The invisible threat of gutworm is seriously affecting dairy cow fertility in up to 80% of UK dairy herds, says Merial Animal Health. Merial is seeking to raise awareness of the damaging impact of Ostertagia and, in doing so, improve dairy productivity.
“The reduction in milk production from a gutworm infection is well documented,” says Sioned Timothy, veterinary adviser for Merial. “Both animal health advisers (Suitably Qualified Persons – SQPs) and vets recognise the threat such infections cause. However, since cows often show no outward signs of disease, even in the face of a massive challenge, dairy farmers could unwittingly suffer heavy losses in milk yield, reduced fertility and increased heifer rearing costs at a time when they can least afford it.”
Yet the extent of a herd’s gutworm exposure can be easily and simply assessed from a sample taken from the bulk milk tank – using the MOO Test. This test determines the amount of antibody to Osteragia ostertagi present in a sample, giving an accurate assessment of the level of herd gutworm challenge.
The metabolic demands placed on cows during the post-calving period can lead to a negative energy balance, when energy gained from feed intake is less than that used for milk production. This natural ‘energy gap’ leads to weight loss; a parasite burden can make matters worse.
Sioned advises taking action to reduce the effect of this post-calving energy gap to maintain productivity levels.
She says: “Management of cows in the weeks following calving should focus on maximising dry matter intake to correct the energy imbalance as quickly as possible. Studies have shown that cows treated for gutworm have improved appetites, and graze for up to an hour longer than untreated cows3. Grass is the cheapest form of nutrition so it makes sense to make the most of it.”
When it comes to fertility, studies have shown that effective parasite control may have a beneficial effect. Reduced body condition scores caused by the energy gap after calving may impact on reproductive parameters. In one study, cows treated for gutworm were back in calf 13 days sooner than untreated animals.
“This has obvious implications for productivity,” says Sioned. “We need to look at employing a range of practical measures to ensure cows are as productive and efficient as possible, and this includes targeted worming where required.”
It’s not just adult cow fertility that can be compromised by a gutworm burden. Effective parasite management of the replacement heifer during the rearing period is key to her future performance and productivity. Achieving breed-appropriate target weights throughout the rearing period is a crucial component of heifer rearing. The onset of puberty and the start of breeding are more closely linked to weight, body size and condition score than age. It is therefore critical to ensure that heifers reach approximately 60% of mature weight by 14 months of age in order to achieve a 24 month average age at calving.
“Losses in potential liveweight gain due to poor parasite control during a heifer’s first grazing season will not be recouped during the second year at grass6. She won’t catch up, and this will impact on her ability to meet important milestones,” warns Sioned.
Getting heifers in-calf at the optimal time will help to reduce breeding costs and maximises the potential productive life of the animal. Heifers treated for gutworm have been shown to have a 20% higher conception rate at first service than untreated cattle.
There is also evidence that parasite burdens exert physiological effects that directly impact on the parameters influencing performance and profitability of heifers, and increased mammary development and earlier onset of puberty have been observed in strategically wormed heifers in comparison to those left untreated.
“Effective worming will mitigate the effect of parasites on fertility levels in growing cattle, while still allowing them to build the necessary immunity required to prevent clinical disease in adulthood,” advises Sioned.
Paul White, a dairy farmer from Wonwell Court Farm in Kingston, Devon, has seen the positive effects of treating for gutworm. The farm aims to maintain a closed herd, and there are plans to increase the milking herd of 100 cows to 120, with home-reared replacements.
Paul discovered the benefits of worming dairy cows several years ago, when he treated his first calvers. He says: “We were interested in using Eprinex® because at the time it was the only product with a zero milk withhold. We saw a big difference with the heifers, so decided to use Eprinex® on the whole herd. Now we treat all the cattle annually, at housing.”
Since the worming programme began Paul has seen an overall improvement in the condition of the cows, and heifers are getting in-calf sooner. An improvement in the longevity of the herd is also apparent, with each cow averaging around six lactations.
Milk yield has also increased. Paul says: “We always used to be pleased if the best heifer did 6000 litres per year, but now our top heifer produced 10,800 litres; the heifers are averaging well over 7000 litres; and the whole herd is averaging over 8000 litres.”
“Paul’s herd is a good example of how removing a gutworm burden can improve both fertility performance and herd productivity,” says Sioned. “Paul has found that treating the herd annually at housing to remove parasite burdens acquired during the grazing season suits his system. Other approaches to treatment timing can be taken; factors such as grazing practices and calving pattern should be taken into account when determining which is most appropriate. There is increasing evidence that targeting treatment around the time of calving can yield benefits throughout the subsequent lactation.”
Source: Farming UK