Effects of melatonin implants on selected hormonal profiles and wool growth in Merino wethers.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 18 EFFECTS OF MELATONIN IMPLANTS ON SELECTED HORMONAL PROFILES AND WOOL GROWTH IN MERINO WETHERS A. FOLDES*, C.A. MAXWELL*, A.J. RINTOUL*, R.J. SCARAMUZZI* and P. BAKER* The effects of melatonin-releasing implants on wool growth and endocrine Melatonin releasing implants profiles were investigated in Merino wethers. (Regulin) were inserted subcutaneously in two groups of animals, and replaced control animals received no at six weekly intervals in one of these groups; implant. Daytime blood samples, taken at weekly intervals and consecutive hourly samples from a 25 h sampling period were analysed for melatonin @MT), prolactin (PRL), thyroxine (T4) and tri-iodothyronine (T3) hormone levels by Wool growth was monitored by four-weekly clippings from a tattooed RIA. annual wool production was determined at midside patch on each sheep; shearing. The results confirm that continuously elevated levels of circulating aMT (i) do not inhibit nocturnal synthesis or release of endogenous aMT (Kennaway et al. l982) but (ii) do suppress circulating PRL levels (Kennaway et al. 1982). Thyroid hormone levels, live weight, monthly patch wool growth and annual wool production all remained unaltered by acute or chronic aMT treatment. INTRODUC!T!ION Melatonin-related treatments influence pelage changes in a variety of species, including arctic foxes, mink, deer and domestic animals [e.g. cashmere production in goats (Foldes and McDonald unpubl. data), and shedding cycles in Soay (Lincoln et al. 1980) and Wiltshire Horn (Williams 1981) sheep]. As part of our studies on the ovine pineal gland (Maxwell et al. 1988, 1989), we now report the effects of continuously elevated circulating aMT levels on wool growth and hormone profiles in Merino wethers. Animals and wool measurements Fine wool Merino wethers (n = 35, September 1987 drop) were housed in single pens for 17 months after weaning and were offered a pelleted diet of lucerne: oaten chaff (60:40 w/w, 15.3% average protein content) and water ad lib. Monthly average temperatures during this period ranged from 10.S�C minimum to 27.1�C maximum. The sheep consumed 1080 g (dry weight) of the pelleted diet daily until they reached a mean live weight of about 40 kg, and were then reduced in two steps, to a maintenance consumption level of 540 g (dry weight/day). At about four months of age, each wether had a 10 x 10 cm patch tattooed onto its midside, under lignocaine local anaesthesia, and the patches were clipped at four-weekly intervals. Wool samples were treated (Maxwell et al. 1988) to determine clean conditioned wool weight (CCWW), and mean fibre diameter. Annual wool production was determined as greasy fleece weight at the time of shearing (April). The wethers were randomly allocated into three experimental groups in February 1988: untreated controls (n = 14), short (n = 6) and long term treated (n = 15). All sheep were weighed at four-weekly intervals. * CSIRO, Division of Animal Production, PO Box 239, Blacktown, N.S.W. 2148, 208 Proc, Aust. Soc. Anim, Prod, Vol. 18 Melatonin treatments Two m-releasing implants (Regulin) were inserted subcutaneously behind the The implants were renewed at six-weekly right ear of each treated wether. intervals throughout the experiment in the case of the long-term treated wethers, but were not renewed in the case of the short-term treated wethers. Blood sampling Weekly daytime blood samples (10 ml) were taken from all treated wethers by venipuncture for the first eight weeks, and from the 15 long-term treated In October 1988, blood wethers for the entire duration of the experiment. samples (10 ml) were taken at hourly intervals for 25 h from six wethers Blood was (randomly selected where appropriate) from each treatment group. sampled via indwelling catheters, inserted into the left jugular vein under lignocaine local anaesthesia. During the hours of darkness, the sheep were exposed to dim red light only. Plasma samples were stored at -2OOC prior to analysis. Hormone analysis Circulating levels of aMT, PRL, T3 and T4 were determined by radioimmunoassays. Previously described methods (Maxwell et al. 1989) were used to determine aMT and PRL levels; thyroid hormones were analysed by the method of Wallace et al. (1978). Statistical Differences in mean wool parameters and compared using a repeated measures ANOVA. methods hormone profiles over time were 209 Proc. Aust, Soc. Anim. Prod- Vol. 18 RESULTS AND DISCUSSION The three treatment groups did not differ significantly in mean live weight Daytime plasma aMT levels were throughout the experiment (Fig. la). undetectable in untreated wethers and were continuously maintained in the long term implanted group above the nocturnal levels exhibited by controls. Similarly high aMT levels in the single dose group decreased to near zero by eight weeks after treatment (Fig. lb). Nocturnal aMT levels increased over the the magnitude of respective daytime levels in all treatment groups (Fig. 2a); this increase was not significantly different in long term treat?& short term treated or untreated control groups (areas under the peaks 157 fr 37, 133 & 34 Circulating PRL levels over-the 25 h -and 129 2 31 pg/ml/h respectively). period were not different (P>O.OS) between control and short term treated wethers, but were lower than control levels in long-term treated wethers No effects of either implant treatment were noted on plasma (P<O.OS, Fig. 2b). T3 levels (P>O.OS, Fig. 2c), or T, levels (P~0.05, Fig. 2d). 210 Proc, Aust. Soc. Anim. Prod. Vol. 18 Wool growth varied significantly (P<O.OS) with time over the 17 months of the Subcutaneous aXT treatment did not influence wool growth; neither experimentCCWW (P>O.OS, Fig. 3a) nor fibre diameter (P>O.OS, Fig. 3b) differed significantly between the three treatment groups. This lack of effect was also Mean fleece weights in the longreflected in annual greasy fleece weights. term treated, short-term treated and control groups were 3.8 + 0.2, 3.9 + 0.'2 and 3.9 + 0.1 kg respectively. (a) Group mean conditioned clean wool weight (four-weekly intervals), Fig. 3. Average 8-e-m. of the 3 groups is 0.24 g. (b) Corresponding group mean fibre diameters, Average 8.e.m. for the 3 groups is 0.36 uM. Symbols as in Fig. 1. Our results confirm that elevated aMT levels (i) do not inhibit nocturnal (ii) synthesis or release of endogenous aMT suppress circulating PRL levels, (Kennaway et al. 1982) (iii) have no significant effect on plasma T,, or T, The results additionally show no effect of acutely or chronically levels. elevated circulating aMT on wool growth parameters in fine wool Merino wethers, more seasonal fibre despite the known effect of aMT supplementation in These results suggest that use of melatonin-releasing producing species. implants for reproductive synchronization of sheep may not affect wool other physiological effects following from the observed endocrine production; changes require further investigation. ACKNOWLEDGEMENT We thank Dr Linton Staples for the initial supplies of Regulin implants. KENNAWAY, D-J,, GILMORE, T.A. and SEAMARK, R-F. (1982). Endocrinology, 110: 2186. LINCOLN, CA,, KLANDORF, H. and ANDERSON, N. (1980). Endocrinology, 107: 1543. 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