Diseases Causing Infertility in Beef Cattle
Poor fertility in a beef cattle herd can be a major cause of economic loss and is likely to be detected at pregnancy testing. A cow of low reproductive efficiency can be classified as one that is not in calf or is late in calf at pregnancy testing, or one that has lost all progeny between pregnancy testing and weaning.
The definition of poor herd fertility depends on individual expectations to a certain extent. Some people would regard a 95% pregnancy rate following an 18 week joining period as good. Others would expect to achieve 95% of cows in calf from a 9 week joining with 80% or more of cows joined conceiving in the first 6 weeks.
If a disease process is involved in an infertility scenario, the percentage will be a lot lower than this. The most likely possibilities include Campylobacteriosis or Leptospirosis.
Campylobacteriosis (Vibriosis)
Campylobacteriosis, formerly known as Vibriosis, is caused by the organism Campylobacter fetus var venerealis. It lives in the reproductive tract of females and the prepuce of bulls, and is spread during joining. The organism infects the vagina and spreads rapidly to infect the lining of the uterus, causing an endometritis which will persist for 4-5 months. Early embryonic death, fetal death and infertility are common sequelae to infection. Immunity to the disease will slowly develop following infection and most cows will subsequently conceive after 2 or more repeat services.
Infected cows may become apparently infertile when they need repeat services at regular or irregular intervals. Irregular intervals are associated with death of the embryo early in the pregnancy, which will prolong the time between heats. Abortion may also occur with most observed between 4 and 7 months gestation. Those less than 4 months are often undetected or suspected following a return to heat. Heifers are most likely to be affected as older cows will have immunity.
Bulls become infected by serving infected females and act simply as a carrier to transmit infection between females. Bulls 4 years or older are more susceptible than younger ones, and are more likely to harbour a chronic infection in their prepuce. Younger bulls can mechanically transmit the disease without becoming infected.
Diagnosis of vibriosis requires examination of available records as well as laboratory tests. The bacteria can be cultured from vaginal mucous or reproductive discharges, aborted fetuses (lung and stomach contents), or sheath aspirates from bulls.
Vaccination is effective as both a control and treatment as it will cause elimination of infection in the uterus of cows and sheaths of bulls. Generally, only the bulls need to be vaccinated as protecting the bulls against infection may safeguard the whole herd, provided that there is no risk of contact with infected cattle from neighbouring properties. If this risk exists, it is advisable to vaccinate all breeding animals as an unprotected bull may infect females and the vaccinated bull then acts to mechanically transmit bacteria without actually becoming infected. Bulls should receive one dose, repeated 4-5 weeks later with annual booster doses. Swelling at the injection site is common and may persist for a long time, but shouldn’t cause any problems.
Leptospirosis
Leptospirosis is caused by the bacteria Leptospira interrogans serovar pomona and serovar hardjo. When considering infertility L. hardjo has the most impact upon a herd as it causes observable signs only in pregnant and lactating cows. There is a sudden onset of fever and a severe drop in milk production followed by abortion some weeks later. The milk may be yellow to orange and contain clots, and the udder flabby. All quarters will be affected.
At least 86% of herd have serological evidence of exposure to Leptospira spp. The source of infection is usually an infected animal which contaminates pasture, drinking water and feed with infected urine, aborted fetuses and infected uterine discharges. The organism can pass between species, including wildlife such as feral pigs and rats and thus is easily spread. Cows that apparently recover can act as ‘carriers’ and excrete the organisms in their urine on and off. Humans are also a risk, especially farmers, butchers and vets. Infection is most likely to occur by contact with infected urine or uterine fluids.
L. Pomona causes ‘red water’ in cattle, with calves up to a month old being most susceptible. The term refers to haemoglobin in the urine which causes it to be reddish in colour. This is accompanied by a high fever, depression and anaemia. Abortion may occur initially or 3-4 weeks after a milder form of the disease. Milk drop is also another sign with all quarters becoming flabby. The mortality rate, especially in calves, is high and recovery is prolonged.
Diagnosis of leptospirosis involves 2 blood samples taken 7-10 days apart from an infected animal. If a herd has a history of abortion, 15-25% of apparently normal animals should be sampled.
Vaccination against leptospirosis in cattle is now in general use and an effective method for control of the disease. Vaccines are available against Leptospirosis alone (Lepto HP or Leptoshield) or in combination with clostridial protection (7-in-1’s). For primary vaccination, 2 doses 4-6 weeks apart must be given under the skin high on the side of the neck, below and behind the base of the ear. Animals should be revaccinated annually to maintain immunity, with this being given 1 month before calving to pass on temporary immunity to calves.
When should I see the vet?
If you have unsatisfactory pregnancy rates following pregnancy testing and a high number of ‘empties’ or ‘late in calf’ cows, it would be well worth considering contacting your veterinarian and investigating the problem further.
- Last updated 16 November 2012
