Genetic structure and diversity among sheep breeds in the United States: identification of the major gene pools

Understanding existing levels of genetic diversity of sheep breeds facilitates in situ and ex situ conservation activities. A comprehensive evaluation of US sheep breeds has not been previously performed; therefore, we evaluated the genetic diversity among and within 28 US sheep breeds. Both major and minor breeds were included in the analysis and consisted of 666 animals from 222 producers located in 38 states. The level of within-breed genetic diversity was variable and not dependent upon status of a breed as a major or minor breed. Bayesian cluster analysis indicated the breeds were grouped more by physiological differences (meat vs. wool production) rather than geographic origin. Results suggest several actionable items to improve in situ and ex situ conservation. The results clearly identify breeds in need of increased in situ and ex situ management (e.g., Hog Island and Karakul) and allow several suggestions for in situ management of flocks. Conversely, several of the breeds appear genetically similar and therefore require less emphasis on collecting germplasm samples for the gene bank. Commercially important breeds (e.g., Rambouillet and Suffolk) were found to have substantial variation, which should enable breeders to proceed, unencumbered by genetic diversity concerns, with selection strategies that maximize profit.     

Evidence‐Based Medicine in Canine Reproduction: Quality of Current Available Literature

The objective of this study was to evaluate the quality of published literature on reproduction in dogs. A systematic search in online databases revealed 287 papers that met the inclusion criteria. For evaluation a questionnaire comprising 40 criteria regarding materials and methodology, study design, statistics, presentation and information content, applicability and conclusions was developed. In a pre‐test including seven independent scientists the applicability and explanatory power of the questionnaire and its results were validated. Out of 287 publications evaluated, 90 (31.4%) were classified as clinical trials. The remaining 197 publications were case reports or contained information based on personal experience. Not a single meta‐analysis was found. Sixty (66.7%) of the 90 clinical trials included a control group. Randomization was conducted in 23 and blinding in eight articles respectively. In total five articles were determined as randomized, controlled and blinded clinical trials. Information content of the publications was variable concerning details on included animals, type or dosage of used remedies or conducted interventions. For example, in 99.7% of the articles, the exact number of animals was given, but in 79.8%, housing and feeding of the animals were not described. Statistical procedures of clinical trials were determined adequate in 55.6%. However, the data of 67.9% of the articles were evaluated to be not sufficient to draw valid conclusions. This study revealed evidence of deficits in the field of canine reproduction. The demand for more high quality clinical research is obvious. Requisite for the further implementation of the evidence‐based veterinary medicine is an improvement of the quantity and the quality of well‐designed, conducted and reported clinical trials. The practitioner should always assess the quality of information before implementing results into practice to provide best available care for the animals.     

Cleaving yeast and Escherichia coli genomes at a single site

The 15-megabase pair Saccharomyces cerevisiae and the 4.7-megabase pair Escherichia coli genomes were completely cleaved at a single predetermined site by means of the Achilles' heel cleavage (AC) procedure. The symmetric lac operator (lacOs) was introduced into the circular Escherichia coli genome and into one of the 16 yeast chromosomes. Intact chromosomes from the resulting strains were prepared in agarose microbeads and methylated with Hha I (5'-GCGC) methyltransferase (M.Hha I) in the presence of lac repressor (LacI). All Hae II sites (5'-[sequence: see text]) with the exception of the one in lacOs, which was protected by LacI, were modified and thus no longer recognized by Hae II. After inactivation of M.Hha I and LacI, Hae II was used to completely cleave the chromosomes specifically at the inserted lacOs. These experiments demonstrate the feasibility of using the AC approach to efficiently extend the specificity of naturally occurring restriction enzymes and create new tools for the mapping and precise molecular dissection of multimegabase genomes.     

Scale-dependent habitat use in three species of prairie wetland birds

We evaluated the influence of scale on habitat use for three wetland-obligate bird species with divergent life history characteristics and possible scale-dependent criteria for nesting and foraging in South Dakota, USA. A stratified, two-stage cluster sample was used to randomly select survey wetlands within strata defined by region, wetland density, and wetland surface area. We used 18-m (0.1 ha) fixed radius circular-plots to survey birds in 412 semipermanent wetlands during the summers of 1995 and 1996. Variation in habitat use by pied-billed grebes (Podilymbus podiceps) and yellow-headed blackbirds (Xanthocephalus xanthocephalus), two sedentary species that rarely exploit resources outside the vicinity of nest wetlands, was explained solely by within-patch variation. Yellow-headed blackbirds were a cosmopolitan species that commonly nested in small wetlands, whereas pied-billed grebes were an area-sensitive species that used larger wetlands regardless of landscape pattern. Area requirements for black terns (Chlidonias niger), a vagile species that typically forages up to 4 km away from the nest wetland, fluctuated in response to landscape structure. Black tern area requirements were small (6.5 ha) in heterogeneous landscapes compared to those in homogeneous landscapes (15.4–32.6 ha). Low wetland density landscapes composed of small wetlands, where few nesting wetlands occurred and potential food sources were spread over large distances, were not widely used by black terns. Landscape-level measurements related to black tern occurrence extended past relationships between wetlands into the surrounding matrix. Black terns were more likely to occur in landscapes where grasslands had not been tilled for agricultural production. Our findings represent empirical evidence that characteristics of entire landscapes, rather than individual patches, must be quantified to assess habitat suitability for wide-ranging species that use resources over large areas.