&#946;-Lactoglobulin Gene Polymorphisms in Sheep and Effects on Milk Production Traits: A Review

Maria Selvaggi; Vito Laudadio; Cataldo Dario; Vincenzo Tufarelli

doi:10.14737/journal.aavs/2015/3.9.478.484

Article · Volume 3, Issue 9, Pages 478–484, 30 July 2015 · Open Access

β-Lactoglobulin Gene Polymorphisms in Sheep and Effects on Milk Production Traits: A Review

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Journal:: Advances in Animal and Veterinary Sciences
DOI:: 10.14737/journal.aavs/2015/3.9.478.484
Published:: 30 July 2015

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It is noteworthy that the available literature provides no conclusive remarks about the effects of different β-lactoglobulin genotypes on milk production traits and coagulation properties in ovine species.
Moreover, the conflicting reports on the association of genetic variants of BLG with milk production traits may be due to the lack of knowledge of the relatedness of the studied animals.
Despite these controversial results, to include molecular genetic markers in selection to improve livestock productive performance is also a target in sheep breeding to enhance the economy of dairy sheep production worldwide.

Selected from the article's own text.

Abstract

Maria Selvaggi, Vito Laudadio, Cataldo Dario*, Vincenzo Tufarelli

Department DETO – Section of Veterinary Science and Animal Production, University of Bari ‘Aldo Moro’, 70010 Valenzano (BA) Italy.

*Correspondence | Cataldo Dario, University of Bari ‘Aldo Moro’, Valenzano, Italy; Email: cataldo.dario@uniba.it

Abstract
β-lactoglobulin is the main whey protein of milk from different species. To date, β-lactoglobulin gene (BLG) is one of the most investigated in ruminants including sheep. β-lactoglobulin was the first protein, in which polymorphism was found. Polymorphisms of BLG gene have been detected in several sheep breeds, but studies on the effects of BLG genetic variants on milk production traits and cheese making ability have given conflicting results. Therefore, this paper represents a detailed and updated review on β-lactoglobulin gene polymorphisms in many sheep breeds worldwide. Moreover, the associations among BLGpolymorphisms and milk yield and composition as well as milk coagulation properties were reported to offer a complete overview on these topics.

Keywords | Sheep, β-lactoglobulin, Gene polymorphisms, Milk production, Milk coagulation

Citation | Selvaggi M, Laudadio V, Dario C, Tufarelli V (2015). β-lactoglobulin gene polymorphisms in sheep and effects on milk production traits: A review. Adv. Anim. Vet. Sci. 3(9): 478-484.

ISSN (Online) | 2307-8316; ISSN (Print) | 2309-3331

Copyright © 2015 Selvaggi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Introduction

Milk and dairy products from small ruminant species represent a significant part of the agricultural economy worldwide especially in marginal areas. However, goat and sheep milks have peculiar composition and properties and, as a consequence, specific productive destinations . In fact, sheep milk is used mainly for cheese production ; . There is a strong association among milk protein polymorphisms and milk yield, composition and technological aspects. So, it is necessary to make available in-depth information regarding genetic polymorphisms of milk proteins in ovine species also considering the great genetic biodiversity of sheep breeds.

β-lactoglobulin is the main whey protein of cow, sheep, goat and horse milk; it is lacking in milk from human, rodents, rabbits and camels in which, instead, another major whey protein (whey acidic protein) is found . The whey proteins showed a high nutritive value being a precious source of digestible proteins. Sheep milk whey proteins account for 17–22% of total proteins. Whey obtained from sheep milk is particularly rich in proteins with a high β-lactoglobulin and low α-lactalbumin content . β-lactoglobulin is a globular protein member of the lipocalin family, small proteins with many properties, such as the ability to bind small hydrophobic molecules. Although its biological function is still unclear, β-lactoglobulin provides amino acids to the offspring and a possible role in the transport of retinol and fatty acids has been suggested . β-lactoglobulin was the first protein in which polymorphism was found; it consists of 162 amino acids and forms stable dimers in milk having a molecular weight of 18 kDa per monomer .

Polymorphisms of BLG gene

β-lactoglobulin is encoded by the BLG gene that has been mapped on chromosome 3 in sheep . This gene is expressed in the mammary gland in a tissue-specific manner during pregnancy and lactation . β-lactoglobulin gene is highly polymorphic in ruminants: in cattle, 12 polymorphic variants of this protein are known, with variants A and B being the most frequent and commonly related to differences in milk protein yield and quality ; . In sheep, β-lactoglobulin polymorphism was widely investigated in many breeds worldwide. Three co-dominant alleles (A, B and C) have been reported in this species differing by one or more amino acid changes. The genetic variant A differs from variant B in the amino acid sequence at position 20 (Tyr→His) ; ; . Later, Erhardt (1989) found a new and rare variant indicated as C that is a subtype of variant A with a single amino acid exchange at position 148 (Arg→Gln). Variants A and B are the most common and have been detected in many breeds (see Table 1, 2 and 3). The rare variant C was detected only in few breeds such as: Merinoland, Lacha, Carranzana, Spanish Merino, Serra da Estrela, White Merino, and Black Merino ; ; ; . Erhardt (1989) suggested that the allele C perhaps originated from the Spanish Merinos considering that both Merinoland and Hungarian Merino, in which the allele C was detected, contain blood from Spanish Merinos. This hypothesis may be strengthened by the allele C detection in Black Merino and White Merino . As reported in Table 1, four sheep breeds from Saudi Arabia were found monomorphic: in particular, in Noami and Sawakni breeds only the allele A was found; whereas Nagdi and Harry breeds were genotyped as BB . Moreover, most of sheep breeds from India showed a prevalence of B allele; as a consequence, Arora et al. (2010) suggested that the B allele could possibly be considered the ancestral variant of BLG in Indian sheep. In fact, in many breeds from India, the frequency of allele B was higher than that reported in breeds from Southwest Asia, Eastern and Central Europe and Mediterranean countries (Table 1 and 2). In addition, only few investigations on BLG polymorphisms were carried out in countries other than Europe and Asia; sheep breeds from Africa, America and Oceania showed a frequency of A allele ranging from 0.704-0.950, and no evidence of C allele was found (Table 3).

Table 1: Summary of published allelic frequencies of β-lactoglobulin gene in different sheep breeds with different purpose from Asia

Breed	Purpose	A	B	C	References
Nagdi	Meat	-	1.000	-
Harry	Meat	-	1.000	-
Muzzafarnagri	Meat, Carpet wool	0.100	0.900	-
Zel	Meat	0.140	0.860	-
Jalauni	Meat, Carpet wool	0.160	0.840	-
Magra	Carpet wool	0.193	0.807	-
Rampur Bushair	Carpet wool	0.273	0.727	-
Mandya	Meat	0.273	0.727	-
Garole	Meat	0.277	0.723	-
Ganjam	Meat, Carpet wool	0.326	0.674	-
Afshari	Meat	0.340	0.660	-
Awassi	Dairy	0.348	0.352	-
Moghani	Meat	0.360	0.640	-
Changthangi	Carpet wool	0.386	0.614	-
Patanwadi	Carpet wool	0.410	0.590	-
Jaisalmeri	Carpet wool	0.425	0.575	-
Kheri	Meat, carpet wool	0.472	0.528	-
Arkharmerino	Fine wool	0.480	0.520	-
Kendrapada	Meat	0.480	0.520	-
Sonadi	Meat, carpet wool	0.499	0.501	-
Dekkani	Meat, coarse wool	0.500	0.500	-
Madgyal	Meat	0.500	0.500	-
Kurdi	Meat	0.510	0.490	-
Malpura	Wool	0.510	0.490	-
Makoei	Meat, Carpet wool	0.530	0.470	-
Chhotanagpuri	Carpet wool	0.531	0.469	-
Ghezel	Meat, Carpet wool	0.560	0.440	-
Morkaraman	Meat, Carpet wool	0.560	0.440	-
Marwari	Carpet wool	0.562	0.438	-
Chokla	Carpet wool	0.569	0.431	-
Awassi	Dairy	0.630	0.370	-
Nali	Carpet wool	0.630	0.370	-
Karakul	Pelt, wool, meat	0.714	0.286	-
Gökçeada	Dairy, meat, wool	0.763	0.237	-	Elmaci et al., 2006
Kivircik	Meat, wool, dairy	0.776	0.224	-	Elmaci et al., 2006
Dumba	Carpet wool	0.950	0.050	-
Sakiz	Dairy, wool, meat	0.976	0.024	-	Elmaci et al., 2006
Noami	Meat	1.000	-	-
Sawakni	Meat	1.000	-	-

Sheep breeds in which the associations among polymorphism and milk traits where investigated are highlighted in bold

Table 2: Summary of published allelic frequencies of β-lactoglobulin gene in different sheep breeds with different purpose from Europe

Breed	Purpose	A	B	C	References
Sarda	Dairy	0.274	0.726	-
Churra	Dairy	0.310	0.690	-
Rhön	Meat	0.324	0.676	-
Carranzana	Dairy	0.350	0.640	0.010
Valle del Belice	Dairy	0.350	0.650	-
Valachian	Dairy, wool, meat	0.353	0.647	-
Black Merino	Fine wool	0.392	0.607	0.001
Romanian Rusty Tsigai	Dairy, wool, meat	0.420	0.580	-
Romanov	Meat, wool	0.430	0.570	-
Gyimesi Racka	Dairy, wool, meat	0.460	0.540	-
White Merino	Fine wool	0.464	0.535	0.001
Lacha	Dairy	0.470	0.530	-
Bosnian Pramenka	Dairy	0.470	0.530	-
Lacaune	Dairy	0.473	0.527	-
Polish Merino	Fine wool	0.480	0.520	-	Kaweka and Radko, 2011
Polish Merino	Fine wool	0.498	0.502	-
Polish Mountain	Carpet wool, dairy	0.500	0.500	-	Kaweka and Radko, 2011
Lacha	Dairy	0.500	0.490	0.010
Comisana	Dairy	0.500	0.500	-
Hungarian Tsigai	Dairy	0.510	0.490	-
Lithuanian Blackface	Meat, wool	0.520	0.480	-
Massese	Dairy	0.520	0.480	-
Pleven	Dairy	0.528	0.472	-
Slovakian Tsigai	Dairy, wool, meat	0.540	0.460	-
Bergschaf	Meat, coarse wool	0.550	0.450	-	Kaweka and Radko, 2011
Serbian Cokanski Tsigai	Dairy, wool, meat	0.550	0.450	-
Merinoland	Fine wool	0.579	0.246	0.175
Spanish Merino	Fine wool	0.580	0.410	0.010
Croatian Tsigai	Dairy, wool, meat	0.580	0.420	-
Manchega	Dairy	0.610	0.390	-
Gentile di Puglia	Wool, meat	0.613	0.387	-
Serra da Estrela	Dairy	0.620	0.378	0.002
Altamurana	Dairy	0.625	0.375	-
Lacaune	Dairy	0.630	0.370	-
Leccese	Dairy	0.630	0.370	-
Racka	Dairy, wool, meat	0.640	0.360	-
Friesian	Dairy	0.660	0.340	-	Kaweka and Radko, 2011
Bulgarian Tsigai	Dairy, wool, meat	0.680	0.320	-
Merino	Fine wool	0.684	0.316	-
Lithuanian Native Coarsewooled	Meat, wool	0.690	0.310	-
East Friesian	Dairy	0.690	0.310	-

Sheep breeds in which the associations among polymorphism and milk traits where investigated are highlighted in bold

Relationship between genetic variants of BLG gene and milk production traits

Polymorphisms of BLG gene may be helpful as informative molecular markers for milk yield and composition as well as for rheological properties of milk. However, the influence of BLG polymorphism on milk yield and composition and cheese-making properties is controversial, indicating superiority of either the A or B allele or no relationship with quantitative traits.

In Valle del Belice ewes, the AA genotype was associated with greater milk production . A similar result was found in Sarda breed; in this case, animals carrying AA and AB genotypes had higher milk yield than BB ewes , 2003). In East Friesian sheep, it was observed a higher milk yield during the first lactation in individuals carrying AA genotype; whereas BB genotype ewes had the highest milk yield in the following lactations . In Portuguese dairy sheep studied by Ramos et al. (2009), homozygous AA ewes presented lower values of milk yield and no differences between AB and BB genotypes were found. No differences in terms of milk production among genotypes were found in Sarda , East Friesian , Polish Mountain, Polish Merino, East Friesian, and Bergschaf (Kaweka and Radko, 2011) and in West African sheep . Some investigations assessed the superiority of the B allele ; . Later, this result was confirmed by Corral et al. (2010) in Merino sheep breed.

As for milk quality, recently Corral et al. (2010) demonstrated that Merino ewes genotyped as AA were those that produced the highest fat and protein percentages. Moreover, heterozygous Serra da Estrela animals presented higher milk fat content than those carrying genotype BB. Besides, AA Merino ewes had higher milk protein content than animals with genotype AB . A positive association was found between AB genotype and fat and lactose percentages in milk from Iranian indigenous Zel sheep breed . Previous findings by Dario et al. (2005, 2008) in Altamurana and Leccese breeds reported a superiority of AA and AB genotypes for fat and whey protein percentages in milk. Martínez et al. (1993) pointed out a highly significant and positive effect of AA and AB genotypes on milk protein and casein contents in Manchega sheep. On the other hand, Giaccone et al. (2000) reported a positive effect of BB genotype on milk protein and fat contents, and Mroczkowski et al. (2004) found a positive relationship between BB genotype and milk protein content in comparison with both AA and AB genotypes in Polish Merino. No association among milk composition traits and BLG genotypes was found in Polish Mountain, Polish Merino, East Friesian, Bergschaf (Kaweka and Radko, 2011), Massese , Sarda , 2003), Merino , and Churra . As reported by Rampilli et al. (1997) in Massese breed, the BB variant of BLG could be related to a higher milk production with

Table 3: Summary of published allelic frequencies of β-lactoglobulin gene in different sheep breeds with different purpose from other countries

	Breed	Purpose	A	B	C	References
Africa	Barki	Carpet wool, meat	0.704	0.296	-
	Ossimi	Carpet wool, meat	0.828	0.172	-
	Rahmani	Carpet wool, meat	0.950	0.050	-
America	West African	Meat	0.900	0.100	-
Oceania	Border Leicester×Merino	Meat, wool	0.750	0.250	-
Oceania	Hyfer	Meat, wool	0.840	0.160	-

Sheep breeds in which the associations among polymorphism and milk traits where investigated are highlighted in bold

lower casein content and greater overall amount of whey proteins. At the same time, the AA and AB genotypes showed higher β-lactoglobulin and total casein contents and were related to a better quality of milk also in terms of rennetability. To date, only one investigation reported the relationship between BLG genotypes and milk fatty acid composition in sheep; in particular, milk from AB individuals had the lowest concentration of medium-chain fatty acids and the highest level of trans fatty acids, monounsaturated fatty acids and long-chain fatty acids, with no significant differences regarding the polyunsaturated fatty acids level .

Many investigations have shown a superiority of milk from AA ewes for cheese processing thanks to its shorter clotting time, a better rate of curd firming and a favourable cheese yield (Lopez Galvez et al., 1993; 1994; 1998; ; Gutierrèz-Gil et al., 2001). In addition, Garzón et al. (1993) reported a superiority of AA and AB genotypes, in comparison to BB homozygotes, in terms of curdling time, medium and maximum firmness, rate of firming, and curd yield in Manchega breed. These results conflict with data reported by Pilla et al. (1995) who found that the B allele positively affected the rennet coagulation properties of milk. No association between BLG polymorphism and milk renneting properties (clotting time, curd firming time and curd firmness) was found by Recio et al. (1997) in Merino ewes and by Nudda et al. (2000) in Sarda breed. More recently, Çelik and Özdemir (2006) investigated the association between BLG genetic variants and rennet clotting time in milk belonging to Awassi and Morkaraman breeds without statistical significant differences.

Conclusions

It is noteworthy that the available literature provides no conclusive remarks about the effects of different β-lactoglobulin genotypes on milk production traits and coagulation properties in ovine species. Sometimes, results from different investigations are not comparable with each other for many reasons: population size, breed, frequency of the considered genotypes, statistical models used for data analysis. Moreover, the conflicting reports on the association of genetic variants of BLG with milk production traits may be due to the lack of knowledge of the relatedness of the studied animals. Despite these controversial results, to include molecular genetic markers in selection to improve livestock productive performance is also a target in sheep breeding to enhance the economy of dairy sheep production worldwide. To improve the local farms productivity in developing countries and in marginal areas of developed countries is a strategy to limit the off-farm migration and safeguard the current wide animal biodiversity. However, the fact remains that to sustain the economy of rural and marginal areas is also a crucial target in developed countries.

Conflict of Interest

The authors declare no competing interests.

Authors contribution

All authors contributed equally to the manuscript.

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Nudda A, Feligini M, Battacone G, Campus RL, Pulina G (2000). Effects of β-lactoglobulin genotypes and parity on milk production and coagulation properties in Sarda dairy ewes. Zoot. Nutr. Anim. 26(3): 137-143.
Nudda A, Feligini M, Battacone G, Macciotta NPP, Pulina G (2003). Effects of lactation stage, parity, beta-lactoglobulin genotype and milk SCC on whey protein composition in Sarda dairy ewes. Ital. J. Anim. Sci. 2: 29-39. http://dx.doi.org/10.4081/ijas.2003.29[CrossRef]
Othman OE, El Fiky SA, Hassan NA, Mahfouz ER, Balabel EA (2012). Genetic polymorphism of whey protein genes β-LG and α-LA in three Egyptian sheep breeds. J. Appl. Biol. Sci. 6(3): 25-30.
Perez MD, Calvo M (1995). Interaction of β-lactoglobulin with retinol and fatty acids and its role as a possible biological function for this protein: a review. J. Dairy Sci. 78: 978–988. http://dx.doi.org/10.3168/jds.S0022-0302(95)76713-3[CrossRef]
Pietrolà E, Carta A, Fraghì A, Piredda G, Pilla F (2000). Effect of β-lactoglobulin locus on milk yield in Sarda ewes. Zoot. Nutr. Anim. 26: 129–133.
Pilla F, Dell’Aquila S, Taibi L, Tripaldi C, Puppo S, Napolitano F, Pallotta ML, Angelucci M, Girolami A (1995). Influenza del polimorfismo genetico della β-lattoglobulina su alcune caratteristiche fisico-chimiche e tecnologiche del latte di pecora. In: Proc. XI Congress Associazione Scientifica Produzione Animale. Avenue Media Ed, Bologna, pp. 207–208.
Ramos A, Matos CAP, Russo-Almeida PA, Bettencourt CMV, Matos J, Martins A, Pinheiro C, Rangel-Figueiredo T (2009). Candidate genes for milk production traits in Portuguese dairy sheep. Small Rum. Res. 82: 117–121. http://dx.doi.org/10.1016/j.smallrumres.2009.02.007[CrossRef]
Rampilli M, Cecchi F, Giuliotti L, Cattaneo TMP (1997). The influence of β-lactoglobulin genetic polymorphism on protein distribution and coagulation properties in milk of Massese breed ewes, in Milk Protein Polymorphism. International Dairy Federation, Brussels, pp. 311–315.
Recio I, Fernandez-Fournier A, Martin-Alvarez PJ, Ramos M (1997). β-lactoglobulin polymorphism in ovine breeds: influence on cheesemaking properties and milk composition. Lait. 77(2): 259-265. http://dx.doi.org/10.1051/lait:1997218[CrossRef]
Sabour MP, Lin CY, Lee AJ, McAllister AJ (1996). Association between milk protein genetic variants and genetic values of Canadian Holstein bulls for milk yield traits. J. Dairy Sci. 79(6): 1050-1056. http://dx.doi.org/10.3168/jds.S0022-0302(96)76458-5[CrossRef]
Schmoll F, Herget I, Hatzipanagiotou A, Tholen E, Wimmers K, Brem G, Schellander K (1999). Associations of beta-lactoglobulin variants with milk production, milk composition and reproductive performance in milk sheep. Wien. Tierärztl. Monat. 86: 57–60.
Selvaggi M, Tufarelli V (2012). Caseins of goat and sheep milk: analytical and technological aspects. In: Casein: Production, Uses and Health Effects, ed. by Ventimiglia AM, Birkenhäger JM. Nova Science Publishers, New York, pp. 1–25.
Selvaggi M, Laudadio V, Dario C, Tufarelli V (2014a). Major proteins in goat milk: an updated overview on genetic variability. Mol. Biol. Rep. 41(2): 1035-1048. http://dx.doi.org/10.1007/s11033-013-2949-9[CrossRef]
Selvaggi M, Laudadio V, Dario C, Tufarelli V (2014b). Investigating the genetic polymorphism of sheep milk proteins: a useful tool for dairy production. J. Sci. Food Agri. 94(15): 3090-3099. http://dx.doi.org/10.1002/jsfa.6750[CrossRef]
Staiger EA, Thonney ML, Buchanan JW, Rogers ER, Oltenacu PA, Mateescu RG (2010). Effect of prolactin, β-lactoglobulin, and κ-casein genotype on milk yield in East Friesian sheep. J. Dairy Sci. 93(4): 1736-1742. http://dx.doi.org/10.3168/jds.2009-2630[CrossRef]
Thomas AS, Dawe ST, Walker RA (1989). Milk protein polymorphism in Hyfer and Border Leicester X Merino sheep. Milchwissenschaft. 44: 686-688.
Yang F, Li L, Liu H, Cai Y, Wang G (2012). Polymorphism in the exon 4 of β-lactoglobulin variant B precursor gene and its association with milk traits and protein structure in Chinese Holstein. Mol. Biol. Rep. 29: 3957–3964. http://dx.doi.org/10.1007/s11033-011-1175-6[CrossRef]
Yousefi S, Azari MA, Zerehdaran S, Samiee R, Khataminejhad R (2013). Effect of β-lactoglobulin and κ-casein genes polymorphism on milk composition in indigenous Zel sheep. Arch. Tierzucht. 56: 216-224.

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[43] Nudda A, Feligini M, Battacone G, Macciotta NPP, Pulina G (2003). Effects of lactation stage, parity, beta-lactoglobulin genotype and milk SCC on whey protein composition in Sarda dairy ewes. Ital. J. Anim. Sci. 2: 29-39. http://dx.doi.org/10.4081/ijas.2003.29[CrossRef]

[44] Othman OE, El Fiky SA, Hassan NA, Mahfouz ER, Balabel EA (2012). Genetic polymorphism of whey protein genes β-LG and α-LA in three Egyptian sheep breeds. J. Appl. Biol. Sci. 6(3): 25-30.

[45] Perez MD, Calvo M (1995). Interaction of β-lactoglobulin with retinol and fatty acids and its role as a possible biological function for this protein: a review. J. Dairy Sci. 78: 978–988. http://dx.doi.org/10.3168/jds.S0022-0302(95)76713-3[CrossRef]

[46] Pietrolà E, Carta A, Fraghì A, Piredda G, Pilla F (2000). Effect of β-lactoglobulin locus on milk yield in Sarda ewes. Zoot. Nutr. Anim. 26: 129–133.

[47] Pilla F, Dell’Aquila S, Taibi L, Tripaldi C, Puppo S, Napolitano F, Pallotta ML, Angelucci M, Girolami A (1995). Influenza del polimorfismo genetico della β-lattoglobulina su alcune caratteristiche fisico-chimiche e tecnologiche del latte di pecora. In: Proc. XI Congress Associazione Scientifica Produzione Animale. Avenue Media Ed, Bologna, pp. 207–208.

[48] Ramos A, Matos CAP, Russo-Almeida PA, Bettencourt CMV, Matos J, Martins A, Pinheiro C, Rangel-Figueiredo T (2009). Candidate genes for milk production traits in Portuguese dairy sheep. Small Rum. Res. 82: 117–121. http://dx.doi.org/10.1016/j.smallrumres.2009.02.007[CrossRef]

[49] Rampilli M, Cecchi F, Giuliotti L, Cattaneo TMP (1997). The influence of β-lactoglobulin genetic polymorphism on protein distribution and coagulation properties in milk of Massese breed ewes, in Milk Protein Polymorphism. International Dairy Federation, Brussels, pp. 311–315.

[50] Recio I, Fernandez-Fournier A, Martin-Alvarez PJ, Ramos M (1997). β-lactoglobulin polymorphism in ovine breeds: influence on cheesemaking properties and milk composition. Lait. 77(2): 259-265. http://dx.doi.org/10.1051/lait:1997218[CrossRef]

[51] Sabour MP, Lin CY, Lee AJ, McAllister AJ (1996). Association between milk protein genetic variants and genetic values of Canadian Holstein bulls for milk yield traits. J. Dairy Sci. 79(6): 1050-1056. http://dx.doi.org/10.3168/jds.S0022-0302(96)76458-5[CrossRef]

[52] Schmoll F, Herget I, Hatzipanagiotou A, Tholen E, Wimmers K, Brem G, Schellander K (1999). Associations of beta-lactoglobulin variants with milk production, milk composition and reproductive performance in milk sheep. Wien. Tierärztl. Monat. 86: 57–60.

[53] Selvaggi M, Tufarelli V (2012). Caseins of goat and sheep milk: analytical and technological aspects. In: Casein: Production, Uses and Health Effects, ed. by Ventimiglia AM, Birkenhäger JM. Nova Science Publishers, New York, pp. 1–25.

[54] Selvaggi M, Laudadio V, Dario C, Tufarelli V (2014a). Major proteins in goat milk: an updated overview on genetic variability. Mol. Biol. Rep. 41(2): 1035-1048. http://dx.doi.org/10.1007/s11033-013-2949-9[CrossRef]

[55] Selvaggi M, Laudadio V, Dario C, Tufarelli V (2014b). Investigating the genetic polymorphism of sheep milk proteins: a useful tool for dairy production. J. Sci. Food Agri. 94(15): 3090-3099. http://dx.doi.org/10.1002/jsfa.6750[CrossRef]

[56] Staiger EA, Thonney ML, Buchanan JW, Rogers ER, Oltenacu PA, Mateescu RG (2010). Effect of prolactin, β-lactoglobulin, and κ-casein genotype on milk yield in East Friesian sheep. J. Dairy Sci. 93(4): 1736-1742. http://dx.doi.org/10.3168/jds.2009-2630[CrossRef]

[57] Thomas AS, Dawe ST, Walker RA (1989). Milk protein polymorphism in Hyfer and Border Leicester X Merino sheep. Milchwissenschaft. 44: 686-688.

[58] Yang F, Li L, Liu H, Cai Y, Wang G (2012). Polymorphism in the exon 4 of β-lactoglobulin variant B precursor gene and its association with milk traits and protein structure in Chinese Holstein. Mol. Biol. Rep. 29: 3957–3964. http://dx.doi.org/10.1007/s11033-011-1175-6[CrossRef]

[59] Yousefi S, Azari MA, Zerehdaran S, Samiee R, Khataminejhad R (2013). Effect of β-lactoglobulin and κ-casein genes polymorphism on milk composition in indigenous Zel sheep. Arch. Tierzucht. 56: 216-224.

From the article

Abstract

Introduction

Polymorphisms of BLG gene

Sheep breeds in which the associations among polymorphism and milk traits where investigated are highlighted in bold

Sheep breeds in which the associations among polymorphism and milk traits where investigated are highlighted in bold

Relationship between genetic variants of BLG gene and milk production traits

Sheep breeds in which the associations among polymorphism and milk traits where investigated are highlighted in bold

Conclusions

Conflict of Interest

Authors contribution

References

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