Down the Throat till they lose their First Winter Coat
Getting parasite control right in young heifers is essential for growth and long-term productivity in New Zealand dairy systems. The saying “down the throat till they lose their first winter coat” reflects the best drenching method through a heifer’s most vulnerable stage—from early pasture grazing through her first winter.
Current data indicates that in cattle, oral drenches are more effective than injections or pour-ons and this is probably because orals deliver a higher concentration of active ingredients to the target parasites in the gut.
Despite this information, most cattle farmers continue to use pour-ons because of their ease of application. This almost certainly results in failure to properly control Cooperia (with an associated production loss) and the likely promotion of drench resistance in Ostertagia.
Once calves are weaned and begin grazing, they face exposure to internal parasites. Young heifers have immature immune systems, making them highly susceptible. Worm burdens reduce appetite, limit nutrient uptake, and slow growth, which can prevent animals from reaching liveweight targets critical for mating and calving success. DairyNZ research shows that even moderate parasite loads can noticeably affect daily weight gain, putting future productivity at risk.
Oral drenching is a key tool in controlling these parasites. When done correctly, it ensures accurate dosing and maintains growth during critical periods. Many New Zealand farmers and grazers follow a routine drench schedule, often every four weeks during spring, summer, and autumn—seasons that favour worm survival on pasture. However, DairyNZ emphasises that drenching shouldn’t be “set and forget.” Instead, it should be guided by growth monitoring, faecal egg counts, and seasonal conditions. Over-drenching is unnecessary and can accelerate drench resistance, while under-drenching leaves animals exposed and risks performance limitation.
Pasture management is just as important as drenching. Around 90% of parasite larvae live on pasture, mostly in the lowest 1–2 cm of the sward, where grazing heifers ingest them. Using cleaner paddocks for younger stock, avoiding overgrazing, and rotating paddocks can significantly reduce larval intake and ease the parasite burden. Strong nutrition also supports immunity, helping heifers cope with any parasite challenge.
Drench resistance is a growing concern in New Zealand. DairyNZ recommends accurate dosing (based on body weight), rotating drench types, and monitoring effectiveness through faecal egg counts. Integrating refugia—leaving some parasites untreated in the population—can also slow drench resistance.
The ultimate goal is steady, uninterrupted growth through to the first winter. Heifers that reach target weights are better positioned for mating and calving at the optimal age, which drives lifetime production. Falling behind early due to parasite burden is difficult to recover from, even with improved feeding later.
In practice, the principle remains simple: “Down the throat till they lose their first winter coat.” Protect young stock’s performance and set the foundation for a healthier, more productive herd.
Sources:
Wormwise Programme, Beef + Lamb NZ
DairyNZ
