P. I. Hynd

The role of activins and follistatins in skin and hair follicle development and function

Investigations of the signalling between epithelial and mesenchymal compartments of skin during hair follicle initiation in utero and hair cycling have revealed the importance of the TGFbeta superfamily in ectodermal organogenesis and morphogenesis. In particular the activins, their receptors and binding proteins such as follistatin, have been shown to be important regulators of cell proliferation, differentiation and apoptosis in hair follicle initiation, hair cycling, normal skin homeostasis and wound healing. Transgenic mice lacking various components of the activin signalling pathways display varying ectodermal pathologies including altered pelage hair follicle initiation. This review summarises the activin signal transduction pathways and the interactions between activins and other TGFbeta signalling systems during hair follicle formation, hair growth cycling, skin function and wound healing.

Quantitative analyses of genes associated with mucin synthesis of broiler chickens with induced necrotic enteritis

Clostridial infection of the intestine can result in necrotic enteritis (NE), compromising production and health of poultry. Mucins play a major role in protecting the intestinal epithelium from infection. The relative roles of different mucins in gut pathology following bacterial challenge are unclear. This study was designed to quantify the expression of mucin and mucin-related genes, using intestinal samples from an NE challenge trial where birds were fed diets with or without in-feed antimicrobials. A method for quantifying mucin gene expression was established using a suite of reference genes to normalize expression data. This method was then used to quantify the expression of 11 candidate genes involved in mucin, inflammatory cytokine, or growth factor biosynthesis (IL-18, KGF, TLR4, TFF2, TNF-α, MUC2, MUC4, MUC5ac, MUC5b, MUC13, and MUC16). The only genes that were differentially expressed in the intestine among treatment groups were MUC2, MUC13, and MUC5ac. Expression of MUC2 and MUC13 was depressed by co-challenge with Eimeria spp. and Clostridium perfringens. Antimicrobial treatment prevented an NE-induced decrease in MUC2 expression but did not affect MUC13. The expression of MUC5ac was elevated in birds challenged with Eimeria spp./C. perfringens compared with unchallenged controls and antimicrobial treatment. Changes to MUC gene expression in challenged birds is most likely a consequence of severe necrosis of the jejunal mucosa.

The effect of zinc deficiency on wool growth and skin and wool follicle histology of male Merino lambs

The aims of this work were to quantify the requirements of Zn for wool growth in growing male Merino lambs, and to describe the histological lesions of Zn deficiency in skin and wool follicles. Four groups of male Merino lambs (n 4) weighing 22 kg were fed ad lib. for 96 d on diets that contained 4 (basal diet), 10, 17 or 27 mg Zn/kg. Sheep in a fifth group were fed on the diet containing 27 mg Zn/kg, but were pair-fed to sheep on the 4 mg Zn/kg diet. Zn was added to the basal diet as ZnSO4 to give the respective treatment concentrations. Sheep fed on the diet containing 4 mg Zn/kg showed clinical signs of Zn deficiency and lower feed intakes and wool growth than sheep in the other groups. Their wool fibres were improperly keratinized and the wool follicles contained a higher proportion of apoptotic bodies than other groups. There was no evidence of parakeratosis and the rate of bulb-cell production was not affected. Sheep from other groups showed no clinical signs of Zn deficiency, and mean feed intakes and growth rates did not differ significantly between sheep fed on diets containing 10, 17 or 27 mg Zn/kg. However, wool growth was reduced in sheep fed on the diet containing 10 mg Zn/kg compared with those fed on diets containing 17 or 27 mg/kg. The mean concentration of Zn in the plasma at which wool growth was 90% of maximum was 0.5 mg/l. The equivalent value for the diet was 12 mg/kg, with 95% confidence intervals of 8 to 16 mg/kg. The results suggest that Zn deficiency reduces wool growth through a specific mechanism, perhaps involving impaired protein synthesis.

Design and phenotyping procedures for recording wool, skin, parasite resistance, growth, carcass yield and quality traits of the SheepGENOMICS mapping flock

A major aim of the research program known as SheepGENOMICS was to deliver DNA markers for commercial breeding programs. To that end, a resource flock was established, comprehensively phenotyped and genotyped with DNA markers. The flock of nearly 5000 sheep, born over two consecutive years, was extensively phenotyped, with more than 100 recorded observations being made on most of the animals. This generated more than 460000 records over 17 months of gathering information on each animal. Here, we describe the experimental design and sample-collection procedures, and provide a summary of the basic measurements taken. Data from this project are being used to identify collections of genome markers for estimating genomic breeding values for new sheep industry traits.

Dynamic expression of ornithine decarboxylase in hair growth.

Ornithine decarboxylase (ODC) is the key enzyme in the synthesis of polyamines, small cationic molecules believed to have a role in many cellular processes such as cell migration, proliferation and differentiation. We show that ODC expression is associated with cell proliferation and commitment in hair follicle development and hair growth. In embryonic epidermis, ODC is expressed in ectodermal cells at sites where follicles develop, and persists in cells at the leading edge of the follicle placode. ODC is abundantly expressed in proliferating bulb cells of anagen follicles, except for a pocket of cells at the base of the bulb. Entry of the follicle into catagen is accompanied by a down-regulation of ODC expression, which is not resumed until a new follicle is initiated. In vibrissae, ODC expression is more complex. ODC is expressed not only in the bulb but also in the hair shaft, presenting a striking biphasic pattern. Additionally, ODC is expressed in a group of outer root sheath cells in the vicinity of the follicle bulge, the putative site of hair follicle stem cells.

Effects of necrotic enteritis challenge on intestinal micro-architecture and mucin profile

1. This study investigated the effect of Eimeria spp./Clostridium perfringens induced necrotic enteritis and traditional antibiotic preventatives on intestinal micro-architecture and mucin profile. 2. A total of 600 Cobb 500 broiler chickens were randomly assigned to the following three groups: (i) unchallenged, (ii) challenged, and (iii) zinc bacitracin/monensin (ZnB/monensin) (n = 25 chickens/pen, 8 pens/group). The challenged and ZnB/monensin chickens were individually inoculated with Eimeria acervulina, E. maxima and E. tenella and C. perfringens type A (EHE-NE18) at 9 and 15 d post-hatch respectively, to induce necrotic enteritis. 3. The challenge procedure significantly decreased villus height, increased villus width and increased crypt depth in the challenged compared to the unchallenged chickens. Zinc bacitracin and monensin maintained villus-crypt structure similar to that of the unchallenged chickens. 4. Mucin profile was not affected by Eimeria spp./C. perfringens challenge as demonstrated by periodic acid-Schiff and high iron diamine-alcian blue pH 2·5 staining. Zinc bacitracin and monensin decreased the number of intestinal mucin-containing goblet cells. 5. Lectin histochemistry showed a trend towards greater Arachis hypogea (PNA) reactivity in unchallenged chickens. 6. In summary, Eimeria spp./C. perfringens challenge disrupted intestinal micro-architecture; however, challenge did not appear to affect intestinal mucin profile. Traditional antibiotics, zinc bacitracin and monensin maintained micro-architecture.

Cortisol-induced follicle shutdown is related to staple strength in Merino sheep

This experiment was conducted to determine the extent to which follicle shutdown and fibre shedding are related to staple strength, and to characterise the histological changes in the wool follicles and fibres of sheep after exposure to elevated cortisol levels. Twenty one South Australian, Strongwool Merino rams (mean fibre diameter 21.6±0.8 μm) were allocated to one of 5 groups with similar mean staple strength and clean wool production. Groups 1 to 5 were injected with 2.86, 1.42, 0.56, 0.19 and 0 mg of cortisol/day/kg liveweight respectively for 4 weeks. Wool growth rate was estimated by clipping a tattooed patch on the midside of the animal at 4-weekly intervals. Fibre diameter was measured on these samples. Staple length was measured every 4 weeks by the dyebanding method. Follicle activity was gauged by histological changes in skin biopsies taken weekly. Blood samples were collected every 2 weeks and plasma cortisol measured. At the end of experiment, wool staples were taken from the shoulder, midside and rump sites for measurement of staple strength. Increased plasma cortisol concentration significantly (P<0.001) reduced clean wool production, while mean fibre diameter did not differ significantly between groups. A significant relationship (r2=0.36; P<0.005) was found between plasma cortisol concentration and clean wool production. At the end of the injection period, wool production was 3.0±0.5, 5.2±0.9, 5.4±1.4, 6.1+1.0 and 9.2±1.1 mg/cm2/2 weeks, in groups 1, 2, 3, 4 and 5 respectively. A significant relationship (r2=0.40; P<0.005) was found between staple strength and plasma cortisol concentration. Midside staple strength values were 13.4±1.3, 22.0±4.0, 24.0±3.3, 27.3±6.7 and 42.3±6.7 N/ktex in groups 1 to 5 respectively. A break appeared in the wool of cortisol-treated sheep as a result of a significant (P<0.0001) increase in the percentage of inactive follicles and shed fibres. Staple strength was significantly related to follicle shutdown (r2=0.43; P<0.0001) and fibre shedding (r2=0.39; P<0.005). Two weeks after cortisol injection stopped the percentage of inactive follicles was 50.0±7.7, 40.0±3.4, 16.3±8.6, 8.8+7.1 and 3.0±2.0 for groups 1, 2, 3, 4 and 5 respectively. It is concluded that stress-induced elevation of plasma cortisol may be responsible for reduced staple strength in Merino sheep, and that this reduction in staple strength is unrelated to changes in fibre diameter, but is related to an increase in the proportion of follicles classified as inactive.

Damara sheep have higher digestible energy intake than Merino sheep when fed low-quality or high-quality feed

The use of animals that are resilient to challenging environments is becoming of increasing importance in animal production systems. Interest in breeds of sheep such as the Damara for sheep meat production is increasing in Australia. Anecdotally this breed outperforms the traditionally grazed Merino in the harsh rangeland environments encountered in the Pastoral Zone of Australia, but little evidence is available to support this claim. A trial was conducted to quantify differences in the efficiency of feed utilisation and growth performance of Damara and Merino sheep under two contrasting dietary regimes. Eighteen castrate males of each breed were offered a ‘low-quality’ diet (L) (7 MJ/kg ME; 8% crude protein, as per manufacturer’s analysis) followed by a ‘high-quality’ diet (H) (11 MJ/kg dry matter and 16% crude protein, as per manufacturer’s analysis). On the L diet, Damaras had similar ad libitum feed intake as Merinos, but the digestibility of feed dry matter and energy was ~10% higher in Damaras than Merinos. Damaras also gained weight (38 g/day) on the L diet, while Merinos lost weight (28 g/day) (P < 0.002). On the H diet the Damaras consumed 14% more feed (P < 0.053) and grew 30% faster than Merinos (P < 0.002), but there was no difference in the apparent dry matter or energy digestibility of the feed. At the conclusion of the trial the Damara carcasses were 22% heavier (28.1 versus 23.1 kg), and had higher dressing percentages (53.2 versus 41.5%) than Merinos, but the proportions of carcass components did not differ. The Damaras achieved higher total digestible energy intakes than the Merinos on both diets. On the low-quality feed this was achieved through higher feed digestibility and on the high-quality feed through greater voluntary feed intake. We speculate that this arises from variation between the breeds in rumen volume, particle flow and the site of digestion, but further studies are required to confirm this contention. The ability of Damara sheep to obtain more nutrients from widely differing feed bases makes them an attractive alternative sheep breed for sheep meat production. Furthermore, the presence of such variation between genotypes offers potential for selective breeding and development of commercial lines of sheep.

Offspring born to ewes fed high salt during pregnancy have altered responses to oral salt loads

Prenatal growth is sensitive to the direct and indirect effects of maternal dietary intake; manipulation can lead to behavioural and physiological changes of the offspring later in life. Here, we report on three aspects of how a high-salt diet during pregnancy (conception to parturition) may affect the offsprings response to high oral salt loads: (i) dietary preferences for salt; (ii) response to salt and water balance and aldosterone and arginine vasopressin (AVP) concentrations after an oral salt challenge; (iii) concentrations of insulin and leptin after an oral salt challenge. We used two groups of lambs born to ewes fed either a high-salt (13% NaCl) diet during pregnancy (S lambs; n = 12) or control animals born to ewes fed a conventional (0.5% NaCl) diet during pregnancy (C lambs; n = 12). Lambs were subjected to short- (5 min) and long-term (24 h) preference tests for a high-salt (13% NaCl) or control diet, and the response to an oral challenge with either water or 25% NaCl solution were also carried out. Weaned lambs born to ewes fed high salt during pregnancy did not differ in their preference for dietary salt, but they did differ in their physiological responses to an oral salt challenge. Results indicate that these differences reflect an alteration in the regulation of water and salt balance as the metabolic hormones, insulin and leptin, were not affected. During the first 2 h after a single salt dose, S lambs had a 25% lower water intake compared to the C lambs. S lambs had, on average, a 13% lower AVP concentration than the C lambs (P = 0.014). The plasma concentration of aldosterone was higher in the S lambs than in the C lambs (P = 0.013). Results suggest that lambs born to ewes that ingest high amounts of salt during pregnancy are programmed to have an altered thirst threshold, and blunted response in aldosterone to oral salt loads.

Phenotypic and genotypic analysis of a barebreech trait in Merino sheep as a potential replacement for surgical mulesing.

The potential for adopting a genetic solution to protect sheep from blowfly strike on the breech was investigated in a flock of sheep that contained several animals expressing a trait characterised by low wool coverage over the breech and through a wide channel from the anus to the udder or scrotum. A scoring system (1, bare to 5, woolly) was developed and used to determine the heritability of the trait and its phenotypic and genetic correlations with other traits of importance in a sheep enterprise. In comparison to animals with woolly breeches, the skin in the breech of animals with a low bareness score was characterised by a low density of follicles producing short, medullated fibres, with histological evidence of immune rejection and follicular atrophy. The bareness score of progeny was influenced by the score of their respective sires suggesting a strong genetic component. The heritability of bareness score was moderate to high (h2 = 0.45 ± 0.02, 0.53 ± 0.01 and 0.38 ± 0.02 at lamb, hogget and adult ages, respectively). The lactation status and age of ewes influenced their bareness score, resulting in a low repeatability (0.42) of the trait between ages in females. Genetic correlations between bareness score and most other economically important traits were low. The weight of belly wool and the weight of skirtings was genetically related to bareness score (rg = +0.52 and +0.48 respectively), indicating that animals with barer breeches tend genetically towards lighter belly wool weights and lower weight of skirtings at wool classing. Selection and breeding for bareness score should achieve relatively rapid progress towards fixing the trait in a flock and without adverse effects on other important traits. Caution should be exercised in extrapolating these results to other bloodlines and environments where genetic mechanisms or environmental influences may be different.