Farm Ireland
Independent.ie

Monday 29 May 2017

Problem pathogens pose a threat to herds

Dr Marijke Beltman

When confronted with reduced reproductive performance in a herd many factors, such as management, nutrition, genetics and environmental effects, should be taken into consideration.

But, more so than ever before, Irish farmers are now having to deal with infectious diseases that are seriously compromising reproductive performance. Sub-fertility caused by infectious diseases can present in several ways, but usually the signs on farm are abortions, poor conception rates or irregular returns to oestrus.

While there are plenty of non-specific infections such as metritis, mastitis and liver fluke that have been impacting on fertility for decades, new problematic pathogens have become endemic in the national herd: Bovine Viral Diarrhoea virus (BVD), bovine herpes virus 1 (IBR), leptospirosis and Neospora caninum.

A word of warning about these diseases. The presenting signs can be unspecific. In all cases where an infectious agent is suspected, on-farm biosecurity measures should be taken to avoid spread, even before any diagnosis has been made.

BVD can be present on a farm without any clinical signs but still has a negative effect on the reproductive performance of both individual animals and the herd in general. Conception rates of animals exposed to BVD will be lower due to reduced conception and increased early embryonic death. When pregnant cattle are exposed, abortions, and weak, malformed and persistently infected calves are commonly seen. If there is a concern that BVD is causing reproductive inefficiency, the first step to take is to determine with your vet whether BVD is actually present. This process is well described by Animal Health Ireland on their website in a manual for BVD screening and control for vets and farmers (http://www.animalhealthireland.ie/bvd.php).

Leptospirosis in a herd can also present in many ways, varying from infertility and early embryonic death to abortion of an autolysed foetus, stillbirth or birth of premature and weak calves. Many leptospiral infections are subclinical, particularly in non-pregnant and non-lactating animals. The diagnosis of it can be facilitated by consulting your vet.

IBR is well known for its respiratory signs but it can also cause conjunctivitis and meningoecephalitis. While there is little clinical evidence for IBR impacting directly on fertility in Ireland, abortions are caused by IBR, usually around the third trimester of pregnancy and can occur in a storm. Abortions usually occur after respiratory signs have been seen on the farm and are related to the spike in temperature that occurs when the animal initially has been infected.

It is important to realise IBR has a negative effect on the fertility of an infected bull, as the temperature spike will negatively affect the viability of the semen for a minimum period of eight weeks after the rise in temperature took place. IBR is also an important venereal disease that can not only affect the reproductive tract locally but can also be transmitted via semen.

Neospora caninum primarily causes reproductive inefficiency via abortion. This may occur at anytime from three months of gestation to full term, with most abortions occurring around 5-6 months in gestation. Neospora may also result in classical abortion storms with more than 10pc of the cows at risk of aborting within 6-8 weeks.

Infected foetuses may be born alive with clinical signs or with a chronic subclinical infection. Clinically affected calves often show a variety of neurological signs, but 90pc of calves born congenitally infected remain clinically normal. Serological examination of blood samples taken from a cow that aborted is only indicative of exposure to Neospora and examination of the foetus is necessary to get a diagnosis.

Dr Marijke Beltman works in the Herd Health and Animal Husbandry section of the Veterinary Sciences Centre in UCD

Indo Farming