BRAHMAN NEWS SEPTEMBER 2011 Issue #172
Many diseases that compromise reproduction are also responsible for production losses, poor performance, wastage and serious economic costs.
Pathological conditions do not necessarily render stock permanently infertile and the seriousness of a reproductive disease depends on its incidence, duration and location of the infection.
Degree of reproduction interference depends on the disease
Precise industry costs of reproductive diseases are difficult to estimate. Nevertheless, individual breeders with a herd disease problem can have serious losses due to reduced conception rates, abortions and other productivity costs (eg mortalities, reduced calving and weaning rates).
Reproduction diseases can cause major financial losses
Diagnosis of the incidence and cause of infectious reproductive disorders can be complex and often requires veterinary inputs to determine the nature and extent of the problem. Veterinarian advice is greatly assisted by the provision of good production records (eg heats, abortions, unsuccessful pregnancies).
The following article outlines the more common diseases associated with reproduction failure.
This disease is caused by a protozoan (Trichomonas fetus). In bulls, the trichomonads normally colonise on the external mucous membrane of the penis and prepuce. Bulls may have the disease for a considerable period of time before showing symptoms.
Cows and heifers that have never been exposed to the disease become infected by a carrier bull. Following contamination, the protozoa first multiply in the vagina and cervix then in the majority of cases the organisms migrate to the uterus.
Trichomoniasis causes infertility, repeat breeding, delayed return to oestrus after mating and early embryonic death. Sometimes abortion occurs between 2-7 months after conception although the foetus may degenerate. The parasite tends to attack the superficial layers of the endometrium and pus may be observed indicating pyometra (pus in the uterus).
Affected cows develop antibodies in their vaginal mucous and this together with hormonal changes during subsequent oestrus cycles tends to protect the cow during an infection but may not prevent re-infection.
After being sexually rested for at least 3 months (4-5 cycles) cows may develop some immunity and their fertility improves.
Contaminated bulls (carriers) can re-infect recovered and susceptible female (eg heifers). Carrier bulls can be treated but the treatment is lengthy and only warranted with special and valuable bulls.
This is caused by a bacterium (Campylobacter fetus) and was formerly known as Vibrio fetus). As the name implies, the organism can cause abortion of the foetus. It has been implicated as the cause of embryo or early foetal loss between 25-60 days after natural service. Abortion can occur in up to 5 per cent of the infected cows around 5 months after endometritis and placentitis have occurred.
In the non pregnant female the disease can cause endometritis (uterine inflammation) which can cause a vulval discharge and often leads to infertility.
A large number of cows in a herd can get infected by a carrier bull. The bull is always a symptomless carrier and its genitals and semen appear normal.
Infections of the uterus causes inflammation and infertility
Infertility may last up to 6 months. Diagnosis based on clinical signs is difficult in the acute stage and breeding records often provide the first indication of a problem.
Many cows return to oestrus after repeated services (repeat breeder syndrome) and oestrus cycles are longer than normal, usually more than 4 weeks indicating early embryonic death.
After variable periods of infertility many cows recover and regain fertility but may be less fertile than normal.
The fertility of the herd will remain low as long as susceptible females (eg heifers) are presented to infected bulls.
The control of the disease involves treatment, possibly culling infertile females and preventing re-infection. The organism is susceptible to antibiotics so that infected valuable bulls may be treated, however, re-infection can occur. Cows require sexual rest and can also be treated with antibiotics but re-infection can occur.
Control, prevention and the introduction of antibiotic and vaccination programs need to be discussed and supervised with your vet.
This is a systemic disease characterised by a fever and sometimes mastitis and abortion.
Infected animals excrete the bacteria in their urine
Direct or indirect contact with the urine of infected cow is the major route of infection of both cattle and humans.
In the pregnant cow the organisms attack the foetus or endometrial capillaries. This may result in abortion during the last trimester or the birth of a weak or dead calf. Foetal membranes may be retained, sometimes causing metritis and infertility.
Cows usually respond to antibiotics but re-infection can occur. Leptospirosis can be controlled by strict hygiene and the isolation of infected animals. Importantly, all aborted materials must be disposed of properly (ie the use of gloves and disposal by burning or deep burial). Vaccination programs may be necessary in some areas.
This disease is an important cause of abortion in cattle particularly in crowded environments and wet conditions. Infected animals excrete the organism in their faeces contaminating pasture and water supplies. Humans are also susceptible to some strains.
Extreme care needs to be taken in handling aborted material
Typical symptoms of the disease include septicaemia and dysentery and sometimes pneumonia can occur. The bacteria are attracted to the uterus causing enteritis and the endotoxins cause painful arthritis and abortion. Following abortion, the uterus may become severely inflamed resulting in the death of the cow. Cows that recover may continue to excrete the bacteria. Vaccination programs may be necessary in some areas.
This disease is caused by a herpes virus and can affect the respiratory, reproductive, nervous and digestive systems of cattle.
The disease can be transmitted sexually or by inhalation
Cows and heifers served by an infected bull develop pustular-vulva-vaginitis which rarely extends past the cervix and therefore pregnancy is rarely terminated. The virus can invade the uterus systemically when cows have the respiratory form of the disease.
Should the cow obtain the inhalation form of the disease, oestrus cycles are disrupted reducing fertility.
After invading the uterus, the virus may lie dormant for several months then cause abortion at 4-7 months. The foetus dies soon after infection and may be retained for several days before being expelled with the appearance of a mummified calf.
Control measures for IBR need to be done in close consultation with your vet.
Some of the systemic and non specific infections cause pathological conditions termed endometritis, metritis and pyometra.
Undetected the situation may persist for a considerable period of time since the animal does not show systemic illness.
Also known as Bovine Pestivirus, this complex array of diseases is caused by a virus (Flavividae) which is widespread throughout Australia. It is estimated that as much as 30-40 per cent of the cattle population is infected with the virus.
Diseases due to pestivirus can be expressed in several different ways, ie reproduction losses, respiratory disease (mucosal disease), illthrift and diarrhoea and suppression of the immune system placing the animal at risk of other diseases.
When unaffected pregnant females are exposed to the disease in early pregnancy (3-4 months) the virus infects the developing foetus.
Signs of reproductive problems include:-
Depending on the stage of pregnancy the infection can cause reduced conception rates, foetal loss or calf wastage (stillbirth and illthrift).
Calves that survive the infection are likely to be "persistently infected" and become a carrier of the virus.
Persistently infected calves play a key role in spreading the virus for the remainder of their life even though their life may be short (6-24 months).
The virus is present in all secretions including saliva, nasal discharge, milk, urine, faeces and semen and close contact (eg sales) increases the risk of transmission.
Persistent carriers are a key source of infection
The key to the survival of the virus is the presence of persistently infected carriers. With their elimination the virus dies out but re-infection must be avoided.
For some herds control and vaccination programs are justified. Veterinary advice needs to be sought re diagnosis, elimination, vaccination and prevention of the disease. (Note – once a vaccination program is started it is necessary to continue otherwise the herd will become fully susceptible to pestivirus).
This is caused by a protozoal parasite of dogs (and perhaps other carnivores eg foxes, dingoes) which causes abortion in cattle.
Cows infected with neospora appear healthy but about 15-20 per cent will abort at least once in their lifetime and some positive animals may abort several times. Cows typically abort between 4-7 months of pregnancy.
Cows that don't abort are likely to pass the infection to their calves. Infected calves are usually born healthy but pass the infection onto their offspring thus the infection perpetuates itself in the herd.
Cattle can be infected through the consumption of feed, pastures and water that are contaminated with oocysts (eggs from the parasite). These oocysts are shed in the faeces of dogs which become infected by eating infected placentas or foetuses.
It appears that the dog sheds oocysts for up to 3 weeks after infection but under certain conditions the oocysts can survive for several months. This can lead to an abortion storm with a number of stock aborting over a period of 1-2 months.
Diagnosis of Neospora includes the examination of a chilled (not frozen) aborted foetus, stillborn calves and/or afterbirth. Control recommendations include:-
Over 90 per cent of calves born to mothers with antibodies to Neospora will have been infected in utero indicating the relevance and importance of vertical transmission.
Vertical transmission alone can maintain infection in the herd
There can be serious abortion storms if infection is introduced to females that do not have immunity. It is subsequently important to prevent infection or re-infection by the introduction of infected stock.
Fungal infections, particularly those caused by mouldy feeds can cause abortions fairly late in pregnancy but can also cause foetal losses in early pregnancy.
It is suggested that a Herd Health Program be developed for each property in consultation with a veterinarian. This program should include protocols for biosecurity, genetics, herd management and the monitoring, diagnosis, treatment and prevention of diseases.
Last but not least, check with your veterinarian on the availability, introduction, management and implications of suitable vaccination programs.
|Trichomoniasis (BVD)||Veneral – Trichomonads (protozoa) invade the uterus attacking and liquefying the foetus causing infections. Sometimes abortion between 3 and 7 months.||Embroryonic deaths, repeat breeding and delayed oestrus. Primary source of infection is from infected bulls which infect non-infected stock and re-infected treated stock.|
|Campylobacteriosis (Vibriosis)||Veneral – bacterium causes early embryonic losses or abortions at 4 to 7 months.||Milk production decreases markedly. Foetal loss. Reduced conception rates in infected stock.|
|Rhinotracheitis (IBR)||(a) Systemic (inhalation) infection of the uterus by the virus causes abortion at 4-7 months.
(b) Veneral transfer (eg natural mating) can cause vaginitis.
|Stock can show respiratory and digestive disorders compromising production. Foetal loss and disrupted and delayed oestrus cycles. Infection can reduce fertility causing repeat breeding.|
|Salmonellosis (Zoonic)||Contaminated pastures and water supplies infect stock. Bacterial infection leads to inflammation of the uterus causing metritis and abortions.||Stock production can be reduced due to septicaemia, scouring and sometimes pneumonia and arthritis. Foetal loss and delayed conception. Severe cases cause cow mortality.|
|Endometritis, metritis and pyometra||Infectious organisms enter the uterus in association with difficult calvings and retained membranes. Often associated with BVD and vibriosis.||Sometimes depression and loss of appetite leads to lost performance. Delayed conception and extended calving intervals due to infection and inflammation causing anoestrous.|
|Bovine Viral Diarrhoea Virus (Pestivirus)||BVD virus infects the developing foetus. Depending on the stage of pregnancy there may be foetal mortality. Infected stock can produce live calves that are persistently infected with the virus. These carriers play a key role in perpetuating the disease in the herd. The disease is spread through saliva, nasal discharge, urine and faeces. Primary or acute infections play an important role in suppressing the immune system thus exposing stock to a variety of diseases (eg bovine respiratory disease).||Significant cause of reproduction failure particularly when an infection is first introduced into a group of pregnant females. Infection can result in reduced conception rates, foetal loss, abortion and stillbirths. Surviving calves can have severe birth defects and die shortly after birth or live for a short lifespan (6-24 months) infecting other stock with the virus. Generally persistently infected stock die from diseases caused by immunosuppressive effects of the virus.|
|Neosporosis (Neospora)||Ingestion of food/water contaminated with protozoal parasites causes abortion at 4-7 months but abortion can occur between 3-9 months. If the cows do not abort they pass the infection to their calves. These calves pass the infection onto their offspring. Abortions tend to be sporadic depending on exposure to the protozoa.||Sporadic infections can cause outbreak storms of aborted foetuses. There can be repeat abortions by affected cows. Live infected calves can be a continual source of infection.|