Skin/leather quality of indigenous and crossbred (Dorper x Indigenous) F1 sheep

Tsegay Teklebrhan, Mengistu Urge and Yoseph Mekasha

Haramaya University, School of Animal and Range Sciences, P.O Box 138, Dire Dawa, Ethiopia
Website: www.haramaya.edu.et
ttmamy06@gmail.com

Abstract

An experiment was conducted to evaluate skin/leather quality of local (Blackhead Ogaden (BO) and Hararghe highland (HH)) and cross breed (Dorper x Blackhead Ogaden (DBO) and Dorper x Hararghe highland (DHH)) F1 lambs at two levels of concentrate supplement. The two diets were native grass hay ad libtum +150 g concentrate mix (D1, Wheat Bran (WB) and noug seed cake (NSC, at a ratio of 2:1) and native grass hay ad libtum + 350 g concentrate mix (D2) in stall feeding. Water and salt lick were available to the animals all the time. Twelve each crossbred (DBO and DHH) and pure (BO and HH) lamb breeds aged 6-8 month at the start of the experiment were used. The experiment employed a completely randomized design in a factorial arrangement (four breeds and two levels of diet). Six lambs per breed were randomly assigned to each diet. After 90 days of feeding, three lambs per--treatment were randomly taken and slaughtered for skin/leather quality study.

Chemical quality of skin/leather, fat and chrome oxide content was not affected by breed as well as diet level. Physico-mechanical quality of skin/leather tensile strength, percentage elongation at break, tear load, distension and strength of grain was similar between pure indigenous and cross breeds. But, skin thickness was significantly higher for D2 groups compared to D1. All lamb breeds produced leathers with quality parameters acceptable for industrial processing. In conclusion the result of the present experiment suggests that crossing of Dorper with black head ogaden and Hararghe highland sheep did not adversely affected skin/leather quality.

Key words: chemical, indigenous and crossbred sheep, physico-mechanical quality of skin and leather

Introduction

Despite the huge number, nearly 25.9 million (CSA 2010), and genetically diverse sheep population in Ethiopia (DAGRIS 2006), off-take is very low and estimated to be 33% (EPA 2002). In addition, the on-farm productivity of local sheep in smallholder production systems is low, because the local sheep breeds grow slowly and reach sexual maturity at old ages and produce smaller carcasses (Tembley 1998). Moreover, data on the carcass weight of various breeds of indigenous sheep is low (10 kg/sheep; FAO 1996). However, the skins of the majority of the indigenous breed have international reputation for their unique natural substance of fineness, flexibility, strength, and compactness of texture (Asfaw 2002). They are suitable for production of high quality dress gloves, sport gloves and garments. For example, products known as Bati genuine and Bati type sheep skins of Ethiopia are characterized by thick, highly flexible and clean inner surfaces and are in high demand for production of suede fashions (Asfaw 2002).

The Ethiopian sheep and Goat Productivity Improvement Program (ESGPIP) launched cross breeding program of indigenous sheep with Dorper with the aim of improving growth performance and carcass quality to meet the standard for export market. Male Dorper sheep breed imported from South Africa is crossed with different indigenous breeds of ewes; among which Black head ogaden and Hararghea highland indigenous breeds form the ewe line. However, introduction of exotic blood may influence leather characteristics. For example, the introduction of wool breeds into a hair breed population adversely affected the physico- mechanical characteristics of skin (Jacinto et al 2004).

Former research findings revealed that Dorper skin is used for the production of glove, and is highly regarded for processing into clothing leather (Terblanche 1979). Comparison of 10 South African woolen sheep breeds leather properties with Dorper also revealed that Dorper leather is superior, but similar with skins of the different indigenous hair sheep breeds (Snyman et al 1998). The leather quality of hair sheep skins is, however, poorly documented. Thus suggest the importance of investigating the impacts of new blood introduction in to indigenous flock on skin/leather quality of the new breed, i.e. the cross breeds obtained from Dorper versus indigenous sheep breeds. The present experiment was therefore, conducted to examine chemical and physico-mechanical skin/leather quality of crossbred lambs vis-a-vise indigenous breed.

Material and methods

Experimental Design

The experiment was conducted at Haramaya University Sheep Farm. A total of 48 ram lambs, 12 from each crossbred lambs (Dorper x Blackhead Ogaden and Dorper x Hararghe Highland) aged 6-8 month and 12 from each indigenous breed (Blackhead Ogaden and Hararghe Highland) were used for the study. The crossbred lambs were obtained from Haramaya University-ESGPIP sheep breeding, distribution and evaluation center. The local lambs were purchased from local markets.The age of indigenous lambs were estimated to be between 6 and 8 months of age.  Purchased lambs were quarantined for two weeks in isolated house for observation of some known parasites and diseases abnormalities. The experimental animals were de-wormed with a broad-spectrum anti-helmentic (albendazole) against internal parasites, and prayed with acaricides (vetacidin 20% EC) against external parasites and vaccinated for pasteurelosis and anthrax when they were in the isolated house. Grass hay harvested from Haramaya University campus was used as source of roughage. The concentrate diets were wheat bran and noug seed cake mixed in 2:1 ratio, respectively, on dry matter basis. Water and salt lick were available to the animals all the time. The experiment design used was a completely randomized block design in a factorial arrangement (four breeds and two levels of diet). The lambs were housed and fed in individual pens with a dimension of 70 x 120 cm that is equipped with feeding trough and watering bucket. After three month of growth trial, lambs were slaughtered for skin/leather quality parameter studies.

Skin handling and Processing for Chemical and Physico- mechanical skin/ leather quality

After completion of the feeding experiment three lambs per treatment were slaughtered, skin was flayed in a very careful manner. Since the skin could not be shipped to the tannery within  four hours as per the recommendation, because of practical reasons and distance, wet salting method was used to preserve skin and prevent putrefaction and quality deterioration until it was transported to the Ethiopian Leather and Leather Products Technology Institute (LLPTI) for further processing. During wet salting, the procedure used was in accordance to Ethiopian standards authority. Before spreading the salt, skins were cleaned according to ESA code-B.J6.003 (1990). The amount of salt used was 50% of the mass of a fresh skin. Skins from all breeds were cured under the same conditions (wet salted) and tanned in the same manner (chrome tanned) so that differences between the varying groups is due to variations in breed, diet and properties of the raw materials.  Skins were processed into sheep garment using Leather and Leather products Technology Institute (LLPTI) recipe prepared for sheep skin according to the following main steps: Soaking, liming, deliming, bating, degreasing, pickling, tanning, neutralization, re-tanning, dying, sammying, drying and finishing. The leather quality of lambs was then assessed for chemical and physico-mechanical characteristics. The finished lamb garment leathers were taken to LLPTI physical laboratory and conditioned at 20±2 ^oC under 65% ±5 relative humidity for 48 h prior to physico-mechanical testing according to the guidelines of LLPTI. Triplicate samples were taken from each skin parallel (horizontal) or perpendicular (vertical) to the backbone prior to physico-mechanical testing and sampling site were determined in accordance to IUP 2 (2000) or ISO-2418 (2002).

Chemical quality of skin/leather

Fat content

The fat content of the moisture free samples were determined using standard Soxhlet extraction method (IUC4 1998). The fat content was extracted from the samples by using the solvent dichloromethane. The process was allowed until the fat is completely extracted, at least for 5 hours. After the solvent was distilled from the flask, the extracted materials were dried at 102±2 ^oC to constant weight. Samples were re-dried if the reduction in weight was more than 0.1% of its original weight. The total drying time was not allowed to exceed eight hours. The formula for determination of fat and other soluble substances by dichloromethane is as follows:

Chrome-oxide content

The chrome-oxide content (Cr₂O₃) of the leather was determined from the leather ash, by oxidizing the leather ash followed by iodometric titration of hexavalent chromium ions (IUC 8 1998).

Physico-mechanical skin/ leather quality

Tensile strength and percentage elongation

Tensile strength and percentage elongation were determined using test method of International Organization for Standardization, ISO-3376 (2002). Sampling method and sampling location were according to ISO-2418 (2005) and ISO-2418 (2002), respectively. The formula used is:

Tear load

Average tear load/arithmetic mean and tear resistance was determined using test method of International Organization for Standardization (ISO-3377 2002) and (ISO-3376 2000), respectively. Samples were conditioned according to ISO-2419 (2002). Sampling method and sampling location were according to ISO-2418 (2005) and ISO-2418 (2002), respectively. Thickness of samples was in accordance with ISO-2589 (2002).

Distension, strength of grain and thickness of lamb skin

Distension and strength of grain were determined by the ball burst test using a lastometer.  The test method used was as described by International Organization for Standardization (ISO-3379 2005) or (IUP-40). Circular samples were taken for the tests, and sampling method and sampling location were according to ISO-2418 (2005) and ISO-2418 (2002), respectively. Thickness of lamb skins were measured using a standard type measuring gauge.

Shrinkage temperature

Samples for shrinkage temperature were taken from individual animals and pooled per breed for laboratory analysis. Shrinkage temperature of leather was determined using test method (IUP-16 or ISO-3380 (2002). Thickness of sample was determined in accordance with ISO-2589 (2002).

 Chemical analysis of feeds

Samples of feeds were dried overnight at 105 ^oC in a forced draft oven for determination of DM. Ash was determined by ashing samples at 550 ^oC for 6 hours. Nitrogen was analyzed by Kjeldahl method (AOAC 1990) and CP was determined as N x 6.25. NDF, ADF and ADL were analyzed using the procedures of Van Soest and Robertson (1985).

 Statistical analysis

Data were analyzed using SAS (2002). No significant breed by diet class interaction was noted for skin/leather quality. Mean differences were tested using Tukey.

The model used was:

Yijk= μ + bi + dj + (bd) ij + eijk      

                                          Where:            Yijk= Response variable

                                                                  μ= mean of the population

                                                                  bi = breed effect

                                                                  dj=diet effect

                                                                 (bd)ij= interaction between breed and diet,

                                                                 eijk= is random error component

Results and Discussion

Chemical composition of experimental feeds

The chemical compositions of the feedstuffs used in this study are shown in Table 1. The CP content of wheat bran was comparable with that reported earlier (Ensminger 2002; McDonald et al 2002; Ameha 2007). The CP content of noug seed cake is comparable to that reported by Ameha (2007). The low CP and high NDF of native grass might render it to be categorized as low quality feed (Cheeke 1999). Nonetheless, the CP content of native grass hay is enough for the maintenance and rumen microbial function, which is within the range of 7-7.5 CP (Van Soest 1994).

Chemical quality of leather

Fat and chrome-oxide content of leather

The natural fat content of pelt lamb skin in the present experiment after degreasing (reducing the natural fat content) ranged from 0.13-0.38% (Table 2) and it is not significantly different (P>0.05) among lamb breeds as well as diet level. In the tannery, low fat content of skin after degreasing, like the present ones, is an indication of better quality leather (Sarkar 1991). Blackhead Ogaden has numerically higher natural fat in the skin than the other lamb breeds. Similarly, lambs supplemented with higher level of concentrate had numerically more fat content than low level of concentrate. The current finding is in accordance with that reported by Stosic (1994) who noted that fat contents of goats fed low level of concentrate consists numerically lower skin fat than the corresponding high level groups.

Similar to the natural fat content characteristics of lamb skin, the chrome-oxide (Cr₂O₃) content of crust leather was not significantly affected (P>0.05) by lamb breed as well as diet level (Table 2). Lambs supplemented with low level of concentrate have numerically higher chrome-oxide content than higher level of concentrate groups. This is supported by Stosic (1994) who observed that  low level concentrate fed goats have significantly higher chrome levels than the high level of concentrate fed group.  In the present study, similar (P>0.05) absorption capacity of all lamb breed skins during processing with chrome tanning was recorded.  The result also showed that chrome level was above (3.5 %) the minimum requirement (BASF 1984) for garment leather.

Physico-mechanical quality of skin/leather 

Physico-mechanical quality of leather is shown in Table 3.  Leathers are expected to have strength and flexibility depending on the field of use (Bitilisli et al 2004). In the present study, significant difference in physico-mechanical properties among lamb breeds was not detected. However, the pure native lamb leathers had numerically higher tensile strength and percentage elongation at break than the crossbred lambs. This is evidence that leather produced from local breeds is stronger and could be extended more before the grain cracks than cross bred leathers. Similar to the present study, Oliveira et al (2007) reported numerically higher values of tensile strength (29.42-N/mm²) for the native sheep genotype (Santa Inˆes) compared to crossbreed (Santa Inˆes x dorper).

Indigenous Blackhead Ogaden lamb produced leather with numerically better tensile strength than indigenous Haraghe highland. However, elasticity (percentage elongation) was numerically higher in indigenous Hararghe Highland compared to indigenous Blackhead Ogaden breed. Dorper x Blackhead Ogaden lambs had numerically higher tensile strength and percentage elongation than Dorper x Hararghe highland.

According to previous research conducted on South African sheep breeds, Damera sheep (wool type) produced leather with higher tensile strength (22.56 Mpa) and Merino (mutton type) produced least tensile strength value, which is 11.86 Mpa. The same research indicated that hair type Dorper produced leather that have significantly higher (P<0.05) tensile strength (18.72 Mpa) than wool type Dorper (14.48) (Snyman et al 2000). Dorper x indigenous lamb breeds in the present study have tensile strength that is comparable to the indigenous hair type Dorper, but higher than pure wool type Dorper. Generally, all lamb breeds produced leather that has quality required by the leather industry (BASF 1984). According to BASF (1984), the   minimum tensile strength for lamb garment should be 12 N/mm² and the acceptable range for percentage elongation is 40–80%. The result for both parameters is within the recommended values for all sheep breeds used in our study. Diet has no significant effect (P>0.05) on tensile strength and percentage elongation. However, high level of concentrate supplementation resulted in numerically better tensile strength and percentage elongation of lamb skin. This may indicate that higher supplementation would improve the physical test of the leather than lower supplementation.

Sampling direction did not affect (P>0.05) tensile strength and percentage elongation. The present result showed that horizontal/parallel sampling direction has numerically better tensile strength than vertical/perpendicular sampling direction to the back bone and the reverse for percentage elongation at break. Contrary to the present result, Stosic (1994) and Oliveira et al (2007) reported that sampling direction significantly affected (P<0.05) tensile strength and percentage elongation. These findings support a previous finding by Craig et al (1987), who noted that higher tensile strength was attributed to the arrangement of leather fibers when horizontal sampling direction was used.

Tear load results are shown in Table 3. Arithmetic mean force (N) and tear strength (N/mm²) values were not significantly affected (P > 0.05) by breeds of lambs. Indigenous Blackhead Ogaden has, however, numerically higher mean force (N) and tear strength (N/mm) than Dorper x Hararghe Highland. Similarly, Dorper x Blackhead Ogaden require numerically higher force to tear the leather than indigenous Hararghe Highland lamb. This indicates that pure Blackhead Ogaden and Dorper x Blackhead Ogaden resist more force. Previous research conducted on Brazilian indigenous x Dorper sheep genotype showed numerically higher progressive tear strength for the genotype Santa Inˆes (indigenous Brazilian sheep) than respective cross (Oliveira et al 2007). Oliveira et al (2007) also observed higher progressive tear strength of goat leather than sheep.

Mean force (N) and tear strength (N/mm) values were not significantly affected (P >0.05) by diet (Table 3). Lambs fed D2 require numerically better mean force (N) and tear strength (N/mm) to tear leather than lambs fed D1. Means force (N) was not significantly affected (P>0.05) by sampling direction. Vertical sampling direction requires numerically higher (P >0.05) force to tear when compared to the horizontally sampled skin. This result is not in agreement to Oliveira et al (2007) who reported that vertically sampled direction has significantly (P <0.05) higher values for both strength and load compared to the horizontal direction of sampling. This result might be explained by the arrangement of the leather fibres (Craig et al 1987; Oliveira et al 2007), similar to that of tensile strength.

The strength and distension at grain crack and break of a leather act as a guide as to how the material will perform when a multi-directional stress is applied. Grain crack is primarily considered as a measure of the strength of the grain layer within the tested material. Generally, these variables are more important in shoe upper leather, although optionally used in garment leather as physical quality parameter. Distension and strength of grain were not significantly affected (P>0.05) by breeds of lamb. However, indigenous Ethiopian sheep had numerically better distension and strength of grain than cross breeds. Comparison between crosses revealed that Dorper x Blackhead Ogaden has better distention than Dorper x Hararghe Highland. The result showed that the distension and strength of grain were above the minimum requirement of leather quality in shoe upper leather, which is 7mm (BASF 1984).

Distension and strength of grain were not significantly affected (P>0.05) by diet. The result also showed that the distension and strength of grain of both diets were above the minimum requirement of leather quality (BASF 1984). However, lambs supplemented with higher level of concentrate have numerically higher distension and strength of grain as compared to low level (Table 3). This is because, nutritionally restricted lambs tended to produce lighter and thinner skins with a thinner grain layer. This is in agreement with Stosic (1994) who reported that leathers made from the skins of animals kept on the high nutritional regime tended to resist higher loads at grain crack and burst and has smaller distensions than leathers from animals in the low nutritional groups. Despite numerical differences in physico-mechanical test among lamb breeds, the results of skin/leather quality parameters of all lamb breeds were above the minimum standard values for quality leather established by the Institute for Assays and Research on Footwear Production (PFI Institute, Pirmasens, Germany, BASF 1984).

Thickness of the leather is shown in Table 3. As it is observed, thickness of skin was not affected by the lamb breed. Previously, high degrees of homogeneity in thickness among different genotypes were obtained (Oliveira et al 2007). Generally, local lamb skin had numerically higher thickness than the cross. This is because local lambs have numerically higher tensile strength and elongation at break test. However, Craig et al (1987) and Jacinto et al (2005) found   poor correlation values that indicate no relationship between the thickness of the leather and the tensile strength and percentage elongation. No significant difference was observed between the local breeds, but pure Blackhead Ogaden lamb had numerically better thickness. This is due to the fact that sheep reared in highland areas had longer hairs, and the leather produced from such animals will be of poor substance/thickness and coarser grain (Kassa 1998). Nonetheless, both crosses have uniform thickness.

There was significant difference (P<0.05) in thickness of leather observed between diet levels (Table 3). Accordingly, lambs supplemented with higher level of concentrate had higher thickness than low level. This might be due to the high level of concentrate supplementation which attributes to better thickness. 

Shrinkage temperature

Shrinkage temperature is considered to be one of the physical quality requirements for leather industry. Shrinkage temperature of leathers may differ depending on the type and amount of tanning and retaining agent used in processing (Bitilisli et al 2004). In the present study, similar tanning and retaining agents were used during processing of lamb skin to avoid variability due to differences in the agents. Leather produced from the lambs in the present study had similar shrinkage temperature. Generally, the shrinkage temperature obtained in the study was above the minimum requirement reported for chrome tanned leather. It is indicated that leather processed using chrome has shrinkage temperature above 100 ^oC. According to the present result, lamb skins of all breeds were not shrunk or changed in length from the original length of the samples until the temperature reached >100 ^oC. Hence, the present result confirmed that the shrinkage temperature for all breeds were above 100 ^oC, which is the recommended value for chrome tanned leather.

Conclusion and Recommendations

• The present study indicated that all lamb genotypes studied produced leathers with chemical and physico-mechanical characteristics compatible with the quality standards required by the leather industry,
  
  
•  The native lamb breeds tended to produce slightly higher quality leather than the cross breeds.
  
  
• Overall assessment of the present result leads to the conclusion that crossing the current indigenous breeds with hair type Dorper did not result in a significant loss in leather quality.

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Received 17 October 2011; Accepted 24 January 2012; Published 2 April 2012

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