Use of biometric measurements to predict age and body weight of bovine fetus*

Abstract Text: Fetal biometric measurements that can be achieved by ultrasonography were used to develop equations to predict fetal age and fetus body weight in Bos indicus cattle. Dataset from 32 purebred Nellore fetuses from 130 to 272 days of gestation, obtained from cows fed corn silage based diet at various feeding levels, was used. Cows were hand mated, with day of mating considered as day zero of pregnancy. Fetal weight and biometric measurements were taken at slaughter and biometrics measurements were (all in cm): body length (BL), thoracic circumference (TC), height at shoulder (HS), height at rump (HR), cranial eyes circumference (CEC) and cranial neck circumference (CNC). Non-linear equations (y=ax^b) were fitted to the data and results are shown in Table 1. Generated functions were evaluated regressing observed values in function of predicted. The joint hypothesis that β₀ = 0 and β₁= 1 was tested and the results shown good fit for all functions generated (P>0.70). However, these regressions do not predict fetal ages accurately in early gestation, thus should not be extrapolated beyond the scope of these data (130 to 272 d of gestation). The results suggest that the gestational age and fetal body weight can be estimated from biometric measurements of fetus using ultrasonography in live cows or directly in fetuses from cows that were slaughtered without specified gestational age. 

Table 1. Functions to predict fetus body weight and fetal age from biometric measures of fetus¹

Biometric predictor measure	Predicting fetal age (days)			Predicting fetus body weight
	Function	r2xy	P-value	Function	r2xy	P-value
Body length, cm	y=14.3×BL0.6516	0.960	0.998	y=0.000155×BL2.701	0.981	0.708
Thoracic circumference, cm	y=16.89×TC0.6588	0.964	0.999	y=0.000263×TC2.769	0.974	0.864
Height at shoulder, cm	y=24.21×HS0.5536	0.975	0.999	y=0.001×HS2.367	0.975	0.985
Height at rump, cm	y=26.42×HR0.5322	0.983	0.999	y=0.00192×HR2.209	0.958	0.944
Cranial eyes circumference, cm	y=10.45×CEC0.8215	0.953	0.999	y=0.000041×CEC3.412	0.946	0.884
Cranial neck circumference, cm	y=9.97×CNC0.8478	0.970	0.995	y=0.000073×CNC3.314	0.962	0.689

¹The r²_xy value is for observed values regressed in function of predicted. P-value is the significance value for testing the joint hypothesis that β₀ = 0 and β₁ = 1, wherein P-values greater than 0.05 means that the H₀hypothesis was accepted.

*Funded by INCT-CA, CNPq and FAPEMIG.

Keywords: Biometric measurements, fetal growth, gestation