INTRODUCTION

Andean camelids show variations in diameter along the staple length (fibre diameter profile, FDP) during the annual or seasonal fibre growth, due to nutritional availability in dry and rainy seasons, physiological conditions (^{Mayhua et al., 2012}; ^{Pinares and Yauri, 2019}; ^{Quispe et al., 2021}; ^{Olarte, 2022}) and other factors associate to stress (^{Elvira and Jacob, 2004}). The variability of alpaca colour remains in the high Andean regions of Peru (^{Oria et al., 2009}; ^{Pinares et al., 2021}, ²⁰²³), that is a potential for crafts and the textile industry. Despite the above, there are few studies in Peruvian alpacas of dark colours, regarding the textile characteristics as fibre diameter and medullation (^{Lozano et al., 2023}; ^{Pinares et al., 2023}) and very limited studies for alpaca and Ch’aku llama regarding the physical or mechanical properties as staple strength (^{Llactahuamani et al., 2020}; ^{Quispe-Ccasa et al., 2020}).

The mean and standard deviation of fibre diameter, medullation, fibre curvature, staple length and staple strength are the main properties that influence on industrial processing and garment production (^{Villarroel, 1963}; ^{Wuliji et al., 2000}; ^{Lupton et al., 2006}; ^{McGregor, 2006}; ^{Simbaina y Raggi, 2019}; ^{Radzik-Rant and Wierciñska, 2021}; ^{Pinares et al., 2023}). The most valued attribute of alpaca fibre is handled soft and very warm, thanks to fragmented, discontinuous and continuous medulla, within the fibres that trap air (^{Czaplicki, 2012}; ^{Pinares et al., 2018}, ²⁰¹⁹). Suri fleece is also valued because it is lustrous (^{Lupton and McColl, 2011}). Those who wear alpaca garments choose them because of their thermal qualities, physical and mechanical properties (strength) of the fibre, as well as some other attributes such astheirimpermeabilityand anti-inflammability, lower fibre density or specific weight (Czaplicki, 2012). Therefore, a smaller mean fibre diameter, but with greater mean staple strength ± SD (50.16 ± 21.40 N/ktex) is required for the textile industry (Lupton et al., 2006).

Staple strength is the force required to break a staple (the maximum break force for staple per unit of average linear density), and it is measured in Newton per kilotex (^{Wuliji et al., 2000}; ^{McGregor, 2006}; ^{Lupton et al., 2006}; ^{Scobie et al., 2015}; ^{Llactahuamani et al., 2020}; ^{Gonzalez et al., 2020}). The breaking point is associated with the fibre minimum diameter profile; therefore, the thinner section of fibre breaks faster. Staple strength could be tested empirically by stretching individual strands between the fingers and applying a tensile force until they break, but this is very subjective (^{Elvira and Jacob, 2004}). The objective of this study was to determine the correlations between the staple strength and the textile characteristics of black and brown alpaca fibre, as well as to evaluate the influence of colour, breed, location, age and sex on the staple strength properties.

MATERIALS AND METHODS

Animal Care and Fibre Sampling

The study was carried out in Pitumarca and Maranganí districts in the province of Canchis, Cusco, Peru, in June 2022 at the XXVI Regional Agricultural Show - Pitumarca, the LXX Expo Show Agricultural -Maranganí, and the South American Camelid Research Centre (CICAS «La Raya») of the Universidad Nacional San Antonio Abad del Cusco (UNSAAC). All procedures were approved by the Ethics Committee of the National University of San Antonio Abad del Cusco (CBI-UNSACC) modified by -No. 079-2021-CU-UNSAAC, in accordance with Peruvian National Law N.° 30407 (Animal Protection and Welfare Law).

A total of 102 fibre samples (5 g) were randomly taken from mid-side (Table 1), centred over the tenth rib, midway between the back line and the belly line (^{Radzik-Rant et al., 2021}). In both shows, coloured fibre sampling was carried out at the animal admission stage, prior to judging. Age category was assigned based on teeth, where A = DL (milk teeth 7-18 months), B = 2D (two teeth 18 months -2 years), C = 4D (four teeth 2-3 years) and D = BL (full mouth >3 years). Fibre colour was classified in black (BA), dark brown (DB) and light brown (LB), as described by ^{Pinares et al. (2023}) using the fleece colour chart of Australian Alpaca Association (²⁰¹²).

Table 1. Number of alpacas sampled according to colour, breed, age and sex from Pitumarca, Maranganí and CICAS La Raya (Cusco, Peru) 

Colour: black (BA), dark brown (DB), light brown (LB); Breed: Huacaya (H), Suri (S); Age: milk teeth (DL), 2 teeth (2D), 4 teeth (4D), full mouth (BL); Sex: male (M), female (F)

RESULTS

Correlation between staple strength and fibre characteristics

The fibre textile characteristics were strongly correlated with the staple strength in dark-coloured alpacas (between -0.23 and 0.53). Likewise, some of these characteristics correlated with the peak force and staple length (between -0.24 and 0.36). Thus, a high correlation (r_s = 0.99) was obtained between staple length and peak force position (Table 2).

Table 2. Spearman’s correlation coefficients between the staple strength properties measured by Staple Length & Strength and the fibre textile characteristics measured by OFDA 2000 in coloured Huacaya and Suri alpacas 

Significant correlations are shown with asterisk (* p<0.05; ** p<0.01; *** p<0.001)

Factors affecting the staple strength

The colour of the fleece, the location and the sex of the alpaca did not influence the staple strength (p>0.05). In the case of Huacaya alpacas, the staple strength and the peak force were higher than those of Suri alpacas. Likewise, staple strength increases with age, between 16.75 and 20.10 N/ktex for young (milk teeth and 2-teeth categories) and 38 N/ktex for 4-teeth category. However, the staple length in Huacaya was shorter compared to Suri (Table 3).

Table 3. Median for staple strength, peak force and staple length by colour, breed, location, age and sex of alpacas 

DISCUSSION

Positive correlations were found among the staple strength with the comfort factor (r_s = 0.20) and with the peak force (r_s = 0.53). Fibre curvature was positively correlated with staple strength (r_s = 0.42) and peak force (r_s = 0.36). A positive correlation (r = 0.30) was found between fibre curvature and staple strength in Huacaya and Suri alpacas by ^{Llactahuamani et al. (2020}), but a negative correlation (r = -0.26) was reported by ^{Lupton et al. (2006}) in Huacaya. The fibre curvature was negatively correlated with staple length (r_s = -0.24), in agreement with -0.28 reported by ^{Wuliji (2019}).

There was a negative correlation between the staple strength with the fibre maximum diameter profile (r_s = -0.21) and with the MFD standard deviation (r_s = -0.23). In this regard, ^{Quispe et al. (2021}) indicate that the fibre diameter profile for annual growth (seasonal variation) is approximated by the maximum, minimum diameter along the staple and the difference in these diameters. Therefore, the positive correlation of 0.24 (p<0.05) between peak force position and difference of fibre diameters, is relevant to improve at the same time staple strength and fibre diameter profile.

The negative correlation (r_s = -0.21) between staple strength and length means that the shorter the length, the greater the staple strength. This finding is corroborated with previous studies by ^{Wuliji et al. (2000}), ^{McGregor (2006}) and ^{Lupton et al. (2006}). Although this study did not find an association between MFD and staple strength (r_s= -0.19), previous reports in Huacaya alpaca with high MFD ≥ 28 µm showed significant positive correlations (r>0.34; Wuliji et al., 2000; ^{Lupton et al., 2006}; ^{McGregor, 2006}). This would affect the mechanical and textile performance of the alpaca industry. No relationship was found between comfort factor and staple length similar to previous studies by ^{Pinares et al. (2023}); however, ^{Simbaina and Raggi (2019}) reported a negative correlation (r_s = -0.32).

The alpaca fleece colour did not influence the staple strength and peak force of the fibre (p>0.05), similar to the results of ^{Lupton et al. (2006}) and ^{Wuliji et al. (2000}). However, Wuliji et al. (2000) found that white crias (31.7 N/ktex) had greater staple strength compared to dark and light brown ones (26.2 N/ktex), but similar to black ones (29.2 N/ktex).

In contrast, for Huacaya alpacas in USA, ^{Lupton et al. (2006}) reported a mean ± SD (50.16 ± 21.40 N/ktex), with minimums and maximums of 5 and 138 N/ktex, respectively. Likewise, in Australian alpacas, ^{McGregor (2006}) reported 81 and 68 N/ktex for Huacaya and Suri, respectively (p<0.05). These high values of staple strength in foreign-alpaca breeding are in part related to their high MFD (e»28 µm; McGregor, 2006; ^{Wuliji et al., 2000}; Lupton et al., 2006).

In Ocongate (Cusco), ^{Llactahuamani et al. (2020}) indicated that Suri alpacas had less staple strength (60.11 N/ktex) than Huacaya (81.66 N/ktex). The median differences found in our research between Huacaya (29.5 N/ktex) and Suri (13.4 N/ktex) could be related with differential distribution of internal cortical cells (^{Shim, 2003}; ^{Holt, 2007}), as the bilateral distribution of cortical cells can differentiate the fibre curvature in Huacaya. In Suri fibres, the ortho and para cortex cells are not distributed bilaterally (^{Shim, 2003}; ^{Holt, 2007}). On the other hand, the greater staple strength in Huacaya was attributed to its more ordered structure (higher crystallinity) in the alpaca helices making up the microfibrils, as revealed by X-ray diffraction (^{Hunter, 2020}).

Staple length in Huacaya was shorter compared to Suri, due to the differentiated fibre growth between these breeds; thus, explaining in part by regulation of FGF5 gene, it can in turn arrest the follicle development during the anagen phase or retard its progression (^{Pallotti et al., 2018}).

Staple strength is affected by age; thus, values of 31.8 ± 2.1 N/ktex (mean ± standard error) have been reported in adult Huacaya alpacas taken to New Zealand (^{Wuliji et al., 2000}), similarly to the present results (38.0 ± 2.1 N/ktex) in 2-3 years old alpacas. Nevertheless, ^{Wuliji et al. (2000)} reported higher values in crias (28.4 ± 1.9 N/ ktex) than 7-18-month-old alpacas in the present study (20.10 ± 4.6 N/ktex).

From the point of view of textile processing, Elvira and Jacob (²⁰⁰⁴) indicate that values higher than 30 N/ktex are appropriate. Therefore, Huacaya alpaca fibre seems to have a good staple strength (^{Wuliji et al., 2000}; ^{Lupton et al., 2006}; ^{McGregor, 2006}; ^{Llactahuamani et al., 2020}).

None of the staple strength properties were influenced by sex (Table 3). Males and females showed medians of 18.0 and 23.2 N/ktex, respectively (p>0.05). The results were consistent with 32.1 and 31.4 N/ktex reported by ^{Wuliji et al. (2000}) in males and females, respectively. Similarly, ^{Llactahuamani et al. (2020}) reported that sex did not influence on the staple strength. However, ^{Lupton et al. (2006}) found that males (44.5 N/ktex) produced stronger fibres than females (38.7 N/ktex). Likewise, ^{Quispe-Ccasa et al. (2020}) found higher staple strength and MFD in males (69.11 N/ktex, 27.31 µm) than in females (57.39 N/ktex, 23.63 µm) in Ch’aku llama.

CONCLUSIONS