Small Ruminant Small Ruminant ReproductionReproduction

D. G. Ely, E. Fink, F. Berry, T. Caudill D. G. Ely, E. Fink, F. Berry, T. Caudill

Important Terms• Estrus (Heat) or Estrous Period

Period of time when ewe or doe will receive the male, ovulate, and egg can be fertilized

–20-42 h long in small ruminants

–Signs include standing, turns head towards male, raises dock or flags tail, bleating

–Ovulation occurs approximately 30 h into heat

Important Terms

• Estrous Cycle Length of time from one estrous period (heat) to another if fertilization does not occur–Ewes – 16 to 17 d long–Does – 19 to 21 d long

Important Terms

• Puberty When an animal reaches sexual maturity and can physically reproduce–Small ruminants – 5 to 8 mo or later

Important Estrous Cycle Events

- Follicle development- Prior to ovulation- Caused by follicle simulating hormone (FSH)- Multiple follicles develop in small ruminants,

can be on both ovaries- Developing follicles secrete estrogen, causes

ewe or doe to show signs of estrus

Important Estrous Cycle Events

- OvulationRelease of egg or eggs from ovary-Caused by luteinizing hormone (LH) from pituitary gland

Developed follicles rupture, eggs drop into fallopian tube, can be fertilized if sperm present

Important Estrous Cycle Events- Corpus Luteum (CL)

Yellow body formed on ovary at site of ovulation-CL produces progesterone (“pregnancy hormone”)

-Progesterone stimulates wall of uterus to accept fertilized egg

-If egg implanted, CL maintained and continues to produce progesterone throughout pregnancy

Important Estrous Cycle Events

- CL RegressionOccurs in non-pregnant animal; allows new estrous cycle to proceed-Caused by release of prostaglandin from non-pregnant uterus-Prostaglandin commonly used in livestock for estrous cycle manipulation or birth induction (e.g., Lutalyse)

Female Reproductive Tract

Seasonally Polyestrus

Recurring estrous cycles if conception does not occur, but only in certain seasons of year

Seasonal small ruminants typically have estrous cycles during late summer, fall and winter

First Estrus of Out-of-Season Breeders

Born 1st Estrus, Mo 1st Estrus, Age

Jan, 14 J - J, 14 5 - 6 mo

Mar, 14 S - O, 14 6 - 7 mo

May, 14 O - D, 14 5 - 7 mo

Sep, 14 M –A, 15 6 - 7 mo

First Estrus of Seasonal Breeders

Born 1st Estrus, Mo 1st Estrus, AgeJan, 14 A - O, 14 (some) 7 - 9 mo

Mar, 14 O - N, 14 (some) 7 - 8 mo

May, 14 O - D, 14(a few) 5 - 7 moor A - O, 15 15 - 17 mo

Sep, 14 A - O, 15 11 - 13 mo(Art. Means)

Selection of Ewes to Lamb as Yearlings

Select early-born lambs

If 6 mo old, age not significant

Select twins – top 2/3 in ADG

Singles exhibit estrus before twins

October optimum month to breed J-F lambs

Advantages of Breeding Ewe Lambs

Growth retardation not permanent

No effect on wool

Cull poor performers prior to breeding as a yearling

Maintenance feed cost before first income is reduced

Sell open lambs as lambs

Market 80 to 130 lb more lamb/ewe/lifetime

Disadvantages ofBreeding Ewe Lambs

Small birth weights

Low conception rate

Require more attention

Parasite control

Shear in spring

Breed, maintain, and feed separately

Breeding and

Lambing/Kidding Seasons

Factors AffectingReproduction

Daylight

• Ewes/does begin cycling when daylight hours <14 after June 22

• Maximum sexual activity = 10-12 hr. daylight

Factors Affecting Reproduction

Temperature

• Related to daylight and humidity

• Ewes/does begin cycling when average night temperature drops to 74° F

• Embyronic mortality first 5 to 7 days after conception

• Lambs born in S-O weight 1-2 lb less than those born in J-F due to heat stress

Factors Affecting Reproduction

Nutrition (Flushing)

• Rising condition at breeding

• Increases ovulation rate

• Increases lambing/kidding rate by 15 to 20%

Anestrus Types

Seasonal

Pregnancy and Post Partum

Lactation

Reproduction in the Male• Testes – primary sex organs that

produce the male gametes (spermatozoa) and hormones (testosterone)– Testes are located in the scrotum which

aids in temperature regulation which is important for sperm viability

– Testosterone gives the male his libido and also develops the male sexual characteristics.

Male Reproductive Tract

Summer (Temporary) Sterilityin Rams and Bucks

• Takes 60 d for sperm to mature

• In period of 20 to 40 d of age is when heat can kill

• If have high temperature spell that kill sperm, decreased fertility seen 2 to 3 wk later

• > 95° F for 4 hr will decrease viability of 20 to 40-d-old sperm

Summer (Temporary) Sterility

Effect of Summer Sterility on Lambing Date

Mating DateAug 25Sep 1Sep 5Sep 10Sep 27 (next heat)Sep 25Oct 12 (next heat)Sep 26

Situation: Breeding Season = Aug 15 to Oct 15Lambing Season = Jan 9 to Mar 11Excessive environmental heat from Aug 25 to Sep 5 kills 20 to 40-d-old sperm.

Lambing Date Jan. 19 Jan 26 Jan 30 - Won’t lamb Feb 21 - Won’t lamb Mar 8 Feb 20

Sterile period: Sep 5 to Sep 25 (approximate)Lambing void: Jan 30 to Feb 20 (approximate)