Dairy: Play it safe over winter - avoid grazing the grass cover too low

Cows on a zero-grazing system tucking in at O'Donnell's, Togher, Portlaoise. Photo: Alf Harvey/HRPhoto.ie
Cows on a zero-grazing system tucking in at O'Donnell's, Togher, Portlaoise. Photo: Alf Harvey/HRPhoto.ie

Mary Kinston

November has seen a significant change in the weather when compared to the glorious and somewhat unexpected dry October.

Declining grass covers and tender grazing conditions have now resulted in many cows being housed either by night or full-time.

A number of farmers have taken the decision to house prematurely based on a rapidly declining pasture cover, in an aim to protect next year's spring grass.

This is by no means the wrong decision but it does need to consider the grass growth of November and winter months to get it right. For example, if you were aiming for an opening cover on February 1 of 800kgDM/ha, it simply requires you to minus away what cover you will grow over the winter to determine the cover at which you should close the farm. Therefore if the farm usually has a small amount of grass growth over winter eg 2kgDM/ha/day, December and January will yield an additional 122kgDM/ha (61 days by 2kgDM/ha/day).

Therefore on December 1 the farm must have a closing cover of no less than around 680kgDM/ha (800-120).

However, if you have found yourself closing up early for example November 1, you must also factor in the growth of November. If on average November grew 8kgDM/ha/day, 30 days will yield an additional 240kgDM/ha, which means that a farm cover should be closed at no less than 440kgDM/ha (680-240) on November 1.

Now obviously grass growth and winter weather vary year to year, so play it reasonably safe, continue to monitor, do not graze the grass cover too low, and avoid carrying covers that are now greater than 1400kgDM/ha over the winter, where possible.

As December draws ever nearer, so too does the drying off of the spring calving herd. Therefore now is a time to give due consideration to the control of parasites at housing.

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Housing is a great time to control parasites due to the abrupt transition from pasture to a silage diet which aids in the effective anthelmintic treatment of animals at or during housing to result in animals free of worms and fluke until they return to pasture.

Doing this well requires a farmer to make an informed decision, as the right decision now may protect your herd against compromises in herd performance in terms of milk yield and composition and on cow body condition score and fertility. However since March 2010, the process has become harder, with many products not being permitted for use on dairy herd.

While I certainly do not profess to have expertise in this area, I, alongside my husband, - like every other dairy farmer around the country - have to devise a dosing strategy this winter. When devising a dosing strategy, assessing the herds parasite status can be a helpful step in effective control.

Use your vet for advice to undertake a parasite investigation, to interpret the results and finally to create an effective dosing regime. Many farmers regularly assess milk from the bulk tank to assess herd health and results will indicate the risk of stomach worms, liver fluke and lungworm infections.

Combining this information with faecal (dung) samples will also indicate the presence of liver fluke and rumen fluke. The assessment of the liver at slaughter can also be useful information.

When devising your dosing strategy at housing you are aiming to effectively target:

• Liver fluke

• Worms - stomach, gut and lung

• Lice (biting and sucking) and mange

• Rumen fluke

Animal Health Ireland has useful information leaflets that can also aid you in this process.

From working with farmers it appears that liver fluke is a big issue on farms.

It's therefore no surprise that studies have suggested that a dry farm is no longer an insurance against a liver fluke burden. However, as one would expect the prevalence of liver fluke is greatest in the west. While many farms experience the traditional rise in autumn/winter liver fluke levels, others are now experiencing high levels of fluke all year round.

Farms in this category have a notable challenge when the products available to control fluke are limited. To date it appears that only three active ingredients are licenced for use on dairy cows, being triclabendazole, oxyclozanide and albendazole.

However, rulings may change so it's worth checking for updates. When considering a product for use, I find it useful to check the product information on the Health Products Regulatory Authority website under www.hpra.ie.

Here you will find details of usage restrictions and the withholding periods of each product in question.

Having done this and read a few of the "summary of product characteristics" most flukicides state that care should be taken to avoid too frequent or repeated use of the same anthelmintic from the same class over an extended period and to avoid under-dosing by the under estimation of body weight, because of the risk of anthelmintic resistant.

As resistant strains of F hepatica have emerged to flukicides such as triclabendazole, I feel it's a concern for our dairy industry that our ability to avoid repeated use of the same anthelmintic is limited by availability of so few active ingredients being used to treat fluke.

In my view, while not F hepatica, the repeated use of the one licenced product (Zanil) for the control of rumen fluke is certainly a cause for concern.

With this in mind here are some key steps for effective parasite control:

• Assess the herd's parasite status

• Discuss the product choice with your vet. Ask whether a single or repeated dose is required, dose rate and the ideal time for its administration. Make sure all aspects of fluke, worms, mange and lice are covered where the parasite is deemed a risk

• A few weeks after treatment assess whether the dose has been effective

• Alternate active ingredients used against liver fluke between years where possible.

Mary Kinston is a discussion group facilitator and consultant, and farms with her husband in Co Kerry

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