Effect of Age and Sex on Medullation Types and Fiber Characteristics in Huacaya Alpacas

Peru concentrates the largest alpaca population with 3.8 million alpacas. South American camelids are characterized by the fact that they efficiently convert nutrient-depleted and stature-poor pastures into high quality products such as fiber and meat, in addition to producing by-products such as hides and skins that have industrial and artisanal uses. Likewise, their manure is a by-product that is used as fuel for cooking and as fertilizer for crops (FAO, 2005).
       
Alpaca fiber is considered a luxury item due to its characteristics of fineness, softness and has a high valuation in the market, as well as Cashemire, Mohair, Yak and Musk Ox (Wang et al., 2003). There are reports that fiber diameter is affected by: age, breed, sex, physiological state, fiber color, nutritional status, (Bustinza, 2001; Canaza et al., 2022; Frank et al., 2006; McGregor  and Butler, 2004; Omachea et al., 2015; Olarte et al., 2023; Quispe et al., 2009; Roque and Ormachea 2018; Wuliji et al., 2000). However, there are fleeces in alpacas that present objectionable or medullated fibers related to the itch factor and it has been shown that fibers with continuous and strongly medullated pith have an effect on fiber diameter variability (McGregor et al., 2013).
       
In this regard, there are studies in which they affirm that the presence of medullated fibers favors the thermoregulation of the alpaca in rather frigid climates, because the medulla has the ability to retain heat (Moore et al., 2011; Wang et al., 2005). Currently, several researchers are trying to explain the behavior of the presence of pith in the fiber, among which the percentage of pith in the fibers has even been proposed as a selection criterion (Cruz et al., 2019; Pinares et al., 2018, 2019; Quispe et al., 2022), in addition, the heritability for wool is moderate to high (Lalit et al., 2017). In this sense, the research work has been planned with the purpose of determining the percentage of medulation and the characteristics of the fiber in Huacaya alpacas (Vicugna pacos).

Sampling
 
The research was conducted in the district of Macusani, Carabaya province, Puno region. A total of 240 Huacaya alpacas used, were distributed across different age groups (1 year = 60, 2 years = 60, 3 years = 60 and older than 4 years = 60), including both sexes (males = 120 and females =120). Fiber samples were collected before shearing the animals during the months of October and November 2022. Each collected sample was labeled with the breed, sex, ear tag number and the age of the animal
 
Fiber analysis
 
Fiber samples were collected from the midrib region at the level of the third to fourth rib on the left side of the alpaca (Mid-side), which is representative for evaluating the mean fiber diameter (Aylan and McGregor, 2002; Radzik et al., 2021). Each collected sample contained approximately 6 grams of fiber. Subsequently, the samples were stored until analysis in the Fiber Laboratory of the School of Textile Engineering and Apparel at the National University of Juliaca using the FIBER MED V 1.0 and FIBER EC V 4.0 equipment, under standard laboratory conditions at 20±2°C temperature and 65±5% relative humidity.
       
Fiber Med is an artificial intelligence-based device that recognizes different medullation types. Before the evaluation, the samples were washed for 3 minutes using a solution composed of 7 parts of 96% alcohol and 3 parts of benzine. After washing, the samples were placed on an absorbent towel for drying. Subsequently, fiber fragments were prepared using the Hardy microtome. These fiber fragments were then mounted on glass slides, homogenized with immersion oil, covered with a cover slip and placed in the medulometer (Fiber Med) for their respective analysis. Medullation types were classified as follows: Non-medullated fibers (NoMed), fragmented medulla (FragMed), discontinuous medulla (DiscMed), continuous medulla (ContMed) and strongly medullated (StrMed) (Quispe et al., 2022).
       
The fiber characteristics in alpacas, such as mean fiber diameter, standard deviation, coefficient of variation, comfort factor and curvature index, were analyzed according to the standards described by the International Wool Textile Organization for wools and other fibers of animal origin. Under standard laboratory conditions at 20±2°C temperature and 65±5% relative humidity, following IWTO-52 procedures (IWTO-52, 2006). Dirty fiber samples were washed with detergent and baking soda in water at 50-60°C; afterward, they were placed in an oven at 70°C for 24 hours. The clean and dry samples were mounted on slide for their respective analysis using the FIBERT EC V 4.0 equipment.
 
Statistical analysis
 
Descriptive statistics and a statistical analysis based on a linear model that included the effects of age and gender were used:        
For creating the graphs, the (Rcmdr) library and the packages: ggplot2, plyr, carData and stats were employed. The Tukey test was used for multiple comparisons of fiber characteristics means and the Wilcoxon test was used to compare medullation percentages in Huacaya alpaca fiber. The statistical analysis was performed using R software, version 4.1.1 (R Core Team, 2021).

Fiber medullation in Huacaya alpacas
 
Table 1 and Fig 1 display the types of medullated fibers, such as non-medullated fibers (NoMed), fragmented medulla (FragMed), discontinuous medulla (DiscMed), continuous medulla (ContMed) and strongly medullated (StrMed), found in Huacaya alpacas, considering the age and sex of the animal. The percentage of non-medullated fibers decreases as the age of the animal increases (1 year = 75.60%, 2 years = 69.43%, 3 years = 69.05% and >4 years = 66.25%) (image B). The highest proportion of fibers with a discontinuous medulla was found in animals older than 4 years and 3 years (>4 years= 4.37, 3 years= 5.06). The presence of fibers with a continuous medulla was greater in alpacas older than 4 years, at 11.95%. The percentage of strongly medullated fibers increases with the age of the animal (1 year= 0.10, 2 years= 0.11, 3 years= 0.21, >4 years = 0.34) (image D). Likewise (Table 1 and Fig 2), the results obtained demonstrate that no statistical difference was found in medullation types based on the gender of the animal (P>0.05).
 

 

 

       
Table 1 shows that image (A) corresponds to the percentage of medullated fibers. In the case of 1-year-old animals, it was 24.40%; 2 years was 30.57%; 3 years was 30.95% and >4 years was 33.59%. Therefore, it can be stated that the percentages of medullated fibers increase as the age of the animal and the number of shearings performed increase.
       
Fig 2 displays the density histograms, where image (E) corresponds to the percentage of medullated fibers, being 31.12% for males and 29.22% for females. Image (F) represents non-medullated fibers, with percentages of 68.77% for males and 70.78% for females. Image (G) illustrates fibers with continuous medulla, showing 11.73% for males and 8.34% for females. Image (H) depicts strongly medullated fibers, with values of 0.28% for males and 0.13% for females.
       
Statistical differences were found based on the age effect in the percentages of medullation. In animals of 1 year old, values of 24.40% were obtained compared to alpacas of 2, 3 and older than 4 years, results that demonstrate an increase in the proportion of medullated fibers due to age. The results obtained corroborate the findings of other researchers (Aruquipa, 2015; Contreras, 2010; Lupton, McColl and Stobart, 2006; McGregor B., 2006; Pinares et al., 2019; Quispe et al., 2022). The increase in medullated fibers due to age is explained by the increase in mean fiber diameter, the decrease in the number of actively growing skin follicles and the ratio of primary to secondary follicles as a result of the animals’ aging (Antonini et al., 2004; Khan et al., 2012; McGregor, 2002). In this regard, McGregor et al., (2012) mention that medullation is related to altered keratinization in the hair follicle bulb, which is associated with insufficient protein synthesis. The results obtained in the study regarding strongly medullated fibers range from 0.10% to 0.34%, which represents a good indicator as a criterion for selecting future alpaca breeders with the aim of eliminating strongly medullated fibers from the fleeces, as recommended by other researchers (Cruz et al., 2019; Pinares et al., 2018, 2019; Quispe et al., 2022). From a textile industry perspective, garments made from fibers with high percentages of continuous medulla and strongly medullated fibers are the ones that cause discomfort or itching when they come into contact with the skin (Frank et al., 2014; Quispe et al., 2022), as they emerge from the surface of the thread (Mamani-Cato et al., 2022). This process leads to a decrease in the price of the product (McGregor and Butler, 2004).
       
The percentages of medullated fibers, also known as objectionable fibers (Lupton et al., 1991), found in the study were 29.22% in males and 31.12% in females. No statistical differences were observed based on gender and these findings are consistent with results from other researchers (Aruquipa, 2015; Quispe et al., 2022; Radzik, Pofelska and Rant, 2018), which support our obtained results. However, our reports differ from the results of Radzick-Rant and Wierckinska (2021), who obtained values of 60.13% in females and 77.7% in males. We attribute this difference to the origin of the animals and the number of animals used in the study.
 
Fiber characteristics in huacaya alpacas
 
Table 2. It presents the mean fiber diameter in Huacaya alpacas, where 1-year-old animals exhibit a smaller diameter with a value of 17.32 mm compared to the other age groups: 2 years = 19.49 mm, 3 years = 19.91 mm and 4 years= 20.10 mm (P≤0.05). However, no difference was observed regarding the gender of the animal (males = 18.67 mm and females = 19.55 mm). The results obtained regarding the coefficient of variation of fiber in alpacas were as follows: 1 year= 21.29%; 2 years= 21.15%; 3 years= 20.31%; >4 years = 21.80%; in males, it was 21.31% and in females, 21.03% (P≤0.05). This indicates a higher uniformity in the fiber of these animals, considering both age and gender.
 

       
As for the comfort factor, considering the age of the animals, they exhibited a value higher than 95%, which is an acceptable characteristic from a textile industry perspective. 1-year-old animals showed the highest percentage at 99.47%, compared to 2-year-olds at 98.02%, 3-year-olds at 97.01% and those older than 4 years at 96.45% (P≤0.05). However, no statistical differences were found with respect to gender (males = 97.94% and females = 97.60%).
       
The fiber curvature index shows no statistical difference based on age; 1-year-old animals have an average of 55.86 °/mm compared to 2-year-olds at 53.42 °/mm, 3-year-olds at 53.99 °/mm and those older than 4 years at 52.23 °/mm.
       
The reports obtained are supported by research work carried out by: McGregor (2006), Bustinza (2001), Lupton, McColl and Stobart (2006), Ormachea et al., (2015), Roque and Ormachea (2018) and Paucar-Chanca et al., (2019), who assert that the values of mean fiber diameter in alpacas are lower in the first year of life and significantly increase as the animal ages. Franco et al., (2009) mention that a diet with low levels of energy and protein will decrease fiber diameter and length growth. However, there are contrasting studies, such as Bryant et al., (1989), who claim that when there is an abundance of natural pasture, fiber thickening occurs due to better nutrition. Furthermore, there are reports indicating that the variation in mean fiber diameter is indirectly influenced by precipitation and pasture availability (Olarte, 2022; Quispe et al., 2021). Thus, the presence of fibers with continuous medulla and strongly medullated fibers would affect the variability of fiber diameter in the fleece (McGregor et al., 2013).
       
Regarding the coefficient of variation in the study, values ranging from 20.32% to 21.81% were found. This demonstrates uniformity in the diameter of individual fibers within the fleece and the produced threads will be more resistant and consistent. This is a desirable aspect from the perspective of the textile industry (Frank et al., 2006; Lupton, McColl and Stobart (2006). The results obtained are in line with the reports of Paucar-Chanca et al., (2019), who state that there is no statistical difference in the coefficient of variation due to the sex and age of the animals.
       
The results revealed in the study show that the comfort factor variable decreases as the age of the animal increases, therefore the comfort factor would be inversely related to the fiber diameter in alpacas, which is corroborated by the reports of, McGregor (2006); Ormachea et al., (2015); Vásquez et al., (2015); Roque and Ormachea (2018). On the other hand, as with other studies, sex did not influence comfort factor (Lupton, McColl and Stobart (2006); Ormachea et al., 2015; Paucar-Chanca et al., 2019; Quispe et al., 2009).

The percentage of medullated fibers, mean fiber diameter, and fiber comfort factor are influenced by age, as a consequence of the number of shearings performed in Huacaya alpacas. However, gender does not influence these characteristics.

The authors declare that there are no conflicts of interest.