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Effects of season on ¯eece traits of Angora does in the US

A.J. Litherland, C. Toerien, T. Sahlu

*

, P. Lee, A.L. Goetsch

E (Kika) de la Garza Institute for Goat Research, Langston University, P.O. Box 730, Langston, OK73050, USA

Received 8 April 1999; accepted 18 February 2000

Abstract

Twenty nonpregnant Angora does were used to determine seasonal effects on ¯eece traits, including ®ber growth and follicle activity. Does grazed pastures and were supplemented with a 50% concentrate diet at a level near that required for BW maintenance. Clean ®ber growth rate was greatest (p<0.05) among seasons in summer and lowest (p<0.05) in winter (1.13, 0.85, 0.98 and 1.20 mg/cm2 per day for autumn, winter, spring and summer, respectively); seasonal differences in ®ber diameter were similar (34.9, 31.7, 33.7 and 36.5mm for autumn, winter, spring and summer, respectively). Fleece ®ber medullation was greatest (p<0.05) in summer (0.48, 0.32, 0.40 and 0.76%), and medullated ®ber diameter was greater in spring and summer than winter (69, 65, 73 and 71mm for autumn, winter, spring and summer, respectively). Primary follicle activity varied with season more than did activity of secondary follicles (primary: 74, 23, 79 and 99%; secondary: 97, 86, 94 and 99%; for autumn, winter, spring and summer, respectively). In summary, Angora goats in the US appear to exhibit seasonal follicle and ®ber growth cycles, the knowledge of which may improve future nutritional management for ef®cient feed use in mohair production. The optimal time of shearing US Angoras for minimal contamination with medullated ®bers may be just before spring and autumn equinoxes when it is likely that medullated ®bers have been recently shed.

#2000 Elsevier Science B.V. All rights reserved.

Keywords:Goat; Season; Fiber; Follicle; Nutrition

1. Introduction

Unlike its seasonally shedding ancestor, the Angora goat and most domestic sheep produce ¯eece con-tinually throughout the year without a visible period of shedding. Nonetheless, Angora goats of Australia and New Zealand, and many domestic sheep breeds, exhi-bit seasonal changes in ®ber growth rate driven by photoperiod (Stapleton, 1978; Black and Reis, 1979; Nixon et al., 1991). In this regard, Margolena, (1974) reported that 27% of follicles of Texan Angora goats were inactive in winter, and suggested that mohair

growth in US goats also ¯uctuates with photoperiod. However, there has not yet been a characterization of the seasonal mohair growth cycle in US goats. This could be of value in a number of ways. For example, if mohair growth in US Angoras is seasonal, then ef®ciency of feed use for mohair production could vary during the year, and most appropriate diets or supplementation strategies will differ among seasons. Relatedly, Hawker and Crosbie, (1985) noted that feed ef®ciency for ®ber growth in sheep possessing a seasonal cycle of ¯eece growth was three times greater in summer compared with winter. Season may also affect mohair quality traits such as ®ber diameter and the proportion of medullated ®bers contaminating the ¯eece (Nixon et al., 1991). Hence, the objective of this experiment was to determine *Corresponding author. Tel.:‡1-405-466-3836;

fax:‡1-405-466-3138.

E-mail address: sahlu@mail.luresext.edu (T. Sahlu)

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seasonal effects on ¯eece traits including ®ber growth in US Angora goats.

2. Materials and methods

2.1. Animals

Twenty 2- to 4-year-old nonpregnant does were randomly selected from the commercial Angora herd of the E (Kika) de la Garza Institute for Goat Research of Langston University. The experiment started on September 13 and ended October 9. Does were sheared on August 31 before the experiment, with a ¯eece weight of 2.45 kg (S.E. 0.09) and ®ber diameter of 33.8mm (S.E. 1.0); BW at the start of the experi-ment was 30.2 kg (S.E. 0.9).

Does were randomly allocated to four groups; initial BW and previous ¯eece weight were similar among treatments. During the experiment, each group occupied a 0.4-ha paddock located >300 m from the nearest arti®cial light source. Thus, does were sub-jected to the natural photoperiod at Langston, OK, with a latitude and longitude of 35.98N and 97.28W, respectively. Does were also exposed to ambient temperature, although goat hutches were present for shelter. The paddocks had been heavily grazed before the experiment began. Does were treated monthly with Ivomec1

(Merck, Rahway, NJ) in the spring and autumn for internal parasites and as required for external parasites. Animal health was good throughout the experiment, and based on visual appearance inter-nal parasitism did not have an obvious marked impact on performance.

2.2. Design

Two groups of does (5 does/group) were subjected to a low plane of nutrition and two to a higher plane. The different nutritional planes were based on (NRC, 1981) to maintain BW or for a relatively low rate of increase in BW (e.g. 25 g per day) by different levels of feeding of a 50% concentrate diet. Major ingredi-ents in the diet were ground corn (17.8%), wheat middlings (10.3%), dehydrated alfalfa meal (20.3%), cottonseed meal (14.5%) and cottonseed hulls (29.7%), and the diet averaged 13.6% CP, 43.4% NDF and 29.5% ADF (DM basis). The diet

also included sources of supplemental of minerals and vitamins. Levels of feeding were altered every 2 weeks based on ADG and visible estimates of growing herbage in the paddocks. In addition, an 20% increase in the levels of feeding after the ®rst shearing mid-way in the experiment occurred, because of lower-than-expected ¯eece-free BW. Over the entire experiment, average supplemental DM intake was 0.68 (S.E. 0.01) and 0.53 kg per day (S.E. 0.01) for high- and low-nutritional planes, respectively.

2.3. Measures

Does were weighed every 2 weeks and shearing was on February 22 and July 31. Fiber and follicle mea-sures were made at1-month intervals, with a total of 14 sampling times for most measures. Fleece within a measured 144-cm2 patch was repeatedly clipped to skin level (Oster animal clippers, McMinnville, TN) on the right mid-side. Clean ®ber yield was deter-mined following standard procedures (ASTM, 1988), and ¯eece regrowth rate was calculated. Fiber dia-meter was measured on 3000±4000 snippets using an optical ®ber distribution analyzer (OFDA 100; Zell-weger Uster, Charlotte, NC). The mohair ¯eece is composed of two types of medullated ®bers, kemp with a continuous medulla occupying >65% of ®ber diameter, and gare having narrow continuous and discontinuous medullas (ASTM, 1980). In follicle observations, no attempt was made to differentiate between the two types of medullated ®bers.

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develop later being positioned to the outside of the central follicle. The percentage of active (anagen) follicles in the two follicle populations was calculated. Diet samples were collected monthly, dried at 558C for 48 h allowed to air-equilibrate and ground in a Wiley mill to pass a 2-mm screen. Samples were analyzed for DM, CP (AOAC, 1984), NDF and ADF (Goering and Van Soest, 1970).

2.4. Statistical analyses

Variables for which there were estimates at different times were analyzed as a repeated measures in time using the Wilks l-test of signi®cance (SAS, 1990). Also, some measures were categorized by season, with autumn being from autumn equinox (September 20) to winter solstice (December 20); winter from winter solstice to spring equinox (March 20); spring from spring equinox to summer solstice (June 20); and

summer from summer solstice to autumn equinox. Of the 14 sampling times for most variables, the ®rst three times and the last were in autumn, with samples 5±7, 8±10 and 11±13 in winter, spring and summer, respectively. These data were analyzed as a split-plot, with the main plot of nutritional plane and subplot of season. This resulted in two degrees of freedom for the main plot error term and 70 for residual error.

3. Results

As alluded to previously, both nutritional treatments elicited ¯eece-free BW loss until the ®rst shearing, and the difference between treatments was nonsigni-®cant (Table 1). The subsequent increased level of supplementation resulted in BW gain between the two shearings in the experiment and may have contributed to signi®cant effects of nutritional plane on some Table 1

Least-squares means of BW, ADG and grease ¯eece weight and ®ber growth rate for Angora does

Item First shearinga Second shearinga

Lb Hb pc< L H p<

BW, before shearing (kg) 30.8 32.1 NS 27.6 29.5 0.05

Fleece-free ADG (g per day) ÿ10.8 ÿ3.8 NS 0.8 14.5 0.05

Grease fleece weight (kg) 2.05 2.35 0.05 1.74 2.06 0.05

Grease fiber growth rate (g per day) 11.9 13.7 0.05 9.0 10.6 0.05

aFirst shearing, August 31 to February 18; and second shearing, February 19 to July 31. bL, low-nutritional plane; and H, high-nutritional plane.

cNonsigni®cant (p>0.05).

Table 2

Least-squares means of BW and ¯eece measures for Angora does in different seasonsa

Item Seasona SE

Autumn Winter Spring Summer

BW (kg) 31.6 29.9 28.0 30.9 1.6

Fleece-free BW (kg) 30.9 28.7 27.3 29.6 1.1

Grease fiber growth rate (mg/cm2per day) 1.46 b 0.96 d 1.30 c 1.68 a 0.05 Clean fiber growth rate (mg/(cm2per day) 1.13 a,b 0.85 c 0.98 b 1.20 a 0.04

Fiber diameter (mm) 34.9 a,b 31.7 c 33.7 b 36.5 a 0.7

Medullation (%) 0.48 b 0.32 c 0.40 b 0.76 a 0.10

Medullated fiber diameter (mm) 68.9 b 65.0 c 72.7a 71.2 a,b 1.4

Primary follicle activity (%) 74.4 b 23.1 c 79.4 b 98.6 a 4.5

Secondary follicle activity (%) 97.0 a,b 86.2 c 94.2 b 99.5 a 1.4

Primary follicle fiber medullation (%) 15.0 a,b 0.9 c 10.8 b 18.4 a 1.8

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variables. However, due to this change in level of supplementation, and because differences in BW and ADG were either nonsigni®cant or of relatively small magnitude and nutritional plane and time did not

interact, nutritional plane was not addressed in later sections.

Average BW and ¯eece-free BW were similar among seasons (p>0.05; Table 2). Grease ®ber growth, Fig. 1. Average clean ®ber growth rate (CFGR) and average ®ber diameter (FD) of Angora does subjected to low (L) or high (H) nutritional planes in different seasons: WS, winter solstice; SE, spring equinox; SS, summer solstice; and AE, autumn equinox. Mean and positive standard error of the mean.

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clean ®ber growth, ®ber diameter and percentage medullation consistently ranked summer>autumn> spring>winter. Values in the rank were signi®cantly different. In the case of grease ®ber growth and ®ber

diameter, values in autumn were not different from those of summer or spring, but were greatest in mid- and late summer. Seasonal differences in ¯eece ®ber diameter patterned those of clean ®ber growth rate (Fig. 1). Fig. 3. Average ®ber medullation in primary central and lateral follicles in Angora does subjected to low (L) or high (H) nutritional planes in different seasons: WS, winter solstice; SE, spring equinox; SS, summer solstice; and AE, autumn equinox. Mean and positive standard error of the mean.

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The secondary:primary follicle ratio was 7.750.14 and was not affected by nutritional plane. Primary follicle activity ranked (p<0.05) summer>autumn and spring>winter (Table 2). Fig. 2 depicts a gradual decline in primary follicle activity in autumn and winter, with lowest activity in mid-winter, and then a gradual increase in late winter through the spring to a plateau in late spring and early summer. Conversely, there was relatively less variability among seasons in secondary follicle activity; seasons ranked (p<0.05) summer>spring>winter, with activity in autumn being similar to that in spring and summer.

Medullated ¯eece was greatest among treatments (p<0.05) in summer (Table 2). The diameter of medul-lated ®ber was lowest (p<0.05) in winter and greater (p<0.05) in spring versus autumn, with diameter in summer being intermediate (p>0.05) to that in spring and autumn. Primary central and lateral follicles differed markedly in ®ber medullation except during winter, being greater for lateral follicles at other times (Fig. 3). There was greater variability in lateral than central primary follicle ®ber medullation. Primary follicle ®ber medullation ranked (p<0.05) summer>spring>winter, with that in autumn inter-mediate (p>0.05) to values for spring and summer. The ¯eece percentage and diameter of medullated ®bers gradually increased from autumn to mid-spring (Fig. 4).

4. Discussion

4.1. Follicle activity

The secondary:primary follicle ratio fell within a reported range for Angora goats of 7 to 10, and variability was similar to that reported in other parts of the world as well (Margolena, 1966; Winklmaier, 1983; Eppleston and Moore, 1990; Nixon et al., 1991). In addition, annual ¯eece production (4.1 kg), ®ber diameter (34.5mm) and kemp (0.49%) were compar-able to averages for US adult Angora goats (Lupton, 1996).

Primary follicles exhibited a highly seasonal pattern of activity, whereas a seasonal cycle in secondary follicle activity was barely discernible. These ®ndings are quite similar to reports for Angora goats world-wide (Dreyer and Marincowitz, 1967; Stapleton,

1978; Nixon et al., 1991); primary follicles of ®ber-producing goats reach minimum activity levels 1 month after the winter solstice and are fully active near the summer solstice (Nixon et al., 1991; Litherland, 1997).

4.2. Fiber growth

Clean ®ber growth rates were slightly lower than treatment means of 1.05±1.55 mg/cm2 per day observed by Sahlu et al., (1999a) with lactating does of the same herd from April to early August, although ®ber diameter in the present experiment was consid-erably lower than seen by Sahlu et al. (1999a); i.e. treatment means of 38.0±41.4mm). Similar grease ¯eece growth rate based on shearings of the present experiment were slightly less than grease or clean ®ber growth rates for Angoras of the same herd noted by Jia et al. (1995), season unknown, Davis et al., (1999) in spring and summer and Sahlu et al., (1999b) in late spring and early summer. Conversely, values of the present experiment compare reasonably well with an average clean mohair growth rate of 11.8 g per day calculated by Reis and Sahlu, (1994) based on ®ber characteristics and number of follicles, and also with most literature values summarized by these workers. Fiber diameter in the present experiment was within the range of values found for Angoras of the same herd in previous reports (Davis et al., 1999; Sahlu et al., 1999b).

Clean ®ber growth rate in summer was 41% greater than during winter and comparable to observations on other Angora goats (Stapleton, 1978; McGregor, 1988) and wool-producing sheep (Butler and Head, 1994). Decreased ¯eece growth in winter appears to be re¯ective of declines in activity of both primary and secondary follicles, reduced ®ber diameter and, pre-sumably, decreased ®ber volume. In sheep, lowest ¯eece growth in winter seems to be a consequence of diminished follicle activity relative to that in other seasons, reduced follicular mitotic rate and, hence, decreased ®ber volume (Holle, 1993).

4.3. Medullation

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1986). Skin and ®ber samples collected on the mid-side are likely to underestimate the whole-body medullation level (Stapleton, 1976; Basset, 1986). In the present experiment, medullated ®bers were identi®ed in ®bers of up to 55% of central and 5% of lateral primary follicles. Medullated ®bers were virtually absent in secondary follicles in this experi-ment corroborating the results of other studies with US Angora goats (Margolena, 1974). In contrast, in Aus-tralian Angoras medullated ®bers have been found in all central and up to 60% of lateral primary follicles and in as many as 5% of periphery secondary follicles (Nixon et al., 1991), which could be attributed to a genetic condition for enhanced growth of medullated ®bers in Australian Angora goats (5%) compared with those in the US (<1%; Stapleton, 1976).

Medullated ®bers growing in central primary folli-cles had two periods of growth, namely spring and autumn. This biannual growth was also mirrored in ®ber diameter changes. Biannual production of kemp and primary follicle activity have been previously reported for cashmere (Litherland, 1997) and Angora goats (Dreyer and Marincowitz, 1967; Stapleton, 1976; Winklmaier, 1983; Nixon et al., 1991). This has important implications in the timing of shearing to minimize presence of kemp in the shorn ¯eece. According to the results of the present experiment, the optimum time of shearing to avoid medullated ®bers would be just prior to spring and autumn equinoxes when medullated ®bers are likely to have been recently shed. Mid-side ¯eece medullation levels and ®ber diameter were highest in summer, in agree-ment with observations of Dreyer and Marincowitz, (1967) in South African Angora goats. The average level of medullated ®bers detected by OFDA was 0.6% and mean ®ber diameter was 69mm, indicating that the OFDA used in the present experiment, at the standard opacity setting, selects predominantly kemp ®bers when measuring medullation.

5. Conclusions

A seasonal cycle of ®ber growth in US Angora goats exists. Primary follicle activity was lower in winter than summer, and clean ®ber growth rate and ®ber diameter were lowest in winter, greatest in summer and intermediate in autumn and spring. Fleece ®ber

medullation was greatest among seasons in summer, and medullated ®ber diameter was greater in spring and summer than winter. These results can be used to design optimal feeding programs for mohair produc-tion and shearing times for minimal medullated ®ber contamination.

Acknowledgements

This research was partially supported by USDA, CSREES Project No. OKLX-2000-01. Appreciation is expressed to the farm crew of the E (Kika) de la Garza Institute for Goat Research of Langston University for care of the animals.

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