from Massey University. Dowling spent 14 years as a farm vet, before joining PGG Wrightson in 2008.
Based in Central Otago once again, Dowling covers the lower South Island and works with PGG Wrightson Field Reps to support farmers across Otago and Southland.
Understanding Fly Strike
Fly strike, a parasitic infection caused by blowflies laying eggs on sheep, remains a persistent issue for sheep farmers in New Zealand.
According to Dowling, the blowflies are attracted to sheep due to factors like wet wool, dermatitis, and the presence of faeces.
This condition creates a prime environment for flies, leading them to seek out and infest sheep, causing severe distress and health problems for the animals.
“The warm, wet conditions and the presence of dags (faecal matter on the fleece) create an irresistible lure for blowflies,” Dowling explained.
“The flies lay their eggs on the sheep, and within a short time, the larvae hatch, feeding on the animal’s flesh, which can quickly escalate into a severe health issue.”
Dowling identified two main types of blowflies responsible for fly strike: primary and secondary strike flies.
Preventive strategies are important in managing fly strike, particularly during high-risk periods.
Primary strike flies are capable of initiating an infestation without the presence of a pre-existing wound.
In contrast, secondary strike flies are attracted to existing wounds, where they feed on the flesh already exposed by previous infestations.
Dowling said the carnivorous behaviour of the maggots can lead to further complications and exacerbate the severity of the strike.
“Most common household flies or cluster flies seen around our homes aren’t the culprits of fly strike,” he noted.
“The real threat lies in specific species of blowflies that are prevalent in farming environments.”
Risk Factors and Impact
Fly strike risk is heavily influenced by environmental factors, with warmer and wetter conditions creating the ideal scenario for blowfly infestations.
Dowling advised farmers to monitor soil temperatures, as pupae, which remain dormant in colder weather, begin hatching when temperatures rise above 12 degrees Celsius.
The resulting increase in fly populations marks the beginning of the risk period for sheep.
“Warm, humid, and sheltered areas are hotspots for flies,” said Dowling.
“Paddocks with high humidity, especially in low-lying, wind-protected areas, have the highest risk for fly strike.”
Fly strike can cause severe physical damage to sheep.
The maggots secrete digestive enzymes that break down the sheep’s skin, leading to significant pain, dehydration, infection, and in severe cases, death.
Even minor infestations can lead to weight loss and prolonged recovery periods.
“A fly strike wound as small as a 50-cent piece can have a major impact on a sheep’s health,” Dowling stated.
“It’s not just about the physical damage; the systemic effects, including the toxins released by maggots, can make the animals extremely ill.”
Andrew Dowling works with PGG Wrightson Field Reps to support farmers across the lower South Island.
Preventing Fly Strike
Dowling emphasised the importance of preventive strategies in managing fly strike, particularly during high-risk periods.
These measures include regular shearing, crutching (removing wool around the rear end to reduce faecal buildup), and chemical treatments such as dips and spray-ons.
“Shearing provides about a month of protection, as it exposes the skin to air and sunlight, which flies dislike,” Dowling noted.
“Using chemical treatments, especially spray-on products, is critical in preventing infestations by inhibiting the development of larvae.”
He also highlighted the importance of proper application techniques.
Listen below as Rowena Duncum speaks withAndrew Dowling:
“Consistency in applying the chemicals is key - farmers need to follow the recommended dosages and avoid diluting products, as this can compromise their effectiveness,” he warned.
Supporting affected stock
When dealing with sheep already affected by fly strike, immediate action is essential.
Dowling recommended isolating and treating infested animals promptly to prevent further spread.
This involves clipping the wool around the affected area, removing maggots, and applying appropriate chemical treatments.
“Animals with fly strike are in a lot of pain and require intensive care,” he said.
“It’s crucial to treat them quickly to reduce suffering and to prevent secondary infections.”
Dowling stressed the need for farmers to adopt comprehensive preventative strategies against fly strike.
He recommended early intervention, regular monitoring, and proper use of chemical treatments to keep fly strike under control and ensure animal welfare.
The final podcast episode in this series will be released on December 11.
