Small Ruminant Reproduction 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 -Ovulation Release 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 Regression Occurs 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 Born1 st Estrus, Mo1 st Estrus, Age Jan, 14J - J, mo Mar, 14S - O, mo May, 14O - D, mo Sep, 14M –A, mo

First Estrus of Seasonal Breeders Born1st Estrus, Mo1st Estrus, Age Jan, 14A - O, 14 (some) mo Mar, 14O - N, 14 (some)7 - 8 mo May, 14O - D, 14(a few)5 - 7 mo or A - O, mo Sep, 14A - O, 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 of Breeding 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 Affecting Reproduction Daylight Ewes/does begin cycling when daylight hours <14 after June 22 Maximum sexual activity = 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) Sterility in 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 Date Aug 25 Sep 1 Sep 5 Sep 10 Sep 27 (next heat) Sep 25 Oct 12 (next heat) Sep 26 Situation: Breeding Season = Aug 15 to Oct 15 Lambing Season = Jan 9 to Mar 11 Excessive 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)