Corpus Luteum–Endometrium–Embryo Interactions in the Dairy Cow: Underlying Mechanisms and Clinical Relevance

Conception rates of dairy cows are currently declining at an estimated 1% every year. Approximately, 35% of embryos fail to prevent luteolysis during the first three weeks of gestation. Interactions between the corpus luteum, endometrium and embryo are critical to the successful establishment of pregnancy and inadequacies will result in the mortality of the embryo. For example, as little as a one day delay in the post-ovulatory rise of progesterone has serious consequences for embryo development and survival. Recently, we found that LH support, degree of vascularization and luteal cell steroidogenic capacity were not the major factors responsible for this luteal inadequacy, but are nevertheless essential for luteal development and function. Progesterone acting on its receptor in the endometrium stimulates the production of endometrial secretions on which the free-living embryo is dependent. However, their exact composition and effects of inadequate progesterone remains to be determined. The embryo is recognized through its secretion of interferon tau (IFNT), which suppresses luteolytic pulses of prostaglandin F_2α. In the cow, it is most likely that IFNT inhibits oxytocin receptor up-regulation directly and does not require the prior inhibition of oestrogen receptor α (ESR1). Unravelling the precise luteal-endometrium and embryo interactions is essential for us to understand pregnancy establishment and development of strategies to reverse the declining fertility of dairy cows.     

Genomic Imprinting in Canis familiaris

For the vast majority of mammalian genes, maternally- and paternally-derived alleles behave identically and are either expressed or repressed, regardless of whether they were inherited from egg or sperm. For imprinted genes, however, this is not the case. The alleles of imprinted genes are epigenetically modified in a parent-of-origin-specific manner and, as a consequence, maternally- and paternally-derived alleles behave differently. Typically one allele is expressed while the other is silent. Although relatively few in number, imprinted genes are the focus of intensive study, as they have important roles in embryonic development. Abnormal expression of imprinted genes results in growth disorders and is implicated in several clinical conditions. Most studies of imprinted genes have been performed in rodents or primates, with limited studies in other mammals such as bovine and opossum. We have recently demonstrated the existence of imprinted genes in the canine, by showing that the canine insulin-like growth factor 2 receptor gene ( IGF2R ) is monoallelically expressed, with predominant expression of the maternally-derived allele and repression of the paternally-inherited allele. Our ultimate goal is to characterize all imprinted genes in the canine, and to understand how they contribute to canine reproduction, development and disease. Such knowledge will be vital for optimizing the success of most reproductive strategies in the canine.     

Post-Partum Involution of the Canine Uterus – Gross Anatomical and Histological Features

We aimed to study the normal puerperium in the bitch. Ovariohysterectomy was performed in nine bitches, each at a different day after normal whelping; their genital tract was subject to gross anatomical examination, as well as to histological examination and electron microscopy scanning. Corpora albicans were evenly distributed in the left and right ovaries and placental sites were evenly distributed among left and right uterine horns. Placental sites were initially of dark green to grey colour, later becoming dark brown; their length and height progressively decreased. Height of the myometrium and diameter of the uterine glands progressively decreased. Trophoblast-like cells were consistently observed at the placental sites and on the surface of the interplacental areas, at all time points where hysterectomy had been performed. It is suggested that involution of the canine genital tract can last up to 3 months and is slow. Continuous (up to D84 post-partum) presence of prominent placental sites should be considered a normal feature of canine uterine post-partum involution.     

Soil water repellency in an old and young pasture in relation to N application

Ageing of pastures is likely to affect the degree of potential water repellency in the long term, whereas seasonal variation on a shorter term affects the actual repellency of soils. A 1-year study on two pastures of different ages was conducted on a sandy soil to assess changes in the degree of potential and actual water repellency in relation to different levels of applied nitrogen (N). Sampling was carried out on four dates (April, June, August and October) to determine soil moisture content and both potential and actual water repellency at three depths (0–25, 25–50 and 50–75 cm). The relative number of potentially wettable samples for the young pasture (5 years) ranged from 64% (0–25 cm) to 96% (25–50 cm) to 100% (50–75 cm). For the old pasture (38 years) this ranged from 29 to 66 to 94%. The transition zone in which topsoil samples could be either wettable or water repellent ranged from 18 to 23% (v/v) for the young pasture compared with a range from 29 to 32% (v/v) for the old pasture. Thus, ageing pastures may result in both moving as well as decreasing transition zones over time. A positive relationship between increased inputs of fertilizer N, higher DM yields, lower soil water contents and higher degrees of water repellency was found for the old pasture for the August series. This suggests that seasonal variation in water repellency can be further re-enforced through nutrient management.     

Growth and cation absorption of some fruit‐vegetable crops grown on rockwool as affected by different cation ratios in the nutrient solution

In a series of experiments, cucumber, eggplant and sweet pepper were grown in rockwool with nutrient solutions of different ratios of potassium (K), calcium (Ca) and magnesium (Mg). The ratios between the anions in the nutrient solutions compared were the same. In addition to yield, the concentrations of cations in the root environment and in different plant tissues were determined.

The results show that the yield for eggplant fruits were strongly reduced by a low Mg level, while the yield of cucumbers seemed to be somewhat reduced by a low Ca supply. Sweet pepper yields were not affected among the cation ratios compared.

Relationships between cation contents in the root environment and cation contents in plant tissues were established. The correlation coefficients for these relationships were very high. The equations calculated for the various cations show remarkable differences. Regression coefficients and intercepts strongly depend on crop and plant part sampled. For Mg, it could be established that Ca strongly affected the uptake of Mg.     

Assessment of a sequential extraction procedure for fractionation of soil arsenic in contaminated soils

A sequential fractionation scheme, based on a soil phosphorous fractionation, was developed to assess the chemical nature, and thus the potential bioavailability and mobility of As, at the sites. Soil As was separated into five fractions with (i) anion exchange resin, (ii) NaHCO₃, (iii) NaOH, (iv) HCl, (v) residual. Most sites contained relatively low concentrations of As in the two most labile fractions. The bulk of the contaminant As at the sites seemed to be associated with soil amorphous Fe and Al minerals and the dominant clay minerals which help in As sorption are montmorillonite and mica. Resin-extractable As in particular might provide a good index of potential As bioavailability and mobility.