An accurate parturition timing is of key importance for breeders and veterinarians in order to give professional assistance to parturition in dogs. However, pregnancy length calculated from the breeding date has a wide variability. Different parameters and formulas have been described and calculated, as well as their accuracy which is affected by various factors: stage of pregnancy, litter and maternal size. Therefore, the selection of the most appropriate parameter panel poses the challenge of weighing their influences and impact on the overall accuracy. The aim of this review is to analyze the parameters useful for parturition timing, especially their accuracy, and to propose the addition of fetal maturity and criteria for its evaluation to detect readiness for parturition. Parameters, as described in literature, are classified as: (i) maternal parameters, (ii) fetal parameters, (iii) ultrasonographic assessment of maternal and fetal heart rate and blood flow, (iv) parameters indicating fetal maturity. A focus on recently described parameters—such as fetal gastrointestinal motility and fetal lung development detected by quantitative ultrasound—is reported. Currently, the most accurate way to predict parturition day is represented by a prepartum progesterone drop, but the identification of a panel of ultrasonographic parameters combining their significance and their accuracy throughout pregnancy is still needed.

Fetal gastrointestinal motility (FGM) was suggested as useful to assess fetal maturity. Our study aimed to quantify FGM in relation to days before parturition (DBP), maternal size, and sex ratio of pups. During the last ten days of pregnancy, 23 clinically healthy pregnant bitches of 16 different breeds ranging in age from 2 to 9 years and body weight from 3.5 to 56.8 kg were monitored twice. The fetal intestine was observed in longitudinal and transversal scan on 3 of the most caudal fetuses in both uterine horns. Gestational age was counted backward from parturition day. The number of fetuses showing FGM was recorded in time in I (−11/−5 DBP) and II (−4/0 DBP). A Mann–Whitney test was performed to analyze variations of FGM% in relation to time and parity. A Kruskal–Wallis test was performed to identify variations of FGM% in relation to maternal size and sex ratio. Statistical significance was set at α = 0.05. A total of 147 FGM observations on 50 ultrasonographic monitoring points were performed. The FGM% was higher during time II compared to time I (median: 33%, range 0–100% vs. 100%, range 33–100%;P< 0.0001). FGM% was higher in small compared to large size bitches (median: 100%, range 67–100% vs. 67%, range 0–100%;P= 0.01). FGM% was not affected by parity and sex ratio. As previously reported, a significant increase in FGM% was observed in the last five DBP. FGM observation may be influenced by the maternal size, with easier evaluation in small size bitches, as well as ultrasound equipment and positioning.

ProAKAP4 is a sperm structural protein involved in motility, capacitation, and fertility. Previous studies suggested it as a suitable marker for canine sperm evaluation. Our study aimed to assess proAKAP4 concentration variations among different ejaculates collected from the same dogs. Fourteen male dogs from 12 different breeds, 1–14 years old and 6.9–95 kg bodyweight, underwent semen collection at least twice (1–4 times) during the same or different days. Sperm concentration, morphology, proAKAP4 concentration, total (TM%), and progressive motility (PM%) were considered. ProAKAP4 values were divided into four classes: ≤15, 15–40, 40–60, and >60 ng/10 M spermatozoa. The time interval between two semen collections was classified as: first collection (T0), semen collection performed 2–3 h after the first one (T0.5) and after ≥1 day (1–36 days, T1). Thirty-three ejaculates were collected. A correlation was found between proAKAP4 classes and TM% (r = 0.40, p = 0.049), whereas no correlation was found neither between proAKAP4 and sperm morphology nor for proAKAP4 classes between collection times (T0 vs. T0.5, p = 0.655; T0 vs. T1, p = 0.564). Our results confirm the correlation between proAKAP4 and TM% in dog semen. ProAKAP4 concentration appears stable in different ejaculates collected from the same dogs. Further studies are needed on the relationship between proAKAP4 and other canine semen parameters and fertility outcomes.

The objective of this study was to assess changes in the echogenicity of the cortex and medulla of canine fetal kidneys in relation to days before parturition (dbp), maternal size and litter size. Monitoring of 10 healthy pregnant bitches (2–8 years old, 8.8–40.3 kg bw) was conducted from −10 to 0 dbp using ultrasound. A single renal sonogram was obtained by scanning in a longitudinal section the three most caudal fetuses. The mean gray level (MGL) and SD of a manually drawn region of interest (ROI) in the renal cortex and medulla were measured using the Fiji Image J software (Image J 1.51h, Java 1.6 0_24 64 bit). A linear mixed model taking into account the maternal size as a fixed effect, dbp and litter size as covariates and the bitch as a random and repeated effect was used. The regression coefficients (b) were estimated. Cortical SD (C-SD) and cortico-medullary SD (C/M-SD) were influenced by dbp, with a significant decrease at the approaching day of parturition (b = 0.23 ± 0.06, p < 0.001 and b = 0.5 ± 0.02, p = 0.038, respectively). Maternal size had a significant impact on C/M-MGL with differences observed in large-sized (1.95 ± 0.13) compared to small- (1.41 ± 0.10, p = 0.027) and medium-sized bitches (1.51 ± 0.09, p = 0.016). The C/M-MGL was influenced by litter size, showing a decrease as the number of pups increased (b = −0.08 ± 0.03, p = 0.018). C-SD and C/M-SD were exclusively affected by dbp, and not by maternal and litter size. This suggests their potential as valuable parameters, warranting further investigations in future studies.