Revista Veterinaria Zacatecas 2004 - UAZ

evaluate uterine capacity in swine. J
Anim Sci 1987; 65: 738-744.
101. Fenton FR, Schwartz FL, Bazer FW,
Robinson OW, Ulberg LC. Stage of
gestation when uterine capacity limits
embryo survival in gilts. J Anim Sci
F J Escobar-Medina
106. Wilson ME, Biensen NJ, Youngs CR,
Ford SP. Development of Meishan or
Yorkshire littermate conceptuses in either
a Meishan or Yorkshire uterine
environment to day 90 of gestation to
term. Biol Reprod 1998; 58: 905-910.
1972; 35: 383-388. 107. Wilson ME, Biensen NJ, Ford SP. Novel
102. Monk EL, Erb RE. Effect of unilateral
ovareictomy and hysterectomy on
reproductive parameters in the gilt during
early pregnancy. J Anim Sci 1974; 39:
insight into the control of litter size in the
pig, using placental efficiency as a
selection tool. J Anim Sci 1999; 1654-
1658.
366-372. 108. Ford SP. Embryonic and fetal
103. Webel SK, Dziuk PJ. Effects of stage of
gestation and uterine space on prenatal
survival in the pig. J Anim Sci 1974; 38:
development in different genotypes in
pigs. J Reprod Fertil Suppl 1997; 52:
165-176.
960-967. 109. Kaminski M, Ford SP, Conley AJ.
104. Hunter MG, Faillace LS, Picton HM.
Imtrautrine and peripheral steroid
concentrations and conceptus
development in Meishan and Large
White hybrid gilts. Reprod Fertil Dev
1994; 6: 783-789.
105. Biensen NJ, Wilson ME, Ford SP.
Differential mechanisms regulating
Meishan (M) and Yorkshire (Y) fetal
growth. J Anim Sci Suppl 1 1996; 74:
215.
ABSTRACT
Differences in the expression of
cytochromes P450 17α-hydroxylase and
aromatase in Meishan and Yorkshire
conceptuses at days 10.5-14.0 of
gestation. J Reprod Fertil 1997; 103:
213-219.
110. Vallet JL, Christenson RK, Trout WE,
Klemcke HG. Conceptus, progesterone,
and breed effects on uterine protein
secretion in swine. J Anim Sci 1998; 76:
2657-2670.
Escobar-Medina FJ. Litter size in sows. This review focuses on the factors affecting litter size in sows.
Litter size depends of the incidence and synchronization of the ovulation and the uterine capacity. Ovulation
incidence is determined by the number of follicles are recruited and by the ability of recruited follicles to
continue to grow and avoid atresia. In pigs, ovulation and fertilization are not instantaneous; some ova are
released and fertilized before others, so there are some variations in embryonic development. Embryos
resulting from ova that ovulated last are the ones most likely to be lost. In the period of pregnancy
establishment, the uterine environment is not favorable to less development embryos. Embryonic survival
could be improved by ovulation synchronization. In some reports, gonadotropin administration before
artificial insemination has improved litter size, perhaps through ovulation synchronization. Uterine capacity is
related with the conceptus and placentas size. Prolific breed pigs develop smaller conceptus and placentas.
Veterinaria Zacatecas 2004; 2: 137-146.
Key words: Litter size, piglets, sows.
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