The effects of long-term exposure to continuous long or short days on conditioned clean wool weight in Wiltshire Horn x Merino ewes.

Abstract

246 Proc. Aust. Soc. Anim. Prod. Vol. 17 THE EFFECTS OF LONG TERM EXPOSURE TO CONTINUOUS LONG OR SHORT DAYS ON CONDITIONED CLEAN WOOL WEIGHT IN WILTSHIRE HORN X MERINO EWES. C.A. MAXWELL*, R.J. SCARAMUZZI*, A. FOLDES* and N.B. CARTER** SUMMARY Thirty-six WH x M ewes were used in a long term experiment to assess the effects of photoperiod on conditioned clean wool weight under controlled The ewes were maintained under natural photoperiod for 14 months nutrition. after which they were transferred to light and temperature controlled environment rooms for a further 22 months. Eighteen of the ewes were placed under continuous long days (18L : 6D), the remainder under continuous short days (6L : 18D). During this entire period the ewes were weighed and samples of wool were clipped from a 10 x 10 cm tattooed mid-side patch at four-weekly The wool was analysed for clean conditioned wool weight. intervals. Under natural photoperiod wool growth followed an annual cycle, clean conditioned wool weight being greatest in summer and least in winter. In continuous short days the seasonal rhythm was gradually suppressed. In continuous long days the frequency of the seasonal rhythm was increased to a cycle of approximately eight months. We conclude that wool growth cycles have an annual rhythm which can be altered by artificial photoperiods; these findings may have practical applications for wool producers. Key words: Photoperiod, wool growth, seasonality INTRODUCTION Wool growth in sheep displays a strong seasonal pattern that varies between breeds. The seasonal pattern of wool growth is regulated by day length (Foldes et al. 1985) and changing photoperiod is the trigger for seasonal shedding in sheep (Slee 1965). These findings can be explained by a photoperiodically entrained endogenous rhythm of wool growth. We have investigated the effects of long term exposure to continuous long day (18L : 6D) or short day (6L : 181)) environments on rhythms of wool growth in mature The aim of the experiment was to Wiltshire Horn x Merino (WH x M) ewes. determine rhythms of wool growth in an unchanging photoperiod. MATERIALS AND METHODS Animals Thirty-six mature Fl Wiltshire Horn x Merino (WH x M) ewes were obtained from the Queensland Department of Primary Industry. These ewes were selected for this study because they have a marked seasonal fluctuation in wool growth (Williams 1981) and exhibit patchy seasonal shedding of wool from the belly and The ewes were brisket regions under natural photoperiod in Sydney (38O S). maintained in single pens under natural photoperiod for 14 months from May 1982. In July 1983, shortly after the winter solstice, they were transferred to single pens in light and temperature controlled rooms for a further 22 months. Eighteen of the ewes were held under continuous long days (18L : 6D) the remainder under continuous short days (6L : 18~) . Photoperiod controls were pre-programmed to provide a 30 minute simulated dawn and a 30 minute simulated dusk in each room. * CSIRO, Div. of Animal Production, PO Box 239, Blacktown, N. S.W. 2148. ** CSIRO, Div. of Mathematics & Statistics, PO Box 218, Lindfi ,eld, N.S.W. 2070. Proc. Aust. Soc. Anim. Prod. Vol. 17 247 The ewes were fed a diet of 800 g of pelleted lucerne hay : oats (60 : 40 W/W) per day and water ad libitum. The ewes were shorn three times during the 36 months of the experiment at 6, 13 and 33 months from the start of the study. Wool sampling During the experiment wool was sampled at four-weekly intervals from a IO x 10 cm tattooed mid-side patch. The permanent tattooed patch was applied under xylocaine local anaesthesia four weeks prior to the first sampling period. The patch was clipped and the wool sample placed in a labelled envelope for conditioning. The ewes were weighed to the nearest 200 g at the times of sampling. Analyses of wool samples Wool samples were. conditioned for a minimum of 5 days at 20�C and 65% The conditioned samples were weighed and washed (Chapman relative humidity. 1960), and re-weighed after further conditioning. Statistical analyses Clean conditioned wool weight data from the series of samples collected under Inatural photoperiod, and, from a series of the same length (n=l6), collected under controlled photoperiod were analysed; the intervening 8 samples which were were omitted included any affected by adaptation to the controlled photoperiod. The purpose of the analysis was to summarize the rhythmic patterns in each series of 16 observations and to compare changes in sheep moved from natural photoperiod to continuous short days with those in sheep moved from ' natural to continuous long days. The rhythmic pattern was analysed using a periodogram analysis to split the variance of the 16 observations into contributions explained by fitting 13 For a particular different frequency components (30x and Jenkins 1976). frequency, the periodogram, values' for each sheep were analysed using the following model: . ln[E(Yijk) 1 = p + Sk + Pj(i) where yijk is the periodogram value of the kth sheep under photoperiod j (natural or controlled) for day length group i (short or long day controlled photoperiod), k is the general mean, sk is the effect of the kth sheep, pj(i) is the effect of photoperiod j in day length group i, and E(y) denotes The contrasts. of interest are p2(1) - pi(l) and the expectation of ye The model was fitted using GLIM with gamma 'error and P2(2)' Pl(2)' The mean clean logarithmic link .function (McCullagh and Nelder 1983). conditioned wool weights over each series of 16 samples 'were analysed using a similar model, with normal error function. RESULTS The mean clean conditioned wool weights .during the exper%ment are presented in Fig. 1 for ewes in continuous long day and continuous short day photoperiod. ' In natural *photoperiod wool growth showed a strong seasonal' variation, the'four-weekly yield of, clean conditioned wool weight was highest in . summer and lowest in winter and was altered'by the change to a continuous long The periodogram analysis 'revealed the or short day photoperiod (Fig. 1). presence of two frequencies corresponding to periods of eight and about five months in sheep moved to continuous long days (P' < 0.001) but not in sheep moved to continuous short days. Over the remaining (eleven) frequencies both groups were similar and, in particular, the normal 12 month period of the wool growth cycle in these sheep was reduced in both photoperiod groups (P < 0. OOl), The analysis of mean clean conditioned wool weights showed that there was significantly less wool grown in the long day photoperiod compared with natural 248 Proc. Aust. Soc. Anim. Prod. Vol. 17 photoperiod (P < 0.001) but no change in the short day photoperiod (Fig. 2). DISCUSSION our results confirm that artificial photoperiod affects the natural wool The nature of these effects is complex and dependent upon the growth cycle. photoperiod used, and the direction of the change, for different effects were observed in response to continuous long and short days (Fig. 1). Mean clean conditioned wool weight at four-weekly intervals for 18 Fig. 1. sheep in natural and short day photoperiod (--- ) and 18 sheep in natural and The vertical bars denote standard errors and long day photoperiod (-). s indicates shearing times. The vertical line represents the transition from natural to controlled photoperiod; the following eight samples (68-96 weeks) were excluded from the analysis (see text). The continuous short day photoperiod decreased amplitude and frequency of cycles of clean conditioned wool weight compared to natural photoperiod, but the overall effect on wool weight was negligible (Fig. 2). Under continuous long days the cycles of clean conditioned wool weight increased in frequency to approximately eight months, amplitude, however was reduced and the overall effect on wool weight was a significant reduction (Fig. 2). These results suggest that wool growth has an endogenous rhythm and that natural photoperiod entrains this eight-monthly rhythm to a 120monthly period. However we found no evidence of eight-monthly cycles in ewes held for 96 weeks under continuous short days, and we have no ready explanation for this. The effects of photoperiod on wool growth appeared to require a period of adaptation going from natural to artificial photoperiods (Fig. 1) The length of the adaptation period may be influenced by the time of year at which the change to the controlled photoperiod environment occurs. This possibility remains to be investigated in further experiments. These findings suggest that ambient photoperiod regulates normal seasonal wool rhythms; manipulation of the photoperiod may thus modify the annual yield of wool per sheep. Further studies based on these observations could provide a practical technology photoperiodic constraints on wool for eliminating production. Proc. Aust. Soc. Anim. Prod. Vbt. 17 Fig. 2. Mean clean conditioned wool weight over.16 four-weekly interval8 for t8 sheep under natural and short day controlled photoperiod (B) and 18 sheep \~*r natural and long day controlled photoperiod (0). ACKNOWLEDGMENTS The authors wish to acknowledge the expert technical assistance of Mr. A.J. Bintoul. Statistical assistance with time series analyses was provided by Dr. M.A. Cameron of CSIRO, Division of Mathematics and\ Statistics. REFERENCES ' I ' BOX, G.E..P. and JEFNS, G.M. (1976). 'Time Series Analysis: Forecasting md .' : Control'. (Holden-Day: San Francisco). CHAPMAN, R.E. (1960). In 'Biology of the Fleece', p.97, ` eds A.S. Fraser and B.F. Short. (CSIRO: Melbourne). . FOLDES, A., DONNELLY, J.B., MAXWELL, C.A., JAMES, S.B. and` CLANCY, S.L. (198'S). . J. Agric. Sci., Camb. 104: 397.. McCULLAGH, P. and NELDER, Jz( 1983). 'Gener&zed Linear Models'/ (Chapa~an . \ ,apd Hall: London). SLEE, J. (1965). I n 'Biology of the Skin and Hair Growth', p.545, eds A.G. Lyne'and B.F. Short. (Angus and Robertson: Sydney). WILLIAMS, A.H. (1981). In 'AWHCON 81, Proceedings of the 2nd National &l r Harvesting Research and Development Conference', p.37, ed. P-R-W. Nudsdn. 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