Active Immunization against Gonadotrophin-releasing Hormone in Chinese Male Pigs

We have investigated, under the normal conditions of local Chinese pig farming, castration of young male pigs by vaccination with a newly developed vaccine against gonadotrophin releasing hormone (GnRH). Because of the very early onset of puberty, long fattening period and relatively harsh circumstances in Chinese pig production, an investigation of the endocrine response of Chinese breeds to this type of vaccination was of particular interest. Fifteen crossbred boars (Yorkshire × Yanan) from three different litters were randomly assigned to three groups of five animals each. The first group was immunized at 13 weeks of age with a GnRH tandem dimer OVA‐conjugate in Specol and received a booster immunization 8 weeks later. The second group was injected with Specol alone and served as untreated controls. The remaining group was surgically castrated at the time of weaning (at 6 weeks of age). Pigs were fed ad libitum from weaning onwards. All animals were slaughtered at 31 weeks of age. Immunized boars had undetectable or low serum testosterone (0.09 ± 0.12 ng/ml), low fat androstenone (0.05 ± 0.01 μg/g) levels and very low testes weights (19.1 ± 4.3 g). Intact controls had much higher serum levels of testosterone (9.76 ± 4.81 ng/ml), fat androstenone levels (2.26 ± 0.87 μg/g) and testes weights (114.3 ± 29.41 g) at slaughter. Both the immunized and castrated group grew significantly faster than intact boars (p < 0.01). Average daily gains in immunized, castrated and intact animals were 0.69 ± 0.08, 0.63 ± 0.05 and 0.42 ± 0.07 kg (mean ± SD), respectively. The present data demonstrate for the first time that the newly developed anti‐GnRH vaccine works very well under practical Chinese pig farming conditions, and can be an attractive alternative to surgical castration.     

Prevalence of Candidatus Mycoplasma haemolamae,bovine viral diarrhoea virus,and gastrointestinal parasitism in a sample of adult New Zealand alpaca (Vicugna pacos)

AIM: To determine the prevalence of infection with Candidatus Mycoplasma haemolamae (Mhl), antibodies to bovine viral diarrhoea virus (BVDV), and BVDV antigen, and the prevalence of animals with elevated faecal nematode egg counts (FEC) in a sample of adult New Zealand alpaca (Vicugna pacos).

METHODS: Blood samples were obtained from 175 alpaca, collected from 15 farms around New Zealand, and from 31 samples sent to a diagnostic laboratory for routine haematology. Blood smears (n=170) were examined microscopically for the presence of haemoplasma, and DNA was extracted from whole blood (n=206) for real-time PCR testing for Mhl. Packed cell volume (PCV) was determined for 193 samples. Serum samples (n=195) were tested for BVDV antibody using ELISA, and for BVDV antigen using a real-time PCR assay. Faecal samples were collected from 143 animals; FEC were measured, and samples pooled for larval culture.

RESULTS: No haemoplasma organisms were present on blood smear examination. Of the 206 blood samples, two (from the same farm) were positive for Mhl by real-time PCR testing, giving a prevalence of infection with Mhl of 0.97%. Of the 195 serum samples tested, four (2.1%) were positive for antibodies to BVDV; animals with BVDV antibodies were from 3/15 (20%) farms, none of which farmed cattle. None of the serum samples were positive by PCR for BVDV antigen. The median FEC was 50?epg (min 0, max 4,700), with 55/143 (38.5%) samples having 0?epg, and 33/143 (23.1%) having ≥250?epg. Haemonchus spp. were the most common nematodes present in faecal larval cultures from the North Island. Log₁₀ FEC was negatively associated with PCV (p=0.02), and was higher in males than females (p<0.001), and in animals that were positive compared with negative for Mhl (p=0.022).

CONCLUSIONS AND CLINICAL RELEVANCE: The number of alpaca infected with Mhl was low, as was the seroprevalence of BVDV. Gastrointestinal parasitism was, however, a common finding in this sample of New Zealand alpaca.