Animal Breeding

4

AnimalBreeding

2.5.1

Woolcontributes about 17 % of the total material that is used in theproduction of apparel in the world, but this percentage has reducedin the recent decades. This decrease in the application of woolimplies that the stakeholders need to introduce novel and newproducts to the wearers in order to sustain and increase the woolmarket. This goal may be achieved by producing wool that has new andnovel properties. The decline in the use of wool in the market can beattributed to the failure on the part of the textile industry tomanufacture products that respond to the market signals. In otherwords, the products presented in the market fail to meet the needs ofthe apparel wearers. The market signals indicate that there has beenan increase in demand for wools that are finer. These finer woolsattract a higher premium than the ordinary ones.

Inthe case of Australia, this demand signal manifest in the form of astrong selection of fiber with the smallest diameter. This trend isconfirmed by the fact that efforts are being applied to breed Merinosheep that can produce the finest wool. The strain replacement andupgrading practices are common in farms that intend to reduce thediameter of the fiber. Studies are also being conducted to determinewhether there exist some relationships between the quality of wooland the genetic composition of the sheep. The outcome of thesestudies will be applied in the development of the breeding strategiesthat will result in the production of finer wool. The scientifictests that focus on the genes will help the researchers determine thepotential of sheep in terms of production quality, efficiency, anddiversity in the breeding programs.

Mostof the traits that determine the quality as well as the economicviability of fiber are influenced by multiple genes and theenvironment (Kendall etal.,2006). However, most of these traits are either interrelated orinteract in different ways. These interactions may be positive ornegative. In addition, most of the genes that code for proteins thatform the wool are linked to each other. This linkage complicates theprocess of dissecting the influence that individual genes have on theoverall features of the wool. Studies have also indicated that itcould be possible that extensive polymorphism that occurs in thegenes affects the traits of the wool through the alteration of theprocess of protein expression, overall structure, andpost-translational modifications. Moreover, variations in the numberof genes as well as loci have been shown to influence differenttraits of the fiber, including the length, staple strength, anddiameter.

Thetraits of the fiber determine the overall processing performance.This performance is influenced by the specific qualities of thefiber, including the diameter, length, and strength of the staple.The weight of the fleece is the most significant factor that has aneconomic value. However, the mean diameter of the fiber hashistorically been considered as the primary determinant of the marketprice or the premium of the wool. This is common in merino wool aswell as the mid-micron fibers since the diameter serves as the keyindicator of their softness and lightness. These qualities determinethe overall quality as well as the price premium of the resultantyarn.

Parsonsetal.(1994b) applied the candidate gene method to determine therelationship that exists between the diameter of the fiber and thehigh-glycine-tyrosine keratin gene loci in the Peppin Merinohalf-sib. The results of this approach indicated that the progenygroups that were obtained from the sire heterozygous for the KRTAP6gene had a mean difference in their fiber diameter. The meandifference was found to be 3.8 microns. The approach also identifiedthat there exists an association between the diameter of the fiberand the KRTAP8 gene. The average difference that exists between thetwo variables was found to be about 2.5 microns. These differencesare important factors that are considered during the processing ofthe fiber (Hunter, 1980). Robinson etal.(1995) also applied the candidate gene approach to study theassociation between the diameter of the fiber, FGF1 gene, and acidicfibroblast growth factors. The findings of the study also indicatedthat there exist some associations between the locus and differencesin the weight of the fleece.

Theapplication of the genome scan method in the analysis of Merino XRomney flock resulted in the identification of 1.7 micron differencebetween the progeny of the unnamed marker (Henry etal.,1998). The use of the segment mapping strategy, on the other hand,indicated that the regions that are occupied by chromosomes 6 and 25represent about 20 % of the genetic variance in the diameter of thefiber in INRA401 half-sibs (Ponz etal.,2001). Moreover, it is estimated that the mean diameter of the fiberand the fleece weight reaches plateau at about 3-4 years of theanimals’ age. The staple length, on the other hand, starts todecrease after the first one year of age of the animal (Brown et al.,1966 Sumner &amp Upsdell, 2001). Therefore, the quality of thefiber that is harvested from the animals is also influenced by theability of the farmers to determine the right time for gathering thewool.

Inmost cases, the diameter is quoted as the average value that obscuresits inherent variation along and between individual fibers. Researchhas shown that about two-thirds of the total variation in thediameter of the fiber in the line of the wool is related to betweenand along the fiber variation (Stobart etal.,1986). The within-fiber difference is estimated to be about two andten times the between-fiber variation (Sumner &amp Revfeim, 1973Stobart, et al., 1986). These variations are determined by differentfactors, including the management practices applied in the farms andthe environmental effects (Kendall etal., 2006).Consequently, variation in genetic control of the diameter of thefiber becomes complex. This notion is being investigated in severalgenes.

Allainetal.(1998) used the within the sire regression procedures to show thatMcM218 on chromosome number is usually linked to the variation in thediameter of the fiber, which occurs within the sample of the sheep’sfiber that is measured for the average diameter. The keratin genecluster that is located in the chromosome 11 has been shown to be thepotential locus that affects the variation in the diameter of thefiber. Two alleles (A and B) of KIF gene and KRT1.2 play the role ofdefining the two progeny groups of dissimilar standard deviation ofthe fiber diameter (B = 3.4 v. A = 3.7 μm μm, P = 0.008). However,the average diameter of the fiber is not significantly different(J.K.R. Abbott, T. Itenge-Mweza, and J.G.H. Hickford). The locusneeds to be investigated further in order to determine whether thereis a better control variation in the diameter of the fiber. Areduction in the size of the diameter in a given flock can result insignificant economic benefits. This benefit is mainly realized whensmall quantities of wool are required for the end-use.

Individualpieces of fiber in a given staple tend to grow at different rates.The coarse fibers grow faster, which leads to the development of a“tippy” appearance. This appearance is observed in the fleecethat has grown for some months. There is no relationship that existsbetween the length of the staple and that of the fiber. Their ratiovaries from 0.9 to 2.1 between different types of fleece (Hunter,1980). Variation in the length of the fiber may increase up to 5-folddue to breakages that occur during its processing (Bownass, 1984).There is a relationship between the length of the staple and the twoalleles of KAP1.1. The average difference in their length is 4.4 mm(Abbott, T., J.G.H. Hickford, and Itenge-Mweza). Studies on thislocus in superfine Merino have shown that there is a relationshipbetween alleles of the gene and the length of the fiber. Theassociation between the length of the fiber and alleles is quitesignificant. Differences in the length of the fiber within the top orcarded sliver vary with its average diameter or the mean of itslength. Differences of 4-5 mm in the length of the fiber are adequatefor the wool of the processing significance (Hunter, 1980).

Individualpieces of fiber are subjected to tensile stress during the processesof combing, carding, and spinning. The stress results in varyingdegrees of breakage where the fiber tends to split at the weakestpoints. The broken pieces of fiber are removed during the processingsteps and separated as waste. The region occupied by chromosome 11has been shown to be a potential for QTL for staple strength,especially in Romney half-sib families (Rogers etal.,1994). About three loci have been identified within the region. Theseregions are strong candidates for association with traits of thewool. One of the loci encodes for keratin intermediate filamentprotein. The other locus encodes for the matrix proteins, includingKAP1.n and KAP3.n.

Theanalysis of the data for pooled progeny at three loci has shown thatthere is a significant genotype-within-sire impact for the strengthof the staple within the half-sib group of the 16 N/ktex as well as24 N/ktex, respectively. Differences in the strength of the staplethat exceed 5 N/ktex have a processing significance (Hunter, 1980).The work done by Abbott, Itenge-Mweza, and Hickford showed thatvariation in KRT1.1 has a significant relationship with the strengthof the staple. This association has a mean difference in the strengthof the staple between the progeny groups obtained from a singleheterozygous half-bred Merino sire of about 3 N/ktex. The associationbetween the strength of the staple and KRT1.2 gene has been confirmedby a preliminary research work genotyping of the half-sib groupsobtained from the superfine Merino flock.

Theprocess of identifying the specific genes that determine the specifictraits of the wool is quite time-consuming, difficult, and expensive.For example, there is an antagonistic relationship between the twosignificant traits, including the mean fiber diameter (MFD) and theclean fleece weight (CFW). It is difficult to achieve a simultaneousenhancement of the two traits. The locus that is involved in theinitiation of follicle can influence the diameter and the density ofthe fiber, but has a limited impact on the weight of the wool. Theloci that affect the voluntary feel intake can influence the weightof clean wool as well as the fiber diameter. However, it has littleeffect on the density of the follicle. A positive and a highcorrelation exist between the length and the diameter of the fiber isunfavorable during the process of selecting the superfine fiber. Inaddition, different breeding objectives are necessary since there isa huge variation in the diameter of the fiber and different agegroups. The process of animal breeding selection needs to beprogrammed efficiently in order to estimate the properties of thewool appropriately [10, 11].