Cattle twins and freemartin diagnosis

Applying real-time quantitative PCR to diagnosis of freemartin in Holstein cattle by quantifying SRY gene: a comparison experiment

BACKGROUND

Freemartinism generally occurs in female offspring of dizygotic twins in a mixed-sex pregnancy. Most bovine heterosexual twin females are freemartins. However, about 10% of bovine heterosexual twin females are fertile. Farmers mostly cull bovine fertile heterosexual twin females due to the lack of a practical diagnostic approach. Culling of such animals results in economic and genetic-material losses both for dairy and beef industry.

METHODS

In this study, a comparative test, including qualitative detection of SRY gene by polymerase chain reaction (PCR), quantitative detection of relative content of SRY by real-time quantitative polymerase chain reaction (qPCR), and quantitative detection of H-Y antigen, was performed to establish the most accurate diagnosis for freemartin. Twelve Holstein heterosexual twin females were used in this study, while three normal Holstein bulls and three normal Holstein cows were used as a positive and negative control, respectively.

RESULTS

Polymerase chain reaction results revealed that SRY gene were absent in three heterosexual twin females and only two of them were verified as fertile in later age. The qPCR results showed that relative content of SRY was more than 14.2% in freemartins and below 0.41% in fertile heterosexual twin females. The H-Y antigen test showed no significant numerical difference between freemartin and fertile heterosexual twin female.

DISCUSSION

Our results show that relative content of SRY quantified by qPCR is a better detection method for diagnosis of freemartin in Holstein cattle as compare to qualitative detection of SRY gene by PCR or quantitative detection of H-Y antigen. To the authors' knowledge, this is the first time we applied qPCR to diagnosing freemartin by quantifying SRY gene and got relative SRY content of each freemartin and fertile heterosexual twin female. We concluded that low-level of SRY would not influence fertility of bovine heterosexual twin female.

Diagnosis of bovine freemartinism by fluorescence in situ hybridization on interphase nuclei using a bovine Y chromosome-specific DNA probe

A heifer co-twin to a bull, in most cases, is a sterile freemartin which needs to be identified and culled from replacement stock. Various methods are available for the diagnosis of freemartinism, but none is ideal in terms of speed, sensitivity, or specificity. The present study was thus conducted to develop and validate a satisfactory fluorescence in situ hybridization procedure on interphase nuclei (I-FISH) for identifying the bovine XX/XY-karyotypic chimerism, the hallmark of freemartinism. A 190-bp DNA FISH probe containing the bovine male-specific BC1.2 DNA sequence was synthesized and labeled with digoxigenin by PCR. The FISH was performed on metaphase spreads and interphase nuclei of blood lymphocytes. Upon FISH, the probe expectedly bound to the nucleus of the male cell or to a region of the p12 locus of the Y chromosome. Twenty-four young heterosexual twins (Holstein-Friesian and Korean Cattle breeds; 10 pairs and 4 singletons) were analyzed in the present study; all but three exhibited the XX/XY-karyotypic chimerism to varying extents in both I-FISH and karyotyping. One heifer was identified to have 100% XX cells by both analyses, whereas two bulls were judged as 100% XY- and XX/XY-chimeric karyotypes by karyotyping and I-FISH, respectively. Nevertheless, the ratios of the XY to XX cells in these animals were very similar between the two analyses. In conclusion, the present I-FISH was a rapid and reliable procedure that can be used for early-life diagnosis of bovine freemartinism.

The freemartin syndrome: an update

The freemartin condition represents the most frequent form of intersexuality found in cattle, and occasionally other species. This review considers the current state of knowledge of freemartin biology, incidence, experimental models, diagnosis, uses for freemartins in cattle herds, occurrence in non-bovine species, effects on the male, and highlights potential new research areas. Freemartins arise when vascular connections form between the placentae of developing heterosexual twin foeti, XX/XY chimerism develops, and ultimately there is masculinisation of the female tubular reproductive tract to varying degrees. With twinning rates in Holstein cows increasing, there will be greater economic importance to establish early diagnosis of the freemartin and the detection of the less common single born freemartin. New diagnostic methods based on the detection of Y-chromosome DNA segments by polymerase chain reaction (PCR) show improved assay sensitivity and efficiency over karyotyping and clinical examination. The implications for the chimeric male animal born co-twin to the freemartin are contentious as to whether fertility is affected; if germ cell chimerism does indeed occur; and, if there are any real effects on the sex ratio of offspring produced. In beef cattle, the freemartin carcass has similar characteristics to normal herdmates. Hormonal treatment of freemartins for use as oestrous detectors has been used to obtain salvage value. The biology of freemartin sheep has recently been studied in detail, and the condition may be increasing in prevalence with the introduction of high fecundity genes into flocks. Potential new research areas are discussed, such as detection of foetal DNA in maternal circulation for prenatal diagnosis and investigation of the anti-tumour properties of Mullerian inhibiting substance (MIS). The freemartin syndrome will always be a limiting factor in cattle and to a lesser extent in sheep production systems that have the goal to produce multiple reproductively normal female offspring from a single dam without using sex predetermination.

Anatomical, cytogenetic and behavioural studies of freemartin ewes

The external phenotype and reproductive behaviour of 21 freemartin sheep and two male pseudohermaphrodite sheep were recorded with the aim of identifying any characteristics which might be used to predict a failure to breed. The size and shape of the vulva and clitoris, the length of the vagina, the size of the teats, the presence or absence of inguinal gonads, and the ultrasonographic characteristics of the inguinal gonads were recorded. A subjective assessment of the masculinity of each animal's body form was also made, and its behavioural responses to a virile ram and to an oestrus ewe were recorded. A number of physical and behavioural abnormalities were detected but the only consistent finding in all 23 animals was a short vagina which varied in length from 3.1 to 7.0 cm, compared with 10 to 14 cm in normal animals.

Retrospective studies on the measurements, karyotyping and pathology of reproductive organs of bovine freemartins

A retrospective study of 217 cases of bovine freemartinism was made. Of these, 14 cases were diagnosed clinically, 141 were karyotyped and 62 were subjected to macroscopical examination of the reproductive tract. Of the 62 cases, 43 were assessed by measuring the reproductive organs (size and/or weight) and 41 were examined microscopically. Complete information on gross, histopathological and karyotyping analysis was available for only 10 animals. Freemartins showed reduced measurements of all reproductive organs. The mean lengths of vulva and vagina were 6.4 cm and 8.1 cm, respectively. Vesicular glands were observed in 30 freemartins. Histologically, these glands had more fibrous and less glandular tissue than the normal male vesicular glands. Uterine changes were variable, ranging from aplasia (two animals) to normal. Likewise, endometrial glands ranged from hypoplastic (decreased number and size) to normal. Glandular and myometrial cells showed prominent nuclei and less than normal cytoplasm, indicating a non-functional status. Gonadal size was reduced and an epididymis was present in seven animals. Rete ovarii were prominent and frequently occupied two-thirds of the gonad. Undifferentiated sex cords and abundant interstitial cells were salient features of the freemartin gonad. Oocytes were not observed. Ovarian follicles were seen in six cases. Karyotypic analyses demonstrated XY chimaerism in all freemartins.

Natural bone marrow transplantation in cattle with Pompe's disease

Adding acid alpha-glucosidase to cultures of Pompe's disease muscle has resulted in enzyme uptake and reduction in concentration of glycogen. However, bone marrow transplantation has been unsuccessful as a treatment. Immune rejection may have contributed to this failure. Twin calves share a placenta and carry lymphoreticular cells of each other's type, they become lymphoreticular chimeras in utero and immune rejection does not occur. One natural and three sets of twins produced by embryo transfer were studied in Pompe's disease cattle. Chimerism persisted throughout life and the situation was analogous to a transplant of histocompatible bone marrow stem cells. The activity of acid alpha-glucosidase in leucocytes and in biopsies of the semitendinosus muscle and the mean activity in diaphragm, spleen and lymph node obtained after death from affected twins were significantly higher than in single affected calves. Glycogen concentration was lowered in liver, spleen and lymph node but not in muscles. The affected twins showed clinical signs and changes in muscle similar to those seen in affected single calves. It is concluded that bone marrow transplantation is unlikely to be a successful treatment for Pompe's disease.