Review of Fox Disease Prevalence in 2001

In 2001, the overall situation of fox reproduction and kit survival across the country was not ideal, making it a year with more problems since fox farming began in China. Below is an analysis of the causes of disease and death problems in fox farming, along with effective preventive measures, in order to promote the healthy development of the fox farming industry, reduce production losses, and achieve higher economic benefits.

1 Purulent endometritis caused by artificial insemination

1.1 Main infectious pathogens

Through extensive epidemiological investigation and pathogen isolation and identification, the main infectious pathogen was Pseudomonas aeruginosa, accounting for 90% of total infection rates, of which single Pseudomonas aeruginosa infection accounted for about 65%, and mixed infection accounted for about 35%. The mixed infection bacteria included Escherichia coli, Staphylococcus aureus, Corynebacterium pyogenes, Streptococcus pyogenes, Proteus, and Salmonella. In mixed infection cases, Pseudomonas aeruginosa remained the dominant infecting bacterium.

1.2 Causes

① Contamination during semen collection, such as failure to disinfect the penis, and failure to soak the hair on the lower abdomen and around the genital area with disinfectant.

② Contamination during semen dilution, such as lacking a sterile environment, operating in an unsanitized room, or even diluting semen under conditions where the floor and workbench have considerable dust.

③ Improper instrument disinfection methods or disinfection temperature being too low.

④ Failure to disinfect the vulva of the female fox or incomplete disinfection.

⑤ Uterine mucosal damage caused by operational technique.

1.3 Prevention

① Pay attention to disinfecting the vulva, penis, and surrounding hair, usually using 0.1% benzalkonium bromide.

② Dilute semen under conditions with a sterile hood or ultra-clean workbench.

③ The insemination needle and dilator must be thoroughly disinfected. Boiling disinfection must reach 30 minutes or more, then dried at 80°C after boiling; dry heat disinfection temperature must reach 80-100°C for 60 minutes.

④ Maintain good hygiene in the operating room, with no dust, and do not allow unauthorized personnel to enter freely. The operating room should be sealed as tightly as possible, prevent direct strong light, install ultraviolet lamps indoors, and irradiate for at least 30 minutes 12 hours before use.

⑤ Strengthen training, improve operational technique, and on the basis of proficiency, be gentle and steady; do not blindly pursue operating speed.

⑥ 15-20 days before artificial insemination, inject foxes with Pseudomonas aeruginosa polyvalent vaccine for prevention.

⑦ After artificial insemination, broad-spectrum antibiotics such as Baytril can be used to eliminate miscellaneous bacteria in the vagina and uterus.

⑧ Once purulent endometritis occurs, treat with alternating gentamicin and ampicillin, combined with low-dose posterior pituitary hormone, while flushing the uterus once daily with fluid containing penicillin and streptomycin, and intravenously inject glucose when necessary.

2 Causes of kit fox death

2.1 Bacterial infection

This was relatively prominent in some fox farms, basically involving kit fox deaths within 10 days after birth. Testing confirmed that the infecting bacteria were mainly Escherichia coli or co-infection with Gram-positive bacteria (mainly Corynebacterium) and other Gram-negative bacteria.

Infection routes have been confirmed: 40% of kit foxes were infected in utero, that is, from asymptomatic mothers through intrauterine infection or vertical transmission, and may also be infected through the reproductive tract at birth; this was confirmed by isolating bacteria from the organs of newborn kit foxes that had just died. However, the birthing female foxes showed only mild symptoms a few days before parturition or after birth, with only a 1%-2% mortality rate. This may be because the infecting bacteria had strong virulence, and after transmission from the mother to the fetus, they were also in a latent infection state; after birth, under external stress, because the immune system had not been activated, the infecting bacteria multiplied in large numbers and produced virulence, causing kit fox disease. 60% of kit foxes were infected after birth, related to bacterial contamination in the nest box, through the umbilical cord or during suckling. Intrauterine infection may occur when bacteria invade the uterus during mating of the female fox, but because bacterial virulence is weak, the incubation period is relatively long, and pathogenicity was not produced in early pregnancy; as bacterial numbers increased, virulence also strengthened, enough to penetrate the placental barrier and enter the fetal body, causing fetal infection and disease.

For treatment and prevention, kit foxes showing symptoms were treated with gentamicin, kanamycin, ampicillin, and ciprofloxacin lactate, with a cure rate of 85%; combining this with medication for the lactating female fox produced even better results. Before mating, the female fox's cage and housing should be thoroughly disinfected, and immediately after mating, treat with ampicillin or ciprofloxacin lactate to eliminate bacteria.

2.2 Death caused by heat stress response

This mainly occurred in kit foxes born after late May. Due to abnormally high temperatures, the female foxes had severe heat stress responses and did not care for the kits in the nest box, causing the kits to starve to death.

For prevention, when selecting young foxes born that year to keep as breeding foxes, it is best to choose those born before May 30. Only in this way can early estrus and early birth of kits be ensured the following year. Before mating, adjust the body condition of the foxes well, ensure the nutritional needs of the feed, and try to make the foxes come into estrus early and concentrate estrus, reducing the number of late-estrus foxes.

2.3 Death caused by abnormal parturition

Due to too many or too large fetuses, the female fox's labor was prolonged; after birth, the female fox was highly weak, with abdominal pain and mechanical damage to the uterine and vaginal mucosa. The female fox often lay motionless in the whelping box, and the kits starved to death or died from infection because they could not get colostrum.

For prevention, check promptly. When this condition is found, usually choose injections of antipyrine, penicillin, gentamicin, or norfloxacin. Giving the female fox analgesia and anti-inflammatory treatment has a good effect.

2.4 Death of kit foxes caused by vitamin B1 deficiency

The age of onset in kit foxes was 10-30 days after birth. They showed hind limb paralysis, flaccid weakness, rough or sticky fur, lethargy, weak suckling ability or no suckling ability, and sometimes paroxysmal convulsions. It generally occurred mostly in the offspring of female foxes with larger litters.

Comprehensive analysis showed that the occurrence of this disease in some fox farms was related to insufficient vitamin B1 in the diet, such as feeding fish or animal offal stored too long during pregnancy, and insufficient supplementation in the feed. However, in most fox farms or households, it was not vitamin B1 deficiency in the feed, but rather caused by excessive litter size in the female fox, large milk production, and overloaded consumption.

For treatment and prevention, each fox farm should ensure the vitamin B1 content in the pregnant female fox's diet and the freshness of the feed. During lactation, add feed rich in vitamin B1 to the diet, such as liver, milk, yeast, etc. For treating diseased foxes, use vitamin B1 injection, twice daily, 50-100 mg each time. At the same time, combining this with more vitamin B1 supplementation for the female fox produces more significant results.

2.5 Death caused by lack of milk in female foxes

This was mainly caused by the female fox being too fat or too thin, and also occurred in older foxes and a small number of first-time birthing foxes.

Generally, injecting prolactin has a certain effect, and increasing the content of milk and eggs in the diet can increase milk production.

2.6 Eperythrozoon infection

This was relatively serious in kit fox infection and prevalence in some fox farms. Affected kit foxes showed elevated body temperature, anemia, jaundice, refusal to suckle or loss of appetite, hind limb weakness, and bloody stools. Some diseased foxes had bleeding from the oral mucosa and ear canal, and swelling of the eyelids and mouth. It generally occurred as whole-litter infections. Blood examination can confirm the presence of Eperythrozoon, with a red blood cell infection rate of over 70%. Treatment with avermectin combined with sulfonamide drugs was effective, with a cure rate of 50%-70%.

For prevention, kit fox infection may be related to the mother fox carrying the bacteria, but postnatal infection cannot be ruled out. Because kit foxes have relatively low immunity, they are susceptible to infection and disease.

From December each year to January of the following year, inject the female fox twice with avermectin (at 0.03 mL/kg body weight) to kill Eperythrozoon in the blood, which may be effective in preventing kit fox infection.

2.7 Death caused by encephalitis infection

After onset, kit foxes mainly showed paroxysmal convulsions, hind limb paralysis, or sudden death. Treatment with antibiotics and vitamin B1 was ineffective.

Survey results showed that in all cases where kit foxes had this type of death, the female foxes had almost never been injected with encephalitis vaccine, so the kit foxes had no protective maternal antibodies and became infected.

For prevention, regularly inject breeding foxes with encephalitis vaccine, which can prevent the occurrence of encephalitis in kit foxes.

3 Abortion and embryonic resorption

At present, abortion and embryonic resorption in pregnant foxes remain relatively prominent problems in China's fox farming production. Apart from feeding spoiled feed during pregnancy causing embryonic resorption and abortion, investigation and testing confirmed that the main cause was Gardnerella infection. Testing aborted and empty foxes on some fox farms with Gardnerella antigen confirmed an infection rate as high as 60%. These fox farms still had not used Gardnerella vaccine to immunize their breeding fox populations. In addition, reproductive disorders caused by natural Pseudomonas aeruginosa infection accounted for 2%-3%. Abortion and embryonic resorption caused by deficiency or insufficiency of protein, vitamins, trace elements, etc. during pregnancy accounted for 10%-15%. Abortion and embryonic resorption caused by diarrhea during pregnancy accounted for 2%-4%. Abortion caused by stress factors accounted for about 1%.

For prevention, use Gardnerella antigen testing, cull diseased foxes, and regularly inject vaccine; inject Pseudomonas aeruginosa vaccine 15-20 days before mating each year; ensure stable and fresh feed during pregnancy, with balanced combinations of various nutrients and sufficient content; use probiotics during pregnancy, which can effectively prevent bacterial diarrhea and has no side effects on the fetus; during fox pregnancy, prevent sudden noise stimulation and rough handling.