To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Causes of variation amongst cattle within a herd in their ability to initiate and maintain pregnancy are largely unknown. An experimental animal resource has recently been established to understand the biology of early reproductive performance. This paper summarises the results achieved during the establishment phase and from several experiments aimed at determining the physiological basis of the difference between sub-herds of contrasting pregnancy rates on Day 60. Each of 155 contemporary yearling heifers received 2 in vitro-produced embryos on 6 separate occasions during a 26-month period. Sixty days after transfer, pregnancy and twinning rates were determined ultrasonically, pregnancies terminated and the process repeated. The interval between successive transfers was greater than 100 days. Heifers were ranked on their aggregate pregnancy rate performance after 6 rounds of transfer, and the highest (High) and lowest (Low) 25 were retained. Differences in reproductive performance during the establishment phase of the herd are reported. In addition, several subsequent experiments examined ovarian follicle turnover and progesterone levels during an oestrous cycle, early embryo development after either AI or embryo transfer, and protein, interferon tau and ubiquitin-cross-reactive protein levels in uterine luminal flushings.Pregnancy rates were 7-folder higher in the High sub-herd (76 vs. 11%), with much of this difference apparent by Day 25. The proportion of heifers observed in standing oestrus prior to embryo transfer and the interval from the end of synchronisation treatment to the onset of oestrus were similar in the sub-herds. Oestrous cycle length, ovarian follicular dynamics and progesterone profiles during the oestrous cycle were also similar. More conceptuses had elongated by Day 14 in the High sub-herd (67 vs. 14%, P<0.05), which also tended to have a higher pregnancy rate after artificial insemination (52 vs. 29, P<0.1). Total protein in flushings from the uterus was similar in the sub-herds on Day 14 and Day 17. Conceptuses in the High sub-herd were longer on Day 17 following embryo transfer (6.5 vs. 4.8, P<0.05). Interferon-tau levels were higher in the High sub-herd (25.9 vs. 16.1, P<0.01), although ubiquitin cross-reactive protein levels were also higher in the High sub-herd, but this difference just failed to reach significance. We conclude that: 1. Most of the difference in sub-herd pregnancy rate occurs within 3 weeks of ET; 2. Ovarian factors are unlikely to contribute to the difference; 3. Major differences occur after blastocyst hatching and probably depend upon a differing endometrial environment before Day 14; 4. Differences in the ability of the uterine milieu to stimulate the expression of interferon-tau may be responsible for the differences in pregnancy rate; 5. The two sub-herds are a unique experimental resource for understanding early pregnancy in cattle following either AI or ET.
The reported post transfer survival rate to term of cloned embryos derived from both undifferentiated blastomeres and differentiated foetal and adult cells is very low (typically less than 20%). Furthermore, it is acknowledged that there are many technical issues that remain to be resolved to improve the efficiency of nuclear transfer before the technique will find widespread, practical and cost-effective use in multiplying valuable livestock in agriculture. The purpose of this study was to compare early embryo morphology following embryo transfer of nuclear transfer blastocysts derived from somatic cells of an adult Friesian cow with that of standard in vitro-produced embryos. In the present study, 150 embryos were transferred in bulk (i.e., 15, 20 or 25 per recipient) to the ipsilateral uterine horn of 8 recipients using standard non-surgical embryo transfer procedures. Embryos were then recovered following necropsy on either Day 14 or Day 23 of pregnancy and developmental traits described. Embryo recovery and elongation rates were similar on Day 14 of pregnancy (Table 1), although cloned conceptuses were longer and narrower (P<0.05). Embryo recovery and viability rates by Day 23 were similar, although many of the developmental traits appeared more advanced in cloned conceptuses. (Table 1). Allantois development was different because of greater widths and the presence of ‘spurs’ that were not observed with in vitro-produced embryos. We conclude that apparently abnormal conceptus development occurs by about 3 weeks of pregnancy following nuclear transfer, but that embryo survival is not compromised at this early stage of development.
Email your librarian or administrator to recommend adding this to your organisation's collection.