Livestock Breeding Cycles

GnRH

Gonadotrophin releasing hormone.

FSH

Follicle stimulating hormone.

LH

Luteinising hormone.

ABP

Androgen-binding protein.

Follicular Phase

GnRH secreted from hypothalamus in a pulsatile manner stimulates release of follicle stimulating hormone (FSH) and pulsatile luteinising hormone (LH).

Follicular Phase

FSH binds to FSH-R on granulosa cells of follicle, increasing follicular growth and development.

Follicular Phase

LH binds to LH-R on theca cells stimulating androstenedione synthesis.

Follicular Phase

Androstenedione diffuses to granulosa cells and is converted to oestrogen (oestradiol 17b) under the influence of FSH.

Follicular Phase

Growing (dominant follicle) secretes inhibin, providing negative feedback at pituitary to inhibit release of FSH.

Follicular Phase

Oestradiol stimulates GnRH and LH secretion (positive feedback loop).

Follicular Phase

Oestradiol levels surge peaking on day 0 of cycle and causing oestrus behaviour.

Ovulation

Rising oestradiol concentrations increase LH pulse frequency, with 1 pulse every 75 min at start of follicular phase and 1 pulse every 45 min on day 0 of oestrous cycle.

Ovulation

Oestradiol peak causes a surge in LH concentrations (the LH surge) lasting approx. 12 h, inducing ovulation.

Ovulation

Granulosa and theca cells luteinise to form the large and small cells of the corpus luteum respectively.

Luteal Phase

LH binds to LH-R on small cells of corpus luteum stimulating the synthesis of progesterone.

Luteal Phase

Progesterone acts at hypothalamic-pituitary axis to suppress LH pulse frequency though LH pulse amplitude increases.

Luteal Phase

Low frequency, high amplitude LH stimulates further progesterone secretion.

Luteal Phase

Large luteal cells synthesise progesterone in absence of an LH stimulus, and progesterone concentration steadily increases to a max on day 8-10 of cycle.

Luteal Phase

Progesterone binds to progesterone receptors in uterine endometrium and myometrium, preparing the uterine environment for pregnancy.

Luteal Phase

Progesterone leads to proliferation of endometrium, increased secretory activity, and increased endometrial vasculature.

Luteolysis

Progesterone remains high until regression of the corpus luteum.

Oestrus/Estrus

The noun for the period of sexual receptivity in female livestock.

Oestrous/Estrous

The adjective describing the period of sexual receptivity in female livestock.

Polyoestrous

Numerous breeding cycles per year without a specified season.

Year round calving

Calving occurs throughout the entire year.

Sexual maturity in Bovine

Reached at 9-12 months of age or 60% of mature body weight.

First calf aim

Aim to have the first calf at 24 months of age.

Breeding age for Bovine

Bred at 14 to 15 months of age.

Calving interval

Calving interval of 365 days.

Oestrus detection in Bovine

Involves observing behavioral cues, physical cues, and changes in activity.

Behavioural cues for Oestrus

Includes standing to be mounted, chin rubbing, chin resting, flehmen, licking, and lordosis.

Physical cues for Oestrus

Swollen vulva and clear, elastic vaginal mucus.

Oestrus detection methods in Bovine

Methods include observing behavioral cues, using teaser bulls, and detection aids.

Teaser bulls reliability

2 x per day: 80-90% reliability.

Heat mount detectors

Detection aids with 40-80% reliability.

Activity monitors

Pedometers measure steps with 80-90% reliability.

Mating in Bovine

Mate when oestrus first detected, with specific conditions for heifers and cows.

Conception rate at first service

Average 40% for Bovine.

Seasonal polyoestrous

Numerous breeding cycles during a specific time of year.

Oestrus detection in Ovine

Limited behavioral cues and some physical cues such as swollen vulva.

Oestrus synchronisation in Ovine

6-8% of ewes in oestrus each day of the breeding season.

Ram:Ewe ratio

Ideal ratio is 1 ram to 10 ewes.

Advantages of Progestogen treatment

Relatively cheap, quickest method of synchronisation in sheep.

Disadvantages of Progestogen treatment

Environmental contamination with residual progesterone and antibiotics.

Advantages of Prostaglandin treatment

Rapidly metabolised in the lung, clean, green, and ethical.

Disadvantages of Simple Application

Pregnancy rates lower than progesterone-treated or untreated ewes. Can't synchronise ewes out of breeding season. Can be more costly than sponges.

Mating: Ovine

Usually natural mating with synchronised oestrus. Introduce ram 48h after sponge removal. No return to oestrus indicates pregnancy (scan to confirm). Cover flock with rams 2 weeks after first mating for any infertile ewes. Use of artificial insemination is limited in commercial flocks. Pedigree flocks use artificial insemination and embryo transfer.

The Breeding Cycle: Porcine

Polyoestrous. Year-round breeding with continuous litters (intensive systems). Sexually active from 7 months of age. Usually first bred at 210 days old. Aim for 2.5 litters per year. Pregnant 3 months, 3 weeks 3 days. Wean piglets at 21-28 days lactation. Inseminate 4-8 days after weaning.

Oestrus Detection: Porcine

Long and variable oestrus period of 36-96 hours. Physical signs include reddening and swelling of vulva (48h prior to oestrus). Behavioural signs include Standing Reflex, Restlessness, Urinating more frequently, Cocking position of ears.

Oestrus Synchronisation: Porcine

Altrenogest: progestin (a synthetic progestogen) mimics progesterone, delays oestrus. Oral administration for 18 consecutive days. Withdrawn on day of weaning (in sows). In oestrus within 5 days.

Oestrus Synchronisation: Sows

Not required for sows. Will come into oestrus 4-8 days post-weaning (typically 5-6 days).

Effect of Season on Breeding: Bovine

Not seasonal breeders (no anoestrus) but seasonal effects. Higher conception rate 90d post-calving in autumn-calving cows. Conception rate higher when inseminated at temperatures between 7 and 15 degC.

Heat Stress in Dairy Cows

Physiological effects include decreased dominance of selected follicle, decreased oestradiol concentrations, altered progesterone concentrations, decreased oocyte and embryo quality, increased failed embryo implantation, and negative energy balance increases calving-conception interval.

Effect of Season on Breeding: Ovine

Seasonal (short-day) breeders. GnRH regulates LH and FSH; secretion of pituitary hormones is also regulated by photoperiod (day length). Melatonin synthesis is suppressed by light; during short days melatonin synthesis increases.

Ram Effects on Breeding

Reduced libido, reduced sperm quality, reduced sperm quantity, altered protein profile of seminal plasma.

Ewe Effects on Breeding

Anoestrus (non-cyclic).

Out of Season Breeding

Use sponges/CIDRs and pregnant mares serum gonadotrophin (PMSG) to induce ovulation. Use semen collected and stored during the breeding season.

Summary of Breeding Cycles

Breeding cycles in females are regulated by hypothalamic, pituitary and ovarian hormones. Livestock species vary in their reproductive physiology. A thorough understanding of the breeding cycle is required to optimise productivity.

Techniques in Livestock Breeding

Techniques such as oestrous synchronisation can aid livestock breeding programmes.

Reproductive Function Influences

Reproductive function is affected by season (sheep) and climate (cattle).