Cow and Ewe Reproduction - Basics

How long is the bovine in Estrus?

4-12 hours

How long is the luteal phase in the cow?

17-18 days

How long is the follicular phase in the cow?

3 days

When does ovulation occur in the cow?

AFTER heat/estrus

Most dairy cows have a __ wave cycle

2

Dominant follicles are typically __ mm in size

9-19

Most beef cows have a __ wave cycle

3

Beef cows estrous cycle length is about

22-24 days

Dairy cow estrous cycle length is about

18-22 days

How long is the gestation period for calves?

9 months

What events need to occur within 3 months post calving for a cow to stay on a 12 month calving interval?

Uterine involution, resumption of ovarian and estrous activity, clearacne of uterine infections, heat detection and successful insemination

If a cow has not cycled in 2.5 months post calving, what can be done?

Induction/synchronization of estrous cyclicity to get the cow in estrus to inseminate within 3 months post calving

By 4-5 weeks post partum, we want to see a resumption of the following

Frequent LH pulsatility, dominant follicle growth and E2 secretion, Dominant follicle ovulation

Cows need to resume normal estrous cycles by __ weeks post partum to be mated or submitted for AI and achieve pregnancy __ months post partum

6-7, 3

What factor can lead to prolonged post partum 1st ovulation in dairy cows?

Negative enregy balacne post partum → loss of more than 0.5 BCS (1-5 scale)

What factors can lead to prolonged post partum 1st ovulation in beef cows?

Low BCS at calving and/or maternal bond

In the dairy cow, when in terms of milk production and appetite do we aim to begin breeding them?

When milk production is peaked and appetite is decreased.

What events can lead to decreased cyclicity in dairy cows?

Changes in BCS can negatviely impact the hypothalamus

Disease can decrease ovarian function (E2)

What heat detection aids are commonly employed on farm?

Synchronization of heat/ovulation (most common)

Tail painting

Kamar heat detector

Vaginal resistance

Pedomoters/activity monitors

What is the am/pm rule when using AI in cattle?

If a cow comes on heat, about 12 hours later, the animal is inseminated.

If you use AI early, what negative effect(s) may happen?

Sperm may die out before ovulation

If you use AI late, what negative effect(s) may happen?

Less sperm selection, aging ovum, low embryo quality

When is pregnancy diagnosis prior to six weeks best achieved in cows?

18-24 days from breeding

OR

Transrectal US ~28 days from breeding

When is pregnancy diagnosis after six weeks best achieved in cows?

42 days (Palpate amniotic vesicle)

OR

3.5 months (Begin fremitus in pregnant horn)

What does the expanding blastocyst produce that leads to maternal recognition of pregnancy in cows?

Bovine trophoblast protein

What does bovine trophoblast protein do in relation to other hormones/structures within the cow?

Negative inhibition on uterus to prevent PGF2-a production leading to no luteolysis of the CL (P4 maintained)

How long is the ewe estrous cycle?

17 days

How long is the ewe luteal phase of estrous?

14 days

How amny follicular waves do ewes have per cycle?

2-4

When in their cycle is ovualtion in ewes?

End of estrus

How long is estrus in ewes?

24-36 hours

How do sheep, in terms of follicles, end up with twins (or more) at such a high rate?

Co-dominant follicles, one dominant follicle from second to last wave and one dominant follice from the final wave prior to ovulation.

What type of estrous cycle do ewes have?

Seasonal, Short day breeders

What regulates ewes to be short day breeders?

Daylength synchronizes with reproductive cycles via melatonin

How long is ewe gestation?

147 days