Sheep and Goats

Sheep and goats reach puberty at 6 8 months of age. However, this time can range from 5 12 months depending on the time of year the animal is born.[5] They have an estrous cycle 16 17 days in length. The follicular phase, several days in length, is the time of rapid follicular growth. Estrus is displayed for about 24 to 36 hours. LH surge is coincident with the onset of estrus, and ovulation occurs about 30 hours after onset of estrus. Following ovulation, a CL forms and is functional until days 14 15,

Fig. 2 Concentrations of LH, progesterone, testosterone, and estradiol 17 b in blood of chickens during the ovulatory cycle. (Values from Ref. 7.)

when increased episodic releases of PGF2a from the uterus cause the demise of the CL.

Chicken

Chickens have only a follicular phase, called the ovulatory cycle.[6] The ovulatory cycle is 24 26 hours in length, determined mainly by the age of the chicken, with older chickens having longer ovulatory cycles. The LH surge, induced by rapidly increasing concentrations of progesterone produced by the granulosa cells of the largest follicle, occurs 4 6 hours before ovulation (Fig. 2).[7] After the follicle that ovulated the preceding day is oviposited (laid), ovulation of the largest follicle occurs

15 45 minutes later. Therefore, time of ovulation is determined by noting the time of oviposition.

CONCLUSION

Whereas there is a certain amount of variation in the reproductive endocrinology among female domestic mammals and certainly between chickens and mammals similar endocrine mechanisms regulate the female reproductive cycle. The differences reflect the various reproductive strategies used by animal species over the years. Future research needs to investigate how the reproductive system can function at an optimum level as animals are produced in more intense and restricted environments and are fed new feedstuffs, and as demands for animal products increase.

REFERENCES

1. Senger, P.L. The Estrous Cylce Terminology and Basic Concepts. Pathways to Pregnancy and Parturition, 1st Rev. Ed.; Current Conceptions, Inc.: Pullman, WA, 1999; 116 128.

2. Cole, D.J.A.; Foxcroft, G.R.; Weir, B.J. Control of pig reproduction III. J. Reprod. Fertil. 1990, (Suppl. 40).

3. Ford, S.F. Control of pig reproduction V. J. Reprod. Fertil. 1997, (Supplement 52).

4. Lucy, M.C.; Savio, J.D.; Badinga, L.; De La Sota, R.L.; Thatcher, W.W. Factors that affect ovarian follicular dynamics in cattle. J. Anim. Sci. 1992, 70, 3615 3626.

5. Bindon, B.M.; Piper, L.R. The reproductive biology of prolific sheep breeds. Oxf. Rev. Reprod. Biol. 1986, 8, 414 451.

6. Johnson, A.J. Reproduction in the Female. In Avian Physiologym, 5th Ed.; Academic Press: New York, 2000; 569 596.

7. Bahr, J.M.; Johnson, P.A. Reproduction in Poultry. In Reproduction in Domestic Animals, 4th Ed.; Academic Press: New York, 1991; 555 575.

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