Effects of Growth Hormone Administration on Wool Growth in Merino Sheep

Abstract

The effects of daily administration of 10 mg of highly purified ovine growth hormone (GH) for a period of 4 weeks on wool growth have been measured in 12 Merino ewes fed either a calculated maintenance energy intake or 1·6 times this amount (six on each ration). Concentrations of hormones, glucose, urea, a-amino N and amino acids in the blood were monitored and faeces and urine collected for measurement of nitrogen balance.Wool growth rate decreased by 200/0 during the 4 weeks of GH treatment in sheep fed the high energy diet, largely because of reduced wool fibre diameter. This was followed by restoration of normal growth and then an increase of up to 20% above control levels, a response which persisted for 12 weeks following cessation of GH administration, and which was due to increases in both fibre length and diameter. GH administration caused marked increases in plasma concentrations of GH, insulin and somatomedin C, glucose and free fatty acids, all of which returned to basal levels following cessation of GH administration. No consistent changes in plasma concentration of T 3 , T 4 , cortisol, prolactin or a amino N were detected. Plasma urea and methionine levels decreased during GH treatment and returned to, or were raised above, basal levels after the GH treatment period. GH injection also resulted in a net retention of N during treatment, followed by a transient period of net N loss.The GH-induced changes in wool growth may be caused by a change in the partitioning of amino acids between the muscle mass and the skin. No other contributing factor(s) were identified.

Genetic study on pelt quality traits in the Gotland sheep breed

“…Studies have shown that wool follicle activity and wool production are hormonally influenced. For example, Wynn et al (1988) observed that wool growth rate decreased and wool fibre diameter was reduced in Merino ewes treated with ovine growth hormone. The authors assumed that the changes in wool growth were caused by a change in the partitioning of amino acids between the muscle mass and the skin.…”

Increased Vibrissa Growth in Transgenic Mice Expressing Insulin-like Growth Factor 1

“…The incorporation of labeled cystine, as previously used to measure the rate of wool growth (Wynn et al, 1988), was applied to the measurement of mouse vibrissa length. At 11, 16, and 21 d of age each mouse received a single, intraperitoneal injection of 0.25 µCi 35 S-L-cystine (specific activity 250 mCi per mM, Amersham) in 0.1 ml 0.9% (wt/vol) NaCl.…”

Differential gene expression profiles in foetal skin of Rex rabbits with different wool density

“…Oakes et al (1992) and Lobie et al (1990) found that GHR was widely distributed in skin fibroblasts, the internal and external root sheath, and dermal papillae etc. Wynn et al (1988) found GHR expression in the primary and secondary hair follicles of goats using in situ hybridisation while Mu et al (2006) also found GHR expression in sheep hair follicles. In the present study, GHR gene expression was upregulated in the higher-hairdensity group, which suggests that GHR controls hair follicle development in Rex rabbit foetuses.…”

“…Upregulation of GHR and KAP6.1 from the KAP (Keratin Associated Protein) family and downregulation of TGF-β1 from the TGF-β family have been previously associated with hair follicle development (Wynn et al, 1988;Zhang et al, Bickel et al, 2008). Additionally, the Small proline-rich protein 3 (SPRP3) has also been associated with hair follicle development (Hohl et al, 1995).…”