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The objectives of this study were 1) to monitor corpus luteum (CL) dynamics after two different protocols of ovulation induction in prepubertal Nellore heifers, and 2) to determine differences in luteal function. Fifty-seven heifers (weight 289.61 ± 32.28 kg, BCS 5.66 ± 0.65, age 17.47 ± 0.81 months) were divided into two groups: GP4+GnRH received a progesterone (P4) device of 3rd use for 10 days, followed by the administration of 0.02 mg buserelin acetate (GnRH) 48 h after removal of the device, and GGnRH received only GnRH. The CLs formed were monitored by ultrasonography every 2 days until their functional regression (decrease in the color Doppler signal and serum P4 concentration < 1 ng/mL), determining their diameter and area, numerical pixel value (NPV), pixel heterogeneity, and vascularization percentage. The peak systolic velocity, end diastolic velocity, resistivity index and pulsatility index (PI) of the ovarian artery and serum P4 concentration were also measured. A lifespan of the CL of more than 16 days was classified as normal-function and of less than 16 days as premature regression. The variables were compared between treatments, CL categories (normal-functional, prematurely regressed or non-functional), days of evaluation, and their interactions using the MIXED procedure of the SAS program (p ≤ 0.05). Three animals of each group (6/57 = 11%) did not respond to treatment, corresponding to an ovulation rate of 89%. There was a higher percentage of normal-function CLs in GP4+GnRH (81%) and a higher percentage of non-functional CLs in GGnRH (52%; P4 concentration < 1 ng/mL in all assessments). Normal-function CLs exhibited a greater area, vascularization percentage and P4 concentration than prematurely regressed and non-functional CLs. Lower diameter, area, NPV and P4 concentration were observed for non-functional CLs, but there was no difference in vascularization percentage compared to prematurely regressed CLs. Progesterone concentration was efficient in diagnosing CL function and was positively correlated with CL area (r = 0.62; p < 0.001) and vascularization percentage (r = 0.38; p < 0.001). Diameter and PI were important for the early diagnosis of non-functional and prematurely regressed CLs, respectively. In conclusion, luteal function differed for the first CL that develops after ovulation induction in prepubertal heifers. Ultrasonographic parameters (diameter, area, NPV, vascularization percentage, and PI) can be used to predict CL function.

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The aim of this study was to evaluate the effect of age of Nellore (Bos indicus) donors on the efficiency of in vitro embryo production (IVEP) and pregnancy rate. Thirty‐six donors, including 11 female calves (13 ± 0.61 months), 17 prepubertal heifers (25 ± 0.78 months) and 8 cows (83 ± 28 months), were submitted to 3 procedures of ovum pickup (OPU) on random days of the estrous cycle at intervals of 21 days. Caspase‐3 and IGFBP2 were quantified in oocytes and blastocysts for the evaluation of oocyte and embryo quality. The produced embryos were vitrified (n = 445) and transferred to synchronized recipients. Cows produced a larger number of follicles (cows: 54.5 ± 6.2; calves: 20.0 ± 0.57; prepubertal heifers: 20.8 ± 0.46), total oocytes (cows: 45.97 ± 7.22; calves: 28.93 ± 6.14; prepubertal heifers: 27.21 ± 4.94) and cleaved oocytes (cows: 21.14 ± 4.22; calves: 13.09 ± 3.72; prepubertal heifers: 12.4 ± 3.19). The cleavage rate was similar between age categories; however, cows tended (p < 0.07) to produce a larger number of blastocysts (9.74 ± 2.26) per OPU than calves (5.57 ± 1.99) and prepubertal heifers tended to have a higher blastocyst yield (35.4%) than calves (27.1%) (p < .07). The expression levels of IGFBP2 and caspase‐3 were higher in oocytes derived from calves compared to the other two categories. The pregnancy rate was higher in calves (43.1%) and cows (40.4%) than in prepubertal heifers (33.8%) (p = .03). Despite the larger numbers of follicles and viable oocytes in cows, the blastocyst production results and pregnancy rates obtained indicate that the use of young females as oocyte donors in IVEP is feasible and may contribute to reduce the generation interval.

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The objective of this study was to determine the correlation between testicular and accessory sex gland measurements in Nellore (Bos taurus indicus) and Caracu (Bos taurus taurus) bulls. Bulls (n=282, including 203 Nellore from 12 to 61 months and 79 Caracu from 12 to 48 months) had their reproductive organs measured. Scrotal circumference was measured with a tape. Length (dorso-ventral) and diameter (mid-lateral) of testes were measured using a graduated ruler. Testicular volume (V) was calculated by the cylinder formula: V=2[(R2)×π×L], where R=radius (diameter/2), L=testicular length and π=3.14 (Fields et al. 1979 J. Anim. Sci. 48, 1299-1304). B-mode ultrasonographic examinations with a 7.5-MHz transrectal linear-array transducer were performed to obtain the mean of 3 vertical dimensions of the vesicular glands, disseminated prostate, ampulla of vas deferens, and lumen of ampulla, and cranio-caudal and dorso-ventral dimensions of the prostate body and bulbourethral glands. For paired organs, the mean was calculated and used in analyses. Biometry data of testes and accessory sex glands were analysed by the PROC CORR (Pearson correlation) of the SAS program (SAS Institute Inc., Cary, NC, USA; P&lt;0.05). Testicular measurements (scrotal circumference, diameter and length) were positively correlated with each other (r=0.69 to 0.92). Similarly, biometrics of the accessory sex glands had positive correlations with testes. The vesicular glands had correlations of r=0.62, 0.43, 0.58 and 0.59 with testes length, diameter, and volume and scrotal circumference, respectively. Correlations testicular biometry characteristics and ampulla of vas deferens ranged from 0.52 to 0.68, whereas those between testicular characteristics and lumen of ampulla were much lower (r=0.28 to 0.37), perhaps due to bulls riding penmates and ejaculating before the ultrasonographic examination. The dorso-ventral measure of the prostate body had positive correlations with size of testes (r=0.13 to 0.28), whereas cranio-caudal measurement of this gland was not correlated with size of testes. Finally, there were positive correlations between testes and disseminated prostate (0.28 to 0.36), and testes and bulbourethral glands, both in the dorso-ventral and cranio-caudal dimensions (0.17 to 0.42). In conclusion, testicular biometry in bulls was correlated with measurements of accessory sex glands, perhaps due to testosterone synthesis, which is essential for accessory sex gland development.