Biological and technological background of estrus synchronization and fixed-time ovulation induction in the pig

Abstract

A technology that allows for manipulating of estrus and ovulation, and would then also allow for fixed-time insemination, can be of great benefit for swine farms that operate using sow batch management. Such technology at least in part, saves labor and permits the production of large batches of evenly developed pigs. Thanks to the current knowledge on endocrine regulation of follicle development and ovulation, and the availability of numerous reproductively active substances such a technology is now available. This 'biotechnology of reproduction' will be reviewed. It covers procedures for synchronizing estrus based on the use of altrenogest in gilts and of batch-wise weaning in sows, for stimulating follicle development using eCG and for inducing of ovulation using hCG or LH as well as GnRH analogues. While the procedures for estrus synchronization stand alone, other procedures require additional treatments. If fixed-time insemination is the goal, estrus needs to be synchronized and follicular development and ovulation induced by the use of GnRH analogues and hCG with ovulation occurring within 36-42 hrs. It is a general recommendation to inseminate those animals twice, i.e. 24 and 40 hrs after ovulation induction. However, the aforementioned technology requires healthy animals and a solid management and cannot be used to compensate for poor management.

Oestrus synchronization with fixed-time artificial insemination in smallholder pig production systems in north-east India: Success rate and benefits

“…Although the practice of oestrus synchronization has been applied frequently in the commercial swine industry to increase the number of litters per sow per year (Kirkwood & Thacker, 1998;Estill, 2000;Brüssow & Wähner, 2011), there is no report about oestrus synchronization with timed AI and its benefits in smallholder pig production systems in India. So the present study was undertaken to assess the potential, feasibility, success, and benefits of oestrus synchronization with fixed-time AI in rural smallholder pig production systems in north-east India.…”

GnRH agonists: Updating fixed‐time artificial insemination protocols in sows

“…Therefore, there must be a balance between the stimulatory (LH and FSH) and inhibitory (P4 and inhibin) factors of the H‐H‐O axis to ensure efficient reproductive function. Multiple internal and external factors are involved in the estrous cycle (Brüssow & Wähner, 2001) (Figure 1).…”

“…Once follicles reach a preovulatory stage, the FSH decreases and the pulsatile high‐amplitude, low‐frequency LH secretion changes to a low‐amplitude, high‐frequency pattern (Thompson & Kaiser, 2014). At this stage, LH receptor expression and E2 production increase, triggering the LH surge mediated by GnRH and initiating ovulation (Brüssow & Wähner, 2001), which is characterized by ruptured vessels and destroyed connective tissue in the follicle wall that releases mature oocytes for fertilization (Mellagi et al, 2010). Time from onset of estrus to beginning of LH preovulatory surge varies 8 ± 11 h; duration of the surge lasts about 24 h, with 30 ± 3 h elapsed from onset to ovulation (Knox, 2015).…”

“…Since then, GnRH agonists have been used to stimulate follicle development and induce ovulation in both nulliparous and multiparous sows (Lopez, 2009). GnRH agonists are considered a possible alternative to gonadotropin administration because they act at the pituitary level and stimulate LH and FSH release (Brüssow & Wähner, 2001), allowing them to carry out FTAI at a time close to ovulation (Kirkwood & Kauffold, 2015).…”

PMSG Pretreatment Before Fixed-Time Artificial Insemination Improves the Reproductive Performance in Replacement Gilts

“…It also has the most effective effect on the follicular development of replacement gilts at a concentration of 800-1000 IU. PMSG treatment may be an effective way to adjust the ovarian status of replacement gilts [12] .…”