Role of the oviduct and oviduct-derived products in ruminant embryo development

The fact that embryos can be obtained in vitro undermines the role of the oviduct. However, it has been demonstrated that when in vitro produced bovine zygotes are cultured in the oviduct of sheep, cattle or mice the embryo quality is improved compared to the embryos produced in vitro. Thus the oviduct is not simply a passive organ required only for transporting the embryo to the uterus but also provides a suitable microenvironment for the early embryo. The study of physiological mechanisms and interactions between the embryo and the oviductal environment is essential to understand the correct processes of early embryo developmental. This knowledge can be used to improve current in vitro procedures providing high quality embryos capable of continued development and implantation, and resulting in viable births.(AU)

Progesterone and conceptus-derived factors important for conceptus survival and growth

Progesterone (P4) from the corpus luteum (CL) is critical for the establishment and maintenance of pregnancy and plays a major role in regulating endometrial secretions essential for stimulating and mediating changes in conceptus growth and differentiation throughout early pregnancy in ruminants. Numerous studies have demonstrated an association between elevated P4 and acceleration in conceptus elongation. A combination of in vivo and in vitro experiments found that the effects of P4 on conceptus elongation are indirect and mediated through P4- induced effects in the endometrium. Despite effects on elongation, data on the impact of post-insemination supplementation of P4 on pregnancy rates are conflicting and typically only result in a modest improvement, if any, in fertility. Differences in conceptus length on the same day of gestation would suggest that factors intrinsic to the blastocysts transferred regulate development, at least in part, and would be consistent with the hypothesis that the quality of the oocyte regulates developmental competence. This paper will review recent knowledge on the effect of P4 on conceptus development in cattle and summarize strategies that have been undertaken to manipulate post fertilization P4 concentrations to increase fertility.(AU)

Progesterone and conceptus-derived factors important for conceptus survival and growth

Progesterone (P4) from the corpus luteum (CL) is critical for the establishment and maintenance of pregnancy and plays a major role in regulating endometrial secretions essential for stimulating and mediating changes in conceptus growth and differentiation throughout early pregnancy in ruminants. Numerous studies have demonstrated an association between elevated P4 and acceleration in conceptus elongation. A combination of in vivo and in vitro experiments found that the effects of P4 on conceptus elongation are indirect and mediated through P4- induced effects in the endometrium. Despite effects on elongation, data on the impact of post-insemination supplementation of P4 on pregnancy rates are conflicting and typically only result in a modest improvement, if any, in fertility. Differences in conceptus length on the same day of gestation would suggest that factors intrinsic to the blastocysts transferred regulate development, at least in part, and would be consistent with the hypothesis that the quality of the oocyte regulates developmental competence. This paper will review recent knowledge on the effect of P4 on conceptus development in cattle and summarize strategies that have been undertaken to manipulate post fertilization P4 concentrations to increase fertility.

Role of the oviduct and oviduct-derived products in ruminant embryo development

The fact that embryos can be obtained in vitro undermines the role of the oviduct. However, it has been demonstrated that when in vitro produced bovine zygotes are cultured in the oviduct of sheep, cattle or mice the embryo quality is improved compared to the embryos produced in vitro. Thus the oviduct is not simply a passive organ required only for transporting the embryo to the uterus but also provides a suitable microenvironment for the early embryo. The study of physiological mechanisms and interactions between the embryo and the oviductal environment is essential to understand the correct processes of early embryo developmental. This knowledge can be used to improve current in vitro procedures providing high quality embryos capable of continued development and implantation, and resulting in viable births.

Variation in the number of ovarian follicles in cattle: possible causes and consequences

Background: Antral follicle count (AFC, follicles e"3 mm in diameter) varies between 5 and 50 follicles in among Bos taurus cattle. AFC is highly repeatable within animals, and is correlated with the total number of follicles in ovaries. Cattle with low AFC have higher circulating concentrations of FSH and LH, but lower concentrations of AMH, progesterone and androgens than animals with high AFC. Review: The cause of the inherently high variation in the number of follicles is unknown but it is reasonable to speculate that maternal nutrition during gestation, at the time of ovarian development in their foetuses, may impact oogonia proliferation and thus follicle numbers postnatally. We have recently started to test this hypothesis by restricting nutrition of beef heifers to 0.6 of their maintenance energy requirements, from shortly before conception to the end of the first trimester of pregnancy (period encompassing the peak in oocyte numbers in foetuses). Results show that calves born to nutritionally restricted mothers have a 60% lower peak, minimum and mean AFC during follicular waves compared with calves born to mothers fed control diets. Interestingly these calves from restricted mothers also had higher blood pressure compared to controls. Additional studies also provide evidence to suggest that fertility may be compromised in animals with low AFC due to effects on oocytes, progesterone and the endometrium compared to animals with high AFC. To test this hypothesis we performed ovarian ultrasonography on 306 dairy cows during the first wave of follicular development 1 to 4 months post partum and recorded their reproductive performances during the breeding season; cows with a high AFC had higher pregnancy rates, shorter calving to conception intervals and received fewer services during the breeding season compared to cows with a low AFC. Conclusion: Recent studies suggest that the numbers of follicles in follicle waves, and in total in the ovaries, may now be an important consideration for further efforts to understand and manipulate fertility. Since ovarian follicle numbers are reflective of the environment during foetal development when all the organ systems are developing, altered follicle numbers may also be reflective of other developmental difference in organs that may have more profound effects on the animals health and welfare beyond effects on reproduction and fertility.