Estimation of gestational age in Shami goats based on transabdominal ultrasonographic measurements of fetal parameters

1. Pregnancy diagnosis and determination of the pregnancy age are very important for breeding of farm animals.
2. The pregnant females require special care and nutrition depending on the duration of pregnancy.
3. Determination of pregnancy age is important to predict the time of delivery to avoid the fetal loss due to dystocia.
4. Ultrasonography is a reliable method for estimation of pregnancy age.
5. Very limited studies have been conducted to estimate the age of pregnancy in Shami goats.

Introduction

Shami goats, also known as Damascus goats, are a native breed of Syria and other nearby countries. Shami goats are one of the vital farm animals that are bred primarily for milk and meat production. They are characterized by high milk production and a high rate of twines (1). Pregnancy diagnosis and determination of the pregnancy age are crucial for breeding farm animals since pregnant females require special care and nutrition, which varies depending on the duration of pregnancy. Another importance of the determination of the age of pregnancy is to predict the delivery time to avoid problems that occur during the parturition and thus reduce the fetal loss due to dystocia (2). The age of pregnancy in farm animals is estimated depending on the time of insemination, which is considered the zero-day of pregnancy (3). This method is more accurate than other methods to determine the age of the pregnancy. However, the method adopted for bred of goats remains rudimentary in many countries, including Iraq, since it does not adopt the recording system and record the date of insemination. Therefore, determining pregnancy age in such animals requires a reliable method to obtain accurate results. Currently, ultrasound imaging technology is considered a reliable method with high success in diagnosing pregnancy. This method provided the possibility of monitoring the uterus and fetus at different periods of pregnancy and obtaining the uterine and fetal measurements (4). Several studies have adopted ultrasonography to estimate the pregnancy age in different breeds of goats. These measurements include; uterine diameter, crown-rump length, fetal head diameter, trunk diameter, measuring the dimensions of the heart, and diameter of the umbilical cord (5-11). In Iraq, minimal studies have adopted ultrasonography to determine pregnancy age in local Iraqi goats (12,13), and only one study was carried out to detect the single and multiple pregnancies according to the ultrasonographic measurement of placentomes in Shami goats (14). There is no study conducted to estimate pregnancy age in Shami goats.

The study aimed to estimate gestational age of Shami does by transabdominal ultrasonographic measurement of fetal and maternal parameters.

Materials and methods

Animals

This study was performed in Sardasht village located in Erbil city northern Iraq. Thirty-three cyclic Shami does were used in this study. The age of does was 2-2.5 years, and they have 1-2 previous pregnancies. The animals are kept in one farm under the same management, environment, and feeding system. All does were labeled to enhance recording and measurements. 

Estrus was synchronized using a polyurethane vaginal sponge soaked with 60 mg of Medroxyprogesterone acetate/sponge (Esponjavet^©, Laboratorios Hipra, S.A., Spain) for 14 days. After 14 days, the sponges were removed, and 500 IU of serum gonadotrophin (PMSG) (Oviser^©, Laboratorios Hipra, S.A., Spain) was injected intramuscularly. Estrus was detected within 72 hours. All does were mated at least one time with fertile males. The date of first mating was considered the first day of gestation.

Ultrasonography

Transabdominal ultrasonography was performed according to the previously described method in goats and sheep without fasting or shaving (7). The does were examined in standing position using a real-time ultrasound scanner ECM- iMAGO (iMAGo, ECM, France) fitted with a 3.5 MHz convex array transducer. Ultrasound transmission gel was used as a coupling medium. The probe was applied to the hairless area immediately cranial to the udder (15).

The does were examined weekly starting on 21 days of pregnancy until parturition. At each time of examination and for each doe, numerous ultrasonographic images of the fetus and uterus were obtained and recorded for later analysis and measurement.

Measurements of fetal and maternal parameters

The fetal ultrasonographic images were processed to obtain the measurements of the parameters using the software Screen Calipers (Version 4.0, ^©2006, Iconico, Inc., http://www.iconico.com/caliper/). The software was calibrated through an image of the ultrasonic device with known distances in millimeters (Figure 1). After that, the measurements of fetal parameters that include; the crown-rump length, head diameter, chest diameter, and trunk diameter (Figure 2-5) were recorded in millimeters (16). 

Figure 1: Calibration of the Screen Caliper software through an image of the ultrasonic device with known distances in millimeters.

Figure 2: Measurements of the fetal crown-rump length in pregnant Shami doe using the Screen Caliper software.

Figure 3: Measurements of the fetal head diameter in pregnant Shami doe using the Screen Caliper software.

Figure 4: Measurements of the fetal chest diameter in pregnant Shami doe using the Screen Caliper software.

Figure 5: Measurements of the fetal trunk diameter in pregnant Shami doe using the Screen Caliper software.

Data analysis

All measurements were in millimeters (mm). The values of all parameters were presented as mean + SE. The relationship between the gestational age and the studied parameters was plotted as an X-Y scatter chart with linear regression and expressed as straight-line equations using the Microsoft Excel application (Microsoft Office Professional Plus 2016). Simple regression equations were established, the gestational age was calculated according to the formula y=ax+b, where y = gestational age, a = predictors (constant), x = measured value, and b = dependent variable. The correlation coefficient between the gestational age and parameters was calculated using SigmaStat (Jandel scientific software V3.1). The results were considered significant if P < 0.05.

Results

Estrus synchronization and pregnancy diagnosis:

After injection of PMSG, all does exhibit estrus within 72 hours. All mated does were pregnant as confirmed at kidding. The first sign of pregnancy was the appearance of a gestational sac, which was circular or an elongated anechoic structure located in the uterus cranial to the bladder. At the same time, the embryos were observed as an area of high echogenic density located on the gestational sac (Figure 6). The gestational sac was detected first on day 21 of gestation, and the first time observation of the embryos was on 35 days of pregnancy. The litter size of pregnant does range between two and three kids.

Figure 6: Ultrasonic image of pregnant Shami doe showing gestational sac and embryo.

Fetal parameters

Crown-rump length

The first measurement of crown-rump length was captured at 41 days of pregnancy, while the last ability to get the crown-rump length was at 60 days of pregnancy. At 41-45 days of gestation, the value of crown-rump length was 24.68 ± 1.32 mm. The crown-rump length was increased to 71.71 ± 1.84 mm at the 56-60 days of gestation (Figure 7).

Figure 7: Measurements (mm, mean ± SE) of the fetal crown-rump length obtained by transabdominal ultrasonography during the gestation period of Shami goats.

Head diameter

The results show that the head diameter can be measured from 51-120 days of pregnancy (Figure 8).  The mean head diameter was 15.63 ± 0.82 mm at 51-60 days of gestation. This head diameter was increased to 45.04 ± 0.92 mm at 111-120 days gestation.

Figure 8: Measurements (mm, mean ± SE) of the head diameter obtained by transabdominal ultrasonography during the gestation period of Shami goats.

Chest diameter

The chest diameter was also one of the fetal parameters to estimate the gestation age in does. Figure 9 shows an apparent increase in chest diameter. It was 11.52 ± 0.84 on 51-60 days of gestation and increased significantly to reach 56.35 ± 0.93 on 101-110 days of gestation.

Figure 9: Measurements (mm, mean ± SE) of the chest diameter obtained by transabdominal ultrasonography during the gestation period of Shami goats.

Trunk diameter

The changes in trunk diameter during the gestation period are shown in Figure 10. The value of trunk diameter was 10.69 ± 0.85 mm on 41-50 days of gestation. The value of this parameter was increased gradually until the 121-130 days of gestation to reach 57.38 ± 0.85 mm.

Figure 10: Measurements (mm, mean ± SE) of the trunk diameter obtained by transabdominal ultrasonography during the gestation period of Shami goats.

Estimation of gestational age

The relationship between the gestational age and the measurements of the fetal parameters are shown in Figure 11. The regression line equations, squares of the correlation coefficient, and P values of these relationships were summarized in Table 1.

The study showed that all the measurements were highly significant positively correlated with gestational age (P<0.01). The highest positive correlations were obtained between the gestational age and the measurements of chest diameter (r=0.935), crown-rump length (r=0.917), head diameter (r=0.917), and trunk diameter (r=903).

Table 1: Regression line equation of the relationship between the measurement of the fetal parameters and gestational age in Shami goats 

Figure 11: The relationship between the gestational age and the measurements of the fetal parameters in pregnant Shami does.

Discussion

According to the available references, this study is the first in Iraq to estimate the gestation age in Shami goats using transabdominal ultrasonography. The last study in Shami goats detected the relation between the fetal number and the placentomes size (14).  Also, there was another study in Syria using a linear array transducer to detect early pregnancy in Shami goats (17).

This study illustrates that ultrasonography is an essential tool for early pregnancy diagnosis in goats, and it agrees with that reported in goats by (18). The accuracy of ultrasound was 100% when detecting pregnant and non‐pregnant cases; this is also in agreement with (19), who found accuracy levels of 100%.

The study showed that the embryos were detected at day 25 of gestation. These results are similar to those obtained by Medan et al. (19), who observed that the embryo in Shiba goats first at 24.3 days of gestation. Also, these results agreed with the results of Khand et al. (20), who reported the first sign of pregnancy in Teddy goats on day 19 of gestation and proper embryo with echoic structure within uterine fluid on day 21. Results of the present study confirm the finding of Sayuti et al. (11), who observed the embryo of Kacang goats firstly at 24 days of pregnancy, and observation of Devi et al. (21), who measured the embryo of Assam hill goats first time on 24 days of pregnancy.

The measurements of the crown-rump length of the fetus have been used successfully to estimate gestational age in different species. The current study measured crown-rump length first on 41-45 days of gestation. The same observation was recorded in Egyptian Baladi goats on 40-49 days of gestation (22). In comparison, the crown-rump length in other species of goats was measured at a less period of gestation; on 21 days in Teddy goats (20) and in local Bulgarian goats (23), on 25 days in Assam hill goats (21), on 30 days in Abaza and Gurcu goats (10), on 35 days in Iraqi back goats (13) and Kacang goats (11).

 The crown-rump length of Shami goats recorded in the current study was ranged between 24.68 and 71.71 mm on 41-60 days of gestation. Similar values of the crown-rump length were recorded at the same period of pregnancy in Abaza goats (30-65 mm), Gurcu goats (33-72 mm) (10), Egyptian Baladi goats (35.9-71.6 mm) (22), and Iraqi back goats (29-64 mm) (13). The value of the crown-rump length recorded in this study is considered smaller than those measurements observed at the same period of pregnancy in local Bulgarian goats (23), Assam hill goats (21), and Kacang goat (11).

A highly significant correlation (R² = 0.91) was recorded in our study between the measurements of the crown-rump length and gestational age of Shami goats. Similar levels of the correlation coefficient were observed between the crown-rump length and gestational age of other spices of goats; local Bulgarian goats (R²=0.92) (9), Abaza goats (R² = 0.929) (10), Saanen goat (R²=0.90) (7). A relatively higher correlation (R² = 0.94) was found between the crown-rump length and gestational age in Anglo-Nubian goats (24), in Gurcu goats (10), and Egyptian native goats (6). In comparison to the results of the present study, higher values of the correlation coefficient (R² ≥ 0.98) between the crown-rump length and gestational age were reported in Iraqi back goats (13), Teddy goats (20), and Shiba goats (25).

The fetal head diameter was measured successfully from 51 days until 120 days of gestation in Shami goats. The value of this parameter ranged between 15.63 and 45.04 mm. Closer results were obtained in Iraqi black goats (40-100 days of gestation; the fetal head diameter was 10.8-44.8 mm) (13). While the value of fetal head diameter in our study was higher than the values recorded in Egyptian Baladi goats at the same pregnancy period (11.9-36.2 mm, 40-109 days) (22).

Other studies were measured the fetal head diameter at a pregnancy period earlier than that presented in the current study. Therefore, the measurement of fetal head diameter was less than those were recorded in our results; in local Bulgarian goats (42-49 day; 9.4-13.8 mm) (23), in Assam hill goat (40-80 day; 9.5-25.49 mm) (21), in Abaza and Gurcu goats (30-90 day; 6-36 mm) (10). Conversely, Sayuti et al. (11) was recorded a value of fetal head diameter in Kacang goats similar to that recorded in our study but at an earlier period of gestation (17.4-21.8 mm on 35-45 days). 

  The present study showed a significant correlation (R²=0.84) between the fetal head diameter and the gestational age of Shami goats. This level of correlation considers low in comparison to those were obtained in local Bulgarian goats (R²=0.956) (9), in Saanen goats (R²=0.956) (7) in Abaza and Gurcu goats (R²= 0.925 and 0.928) (10), and Iraqi back goats (R² = 0.95) (13). Conversely, our study's correlation level was higher than that recorded in Korean black goats between 60 and 135 days of gestation (R² = 0.65) (5).

The chest diameter was easily observed and measured using transabdominal ultrasonography. This parameter was obtained in the present study between days 51 and 110 of pregnancy (11.52 - 56.35 mm). A significant positive correlation (R² = 0.88) was recorded in the present study between the chest diameter measurements and the gestational age of Shami goats. According to our knowledge, only two studies have measured the chest diameter in goats and its association with the pregnancy age. The first study recorded a similar level of the correlation coefficient (R² = 0.869) between the measurement of chest diameter and gestational age of Shiba goats (25). At the same time, the value of the correlation coefficient calculated in the current study was lower than that recorded in Saanen goats (R² = 0.98) (26).

In the present study, trunk diameter was measured on 41-50 days of gestation for the first time. The same observation was recorded in Egyptian native goats on 40 days of gestation (6) and Shiba goats on day 42 of pregnancy (25). In contrast, the trunk diameter in other species of goats was measured at an earlier period of gestation; on 21 days in Teddy goats (20), on 28 days in local Bulgarian goats (23), on 30 days in Abaza and Gurcu goats (10).

 The fetal trunk diameter of Shami goats recorded in the current study was ranged between 10.96 and 57.38 mm on 41-130 days of gestation. Similar values of trunk diameter were recorded on 45-90 days of gestation in Abaza and Gurcu goats (16-45 mm) (10). The value of trunk diameter recorded in this study is considered smaller than those measurements observed at the same period of pregnancy in Teddy goats (20), Local Bulgarian goats (23), and Korean black goats (5).

A significant correlation (R² = 0.812) was recorded in our study between the measurements of trunk diameter and the gestational age of Shami goats. Closer values of the correlation coefficient (R² = 0.89) were found between the trunk diameter and gestational age in Shiba goats (25) and Korean black goats (5). In comparison to the results of the present study, higher values of the correlation coefficient (R² ≥ 0.92) between the fetal trunk diameter and gestational age were reported in Egyptian native goats (6), Teddy goats (20), Abaza and Gurcu goats (10).

According to the above information, we find significant differences between the measurements of fetal parameters recorded in the current study for Shami goats compared to those presented in other studies of other goat breeds. These differences may be mainly due to different goat breeds, especially the difference in body size, which reflects and influences the measurements of fetal parameters.

The other reason for the above differences may be the ultrasonography approach. The transabdominal ultrasonography approach depended on the current study for pregnancy diagnosis, pregnancy observation, and obtaining the measurements of fetal parameters. This approach was considered safe and not harmful for animals during the examination. On the contrary, the transrectal approach of ultrasonography gives more accurate results and at an earlier period of pregnancy.

Conclusions

In conclusion, transabdominal ultrasonography is a practical method for pregnancy diagnosis in goats and embryo monitoring. However, it is reliable to estimate gestation age starting on 41 days of pregnancy. The chest diameter was the best fetal parameter, but trunk diameter can be used for the most extended period to estimate the gestational age of Shami goats.

Acknowledgments

The data of this study is part of the MSc thesis of the first author, which was supported by the College of Veterinary Medicine, University of Mosul, Mosul, Iraq.

Conflict of interest

There are no conflicts regarding the publication of this manuscript.