THE FERTILITY OF SHEEP GRAZING OESTROGENIC PASTURES

Endocrine disrupting chemicals in the pathogenesis of hypospadias; developmental and toxicological perspectives

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Penis development is regulated by a tight balance of androgens and estrogens.

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EDCs that impact androgen/estrogen balance during development cause hypospadias.

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Cross-disciplinary collaborations are needed to define a mechanistic link.

Hypospadias is a defect in penile urethral closure that occurs in approximately 1/150 live male births in developed nations, making it one of the most common congenital abnormalities worldwide. Alarmingly, the frequency of hypospadias has increased rapidly over recent decades and is continuing to rise. Recent research reviewed herein suggests that the rise in hypospadias rates can be directly linked to our increasing exposure to endocrine disrupting chemicals (EDCs), especially those that affect estrogen and androgen signalling. Understanding the mechanistic links between endocrine disruptors and hypospadias requires toxicologists and developmental biologists to define exposures and biological impacts on penis development. In this review we examine recent insights from toxicological, developmental and epidemiological studies on the hormonal control of normal penis development and describe the rationale and evidence for EDC exposures that impact these pathways to cause hypospadias. Continued collaboration across these fields is imperative to understand the full impact of endocrine disrupting chemicals on the increasing rates of hypospadias.

Do calcium and magnesium deficiencies in reproducing ewes contribute to high lamb mortality?

High lamb mortality continues to be a significant economic and welfare problem within the Australian sheep industry, with 20–30% of lambs born in commercial flocks dying mostly within 3 days of birth. Clinical hypocalcaemia and hypomagnesaemia cause ewe mortality, and, subsequently, either fetal or lamb death, but it is not known whether subclinical deficiencies of calcium (Ca) and magnesium (Mg) compromise lamb survival. This review considers the potential mechanisms through which Ca and Mg deficiencies may influence lamb survival, and factors influencing the risk of deficiency. Pastures grazed by lambing ewes may be marginal in calcium (Ca; <4 g/kg DM) and magnesium (Mg; <0.9 g/kg DM) but also have a high dietary cation–anion difference (>12 meq/100 g DM) and high concentrations of potassium (K; >30 g/kg DM) and nitrogen. In young cereal crops, sodium concentrations are also often low (<0.9 g/kg DM). This combination of minerals and other nutrients creates an imbalance in supply and increases susceptibility to acute Ca (hypocalcaemia) and Mg (hypomagnesaemia) deficiency. Calcium is required for smooth muscle function and has a direct role in uterine contraction, so may influence the duration of parturition. Low Ca and Mg intake both influence insulin release and sensitivity, low Mg results in poor glycaemic control and insulin resistance by impairing both insulin secretion and its action on peripheral tissues, also potentially altering the duration of parturition as well as risk of metabolic disease. Magnesium is also a neuroprotectant that slows the neuronal damage during hypoxia and has been linked with thermogenesis in offspring and increased immunoglobulins in colostrum. These functions indicate potential importance in improving the ease of parturition and improved ability of the newborn lamb to thermoregulate and survive after birth. Subclinical Ca and Mg deficiencies commonly occur in 20% of lambing ewes grazing temperate pastures, so further studies are warranted to investigate whether correction of these deficiencies can improve lamb survival.

Development of black pigmented skin spots and pigmented wool fibres in a Merino flock—causes, field observations, and wool measurement

The development of black-grey pigmented skin spots and pigmented wool fibres on adult Merino sheep over a 3-year period was assessed. Effects of long-term grazing of oestrogenic pasture and multiple shearing were studied. The number of affected sheep and number of pigmented spots on affected sheep increased with age, with the greatest increase at 8.5 years age. Grazing of oestrogenic pastures had no effect but twice yearly shearing increased the development of pigmented spots after 2 years of treatment. Measurements on fleeces and top from sheep with no apparent pigmented spots showed that this wool was generally free of pigmented fibres. In contrast, wool from affected individuals generally had high concentrations of pigmented wool fibres, with substantial pigmented lengths (means 20–40 mm) and intensely darkened, which related to the field records of black-grey pigmented skin spots. The amounts of dark pigmented fibres found in the processed top from affected fleeces ranged between 262 and 1293/kg. Based on these findings, sheep age is an important factor for inclusion in decision systems alerting wool buyers to the risk of hidden dark fibres. However, if adequate inspection of sheep during shearing is practical to isolate fleeces from sheep with black-grey pigmented skin spots in the fleece areas, then the risk level applied could be lowered or removed for the wool from the unaffected sheep.