Dual effects of gonadotropin-inhibitory hormone on testicular development in prepubertal Minxinan Black rabbits (Oryctolagus cuniculus).

Gonadotropin-inhibitory hormone (GnIH) is a neurohormone that not only suppresses reproduction at the brain level but also regulates steroidogenesis and gametogenesis at the gonad level. However, its function in gonadal physiology has received little attention in rabbits. The main objective of this study was to evaluate the effects of GnIH on testicular development and function in prepubertal Minxinan Black rabbits (Oryctolagus cuniculus). In the present study, we investigated the serum reproductive hormone concentration, testicular parameters, morphology of seminiferous tubules, apoptosis of testicular cells, and expression of reproductive-related genes in male prepubertal Minxinan Black rabbits intraperitoneally administered with 0, 0.5, 5, or 50 µg quail GnIH-related peptides (qGnIH) for 10 days. Compared with the vehicle, administration with 5 µg of qGnIH downregulated the serum testosterone concentration and mRNA levels of spermatogenic genes (PCNA, FSHR, INHßA, HSF1, and AR) and upregulated the apoptosis rate of testicular cells; administration with 50 µg of qGnIH decreased the serum testosterone concentration and hypothalamic GnIH gene mRNA level and increased the serum LH concentration, pituitary LHß gene mRNA level, testicular weight, gonadosomatic index (GSI), and spermatogenic cell layer thickness. It is concluded that GnIH could exert dual actions on testicular development depending on the male prepubertal rabbits receiving different intraperitoneal doses.

Pathogenic and genomic characterization of rabbit-sourced Pasteurella multocida serogroup F isolates recovered from dead rabbits with respiratory disease.

Pasteurella multocida serogroup F can infect a number of animals. However, the pathogenicity and genomic features of this serogroup are still largely unknown. In the present study, the pathogenicity and genomic sequences of 19 rabbit-sourced P. multocida serogroup F isolates were determined. The 19 isolates were highly pathogenic for rabbits causing severe pathologic lesions and high mortality in inoculated rabbits. Nevertheless, the pathologic lesions in rabbits caused by the 19 isolates were distinct from those caused by the previously reported high-virulent serogroup F strains J-4103 (rabbit), P-4218 (turkey), and C21724H3km7 (chicken). Moreover, the 19 isolates were avirulent to white feather broilers. The genomes of the 19 isolates were determined to understand the pathogenicity of these isolates. The finding of a number of functional genes in the 19 isolates by comparison with the low-virulent rabbit-sourced serogroup F strain s4 might contribute to the high virulence of these isolates. Notably, polymorphisms were determined in the lipopolysaccharide outer core biosynthetic genes natC and gatF among the serogroup F strains of different hosts. However, the sequences of natC and gatF from rabbit-sourced strains (except for SD11) were identical, which might be responsible for the host specific of the 19 isolates. The observations and findings in this study would be helpful for the understanding of the pathogenicity variation and host predilection of P. multocida. IMPORTANCE: The 19 rabbit-sourced Pasteurella multocida serogroup F isolates showing high virulence to rabbits were avirulent to the broilers. Notably, polymorphisms were determined in the lipopolysaccharide outer core biosynthetic genes natC and gatF among all serogroup F strains of different hosts. However, the sequences of natC and gatF from rabbit-sourced strains (except for SD11) were identical, which might be responsible for the host specific of the 19 isolates.

Effects of feeding methods on growth and slaughter performance, blood biochemical indices, and intestinal morphology in Minxinan black rabbits (Oryctolagus cuniculus).

Feed restriction after weaning is a common strategy used in commercial rabbit farms to improve feed efficiency, promote health, and reduce mortality. However, few studies have investigated the feed restrictions of Minxinan black rabbits (Oryctolagus cuniculus). Thus, the effects of feed restriction on growth and slaughter performance, intestinal morphology, and blood biochemical indices of Minxinan black rabbits were evaluated in this study. Rabbits in group A (control group) had ad libitum intake, while those in feed restriction groups (groups B, C, and D) were restricted to 80% of the average daily feed intake (ADFI) of group A the day before. The rabbits in group B were fed once per day at 8:00 am. Rabbits in groups C and D were fed twice per day at 8:00 am (50%) and 4:00 pm (50%) and 8:00 am (30%) and 4:00 pm (70%), respectively. The experimental period lasted for 8 weeks. Compared to that in group A, the diarrhea rate of group C was significantly decreased (P < 0.05), and the ADFI, feed conversion ratio, abdominal fat weight, abdominal fat rate, total protein, albumin, globulin, alanine aminotransferase (ALT), low-density lipoprotein, and intestinal crypt depth of all feed restriction groups were significantly reduced (P < 0.01). Feed conversion ratio in group D was significantly better than that in groups B and C (P < 0.05). The efficiency index (EI) of groups C and D was higher than that of groups A and B (P < 0.01). Triglyceride levels in groups C and D were significantly lower than those in group A. The villus length to crypt depth of the duodenum and jejunum in group D was significantly higher than that in group A (P < 0.01). In conclusion, the following parameters can be improved by feed restriction: feed conversion ratio, diarrhea rate, abdominal fat rate, serum ALT, lipid indices and intestinal health of Minxinan black rabbits, and the EI of the farm. Feeding twice per day, 30% at 8:00 am and 70% at 4:00 pm, had the best comprehensive effects.

Pathogenic and genomic characterisation of a rabbit sourced Pasteurella multocida serogroup F isolate s4.

BACKGROUND: Pasteurella multocida is one of the most significant pathogens for a number of animals. In rabbits, the infection is generally associated with the P. multocida serogroups A and D, and the knowledge about the serogroup F is limited. In the present study, a P. multocida serogroup F isolate designated s4 was recovered from the lungs of rabbits died of respiratory disease in Fujian, in the southeast of China. The pathogenicity and genomic features of the s4 were then determined. RESULTS: The serotype and sequence type of s4 were F:L3 and ST12, respectively. The s4 was pathogenic for rabbits, but it was a low virulent strain comparing to the previously reported highly pathogenic P. multocida serogroup F strains J-4103, C21724H3km7, P-4218 and HN07. The whole genome of the s4 was then sequenced to understand the genomic basis for pathogenicity. Particularly, a large-sized fragment of approximate 275 kb in length was truncated from the chromosome to form a plasmid. Moreover, the in-frame deletion of natC and N-terminal redundance of gatF would resulted in the production of a mutant L3 outer core structure that was distinct from those of the other P. multocida strains belonging to the lipopolysaccharide genotype L3. We deduced that these features detected in the genome of s4 might impair the pathogenicity of the bacterium. CONCLUSIONS: This study evaluated the pathogenicity and determined the genomic features of the rabbit sourced P. multocida serogroup F isolate s4, the observations and findings would helpful for the understanding of the pathogenicity variability and genetic diversity of P. multocida.

Characterization of Pasteurella multocida isolated from dead rabbits with respiratory disease in Fujian, China.

BACKGROUND: Pasteurella multocida is one of the important pathogens that infect rabbits, causing major economic losses in commercial rabbit farming. In this study, 205 P. multocida isolates recovered from lungs of dead rabbits with respiratory disease were defined by capsular serogroups, lipopolysaccharide (LPS) genotypes, multi-locus sequence types and screened virulence factors by using PCR assays, and tested antimicrobial susceptibility. RESULTS: The 205 isolates were assigned into 2 capsular types, A and D, and 2 LPS genotypes, L3 and L6. When combining capsular types with LPS genotypes, 4 serotypes were detected. A:L3 (51.22%, 105/205) was the most predominant serotype, followed by A:L6 (24.88%, 51/205), D:L6 (19.02%, 39/205) and D:L3 (4.88%, 10/205). The 205 isolates were grouped into 3 sequence types, ST10, ST11 and ST12. ST12 (56.10%, 115/205) was the most prevalent sequence type, followed by ST10 (24.88%, 51/205) and ST11 (19.02%, 39/205). In the 205 isolates, virulence associated genes ptfA, fur, hgbB, ompA, ompH and oma87 were positive in the PCR screening, whereas the toxA and tbpA genes were negative. Notably, the 156 capsular serogroup A isolates carried the pmHAS gene. All the 205 isolates were susceptible to most of the used antibiotics, except for streptomycin, gentamycin, kanamycin and ceftriaxone, and the resistance rates of which were 27.80, 15.61, 9.27 and 2.44%, respectively. CONCLUSIONS: This study, for the first time, described the prevalence and characteristics of P. multocida causing respiratory disease in rabbits in Fujian Province, which might be useful for tracking the epidemic strains and development of efficient vaccines and methods to prevent and control the pathogen.