Grouping has been widely accepted as a mechanism for protection from predation. Just as has been apparent with predation, there is now ample evidence that parasites (biting flies, warble flies and parasitoids) can impact an animal's individual fitness. Some aspects of grouping, namely an encounter-dilution effect and the selfish herd effect, appear to apply as much to protection of animals from flying parasites as protection from predators. The encounter-dilution effect provides protection when the probability of detection of a group does not increase in proportion to an increase in group size (the encounter effect), provided that the parasites do not offset the encounter effect by attacking more members of the group (the dilution effect). The selfish herd effect provides protection from flying parasites to animals that are in the center of a group or more closely placed to other animals. Most of the quantitative evidence for the protection from flying parasites from grouping comes from studies on ungulates. Further investigation of these effects among a variety of taxa is needed for a full appreciation of the role of parasites in animal grouping and sociality.

In contrast to European countries, the overwhelming majority of dogs in the U.S. are neutered (including spaying), usually done before one year of age. Given the importance of gonadal hormones in growth and development, this cultural contrast invites an analysis of the multiple organ systems that may be adversely affected by neutering. Using a single breed-specific dataset, the objective was to examine the variables of gender and age at the time of neutering versus leaving dogs gonadally intact, on all diseases occurring with sufficient frequency for statistical analyses. Given its popularity and vulnerability to various cancers and joint disorders, the Golden Retriever was chosen for this study. Veterinary hospital records of 759 client-owned, intact and neutered female and male dogs, 1–8 years old, were examined for diagnoses of hip dysplasia (HD), cranial cruciate ligament tear (CCL), lymphosarcoma (LSA), hemangiosarcoma (HSA), and mast cell tumor (MCT). Patients were classified as intact, or neutered early (<12 mo) or late (≥12 mo). Statistical analyses involved survival analyses and incidence rate comparisons. Outcomes at the 5 percent level of significance are reported. Of early-neutered males, 10 percent were diagnosed with HD, double the occurrence in intact males. There were no cases of CCL diagnosed in intact males or females, but in early-neutered males and females the occurrences were 5 percent and 8 percent, respectively. Almost 10 percent of early-neutered males were diagnosed with LSA, 3 times more than intact males. The percentage of HSA cases in late-neutered females (about 8 percent) was 4 times more than intact and early-neutered females. There were no cases of MCT in intact females, but the occurrence was nearly 6 percent in late-neutered females. The results have health implications for Golden Retriever companion and service dogs, and for oncologists using dogs as models of cancers that occur in humans.

Objective—To determine the prevalence of age-related behavioral changes, namely impairment, in a randomly chosen population of dogs. Design—Age-stratified cohort study. Animals—97 spayed female and 83 castrated male dogs that were 11 to 16 years old. Procedure—Data on possible impairment in 4 behavioral categories (ie, orientation in the home and yard, social interaction, house training, and sleep-wake cycle) linked to cognitive dysfunction were obtained from dog owners, using a structured telephone interview. Hospital records of dogs had been screened to exclude dogs with dysfunction in organ systems that may cause behavioral changes. Dogs with behavioral impairment were those with ≥ 2 signs of dysfunction within a category. Dogs with impairment in 1 category were considered mildly impaired and those with impairment in ≥ 2 categories were considered severely impaired. Results—Age by sex interactions for dogs with impairment in any category were not significant, and, therefore, data on castrated males and spayed females were pooled for analyses across ages. The prevalence of age-related progressive impairment was significant in all categories. The percentage of 11- to 12-year-old dogs with impairment in ≥ 1 category was 28% (22/80), of which 10% (8/80) had impairment in ≥ 2 behavioral categories. Of 15- to 16- year-old dogs, 68% (23/34) had impairment in ≥ 1 category, of which 35% (12/34) had impairments in ≥ 2 categories. There were no significant effects of body weight on the prevalence of signs of dysfunction in the behavioral categories. Conclusions and Clinical Relevance—Data collected provide estimates of the prevalence of various degrees of age-related behavioral changes associated with cognitive dysfunction in dogs. Age-related behavioral changes may be useful indicators for medical intervention for dogs with signs of cognitive impairment. (J Am Vet Med Assoc 2001;218:1787–1791)