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Ovine Observer

Stress and reproductive hormones are imprinted in sheep wool

Dr Edward Narayan and Gregory Sawyer (Western Sydney University)
Author correspondence: e.narayan@westernsydney.edu.au

Introduction

Reproductive wastage is a major economic issue for the sheep (meat and wool) sector because it leads to massive losses of progeny through reduced embryo quality and early lamb losses during pregnancy. Reproductive wastage is influenced by numerous on-farm factors such as extreme climate, nutritional and management factors which can lead to underlying changes in the hormonal physiology of livestock. Reproductive and stress hormonal assessment tools are valuable for understanding the changes in hormonal physiology of production animals, especially during a metabolically demanding reproductive phase such as pregnancy.
 
Traditional methods of hormone monitoring such as blood sampling do not measure the long-term changes in hormones due to the minute variation in hormones present in systemic blood circulation. It is known in human studies that steroid hormones such as glucocorticoids (e.g. cortisol) and reproductive hormones such as progesterone can be incorporated into the hair follicles through time via the blood-integumentary system connectivity and hormones get stored into the hair.

General aims

The study was conducted by the Western Sydney University to validate the methods for the assessment of the stress hormone cortisol and reproductive hormone progesterone in sheep wool. The focus was using the merino sheep breed and maiden ewes because of the further research that can be undertaken to assess the relationship between wool hormones and wool quality indices. The technique of wool hormone assessment presented here is applicable in other sheep breeds, both hair and wool.

Materials and methods

In this experiment, wool samples were collected from a group of n = 46 maiden merino ewes (22-25 months old), naturally joined in southern New South Wales (NSW). The wool samples were collected at three different times during 2017, January (prior to rams being put out with the mob and to provide a baseline level since previous shearing in May 2016), September (during very late stages of gestation – approximately 2 weeks prior to parturition) and December (ewes had given birth and ~2-month-old lambs were at foot).
 
Ewes underwent full shearing in January 2017, while a single wool clip was taken from the top-knot of each sheep during September and December. A 60 mg sample from each wool clip was weighed in the laboratory for analysis. Wool progesterone and cortisol enzyme-immunoassays were validated using laboratory methods conducted at the Stress Lab, Western Sydney University, Hawkesbury campus. Validation included demonstration of the detectability of hormones in wool against standards of progesterone and cortisol.

Results and discussion

Figure 4 shows quantified levels of wool progesterone and cortisol from merino ewes. Wool cortisol concentrations increased from pre-joining in January (1.33±0.12 ng/g) to late gestation in September (3.59±0.12 ng/g). Concentration of wool cortisol post-lambing in December (3.27±0.14 ng/g) did not decline after gestation however remained higher than pre-joining levels. Wool progesterone (PG) concentrations increased significantly from pre-joining (0.04±0.005 ng/g) in January to late gestation in September (5.53±0.13 ng/g) with a decline observed in December (0.05±0.003 ng/g) to post- pregnancy concentrations.
 
Figure 4 Merino ewe wool cortisol and progesterone levels before, during and after pregnancy.
Figure 4 Merino ewe wool cortisol and progesterone levels before, during and after pregnancy
The results show the first-ever measurement of wool progesterone and cortisol in merino sheep. The applications of this method can be many such as longitudinal monitoring of stress and reproductive health to identify potential hormonal issues (e.g. high stress levels or detect early pregnancy) and modify management intervention to reduce the risk of reproductive wastage.

Conclusion

Wool progesterone levels were high during gestation and decreased post-lambing. Wool cortisol levels increased through gestation and remained high post-lambing. Further analysis is underway to determine the predictive power of wool hormones for differentiating between single/twin bearing ewes early in pregnancy and predicting critical time periods for potential lamb losses occurring during gestation. Thus, the overall application of this novel method is to boost sheep welfare and productivity on-farm.
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