Optimizing Reproduction in Dairy Cattle

1
Optimizing Reproduction in Dairy Cattle
2
Reproductive Management of the Bull
3
Managing Natural Service Sires

• About 25 of dairy farms maintain one or more
  mature bulls
• More costly than using only artificial
  insemination
• Kept on the farm to improve pregnancy rates
• Can present dangers and health risks

4
Bulls Age and Intensity of Use

• Young bulls shouldnt be used as heavily as older
  bulls
• Young bulls can service 2-4 cows per week
• Old bulls can service up to 12 per week
• Younger bulls tend to be preferred
• Less dangerous
• More likely to be reproductively and functionally
  sound
• Bulls under 1,000 lbs should only service heifers

5
Housing Bulls

• Bulls housed with breeding age females
• Drawbacks
• Dominant bull may prevent subordinates from
  breeding
• Destructive behaviors
• Bulls are housed separately, females are brought
  to bull for breeding
• Drawbacks
• Heat detection required

6
Fig 25-4. Herd bulls are not only a safety hazard
for people, they are hard on facilities as well
(Courtesy of Mark Kirkpatrick)
7
Fig 25-5. Although this bull appears healthy, he
will spread trichomoniasis to cows during natural
service (Courtesy of University of Illinois)
8
Natural Service (NS) vs. AI
Smith et al., 2004
9
Natural Service Issues

• Daughter performance
• Although the genetics of herd bulls continues to
  improve, the gap between herd bulls and AI bulls
  continues to widen
• 600 lbs milk (1972) to gt1500 lbs of milk (now)
• However, in one study, increase of 700 lbs of
  milk/cow in NS herds
• Improved pregnancy rate, shorter calving interval
• http//dairy.ifas.ufl.edu/dpc/2002/Risco.pdf
• Costs are greater for bull maintenance
• Safety issues HUGE!!!
• Facility issues

10
Reproductive Management of the Cow
11
Heat Detection and Synchronization of Estrus
12
WATCHING FOR HEATS IS?

• 1. BORING!!!!!
• 2. Time consuming (up to 1.5 hrs./day)
• 3. Tough cows only stand for 2-7 seconds
• at a time - 1 of heat
  cycle
• need more than one cow to have a
  party only cows in follicular
  phase want to play
• more cows more estrus activity
• 4. Everything happens at night

13
Fun Facts

• Over 40 of all cows in estrus are missed
• 20 of all cows bred are not in estrus
• Up to 90 of all estrus activity occurs between 6
  pm and 12 noon
• 70 between 6 pm and 6 am
• Two 30-min detection periods will catch 80 of
  all cows in estrus
• Three periods will catch 90
• For 3 breeding groups, this requires 3-5 hours
  daily

14
Fig 26-4. Inseminating a pregnant cow breaches
the cervical plug, greatly increasing the risk of
abortion (Courtesy of Select Sires)
15
Problems with Heat Detection

• Even if time is devoted to observe heats, it is
  still challenging
• Multiple groups of animals requiring observation
• Two 30-minute observation periods will detect 80
  of heats
• But that is only for 1 group of animals

16
Fig 26-5. Cows in the follicular phase of the
estrous cycle often form sexually active groups
with increased mounting activity (Courtesy of
Iowa State University)
17
Heat Detection Aids

• 1. Whats available?
• 2. How do they work (or not work)?
• 3. How good are they?
• 4. Whats it gonna cost ()?
• Heat detection rules
• What makes everything work (not work)?

18
RECORDS
CRITICAL!!
A 1 PRIORITY
19
Heat Detection Methods and Devices

• Three categories of heat detection aids
• Those that detect primary signs of heat
• Those that detect secondary signs of heat
• Those that measure hormonal changes associated
  with estrus

20
Aids Measuring Mounting Behavior

• Tailhead markers
• Coat of wax crayon or latex paint applied to
  tailhead region of the cow
• Mounting activity rubs the paint off
• Cost of markers low, but labor intensive
• Accuracy is affected by rainy weather and oily
  haircoats
• Dye-filled tailhead patches
• A 2 by 4 inch fabric base with a plastic capsule
  attached
• When cow stands to be mounted, pressure ruptures
  the dye-filled capsule which releases dye
• An example of this is a Kamar patch

21
Fig 26-6. Marking crayons are an inexpensive
method for marking tailheads to detect mounting
activity (Courtesy of Mark Kirkpatrick)
22
TAIL CHALKING / PAINTING

• Easy to apply
• Need for reapplication?
• 50-60 accuracy (chores)
• 67-79 checked 2X/day
• 72-81 checked 3X/day
• Cot? material/labor

23
TAIL CHALKING

• Must be reapplied daily
• Must be interpreted daily?
• Interpretation?
• .01-.05/ application labor
• color coding

24
TAIL CHALKING
25
TAIL PAINTING

• Reapply every 1-3 weeks
• Must be interpreted daily?
• Interpretation?
• 5 - 25/gallon?
• 10/ bottle - .10/application labor
• color coded

26
Fig 26-7. Heat mount detectors are glued to the
tailhead region of the cow and are activated by
pressure (Courtesy of M.E. Ensminger)
27
Fig 26-8. Mounting activity ruptures the internal
dye capsule in a heat mount detector, changing
the detector color to bright red (Courtesy of
Iowa State University)
28

• Easy to apply
• Must stay on to work!
• False mounts - what can trigger?
• 50-60 accuracy (chores)
• 67-79 - checked 2X/day
• 72-81 - 3X/day
• 0.65 - 5.00 labor

Glue, get dirty!
29
Never stayed on, Never triggered if it did
5.00

• Can they stay on
• Can they trigger (easy or hard)

H a r d
E a s y
1.25

2
Glows in the dark
30
STICK AND SCRATCH
1-1.50 NO GLUE!?
31
Aids Measuring Mounting Behavior

• Electronic pressure-sensitive sensors
• A transmitter inside of a fabric patch is glued
  to tailhead
• Mounting behavior activates the transmitter which
  sends signal to computer
• Computer stores cow ID and time of each mount
• This eliminates need for visual observation, but
  includes a high initial capital investment and
  high cost of transmitter loss

32
Fig 26-9. Electronic mount detectors are secured
to the cow's tailhead with a large fabric patch
(Courtesy of Mark Kirkpatrick)
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34
Electronic rump mounting devices(computerized)
Radio waves
35
Electronic rump mounting devices(computerized)
36
Electronic rump mounting devices(computerized)
Standing heat 3 mounts in a 4 hr.
period Suspect heat any mounts
37

• Must glue or attach well
• Easy to use - computer
• (data comes to you)
• 85-95 efficient (suspects)
• 90 accuracy (false mount)
• mounts when, how many!

• COSTS
• - 6-7 / patch glue
• - 55 / transmitter
• - 3000-4500 (computer equip)
• annual cost 6 55/years X cows
• 3000/years X cows
• Labor costs lt 50 of visual

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The only good patch is the one that STAYS ON!
This will transmit well! Patches must be checked
daily! The system takes some labor.

• Very good, highly accurate system
• Must weigh out the costs (capital and labor)

39
ISU TRIAL

• Visual / Kamar vs. Heatwatch
• 60 day breeding period
• No difference in
• - total animals detected in heat
• - conception rates at all services
• - overall pregnancy rates
• Heatwatch saved time!!!

40
Electronic rump mounting devices( not
computerized)
Reset button
Lights breed heat suspect
Pressure switch
60/ 20 mounts - 3/mount 6/ patch glue Visual
labor is crucial! Accuracy gt patch lt HW
41
Aids Measuring Mounting Behavior

• Teaser animals
• Either testosterone treated heifers or surgically
  modified teaser bulls
• Risk to personal safety
• Expensive to feed and manage
• Can be destructive to equipment
• Chin-ball marker
• Ball point pen attached to halter of teaser
  animal
• When mounting cow, ink is smeared on cows rump
• Relies on presence of teaser animal
• Cows not in estrus will be marked as well

42
Teaser / Masculinized Animals

• Sound feet and legs
• Hormone shots / implants (synovex H)
• 1 month adjustment / good for 6 months
• may only need for 1 week Synchronize happy /
  exhausted

Best detectors may be the existing females in
your herd!!!
43
Aids Measuring Secondary Signs of Heat

• Pedometers
• Electronic devices strapped to rear leg of cow
  measure activity level of animal
• Can provide information regarding time of onset
  of increased activity that occurs during estrus
• Increase in activity can also be due to weather
  or changes in management, making this aid less
  accurate

44
PEDOMETERS/ ACTIVITY

• Accurate
• Insemination timing
• Easy to use
• Visual crucial
• Cost 50-200
• False positives

45
Aids Measuring Secondary Signs of Heat

• Vaginal probes
• Measure electrical impedance of vaginal mucus
• Decrease in electrical resistance when estrus
  occurs
• More accurate than visual observation, but
  requires individual response curves for each
  animal
• Each animal must be probed daily, increasing risk
  of infection

46
Electrical resistance - vaginal mucus
47
Electrical resistance - vaginal mucus

• Very accurate
• Can use to time insemination
• Can use to breed early for females
• Missouri yes (92 males/females)
• ISU / Arkansas NO!
• Labor intensive 2X/day around estrus
• Infection risk if not sanitary!!!!!!!!!!

48
Electrical resistance - vaginal mucus
1600 (dead)
2500

• Currently evaluating
• - heat detection
• -pregnancy detection
• - sexing ( breeding)
• (post breeding)

150
49
Aids Directly Measuring Hormones

• Milk progesterone kits
• Can be used to identify cows with low
  progesterone, but not to determine that a cow is
  in estrus
• Fairly expensive and labor intensive

50
IDEAL HEAT DETECTION SYSTEM

• Continuous surveillance (24 hrs./day)
• Accurate / automatic animal ID
• Operate for productive lifetime of animal
• High accuracy at identifying events
• Minimal or no labor requirement
• Cot cheap or effective?

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Summarizing Use of Heat Detection Aids

• Usefulness depends on cost of aid and value put
  on labor for visual observation
• Will not solve all problems associated with
  reproductive failure

53
Evaluating Reproductive Performance
54
Factors Driving Reproductive Performance of the
Dairy Herd

• 1. Voluntary Waiting Period
• 2. Pregnancy Rate on First Cycle
• 3. Pregnancy Rate on gt 1st Cycle
• 4. Culling Rate

55
Factors Affecting Reproductive Performance of
Dairy Herds
1st Cycle Preg Rate
VWP
2nd Cycle Preg Rate
Culling Rate
56
Pregnancy Rate

• The Percentage of ELIGIBLE Cows that become
  pregnant every
• 21 Day Interval
• equals
• Heat Detection X Conception Rate

57
Pregnancy Rate 18 cows/ 100 18
58
Survival Curve for Various Pregnancy Rates
50 Preg
59
Assisted Reproductive Technologies
60
Assisted Reproductive Technologies

• This term covers many areas
• Artificial insemination
• Multiple ovulation embryo transfer programs
  (MOET)
• In-vitro fertilization
• Cloning
• Natural service is no longer the most common
  approach towards establishing pregnancy in the
  dairy cow

61
Artificial Insemination

• More than 65 of dairy cattle are artificially
  inseminated
• Genetic progress has been phenomenal
• AI bulls advancing cows genetics at rate of 250
  pounds per year

62
Fig 27-1. A cow is inseminated using frozen semen
(Courtesy of Mark Kirkpatrick)
63
Advantages of AI

• Increases use of outstanding sires
• All producers have equal access
• Alleviates danger and expense of keeping a bull
• Decreases breeding costs
• Helps control diseases
• Makes it feasible to prove more sires
• Increases pride of ownership
• Alleviates distance and time as limiting factors
• Increases profits
• Daughters of outstanding sires are higher
  producers

64
Limitations of AI

• It requires training
• May accentuate damage of a poor sire
• Increased number of progeny
• May increase spread of disease

65
Insemination Procedures

• Semen handling is very important
• Exposure to temperatures above -112 degrees F
  harms sperm
• Repeated exposure increases damage
• Ice crystals enlarge damaging cell membranes
• Maintain over four inches of liquid nitrogen in
  tank
• Check twice a week with a measuring stick

66
History of Embryo Transfer

• NOT a new technology
• First embryo transfer in Wisconsin in 1943
• First calf in 1951
• First non-surgical calf in 1964

67
Multiple Ovulation Embryo Transfer (MOET)

• For ET to be profitable, donor cows must truly be
  genetically elite
• Process is less expensive if several cows can be
  flushed at the same time
• The use of ET for improving the genetic status of
  a herd is not typically profitable unless some
  offspring can be marketed at a price that will
  offset the cost of the transfers

68
Considerations for MOET

• Offspring must be valuable enough to warrant
  costs
• 750-1000 per procedure if multiple cows flushed
• Over 1500 if single cow flushed
• Average 4-5 pregnancies per flush
• Average 2 heifer calves per flush
• Cost per heifer calf is 150-550 if bulls have no
  additional value beyond sale barn

69
Management Considerations

• Donor cows receive 33-37 mg FSH in decreasing
  doses
• No decrease in estrus intensity or duration
• Shorter interval from PG administration to estrus
  --- and more variable
• Greater than 12 hour synchrony difference between
  donors and recipients decreases pregnancy rate
• Number of follicles present affect timing of
  insemination
• More follicles results in more CLs, more P4
• More P4 results in faster ova migration
• Requires multiple inseminations to ensure
  fertilization

70
Fig 27-13. Embryo transfer derived offspring and
the donor cow from which they originated
(Courtesy of Iowa State University)
71
Synchrony

• Synchrony between the donor cow and recipients is
  critical
• As little as a 12 hour difference between time of
  donor and recipient ovulations can reduce
  possibility of successful pregnancy
• Embryos not immediately transferred can be frozen
  for later transfer
• Glycol or glycerol as cryoprotectant
• Pregnancy rates slightly lower

72
In Vitro Maturation and Fertilization

• Ability to mature or fertilize ova in a culture
  dish
• Infertile or pre-pubertal animals can reproduce
• Immature oocytes are aspirated from follicles of
  superovulated animals
• Done by transvaginal ultrasound imaging
• These oocytes are cultured for 24 hours
• Fertilized by addition of capacitated sperm to
  the culture media
• Cultured further until blastocyst stage is reached

73
Transgenics

• Pharmaceuticals
• Improved performance
• Challenges in controlling expression of transgene
  (very few express optimally)
• Monitor transgenic offspring for optimal
  expression and clone the successes
• Limits practical applications to very profitable
  options only

74
Patented Animals

• April 1987, the US PTO ruled that patents could
  be issued on genetically engineered animals
• Livestock producers pay fees to those who patent
  these animals
• Livestock producers must pay royalties to the
  patent holder on each generation of patented
  animals for life of the patent
• May be 17 years

75
Cloning

• Production of an exact genetic copy
• Nucleus of any cell replaces genetic information
  present in a one-cell embryo
• Does not mean clones are phenotypically identical
• Cloned calves are currently being routinely
  produced
• Profitability is limited

76
Fig 27-18. Annie, born March 3, 2000, is a clone
of a pure-bred Jersey calf (Courtesy of USDA-ARS)
77
Why Clone??

• Reproduce animals with a unique ability
• expressed transgene
• growth or lactation
• Reproduce animals with a unique value
• pets, family members
• spare parts
• endangered species
• extinct species

78
Challenges for Cloning

• Expensive
• Inefficient
• 692 embryos
• 81 blastocysts
• 8 pregnancies
• 1 live calf
• Genetic diversity
• Genetic improvement
• Developmental problems
• embryo
• fetus
• newborn

79
Challenges at Birth

• Placental insufficiency
• Gestation length
• Birth weight
• Signaling for parturition
• C-section required
• Umbilical cord
• Colostrogenesis

80
Challenges After Birth

• Pulmonary development
• Hypoxic
• Acidotic
• Hypoglycemic
• Thermoregulation
• Immune function
• Fluid balance
• Genetic expression different than original

81
Clones

• Theoretically identical animals
• Genetically they are NEARLY identical
• Nuclear DNA identical but cytoplasmic factors and
  mitochondrial DNA are different
• Phenotypically can be quite different
• Environmental influences impinge on expression of
  genes
• Altered methylation patterns for 25 of genes

82
Pregnancy and Parturition
83
Pregnancy

• Initiated at conception
• Embryo survives on uterine secretions until
  implantation (day 32)
• Cattle develop a cotyledonary placenta
• Attaches to caruncles
• Risk of pregnancy loss decreases as pregnancy
  progresses

84
Pregnancy Loss in Lactating Dairy Cows
n 512 breedings 480 calvings Total loss (d28
to calving) 24.7
Day 28 - 56 13.5 (12/89) Fricke et al., 1998

28
56
70
98
282
42
Vasconcelos et al., 1997. Biol. Reprod. 56(Suppl
1)140 (Abstr.)
85
Early Embryo Losses

• Significant problem
• 15-40 of fertilized ova fail to develop through
  43 days
• Most losses occur between days 8 and 19 after
  breeding
• Many losses are associated with inadequacies in
  nutritional management
• Important to balance rations properly

86
Early Embryo Losses

• Critical time and steroid requirements in uterus
  for proper protein synthesis
• Uterine secretions differ between normal cows and
  repeat breeders
• Levels of electrolytes and other minerals

87
Fetal Losses

• Fetal death pregnancy losses between day 43 and
  term delivery
• Mummification can occur
• Can be palpated and expelled with treatment with
  prostaglandins
• Early fetal death can go unnoticed
• Expelled
• Abortions are calves expelled prior to 271 days
  of gestation
• May be born dead or alive

88
Fetal Development

• Developing embryo is considered a fetus when all
  organ systems are present
• About 45 days into pregnancy
• Fetus is surrounded by two membranes
• Fluid filled amnion
• Fluid is viscous and acts like lubricant during
  delivery
• Chorio-allantois
• Allantoic fluid is the water bag

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Fetal Development

• Placenta is a fetal organ
• Doesnt exchange blood with cow
• Obtains nutrients and oxygen from dam and removes
  waste products
• Through caruncles and cotyledons
• Umbilical cord is lifeline between placental
  cotyledons and fetus

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Placentation

• Cotyledonary placenta
• Maternal caruncles
• 80-100
• Fetal cotyledons

• Placentome
• Complete attachment by 45 d

94
Fig 28-7. Placental cotyledonary tissue wraps
around uterine caruncular tissue to create sites
of nutrient and gas exchange between the fetus
and dam (Courtesy of Select Sires)
95
Hormones
96
Preparing for the Calving Process

• Timing of birth is decided by fetus
• Three weeks prior to birth adrenal glands produce
  more cortisol
• Triggers changes required for normal delivery and
  lactation
• Placenta produces estrogen from progesterone
• Initiates colostrogenesis
• Stimulates maturation of calfs gut and lungs
• Few days before calving cortisol triggers hormone
  cascade
• Decrease in progesterone
• Relaxin

97
Fetal Control of Birth

• Cortisol (fetal adrenal gland)
• Placenta Fetus
• (P4 E) lung and gut
  development
• relaxin
• Ligaments Uterus (PGs) Mammary Gland
• pelvis increased tone alveolar
  regeneration
• vertebral colostrogenesis

98
Induced Calving

• Administer a glucocorticoid which stimulates
  dams preparation for calving
• Stimulates development of calfs gut and lungs
• Can be induced too early
• No colostrum
• Calf not fully developed
• Retained placenta almost always occurs

99
Induced Calving

• Adding relaxin and a progesterone antagonist can
  help create a more normal hormone pattern for
  delivery
• Still difficult to know when to induce calving
  due to variability of gestation period

100
Signs of Impending Calving

• Udder fills with colostrum, teats fill last
• Udder edema front to back
• Vulva swells, mucous discharge
• Mucus consistency changes
• Sticky to clear and free flowing
• Sacrosciatic ligament loosens, pins drop, tail
  flexibility increases
• Cow shape changes
• Barrel shape (last 3 weeks) to pear shape (1 wk)
  to calf disappears (day of calving)
• Timing of changes aid in prediction of calving
• Length of gestation is controlled by genetic and
  environmental factors

101
The Birth Process - Stage 1

• Period of cervical dilation
• Influence of progesterone decreases
• Uterine contractions increase in frequency
• Fetus is moved towards birth canal
• Pressure from chorioallantoic sac induces
  cervical relaxation
• Behavioral changes are subtle
• Cervix dilates to 3-6 inches
• Stage 1 lasts for 2-16 hours

102
Fig 28-10. The first stage of labor is
characterized by circling behaviors, raised tail,
and increased defecation and urination (Courtesy
of Howard Tyler)
103
Fig 28-10. Mucus consistency and quantity both
change dramatically shortly before calving
(Courtesy of Howard Tyler)
104
The Birth Process Stage 2

• Initiated as fetus enters the cervix
• Uterine contractions increase in frequency and
  develop a rhythm
• Labor pains occur as clusters of 5-8 contractions
• Stretching of birth canal
• Induces release of oxytocin
• Pressure from fetal head and shoulders fully
  dilate cervix

105
Oxytocin

• Produced by hypothalamus
• Released from posterior pituitary
• Release stimulated by pressure receptors in
  cervix (cervical stretching)
• Receptors increase greatly during calving
• disappear within hours of calving
• Causes uterine contractions and abdominal
  straining

106
The Birth Process Stage 2

• Premature rupture of the chorioallantois
  temporarily stops abdominal contractions
• Feet of fetus appear 30 minutes after the fetus
  enters the cervix
• After this point progress is slower because head
  and shoulders require further dilation
• Between 5-45 minutes after feet appear,
  contractions increase in intensity and fetus is
  expelled within 15-30 minutes
• Stage 2 labor lasts 15 minutes to 3 hours
• Breed and parity dependent

107
Fig 28-11. The normal birth presentation for a
calf (Courtesy of Select Sires)
108
Fig 28-12. A Jersey cow in early Stage 2 labor
(Courtesy of Howard Tyler)
109
Fig 18-13. The goal of a successful reproduction
program is the delivery of a healthy calf
(Courtesy of Mark Kirkpatrick)
110
The Birth Process - Stage 3

• Period leading to expulsion of fetal membranes
• Usually takes 4-6 hours
• If not expelled within 12 hours it is termed a
  retained placenta
• Dystocia increases incidence of retained placenta

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Gestation Length

• Average 283 d (9 months)
• Shorter for first-calf heifers
• Longer for bull calves

113
Single vs. Twin Delivery
114
Multiple Births

• Twins occur in 2 out of 100 births
• Triplets in 1 out of 10,000 births
• Individual twin weights are 20 lighter than
  single calf weight
• Identical twins have single placenta
• Fraternal twins have two placentae

115
Reproductive Success

• NOT fertilization
• NOT 60-day pregnancy rates
• NOT pregnancy
• NOT delivery of a calf
• Reproduction is not successful unless you produce
  a live calf delivered with a minimal amount of
  stress on the dam!!
• Lactation performance depends on the success of
  the reproductive process

116
Primary Causes of Reproductive Failure

• 1 - cows bred at wrong stage of heat
• 15 pregnancy rate
• 2 insemination techniques
• 66 fail to place semen in body of uterus
• 25 never reach uterus at all
• Improper handling and timing
• Decreased conception rates after 2nd straw
• 3 early embryo losses
• 4 abortions and stillbirths

117
Does High Milk Production Affect Reproductive
Function?

• Estrogen and progesterone control uterine
  environment
• High estrogen, low progesterone high oxygen
• Low estrogen, high progesterone low oxygen
• Progesterone drives secretion of uterine milk
• Therefore, hormonal imbalances alter embryo
  survival rates!!
• Same embryo survival issues (and reasons) occur
  with increasing age (after 8 years of age in
  cattle)
• Same across all species

118
Reproductive Hormones and Milk Production

• Estradiol levels lower in high-producing dairy
  cows than in heifers
• Progesterone levels lower in cows
• Despite the fact that CL size is larger!!
• Rate of progesterone breakdown 2/3 faster
• Fertilization rate is similar in lactating cows
  and heifers (90-95)
• Embryo quality lower in cows
• Survival rates for embryos is lower

119
More Problems
Cows Heifers
Estrus duration (hrs) 7.3 11.3
Ovulation Failure () 20 lt1
Cells per Embryo 19 38
Multiple Ovulations () 25 2
Twinning Rate () 10 1
Pregnancy Rate () 35 70
Pregnancy Loss () 20 lt1
120
More Problems

• Cows producing gt 100 lbs milk have 20 double
  ovulations vs. 7 in low producers
• Higher twinning rate
• Best genetics not being transferred to next
  generation

121
Biological Mechanisms

• High Milk Production (gt100 lbs)
• Increased Feed Intake
• Increased Blood Flow to the Gut and Liver
• Increased Steroid Clearance Rates (E and P4)

122
The Crucial Role of Changes in Blood Flow

• Rate of blood flow drives all metabolic processes
• Re-directing blood flow alters metabolic
  processes
• Digestion
• Reproduction
• Lactation
• Always consider how management decisions affects
  blood flow
• Feed intake
• Exogenous bST (through IGF-I)
• Stress or fear (fight or flight)
• Temperature