2017 - Calving date prediction based on transrectal ultrasonography determination of gestational age in beef cattle � Calving date prediction based on transrectal ultrasonography determination of gestational age in beef cattle R.K. Kasimanickam,a Rabie L. Abdel Aziz,a,c V.R. Kasimanickam,a,b C. Formend aDepartment of Veterinary Clinical Sciences, bSchool of Molecular Biosciences, College of Veterinary Medicine, Washington State University, Pullman, WA; cDepartment of Theriogenology, Faculty of Veterinary Medicine, Beni-Suef University, Beni-Suef 62512, Egypt; dTrinity farm, Ellensburg, WA Abstract In cattle, accurate gestation length determination during pregnancy diagnosis helps to determine calving date. This aids beef cattle producers to estimate length of calving season, labor availability and labor cost and to make nutritional management decisions. The objective of the study was to determine the error rates for projected calving date based on ultrasound determined gestational age in comparison to actual gestational age (derived as the number of days from artificial insemination [AI] date). Reproductive tract ultrasound examinations were performed in 8887 Angus cross beef females that were artificially inseminated in 12 spring calving herds between 2011 and 2016 to determine gestational age of the embryo or fetus. Only pregnancies estimated to be between 30 and 120 days (n = 6355 heifers and n = 2532 cows) were used in this study. The projected calving dates for actual and ultrasonography based gestational ages were determined using gestational length for beef cattle breed. Actual calving date, number of calves delivered at birth, gender of calf born, calf weight, and incidence of assisted birth were recorded. In heifers, the error rates for calving date prediction for actual and ultrasonography gestational ages were 22.1 and 9.9% respectively (P<0.0001); whereas in cows the error rates for actual and ultrasonography gestational ages were 13.5 and 9.1% respectively (P<0.01). The results of the multivariate analysis revealed dam’s age and sire’s calving ease estimated progeny difference (EPD) score influenced the accuracy of calving date prediction based on ultrasound determined gestational age (P<0.01). In conclusion, ultrasound determination of calving prediction was more accurate than traditional breeding date based calving prediction. Keywords: Beef female, pregnancy diagnosis, ultrasonography, calving, error rate Introduction In bovine practice, various techniques have been successfully adopted for the diagnosis of pregnancy. The most commonly used techniques are per-rectal palpation of the reproductive tract and transrectal ultrasonography of the reproductive tract and its contents.1-5 These two methods are direct, reliable and fairly quick methods for diagnosis of pregnancy. Other methods in use are estimation of progesterone,5-7, pregnancy specific protein5.8 and early conception factors9 concentrations in serum. Under most on-farm conditions, pregnancy can be rapidly and accurately diagnosed using ultrasound as early as 26 days after breeding.10 Sensitivity and specificity of pregnancy diagnosis in lactating dairy cows based on ultrasonographic detection of uterine fluid as well as embryonic membranes from 28 to 35 days after AI was 96% and 97%, respectively.11 Use of ultrasound to diagnose pregnancy offers several advantages over rectal palpation such as accurate earlier pregnancy diagnosis, establishing fetal age, determination of fetal gender, and identifying abnormalities in embryonic or fetal development. Sizes of maternal, placental and fetal components evaluated during ultrasonography examination have been used to explain reliable parameters to predict gestational age in cattle.9,12-14 The manifestation of a heartbeat, crown rump length, occipitonasal length, orbital diameter, abdominal diameter, umbilical cord diameter, amniotic sac diameter, thoracic diameter, head circumference, and chest depth of the fetus and placentome size are all proposed approaches to estimate gestational age.9,12-18 Studies have shown that several factors contribute to the growth rate of developing embryo and fetus and that growth rate is not always uniform. Both maternal and embryonic or fetal factors, as well as farm management factors, can contribute to less than perfect prediction. In addition, in utero development may be linked to increased risk of smaller sized calves12,13 or associated with larger birth size. Twin calves, calves born to primiparous cows and heifer calves tend to be lighter at birth compared 573 Clinical Theriogenology • Volume 9 Number 4 • December 2017 � to singletons, calves born to multiparous cows, or bull calves respectively.15-17 Poor maternal nutrition or reduced uterine capacity can limit conceptus growth.19.20 In addition fetuess in larger offspring syndrome, an overgrowth disorder caused by assisted reproductive technologies in ruminants, featured with excessive birth weight. Pregnancy is a measure of success for any breeding programs of beef cattle. Non-pregnant cows need to be identified as early as possible after the breeding season in order to determine reproductive efficiency, pregnancy rate and for culling decisions. Further, accurate gestation length determination helps to determine calving date which helps producer to estimate length of calving season, labor availability and labor cost. This also assists producers to make nutritional management preferences for the pregnant females. The objective of the study was to determine the error rates for projected calving date for ultrasound determined gestational age in comparison to actual gestational age (derived as the number of days from the most recent AI date). Materials and methods: Pregnancy diagnosis Reproductive tract ultrasound examinations were performed in 8887 beef females (6355 heifers and 2532 cows) that were artificially inseminated in 12 spring calving herds between 2011 and 2016. Transrectal ultrasonography was performed by one clinician using a real-time, b-mode ultrasound scanner with a 5-MHz transducer (Aloka 500, Sysmed Lab Inc., Chicago, IL or SonoScape S8, Universal Diagnostic Solutions, Oceanside, CA). Only pregnancies between 30 and 120 days were included in this study. The following embryo or fetal parameters unique to specific stages of development were used to estimate the gestational age - an embryo (1 cm wide) with heartbeat by Day 30 of gestation; differentiation of the head and abdominal regions by Day 35 of gestation; budding of the limbs by Day 45 of gestation; crown to rump length, abdominal, thoracic, head (width and/or occipitonasal length), placentome and umbilical cord sizes; amniotic sac and orbital diameters. Data management Only cows bred to Angus sires and cows that calved between 260 and 300 d after fixed time AI (FTAI) were used in the analysis. Gestational age difference was calculated as actual (i.e., days since most recent breeding) minus estimated (i.e., based on estimate from ultrasonography) age of the conceptus. Therefore, an underestimation (positive gestational age difference) means the ultrasound estimated age of the conceptus was younger than the actual gestational age and an overestimation (negative gestational age difference value) means the ultrasound-estimated age of the conceptus was older than the actual gestational age. Projected calving dates for a gestation length of 283 d were calculated for ultrasonography gestational age and actual breeding dates. These dates were compared to actual calf birthdates to determine error in pregnancy diagnosis. The error rate was defined as number of calving over/underestimated (occurred before 278 and after 287 days after FTAI) divided by total number of calving. Sensitivity analysis for the gestation lengths 281 and 285 d were also calculated. Data including age of the dam, body condition of the dam (1 to 9; 1, emaciated; 9, obese), sire of the calf, sire’s calving ease estimated progeny difference (EPD) score, date of insemination, date of ultrasound pregnancy diagnosis, date of calving, number of calves recorded at birth, gender of calf born, calf weight, dystocia in the subsequent calving, and stillbirths were recorded. Age records were categorized as 1, 2, 3 to 6, 6 to 10 and >10. Body condition were categorized as <5, 5 to 7 and >7. Statistical analysis Data were analyzed with a statistical software program (SAS Version 9.4 for Windows, SAS Institute, Cary, NC). Differences in the mean gestation length were analyzed using ANOVA (PROC GLM of SAS). The Bartlett test was used to assess homogeneity of variance. The data for heifer and cow groups were analyzed separately. Wherever variances for the mean gestation length were heterogeneous, 574Clinical Theriogenology • Volume 9 Number 4 • December 2017 � a log10 transformation was performed. All values are presented with non-transformed values. All pairwise differences between factor level means were analyzed by Tukey’s method. Factors associated to differences in birthweight of calf were determined by ordinal regression analysis. Variables included in the model were calf’s gender, dystocia, calving ease estimated progeny difference and age of the dam. Factors associated gestational age differences were determined using a mixed model. Fixed variables included in the model were calf gender, calf body weight, sires calving ease EPD and age of the dam and dam’s body condition score. Location clustered with in the year (year [location]) was included as random variables in the model. Factors associated with prediction accuracy of calving date by ultrasound based gestational age were determined using a mixed model. Fixed variables included in the model were calf gender, calf body weight, sires calving ease EPD score and dams’ age. Year (location) offered as random effects. The error rates on the accuracy of calving date prediction for ultrasound and actual gestational ages in heifers and cows were calculated. The error rate was defined as number of calving that occurred outside the gestation length window divided by total number of calving (for gestation length 283 ± 7 days [mean ± 2 standard deviation {sd}], any calving that occurred < 276 or > 290 days was considered as error in calving prediction for both methods). Results The mean (± SD) gestation length for the study population is 283.68 ± 3.52 days. The frequency histogram for gestation length based on breeding date is given in the figure. Least square mean (± SEM) gestational length for heifers and cows are given in Table 1. The gestation length was different for gender of calf, calves that experienced difficult birth or not, sire’s calving ease EPD and parity of cow. Calf’s gender (P<0.0001), incidence of dystocia (P<0.01), sire’s calving ease EPD (P<0.0001) and age of the dam (P<0.0001) influenced the mean birth weight of calves (Table 2). The mean (± SEM) birth weight of male and female calves were 82 ± 0.22 and 78 ± 0.36, respectively. The mean (± SEM) birth weight of calves that experienced dystocia or not were 86 ± 0.32 and 79.0 ± 0.28, respectively. The result of multivariate analysis for the effect of calf gender, dystocia, calf birth weight, and dam age on the gestation length is given in Table 3. The calf gender, dystocia, calf birth weight, and dam age affected the gestation length (P<0.01). The result of multivariate analysis for the effect of calf gender, dystocia, calf birth weight, and dam age on the accuracy of calving date prediction based on ultrasound pregnancy diagnosis is given in Table 4. Age of dam and sire’s calving ease EPD score influenced the accuracy of calving prediction (P<0.01). The differences in the accuracy of calving prediction for both methods is given in Table 5. For 283 ± 7 days gestation length in heifers, the error rate for calving date prediction accuracy by ultrasonography and calving calendar was 22.1 and 9.9% respectively; whereas for similar gestation length in cows, the error rate for calving date prediction accuracy by ultrasonography and calving calendar was 13.5 and 9.1%, respectively. Similarly for 285 ± 11 days gestation length in heifers, the error rate for calving date prediction accuracy by ultrasonography and calving calendar was 18.3 and 8.4%, respectively; whereas for similar gestation length in cows, the error rate for calving date prediction accuracy by ultrasonography and calving calendar was 9.1 and 4.7%, respectively. In addition, the differences on the accuracy of calving date prediction based on ultrasound pregnancy diagnosis and breeding date for different gestational ages are given in Table 6. Discussion In this study, errors rates for calving date prediction were evaluated to determine whether producers can rely on breeding date or ultrasonography pregnancy diagnosis. The error rates for calving date prediction was lower for ultrasonography compared to breeding date validated the importance of ultrasonography pregnancy diagnosis. In this study, gender of the calf, age of dam, calf sire EPD and dystocia influenced the gestational length. The effects of gender of the calf were significant for birth weight, (heifer calf - 76.3 lbs vs. bull calf - 81.2 lbs). Birth weight of calves that were born to dams in 2, 3 to 6 and >6 years age groups were 575 Clinical Theriogenology • Volume 9 Number 4 • December 2017 � significantly different, 72.3, 2 80.6 and 82.4 lbs, respectively. Calves born to sires with greater calving ease EPD had lower birth weight. Birth weight for calves that were delivered with assistance was greater (82.3 lbs) compared to calves that were born normally (79.0 lbs). It is plausible that the traits that contributed to increased birth weight may have led to prolonged gestation length. In this study, the gestational age using ultrasonography was determined using different fetal and maternal parameters. Pregnancies were examined with at least two measurable characteristics defined in the material and methods. Embryo size, fetal size (crown-rump length), placentome sizes, size of the head (width and/or occipitonasal length) of the fetus, and diameters of the abdomen and thorax were visualized more frequently, and the diameter of umbilicus less frequently. Studies that investigated the associations of gestational age and fetal parameters concluded that fetal size provided the most precise estimate of gestational age. Hannum et al showed residual sd + 4.5 days for fetal size, ± 6.9 to 8.7 days for head length and the diameters of trunk, head and nose and ± 12.6 days for uterine diameter.14 In the current study the residual sd was +3.5 days. The placenta plays a crucial role in the development of the fetus. Placental characteristics such as the weight and volume of the placentomes, sizes including length, height and change in the placentomes density was used to estimate gestational age. During transrectal ultrasonography pregnancy diagnosis, placentomes were first visible around Day 35 of gestation. These can be viewed as flattened, semicircular elevations on the surface of the uterine lumen. Results from studies that evaluated the usefulness of placentome parameters to determine gestational ages, revealed that placentomes sizes are not significantly associated with gestational age during both transrecatal21 and transabdominal9 untrasonography. Blankenvoorde claimed that there was no significant effect of the breed and age of the dam or uterine horn (gravid vs. non-gravid) on placentome size (P > 0.05) but observed significant association between gestational age and placentome size (P< 0.001).22 Collectively, significant variations in size of placentomes impedes their use as a criteria for fetal ageing. However, a recent study claimed that the measurement of several placentomes sizes could be used to determine fetal age in late gestation.23 Others have noted that there is a significant increase in the average placentome length with increasing gestational age should be taken into account while determining fetal age.23 There was a strong positive correlation between estimated gestational age from ultrasonography and actual gestational age based on the breeding date consistent with similar studies that used ultrasonography to estimate gestational age in cows.3,24 Overestimation of the gestational age by ultrasonography was observed in the current study. Fitzgerald et al observed overestimation of the embryonic age and underestimation of the fetal age and suggested that alterations in the conceptus-to- uterine lumen volume ratio may have contributed to this inconsistency.24 It is interesting to note that the error rate for ultrasonography in heifers was less for 60 to 90 days and higher for 30 to 60 and 90 to 120 days of gestation; whereas the error rate in cows was higher for 60 to 90 days gestational age and less for 30 to 60 and 90 to 120 days of gestation in the current study. It is possible that a combination of distinct fetal differentiation in older-stage pregnancies along with greater uterine capacity in multiparous cows may interfere with the estimation of gestational age using ultrasonography and may account for some of this prediction error. It should be noted that conceptus-to-uterine lumen volume ratio was not studied in the current study. However when fetal, abdominal and thorax sizes were considered to estimate fetal ages, differences in the uterine volume in relation to position of the fetus may have contributed to the error. The error rate for calving date prediction for ultrasonography was minimal when pregnancy diagnosis occurred between 60 and 90 days gestational age compared to 30 and 60 or 90 to 120 days gestational ages. Normal intrauterine growth takes place in phases–an embryonic and a fetal phase.25 The embryonic phase consists of proliferation, organization and differentiation of the embryo, whereas the fetal phase consists of continuing growth and functional maturation of the various tissues and organs. The fetal phase of intrauterine development depends on genetic, placental, and maternal factors. These factors plausibly contribute to the asymmetric fetal growth which occurs in late gestation. It is possible that variation in proliferation, organization and differentiation of the embryo during embryonic phase (<60 days gestational age) and asymmetry growth during later fetal phase (>90 days gestational age) 576Clinical Theriogenology • Volume 9 Number 4 • December 2017 � could be contributed to higher error rate compared to transition phase from embryo to fetus ( between 60 and 90 days gestational age) with minimal error rate. In heifers, the error rates were higher than for cows. Kramer et al. concluded that first parity influenced the calving date prediction.26 Crews Jr. suggested a linear effect of age of dam on gestation in which increasing age of dam was associated with longer gestation27 consistent with the current study. It should be noted that the size (length and width) of the uterus increase progressively with increasing parity, and therefore, gestational age may be overestimated because of the increased conceptus-to uterine lumen ratio in heifers. Tactical use of reproductive ultrasound can help enhance the overall productivity of the herd. Given the seasonal nature of the beef farming, the use of ultrasound for reproductive management tools tends to be concentrated during various stages of the production cycle. Pregnancy diagnosis at an early stage of pregnancy provides a tool for many producers, both seedstock and commercial, to identify AI- impregnated versus cleanup bull-sired calves.28 In addition, earlier detection of non-pregnancy diagnosis assists with management decisions to cull open cows. Further identification of cows that were to become pregnant very late in the breeding season also assists with management decisions to sell them as pregnant animals in order to maintain a short calving season. This study was conducted to determine the error rates for projected calving date based on ultrasound determined gestational age in comparison to actual gestational age. The results from the study revealed that the ultrasound determination of calving prediction was more accurate than traditional breeding date based calving prediction. Acknowledgements The authors thank all beef cattle producers who participated in this study for their support. Dr. Rabie Abdel Aziz, Beni-Suef 306 University, Beni-Suef, Egypt was financially supported by Egyptian Government Research 307 Scholarship (SAB 2086), Egypt Cultural and Educational Bureau, The Arab Republic of Egypt. References 1. Roberts SJ: Veterinary obstetrics and genital diseases. 2nd ed. Ithaca(NY): Published by the author; 1971. p. 14-35. 2. Momont H: Rectal palpation: safety issues. Bovine Pract 1990;25:122-123. 3. Youngquist RS: Pregnancy diagnosis. In: Youngquist RS, editor. Current therapy in large animal theriogenology. Philadelphia: WB Saunders Co., 1997. p. 295-303. 4. Ball PJ, Logue DD: Ultrasound diagnosis of pregnancy in cattle. Vet Rec 1994;134:532. 5. Sasser RG, Ruder CA: Detection of early pregnancy in domestic ruminants-review. J Reprod Fertil Suppl 1987;34:261- 271. 6. Shemesh M, Ayalon N, Shalev E, et al: Milk progesterone measurement in dairy cows: correlation with estrus and pregnancy determination. Theriogenology 1978;9:343-353. 7. Pennington JA, Spahr SL, Lodge JR: Factors affecting progesterone in milk for pregnancy diagnosis in dairy cattle. Br Vet J 1976;132:487-495. 8. Maurer RR, Ruder CA, Sasser RG: Effectiveness of the protein B radioimmunoassay to diagnose pregnancy in beef cattle. J Anim Sci Suppl 1 1985;61:390 [abstract]. 9. White IR, Russel AJ, Wright IA, et al: Real-time ultrasonic scanning in the diagnosis of pregnancy and the estimation of gestational age in cattle. Vet Rec 1985;117:5-8. 10. Filteau V, DesCôteaux L. Predictive values of early pregnancy diagnosis by ultrasonography in dairy cattle. Proc Am Assoc Bovine Pract Annu Mtg 1998; 31:170-171. 11. Nation DP, Malmo J, Davis GM, et al: Accuracy of bovine pregnancy detection using transrectal ultrasonography at 28 to 35 days after insemination. Aust Vet J 2003; 81:63-65. 12. Beal WE, Perry RC, Corah LR. The use of ultrasound in monitoring reproductive physiology of beef cattle. J Anim Sci 1992;70:924-929. 13. Bergamaschi MACM, Vicente WRR, Barbosa RT, et al: Ultrasound assessment of fetal development in Nelore cows. Arch Zootec 2004;53:371-374. 14. Hunnam JC, Parkinson TJ, Lopez-Villalobos N, et al: Association between gestational age and bovine fetal characteristics measured by transcutaneous ultrasound over the right flank of the dairy cows. Aust Vet J 2009;87:379- 383. 577 Clinical Theriogenology • Volume 9 Number 4 • December 2017 � 15. Singh NS, Gawande OH, Mishra OP, et al: Accuracy of ultrasonography in early pregnancy diagnosis in doe. Asian- Australas J Anim Sci 2004;17:760-768. 16. Nwaogou IC, Anya KO, Agada PC: Estimation of feetal age using ultrasonic measurements of different foetal parameters in red Sokoto goats (Capra hircus). Veterinarski Arhiv 2010;80:225-233. 17. Abdelghafar RM, Ahmed BH, Ibrahim MT, et al: Prediction of gestational age by transabdominal real-time ultrasonographic measurements in Saanen goats (Capra hircus). Glob Veterinaria 2011;6:346-351. 18. Harris RM, Snyder BG, Meyer R, et al: The relationship of bovine crown-rump measurement to fetal age. Agri- pracitce. 1983;4:16-22. 19. Long NM, Vonnahme KA, Hess BW, et al: Effects of early gestational undernutrition on fetal growth, organ development, and placentomal composition in the bovine. J Anim Sci 2009;87:1950-1959. 20. Fowden AL, Forhead AJ. Endocrine mechanisms of intrauterine programming. Reproduction 2004;127:515-526. 21. Adeyinka FD1, Laven RA, Lawrence KE, et al: Association between placentome size, measured using transrectal ultrasonography, and gestational age in cattle. N Z Vet J. 2014;62:51-56. 22. Blankenvoorde G. Determination of gestational age in dairy cattle using transrectal ultrasound measurements of placentome size [thesis]. Palmerston North (NZ); Masey University; 2011. 23. Lawrence KE, Adeyinka FD1, Laven RA, et al:�Assessment of the accuracy of estimation of gestational age in cattle from placentome size using inverse regression. N Z Vet J. 2016;64:248-252. 24. Fitzgerald AM, Ryan DP, Berry DP. Factors associated with the differential in actual gestational age and gestational age predicted from transrectal ultrasonography in pregnant dairy cows. Theriogenology 2015;84:358-364. 25. Kasimanickam RK, Kasimanickam VR, Kastelic JP. Intrauterine fetal growth restriction, adaptation and programming– a review. Clin Therio 2012;4;133-148. 26. Kramer RW, Smith DR, Rupp GR, et al: Estimation of calving date in beef cattle with real-time ultrasound. Prof Anim Sci 2016;32:322-327. 27. Crews Jr DH: Age of dam and sex of calf adjustments and genetic parameters for gestation length in Charolais cattle. J Anim Sci 2006;84:25-31 28. Kasimanickam R, Whittier WD, Tibary A, et al: Error in pregnancy diagnosis by per-rectal palpation in beef cows. Clin Therio 2011;3:43-47. 578Clinical Theriogenology • Volume 9 Number 4 • December 2017 � Table 1. Gestation length least squares mean ± SEM for calf gender, sires’ calving ease EPD, and dam age and breed Age group Effect n Gestation length Heifer Gender Bull 3396 281.11 ± 0.66a Heifer 2959 283.63 ± 0.67b Sire calving ease EPD � 5 1067 282.91 ± 0.52a 6 to 10 3056 281.22 ± 0.43ab >10 2232 280.90 ± 0.31b Dystocia Yes 181 284.12 ± 0.16a No 6174 281.19 ± 0.73b Cow Gender Bull 2367 283.23 ± 0.52a Heifer 1981 285.41 ± 0.56a Sire calving ease EPD � 5 563 281.92 ± 0.63a 6 to 10 1668 283.67 ± 0.34b >10 2117 285.23 ± 0.54c Age 2 832 281.25 ± 0.32a 3 to 6 1519 282.19 ± 0.29ab 7 to 10 1144 283.92 ± 0.32b >10 853 285.55 ± 0.39c Dystocia Yes 219 286.12 ± 0.22a No 4129 283.94 ± 0.85b Table 2. Effect of calf’s gender, dystocia, calving ease estimated progeny difference (EPD) score, and dam’s age on birth weight of the calf Predictor Coef SE Coef Z P Odds Ratio Lower 95% CI Upper 95% CI Constant 7.97635 1.00703 7.92 0 Calf’s gender -0.86312 0.120359 -7.17 0.0001 0.42 0.33 0.53 Dystocia 1.03038 0.215744 2.48 0.013 1.36 1.16 1.81 Calving ease EPD score -0.05432 0.010617 -5.12 0.000 0.56 0.33 0.68 Age of dam (yrs) -0.21567 0.024057 -8.96 0.000 0.81 0.77 0.84 Table 3. Multivariate analysis for the effect of gender of calf, dystocia, calving ease EPD, birth weight of calf, and age of the dam on gestation length. Predictor Coef SE Coef Z P Odds Ratio Lower 95% CI Upper 95% CI Constant 8.73983 1.09137 8.01 0 - - - Gender of calf -0.0486 0.116411 -0.42 0.0167 1.95 1.76 2.20 Dystocia 0.372988 0.14422 3.66 0.0142 1.58 1.31 2.96 Calving ease EPD -0.02125 0.005781 -3.68 0.0001 0.88 0.87 0.89 Age of dam 0.0304 0.022754 3.34 0.0116 1.17 1.11 1.23 Calf birth weight 0.414523 0.161287 4.12 0.0018 1.40 1.22 1.51 579 Clinical Theriogenology • Volume 9 Number 4 • December 2017 � Table 4. Multivariate analysis for the effect of gender of calf, dystocia, sire calving ease EPD, birth weight of calf, age of the dam on the accuracy of calving date prediction based on ultrasound pregnancy diagnosis. Predictor Coef SE Coef Z P Odds Ratio Lower 95% CI Upper 95% CI Constant 3.27163 0.389028 8.41 0 - - - Calf gender -0.1326 0.207646 -0.64 0.0523 0.88 0.58 1.32 Dystocia 0.298869 0.659154 0.45 0.65 1.35 0.37 4.91 Age of dam (yrs) 0.390264 0.150928 2.59 0.01 1.48 1.1 1.99 Sire calving ease EPD 0.219147 0.05572 3.93 0 1.25 1.12 1.39 Calf birth weight 0.004658 0.040815 0.11 0.909 1.42 0.75 4.87 580Clinical Theriogenology • Volume 9 Number 4 • December 2017 �T ab le 4 . E rr o r ra te f o r ca lv in g d at e p re d ic ti o n f o r u lt ra so n o g ra p h y a n d a ct u al g es ta ti o n al a g es P ar am et er H ei fe r (n = 6 3 5 5 ) C o w s (n = 4 3 4 8 ) B as ed o n A I d at e an d ac tu al c al v in g B as ed o n U S g es ta ti o n al ag e an d a ct u al c al v in g B as ed o n A I d at e an d a ct u al c al v in g B as ed o n U S g es ta ti o n al ag e an d a ct u al c al v in g # o f ca lv es b o rn o u ts id e o f 2 8 1 ± 7 ( % ) 1 2 4 8 ( 1 9 .6 )* * * 5 8 8 ( 9 .3 )* * * 4 1 3 ( 9 .5 )* 2 7 8 ( 6 .4 )* # o f ca lv es b o rn o u ts id e o f 2 8 3 ± 7 ( % ) 1 4 0 4 ( 2 2 .1 )* * * 6 2 9 ( 9 .9 )* * * 5 8 5 ( 1 3 .5 )* 3 9 5 ( 9 .1 )* # o f ca lv es b o rn o u ts id e o f 2 8 5 ± 7 ( % ) 1 1 6 3 ( 1 8 .3 )* * 5 3 4 ( 8 .4 )* * 3 9 5 ( 9 .1 )* 2 0 7 ( 4 .7 )* W it h in h ei fe rs a n d w it h in r o w s: * = < 0 .0 5 ; * * = < 0 .0 1 ; W it h in c o w s an d w it h in r o w s: * * = < 0 .0 1 ; * * * = < 0 .0 0 1 ; 581 Clinical Theriogenology • Volume 9 Number 4 • December 2017 � Table 5. Error rate for calving date prediction for ultrasonography and actual gestational ages at different stages (gestation length 283±7). Group Embryo or fetal age @ US n Error rate (%) based on US determination of gestational age and actual calving (n) Error rate (%) based on breeding date and actual calving (n) Heifer 30 to 45 393 10.9 (43) 24.4 (96) 46 to 60 1006 10.5 (106) 24.1 (243) 61 to 75 1914 9.2 (176) 21.3 (407) 76 to 90 1756 9.7 (170) 21.2 (372) 91 to 105 874 10.5 (92) 22.4 (196) 106 to 120 413 10.2 (42) 21.8 (90) Total 6355 9.9 (629) 22.1 (1404) Cow 30 to 45 222 7.2 (16) 15.3 (34) 46 to 60 721 9.6 (69) 11.8 (85) 61 to 75 1314 9.7 (128) 14.0 (184) 76 to 90 1222 9.2 (112) 13.5 (165) 91 to 105 556 7.7 (43) 13.1 (73) 106 to 120 313 8.9 (28) 14.7 (46) Total 4348 9.1 (396) 13.5 (587) Table 6. Error rate (%) due to over or under estimation in gestational ages and calving prediction. Gestation length Estimation Heifer Cow Breeding date (n=1404) Ultrasound (n=629) Breeding date (n=585) Ultrasound (n=395) 281 Under 70.8 (994) 15.7 (99) 66.3 (388) 29.9 (118) Over 29.2 (410) 84.3 (530) 33.7 (197) 70.1 (277) 283 Under 67.2 (943) 13.8 (87) 61.4 (359) 28.1 (111) Over 32.8 (461) 86.2 (542) 38.6 (226) 71.9 (284) 285 Under 69.2 (972) 16.9 (106) 64.8 (256) 26.6 (105) Over 30.8 (432) 83.1 (523) 35.2 (139) 73.4 (290) Figure. Histogram of gestation length frequency;mean ± SD: 283.68 ± 3.52 0 100 200 300 400 500 600 700 800 2 6 0 2 6 5 2 6 9 2 7 1 2 7 3 2 7 5 2 7 7 2 7 9 2 8 1 2 8 3 2 8 5 2 8 7 2 8 9 2 9 1 2 9 3 2 9 5 2 9 6 2 9 8 3 0 0 N u m b er o f fe m al es Gestation length 582Clinical Theriogenology • Volume 9 Number 4 • December 2017