During the last decade, researchers have studied the differences in the reproductive physiology between Bos taurus and Bos indicus breeds. This manuscript focuses on the main aspects of ovarian function and circulating hormones of B. taurus and B. indicus cows and heifers. In general, there is no difference in the number of follicle waves during the estrous cycle, however B. indicus have greater antral follicle count, circulating insulin, and insulin-like growth factor 1 (IGF1) than B. taurus. Moreover, despite of B. taurus having larger ovulatory follicle diameter and maximum CL volume, they have lesser peak circulating estradiol concentrations and lesser circulating progesterone concentrations than B. indicus. We may speculate that there are two main factors related to lesser circulating concentrations of estradiol and progesterone in B. taurus when compared with B. indicus: increased liver metabolism of steroid hormones and lesser production by follicles and CL. Differences between the two genetic groups are also observed with respect to in vitro embryo production because in addition to B. indicus having greater numbers of retrieved oocytes, due to greater antral follicle count, they also have greater percentages of viable oocytes, number of blastocysts, and blastocyst rates when compared with B. taurus. Effects of dietary intake on embryo quality may differ between B. taurus and B. indicus due to different concentrations of circulating insulin and IGF1. For in vivo and in vitro embryo production, an increase in circulating insulin concentrations is negatively associated with oocyte/embryo quality and conception rates. However, this seems to be more pronounced in B. taurus breeds. Differences in ovarian function related or not to nutrition between these two genetic groups are very consistent and may be related to the influence of metabolic hormones such as insulin and IGF1.

The performance of magnetic field sensors based upon the giant magnetoimpedance (GMI) effect in soft magnetic wires is investigated in the MHz frequency range. The performance of the sensor is based on its sensitivity, voltage noise level and (voltage) noise-to-sensitivity ratio, or intrinsic magnetic noise level. Optimization of the sensitivity and noise response of the sensor through variation of the sample anisotropy direction and external applied axial field and dc bias current suggest an intrinsic noise level in the fT/Hz level. Qualitative agreement is obtained between theory and experiment on a CoFeSiB microwire, for the maximum sensitivity and the corresponding noise, as a function of the external field and dc bias current.

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Our objectives were to evaluate ovarian dynamics and fertility comparing 2 treatments at the start of a progesterone (P4)-based fixed-time artificial insemination (FTAI) protocol and 2 treatments at the end of the protocol. Thus, 1,035 lactating Holstein cows were assigned in a random phase of the estrous cycle to 1 of 4 treatments using a completely randomized design with a 2×2 factorial arrangement. At the beginning of the protocol (d -10), cows received GnRH or estradiol benzoate (EB) and, at the end, EB (d -1) or estradiol cypionate (ECP; d -2), resulting in 4 treatments: GnRH-EB, GnRH-ECP, EB-EB, and EB-ECP. All cows received an intravaginal P4 device on d -10, which was removed on d -2. Cows also received PGF on d -3 and -2. The FTAI was performed on d 0. Ovaries were evaluated by ultrasound for corpus luteum (CL) presence and regression (d -10 and -3) and follicle measurements (d -10 and 0), as well as the uterus for percentage pregnant per AI (P/AI; d 32 and 60). Blood samples were collected (d -10 and -3) for P4 measurements. Treatment with GnRH rather than EB tended to increase P/AI on d 32 (38.2 vs. 33.7%) and on d 60 (32.9 vs. 28.9%). More cows treated with GnRH had CL on d -3 compared with EB-treated cows (77.3 vs. 58.3%), due to less CL regression between d -10 and -3 (24.7 vs. 43.8%) and more cows with a new CL on d -3 (35.9 vs. 25.0%). Cows treated with GnRH also had greater P4 concentrations on d -3 than EB cows (3.4 vs. 2.0 ng/mL). Increased circulating P4 at the start of the protocol (d -10) decreased the probability of ovulation to EB or GnRH at that time. Cows from GnRH group also ovulated a larger-diameter follicle at the end of the protocol (15.5 vs. 14.7mm). No difference between EB and ECP in P/AI on d 32 (34.8 vs. 37.0) and 60 (30.8 vs. 31.0%) or in pregnancy loss (11.1 vs. 15.4%) was detected and we found no interaction between treatments for P/AI. Independent of treatment, cows with CL on d -10 and -3 had the greatest P/AI on d 60 (36.9%). In conclusion, treatments at the end of the protocol were similar for ECP or EB and we found no additive effect or interactions on P/AI between treatments. However, cows treated with GnRH rather than EB on d -10 had less luteolysis and tended to have greater P/AI, probably because P4 concentrations were greater during the protocol. Finally, regardless of treatments, cows with CL at the beginning of the protocol as well as at the time of PGF had greater fertility.