Final answer:
Biological assessments and observational methods can help determine if an animal is infested with diseases or parasites and assess its reproductive health, despite potential phenotypic differences that may be misleading.
Step-by-step explanation:
To determine if an animal is infested with disease or parasites, or to assess its reproductive soundness, various biological methods and tools can be used. For instance, the presence of extrachromosomal genes can be detected using fluorescence in situ hybridization (FISH), while reproductive capability might be assessed by evaluating specific indicators such as the percentage of ovigerous (egg-bearing) individuals within a species. Observational and experimental techniques, like the mark and recapture method, can be employed for determining mortality rates and population densities which are indicators of species health, especially during the critical developmental period before sexual maturity.
Despite phenotypic differences, such as size, build, and coat, many species like domestic dogs (Canis lupus familiaris) can interbreed and produce viable offspring. This underscores the fact that external appearance can sometimes be misleading in determining an animal's health or reproductive status. Health of animals is a relative term and encompasses their ability to perform optimally in various biological and ecological tasks including mating and raising young.