Abstract
Due to the peculiarities of the reproductive cycle of the female dog, which makes it difficult to accurately ascertain the date of conception, it may be challenging to precisely estimate the gestational age in bitches. Using fetal measurements obtained by ultrasound, it is possible to estimate the gestational age in dogs; however, due to the differences in size of the various breeds, such estimates may have a significant standard deviation, which represents less accuracy when specifying the date of birth. The purpose of this study was to evaluate pregnant female Chihuahuas, establishing relations between the fetal dimensions measured by ultrasound and the remaining time until delivery. Using 13 pregnant female Chihuahuas, weekly ultrasound assessments and measurements were performed, of the inner chorionic cavity, cranial-caudal length, biparietal diameter, abdominal diameter and thoracic diameter. Such parameters were retroactively correlated to the date of delivery, and linear regressions were established between the gestational measurements and remaining days until delivery. The fetal measurement presenting the highest correlation (r = 0.99; P<0.0001) and reliability (R2 = 0.98, P<0.0001) with the probable date of delivery was the biparietal diameter, a measurement that can be easily and safely obtained and, when applying a specific formula (Y = -15.46X1 + 38.72), can accurately predict the date of delivery in Chihuahua female dogs.
Highlights
The time elapsed from the date of mating does not necessarily coincide with the gestational time
To perform the obstetric ultrasound exam, the dogs were positioned and restrained in dorsal decubitus on a padded surface specific for the purpose, without sedation, and the females were prepared with abdominal trichotomy from the xiphoid cartilage to the pubis, extending laterally to the renal region
The size of the litters ranged from 1-7 puppies, with an average of 3.2 offspring per female
Summary
The time elapsed from the date of mating does not necessarily coincide with the gestational time. This is due to the long period of sexual receptivity of the female bitch, such that the bitch may stand to be bred either long before of well after ovulation occurs. Parturition occurs 65 ± 1 days after LH peak and 63 ± 1 days after ovulation (Concannon et al, 1983).
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