Repro Lab #10

Most reliable sign of estrus in cattle?

Standing to be mounted (standing heat)

How long do cows stay in standing estrus?

~18 hours

When does ovulation occur relative to estrus?

~10-14 hours after onset of standing heat (~30 h after first signs)

When is the optimal time to inseminate a cow?

Last 9 hours of estrus or first 6 hours after it ends

What is the A.M/P.M rule?

Detect estrus in AM → breed PM → breed next AM

Why is accurate estrus detection critical?

Ensures insemination occurs before ovulation → higher fertility

When are cows most active for estrus behaviors?

Near sunrise and sunset

Early (proestrus) signs in cattle

• restlessness

• Mounting others

• Aggression

• Mucus discharge

What indicates a cow has already been mounted?

Chalk rubbed off on rump

What does partially rubbed chalk indicate?

Attempted mounting, but not true standing estrus

What does completely rubbed-off chalk indicate?

True standing event occured

What does bloody discharge after estrus indicate?

Metestrus (after ovulation)

What estrus detection behaviors are scored highest?

• standing to be mounted

• Positive estrus indicator

What score threshold indicates estrus in this lab system?

More than or equal to 20

Why should cattle not be disturbed during observation?

Stress alters natural estrus behavior

How often should estrus detection occur?

At least twice daily (~1 hour sessions)

What is the purpose of estrus synchronization?

Control timing of ovulation → reduce need for detection

What hormone causes luteolysis (CL regression)?

Prostaglandin F2alpha

What hormone maintains pregnancy?

Progesterone (from corpus luteum)

What hormone triggers ovulation?

LH (Luteinizing hormone surge)