Characterization of fetal growth by repeated ultrasound measurements in the wild guinea pig (Cavia aperea)

Abstract

Fetal growth during pregnancy has previously been studied in the domesticated guinea pig (Cavia aperea f. porcellus) after dissecting pregnant females, but there are no studies describing the fetal growth in their wild progenitor, the wild guinea pig (C aperea). In this study, 50 pregnancies of wild guinea pig sows were investigated using modern ultrasound technique. The two most common fetal growth parameters (biparietal diameter [BPD] and crown-rump-length [CRL]) and uterine position were measured. Data revealed similar fetal growth patterns in the wild guinea pig and domesticated guinea pig in the investigated gestation period, although they differ in reproductive milestones such as gestation length (average duration of pregnancy 68 days), average birth weight, and litter mass. In this study, pregnancy lasted on average 60.2 days with a variance of less than a day (0.96 days). The measured fetal growth parameters are strongly correlated with each (R = 0.91; P < 0.001) other and with gestational age (BPD regression equation y = 0.04x − 0.29; P < 0.001 and CRL regression equation y = 0.17x − 2.21; P < 0.01). Furthermore, fetuses in the most frequent uterine positions did not differ in their growth parameters and were not influenced by the mother ID. Our results imply that ultrasound measurement of a single fetal growth parameter is sufficient to reliably estimate gestational age in the wild guinea pig.

Introduction

The domesticated guinea pig (Cavia aperea f. porcellus) is a common model species for experimental research; however, only little is known about its wild progenitor, the wild guinea pig (C aperea).

Studies comparing domesticated form of a species and its wild progenitor are rare. However, understanding of the genesis of, for example, physiological, morphologic, or behavioral traits of domesticated species requires consideration of parallel patterns in their wild progenitors. These traits are highly likely to be affected by the process of domestication [1]. Künzl and Sachser [2] examined differences in endocrinological patterns between domesticated and wild guinea pigs and found varying values in the basal activity and physiological reactivity of their stress response. Because of their long gestation period and huge prenatal investment, wild and domesticated guinea pigs are used as model species for research of prenatal influences on postnatal morphologic, physiological, and behavioral development [3], [4], [5], [6]. It is known that the wild and domesticated forms differ in reproductive milestones such as gestation length, average birth weight, and litter mass [7], [8], [9], [10], [11]. However, studies on fetal growth during pregnancy were only conducted in C aperea f. porcellus by dissecting pregnant females at different stages of pregnancy [12], [13]. To our knowledge the report by Turner and Trudinger [14] is the only study in which ultrasonography was used to measure fetal growth parameters during pregnancy in domesticated guinea pigs. The technique allows a reliable estimation of gestational age in the living organism. A similar study in wild guinea pigs is lacking.

To characterize fetal growth in wild guinea pigs, we chose ultrasonography, a widely used imaging technique for pregnancy diagnosis and monitoring in human and veterinary medicine. Following the lead of Turner and Trudinger [14], we conducted longitudinal in vivo measurements of the biparietal diameter (BPD). Additionally, we also determined the second most common growth parameter in prenatal diagnosis, the crown-rump-length (CRL).

The aim of this study was to characterize and evaluate fetal growth parameters in wild guinea pigs measured by ultrasonography as a mean of estimating gestational age. To that end, we correlated the two most commonly used fetal growth parameters and determined their relationship to gestational age. Furthermore, we compared our results to those reported for the domesticated guinea pig. Because of their relativly large abdomen, expansion of the fetuses is considerable and thus the field required to prepare for ultrasound measurements is large. With the knowledge that either BPD or CRL measures are sufficient for gestational age estimation, the procedure can be simplified and shortened, and consequently reduce the stress cause to animal.