* Corresponding author. Tel.: #47-64-94-85-50; fax: #47-94-94- 37-89. E-mail address: gerd.vegarud@inf.nlh.no (G.E. Vegarud) International Dairy Journal 9 (1999) 367 } 368 Genetic variants of Norwegian goats milk composition, micellar size and renneting properties G.E. Vegarud!,*, T.G. Devold!, R. Opheim!, E. Loeding!, C. Svenning!, R.K. Abrahamsen!, S. Lien", T. Langsrud! !Department of Food Science, Agricultural University of Norway, P.O.B. 5036, 1432 Aas-NLH, Norway "Department of Animal Science, Agricultural University of Norway, P.O.B. 5025, 1432 Aas-NLH, Norway Abstract A survey has been conducted of the allele frequency of genetic variants of various caseins, mainly a 41 -casein, in herds of Norwegian goats located in north, west and southeast Norway. In addition, identifying the variants, milk composition, micellar size and renneting properties of the milks have been determined. ( 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction Poor coagulating properties have been observed in milks from goats expecially in the North of Norway. This study began as a consequence of requiring more know- ledge of this problem and its aim was to identify genetic polymorphisms in the Norwegian goat breeds and to further study the relation between a 41 -casein (CN) vari- ants, composition, micellar size and renneting properties. A possible relationship of a 41 -CN to coagulation prob- lems of the milk has been proposed by Amrosoli, Distasio and Mazzocco (1988) and Remeuf (1993). 2. Materials and methods Milk from the Norwegian goat herds in north, west (Vinje) and southeast (Aas) Norway were collected thrice during the lactation period. Screening of the protein variants was done at both the protein level and at the DNA level. Identi"cation of polymorphisms at the pro- tein level were performed using PAGE IEF gels (Erhardt, 1989) and capillary electrophoresis (Recio, Perez-Rod- riguez, Ramos & Amigo, 1997). Identi"cation of genetic variants at the DNA level was done using biopsies from the lactating mammary gland, mRNA isolation, cDNA synthesis and PCR and sequencing analysis (Lien, 1995). Quality and composition of the milk were de"ned by goat's age and lactation period, somatic cell counts and milk yield, pH, fat, lactose, citrate, protein, casein and casein number, NPN and urea, Ca‘‘ and total Ca and relative composition of a 41 -CN, b-CN and i-CN. Particle size of native and heated (70, 80 and 903C) micelles were measured by photon correlation spectroscopy (PCS) and electron microscopy. Renneting properties (RCT, K 20 and A 30 ) measured by Formagraph (Foss Electric, Denmark), syneresis and whey drainage were measured. 3. Results Seven polymorphic forms within a 41 -CN have been identi"ed in the Norwegian goat breeds. Our studies so far showed that more than 70% of the goats contained the a 41 -CN null allele, 5% the a 41 -CN A variant, 1% a 41 -CN C variant and 7% a 41 -CN E variant, 11% BF and 0.8% DF variants were also identi"ed in these milks. Of b-CN the b1 and b2 forms were identi"ed and no goats seemed to have the b-CN null allele and two unclassi"ed i-CN forms. When comparing herds from north, west and south- east of Norway a higher frequency of a 41 -CN null variant was found in herds from west Norway (79%), while goats from southeast of Norway showed a frequency of 75% and north Norway (58%) of the a 41 -CN null allele. The sequence of a 41 -CN A allele was the same as that reported in the french breed (Martin, 1993). The sequence of the a 41 -CN F allele seemed to be di!erent than that reported by the French group (Lien, 1995). 0958-6946/99/$ - see front matter ( 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 8 - 6 9 4 6 ( 9 9 ) 0 0 0 9 0 - 4