Livestock Breeding Cycles Flashcards
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)
• FSH binds to FSH-R on granulosa cells of follicle
• Increased follicular growth and development
• LH binds to LH-R on theca cells stimulating androstenedione synthesis
• Androstenedione diffuses to granulosa cells and is converted to oestrogen (oestradiol 17b) under the influence of FSH
- Growing (dominant follicle) secretes inhibin • Negative feedback at pituitary
- Inhibits release of FSH
- Ensures small follicles do not mature
- Oestradiol stimulates GnRH and LH secretion (positive feedback loop)
- Oestradiol levels surge peaking on day 0 of cycle and causing oestrus behaviour
Ovulation
- Rising oestradiol concentrations increase LH pulse frequency
- 1 pulse every 75 min at start of follicular phase
- 1 pulse every 45 min on day 0 of oestrous cycle
- Oestradiol peak causing a surge in LH concentrations (the LH surge)
- Lasts approx. 12 h
- Induces ovulation (timing dependent on species)
- 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.
• Progesterone acts at hypothalamic-pituitary axis to suppress LH pulse frequency though LH pulse amplitude increases.
• Low frequency, high amplitude LH stimulate further progesterone secretion. • Large luteal cells synthesis progesterone in absence of an LH stimulus, and
progesterone concentration steadily increase to a max on day 8-10 of cycle.
- Progesterone binds to progesterone receptors in uterine endometrium and myometrium
- Preparation of uterine environment for pregnancy
- Proliferation of endometrium
- Increased secretory activity
- Increased endometrial vasculature
Luteolysis
• Progesterone remains high until regression of the corpus luteum
Luteolysis (also known as luteal regression) is the structural and functional degradation of the corpus luteum (CL), which occurs at the end of the luteal phase of both the estrous and menstrual cycles in the absence of pregnancy.
Bovine. Reproductive cycle
Polyoestrous
Bovine Length of Oestrus (hours)
18
Bovine Gestation Length (days) (average)
279-290 (283)
Ovine Reproductive cycle
Seasonal Polyoestrous
Ovine Length of Oestrous cycle (days) (range)
17 (16-17)
Ovine Gestation Length (days) (average)
145-152 (147)
Porcine Reproductive cycle
Polyoestrous
Porcine Length of Oestrus
36-96
Porcine Gestation Length (days) (average)
111-120 (115)
Caprine Reproductive cycle
Seasonal Polyoestrous
Caprine Length of Oestrous cycle (days) (range)
21 (19-21)
Caprine Gestation Length (days) (average)
144-155 (150)
Poultry Reproductive cycle
Seasonal polyoestrous
Poultry Length of Oestrous cycle (days) (range)
1 egg/day
Poultry Gestation Length (days) (average)
20-30d incubation
Alpaca Reproductive cycle
Induced ovulators.
Alpaca Length of Oestrous cycle (days) (range)
No oestrous cycle
Alpaca Gestation Length (days) (average)
330-370 (345)
The Breeding Cycle: Bovine
- Polyoestrous
- Numerous breeding cycles per year
- Breeding not in a specified season • Yearroundcalving
- Spring calving
- Autumncalving
- Sexual maturity reached at 9-12 months of age • Aim to have first calf at 24 months of age
- Breed at 14 to 15 months
- Aim for 1 offspring per year (twins rare)
- Calving interval of 365 days
- Increased milk yield (dairy) increased offspring (beef)
Oestrous Detection: Bovine
• Behavioural cues
• Standing to be mounted, chin rubbing, chin resting,
flehmen, licking, lordosis (back arching)
• Physical cues
• Swollen vulva, vaginal mucus (clear and elastic)
• Change in activity
• Restlessness, reduced feed intake
Oestrus Detection Methods: Bovine
- Observe behavioural cues
- 3 x per day, 20 minute intervals: 70-80% reliability
- Time consuming
- Teaser bulls
- 2 x per day: 80-90% reliability
- High maintenance
- Detection Aids
- Heat mount detectors (tail paint, ink pockets, scratch cards): 40-80% reliability
- Activity Monitors
- Pedometers measure steps
- Minimal work, costly
- 80-90% reliability
Mating: Bovine
- Mate when oestrus first detected
- If heifer 14-15 months of age
- If cow within 70 days of calving
- Rarely natural mating
- Artificial insemination (AI) in dairy industry
- Natural and AI in beef industry
- Sex-sorted semen
- Conception at first service average 40%
- If no signs of oestrus within 3 weeks of mating, assume pregnant and scan
Breeding Cycle: Ovine
- Seasonal polyoestrous
- Numerous breeding cycles during a specific time of year
- Short-day breeders
- Sexually active August to February
- Anoestrus during spring and summer months
- Lambs born Jan-Feb if autumn mating
- Sexual maturity reached at 6-8 months (female) and 4-6 months (ram)
- Usually bred at >1 yr of age, can breed <1 year
- Aim for 2 lambs/ewe per year
- Breed and management dependent
- 200% lambing rate
- Typically 183% for lowland sheep farms
Oestrus Detection: Ovine
- Limited behavioural cues amongst females • Tail wagging
- Will show interest in ram and stand to be mounted by teaser ram
- Some physical cues
- Swollen vulva
- Vaginal mucus
Oestrus Synchronisation: Ovine
- 6-8% of ewes in oestrus each day of the breeding season (100/16 days)
- Ram:Ewe ration of 1:50
- Ram would need to mate 3-4 ewes per day over 17 days
- Risk of lowered fertility
- Ewesmaycomeintooestrusatthesametime
- Easier to synchronise oestrus • Ewes mated at same time
- 1 ram to 10 ewes ideal
- Synchronises lambing period also
Oestrus Synchronisation: Progestogen
Advantages: Relatively cheap (£4-5/ewe). Quickest (days to ovulation) and most reliable method of synchronisation.
Disadvantages: Environmental contamination: residual progesterone and antibiotics (accumulate in tissues) not “clean, green, ethical”.
Oestrus Synchronisation: Prostaglandin
Advantages: PG rapidly metabolised in lung (no accumulation in tissue) Clean, green and ethical. Simple application
Disadvantages: Pregnancy rates lower than Progesterone-treated, and 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
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
Mating: Porcine
- Oestrus detection / Oestrus synchronisation • Mating / insemination
- Maintenance of pregnancy
- Weaning
- Oestrus detection
Oestrus Detection: Porcine
- Long and variable oestrus period
- 36-96 h
- Physical signs
- Reddening and swelling of vulva (48h prior to oestrus)
- Behavioural signs
- Standing Reflex
- Restlessness
- Urinating more frequently
- Cocking position of ears
Oestrus Synchronisation: Porcine
- Not required for sows
- Will come into oestrus 4-8 days post-weaning (typically 5-6d)
- Gilts synchronised
- 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
Effect of Season on Breeding: Bovine
- Not seasonal breeders (no anoestrus) but seasonal effects
- In UK research (University of Nottingham)
- Autumn calves inseminated earlier than spring or summer bred animal
- Higher conception rate 90 post-calving in autumn-calving cows
- Conception rate higher when inseminated at temperatures between 7 and 15 degC
- Zeebaree, Bayar (2016) Mechanisms of seasonal reproduction in cattle. PhD thesis, University of Nottingham
- Decreased fertility when mated in hotter months of the year • Increased temperature and humidity
- Decreased expression of oestrus • Decreased dry matter intake HEAT SRESS
Physiological Effects of Heat Stress
- Decreased dominance of selected follicle
- Decreased oestradiol concentrations
- Altered progesterone concentrations
- Decreased oocyte and embryo quality
- Increased failed embryo implantation
- Negative energy balance increases calving-conception interval
Effect of Season on Breeding: Ovine
• Seasonal (short-day) breeders
• Whilst GnRH regulates LH and FSH, secretion of pituitary hormones is also
regulated by photoperiod (day length)
• Melatonin synthesis is supressed by light
• During short days melatonin synthesis increases
• Increased secretion of melatonin from the pineal gland
• Melatonin binds to melatonin receptors on pars tuberalis of the pituitary gland
• Activation of melatonin receptor stimulates prolactin secretion
• Prolactin has a paracrine function and regulates gonadotrophe function.
- Ram
- Reduced libido
- Reduced sperm quality
- Reduced sperm quantity
- Altered protein profile of seminal plasma
- Ewe
- Anoestrus (non-cyclic)
- Out of season breeding
- Use sponges and pregnant mares serum gonadotrophin (PMSG) to induce ovulation
- Use semen collected and stored during the breeding season
Measures of Fertility in Livestock Bovine
Conception rates- (% pregnant per service/ services per pregnancy). >40%
Non-return rate (% of served cows not served again after 30-60d). >75%
Calving to conception interval. 85 days
Calving to 1st service interval. 65 days
100 d in calf rate 50%
Sperm quality
Measures of Fertility in Livestock Ovine
Conception rates (% ewes pregnant put to ram). >90% (natural service)
Lambing percentage (lambs/ewe) LL 183, UL 166, Hill 112
Mean age at first lambing 12- 24 months
Sperm quality
Measures of Fertility in Livestock Porcine
Pigs weaned/sow/year 30 PWSY (aiming for 40) Influenced by pigs born alive and pre-weaning mortality
Litters/sow/year 2-2.5 (28d lactation, 115d gestation)
Non-productive sow days (day/yr not lactating/pregnant)
Weaning to first mating interval (WMI) 3-8 days
Pigs born alive 15-20/litter
Sperm quality
Measures of Fertility in Livestock Poultry
% fertile eggs (incubated)
% hatchability (% of fertile eggs that hatch)
Hatch rate (% hatched eggs from all in incubator)
Sperm quality (turkey esp)
Influencing the breeding cycle
- Earlier sexual maturity
- Improved nutrition
- Bovines sexually mature from 6 months
- Earlier breeding season
- Introduce ram earlier to ewes
- Use oestrus synchronisation with progesterone sponges
- Increased fecundity
- Improved nutrition 3-4 weeks prior to mating (flushing)
- Increases follicular growth through aromatase enzyme expression • Very effect in ewes – increased twinning rates
- Quicker return to oestrus
- Earlier weaning/removal of offspring
- Oestrus detection is key
