BRAHMAN NEWS MARCH 2011 Issue #170

from Beeftalk SPRING/SUMMER 2010

Vibriosis and trichomoniasis are prevalent venereal diseases of the extensive cattle herds of northern Australia and are characterised by causing low fertility in heifers.

These diseases present a similar epidemiological pattern. It is not uncommon for both diseases to exist on the one property and even in the one animal.

For practical purposes, infection is only transmitted venereally for both diseases. In endemically infected herds the fertility of cows may be only slightly below normal, but infertility is seen to a greater degree in each successive group of heifers that are mated. Bulls carry both organisms in the prepuce and there is good evidence that permanent infections are more common in older bulls.

VIBRIOSIS

Caused by Campylobacteriosis fetus type 1 and subtype 1. Disease is known as Campylobacteriosis but for obvious reasons is still referred to as ‘Vibrio’. Infection causes no outward signs of illness. In females there may be increased vaginal mucus for a short time, which may be cloudy. Repeated return to service occurs but this is not normally noted under extensive conditions. It is more usual to find a low level of conception and a widened period of conception when pregnancy diagnosis is carried out. After a successful conception up to 10% of females can abort, most commonly at 5 to 7 months of gestation.

Permanent changes can occur in the oviducts in some cows leading to permanent infertility.

Infected females develop a resistance to the disease over time so that where the condition is endemic the overall disease rate drops, but reinfection can occur. Heifers exposed to infected bulls will show the highest rate of infertility within a particular herd. 

A high proportion of heifers return to service for 3 to 5 months and eventually become pregnant. In controlled mating herds the return to cycling may be after the bulls have been removed.

A variable number do not become pregnant. Pregnancy diagnosis should be used to eliminate these animals because they are reservoirs of infection.

Heifer vaccination can lead to significant improvements in fertility in infected herds. However, there are often practical difficulties in extensive herds in following the procedures which require 2 premating vaccinations to be given 6 weeks apart, with the second dose being given about 6 weeks before mating. An alternative program for heifers that are sexually mature is to give a single 5 ml dose of Vibriovax (CSL) 6 weeks before mating.

Bulls can be transiently or chronically infected. There appears to be no natural immune response in the bull. Bull vaccination involving two doses 4 to 6 weeks apart with annual revaccination has been shown to clear infection and greatly reduce their susceptibility to reinfection.

RECOMMENDED CONTROL MEASURES

• Either give heifers two premating vaccinations at 12 and 6 weeks before mating, or give heifers that are sexually mature a single 5 ml dose of Vibriovax (CSL) 6 weeks before mating. Join maiden heifers only to maiden bulls.
• Test for pregnancy and foetal ageing after joining maiden heifers. Eliminate those that are not pregnant and likely to be reservoirs of infection. Also remove the less fertile animals that conceived late as indicated by foetal ageing testing.
• Vaccinate maiden bulls twice 4 to 6 weeks apart, with the second dose being given 6 weeks before mating is due to commence.
• Vaccinate all herd bulls annually.
• Where possible, cull bulls at 6 to 7 years of age.

TRICHOMONIASIS

Trichomoniasis is a venereally transmitted disease of cattle caused by Trichomonas fetus. It is prevalent on extensively managed properties in Queensland.

Conception rates of heifers in one study improved from 40% to 95% when uninfected bulls were used. Other studies have estimated losses of up to 17.5%. Abortions occur in the first five months of gestation and have the effect of lengthening calving patterns. Infections do not normally persist for more than a few months in non-pregnant females.

Chronic uterine infections and mummified foetuses are seen in herds with trichomoniasis. Sometimes an odourless discharge with particles of mucus/pus is seen.

In bulls the organism lives in secretions around the penis and prepuce. Older bulls do not readily eliminate infection and are therefore more significant in perpetuating the disease. There is some evidence that young bulls (under 4 years) are resistant to infection.

RECOMMENDED CONTROL MEASURES

• Join maiden heifers only to maiden bulls or at least to bulls less than 4 years old.
• Eliminate non-pregnant heifers using post-joining pregnancy diagnosis.
• Consider other control measures that have been used successfully in more intensive herds, such as:
  • Destocking/restocking
  • Using artificial insemination rather than bulls
  • Operating a two herd system exposed/unexposed
  • Removing infected bulls and providing cows with sexual rest for 90 days.