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Capybaras (Hydrochoerus hydrochaeris) are the world's largest rodent. Owing to its uniqueness, 50 AZA institutions in North America display this species. As shown by a survey, no standard anesthetic protocol has been developed for this species. As a part of an ongoing behavioral study in Venezuela, capybaras were surgically implanted with radio transmitters. Animals were randomly assigned to one of the three immobilization protocols: (1) Tiletamine HCl/Zolazepam HCl, (2) Tiletamine HCl/Zolazepam HCl/Medetomidine HCl, and (3) Tiletamine HCl/Zolazepam HCl/Medetomidine HCl/Butorphanol tartrate. The protocol recommended for minimally invasive procedures when inhalant anesthetics are unavailable is a combination of Tiletamine HCl/Zolazepam HCl/Medetomidine HCl/Butorphanol tartrate. This is based on ease of administration, volume, onset of action, depth of anesthetic achieved, reversibility, safety, and costs.

The capybara (Hydrochoerus hydrochaeris), the largest living rodent, probably has a “mucus‐trap” colonic separation mechanism. To test this hypothesis, we measured the mean retention time of a solute marker (MRTSolute), 2 mm (MRT2 mm), 10 mm (MRT10 mm), and 20 mm (MRT20 mm) particle markers and nutrient digestibility in adult captive capybaras (27–52 kg body mass (BM), 2–11 yr). In addition, total gut fill and the selectivity factor (MRTSolute/MRT2 mm) were calculated, and mean faecal particle size and metabolic fecal nitrogen of captive capybaras were compared to those of free‐ranging specimens. Finally, we also measured methane production in one animal. The MRT2 mm (29.2 ± 8.2 hr) was different (p < 0.01) from MRTSolute (37.0 ± 13.1 hr), MRT10 mm (36.5 ± 8.2 hr), and MRT20 mm (35.1 ± 9.6 hr). The selectivity factor (1.26 ± 0.30) was in the range considered typical for a “mucus‐trap” colonic separation mechanism. The estimated total gut fill was 1.50 ± 0.37% and 1.73 ± 0.25% of BM calculated from the results of the 2‐mm and 10‐mm particle markers, respectively. The CH4 emission was 13.7 L/day. Captive capybaras had greater mean fecal particle size (0.44 ± 0.06 vs. 0.29 ± 0.05 mm, p < 0.001) and metabolic fecal nitrogen (65.5 ± 3.91 vs. 46.8 ± 10.5% of fecal nitrogen, p < 0.001) than free‐ranging capybaras. Organic matter digestibility decreased less steeply with increasing dietary crude fiber content in capybaras as compared to published data from rabbits or guinea pigs. Accordingly, the digestive physiology of the capybara is characterized by a comparatively high fiber digestibility, with a “mucus‐trap” colonic separation mechanism, allowing capybaras to thrive on forage‐only diets.

No abstract

Abstract Capybaras, Hydrochoerus hydrochaeris (Rodentia: Caviidae: Hydrochoerinae), show a strict social hierarchy among males, wherein the top-ranking male gains preferential access to females. Despite minimal sexual size dimorphism, males have a prominent scent gland on their snouts that is greatly reduced in the females. Top-ranking males have a larger gland and mark more frequently than subordinate males. This species also shows a moderately complex courtship that seems to be modulated by female behavior. In this study, we evaluated several components of courtship, as well as the females’ interactions with males during and outside courtship, in relation to the hierarchy rank of males. We found that subordinate males engaged in longer courtships than top-ranking males. However, there was no difference in the number of mount attempts or the success rate of these mounts as a function of the social status of the male, despite the longer courtship performed by subordinate males in comparison to top-ranking males. Outside courtship, females directed the same number of social interactions to males regardless of status. However, during courtship, females avoided copulation by subordinate males both directly and indirectly by encouraging courtship disruption by higher-ranking males. Females’ avoidance of subordinates may force these males to invest a higher amount of effort in courtships, thus engaging in longer courtships, yet achieving similar mount success as top-ranking males. We show that the original assumption of male hierarchy as the main mechanism of reproductive distribution is incomplete, and female mate choice plays an important role in determining which males reproduce.