Morphoquantitative evaluation of the heart of cutia ( Dasyprocta agouti ) and capybara ( Hydrochoerus hydrochaeris )

The cutia ( Dasyprocta agouti ) and capybara ( Hydrochoerus hydrochaeris ) are hystricomorphic rodents of the Brazilian fauna. The wild animal anatomy is essential to the clinic and surgery practices and conservation programs. This work aimed to evaluate the heart quantitative morphology of the cutia and the capybara. For this, three hearts of cutia and three of capybaras were used from the collection of the Anatomy Sector of Domestic and Wild Animals of the Faculty of Veterinary Medicine and Animal Science of the University of São Paulo. The hearts were weighted and measured with a pachymeter. The left ventricle volume was estimated through the Cavalieri method. The hearts’ mean weight was 16.76g (cutias) and 104.2g (capybaras). The mean values for the axis, width and base dimensions were of the cutia 4.3cm, 3.3cm and 3.3cm and for the capybara were 7.6cm, 6.0cm and 6.1cm, respectively. The mean volume of the left ventricle of the cutia and the capybara was 5.03cm 3 and 54.55cm 3 , respectively. The quantitative results of the hearts were compatible with the average body weight of the rodents. Thus, these numerical data can be applied to veterinary cardiology.

Several anatomical studies of wild animals have already been described in the scientific literature, however, there are few involving the quantitative morphology of the heart of these rodents. Such research, in addition to contributing to the collection of species, facilitate breeding for commercial purposes, clinical-surgical practice and conservation programs (Aversi et al., 2005). In this context, quantitative anatomy or morphometry consists of measuring anatomical structures for comparative purposes and describing the physiological or pathological state of an organ (Phalen et al., 1978). The heart is the main organ in the circulatory system (Konig and Liebich, 2011), and the estimation of its ventricular volume in healthy animals can establish reference values for the diagnosis of cardiomyopathies such as dilated cardiomyopathy and ventricle hypertrophy (Werner et al., 2001).
Thus, given the scarcity of scientific work on the cardiac morphology of wild rodents and the need for anatomical knowledge for medical, surgical, commercial and conservation applications, the objective of this work was to describe the morphology of cutia and capybara hearts under the quantitative aspect.

MATERIAL AND METHODS
Three cutia hearts and three adult capybara hearts, male and female, from the collection of the Sector of Anatomy of Domestic and Wild Animals of the Faculty of Veterinary Medicine and Zootechnics of the University of São Paulo were used (FMVZ-USP), fixated with a 10% formaldehyde solution at (Neon Comercial Ltda, São Paulo -SP). To obtain morphometric data, hearts were weighed (g) on a precision semi-analytical scale (Mettler Toledo Indústria e Comércio Ltda, Barueri -SP) and measured with the aid of Pachymeter (Mitutoyo Sul Americana, Suzano -SP) as for the length of the vertical axis (determined in cm by the distance between the apex and base of the organ), width (latero-lateral in cm from the organ) and width of the base (diameter of the cardiac base in cm).
The Cavalieri method was used to estimate the volume of left ventricles (Gundersen et al., 1999;Tinajero-Bravo et al., 2014); thus, the hearts were cross-sectioned into small serial fragments of approximately 0.6cm in cutias and 1.0cm in capybaras and subsequently photographed with a digital camera (Canon ® EOS 400D coupled with digital Sigma lens 1:100 macro). The digitalized photographic images were randomly superimposed on a system of points spaced at regular intervals (point counting), counting the points that hit the left ventricle ( Fig.1) and subsequently applied the following formula: V(VE) = p x a(p) x t V: left ventricular volume (VE) p: sum of points that touch the VE a(p): area by point t: cut thickness: 0.6cm (cutia) and 1.0cm (capybara) For the naming of the anatomical structures, the terminologies recommended in Nomina Anatomic Veterinary (2012) were used as standard.

RESULTS
The individual results and the average of the morphometric parameters of the hearts of the cutias and capybaras are shown in Table1 and the mean of the volume of the left ventricle of the hearts are shown in Table 2.

DISCUSSION
Morpho-quantitative data on the heart of cutias and capybaras are still scarce in the literature, which makes the discussion restricted. Thus, the current work aimed to contribute to the formation of reference parameters for the macroscopic assessment of cardiac normality in these rodents. Studies involving cardiac morphology, under the quantitative aspect, were carried out in dogs (Werner et al., 2001), marmosets (Senos et al., 2014), goats (Silva et al., 2016), rats (Engelmann et al., 1987) and equine (Leite et al., 2004), facilitating early assessments of cardiomyopathies that manifest with changes in the dimensions and weight of the heart (Werner et al., 2001). Still, in rats and mice, morphometry was used to investigate the consequences of arterial hypertension in the development of left ventricular hypertrophy (Engelmann et al., 1987;Schipke et al., 2016).
In accordance with other rodents such as paca (Ávila et al., 2010), rat and mouse, the hearts of cutias and capybaras in the current study were elongated cone shaped, consisting of two atria and two right and left ventricles (tetracavitary) easily distinguishable; furthermore, similarity with that described in the literature in relation to domestic animals (Ciszek et al., 2007;Ávila et al., 2010;Dyce et al., 2010;Konig and Liebich, 2011;Silva et al., 2016), Pantanal alligators (Alves et al., 2016) and swine (Lelovas et al., 2014), especially as to the thickness of the left ventricular wall compared to the right.
In the present study, the mean heart weight of cutias and capybaras was 16.7g and 104.2g, respectively, equivalent to 0.2% of body weight in both species. On the other hand, in dogs, this percentage varied from 0.9 to 2.2%, although in this species this increase may occur due to variables such as physical training in athletes and game animals, obesity and physical inactivity (Ghoshal, 1986). Regarding the morphometric parameters, it was observed that the mean value of the apex-base axis and the width of the cutia heart corroborated with the descriptions by Ávila et al. (2010) when investigating the pacas. This similarity is probably related to the proximity of body weight between the two rodents. Conversely, in the capybara, these values were higher, possibly due to the greater body weight when compared to that of cutia and paca. . Med. Vet. Zootec., v.72, n.5, p.1737-1741, 2020 In dogs, as cardiac morphometric differences in relation to genders were not used by Bienvenu and Drolet (1991), in accordance with what was observed in the cutias and capybaras of this study. As for the volume of the left ventricle, the cutia had an average value of 9.54cm 3 and the capybara was 54.45cm 3 . In goats, the mean value found by Silva et al. (2016) was 25.85cm 3 and, in humans, 160cm 3 for men and 123cm 3 for women, both with an average body weight of 67 kg (Tang et al., 2009). Based on the findings of Tang et al. (2009) it is suggested that the ventricular volume may vary with the individual's gender; however, in this study, this variable could not be evaluated due to the lack of knowledge of the animals' sex.

Arq. Bras
In view of the applied methodology and the results obtained, it is assumed that the quantitative values of the heart are compatible with the average body weight of cutia and capybara, regardless of gender, as well as the average ventricular volume with the average weight of the organ, in both rodents. In this way, the estimation of twodimensional and three-dimensional measurements of the heart of wild rodents, using quantitative morphology tools, can be applied to veterinary physiology and cardiology.  Sci. Vet., v.38, p.191-195, 2010. BIENVENU, J.G.; DROLET, R. A quantitative study of cardiac ventricular mass in dogs. Can. J. Vet. Res., v.55, p.305-309, 1991.  Res., v.60, p.487-494, 1987.