The objective of this study was to investigate 3D-kinematics as a method to determine if primiparous dairy cows display differences in movement biomechanics during the estimated estrus period as ovulation approaches. Fourteen primiparous naturally cycling dairy cows (n = 14) were used in a split-plot overtime design. 3D-Kinematic assessments were undertaken and milk samples were collected from d 14 post-ovulation until 2 d after each cow’s second ovulation. Frequency of event (Events/5min) data were collected for Pelvic tilt (Pt) and shift angles (Ps), Feet strikes (Fs), and Micro (Mic; 85–95°), Middle (Mid; 95–100°) and Macro (Mac; >100°) tail angle movements (T). Statistical analysis (Proc Glimmix in SAS) compared behavioral data at baseline (luteal phase), estimated estrus period (−24 h) and ovulation day within EU and between EUs (Sample time and Cow effect). The largest follicular diameter and estradiol concentration occurred at −24 h (Table 1). The frequency of almost all behavioral parameters measured significantly decreased during the estimated estrus time (−24 h) compared with baseline and ovulation with the exception of Pt and Ps (Table 1). The accuracy of behavioral biometrics as estrus indicators were analyzed using sensitivity (Se), specificity (Sp) and Youden index (J index) levels (ROC curves). Feet strikes had the highest J index and Se-Sp level followed by Pt, Ps, TMid, and TMicro movements as estrus indicators. Our data indicates that primiparous tie-stall housed dairy cows exhibit movement-biomechanic changes as spontaneous ovulation approaches. Table 1 (Abstr. 106). Comparison between physiological and behavioral parameters (LSM ± SEM), significance level, and receiver operating characteristic curve results

Parameter	Baseline	−24 H	Ovulation	P-value	Se1	Sp2	J index3
Follicle diameter (mm)	13.9 ± 0.5	17 ± 0.5	—	0.01	1.0	0.6	0.6
E2 (pg/mL)	15.7 ± 1.6	17.4 ± 1.7	16.0 ± 1.6	0.99	0.9	0.6	0.4
Pt	13.1 ± 8.3	17.4 ± 11.0	11.7 ± 7.4	0.01	0.7	0.5	0.4
Ps	3.5 ± 2.5	10.6 ± 7.1	3.4 ± 2.3	0.01	0.7	0.6	0.3
Fs	14.4 ± 2.7	9.9 ± 1.9	12.4 ± 2.4	0.07	0.9	0.6	0.5
Tmac	1.8 ± 1.1	1.7 ± 1.0	1.9 ± 1.1	0.41	1.0	0.3	0.3
Tmid	6.1 ± 3.2	1.8 ± 1.0	3.8 ± 2.0	0.01	1.0	0.3	0.3
Tmic	14.6 ± 7.2	7.3 ± 3.6	15.3 ± 7.5	0.01	0.9	0.4	0.3

¹Sensitivity. ²Specificity. ³Youden index.