Learning Reproduction in Farm Animals

LEARNING OBJECTIVES

• To understand what the different parts of the estrous cycle are.
• To understand the hormonal changes of the estrous cycle.
• To understand how the estrous cycle coordinates the events of female reproduction so it can be successful.

Anestrus

Proestrus

• Tertiary follicle(s) and oocytes undergo final maturation.

 
• Estrogen levels ­

 
• Female becomes receptive

 
• Estrogen prepares uterus and oviducts for sperm transport and fertilization

 
• Estrogen initiates uterine changes for later embryo development

 

Estrus

• Female in heat

 
• High estrogens cause LH surge

 
• LH surge causes ovulation

 

 
 
 
 
 

• LH surge initiates corpus luteum fomation

 

 
 
 
 
 

Metestrus

• Estrogen levels have decreased

 
• Corpus luteum is forming

 
• Progesterone levels start to ­

 

 
 
 

• Progesterone begins preparing the uterus for the embryo

 
• Embryo partially develops in the oviduct and moves into the uterus

 

Diestrus

• Maximum coprus luteum size

 

 
 
 

• High progesterone levels inhibit final follicular development, ovulation and estrus

 

 
 
 

• Embryo continues to develop in the uterus

 
• Embryo signals the uterus it is present - no CL regression

 

 

 If embryo is not present - uterus releases PFG2a to cause CL regression
 

If CL regresses, progesterone in blood decreases and Graafian follicle(s) begin final development that occurs in proestrus for ovulation at estrus.

 

 
 
 
 
 
 
 

Cow and Mare Estrous Cycles

Phases of the Estrous Cycle

Follicular

Luteal
 
 
 

Species Variation in Estrous Cycle Characteristics

	Ewe	Sow	Cow	Mare
Length of Cycle	14-19 days	17-22 days	18-24 days	16-24 days
Length of Estrus	24-36 hours	48-72 hours	12-19 hours	2-11 days
Time of Ovulation	24-36 hours (after onset  of estrus)	35-45 hours (after onset  of estrus)	10-11 hours (after end  of estrus)	1-2 days (before the  end of estrus)
Time of A.I.	12-18 hours after onset  of estrus	16-24 hours after onset  of estrus  and again  8-24 hrs later	7-18 hours after onset  of estrus	Second day and every other day  in estrus

 

Learning Objectives:

To understand how estrus synchronization works and how to use it successfully.

Estrous synchronization:

Why
1. Group females for parturition:

 
1. Labor, Calving period

 
2. More uniform weaning weights.

 
2. Reduce time required for estrus detection.

 
3. Eliminate estrus detection with timed insemination:

 

Cattle:

• Prostaglandins: PGF2a
• Lutalyse - Natural compound 25 mg dose I.M.
• Estrumate - Analogue 500 ug dose I.M.
• Bovilene - Analogue 1 mg dose s.q.
• Prosolvin - Analogue 15 mg dose I.M.
• Equimate - Analogue used in Mare
 
• Principle - Regress active corpus luteum
• i.e., Day 5-17 corpus luteum.

 
• In estrus 2-5 days after injection
• heifers ~50 hours;  cows ~72 hours

 
• ~60-65% of herd should respond to injection.

 
• To get whole herd synchronized, give 2nd injection 11 days after 1st
• Cows responding to 1st injection have day 6-9 corpora lutea
• Unresponding cows now have day 6-17 corpora lutea

 
• Reasons for variation of response.
• Young and old corpora lutea may respond different

 

 
 
 

• Heifers react sooner than cows.

 

 
 
 

• Animal may be pregnant - Abortion

 
• Females do not have a corpora luteum, i.e. are anestrus

 

 
 
 

Brahman Cattle
 
 
 
 


Management Consideration:

• Have proper facilities to handle animals

 
• Good reproductive records

 
• Have enough A.I. technician help

 
• Be sure cows & heifers cycling

 
• Use good fertility semen

 

Breeding with prostaglandins:

 

	Conception Rate
1. Breed 80 hours after 2nd injection	30 - 75 %
2. Breed based on estrus after PGF2a	67%
3. Control cows bred based on estrus	75%

 
Based on estrus - Breed 12 hours after the 1st observed estrus activity
 
 

Improving ovulation synchronization

48 hours after PGF_2a

-Give GnRH
	Cause LH surge; achieved slight increase in conception rates

 

Use of progestogens for Estrus synchronization

Principle:
Maintain the cow under the influence of progesterone until copur luteum regresses, remove progesterone - animal respond to ¯ progesterone with estrus. 2-5 days later.
Administration:
• Injection

 
• Feed

 
• Implant

 
• Pessary or Control Internal Drug Release (CIDR)

 
1. Synchromate B system:

Day 1
• Inject 5 mg estradiol valerate & 3 mg norgestomet
• Implant Norgestomet (Progestagen) 6 mg

 
2. Remove implant 9 days later.
 
3. Breed 48 to 60 hours later or 54 hours later.
 
• Estradiol - Luteolytic to d 3-9 corpora lutea.
• Norgestomet - Inhibits early C.L. development.

 

 
 
 
 
 
 
 
 


 

Melengesterol Acetate (MGA) System
 
• Feed progestogen for 7 days

  Prevents estrus in diestrous and proestrous animals
• Give PGF2a on Day 8 to regress CL's
• Remove progestogen on Day 9

  Cows are in heat in 2-5 days
• Alternative:

 

 
 
 
 


 
 
 


 

• EAZI-BREED CIDR System
• Insert CIDR (progestin) with CIDIROL capsule (estrogen) in vagina

 
• Day 6 inject with PGF2a
• Remove CIDR Day 7 and breed on heat detection

 

 

Ewe estrus synchronization:

• Implant progestogen for 12-14 days

 
• Remove implant, ewes in heat in 36-60 hours

 
• May use eCG at implant removal to stimulate follicular growth

 
• Sperm transport is impaired, fertility good 1 ram/10 ewes

 

 


 



Sow estrus synchronization:

• PGF_2a will not cause C.L. regression until day 12 of the cycle.

 

 
 
 

• Common progestogens will synchronize estrus but cause ovarian cysts

 
• Progestogen -

Allyl trenobolone fed at 20 mg/head/day for 18 days - remove from feed - in heat in 4-8 days. Fertility normal - a minor incidence of cysts.
 
 
• Prepubertal Gilts

 

 

 P.G. 600
 

Mare estrus synchronization:

1. Luteolytic PGF_2ain diestrus, in heat in 4-5 days

 
2. -Use of prostaglandins in horses:
• Equimate (Fluprosterol)
• Other prostaglandins ~1/5 cow dose
• Mare C.L. more sensitive
• Side effects:

 
Treatments with PGF2a
 
 
 
 
 
 
 
 
 
1. Use of progestins in horses
• Regumate
• .044 mg/Kg body weight in feed
• Feed for 12 days
• Remove from feed; give equimate
• In heat 3-4 days later

 

 

Utilization
 
 
 
 
 
 

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