Embryonic and fetal development of the red brocket deer (Mazama americana)

The red brocket deer (Mazama americana), a medium-sized Neotropical ungulate, is one of the most hunted mammals in the Amazon. This study analyzes the intrauterine development in the red brocket deer through the description of the external and internal morphology in one embryo and 38 fetuses collected from animals hunted for subsistence in the Amazon. The chronological order of occurrence of external characteristics in relation to the total dorsal length (TDL) was: differentiated genitalia, limbs and eyelid buds (TDL = 3.9 cm), fusioned eyelids, outer ear and hooves (TDL ≥ 9.5 cm), skin (TDL ≥ 20.4 cm), tactile pelage and nasal pigmentation (TDL ≥ 21.5 cm), covering pelage and skin spots (TDL ≥ 31.3 cm), and teeth eruption and opened eyelids (TDL ≥ 34.2 cm). The formula of fetal age was ∛W = 0.072 (t - 42), with a high linear relationship between TDL and gestational age. Multiple linear and non-linear regressions showed strong positive associations between biometric measures and absolute visceral weights with TDL. The relative weight of the tubular gastrointestinal organs, spleen and thymus increased during the fetal development; in contrast, the liver and kidneys' relative weight diminished during the fetal development. Advanced fetuses (≥44.0 cm TDL) had lower proportion of liver and larger tubular gastrointestinal organs within the visceral weight than adults. The chronology of appearance of the main events of the fetal development suggests that the red brocket deer adopt some precocial features, such as the early development of the sensorial function, including the early development of eyelids, outer ear and tactile pelage, the early development of the covering pelage which acts in thermoregulation and the early teeth eruption which allows the early foraging. Nevertheless, the precocial level of the red brocket deer is apparently lower than other species more frequently predated by large felids, such as peccaries and the paca.

Embryonic and fetal development of the white-lipped peccary (Tayassu pecari)

The white-lipped peccary (Tayassu pecari) is an endangered large-sized Neotropical ungulate that is one of the most hunted mammals in the Amazon. Here, we used two embryos and 102 white-lipped peccary fetuses originated from animals hunted for subsistence in the Peruvian and Brazilian Amazon to describe the intrauterine development of external and internal morphology of this Neotropical ungulate. Logistic regressions were used to estimate the probability of occurrence of main external characteristics in relation to the total dorsal length (TDL), while multiple linear and non-linear regressions were conducted to assess the relationship between external and visceral biometry with TDL. External characteristics appeared in the following chronological order: limbs, differentiated genitalia and opened eyelids (≥5.1 cm TDL), fused eyelids (≥6.2 cm TDL), hooves and outer ear (≥7.9 cm TDL), dorsal gland (≥9.4 cm TDL), skin (≥11.5 cm TDL); tactile pelage (≥13.8 cm TDL), covering pelage (≥20.9 cm TDL), tooth eruption (≥26.4 cm TDL) and opened eyelids (≥27.8 cm TDL). The formula of fetal age was ∛W = 0.084 (t - 31.80), with a high linear relationship between TDL and gestational age. All external biometric parameters and absolute volume of visceral organs showed strong positive relationship with TDL. Except for the liver, we found differences in the relative volume of most visceral organs between advanced fetuses (≥34.2 cm TDL) and adults. The most important events during the intrauterine development in the white-lipped peccary show that, in contrast with the domestic pig, it is a highly precocial species producing newborns with a high fetal growth velocity which allows newborns to achieve an early autonomous functionality. Our results are relevant to improve imaging techniques and assist the reproductive and clinical management for the white-lipped peccary both in captivity and in the wild.