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Sunday 22 October 2017

Why the recent heatwave has increased the risk of embryo loss in cows

The average dairy cow drinks 25 gallons of water daily
The average dairy cow drinks 25 gallons of water daily
IFA president Joe Healy, young Setanta Gaynor and Arthur Walker, lifelong Virginia Agricultural Show committee member, together check out the programme for the 76th annual Virginia Agricultural show which takes place on August 23. Photo: Lorraine Teevan
Dan Ryan

Dan Ryan

The weather in June brought the challenges of both a heatwave and some heavy rain.

The wet spell delayed silage harvesting by two weeks on many farms. This will have an adverse knock-on effect on the DMD of silages fed during the dry cow and fresh cow transition periods next winter.

It will be important to carry out silage sampling next autumn. This will ensure that correct dietary supplementation occurs in the winter months.

The heatwave highlighted the demand cows have for water. As herd size increases and cows travel further on the grazing platform, there is an exponential increase in demand for water.

Larger rapid-fill tanks are required to pump water to a network of feed stations on the grazing platform.

Water deprivation not alone reduces milk production, it also increases the risk of embryonic mortality.

Cows that have lost an embryo will not return to heat before the end of the breeding season. The signal for pregnancy maintenance emanates from the trophoblast, which envelops the developing embryo. This trophoblast ultimately is described as the afterbirth seen when the cow calves.

The trophoblast continues to produce the signalling factor for pregnancy maintenance up to six weeks after an embryonic death. Blood and milk tests for pregnancy will give false positive results where embryonic death maintains a pregnancy status in cows.

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Ultrasonography of the uterus will enable a definite assessment of embryo/foetal viability from day 30 of pregnancy.

It is essential that your ultrasonographer is competent in identifying cows carrying twins.

There is a greater risk of embryonic mortality among cows carrying twins. Higher- production-type cows have a greater risk of starting pregnancy with twins.

Embryonic mortality will also occur over a longer period among cows carrying twins. Identifying cows carrying twins becomes difficult after the third month of pregnancy.

Having identified those cows carrying dead embryos, a prostaglandin jab can be administered by your vet to terminate the pregnancy status.

The heat induced following embryonic death has a normal fertility status based on previous studies.

Neospora

An exception to this rule is where cows are infected with neospora. This disease will result in repeated incidence of embryonic and foetal death.

Stock bulls are currently the primary mode of breeding cows.

As the breeding season nears an end, it is essential that these bulls are fit for purpose. Remember that a bull will be sub-fertile six weeks after a previous injury which impairs sperm production.

Bulls can be selective and bull power becomes an issue if there are several repeat breeders in heat on the one day.

A separate issue is the nuisance factor of wasted bull power when a cystic cow is among the bulling group, drawing favour with the bull.

This cystic condition needs to be identified and resolved using hormonal treatment.

Use AI in conjunction with stock bulls if there are any question marks over a bull's fertility.

You should definitely use AI where more than three cows to one stock bull are in heat on the one day.

Get your herd scanned now to optimise next year's breeding potential. Scanning up to three months of pregnancy will provide accurate ageing, which will be essential this year as farmers will reap the final financial reward from late lactation milk with a favourable milk price.

It is important to have accurate ageing of pregnancy to optimise the opportunity for dry and fresh cow transition management.

Use the final weeks of the breeding-season period to assess risk of diseases such as stomach and liver fluke, worms and Infectious Bovine Rhinotracheitis (IBR).

Addressing these risks in conjunction with Body Condition Score (BCS) and locomotion score management will give a rebound in fertility status of those cows which will be the bonus late calvers in your team next year.

Dr Dan Ryan is a bovine reproductive physiologist and can be contacted at www.reprodoc.ie


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