The effect of different feeding system on fatty acids composition of cow’s milk

© Slovak University of Agriculture in Nitra Faculty of Agrobiology and Food Resources


Introduction
Milk and dairy products are traditional foods in human nutrition (Haug et al., 2007;Kubicová and Habánová, 2012;Lorková et al., 2017). Milk contains water, lipids, FA, amino acids, proteins, minerals, and vitamins. It includes the available basic and essential nutrients needed for growth and development for the neonates in population of human's and animal's (Filipejová et al., 2010;Boro et al., 2016). Cow's milk has an average content of 3.5% proteins (80.0% caseins, 20.0% serum proteins), 3.0-4.0% lipids, 4.6% lactose, 1.0% ash (Ca, P, K, Mg, Na), vitamins (particularly thiamin, riboflavin, pyridoxine, tocopherol, retinol, carotenes) and 12.0% of dry matter (Muehlhoff et al., 2013). Slovak spotted breed, one from two national breeds in Slovakia, is combined meat-dairy utility type with medium to larger body frame, harmony structure of body and very good musculature (Kadlečík et al., 2013). According to performance control in 2017 and 2018, the average utility of 6 626 and 6 843 kg of milk with average fat content of 3.95 and 3.93% and 262 and 269 kg production of fat, with an average protein content of 3.39 and 3.40% in protein production 224 and 233 kg for lactation (BSSR 2017;. Genetic and non-genetic factors play a significant effect on the variations of milk yield and their components (Boro et al., 2016;Miluchová et al., 2014;Bujko et al., 2018). In terms of nutrition, not only is the fat content of milk but also its qualitative parameters forcefully on the content and ratio of FA is crucial. Cow's milk is an important source of saturated FA (Bagnicka et al., 2010;Gálik et al., 2011;Szwajkowska et al., 2011). The fat of bovine milk was often associated with cardiovascular disease because of saturated FA (Kajaba et al., 2009;Kalač and Samková, 2010). Changing the composition of FA is a long-term nutrition strategy.
The forages, although are low in fat content, are the main and cheapest source of unsaturated FA in ruminant nutrition. Current research is focussed on effects of different forages (fresh, silage, haylage) on fat content and FA profile in milk. Intake of pasture herbage rich on grassland and legume species positively affects ratio of FA (unsaturated/saturated) and increases content of conjugated linoleic acid (CLA) and vaccenic acid in cow's milk in comparison with milk from cows fed with conserved forages (hay or silage) (Kalač and Samková, 2010). Milk from cows grazed by pasture with wider biological diversity of plants contains lower portion of saturated FA, higher portion of polyunsaturated FA and it's characterized by lower n6/n3 FA ratio contrast to the milk from housed cows (Martin et al., 2002;Martin et al., 2004;D'urso et al., 2008).

Farm A: grazing feeding system
Farm A operates in Central Slovakia and cultivates 397 hectares of agricultural land in the foothills. The altitude is in the range from 400 to 700 m. above see level. Annual average precipitation in the year 2016 was 750 mm and has a decreasing trend. The average annual temperature reached 8 °C. At the time of the realization of the experiment, 64 cows of Slovak spotted cattle were bred. Daily milk production was about 150 kg and for the entire herd 55,000 kg of milk per year. Milking was provided by Alfa Laval Agri no. 906601-82 series 415 MA, with frequency 2× daily.

Farm B: silage feeding system
The agricultural grange is located in the south of western Slovakia, a maize production area with an altitude of 150 m above see level. The company managed 1,820 ha of agricultural land in 2016. Average annual precipitation reached 568 mm in 2016 and an average temperature of 9.6 °C. At the time of the research, on the farm were 280 pieces of dairy cattle -Slovak spotted breed with an average daily production of 5,000 kg and an annual production of 1,800,000 kg per year. Milking was realized twice a day in herringbone parlour Fullwood 2 × 10. Type of stabling -free.

Farm A: grazing feeding system
The dairy cows were grazed daily between 6:30 and 15:30. Pasture grassland was from a botanical point of view consisted of 53% of grasses dominated by Trisetum flavescens, 4% of legumes with predominant Trifolium repens, 40% of other meadow and pasture herbs and 3% of blank places. The botanical evaluation of grassland was done by the method of reduced projective dominance (D in %) according to Regal (1956).
At the time off grazing, dairy cows were supplementary fed with a feed ration of 15 kg of meadow hay, 25 kg of fresh clover, 2 kg of feed mixture (50% wheat and 50% barley), and 0.5 kg of molasses. The intake of pasture, water and mineral block was ad libitum.

Farm B: silage feeding system
Feed ration (on the base total mixed ration -TMR): maize silage 17 kg, protein-energy feed (residue of corn grain) 6 kg, 8 kg of sugar beet pulps, 8 kg of feed mixture, 2 kg of extracted rapeseed meal, 1 kg of straw and 1 kg of meadow hay was fed by dairy cows. Water intake and mineral block were ad libitum.

Sampling and laboratory analysis
Collection of tank's milk samples (200 ml) from both farms (n = 12) was carried out on the 16 th of June 2016 (summer feeding season). The content of crude fat and FA profile were analysed in the milk samples. Analyses in Laboratory of Quality and Nutritive Value of Feeds (Department of Animal Nutrition, FAFR, SUA in Nitra) were realized. The crude fat content after acid hydrolysis was determined by extraction according to the Soxhlet principle. For determination of FAME´s (FA methyl esters) was used GC system Agilent 6890A (Agilent technologies). The GC system was equipped with split injection autosampler, DB 23 analytical column (lenght 60 m, diam. 0.250 mm, film 0.15 µm, Agilent technologies) and flame ionisation detector (FID).

Statistical analysis
Statistical evaluation of results was realized using one-way ANOVA by IBM SPSS v. 20.0. For evaluation of statistical significance between variables (FA and fat content) Tukey test was used.

Results and Discussion
Average content of fat in analysed milk samples was 3.38% from farm with grazing feeding system and 3.46% from farm with silage feeding system (Table 1.). Mendoza et al. (2016) also confirmed tend to decrease fat yields with increasing pasture in the diet of dairy cows. Significant (P <0.05) differences between milk samples in the content of butyric acid (C4:0) were found. The higher percentage (2.30%) was found in milk from grazed cows. In the myristic acid (C14:0) percentage, the higher (P <0.05) value was determined in the milk from silage system (12.01%) in comparison with the milk from grazing system (9.04%). Palmitic acid (C16:0) was detected as a major acid in the analysed milk samples from both feeding systems. Differences in palmitic acid content were not statistically significant. Significance (P <0.05) was determined in heptadecanoic acid (C17:0) with higher concentration in samples from grazing system. Cow's milk is the richest source of oleic acid (24%) (Markiewicz-Keszycka et al., 2013). In C18:1 cis n9 (oleic acid) concentration, the higher (P <0.05) value was found in the milk from farm with grazing feeding system. Morales-Almaráz et al. (2017) confirmed that the concentration of 18:1 cis n9 increase in cow's milk with increasing grazing time. In linoleidic acid (C18:2 cis n6), significant (P <0.05) differences were detected, with higher content in samples from silage feeding system. The TMR feeding system resulted in milk with increased concentrations of C18:2 cis n6 in experiment of O'Callaghan et al. (2016) too. Guler et al. (2010) reported the average total CLA (conjugated linoleic acid) content in milk samples from Turkey 1.02% and Blaško et al. (2010) reported the average CLA content in summer cow's milk from 6 farms in Slovakia 0.08%. In our experiment, the concentration of CLA (C18:2 cis n9) had values 0.35 and 1.19%. Higher (P <0.05) CLA value in samples from grazing feeding system was determined. This is in agreement with the results of Alothman et al. (2019) and Rolinec et al. (2018). The predominant n-3 FA in milk fat of the majority of mammals is α-linolenic acid (Markiewicz-Keszycka et al., 2013). Significantly Table 1 Fatty acid profile in cow's milk from different feeding system (g 100 g -1 FA) Trait (P <0.05) higher content of α-linolenic acid (C18:3 n3) in milk from grazing feeding system was found. Samples of milk collected from the farm with silage feeding system contained less arachidic acid (C20:0) compared to milk from the farm with different feeding system (P <0.05). Eicosapentaenoic acid (C20:5 n3) was detected only in milk from pasture fed cows. Presence of tridecanoic acid (C13:0), eicosatrienoic acid (C20:3 n6) and arachidonic acid (C20:4 n6) was determined only in milk samples from farm with silage feeding system. The polyunsaturated FA (PUFA) in cow milk represents small proportion, less than 3% of all FA (Lindmark-Månsson, 2008). Differently in the experiment, a PUFA portion of more than 3% in the milk from both types of feeding was found. The effect of different feeding system on PUFA was significant (P <0.05). Higher proportion of PUFA was determined in the milk of cows fed on the base of silage. Similar as in this study, Markiewicz-Keszycka et al. (2013) reported more than 4% of PUFA in cow milk.
In MUFA content, non-significant (P >0.05) differences were determined. In saturated FA (SFA) content, a significant (P <0.05) lower content was found in milk samples from farm with grazing feeding system, consistent with Elgersma (2015). According to Hudečková et al. (2011) recommended n6/n3 FA ratio in human and animal nutrition is 5 : 1. Ratio of n6/ n3 in samples from farm with grazing feeding system was under this recommendation and from different feeding system was above the recommend ratio (1.36 farm A and 9.12 farm B). The data were consistent with the results of Barca et al. (2018) where n6/n3 ratio was greater in milk of cows fed with TMR than in milk of grazing cows.

Conclusions
Milk is an important source of nutrients in animal and human nutrition. Feeding system affects FA profile of cow's milk. Significantly higher proportion of butyric acid, heptadecanoic acid, oleic acid, α-linolenic acid, arachidic acid in milk samples from farm with grazing feeding system (farm A) was detected. Conjugated linoleic acid was more than three times higher in milk from grazing system. Milk samples only from this feeding system contained the eisosapentaenoic acid. The results confirmed that in milk from farm with silage feeding system (farm B) significantly higher content of linoleic acid and presence of tridecanoic acid, eicosatrienoic acid and arachidonic acid was determined only in these samples. Significantly lower proportion of saturated FA was typical for the examined samples from grazing feeding system and significantly higher proportion of polyunsaturated FA was characteristic for the samples from silage feeding system. The influence of the feeding system on the monounsaturated FA content was not confirmed. In milk samples from both feeding systems very different n6/n3 FA ratio was detected (1.36 vs. 9.12, milk from farm A vs. farm B).