Yield and composition of milk from Polish Holstein-Friesian and Jersey cows in particular months of the first lactations as dependent on milk protein polymorphism (short communication)

The experiment was performed on 121 primiparous Polish Holstein-Friesian (PHF) cows and 36 primiparous Jersey (JER) cows. The highest decrease in casein yield was noted in JER cows at 7.36 % on day 90 of lactation, 15.95 % on day 150, 26.78 % on day 210, 37.01 % on day 270 and 39.67 % on day 330. In PHF cows this decrease was substantially lower, at 4.98 %, 7.65 %, 8.72 %, 10.50 % and 16.19 % respectively. The casein content of milk from primiparous PHF cows ranged from 2.38 % (LGB – day 60) to 3.09 % (LGB BB – day 330), and it was found to be considerably lower in JER cows, varying between 2.35 % (CSN3 BB – day 30) and 3.61 % (CSN3 BB – day 210). The highest casein yield was recorded in PHF cows with the following genotypes: LGB AA (day 60), CSN1S1 BB (day 60), CSN2 AB (day 270), CSN3 BB (day 150). In JER cows the highest casein yield was noted on day 90 of lactation with respect to the following genotypes: LGB BB, CSN1S1 BC, CSN2 AA and CSN3 BB. In PHF cows the greatest effect on whey protein yield was exerted by the following genotypes: LGB AA (day 90), CSN1S1 BC (day 60), CSN2 AA (day 90); the CSN3 BB genotype influenced whey protein yield in cattle of both breeds (day 90). In JER cows the highest daily yield of whey proteins was observed on day 90 of lactation, with regard to the following genotypes: LGB BB, CSN1S1 BC, CSN2 AB and CSN3 BB.

Schlüsselwörter: Holstein-Friesian, Jersey, Erstlaktation, Laktationmonate, Kasein, Fett, Molkeneiweiß, Milcheiweißpolymorphismus Introduction It was demonstrated that two whey proteins, α-lactalbumin (LALBA) and β-lactoglobulin (LGB), and four casein fractions, αs1 (CSN1S1), αs2 (CSN1S2), β (CSN2) and κ (CSN3) exhibit polymorphism.Many authors who study milk protein polymorphism search for linkages between milk protein genes and the genes determining quantitative traits (JANN et al., 2002;GRAML and PIRCHNER, 2003).However, the above genes are located on numerous chromosomes, so such simple relationships cannot be found (ADACHI et al., 1996;KAMIŃSKI, 1996;KAMIŃSKI, 2000;KAMIŃSKI et al., 2002;JANN et al., 2002;CZERNIAWSKA-PIĄTKOWSKA et al., 2004).It has been reported that milk from cows with the CSN3 BB genotype has a higher percentage content of total protein, casein proteins and fat, is characterized by a shorter (by 10 to 30 %) coagulation time, provides a coagulate of greater firmness (by 20 to 100 %), retains more fat in the curd and ensures a higher cheese yield (JAKOB and PUCHAN, 1992;GERNAND and HARTUNG, 1997;KAMIŃSKI, 2000;JUSZCZAK et al., 2001).As regards the whey protein LGB, a higher milk yield is generally associated with the LGB AA genotype (OJALA et al., 1997;KAMIŃSKI et al., 2002), while a higher percentage content of fat and casein proteins -with the LGB BB genotype (WALAWSKI et al., 1994;LITWIŃCZUK et al., 1998).The selection of Black-and-White cattle oriented towards a higher milk yield results in an increased frequency of the CSN3 A allele and a decreased frequency of the B allele (KAMIŃSKI et al., 2002;CZERNIAWSKA-PIĄTKOWSKA et al., 2004).Therefore, Black-and-White bulls with the AB genotype (containing the desired B allele) should be selected for breeding, and the relevant information should be placed in performance-tested bull catalogs.In Jersey cattle populations the frequency of the CSN1S1 B genotype is much higher, and milk has a high content of protein and fat (ALEANDRI et al., 1990;JANN et al., 2002).The objective of this study was to characterize the yield and composition of milk as dependent on polymorphic milk protein variants, as well as to determine the yield and content of casein and whey proteins in milk in particular months of lactation of primiparous Polish Holstein-Friesian and Jersey cows.

Materials and Methods
The experiment was performed during the years 2002-2006, on 121 primiparous Polish Holstein-Friesian (PHF) cows and 36 primiparous Jersey (JER) cows.The following milk performance traits were analyzed: milk yield, milk fat yield, milk protein yield, casein yield, dry matter content of milk, whey protein yield.Milk samples were collected individually from cows of both breeds on the following days during the first lactation (± 5 days): 30, 60, 90, 150, 210, 270 and 330.In addition, at the beginning of lactation milk samples for the determination of milk protein genetic variants were taken directly from the teats of each cow, and poured into 1.5 ml Eppendorf tubes.Those samples were used to determine the genetic variants of milk protein fractions by starch gel electrophoresis in the alkaline environment -according to the method developed by SCHMIDT (1964) and modified by Michalak (1969), and in the acid environment -as described by PETERSON and KOPFLER (1966).Four major proteins were obtained as a result of separation, i.e. αs1-casein (CSN1S1), β-lactoglobulin (LGB), κ-casein (CSN3) and β-casein (CSN2).
The numerical data were verified using the following mathematical model: Y ijk =μ + A i + B j + C k + E ijk where: Y ijk -analyzed trait, μ -overall mean, A i -effect of the i th breed group (i=1,2), B j -effect of the j th group of the investigated polymorphic protein system (j=1,…4), C k -effect of the k th genotype (k=1,…10), E ijk -random error.The results were verified statistically by analysis of variance and Tukey's test, using Statistica ver.6.0 software (STATSOFT, 2003).

Results
In the case of the proteins LGB, CSN2 and CSN3, the AA and AB genotypes and the A gene occurred most frequently in the investigated population, regardless of breed.As regards the protein CSN1S1, almost all animals (120 PHF cows and 31 JER cows) had the BB genotype.Table 1 presents the daily yields of milk and selected milk components in cattle of both breeds.In PHF cows the highest average yield of milk and milk components was noted in the second month of lactation (day 60), which was confirmed by statistically significant differences (p≤0.01 and p≤0.05) between the mean values of the analyzed traits.In JER cows the highest productivity was recorded in the first and second month of lactation, and it remained at a high level until day 90.Average daily milk yield was lower in JER cows than in PHF cows.In the first and second month of lactation, JER cows produced 4 and 6 kg milk less than PHF cows, respectively, whereas in the last month of lactation (day 330) this difference reached 8 kg.Means within traits, determined for particular lactation days, followed by the same letters differ significantly at: capital letters (p≤0.01);small letters (p≤0.05) The opposite tendency was observed only with respect to the daily yields of fat and whey proteins, which were higher in JER cows than in PHF cows during the first three months of lactation, and amounted to 886 g and 170 g (day 30), 903 g and 151 g (day 60), 871 g and 153 g (day 90), respectively.Considerable interbreed differences were found with regard to the yield of the most valuable milk protein -casein.Differences between the above value and those determined in the other months were statistically significant at p≤0.01 and p≤0.05.In JER cows the highest casein content of milk was noted on day 210 and 270 of lactation (p≤0.01).During the first lactation analyzed in the study the casein content of milk from PHF cows ranged from 2.38 (LGB -day 60) to 3.09 % (LGB BB -day 330), and it was found to be considerably lower in JER cows, varying between 2.35 % (CSN3 BB -day 30) and 3.61 % (CSN3 BB -day 210).In milk from cows of both breeds casein concentration increased with the progress of lactation.In PHF cows this increase started in the second month, while in JER cows -at the beginning of lactation.In the JER population a tendency to a higher casein content of milk was observed in cows with the following genotypes: LGB (BB>AA, AB), CSN1S1 (BB>BC), CSN2 (AB>AA) and CSN3 (BB>AB, AA).Table 3 presents relationships between daily casein yield in particular phases of lactation and the genetic variants of milk proteins.Daily casein yield decreased with the progress of lactation, as confirmed by statistically significant differences at p≤0.01.The highest casein yield was recorded in PHF cows with the following genotypes: LGB AA (day 60), CSN1S1 BB (day 60), CSN2 AB (day 270), CSN3 BB (day 150).
In JER cows the highest casein yield was noted on day 90 of lactation, with respect to the following genotypes: LGB BB, CSN1S1 BC, CSN2 AA and CSN3 BB.WALAWSKI et al. (1994), the CSN3 B gene -associated with a higher protein content of milk and higher processing suitability of milk in respect of cheese production -occurs with a higher frequency in JER cattle.The above authors demonstrated that regardless of lactation and sampling time the highest casein content was observed in cows with the LGB (AA>AB.BB) and CSN3 (AB>AA.BB) genotypes.Means followed by the same letters in columns differ significantly at: capital letters (p≤0.01);small letters (p≤0.05) Over the analyzed lactation the highest average casein yield was 562 g (PHF cows, day 60, p≤0.05) and 489 g (JER cows, day 30, p≤0.05).The highest decrease in casein yield (in comparison with the highest casein yield recorded on day 30) was noted in JER cows, at 7.36 % on day 90 of lactation, 15.957 % on day 150, 26.78 % on day 210, 37.01 % on day 270 and 39.67 % on day 330.In PHF cows this decrease was lower, at 4.98 %, 7.65 %, 8.72 %, 10.50 % and 16.19 % respectively.Table2shows dependencies between casein content and the genetic variants of milk proteins.In PHF cows the highest casein content of milk was recorded on day 330 of lactation.

Table 4
JANN et al. (2002))es between the daily yield of whey proteins in particular phases of lactation and the genetic variants of milk proteins.In PHF cows the greatest effect on whey protein yield was exerted by the following genotypes: LGB AA (day 90), CSN1S1 BC (day 60), CSN2 AA (day 90) and CSN3 BB (day 90).In JER cows the highest daily yield of whey proteins was observed on day 90 of lactation, with regard to the following genotypes: LGB BB, CSN1S1 BC, CSN2 AB and CSN3 BB.Until day 210 of lactation, PHF and JER cows were characterized by a comparable average yield of whey proteins, which decreased in the JER population towards the end of lactation, i.e. on day 270 and 330.DiscussionOJALA et al. (1997)reported similar genotype frequencies for the Holstein-Friesian breed, but somewhat different for the Jersey breed, i.e. 0.07 (LGB AA), 0.58 (LGB AB) and 0.35 (LGB BB).JANN et al. (2002)determined the frequency of the CSN1S1 B allele in the Jersey population at 0.63, compared to 0.93 in the present study.According to