SummaryHamartoma is a developmental disorder of various body parts and organs. It is characterized by a nonneoplastic growth of tissue with an uneven distribution and proportion of individual cells. Lesions progress for several years, but usually do not give clinical symptoms, and do not undergo malignant transformation. They occur alone or coexist with other defects, sometimes forming a characteristic clinical picture of a syndrome of congenital defects. Mutations in genes, such as PTEN, GLI3, SDH B/D, PIK3CA and ACT1, cause a dysfunction of the tumor suppressor gene and result in an increased neoplastic transformation. Hamartoma is a lesion between developmental disorders and benign tumors, which occurs frequently in humans, but is very rare in domestic animals. In a histopathological examination, however, it is diagnosed relatively often. In the veterinary literature, both hamartoma and choristoma are attributed mostly to errors in embryogenesis and are not considered as preneoplastic lesions.

Parasitological examinations and the investigation of polymorphism in locus DRB1, belonging to MHC class II, were conducted in a flock of Polish Heath Sheep in the years 1995-1998. The intensity of parasite infection of dams ranged from 0 to 24 000 eggs, whereas for lambs it reached up to 27 000 nematode eggs in 1 gram of faeces. In the years 1995-1997 nematode species dominant in the infection were//, contortus and T. colubriformis, while in 1998 the predominant was T. circumcincta. DNA analysis of the examined sheep showed the presence of 20 alleles in locus DRB1, established on the basis of the length of a fragment of this gene amplified using PCR (exon 2 and microsatellite in intron 2). The analysis of variance conducted for the FEC trait in genotypic groups showed a statistically significant (P<0.01) association between the genotype in locus DRB1 and number of nematode eggs in sheep faeces. The presence of a given DRB1 allele in the genotype of animals examined had significant effect on parasite resistance. Moreover, the significant association between the FEC value in allelic groups of paternal half-sibs and the segregation of paternal alleles was also significant (P<0.05).

Possible correlation between Toll-like receptor (TLR)-gene mutations and the susceptibility of the mammary gland to bacterial infections and also the associate breed-dependent aspects of somatic cell concentration (SCC), bacterial infection and TLR-gene mutations in sheep are described. In Polish Lowland Sheep (PLS), milk samples exceeding the level of 500/microL (i.e. 5 x 10(5) per mL) of SCC were recorded almost twice more frequently than in Polish Heath Sheep (PHS) (40 and 22.3%, respectively). The frequency of bacterial infections was also found in a similar ratio (20 and 12.7%, respectively). During detection of the TLR-gene mutation we recorded 2 alleles of TLR1, 6 alleles of TLR2 and 10 alleles of TLR4 genes in PHS sheep, while PLS sheep possessed 2, 4 and 6 alleles, respectively. Statistical analyses revealed a relationship between the specified TLR alleles, SCC and the frequency of incidence of bacterial inflammations of mammary gland. The data may serve as a benchmark for further study of TLR-gene mutation-dependent predisposition of mammary gland defensive cells to recognize the pathogen properly and initiate the immunological response, and may help in identifying one of the markers of natural resistance against sheep mastitis.

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Research on the impact of the European beaver population on the species composition of forest stands was conducted in Wigry National Park, situated in north-eastern Poland. The study was conducted in forest stands on a dystrophic lake of the ‘suchar’ type,� i.e. a dystrophic lake with high acidity and low species diversity of vegetation on its shores, on the banks of a river and a drainage ditch, and in a field environment. A ThermoPro TP8 thermal imaging camera with an uncooled microbolometer matrix of 384x288 pixels was used to confirm that the designated observation areas were inhabited by beavers. In each research area five transects four metres in width were established, where measurements were taken of five classes of trunk damage and two classes of trunk diameter. We examined the seasonal preferences of beavers in gnawing particular species of woody plants. An analysis was performed for each environment. The results indicate that after an average 15-year presence of beavers in the areas, which they inhabited rotationally, the percentage of healthy woody plants was 73.09%. Of the 17 species of woody plants, the ones most readily cut down by the beavers were grey willow (25.19%) and common hazel (32.36%). The analysis demonstrated that the rodents showed the greatest interest in plants with a trunk diameter of <10 cm (98.28%). The river and drainage ditch were the most exploited environments; here beavers cut down 40.27% and 42.70%, respectively, of the available woody plants.