Dr. Julio Giordano

GnRH

Follicle Corpus LuteumOvulation

CL Progesterone

Estrus Estrus5 10 15

Hormon

e  Con

centratio

n

Ovulation

E2FSHLH

Days

Ovulation

Hypothalamic hormones – Gonadotropin releasing hormone (GnRH)

Control LH synthesis and

release

0

2

4

6

8

10

12

-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

LH (n

g/m

L)

Time (h)

LH Response Cows Treated with GnRHGnRH

Ovulation

28 h (22-36)

Hypothalamic hormones – Gonadotropin releasing hormone (GnRH)

Control LH synthesis and

release

1. Regular dose is 100 µg (2 cc or 1 cc)

1. Treatment with GnRH in pregnant cows neither detrimental nor beneficial for current pregnancy

2. Greatest detriment to GnRH function is progesterone level

(370/962)

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

LH (n

g/m

L)

Time after GnRH Injection (h)

High P4 EnvLow P4 Env

P4 Env P < 0.001Time P < 0.001P4 Env X Time P < 0.001

100 μg of GnRH

* **

**

**

**

**

*

(n = 981) (n = 956)

0

10

20

30

40

50

60

70

Low Medium High

Ovu

lato

ry R

espo

nse

to G

1 (%

)

Progesterone concentration at G1

c

b

a

(134/227) (115/302) (33/211)

P 90% cows fol ≥ 10 mm Uterine hormones

– Prostaglandin F2α (PGF)

Causes luteal regression

Exogenous PGF is responsible for “triggering” rather than

causing luteolysis

Endogenous pulses of PGF Prostaglandin F2α (PGF)

– Natural form of PGFDinoprost – 25 mg (5 cc or 2 cc)

– Synthetic form of PGF Cloprostenol – 500 µg(2 cc)

Causes luteal regression

Progesterone– Main secretion of the CL

Multiple functions:– Regulates gonadotropin

(mostly LH) secretion• Blocks estrus and Ovulation• Promotes development of healthy (fertile oocyte/egg)

Corpus Luteum

CL Progesterone

Estrus Estrus5 10 15

Ho

rmo

ne

Co

nc

en

trat

ion

Ovulation E2FSH

LH

Days

Ovulation

UT PGF

– Consistent and systematic implementation of estrus detection method

– Heifers DO NOT present same limitations to estrus expression as cows• No milk production• Less metabolically

challenged• Fewer health issues

– Key factors for success• Good nutrition• Good health• Reasonable

environmental conditions

PM Fricke, Ph.D.

27.6 ± 5.4 h after the first standing event of estrus (Walker et al., 1996)

4 to 12 h of the onset of estrus

Sperm needs to be “ready”

to fertilize before oocyte is “released”

PGF2α PGF2α

11 or 14 d

Estrus EstrusPGF-based programs

• Only effective in cyclic animals (CL present)

• Heifer expected to regress CL, show estrus, and ovulate

• Timing of ovulation not as tightly controlled

PGF2α

7 d

EstrusP4-based programs

• Only synchronizes estrus

• Progesterone blocks ovulation and may favor follicular wave turnover

• Heifer expected to regress CL, show estrus, and ovulate (unless GnRH is used at the end)

Progesterone

PGF2αGnRH TAIGnRH

7 days 56 h 16 h

Pursley et al. 1995

PGF2αGnRH TAIGnRH

7 days 56 h 16 h

Pursley et al. 1995

Critical events for successful AI are those closer to the time of AI – critical to respect timing!!!

~8 d fol. growth

~6 d fol. growth

PGF PGFGnRH + TAI

5 days 1 d 2 d

GnRH

Progesterone device

ExpectedP/AI* = ~50-65%

*with conventional semenRabaglino et al., 2010, Lima et al., 2013; Santos et al., 2011

GnRH + TAI

5 days 1 d 2 d

±GnRH

Progesterone device

ExpectedP/AI* = ~50-65%

1X PGF vs. 2X PGF = ~3-4-percentage points - ???

GnRH vs No GnRH = ~4-5-percentage points Rabaglino et al., 2010, Lima et al., 2013; Santos et al., 2011*with conventional semen

PGF PGF

PGF PGFGnRH + TAI

5 days 1 d 2 d

GnRH

Progesterone device

ExpectedHighest P/AI* = 60-65%

*with conventional semenRabaglino et al., 2010, Lima et al., 2013; Santos et al., 2011

PGFGnRH + TAI

5 days 3 d

Progesterone device

ExpectedLowest P/AI* = 50-55%

*with conventional semenRabaglino et al., 2010, Lima et al., 2013; Santos et al., 2011

21d-Preg Risk

21d-Service Risk

Conception Risk

AI Tech

Male factors (semen)

Sexed Semen

AI #

Estrus detection

TAI interbreeding

interval

Health Nutrition

AgeEnvironmental conditions

Housing

Synch protocol

21d-Preg Risk

21d-Service Risk

Conception Risk

11.7 months

13.3 months

Does the actual AGE at the first inseminations match the stated VWP?

Using AIDAT item ideal for herds that do use AGE to determine

end of VWP

Not using AIDAT in these herds

artificially reduces 21d-Pregnancy Risk

Individual (or subgroup) heifer VWP

Successful repro program:

1. proactive, systematic, and consistent

2. conducted by committed personnel -prioritizes attention to detail

3. Healthy animals!

Thank you!

Julio Giordanohttp://blogs.cornell.edu/giordano/

jog25@cornell.edu