Ultrasonographic parameters of fetal well-being and development in alpacas

In this study, a database of fetal and maternal parameters was developed in pregnant alpacas from 120 days of gestation to term for evaluation of fetal well-being and development. Ten pregnancies were examined every 2 weeks from 120 to 300 days of gestation, then weekly until parturition. Five more pregnancies were evaluated weekly during the last 4 weeks prepartum. Maternal weight and heart rate were recorded. Indicators of fetal well-being (mean, minimum, and maximum fetal heart rate, fetal movement, and tone), development (size of the aorta, thorax, abdomen, stomach, kidney, head, eye orbit, radius, and umbilical vessels), and uterine environment (combined thickness of the uterus and placenta, depth and character of allantoic and amnionic fluids) were assessed using transabdominal ultrasound. Reference values and fetal growth curves were created. Weights of the cria, fetal membranes, and dam at parturition were associated with parameters of fetal growth. Mean (R(2) = 0.65), minimum (R(2) = 0.57), and maximum (R(2) = 0.64) fetal heart rate decreased from midgestation to term (P < 0.0001). Fetal activity also decreased as pregnancy advanced (P < 0.0001). Fetal presentation was anterior in all fetuses by 10 months. Increases in depth of allantoic (R(2) = 0.11) and amniotic (R(2) = 0.02) fluid, combined thickness of the uterus and placenta (R(2) = 0.31), and maternal weight (R(2) = 0.09) were significantly but poorly associated with gestation length. All parameters of fetal development were positively associated with gestational age (P < 0.0001). Size of the aorta (R(2) = 0.88), abdomen (R(2) = 0.87), kidney (R(2) = 0.83), and thorax (R(2) = 0.82) provided the best estimates of gestational age. Birth weight was associated with the size of the aorta (R(2) = 0.71), kidney (R(2) = 0.61), and radius (R(2) = 0.73) (P < 0.05). This information might be of value in the assessment of fetal well-being and development in alpacas.