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    Studies of the coat in the New Zealand Romney Marsh N-type sheep / Code Number 148
    (Massey University, 1945) Ross, Janet
    Kemps may be defined as hairy fibres which are shed after a short period of growth. Birthcoat kemps are succeeded by fibres in the same follicle, and there may be varying amounts of this second generation that are also shed. Thus, successions of kemp often continue throughout the life of the sheep making the fleece uneven in a way usually undesirable. Previous studies have shown that selection against high abundance of halo-hairs is effective in elimination kemp. Although kemps are associated with coarse fleeces with high abundance of halo-hairs, they are not always present. A hairy birthcoat follicle after growing and shedding a kemp may produce fibres of persistent growth; hence this study should have significance for breeders of Mountain Sheep which characteristically have hairy birthcoats. It is understood that a thick, hairy birthcoat of halo-hairs with a minimum of kemp in the adult fleece is desirable in the Scotch Black-face lamb. The various characteristic fibre types of the sheep's fleece have been studied and classified by Dry (1933). According to the collection of these types present in one sample of wool, certain characteristic arrays can be recognised (Dry 1934). There arrays can be arranged in a series:- those with sickle fibres are non-Plateau with few halo hairs and include Salle, Ravine, Valley and Plain arrays; those without sickle fibres are Plateau, coarse arrays with many large hairy halo-hairs. The former type of array, non-Plateau, is found on finer woolled sheep such as Wensleydales, fine Romneys ets. while the latter type of array, Plateau, is found on N-type Romneys and Mountain breeds such as Scottish Blackface.
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    The effects of prolactin on prolactin receptor gene expression and wool growth in Romney ewes : Doctor of Philosophy in Animal Science at Massey University
    (Massey University, 2003) Montenegro, Renata
    The effect of exogenous prolactin on prolactin receptor (PRLR) gene expression and wool growth in pregnant and non-pregnant Romney ewes was assessed. Three experiments were performed where exogenous prolactin was administered by subcutaneous injection (daily for 18 days) or constant infusions (for 3, 9 or 18 days) and endogenous prolactin secretion was altered by exposing ewes to long day or short day photoperiods. Prolactin administration started a week after mating (in autumn), or in non pregnant ewes in mid-spring. Blood samples were collected for measurement of circulating prolactin by radioimmunoassay, skin biopsies were collected for the quantification of PRLR long (PRLR-L) and PRLR short form (PRLR-S) mRNA expression using real-time PCR assay. Wool patch samples were clipped monthly for assessing wool growth. Constant prolactin infusion of more than 3 days activated a positive feedback mechanism for PRLR-L synthesis, resulting in a sustained elevation PRLR-L mRNA expression for up to 38 days after infusion was over. This was associated with short- and long-term stimulation of wool growth in the pregnant Romney ewe. The main increase in wool production happened after parturition. This positive effect on wool growth by prolactin treatment was related to the length of prolactin treatment. A 3 day infusion resulted in a smaller degree of enhancement compared to the 9 days and 18 days. The biggest impact on wool growth was observed in one of the 18 days infused group, which resulted in a 25% increase in clean fibre production when compared to the pregnant group. The expression of PRLR-S mRNA was not associated with an elevation of prolactin levels. Daily injections neither increased PRLR-L mRNA expression nor increased wool growth, demonstrating that a constant and moderate increase in prolactin levels is necessary to stimulate PRLR synthesis. Data obtained in these trials also suggests that other reproductive hormones may influence PRLR expression and wool growth. The non-pregnant groups showed steady levels of PRLR-L mRNA expression, which could be associated with changes in hormonal levels due to the reproductive cycle. Seasonal molecules could also interfere with the system, as prolactin manipulation in non-pregnant ewes exposed to an artificial short day environment during spring time showed a different pattern of PRLR-L and PRLR-S mRNA expression and no wool growth effect. A mathematical model of prolactin/PRLR interaction was shown to be a good predictor of short-term PRLR gene expression, as its simulations agreed with our biological data. However, the inclusion of other gestational and seasonal hormones may be necessary if the model is to be used for simulations of long-term PRLR expression and wool growth during pregnancy and lactation. Overall, these results suggest that seasonal wool growth can be manipulated via prolactin, which increases PRLR-L mRNA expression resulting in enhancement of wool growth. However, there is a minimum period of constant prolactin elevation necessary to activate this positive feedback mechanism, Also there is a window of opportunity where this mechanism can be manipulated. This window is most likely associated with the animals interpretation of photoperiod, which also regulates the reproductive seasonality and therefore, could as well interact with prolactin in the regulation of PRLR mRNA expression and seasonal wool growth. This observation could lead to the development of products, suitable for on farm conditions, to enhance wool production.
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    Aspects of wool follicle morphology and cell proliferation in Romney sheep selected for high fleece production : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University
    (Massey University, 1992) Holle, Sabina Antonia
    The mechanisms involved in the expression of genotypic differences in wool production have been investigated. Understanding the control of wool growth involves the understanding of the function of the follicle. The specific objectives were to clarify some of these mechanisms within the wool follicle in this thesis using histological techniques on two lines of New Zealand Romney sheep differing in their level of annual wool production. A method was established to identify replicating cells in the follicle bulb, by administering the thymidine analogue bromodeoxyuridine (BrdU) to the skin, by either local infusion or intracutaneous injection. Immunocytochemical detection of incorporated BrdU allowed visualization of BrdU labelled, proliferating cells. Various follicle dimensional measurements made using image analysis were tested for their ability to discriminate between morphological variations related to functional changes in the follicle bulb. The characteristics of the wool fibres of both lines, such as length and diameter, were determined at three stages of the year and subsequently related to results obtained on follicle characteristics. Fibre volume output was increased in sheep with a higher level of wool production, with the diameter being the component contributing most to this increase. Metabolic measurements (glycogen, SDH) of follicles using histochemical techniques were undertaken to determine, whether they reflect differences in follicle activity at a time during the year, when line differences in wool production were expected to be greatest. Glycogen storage was not associated with energy requirements of the follicle bulb cells. SDH activity was low, suggesting that the follicle utilises glucose mainly by anaerobic glycolysis. Investigations of individual follicles emphasised follicle dimensions and the proliferating bulb cell population at three stages of the year. Measurements were based upon the use of intracutaneously administered BrdU to assess the replicating cell population in wool follicles. Immunocytochemical detection techniques in association with image analysis enabled quantification of changes in bulb cell replication and follicle dimensions Both genotypes exhibited a seasonal pattern of follicle changes, with higher values occurring during summer. The higher producing line of sheep showed their advantage by developing larger follicles, larger dermal papillae and larger germinative tissue areas, and therefore larger numbers of proliferating bulb cells. Close relationships between follicle diameters and fibre diameters of fibre sections measured within the hair canal and at the surface existed. The width and area of the fibre cortex and the IRS at a level above the top of the dermal papilla was determined. Proportional changes were observed. This indicates the existence of a redistribution mechanism of cells to cortex or IRS, which is partly influenced by genotype. In sheep genetically inferior in wool production, relatively more bulb cells migrate into the IRS during times of increased bulb cells production (summer) than do cells of sheep on higher production levels. Theories on the possible influence of the dermal papilla on cell migration in the bulb and on the expression of different follicle components are discussed.
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    The role of plasma prolactin concentration in seasonal fibre growth cycles in down-producing goats and Wiltshire sheep : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University
    (Massey University, 1996) Litherland, A. J.
    This study examined the role of plasma PRL concentration in regulating seasonal fibre growth following the transition from short to long day photoperiod. In three down goat genotypes higher proportions of Angora genes extended the duration of guard hair growth, decreased biannual down growth and reduced the period of secondary follicles inactivity. The timing of follicle reactivation in spring and seasonal changes in plasma PRL concentrations were similar in all genotypes. Plasma PRL concentration increase, in spring, was associated with primary, but not secondary, follicle reactivation. Secondary follicle reactivation produced down of less than 2 mm which was associated with the shedding of winter down. Plasma PRL concentrations were suppressed, in spring and long-photoperiods (16L:8D), by injections of 1-5 mg/goat/day of bromocryptine and 2-3 weekly injections of long-acting bromocryptine (Parlodel). Injections of 1-5 mg/goat/day of domperidone elevated plasma PRL concentrations for 12 hours by and shedding was advanced. The circulating half-life of PRL, in sheep and goats, was 42±6 and 104±14 minutes following PRL injection or constant infusion respectively. In down goats, the normal spring-rise in plasma PRL concentration was suppressed using Parlodel or advanced by long day photoperiod. Increased plasma PRL concentration in spring provided anagenic signals to telogen primary and secondary follicles and catagenic signals to anagen secondary follicles. Following a reversal from short to long photoperiod anagen follicles of both goats and sheep entered telogen. Shedding occurred when the follicles subsequently reactivated. The suppression of plasma PRL concentration using Parlodel, during long photoperiod reversal, prevented the catagenic effect of long-photoperiod on anagen Wiltshire sheep follicles. In goats, however bromocryptine did not prevent follicles entering catagen but delayed follicle reactivation. The intravenous infusion of PRL had no effect on fibre growth in down goats or Wiltshire sheep. While the direct infusion of PRL to the skin caused an extreme local tissue reaction. Plasma PRL concentration has a role in regulating seasonal fibre growth cycles in down-producing goats but it is not a simple causal relationship and is dependent on follicle growth stage.
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    Prolactin and wool growth in the Romney ewe : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in animal science at Massey University
    (Massey University, 1999) Kendall, Paul Edward; Kendall, Paul Edward
    The effects of seasonal and experimental changes m plasma prolactin (PRL) concentration on wool growth in non-pregnant and breeding Romney ewes were assessed. Seasonal changes in plasma PRL concentration appeared to be primarily determined by photoperiod, rather than ambient temperature. The seasonal winter decline in wool production was prevented when circulating PRL levels were elevated during the winter by long day photoperiod. Endogenous PRL secretion was inhibited during pregnancy in breeding ewes, but was also influenced by photoperiod and season. A significant depression in wool growth was measured within the first 60 days of gestation, which was not associated with feed intake or changes in live weight. The reduction in wool growth was not associated with changes in circulating PRL concentration but is likely to be mediated by one or a combination of other maternal hormones. Clean wool growth rate, mean fibre diameter and fibre length growth rate all increased at or before parturition indicating that an inhibitory effect on wool growth was removed after the birth of the lamb. A consequence of higher wool growth rates during lactation was increased winter wool production in winter-lambing ewes. Photoperiod-induced increases in PRL concentration during pregnancy, at parturition, and during lactation were associated with significant medium- to long-term stimulatory effects on wool growth. The suppression of PRL concentration with bromocriptine, was associated with lower rates of long-term wool growth. Collectively these results suggest that plasma PRL has a stimulatory effect on wool growth in the Romney ewe.