Biomedical subjects

I Martin Sheldon

Publications and source records attributed to I Martin Sheldon.

7 recordsLinked to original sources

PubMed2006

The management of bovine reproduction in elite herds.

The management of bovine reproduction is the cornerstone of health provision in elite herds. Aims and objectives for reproductive performance should be herd specific and data to monitor progress should not only be frequently collected, but also analysed and reported. Strategic monitoring of animals should include a vaginal examination for evidence of uterine disease, as well as transrectal ultrasonography of the genital tract. There has been considerable advancement in our ability to intervene in the reproduction of cattle during the last 50 years. However, it is salutary to note that during this time fertility has consistently declined, despite increasing veterinary intervention. Most elite herds use artificial insemination and success depends on accurate detection of oestrus expression, but this appears to be less overt than 25 years ago. In addition, half the cattle have abnormal oestrous cycles after parturition and conception rates are decreasing by 1% per year. Risk factors for abnormal oestrous cycles include puerperal problems, negative energy balance, which can be evaluated by body condition scoring, and uterine disease. Bacterial contamination of the uterus is ubiquitous after parturition in cattle and disease disrupts ovarian follicle growth and function. Reproduction is also disrupted by stress associated with clinical disease, pain or a sub-optimal environment. The challenge for veterinarians providing reproduction control programmes to elite herds is to transfer our knowledge of the problems underlying subfertility to the farm, in order to provide effective solutions.

Animals↗

PubMed2005

Defining postpartum uterine disease in cattle.

Uterine function is often compromised in cattle by bacterial contamination of the uterine lumen after parturition, and pathogenic bacteria often persist, causing uterine disease, a key cause of infertility in cattle. However, the definition or characterization of uterine disease frequently lacks precision or varies among research groups. The aim of the present paper was to provide clear clinical definitions of uterine disease that researchers could adopt. Puerperal metritis should be defined as an animal with an abnormally enlarged uterus and a fetid watery red-brown uterine discharge, associated with signs of systemic illness (decreased milk yield, dullness or other signs of toxemia) and fever > 39.5 degrees C, within 21 days after parturition. Animals that are not systemically ill, but have an abnormally enlarged uterus and a purulent uterine discharge detectable in the vagina, within 21 days post partum, may be classified as having clinical metritis. Clinical endometritis is characterised by the presence of purulent (> 50% pus) uterine discharge detectable in the vagina 21 days or more after parturition, or mucuopurulent (approximately 50% pus, 50% mucus) discharge detectable in the vagina after 26 days post partum. In the absence of clinical endometritis, a cow with subclinical endometritis is defined by > 18% neutrophils in uterine cytology samples collected 21-33 days post partum, or > 10% neutrophils at 34-47 days. Pyometra is defined as the accumulation of purulent material within the uterine lumen in the presence of a persistent corpus luteum and a closed cervix. In conclusion, we have suggested definitions for common postpartum uterine diseases, which can be readily adopted by researchers and veterinarians.

Animals↗

PubMed2005

Expression and function of Toll-like receptor 4 in the endometrial cells of the uterus.

Prostaglandins have a central role in many endocrine functions in mammals, including regulation of the life span of the corpus luteum by prostaglandin F(2alpha) (PGF) and prostaglandin E2 (PGE), which are secreted by the uterine endometrium. However, the uterus is readily infected with bacteria such as Escherichia coli, which disrupt luteolysis. Immune cells detect E. coli by Toll-like receptor 4 (TLR4) binding its pathogenic ligand, lipopolysaccharide (LPS), although signaling requires accessory molecules such as CD14. The objective of this study was to determine the effect of E. coli or LPS on the function of bovine endometrial cells, and whether purified populations of epithelial and stromal cells express the molecules involved in LPS recognition. In addition, because the female sex hormones estradiol and progesterone modify the risk of uterine infection, their effect on the LPS response was investigated. Endometrial explants produced prostaglandins in response to LPS, with an increased ratio of PGE to PGF. Addition of LPS or E. coli to stromal and epithelial cells stimulated production of PGE and PGF and increased their cyclooxygenase 2 mRNA expression. The production of prostaglandins was abrogated by an LPS antagonist. In addition, estradiol and progesterone inhibited the production of PGE and PGF in response to LPS, indicating a role for steroid hormones in the response to bacterial infection. For the first time, Toll-like receptor 4 mRNA and CD14 mRNA and protein were detected in bovine endometrial stromal and epithelial cells by RT-PCR and flow cytometry. In conclusion, epithelial and stromal cells detect and respond to bacteria, which modulate their endocrine function.

Animals↗

PubMed2005

Clinical evaluation of postpartum vaginal mucus reflects uterine bacterial infection and the immune response in cattle.

Bacteria contaminate the uterus of most dairy cattle after parturition and endometritis causes infertility. An endometritis score can be ascribed based on the vaginal mucus character and odour but it is not clear if the clinical score reflects the number of uterine bacteria or the inflammatory response. The present study tested the hypothesis that clinical evaluation of endometritis reflects the number of bacteria present in the uterus, and the acute phase protein response. Swabs (n = 328) were collected from the uterine lumen of dairy cattle, 21 and 28 days postpartum, vaginal mucus was scored for character and odour, and blood samples collected for acute phase protein measurement. Bacteria were identified following aerobic and anaerobic culture, and the bacterial growth density was scored semi-quantitatively. When bacteria were categorised by their expected pathogenic potential in the uterus, purulent or fetid odour vaginal mucus was associated with the growth density of pathogenic bacteria but not opportunist contaminants. When bacteria were analysed independently, Arcanobacterium pyogenes, Proteus and Fusobacterium necrophorum growth densities were associated with mucopurulent or purulent vaginal mucus. The bacterial growth densities for A. pyogenes, Escherichia coli, non-hemolytic Streptococci, and Mannheimia haemolytica were associated with a fetid mucus odour. Peripheral plasma concentrations of alpha(1)-acid glycoprotein were higher if there was a fetid compared with a normal vaginal mucus odour (1.50 +/- 0.09 mg/mL versus 1.05 +/- 0.02 mg/mL, P < 0.001), but did not differ significantly between vaginal mucus character scores. The evaluation of the character and odour of vaginal mucus reflects the number of bacteria in the uterus, and the acute phase protein response.

Actinomycetaceae↗

PubMed2004

The postpartum uterus.

The cow is notable among the domestic species for the almost ubiquitous bacterial contamination of the uterine lumen after parturition and the high incidence of clinical uterine disease. Such uterine disease not only disrupts uterine tissues, but also ovarian follicle growth and function by perturbation of the hypothalamus, pituitary, and ovary. Other events such as the postpartum negative energy balance also have similar multilevel effects on postpartum endocrinology. Return of ovarian cyclical activity is dependent on the innate immune system resolving uterine bacterial contamination,prompt uterine involution, and a short interval to the negative energy balance nadir. Although the risk factors for uterine disease have been described, preventive strategies are not widely adopted. Thus, veterinarians must identify and treat uterine disease efficiently to limit their negative effect on fertility.

Animals↗

PubMed2003

The effect of intrauterine administration of estradiol on postpartum uterine involution in cattle.

In cattle, the first postpartum dominant follicle has a predilection for the ovary contralateral to the previously gravid uterine horn. However, the presence of an estradiol-secreting dominant follicle in the ipsilateral ovary is a marker of subsequent fertility, possibly due to a localized effect of ovarian estradiol on uterine involution. The present study tested the hypothesis that estradiol increases the rate of uterine involution when administered into the previously gravid uterine horn around the expected time of selection of the first postpartum dominant follicle. Dairy cows were treated with 10 mg estradiol benzoate (n=15) or saline (n=14) administered through the cervix into the previously gravid uterine horn lumen on Days 7 and 10 postpartum. Uterine involution was monitored by daily transrectal ultrasonography and estimation of peripheral plasma concentrations of PGFM and acute phase proteins, while ovarian function was monitored by ultrasonography and measurement of plasma hormone concentrations. There was no effect of estradiol treatment on the diameter of the previously gravid or nongravid uterine horns, nor on the plasma concentrations of PGFM or acute phase proteins. However, cows in which the first postpartum dominant follicle ovulated during the study period had a smaller diameter of the previously gravid (P<0.01) or nongravid uterine horns (P<0.001) compared with cows in which the follicle regressed. Thus, our hypothesis was not proven, and the opposite pathway of utero-ovarian signaling may be more important during the postpartum period.

Administration, Intravaginal↗

PubMed2002

Effect of the regressing corpus luteum of pregnancy on ovarian folliculogenesis after parturition in cattle.

In cattle, the first postpartum dominant follicle has a predilection for the ovary contralateral to the previously gravid uterine horn, possibly due to a local inhibitory effect of the regressing corpus luteum of pregnancy in the ipsilateral ovary. The aim of the present study was to test the hypothesis that the regressing corpus luteum of pregnancy suppresses folliculogenesis in the ipsilateral ovary after parturition. Dairy cows were treated with prostaglandin F2alpha between 190 and 220 days of gestation to cause luteolysis without inducing parturition (n = 14) or were untreated controls (n = 32). Follicular growth and function were monitored by daily transrectal ultrasonography and collection of plasma samples for estimation of FSH, estradiol, and progesterone concentrations. The proportion of first dominant follicles in the ipsilateral ovary was similar for treated and control animals (4/14 vs. 8/32), as was the time interval between calving and establishment of a dominant follicle (mean +/- SEM, 10.1 +/- 0.4 vs. 10.7 +/- 0.5 days). Furthermore, no significant effect of treatment on dominant follicle growth or function was found as determined by plasma hormone concentrations. Although greater folliculogenesis was found in the ovary contralateral to the previously gravid uterine horn, once the location of the future first dominant follicle was selected, the timing of events was independent of location. We suggest that the corpus luteum of pregnancy does not have a local effect on postpartum ovarian folliculogenesis and that, instead, an effect of the previously gravid uterine horn shortly after parturition should be considered.

Animals↗