Abstract. Milk composition is of prime economic importance for farmers. Milk total proteins are composed of casein, whey proteins and non-protein nitrogen. The objective of this work was to establish milk crude protein, non-protein nitrogen (NPN) and urea content in dairy cow milk produced in different farms in Latvia. Cow milk samples (n=30) were collected in September 2012 from four different farms breeding diverse cow breeds. Average crude protein, casein and urea content in milk varied significantly among farms. NPN content in cow milk varies among farms -from 0.194% to 0.232%. Average crude protein and casein content was significantly higher (p<0.05) for Latvia Brown breed cows, while NPN content did not differ significantly among breeds. Regression between NPN and urea content in milk was R² = 0.458. Correlation between NPN and urea content was significant (r = 0.677). This study allowed establishing that crude protein and NPN content in milk varied significantly (p<0.05) in farms with differing dairy cow housing and feeding technologies. Key words: crude protein, casein, NPN, urea. IntroductionMilk of dairy cows is biological solution containing approximately 12.8% of dry matter. Milk dry matter consists of proteins, carbohydrates, fats, minerals and vitamins. Depending on animal breed, genotype, phase in lactation, nutritional value of feed, milking technology, animal health status, environmental conditions, animal age, interval between milking, as well as other factors milk composition may change (Coballero et al., 2003;Roginski et al., 2003).Recently increasingly higher interest has been devoted to researches on milk proteins, since they are the main component used to produce curd and cheese. Analysis of milk samples with standard Kjeldahl method helps in finding out volume of total nitrogen (N) in milk, and multiplying the acquired result by 6.38 we may acquire crude protein content in milk (ISO, 2001). Proteins in cow milk comprise 95 -97% of the crude protein content, and non-protein nitrogen (NPN) accounts for 3 -5%. Proteins in milk are represented by casein and whey proteins. Average proportions of proteins in crude protein are the following: 75 -85% casein, 18 -20% whey proteins. Casein content in proteins accounts for 85 -90% (Hui, 1993). Non-protein nitrogen (NPN) gets into milk from animal blood after protein metabolism. One of the largest (~50%) and most stable NPN parts is formed by milk urea. Apart from milk urea, NPN consists also of free amino acids, creatine, uric acid, peptides, organic acids and phospholipids (DePeter and Ferguson, 1992;DePeters and Cant, 1992;Твердохлеб и Раманаускас, 2006). Nutrition experts point out that evaluation of food quality from nutritional point of view requires finding out quality of proteins, as human body, unlike one of ruminants, may use only proteins formed from amino acids. Thus, the content of crude protein in milk should be taken into account when balancing diet; otherwise, expected results may not be achieved (Moughan, 2012).Lately interest tow...
The aim of our study was to determine up to what extent the number of services per calving (NSPC) affects dairy cow productive and reproductive performance. The study contains data from the Latvian Agricultural Data center about 26888 Latvian Brown (LB) and Holstein Black and White (HBW) breed cows that were born from year 2005 -2010, closed at least 5 full lactations and were culled from herds. In data set we have included data about cow milk productivity (calculated in ECM), longevity traits and reproduction traits. The reproduction traits included the number of services per conception (NSPC), calving interval (CI) and calving to conception interval (CCI) in the first five lactations. The average lifespan of LB and HBW dairy cows was 3149.5 days and in this period 39570.6 kg ECM were obtained. LB breed cows were characterized by 23.5 days longer lifespan and by 6035.4 kg ECM lower lifetime milk productivity than HBW breed cows, but they showed higher reproduction trait scores than LB breed group. HBW cows had a significantly (p < 0.05) higher NSPC, CCI, number of milking days (MD) and CI than LB breed cows in all five analyzed lactations. The NSPC in the first lactation increased the calving age at the fifth lactationcows with NSPC in the first lactation > 4, fifth time calved 170.7 days in LB breed group and 190.8 days in HBW breed group later than cows with one NSPC in the first lactation.
The experiment was conducted to analyse the effect of fermented acid whey permeate on milk yield and composition in the lactating cows. Propionic acid bacteria and their metabolites have been used in the lactating cows feeding over decades, primarily to improve growth performance, feed conversation and milk production efficiency. Two groups of the lactating cows were arranged in the study: control group (n=50) and experimental group (n=50). Experimental group’s animals received 0.5 L of fermented whey permeate daily. Acid whey permeate was inoculated with the freeze-dried PS-4 (Propionibacterium freudenreichii subsp. shermanii, Chr.Hansen, Denmark) starter and fermented anaerobically for 48 hours at 20±2 oC. Fat, protein, lactose and total solids concentration in acid whey permeate and fermented acid whey permeate was analysed by the standard methods, but propionic acid was detected by HPLC. Milk composition and quality indices were determined at the beginning of the study and each month during 6 months period. At the end of the study the feeding of fermented acid whey permeate was stopped, but milk composition and quality data were monitored additionally after one month. Milk fat, protein, lactose, total solids, urea concentration and somatic cell count were analysed by a near infrared spectroscopy.The variability in milk composition and quality data across trial was greater in the experiment group than in the control. Milk fat and somatic cell count were significantly different (p<0.05) than other studied parameters in the experimental group cows’ milk. Milk yield and lactose concentration were tended to increase during feeding of fermented acid whey permeate in the lactating cows without significant differences between control and experimental groups. Fermented acid whey permeate as feed supplement improves energy metabolism for dairy cows which results in the higher milk yield and fat concentration.
Milk yield, composition and milk coagulation properties can be affected by kappa-casein (κ-CN) and beta-lactoglobulin (β-LG) genotypes and breed. Latvian Brown (LB) and Latvian Blue (LZ) are local dairy breeds in Latvia. These breeds are not so high-yielding than other commercial dairy breeds, besides, the number of those animals decrease each year. The aim of the research was to analyze the influence of κ-CN, β-LG and breed on milk composition and milk coagulation properties. Data were collected from 56 Latvian Brown and 26 Latvian Blue in 2016. Widespread κ-CN genotype was AA (0.593) in LB breed and AB (0.636) in LZ breed, while β-LG highest frequency was BB genotype. Significant effect was not observed on milk yield, however the highest daily milk yield was from AB κ-CN genotype (19.7 ± 1.52 kg) in LB breed. Significant differences were observed in fat content -the highest fat content accordingly κ-CN was from AA genotype in LB (46.3 ± 1.89 g kg -1) and 45.5 ± 1.37 g kg -1 from BB β-LG genotype in LB breed (p < 0.05). A lower protein content was observed from AA κ-CN genotype in LZ breed (33.8 ± 1.30 g kg -1 ), while highest from BB genotype in both breeds. Curd firmness was not significantly different by genotypes and breed. Significantly shorter milk renneting time of β-LG was obtained from LB breed (14.6 ± 2.76 min, p < 0.05), while κ-CN genotype was not significantly affected.
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