Large Animal - Fertility Flashcards
What is a fertile cow?
A cow that meets the fertility criteria established for the herd/unit
What is the fertility criteria of a cow in a herd that calves all-year-round?
Has to calve every 12 months
What is the fertility criteria for a cow in a herd with a tight seasonal calving pattern?
Calving within a certain time period to match availability of pasture
What is a sub-fertile cow?
One that fails to achieve its fertility target, or that of the herd or group
What is an infertile cow?
Sometimes considered a sub-fertile cow but sometimes considered a sterile cow
What is a sterile cow?
Cow that is incapable of becoming pregnant no matter how long a period she is given
What are the four causes of sub-fertility described as traditionally?
Structural causes
Functional causes
Management causes
Infectious agents
What is it simpler to consider causes of sub-fertility from?
The presenting clinical signs observed by stockperson or veterinarian
What are the signs of sub-fertility?
No observed oestrus
Regular or irregular returns to oestrus after service
Presence of abnormal vulval discharge
Abortion and stillbirth
How often will a cow come into oestrus if not pregnant or 4-6 weeks post-partum?
Every 18-24 days
What is the commonest cause of no observed oestrus in heifers?
Congenital abnormalities - ovarian aplasia/hypoplasia, freemartinism
What are the causes for no observed oestrus in dairy cattle?
Congenital abnormalities Acyclical or anoestrus Ovarian cysts Persistent corpus luteum Pyometra with persistent CL Cyclical ovarian activity occurring but no behavioural signs Showing signs but not being detected
What percentage of co-twin heifers to bull calves are freemartins?
92%
What are freemartin cows?
Heifers that never cycle
Small vestigial tract with no ovaries
Diagnosed as calves by test tube or thermometer case test
Confirmed by karyotyping
What are the causes of anoestrus or true acyclicity?
High milk yields
Inadequate feeding - especially energy
Poor BCS
Stress - lameness, intercurrent disease
What would a clinical examination show with anoestrus or acyclicity?
Rectal palpation - involuted tract, ovaries feel small, smooth and flat
Ultrasound - follicles <1.5cm, no CL
Milk progesterone - intervals low at day 10
How can inadequte nutrition affect fertility?
Through reduced IGF-1 production - hypothalamus (decreased GnRH secretion, decreased +ve feedback to embryo), pituitary (decreased LH and FSH secretion, decreased response to GnRH), ovary (decreased granulosa proliferation and differentiation, decreased LH/FSH supported steroidogenesis, decreased aromatase activity, decreased luteal activity and steroidogenesis), embryo (decreased embryo growth, decreased IFN-tau production)
How can anoestrus or true acyclicity be treated?
Wait until milk yield falls or cow returns to positive energy balance
Increase energy intake if possible
Hormonal treatment - GnRH or analogue, progesterone/progestagens (PRID), controlled internal drug release (CIDR) alone or with GnRH or eCG at low dose rate
Better response to hormones if nutrition improved concurrently
What are the two normal structures present in bovine ovaries?
Follicles
Vacuolated CL
Describe normal follicles in the bovine ovary
Transient, dynamic, soft, fluctuant structures
1.5-2.0cm in diameter during or just after oestrus
<1.5cm diameter during rest of cycle
Associated with normal cyclical activity
Describe a vacuolated CL in a bovine ovary
Same size as non-vacuolated CL Ovulation point identifiable with ultrasound Vacuole disappears during pregnancy Usually single Occurs in about 25% of ovulations Associated with normal cyclical activity
What are three abnormal structures within a bovine ovary?
Luteinised follicles
Follicular and inactive cysts
Luteal cysts
Describe luteinised follicles in a bovine ovary
<2.5cm in diameter No sign of ovulation Larger cavit than vacuolated CL Usually single Formed from anovulatory mature follicle
Describe follicular and inactive cysts in a bovine ovary
Soft, thin walled fulid filled structure >2.5cm diameter Single or multiple One or both ovaries Formed from anovulatory mature follicle
Describe luteal cysts in bovine ovaries
Thick walled fluid filled structure
>2.5cm in diameter
Usually single
Formed from anovulation of mature follicle
What are ovarian cysts?
Fluid filled structures on the ovaries
>2.5cm diameter
Persist for longer than 10 days
Result in aberrant reproductive function
How are ovarian cysts formed?
Develop from anovulatory Graafian follicles
Granulosa layer degenerates
Normal cyclical activity cessates
Cow becomes either acyclical or nymphomaniacal
What are the three types of cysts?
True follicular cyst - thin walled, oestradiol secreting follicular cyst
Luteal cyst - thick walled, progesterone secreting luteal cyst
Inactive cyst - thin walled, functionally undifferentiated inactive cyst
What do thin walled follicular cysts result in?
Acyclicity
Nymphomania - less frequently
What do thick walled luteal cysts result in?
Acyclicity - negative feedback of progesterone on anterior pituitary
What causes ovulation of the dominant follicle?
LH surge
Induced by increased secretion of oestradiol by mature dominant follicle
Why do cysts occur?
Normally LH surge absent or attenuated after calving (recovery period)
Failure of the pre-ovulatory LH surge after the end of the recovery period
What occurs post-calving in the hypothalamus? How can this cause a failure of the LH surge?
Progressive restoration of hypothalamic response to oestradiol
Produces LH surge due to - lack of sensitivity to oestradiol, failure of GnRH release
LH surge fails when oestradiol fails to elicit a normal positive feedback stimulation of LH surge
What are the ovarian causes of cysts?
Reduced numbers of LH receptors in granulosa cells of cysts
Low insulin, IGF-1 and negative energy balance cause greater non-esterified fatty acids
These impair follicular cell proliferation and function
With cysts developed in the immediate postpartum period what needs to be done?
Nothing - generally regress spontaneously, do not need treatment
What should not be done with ovarian cysts?
Rupture by squeezing transrectally
How should ovarian cysts be treated?
Luteal cysts - PGF2alpha
Follicular cysts - GnRH or hCG, cause luteinisation, follow with PGF2alpha or CIDR/PRID for 10-12 days
What is the recovery rate for ovarian cyst treatment?
Good
How can persistent CL occur?
Associated with pyometra
Pathological changes to uterus interfere with luteolysin production
CL persists
How should persistent CL be treated?
PGF2alpha
What are the signs of oestrus in the cow?
Restlessness Not eating Reduced milk yield Searches for other cows in oestrus to elicit mounting Grouping of sexually active cows Bellowing if separated Clear vulval elastic mucus discharge Head mounting other cows Standing to be mounted for at least 5 seconds
What is the usual cause of oestrus not being detected?
Person problem - poor facilities, poor observational regimen
How often should cows be examined for oestrus?
At least 3 times a day for 20-30 minutes - not at milking times, undisturbed
What can be used to help with oestrus detection?
Detection aids
Synchronise oestrus with AI
What are some examples of oestrus-detection aids?
KaMaR, Beacon, Estrotect heat mount detector, tail paint
Pedometers
Changes in vaginal impedence
CCTV
Sequential milk progesterone assays
Abolish detection - oestrus-synchronisation
What are the two main ways of modifying normal ovarian cyclical activity?
PGF2alpha injections - two injections 11 days apart, single AI at 72-84 hours after 2nd injection, double AI at 72 and 96 hours
PRID or CIDR - insert for 7-9 days, PGF2alpha injected 24 hours before removal, double fixed-time AI at 48 and 72 hours, or single AI at 56 hours
What are the reasons for a cow not calving after service/AI?
Oocytes not fertilised - 10-15%
Embryos die under 13 days - 15-20%
Embryos die between 13-42 days - 10%
Foetal death after 42 days - 5%
What four things can foetal death after 42 days result in?
Abortion
Maceration
Mummification
Abortion
What is a regular return to oestrus?
Interval between service and return is 18-24 days
Due to either fertilisation failure or early embryonic death
What is an irregular return to oestrus?
Interval between service and return is greater than 24 days
Cause is late embryonic or foetal death
Interval of less than 18 days means oestrus not correctly identifies - mistimed AI
What are the causes of fertilisation that aren’t due to bull or poor semen?
Anovulation Delayed ovulation Incorrect timing of AI Serving too early postpartum Hormonal deficiencies or imbalance Structural defects of tubular genital tract Infection of genital tract and endometritis Nutritional deficiencies or imbalances Stress
What are the causes of early and late embryonic death?
Luteal deficiency
Hormonal imbalance
Uterine infection with specific microorganisms
Infection with opportunist pathogens and endometritis
Nutritional deficiencies and excesses
Genetic factors
Heat and other stressors
Describe the diagnosis and treatment of luteal deficiency/hormonal imbalance
Difficult to diagnose
Some success with P4 supplementation (PRID or CIDR)
hCG 4-9 days post AI can cause accessory CL formation
What is an unlikely cause of embryonic death in the absence of clinical signs? How would you treat it?
Opportunist pathogens and endometritis
Treat as for endometritis
What are the sseven specific embryopathic micro-organisms?
Campylobacter fetus Tritrichomonas fetus Mycoplasma, ureaplasma and acholeplasma BVDV Infectious bovine rhinotracheitis (IBR) Blue tongue virus Chlamydophila psittaci
What is a repeat breeded cow?
Cow returned to oestrus at normal or extended intervals on three or four consecutive occasions
How does pregnancy rate trend with milk yield?
The higher the milk yield the lower the pregnancy rate
Describe the empirical approach to treating the repeat breeder cow
Change sire if used repeatedly Natural service if possible Use semen from bull with good fertility Inseminate at normal time and 24 hours later hCG or GnRH at time of first AI 11-12 days after AI give GnRH analogue 11-12 days after consider PRID or CIDR
What does the effect of infectious agents on fertility depend upon?
Reproductive process where it exerts its effect
What are the effects of infectious agents on fertility?
Prevent fertilisation - return to oestrus at normal interval
Cause early embryonic death - return to oestrus at normal interval
Cause late embryonic death - return to oestrus after extended interval
Cause abortion, still birth or weakly calves
What are the predisposing factors for endometritis?
Longer/shorter gestation length Retained foetal membranes Parity Increased milk yield Dystocia Trauma Hygiene Season of the year Intercurrent disease Nutrition Early or delayed return to oestrus
How can endometritis be diagnosed?
Vaginal examination essential - character, volume, smell
Scoring for severity
Bacteriology very difficult
What are frequent bacterial causes of endometritis?
Trueperella pyogenes Prevotella species E. coli Fusobacterium necrophorum Fusobacterium nucleatum