Cyclic Activity Manipulation

• Manipulation of normal cyclic activity can be utilized for convenience.
• Examples include timing estrous in bitches for mating and avoiding estrous detection in dairy heifers.
• This is commonly used in livestock to improve productivity.
• Potential benefits include producing offspring out of season in seasonal breeders and reducing the interval from birth to next pregnancy in non-seasonal breeders.

Non Exogenous Hormone Methods

• Methods of manipulating cyclic activity without using reproductive hormones are available.
• This includes altering exposure to light, timing of weaning, and exposing females to fertile males.

Light

• Introducing a male into a group of females can induce estrous, especially in animals that were in seasonal anestrous.
• Produced in goats and sheep in response to a range of signals from the male, including odor and behavior.
• Exposure to these signals stimulates LH secretion followed by ovulation and the return of cyclical ovarian activity.

Weaning and Lactational Anestrous

• Lactation in sows can inhibit LH release, but this inhibition decreases as lactation progresses.
• Weaning removes suckling-induced neuroendocrine reflexes and the nutritional impact of milk production.
• Weaning results in a rapid restoration of cyclicity as the inhibition of LH secretion disappears.
• Early weaning of piglets (3-4 weeks) commonly optimizes reproductive performance on commercial pig farms.

Hormonal Control of Estrous

• Includes Melatonin, Estrogens, progestogens, and prostaglandins.

Melatonin

• Melatonin affects fertility by influencing the synthesis of melatonin produced by the pineal gland.
• A light signal transmits from the retina to the pineal gland.
• This produces a circadian rhythm in melatonin synthesis and secretion, with high concentrations at night and low during the day.
• Melatonin concentration influences reproductive function, appetite and fooV.
• Exogenous melatonin advances cyclical ovarian activity in species responsive to short days and increasing melatonin concentrations.
• Susceptible species can be supplemented with oral melatonin or a subcutaneous implant.
• Ewes and does should be separated from males for 7 days before implant insertion and remain separated for 30-40 days after.
• Males should be introduced after this period, with peak mating activities occurring 60 days post-implantation.
• Melatonin implants can stimulate reproductive behavior in bucks and rams, but require different dosages than in females.
• Melatonin should NOT be used in nulliparous females.

Oestrogens

• Play an essential part of the hormone cascade that leads to ovulation.
• They are responsible for the behavioral changes in estrous, stimulating sexual receptivity and increasing attractiveness to males.
• Has effects on follicular dynamics and corpus luteum.

Progestagens

• Used extensively to control estrous cycle.
• They synchronize estrous activity within a group, mimicking the function of the corpus luteum (CL).
• Progestagens produce negative feedback on the anterior pituitary, suppressing cyclical activity by inhibiting gonadotropin release.
• In horses, progestagens prevent estrous during training and performance in competition horses.
• Daily injection of 0.3 mg/ml progesterone prevents estrous, with a normal fertile estrous occurring 3-7 days after treatment.
• Multiple daily injections may not be tolerated by the horse, injection site reactions are common.
• Progesterone has an anabolic effect, preventing its use in competition horses.
• Allyltrenbolone or altrenogest, a potent oral progestogen, has no anabolic activity.
• Altrenogest is used to stimulate cyclical activity onset in the early breeding season.
• It is commonly used towards the end of artificial lighting period.
• Treatment for 10 days at 0.044mg/kg body weight is recommended.
• Altrenogest suppresses estrous in mares with prolonged estrous or other aberrant sexual behavior.
• Recommended treatment is 10 days at 0.044 mg/kg body weight.
• It also suppresses estrous in mares with normal estrous activity, treat for 15 days at 0.044 mg/kg.
• Altrenogest control’s estrous timing for effective stallion use or artificial insemination (AI).
• For this treatment, use 0.044 mg/kg for 15 days and expect estrous 2-3 days later.
• A long-acting altrenogest injection is used as an alternative to supplemental feeding.
• A single 0.3mg/kg altrenogest injection suppressed estrous in mares within 24 hours, lasting for 6 days.
• In cattle, progestogens synchronize groups of cows and heifers for artificial insemination, eliminating the need for long estrous detection periods.
• Progesterone supplementation, combined with additional hormones, prevents the persistence of naturally occurring luteal tissue and reduces synchronization.
• A widely used program combines a subcutaneous norgestomet implant with estradiol valerate injections.
• Removing the norgestomet implant after 9 days yields good synchronization (95% within 5 days) and satisfactory conception rates after two inseminations at 48 and 60 hours post-removal.
• A key disadvantage is the requirement for a second handling to remove the implant.
• This protocol is still in use more than 40 years after development, at least in countries where estradiol is permitted.
• Intravaginal progesterone releasing devices are the most common method of progesterone supplementation
• The first device developed was a 1.55 PRID steel coil covered with an inert elastomere.
• PRID is a progesterone releasing intravaginal device.
• It was replaced with polyethylene and ethyl vinyl acetate triangle to increase retention rates.
• Most other intravaginal progesterone-releasing devices have a T-shape flexible arm design.
• All devices are inserted into the vagina with an introducer.
• Progesterone is absorbed into the blood stream via the peripheral blood with a concentration between 3 to 5 ng/ml.
• Removing the device after 7-10 days results in estrous 2-3 days later, provided the tissue doesn't contain luteal.
• Standard protocol with PGF2a involves inserting a progesterone device on day 0, injecting PGF2a on day 6, and removing the device on day 7.
• High conception rates are achieved with two timed inseminations at 48 and 72 hours post-device removal.
• A Progesterone device synchronizes estrus in nonpregnant cows before insemination.
• The device is inserted 1-4 days after insemination, then removed on day 21.
• Cows are observed for estrus on days 22-25, increasing re-inseminated nonpregnant cows at the next estrous.
• Progesterone devices can treat anestrous cows.
• In sheep, progestogens control reproduction in the ewe alone or with combination of other hormones..
• Progestogens induce estrous in anestrous ewes during the nonbreeding season.
• Progestogens synchronize groups of ewes that are showing cyclical activity.
• The most common route of supplementation is the intravaginal route that utilizes impregnated sponges or a T-shaped silicone device.
• Progesterone-used sponges are superseded by potent short-acting progesterone analogues such as Flourogestone acetate (FGA) and Medroxyprogesterone acetate (MAP).
• A 14 day treatment programme is the standard recommendation protocol for using intravaginal progestogens.
• Outside the normal breeding season, using eCG at the end of progesterone priming, i.e., on device removal, is essential if advancement to the breeding season used with melatonin.
• A shorter 6 or 7 day programme was developed.
• Outside the breeding, the device is removed on day 6 along with an eCG injection.
• During the breeding season use PGF2a for shorter programs to be effective at the time of device insertion or 24 hours before removal.

Prostaglandins

• Exogenous Prostaglandins (PGF2a or its analogue) can induce luteolysis and manipulate the normal pattern of cyclic activity.
• CL of the cow, mare, sow, ewe and goat normally respond to the administration of exogenous prostaglandins.
• Prostaglandins are not of clinical value in the bitch and queen
• Prostaglandins are abortifacients that must not be used in animals that might be pregnant.
• Pregnancy Diagnosis must be performed if there is any doubt.In.
• In cattle, used successfully to synchronize estrous in groups of cows and heifers.
• The prostaglandin-based programcan use estrous detection or fixed-Timed AI
• If estrous detection is feasible, then a group of cows are injected and responsive animals with CL will come into estrous 2 to 7 days later and can be inseminated.
• Cows which do not respond or have an unobserved estrous can be injected again 11-14 days later.
• Most cows will show estrous between 3-5 days later and can be inseminated.
• If estrous detection is not feasible then a double fixed - time Al is done at 72 and 96 hours or 72 and 90 hours after the second injection.
• This conception results in rates similar to those following insemination at a spontaneous estrous
• Single fixed time insemination (at 48 hours) can be used but will result in reduced conception rates.
• The mixed program utilizes estrous detection after the first injection, then fixed-time Al after the second.
• Prostaglandins on its own does not produce tight synchronization, it is dependent on the stage of the development of the dominant follicle.
• The "follicle effect" is improved by giving progesterone.
• Follicle stage is important in determining the response of prostaglandins and development of the Ovsynchprogramme.
• Ovysynch – a timed artificial insemination (TAI) protocol in cattle breeding synchronizes ovulation.
• Ovysynch allows insemination at a fixed time, rather than waiting for the detection of heat.

Uses in horses

• Prostaglandins are commonly used as a compound to manipulate the estrous cycle in mares.
• If given more than 5 days but less than 14 days after ovulation, a single injection of prostaglandin will reliably induce estrous on average after 3-5 days later.
• Prostaglandins enable mares to be mated or artificially inseminated on pre-determined days, eliminating the need for frequent teasing of mares.
• Prostaglandins simplify travel arrangements for either the mare or stallion.
• They are useful when an estrous has been missed, especially the 'foal heat', eliminating the need to wait for the next spontaneous heat.