Correlation between mean fibre diameter and total follicle density in alpacas of differing age and colour in the Parinacota province of the Chilean high plain

Abstract

This investigation aimed to determine and correlate mean fibre diameter (MFD) and total follicle density (TFD) in juvenile (1–2 years) and adult (3–6 years) white and brown alpacas in the Parinacota Region of northern Chile. Fibre samples and skin biopsies were taken from the mid-side regions of 77 individuals. The observed MFD for all individuals (22.6±3.76 µm) was lower than that obtained by previous research in the same geographic region. There was no demonstrated statistical difference between MFD and TFD based on fleece colour (p>0.05). Demonstrated MFD in white alpacas was 22.57±3.92 µm with a TFD of 21.97±6.37 foll/mm²; in brown alpacas MFD was 22.63±3.66 µm and TFD 21.56±7.25 foll/mm². MFD in juvenile alpacas was 21.61±2.78 µm with a TFD of 24.2±7.49 foll/mm² and in adults MFD was 23.47±4.3 µm with a TFD of 19.62±5.34 foll/mm², demonstrating a statistically significant difference between age groups of lower MFD but higher TFD in juvenile individuals (p<0.05). A correlation (−0.42, p<0.05) between lower mean fiber diameter and higher TFD was observed for all individuals. These results contribute to regional efforts to advance genetic selection based on TFD and improve fleece productivity and economic viability of the local industry.

Keywords:

• alpaca
• fibre diameter
• follicle density
• correlation

1. Introduction

Alpacas (Lama pacos) are domestic South American camelids that reside primarily in zones 3000 or more metres above sea level in the Peruvian, Bolivian, Argentinean and Chilean high plains. Populations can also be found in the USA, Australia, New Zealand, and other countries where they have been introduced for commercial fleece production (Lupton et al. 2006; Quispe et al. 2009).

One of the most important characteristics of alpaca fibre is its diameter, which is used to evaluate fibre quality. Fibre diameter represents a more commonly employed indicator of fibre quality than follicle density because of its comparatively simple and economic sampling process. Nevertheless, follicle density may more accurately reflect heritable characteristics and as a result represent a more valuable indicator for genetic selection for fleece quality and productivity. Fibre diameter varies greatly dependent upon many factors such as individual race (huacaya or suri), colour, age and corporal zone sampled (Castellaro & García-Huidobro 1993).

With respect to the colour variable, available information is inconclusive. Some authors indicate significant differences between white and brown alpacas (Martinic 1993; Bas & Bonacic 1995), while others such as Valjalo (1964) do not report significant variation in fibre density based on colour. With respect to age, various authors agree that young animals present thinner fibre diameter (Martinic 1993; Bas & Bonacic 1995; Lupton et al. 2006).

Environmental factors such as winter weather conditions (Wuliji et al. 2000) and nutrition (Florez et al. 1986; McGregor 2002; Frank et al. 2006) can also influence fibre diameter. Consequently, diameter has relatively low heritability; Frank et al. (2006) estimate medium heritability of 0.28, and Cervantes et al. (2010) estimate heritability within the range of 0.255 and 0.417. As a result, more rigorous genetic selection cannot rely solely on fibre diameter, and future investigation of the heritability of follicle density will be necessary.

The production of alpaca fibre and other alpaca products constitutes the principal economic resource of the inhabitants of the Andean high plains (Quispe et al. 2009). However, within the Chilean Parinacota Region, fleece productivity is notably low, due in part to limited standardisation of productive modules and a lack of any effective information system (Programa de Innovación Territorial 2008).

The objective of this investigation was to contribute to limited data on follicle density within the region in order to evaluate the relationship between fibre diameter and follicle density in alpacas of varying age and fleece colour and to support improved understanding of fleece quality and its dependence on environmental and other external factors. The resultant data represents a supplement to advance productivity within the regional industry.

2. Materials and methods

2.1. Description of samples and measurements

Seventy-seven huacaya alpacas from four producers in zones with similar environmental conditions of the Parinacota Province of Chile were sampled.

Individuals were classified based on two criteria: by colour (white or brown) and by age (1–2 years defined as juvenile and 3–6 years as adult). Seventy-seven animals were selected from a total population of 550. Animals with greater colour purity were favoured for selection; alpacas designated as white presented exclusively white face and body fibre and brown alpacas presented entirely brown body fibre and black face fibre. The sex of the animals was not evaluated; previous research has not shown significant differences between mean fibre diameter of females and males (Valjalo 1964; Martinic 1993; Bas & Bonacic 1995; McGregor & Butler 2004; Lupton et al. 2006; Sequeiros et al. 2006).

One fleece sample was taken from the mid-side region of each alpaca (Aylan-Parker & McGregor 2002), and fiber diameter was measured using the optical fibre diameter analyzer (OFDA) 2000®. Mean fibre diameter (MFD) in µm, standard deviation of fibre diameter (also in µm) and coefficient of variation of fibre diameter (as a percentage) were calculated.

Total follicle density (TFD) (in foll/mm²) was determined using the McCloghry (1997) histological technique protocol. Using an 8 mm diameter biopunch, a skin biopsy was taken from the region corresponding to each fleece sample. Buffered formalin (10%) was used to preserve biopsy samples until their laboratory processing within seven days.

TFD was determined manually in an optical microscope at a magnification of 40x by establishing the number of total primary and secondary follicles in 10 fields and obtaining an average. The number of follicles was determined using a blindfolded method to ensure impartiality, and values were corrected to avoid potential overestimation from biopsy shrinks (McCloghry 1997) (Figures 1 and 2).

Figure 1. Histological section of white alpaca skin at magnification 40×. Arrows indicate primary and secondary follicles within the 1 mm² quadrant. Note: Micrograph obtained at Universidad Santo Tomas microscopy laboratory, Santiago.

Figure 2. Histological section of white alpaca skin at magnification 100×. Number 1 indicates primary follicles and number 2 secondary follicles. Note: Micrograph obtained at Universidad Santo Tomas microscopy laboratory, Santiago.

2.2. Statistical analysis

MFD and TFD for each fleece colour and age group were statistically expressed as median, standard deviation and variation coefficient. Variation between groups was determined using a Student's t-test (in IBM SPSS® Statistics data Editor 19.0 Chicago, IL, USA) for independent samples (p<0.05).

Pearson's correlations and their statistical significance between the MFD and TFD variables were calculated according to age group and fleece colour.

3. Results

The 77 animals studied were selected from a population of 550. Their selection permitted the formation of homogenous groups based on colour and on age (Table 1).

Table 1. Distribution of sampled alpacas by fleece colour and age division.

Colour	White	Brown	Total
	38	39	77
Age	Juvenile (1–2 years)	Adult (3–6 years)	Total
	36	41	77

3.1. Mean fibre diameter and total follicle density

The MFD for all sampled individuals was 22.6±3.76 µm, with a coefficient of variation of 16.65% and a range between 17.6 and 35.1 µm. The overall mean TFD was 21.76±6.79 foll/mm², with a coefficient of variation of 31.21% and a range between 10.9 and 48.9 foll/mm².

No significant variation (p>0.05) was observed for MFD and TFD by fleece colour (Table 2).

Table 2. Mean fibre diameter (MFD) and total follicle density (TFD) in alpacas by fleece colour.

Parameter	White	Brown
MFD (µm)	22.57±3.92a	22.63±3.66a
CV (%)	17.37	16.15
Range (µm)	17.6–33.8	17.9–35.1
TFD (foll/mm^2)	21.97±6.37a	21.56±7.25a
CV (%)	29.1	33.64
Range (µm)	10.9–33.4	12.1–48.9

Note: Differing letters on the same line indicate statistically significant differences (p<0.05).

A comparison of juvenile and adult individuals presented significant differences (p<0.05) for both MFD and TFD measurements, with lower fibre diameter and greater follicle density in juvenile samples (Table 3).

Table 3. Mean fiber diameter (MFD) and total follicle density (TFD) in alpacas by age group.

Parameter	Juvenile	Adult
MFD (µm)	21.61±2.78a	23.47±4.3b
CV (%)	12.87	18.32
FD Range (µm)	17.6–27.7	18.1–35.1
TFD (foll/mm^2)	24.2±7.49a	19.62±5.34b
CV (%)	30.93	27.22
Range (µm)	11.6–48.9	10.9–33.3

Note: Differing letters on the same line indicate statistically significant differences (p<0.05).

3.2. Correlations between MFD and TFD

MFD and TFD for the 77 sampled individuals demonstrated a negative correlation with statistical significance (p<0.05). Colour and age variations also demonstrated a negative and significant correlation (p<0.05) (Table 4); juvenile individuals presented overall finer fibre.

Table 4. Correlation between mean fiber diameter (MFD) and total follicle density (TFD) among sampled alpacas.

	Mean fiber diameter
	White	Brown	Juvenile	Adult
Total Follicle Density
White	−0.47
Brown		−0.39
Juvenile			−0.35
Adult				−0.43

4. Discussion

4.1. Mean fibre diameter

Results from this investigation were compared with previous research from areas with similar climatic, altitudinal, environmental and feeding conditions.

The MFD of sampled individuals was 22.6 µm, significantly lower than that previously reported by Valjalo (1964), González (1990), Martinic (1993), Benavente et al. (1993) and Bas and Bonacic (1995). A majority of the fibres (75.32%) sampled in this investigation would be classified as ‘fine’ as compared with values recorded by other authors in the same region (Castellaro & Garcia-Huidobro 1993; Bas & Bonacic 1995). This difference may be in part attributable to regional efforts to improve fleece productivity. Much of the existing research and the data compared to this study's results are dated over 15 years – long enough for improved herd management to have increased fibre quality. Additionally, fibre analysis in cited works was performed using a projection microscope and consequently a method that requires several steps, measures a lower number of fibres per specimen and increases potential human error relative to the OFDA 2000® used in this investigation. Both the standard deviation and the coefficient of variation calculated in this investigation are lower than those of comparable research, also suggesting that the diameters of sampled fibres are more homogeneous than those sampled in previous studies (Bas & Bonacic 1995; Castellaro & Garcia-Huidobro 1993).

No significant difference (p>0.05) was observed between the MFD of white and brown individuals (22.57 µm and 22.63 µm, respectively), which supports the findings of Valjalo (1964). Nonetheless, Martinic (1993) and Bas and Bonacic (1995) reported statistical differences between MFD by colour, with white having a higher diameter, while González (1990) reported lesser average diameter for white fleece. Conflicting results may again be partially explained by the method of measurement employed (projection microscope) and its limited precision as compared to OFDA 2000®.

The MFD was 21.61 µm in juvenile alpacas and 23.47 µm in adult individuals, demonstrating a statistically significant difference (p<0.05). Martinic (1993) and Bas and Bonacic (1995) reported a positive correlation between age and fibre diameter. The results of this investigation agree with those of Lupton et al. (2006): sampled individuals were grouped as 1, 2 and >2 years of age, and statistically significant differences between age groups were observed.

4.2. Total follicle density

Mean TFD of sampled alpacas was 21.76 foll/mm², with a standard deviation of 6.79 and a coefficient of variation of 31.21%. Measured density falls within the normal range defined by Watts (2006) but above the range indicated by Ferguson et al. (2000). A high coefficient of variation may indicate heterogeneous samples explained by errors during biopsy processing or TFD determination.

4.3. Correlation between MFD and TFD

A negative correlation (of moderate magnitude: r= − 0.42) was observed between overall MFD and TFD; as described by Bustinza (2001), a greater TFD implies lower MFD. Vonderhaar (2009) also demonstrated this relationship with a greater magnitude and significance: r= − 0.57, p<0.0001.

A statistically significant negative correlation was observed for colour and age variation; greater magnitude (r= − 0.47) was demonstrated in white fleece individuals and lesser (r= − 0.35) in juveniles.

Determination of TFD by skin biopsy represents an objective method of measuring potential fibre productivity. As an indicator of fibre quality with the goal of improved genetic selection, TFD is observed to be less affected by environmental factors than simple fibre diameter measurement, and consequently to present greater stability. Despite current obstacles to its widespread use within the region, TFD holds potential as an indicator for genetic selection, and improved understanding of the relationship between TFD and MFD also has potential for improved herd management and genetic selection.

Inevitably, small sample size represents the greatest limitation to the significance of these results. Nevertheless, this study represents a valuable contribution to ongoing research and management of local fleece production.

5. Conclusions

The alpaca fibre industry represents an essential economic resource for residents of the Chilean high plain and similar regions worldwide. Current efforts to improve herd management and ultimately fleece productivity lack the guidance of a significant body of regional research. This investigation determined MFD and TFD within alpacas from regional producers to allow evaluation of the relationship among MFD, TFD, animal age, and fleece colour. The results demonstrate a negative and significant correlation (p<0.05) between MFD and TFD. No statistically significant differences (p>0.05) were observed for MFD or TDF based on fleece colour, while a significant statistical difference between age groups (p<0.05) for MFD and TFD was evidenced, with juveniles having thinner fibre quality, greater follicle density and, consequently, fibre of better quality and greater commercial value.

An understanding and documentation of these correlations is valuable to MFD- or TFD-based genetic selection, herd management and commercial viability of this vital regional industry.