Causes of infertility in cows
Cows are considered infertile when they are neither normally fertile nor completely sterile. There are various reasons for infertility and reproductive disorders which often affect lactations. Some of the causes of infertility are complex. Nevertheless prevention and control are important to ensure productivity.
Non infectious causes of infertility
This has to do with nutrition, genetics and stress, the most common being nutrition. Body conditions before and after calving, and during breeding have a bearing on conception. Thin cows that gain weight by the time they are breeding have better conception rates than those that remain thin. Then again, cows that maintain good body condition throughout pregnancy have the best chance of breeding back. Protein and energy are usually deficient in the diet and sometimes minerals and vitamins. Over-conditioning can also be detrimental especially for heifers. Inborn causes of infertility are normally inherited and they include abnormalities of the ovaries, oviducts, uterus, cervix, vagina and vulva. Stress can cause pregnancy wastage at any stage of gestation. Heat stress is also a major cause of infertility, especially early in pregnancy.
Infectious causes of infertility
Infectious agents include several bacterial, protozoan, viral and mycoplasmal infections. Details of the most common and economically important ones are given below. Several are important zoonoses.
Brucellosis affects humans, domestic animals and wildlife. It is caused by Brucella spp. The disease is most severe in cows infected during pregnancy and usually results in abortion at about 6 to 8 months of gestation. In some cases the dead fetus is not aborted, but is retained in a mummified or macerated form. Calves born alive are usually very weak, contract calf scours easily and most die soon after delivery. Brucellosis is a professional hazard for cattle keepers and veterinarians.
Trichomoniasis is caused by a protozoan Trichomonas fetus. Cows and heifers become infected by an infected bull or artificial inseminations with contaminated semen. The disease causes infertility, repeat breeding, delayed return to estrus after mating, early embryonic death and, sometimes, abortion.
Also referred to as Vibriosis, Campylobacteriosis is a venereal disease that may cause abortion at any time of pregnancy, usually 5 to 6 months. Cows in a herd get infected from infected bulls or improperly prepared semen. Cows have irregular estrous cycles and manifest repeat breeder syndrome i.e. return to heat after repeated service. Vaccinations can prevent infections.
The disease is caused by Leptospira bacteria. Animals infected with Leptospira excrete the bacteria in their urine. Direct or indirect contact with the urine of infected animals is the major route of infection in both animals and man. In the pregnant cow this may result in abortion during the last trimester or the birth of a weak or dead calf. Vaccination can help prevent infections.
Salmonellosis is a zoonotic disease that causes abortion in cattle. Following abortion, the uterus may become severely inflamed, resulting in the death of the cow. Cows that recover may continue to excrete the bacteria for years.
Infectious Bovine Rhinotracheitis (IBR)
IBR is caused by a herpes virus. This is a respiratory disease that also causes pinkeye. IBR can cause failure to conceive, early embryonic death, and abortions later in pregnancy. Commercial vaccines can help control IBR.
Bovine Viral Diarrhea Virus (BVD)
This is a viral disease that can cause failure to conceive, early embryonic death, and abortions later in pregnancy. When the virus infects a pregnant cow it may also infect the fetus and kill it or cause fetal abnormalities. Calves born alive may be stunted.
Infectious (contagious) bovine epididymitis and vaginitis complex
Epivag is a venereal disease which can cause permanent lesions on the Fallopian tubes. The disease can be controlled by slaughtering infected bulls and by using artificial insemination.
Whether infertility is caused through infection or otherwise the functional manifestations are exhibited in one or more of the following disorders.
Retained placenta (afterbirth)
The cow fails to expel the placenta (afterbirth) within 12 hours after calving down. This may be as a result of infections of the reproductive tract. Twin births and abnormal deliveries, including prolonged or difficult deliveries or caesarian sections, are often followed by placental retention. Retained placenta can also be caused by deficiencies of selenium, vitamin A or vitamin E and over-conditioning of dry cows.
Treatment is by expelling the afterbirth and preventing infection of the uterus. Removing the afterbirth by hand may be harmful to the cow because it can damage the uterus reducing subsequent fertility.
This is the infection of the uterus and cows normally have a red-to-brown foul-smelling discharge that persists beyond 2 weeks after calving.
Metritis can be caused by retained placenta develop, injury to the reproductive tract during difficult calving or excessive force used to assist at calving. Injuries can also occur at the time of breeding or uterine treatment. Contamination of the reproductive tract can happen at calving when cows and heifers are highly susceptible to infection. If the calving area is unclean or if assistance and/or treatment around calving time are unsanitary, metritis is a probable result. Selenium or vitamin E deficiency may cause metritis.
Endometritis can be treated by infusing antibiotic or sulphonamides into the uterus. Cows with chronic metritis have a retained (persistent) corpus luteum and treatment should aim at removing it by an intramuscular injection of prostaglandin.
Ovarian cysts are structures that persist on one or both ovaries for 10 days or more. Fertility in cystic cows is reduced due to hormonal changes, changes in uterine tone and, in many cases, failure to release an ovum (egg). This can be caused by excessive calcium intake or wide calcium/phosphorus ratio in the diet. High estrogen intake by injection or through fresh legume forage or from some mold toxins can also increase the incidence of cystic ovaries.
Anoestrus is failure to show signs of heat or estrus although in most cases it is a failure to detect heat. Undetected estrous signs in cows with normal ovarian activity result from inadequate estrous detection because majority of estrous signs are shown between 6 p.m. and 6 a.m. Cows with short estrus (less than 12 hours in length) may be missed even with twice-a-day estrous detection.
True anestrous is due to lack of ovarian activity caused by anemia, energy deficiency, low hormone levels cystic ovaries or pyometra (pus in the uterus).
Quiet estrus or silent estrus is when there is normal ovarian activity with little or no signs of estrus. Most of the factors associated with true anestrous can also be associated with quiet oestrus.
Ensure that animals are well managed and are fed to maintain good condition during critical periods, i.e. prior to mating and during lactation, in order to avoid anoestrus.
Repeat breeders are those cows that require three or more services to conceive. Repeat breeding can be caused by a number of factors, including sub-fertile bulls, endocrine problems, malnutrition, reproductive tract infections and poor management.
Repeat breeding can be treated by enucleating the corpus luteum or causing its lysis by prostaglandins, uterine massage or manual stimulation of the clitoris after artificial insemination or infusion of the uterus with 50-200 ml of 1 to 5% Lugol's iodine, which has a stimulating effect on the uterus.
Causes of abortion can be either infectious or non-infectious. Non infectious causes genetic defects, multiple fetuses, injuries, toxicities or drug induced.