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Puerperium

• The postpartum period when the reproductive tract returns to its non-pregnant condition so that the female may become pregnant again

• Initiated immediately after parturition and lasts until reproductive function is reestablished

Lactation

• The synthesis, secretion, and removal of milk from the mammary gland for the nourishment and survival of the newborn

• Initiated immediately after parturition and lasts until weaning of the offspring ('dry-off' in dairy females)

Puerperium main events

1. Expulsion of fetal membranes and lochia

2. Uterine involution and endometrial repair

3. Elimination of microbial contamination of the reproductive

tract

4. Resumption of regular ovarian function and estrus cyclicity

Expulsion of fetal membranes

1. Maturation of chorionic villi prepartum - periparturient

endocrine changes lead to activation of collagenases

2. Myometrium contractions and vasoconstriction

3. Recognition of fetal membranes as foreign by maternal

immune system and production of cytokines

4. Migration of neutrophils to the maternal-fetal interface

5. Detachment of chorionic villi

6. Expulsion of the fetal membranes

Expulsion of fetal membrane failure

retained fetal membranes (>12h in ruminants and >3h

in mares); increased susceptibility to uterine infections and

development of metritis

how neutrophil function is impaired in cows that retain their placenta after giving birth

• Reduced ability to destroy harmful material (phagocytosis)

• Reduced ability to move to where they're needed (migration)

• Reduced ability to be called into action (recruitment)

• Selenium, vitamin E deficiency, stress, and abortion increase the risk of this issue.

• Impaired neutrophil function leads to poor clean-up of the placenta, causing it to stay stuck

Uterine involution and endometrial repair in a

postpartum cow

• Vasoconstriction induces necrosis and sloughing of caruncles

• Reestablishment of caruncular and intercaruncular endometrium

Time to resumption of cyclicity

~ variable among individuals

~ associated with energy status and suckling activity

Resumption of estrus cyclicity

•GnRH pulses increase due to estradiol's positive feedback.

•Leads to a surge in LH, which triggers ovulation of dominant follicles.

•Postpartum metabolism and health affect estrus return.

•In some species, suckling or offspring suppress GnRH release through opioid signals, delaying cycling.

Nutritional anestrous in dairy cows <2 BCS

~ low-low cows = anovular

• Unfavourable energy balance extended

• Lower insulin and IGF1

• Higher NEFA and BHBA

• Reduced steroidogenesis of dominant follicle

• Impaired responsiveness of dominant follicle to LH

• Extended anovulation

Nutritional anestrous in dairy cows >3.75 BCS

• Favourable energy balance reestablished faster

• Higher insulin and IGF1

• Lower NEFA and BHBA

• Enhanced steroidogenesis of dominant follicle

• Improved responsiveness of dominant follicle to LH

• Earlier resumption of estrous cyclicity

Seasonal, nutritional, and lactational anestrous in

ewes and does

• Lambing and kidding season are normally outside of the breeding season

• When proper light regime is provided, nutritional and lactational anestrous become important

Mares in good condition don't have lactational

anestrous

• Foal heat: estrus event occurring 7-12 days postpartum

• Pregnancy per breeding is 10-20% lower in foal heat compared with subsequent heats

• Higher pregnancy losses are sometimes reported

Prolonged physiological anestrous in bitches

•Bitches have a long anestrus (5 months) - unlike cows or horses.

•Estrus is the fertile period with ovulation happening after mating begins.

•The cycle is strongly regulated by E₂, LH, FSH, and P₄ levels.

Lactational and nutritional anovulation in women

1.Women who are NOT lactating:

•Resume menstruation much faster (sharp increase in USA and UK by 4-8 months).

•By 12 months, ~90-100% are menstruating again.

2. Women who ARE lactating:

•Resume menstruation slower, and the rate varies by country.

•In developed countries (USA, UK), ~50-60% menstruate by 12 months.

End of anestrus/gestation

•The female has just finished pregnancy (cow) or seasonal anestrus (ewe).

•First ovulatory follicles develop.

Silent ovulation (no behavioral estrus)

•The brain sees estrogen (E₂) from the growing follicle.

•But since the brain hasn't been primed by progesterone (P₄) yet, it doesn't trigger estrus behavior.

•Ovulation occurs, but there's no outward sign (no standing heat).

First postpartum luteal phase

•A corpus luteum (CL) forms after silent ovulation and releases progesterone (P₄).

•P₄ exposure primes the brain to respond to estrogen next time.

•There's still no behavioral estrus during this phase.

First behavioral estrus

•In the next follicular phase, estrogen (E₂) rises again.

•Now that the brain has been primed by P₄, it responds to E₂ by triggering estrus behavior.

•The animal shows visible heat and is ready for mating.

Mammary gland

• Distinguishes mammals from other animals

• Highly evolved and complex epidermal gland with a branched tubulo-alveolar structure and an apocrine mode of secretion

• Secretes milk for the nourishment and survival of the newborn

• Reproductive strategy

• Final investment of the mother in the survival of the species

• Colostrum supplies nutrition and immune protection to the newborn

Mammary gland - internal anatomy - parenchyma

• Derived from ectoderm

• Glandular or secretory portion of the gland

• Epithelial cells, alveoli, ducts, and cisterns

• Embedded in stroma

Mammary gland - internal anatomy - stroma

• Derived from mesoderm

• Cellular: adipose tissue, blood vessels, nerves, myoepithelial cells, fibroblasts, immune cells

• Acellular: supportive connective tissue, extracellular

matrix, and collagen

Tissue proliferation and involutiom in mammary gland

• Dairy cows: peak secretory tissue proliferation normally observed in the 3rd lactation

1. Before puberty: Only a small amount of stromal and ductal tissue.

2. After puberty: Slow increase in ductal and secretory tissue.

3. During pregnancy: Major growth in secretory tissue, especially right before parturition.

4. Lactation: High levels of secretory tissue for milk production.

5. Involution: Tissue regresses when lactation ends.

6. Second lactation: More tissue than the first; peak secretory tissue usually seen in 3rd lactation (not shown, but implied).

Parenchyma alveolus

~ Secretory basic unit of gland

~ lined by secretory epithelial cells

Parenchyma ducts

Drainage of milk from alveoli

Parenchyma lobules + lobes

Group of adjacent lobules drained by a common duct and encased in connective tissue septum

Parenchyma gland + teat cistern

Storage:

Gland ~ 400mL

Teat ~ 40mL

Parenchyma streak canal and sphincter muscle

Keeps milk inside the bacteria outside of the udder

Secretory pathways

1. Paracellular pathway: plasma components and leukocytes

2. Exocytosis: proteins, lactose, calcium, etc.

3. Transcytosis: from bloodstream eg. Ig

4. Lipid: milk fat MFMG

5. Apical transport: ions, water, glucose

Mammary epithelium

• Lined by epithelial cells that synthesize and secrete milk

• Alveolus: small, bulb-shaped structure with hollow center lumen that collects milk components and water

• Terminal ducts

Terminal ducts provide a way out for the milk produced

• Lined by 2 layers of epithelium

• Myoepithelial cells arranged longitudinally

Alveolus surrounded by

• Network of capillaries (supply milk precursors and deliver hormones)

• Myoepithelial cells (induce milk ejection by contraction when stimulated by oxytocin

• Basement membrane (selective transfer of molecules)

• Interstice

Neural regulation of milk letdown: ANS

Autonomic nervous system: maintains homeostasis

• Parasympathetic: normal activity

• Sympathetic: fight/flight response

• Inhibits milk letdown

• Vasoconstriction

Neural regulation of milk letdown: SNS

Somatic nervous system: responds to external stimuli

• Stimulus:

• Touch (calf suckling, udder wipe, etc.)

• Sound (milking machine, music, etc.)

• Visual (something different)

• Response:

• Oxytocin release

• Muscle contraction (myoepithelial cells of the alveoli)

• Milk ejection

Milk ejection (let-down reflex)

1. Suckling -> stimulated teat nerve endings

2. Signal from udder go to spinal cord then brain

3. Hypothalamus make pituitary gland release oxytocin into blood

4. Oxytocin moves through bloodstream to mammary gland

5. Oxytocin makes milk sacs contract -> pushes milk into ducts through teat cistern and out of teat

Colostrum

• High concentration of immunoglobins

• Ideally >50g of IgG/L of colostrum in cows (>22 %BRIX)

• Transfer of passive immunity (TPI)

• 24h after feeding colostrum fetus expected to have total IgG in serum

>10g/L and total protein in serum >5.1g/L

Before colostrum

• newborns are immunocompromised (no

transfer of antibodies through placenta)

• Failure of transfer of passive immunity (FTPI) results in greater mortality/morbidity and reduced performance

Mammogenesis

The process of structural gland development

• Prenatal and postnatal

• Most structural development occurs during late pregnancy

Lactogenesis

The process of milk synthesis and secretion

• Few weeks prior to parturition (formation of colostrum)

• After parturition

Milk secretion

The synthesis/secretion by epithelial cells to

alveolar lumen

Milk removal

The passive removal from the cisterns and the

ejection of milk from the alveolar lumen

Milk secretion + removal

• The combined processes of milk secretion and milk removal is lactation

• Once established, lactation is maintained or even enhanced by galactopoiesis

Cost of rearing replacement heifers

• Second largest expense in a dairy operation (~20%)

• Future of the dairy operation

• Investment in feed, labour, and capital for 22-24 months

without receiving any realized benefits

• ~60% of total costs come from feed costs

• Delay in age at first calving is costly

Goals of a reproductive program for heifers

• Decrease age at first calving with adequate body size, without compromising mammary development and future lactation performance

• focus on puberty, breeding, and pregnancy first and then calving

• Economically sound

• Timed AI programs for heifers are economically attractive when estrous detection rate is <70%

Goals of nutritional/reproductive program for heifers

1. Achieve puberty and sexual maturity early

2. Achieve adequate body weight, height, and frame size at

calving

Achieve puberty and sexual maturity early

• Puberty at 9-10 months of age (260-280 kg body weight)

• 1st AI at third estrous cycle after puberty (improved fertility)

• Pregnancy at 13-15 months of age (350-380 kg body weight)

Achieve adequate body weight, height, and frame size at

calving

• Calving at 22-24 months of age

• 82% of mature body weight: 600-640 kg pre-calving, or 540-570 kg post-calving

• Body condition score <3.75 at calving (ideally between 3.00-3.50)

Measuring heifer growth: snapshot

• Measure a representative subgroup of heifers in different age groups on the same day

• Plot weight or height by age

• Calculate the parameters for the line (slope and intercept)

• Quick i.e. can take action immediately

• May not be very accurate because you are not looking at the same heifer over time

Measuring heifer growth: longitudinal

• Measure each heifer or cohorts of heifers and follow at specific time points

• Analyze grouped data

• Accurate but does not allow a quick decision

Effect of prepubertal average daily gain on performance

during first lactation

ADG 800g/day

• Gland weight = 914g

• Parenchymal tissue weight = 440g

ADG 1150g/day

• Gland weight = 1971g

• Parenchymal tissue weight = 245g

Disadvantages of underfeeding heifers

1. Reach puberty and calve later in life

2. Lighter heifers produce less milk during first lactation

3. Smaller frame heifers have increased risk of dystocia and limited capacity to compete for food/ingest nutrients

When heifers reach puberty and calve later in life

• Increased rearing costs (feed, labour, depreciation)

• Increased farm inventory of heifers

• Delayed milk income

• Lifetime milk production is lowe

When lighter heifers produce less milk during first lactation

• Reduced circulation of hormones and growth factors

• Less developed mammary gland

Smaller-frame heifers have increased risk of dystocia and limited capacity to compete for food/ingest nutrients

• Additional problems associated: retained fetal membranes, metritis, severe negative energy balance, loss of body condition score, etc.

• Compromised milk production and reproduction

Reasons for slower growth rates

~ poor management

~ feeding forage of poor quality and quantity

~ underfeeding grain supplements

~ inadequate bunk space

~ dominant vs submissive heifers

Prepubertal anestrus

• Not a major problem unless the feeding program is poor or

heifers are being inseminated before 12 months of age (not

recommended)

• In suitable circumstances, will affect only 5-10% of heifers by 12 months of age

Importance of reproductive efficiency in heifers

• Reduces rearing costs

• Reduced variability in age at first calving

Reproductive programs

• Recommended duration = 84 days or 4 cycles

• Natural breeding not recommended

• Efficiency of estrus detection is essential for good insemination rate (target >70%)

• Detection of spontaneous estrus

• Detection of spontaneous and induced estrus (PGF2ɑ injections every 14 days)

Timed AI programs

eliminate the need for estrus detection but can be

combined with estrus detection for AI heifers that return to estrus

Synchronization protocol for dairy heifers: 5-day CIDR

Cosynch

Timed AI

• Prescheduled

• No need for estrous detection

• Maximizes submission to AI

• Pregnancy/AI = 55-65%

TAI + DE or high estrus detection

•Higher pregnancy rates

•Lower labor

•Lower feed and total costs

•TAI only is labor-efficient but more costly per AI

•Best balance = combo programs (TAI + DE) with good estrus detection

Dairy heifer reproduction

• Nutritional management of dairy heifers is key to reproductive success

• Puberty (9 months), breeding (13 months), pregnancy (14 months), calving (23 months)

• Body weight at entrance in the breeding pen has an effect on subsequent reproductive performance

• Estrous detection efficiency is the major determinant of reproductive success in herds that rely solely on estrous

detection for breeding heifers

Timed AI + hormone summary

• PGF2α can be used to induce estrus in heifers bearing a mature CL (day 7-17 of cycle)

• The P/AI of heifers subjected to the 5-day timed AI protocol is comparable to the P/AI of heifers inseminated after detection of estrus

• The use of times AI improves insemination rate with similar P/AI and therefore increases pregnancy rate

• The benefits of times AI seem to occur even when insemination rate is relatively high, but are more attractive when estrous detection efficiency is 70% or lower

Income over feed cost in lactating cows

~ Cows are most profitable early in lactation when milk production is high and feed efficiency is best

~ Shorter calving intervals (earlier rebreeding) = more milk per year and better profitability.

Average milk production per lactation

Lactation 1: ~78% peak milk production

Lactation 2: ~ 92% peak milk production

Lactation 3: peak milk production per lactation

~ every additional kg of milk during peak is an additional 250kg over the total lactation

Replacement heifers vs cull cows

Reproductive failure is still the number 1 reason for culling cows in Canada!

~65,000 cows/year

importance of reproductive efficiency to

the economy of the dairy farm

~ Replacement heifers: reduce rearing costs, reduce variability in age at first calving

Importance of reproductive efficiency with lactating cows

Improve milk production:

• Decreases average days in milk of the herd

• Faster transition to more productive stage in following lactation

Increase # of replacement heifers:

• Allows greater genetic selection intensity

• Allows selling heifers/cows for milk production to other producers

Facilitates adequate culling policies:

• Culling of problem cows

• Younger herd = better fertility, health, and genetic merit

To have good reproductive efficiency in a

dairy herd, cows need:

1. To be inseminated within an optimal time postpartum

2. To become pregnant within an optimal time postpartum and maintain pregnancy

To be inseminated within an optimal time postpartum

Evaluated by: voluntary waiting period, DMI at first AI, insemination rate

Risk Factors: anovulation, low detection of estrus, management inconsistencies

Solutions: reduction of risk factors, heat detection aids, timed AI, systematic breeding program

To become pregnant within an optimal time postpartum and maintain pregnancy

Evaluated by: pregnancy/AI, pregnancy loss

Risk factors: disease, low BCS, anovulation, nutritional deficiencies, genetics, heat stress

Solutions: reduction of risk factors, genetic selection, fertility treatments

Reproductive indices

• Insemination rate = (number of inseminated cows) ÷ (number of eligible cows to be inseminated)

• Pregnancy per AI = (number of pregnant cows) ÷ (number of inseminated cows)

• Pregnancy rate = (number of pregnant cows) ÷ (number of

eligible cows to become pregnant)

*rate = measured over time i.e. 21-day intervals (average duration of estrous cycle)

Optimal time for insemination rate

~ 12 hours post onset of estrus

~ too early: low fertilization rate, high embryo quality

~ too late: high fertilization rate, low embryo quality

Risk factors for low insemination rate - poor estrous detection

• High milk yield

• Flooring

• Lameness

• Low body condition score

• Heat stress

• Inadequate training of employees

• Inconsistent management

Risk factors for low insemination rate - anovulation

• No estrous activity

• Directly related to energy balance postpartum - severe negative energy balance results in:

• Low glucose, insulin, and IGF-1

• High NEFA and BHBA

• Low steroidogenic capacity of the follicle and responsiveness to LH

• ~20% of cows reach the end of the VWP as anovular

• Delays first AI and reduces reproductive efficiency

Proportion of anovular cows at 60 DIM in Ontario

dairy herds

• Cow-level prevalence: 19.5%

• Herd-level range: 5-45%

Synchronization of the estrous cycle and timed AI

• Inseminate all cows in a prescheduled time with no need for estrous detection

• Maximize insemination rate (100%) and consequently improve pregnancy rate

Estrus synchronization hormones

Synchronization of the estrous cycle

Better results when protocol is initiated in early diestrus (GnRH-1 ~day 5-9)

Optimizing programs for synchronization of the estrous

cycle and timed AI: ovulation response to a GnRH injection

Day 1-4: ovulation is at 23%

Day-5-9: ovulation = 95%

Day 10-16: ovulation = 54%

Day 17-21: ovulation = 77%

presynchronization

~ target cows to be in early diestrus at initiation of Ovsynch

~ increase ovulation to GnRH-1

~ increase synchronization

~ increase P/AI

Synchronization program variations

Combination of estrous detection and synchronization programs

Nonpregnant cows should be re-inseminated within a ~30-day interval:

~50 to 70% nonpregnant cows will be inseminated before pregnancy diagnosis

~30 to 50% nonpregnant cows will be resynchronized and reinseminated within 10 days of nonpregnant diagnosis

Pregnancy diagnosis 28-34 days after AI

1. Pregnant

• Reconfirm 30 days later for diagnosis of pregnancy loss

2. Nonpregnant

A. Re-synchronization and timed AI

• Reduced alternatives for pre-synchronization

• Luteolysis during treatment and premature ovulation

B. Re-insemination at estrus

• Might result in delayed re-insemination

C. Cull/don't breed

• Late lactation cows

Considerations for timed AI programs

• Low estrous detection rate makes timed AI more attractive

• High estrous detection rate (>60%) - impact of timed AI becomes less evident

• Allows flexibility but won't necessarily improve performance

• Timed AI reduces estrous detection labor but also creates

additional work and requires tight compliance

• Best response to timed AI: management of first postpartum AI (all cows are eligible)

Fundamentals in reproductive management of dairy cows

• Work with groups of cows i.e. pro-management

• increase the rate at which cows become pregnant past the voluntary waiting period

• Use systematic breeding programs to minimize the missed

opportunities

• Increase 21-day pregnancy rate

• Reduce interval and minimize variability between the end of the voluntary waiting period and pregnancy in a consistent manner

Dairy cow embryonic mortality

~19% of fertilized eggs will fail to make it to a viable blastocyst

~39% of viable blastocysts will fail to make it to the 30-day

pregnancy mark

• Fail to undergo the processes of shedding the zona pellucida, elongating, and early implantation

Dairy cow late pregnancy loss

~19.5% of cows won't carry their calf to term

• Very expensive!

Embryo survival factors

~ clinical disease

~ low BCS at AI

~ heat stress + hyperthermia

~ anovulation at initiation of synchronization

~ low concentration of circulation steroids and IGF1

~ genetics

Heat stress and oocyte development

• highly susceptible to heat stress

• May lead to reduced fertilization, high embryonic mortality, and low P/AI

• Heat stress tolerance increases over time

• For the cow: low DMI, compromised immune system, low IGF1

Incidence of clinical diseases before first breeding

• 21% diagnosed with uterine diseases

• 25% diagnosed with non-uterine diseases

• 40% diagnosed with at lease one clinical disease

Clinical disease postpartum

~ lower rates of pregnancy, calving, increased pregnancy loss

~ not associated with expression of estrus or success of ovulation

~ decrease morula development

~ significantly decreased conceptus elongation

Does disease impact reproduction in an embryo transfer

program?

embryo transfer minimizes but does not eliminate the

reduction in fertility

Clinical disease postpartum has negative effects on

• Oocyte fertilization

• Development to morula

• Elongation of the conceptus

• Survival of the developing fetus

Genetics of the embryo - lethal haplotypes

Fertilization -> formation of maternal and paternal pronuclei-> fusion of the pronuclei by syngamy and formation of diploid zygote

Major goal in cow-calf operations

• Maximize the quantity and quality of calves born each year

• Reproductive efficiency is key!

Beef cattle breeding season

• Pre-established period of the year in which cows and heifers should become pregnant

• Should consider local environmental and market conditions (Weather, labour, Availability and price of feed, demand for market price)

• Should be short (ideally <3 months)

• Optimizes production, Requires high service (insemination) rate at earlier stages of breeding season

Impact of first calving date

•Heifers that calve earlier in the season are more likely to stay longer in the herd.

•Longevity decreases faster for heifers that calve later

•Calves from early-calving heifers (1-21 days) had higher weaning weights (especially in the first 6 seasons)

•Later calving = lighter calves at weaning

Beef cattle natural breeding

~ most common method

~ sire fertility is critical

~ annual BSE

~ ideal ratio of cows to bull

~ postpartum cow cyclicity and subsequent fertility is critical

Timed AI programs for beef cattle

• Alone/in combination with natural service

• Timed AI costs: hormones, semen, labour

• Natural breeding costs: bull purchase, infrastructure, nutrition, health, BSE

• Increases service rate, and if performed correctly, improves reproductive efficiency and profitability

• Genetics: quality of calves and replacements