The time of detection of oestrone sulphate in milk and the diagnosis of pregnancy in cows

Changes in plasma PLAC-1 concentration and its expression during early-mid pregnancy in bovine placental tissues - a pilot study

BACKGROUND

Placenta-specific protein 1 (PLAC1) is a small secreted protein considered to be a molecule with a significant role in the development of the placenta and the establishment of the mother-foetus interface. This study aimed to confirm the presence of bovine PLAC1 and to examine its profile in the placenta and plasma in the first six months of pregnancy. The expression pattern of PLAC1 was analysed by RT-qPCR and Western Blotting. Quantitative evaluation was carried out using ELISA.

RESULTS

PLAC1 concentrations in the plasma of pregnant cows were significantly higher (p < 0.05) than those obtained from non-pregnant animals. PLAC1 protein concentrations in the placental tissues of the foetal part were significantly (p < 0.05) higher than in the tissues of the maternal part of the placenta. PLAC1 transcripts were detected in both placental tissue samples and epithelial cell cultures.

CONCLUSIONS

In conclusion, the results of the present preliminary study suggest that PLAC1 is involved in the development of bovine placenta. The presence of this protein in the plasma of pregnant animals as early as the first month may make it a potential candidate as a pregnancy marker in cows. Further studies on exact mechanisms of action of PLAC1 in bovine placenta are necessary.

Oestrogens in milk and breast cancer: a cause for concern…or not?

In this short Research Reflection I address and refute the suggestion that oestrogens consumed in milk might contribute in a significant way to endogenous levels and thereby have a physiological action, possibly resulting in adverse consequences including increased breast cancer risk. Quantitative analysis based on published data shows that, even in worst case scenarios, oestrogen consumption in milk is considerably less than regulatory bodies regard as entirely safe.

Early pregnancy diagnosis in bovines: current status and future directions

An early and accurate diagnosis of reproductive dysfunctions or aberrations is crucial to better reproductive management in livestock. High reproductive efficiency is a prerequisite for high life-time production in dairy animals. Early pregnancy diagnosis is key to shorten the calving interval through early identification of open animals and their timely treatment and rebreeding so as to maintain a postpartum barren interval close to 60 days. A buffalo, the most important dairy animal in the Indian subcontinent, is known for problems related to high calving interval, late puberty, and high incidence of anestrus. Lack of reliable cow-side early pregnancy diagnosis methods further aggravates the situation. Several methods of pregnancy diagnosis are being practiced in bovine species, yet none qualifies as the ideal pregnancy diagnosis method due to the inherent limitations of sensitivity, accuracy, specificity, speed, and ease of performing the test. The advancement of molecular techniques like proteomics and their applications in animal research has given a new hope to look for pregnancy biomarker molecules in these animals. This review attempts to examine common pregnancy diagnosis methods available for dairy animals, while assessing the usefulness of the modern technologies in detecting novel pregnancy markers and designing future strategies for research in this area.

Pregnancy diagnosis based on the fecal progesterone concentration in beef and dairy heifers and beef cows

The present study was undertaken to examine whether pregnancy diagnosis was possible by measuring fecal progesterone concentrations in beef and dairy heifers and beef cows. Rectal fecal samples collected on days 18-24 after insemination or days 11-17 after embryo transfer were mixed with methanol and shaken for preparation of a fecal solution. After centrifugation, the supernatant was extracted with petroleum ether followed by an enzyme immunoassay for progesterone. All pregnant animals showed fecal progesterone concentrations greater than 50 ng/g of fecal material on days 18-24 after AI or estrus. In non-pregnant animals, however, the fecal progesterone concentrations ranged widely from 5 to 180 ng/g of fecal material. In non-pregnant cattle, the percentage of cattle with <50 ng progesterone/g of fecal material compared with the total number was 37-60% on days 18-20, whereas the percentages increased more than 70% to a maximum of 78.1% on day 23. When 50 ng/g was considered as the cut-off value, the sensitivity and specificity of positive pregnancy tests were less than 70% on days 21-24, and 100% for negative pregnancy tests on days 18-24. There were significant differences in the mean fecal progesterone concentrations between pregnant and non-pregnant cattle on days 19-24. These results suggest that feces can be utilized to substitute for plasma and milk to measure progesterone for the purpose of pregnancy diagnosis in heifers and cows.

Concentrations of oestrone sulphate during pregnancy in milk from Jersey and Friesian dairy cows differing in milk yields and composition

Oestrone sulphate concentrations were measured by radioimmunoassay in milk samples obtained weekly during pregnancy from Jersey and Friesian cows, with each breed grazed at two different stocking rates. Mean milk yields differed significantly (P<0.05) between the four herds, while mean percentage milk fat and protein values differed significantly (P<0.05) between the two breeds. In all four herds, oestrone sulphate concentrations in milk rose progressively during pregnancy from a mean value of approximately 80-100 pg/ml at 60-80 days of pregnancy to a plateau value of approximately 1 ng/ml at 181-200 days. In non-pregnant cows, oestrone sulphate concentrations in milk ranged from non-detectable to 110 pg/ml, with a mean +/- s.e.m. value of 59 +/- 4 pg/ml. There was considerable variation in milk oestrone sulphate concentrations between cows in each herd, and oestrone sulphate concentrations could also fluctuate markedly within cows from week to week. Despite this variation, the concentration of oestrone sulphate in 98% of milk samples obtained after 120 days of pregnancy was greater than the highest concentration found in milk from non-pregnant cows. Measurement of oestrone sulphate concentrations in milk samples taken at least 120 days after mating or insemination may provide an alternative, non-invasive means of determining or confirming pregnancy in New Zealand dairy cows.

Is milk responsible for male reproductive disorders?

The role of environmental compounds with estrogenic activity in the development of male reproductive disorders has been a source of great concern. Among the routes of human exposure to estrogens, we are particularly concerned about cows' milk, which contains considerable amounts of estrogens. The major sources of animal-derived estrogens in the human diet are milk and dairy products, which account for 60-70% of the estrogens consumed. Humans consume milk obtained from heifers in the latter half of pregnancy, when the estrogen levels in cows are markedly elevated. The milk that we now consume may be quite unlike that consumed 100 years ago. Modern genetically-improved dairy cows, such as the Holstein, are usually fed a combination of grass and concentrates (grain/protein mixes and various by-products), allowing them to lactate during the latter half of pregnancy, even at 220 days of gestation. We hypothesize that milk is responsible, at least in part, for some male reproductive disorders.

Application of enzymeimmunoassay to measure oestrone sulphate concentrations in cow's milk during pregnancy

The characteristics of antigen- and antibody-coated enzymeimmunoassay (EIA) formats to measure oestrone sulphate (OS) were studied using a murine monoclonal antibody as the primary antibody. In an antigen-coated format the most sensitive EIA (9 fmol/well) was achieved using 6-ketoestrone-6-O-carboxymethyloxime (OCMO) coupled to bovine serum albumin (BSA), as the coating antigen, and horseradish peroxidase (HRP), as the enzyme label. In an antibody-coated format, comparable sensitivity could be achieved using HRP conjugated to either OCMO, oestrone-3-glucuronide (OG) or oestrone-3-hemisuccinate (OHS) as the steroid 'tracer'. In both the antigen- and antibody-coated formats replacing HRP with alkaline phosphatase (AP) markedly aggravated the assay sensitivity. The antigen-coated EIA format was used to measure OS concentrations in cow's milk directly without an initial defatting step, and a progressive increase in OS concentrations in milk as pregnancy progressed was observed. Median OS concentrations rose from 1.1 nmol/l at days 70-99 of pregnancy (n = 44) to 3.2 nmol/l at days 140-160 (n = 92). Oestrone sulphate concentrations in milk from non-pregnant cows (n = 51) ranged from non-detectable to 1.3 nmol/l with a median value of 0.4 nmol/l. Only 5% of cows 120 or more days pregnant had milk OS concentrations within the range of values found in milk from non-pregnant cows. Accurate discrimination of non-pregnant and pregnant cows can thus be achieved on the basis of OS concentrations in milk samples taken at least 120 days after mating/insemination. This EIA for OS may have a role in the dairy industry as an alternative non-invasive means of determining pregnancy status in cows.

Influence of gestation on oestrone sulphate concentration in milk of zebu and crossbred cows and Murrah buffaloes

Single milk samples collected during pregnancy from 128 Sahiwal (zebu), 295 Karan Swiss and 198 Karan Fries cows and 164 Murrah buffaloes were analysed for oestrone sulphate by a sensitive, direct, radioimmunoassay procedure developed in the laboratory. Mean oestrone sulphate levels were below detection limit (< 50 pg/ml) during the first 2 months of pregnancy in all animals. There was an exponential increase in the hormone concentration beginning at the fourth month of pregnancy in cows, although the rate of increase was greatest among Sahiwal cows, followed by Karan Swiss and Karan Fries cows in that order (P < 0.01). An exponential increase in oestrone sulphate levels was also recorded in buffaloes beginning at the fourth month of gestation. However, the mean hormone levels in this species, after initially being lower than Sahiwal and Karan Swiss cows up to 6 months of pregnancy, increased to higher levels thereafter. From this study it was concluded that in addition to genetic factors, environmental adaptation could also influence the oestrone sulphate levels. In addition, the study also provided a basis for pregnancy confirmation by milk oestrone sulphate determination after 110 days in gestation in cattle and buffaloes using a simple, direct, assay procedure.

Hormones in milk

Protein hormones (especially prolactin) and steroid hormones (gestagens, estrogens, corticoids, and androgens) can be detected by bioassay and radioimmunoassay in milk in a variety of species. In addition, milk contains vitamin D and beta-casomorphins (opiate-like peptides). It has been assumed that most of the hormones are transferred into milk by diffusion. However, evidence is available for active mechanisms like those for progesterone in goats and prolactin in cows. Most of the hormone profiles in milk are similar to the ones in blood plasma. Hormone concentrations in milk seem to be a good estimate of the average hormone content in plasma, especially for the measurement of longer-lasting secretory activities like progesterone and estrogen release during the estrous cycle or seasonal changes of prolactin in ruminants. Determination of progesterone and estrone sulfate in milk serves as a diagnostic tool in fertility control, especially in cows. Enzyme immunoassay kits are available for this monitoring purpose. Exogenously administered hormones are also transferred into milk. Residue studies have shown that the dilution is so great that it may be assumed that there is no potential risk for the consumer.