Presynchronization by induction of a largest follicle using a progesterone device in GnRH-based-ovulation synchronization protocol in crossbred dairy cows

Evolution over the last 40 years of the assisted reproduction technologies in cattle - the Brazilian perspective I - timed artificial insemination

The reproductive efficiency of the herd is correlated with higher productivity in livestock. Reproduction biotechniques, such as ovulation synchronization protocols, are important to optimize production and accelerate genetic profit in beef and dairy herds. The objective of this review is to describe the evolution over the last 40 years of the artificial insemination (AI) and the timed-AI (TAI) protocols in cattle from a Brazilian perspective. TAI protocols are based on synchronizing emergence of the wave of follicular growth, controlling circulating progesterone (P4) concentrations, stimulating the final growth of the follicle and inducing a synchronized ovulation. Hormonal alternatives that optimize the response at the end of the protocol and strategies to induce final follicle growth and ovulation in categories of females with low expression of estrus are described. Furthermore, the potential positive effect of previous exposure to injectable P4 on fertility of Bos indicus and Bos taurus cows is also discussed.

Rectifying cow infertility under heat stress by immunization against inhibin and supplementation of progesterone

This study was undertaken for the development of novel techniques that are based on immunoneutralization of inhibin bioactivity to improve Holstein cow fertility. A series of 4 experiments were carried out on 2 farms that were located in subtropical or temperate regions, to test the effects of immunization against inhibin alpha subunit on cow fertility under varying degrees of heat stress conditions. Though immunization against inhibin alone improved conception rate (CR) after TAI moderately in cows under mild heat stress conditions, the treatment plus progesterone supplementation substantially enhanced CR in the range of 25 to 35 percentages from severe heat stress to comfortable weather conditions. There existed an additive effect between immunization against inhibin and progesterone supplementation that maximally enhanced CR. Further, immunization against inhibin increased both FSH and activin A concentrations in blood during both follicular and luteal phases. It also significantly increased blood concentrations of E2 in the follicular phase but decreased P4 concentrations during the early pregnancy. However, interferon-tau concentrations in blood around the time of pregnancy recognition were doubled in the inhibin immunized cows. In conclusion, immunization against inhibin plus P4 treatment enhances ovarian follicle and the subsequent early embryo developments that help to greatly improve the fertility of Holstein dairy cows.

Pre-TAI protocol strategies to increase reproductive efficiency in beef and dairy cows

Ovulation synchronization protocols are well established in beef and dairy cows. However, the protocol response rate is around 70-90%. In beef cows, factors such as inadequate nutrition and calf presence negatively impact the response of progesterone (P4)/estradiol-based ovulation synchronization protocols by interfering with GnRH release and consequently reducing LH pulsatility and final follicular development. In dairy cows, protocols based on GnRH and prostaglandin (Ovsynch) are the most widely used in the world. However, the efficiency of Ovsynch is dependent on the presence of a large follicle at the time of administration of the first GnRH. In these ovulation synchronization protocols, pre-synchronization protocols (Prostaglandins, Double Ovsynch and P4synch) are usually attempted in an effort to increase responses. Thus, the objective of this review was to discuss pre-ovulation synchronization strategies (administration of injectable P4 or energetic/protein supplementation or pre-synchronization with intra-vaginal progesterone devices) aiming to increase the LH pulsatility in beef cows or induce the formation of a GnRH-responsive follicle at the beginning of the Ovsynch protocol in dairy cows.