Comparative characteristics of correlations between goat and sheep milk components

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Introduction
In the last decade in Russia, we can observe the increasing in the number of small cattlegoats and sheep of the dairy direction of productivity.However, if dairy goat breeding is actively developing, then dairy sheep breeding is a new branch in animal husbandry in Russia.For example, in 2005 there were no dairy goats in the structure of Russian goat breeding, but in 2021 they already accounted for 32.2% [1].As for the production of sheep milk, one of the first projects for the industrial production and processing of sheep milk obtained from sheep of the Lacon breed was implemented in 2015 in the Krasnodar region by the family enterprise KFH Nikolaev M.I. [2].The following sheep milk producers were the Lukoz enterprise located in the Republic of Mari El, where for the first time they began to breed sheep of the East Friesian breed for industrial milk processing, as well as LLC Tverskoy Urozhe, Tver Region [3][4].
It should be noted that not only in Russia, but the total volume of sheep milk in the world, according to official FAOSTAT data for 2019, amounted to about 1.10 million thousand tons, which is 25.0% more (0.85 million tons) compared to 2000 [5][6].
Taking into account the global trend and the prospect of expanding the domestic sector of dairy products for infants, as well as products with a pronounced therapeutic value, it is possible to predict a further positive trend in the increase in the number of dairy goats and sheep in Russia [7][8][9].
As for the study of the composition of sheep and goat milk, little attention is still paid in our country to the study of the nutritional and biological value of small cattle milk for use in the production of dairy products [10,11].At the same time, studies were carried out in France to study the nutritional characteristics of sheep's and goat's milk and cheeses, as well as the composition of milk, taking into account the place of its production [12].In different countries of Europe, work was carried out on a comparative assessment of the physicochemical properties of milk from goats and sheep of European breeds [13,14].
However, most of such studies are aimed at establishing the numerical characteristics of milk components, and not at assessing the relationship between these components.
It seems to us relevant to determine the exist and direction of the correlation between the components of milk, since this information can be used as the basis for developing a breeding strategy in dairy goat and sheep breeding.Also, these obtained materials will be important to accumulate data on the composition of goat and sheep milk, to determine its species characteristics in a comparative aspect.
Therefore, the purpose of the research was to study the composition of goat and sheep milk using the methods of IR spectroscopy and cell cytometry and to establish the relationship between its components.

Material and methods
The object of the research was dairy goats of the Saanen breed (n=134, Ecofarm Klimovskoe LLC, Kaluga region) and sheep of the Lacon breed (n=96, KFH Nikolaev M.I., Krasnodar region).The goat milk production technology involved milking goats twice a day using DeLaval milking equipment (Germany).Sheep milk was also obtained by double milking on a Gea Farm Technologies milking machine parallel to Mdisplacement 2x16, milking machine -TOP FLOW.
Groups of goats and sheep were formed in such a way that in them the share of animals of lactation I was about 35%, lactation II -33%, III and IV -32%.At the same time, the differences in the beginning of lactation did not exceed two months.Goat milk samples were taken during the control milking period for three months (May-July) and preserved using Microtabs tablets (USA).Sheep milk samples were also taken three times during the period of control milkings, which were carried out every 14 days (May-June).
Descriptive statistics were calculated using Microsoft Excel 2013.The tables show the correlation coefficients (r).The revealed differences for milk components were considered statistically significant at p≤0.05, for correlation coefficients -at p≤0.05.Cluster analysis was carried out in the program Statistica 10, 2021.

Results and discussion
The calculation of the correlation coefficients revealed that the nature of the relationship between MFF and other components of milk in goats and sheep was similar (Table 1).So, between MFF and TTP, casein, the content of fatty acids, both saturated (SFA, LCFA, SCFA) and unsaturated (MUFA, PUFA, SCFA), an average and high positive relationship was revealed.At the same time, it was more pronounced in sheep milk (r = 0.41 ... 0.97) than in goat milk (r = 0.38 ... 0.84).
For goat and sheep milk, a high positive, close to unity (r = 0.95 and 0.99), i.e., functional relationship between the content of casein and MDB was characteristic.Also common for goat and sheep milk was that saturated (SFA, LCFA, STFA, myristic, palmitic) and unsaturated (MUFA, PUFA, SCFA, oleic, stearic) fatty acids showed medium and high positive relationship between themselves (r = 0 .48... 0.96).
A general pattern in the nature of the relationship should be noted for such indicators as acetone and BGB, which were positively related to each other both in goat and sheep milk (r = 0.87), but negatively correlated with other components (r = -0.21... -0.66).Differences in the nature of the relationship between the indicators of goat and sheep milk were revealed for such an indicator as trans-fatty acids (TFA).It equally negatively correlated with urea and lactose in the milk of the compared animal species, however, in sheep milk, the relationship between other components was positive, medium and strong (r = 0.46 ... 0.93), while in goat milk it was positive and very low (r = 0.17 ... 0.30).Also, there is weak positive relationship between the number of somatic cells (SSC) and the differential number of somatic cells (DKSK) in sheep and goat milk (r = 0.36 ... 0.33), Recently, much attention has been paid to such an indicator as the number of somatic cells.GOST 32940-2014 Raw goat milk.Specifications" provides for their number not more than 1000.0thousand units/ml.For sheep's milk, the number of somatic cells has not been determined, since so far GOST for raw sheep's milk has not been developed in our country.According to GOST 31449-2013 "Raw cow's milk.Specifications" in the milk of cows, the number of somatic cells should not exceed 400.0 thousand units / ml.In our study, it was found that in sheep's milk they were 510 thousand units / ml, which is slightly higher than is acceptable for cow's milk, but almost two times lower than in goat's milk.For a more detailed discussion of this indicator, both directly for sheep milk and in a comparative aspect with goat milk, it is necessary to accumulate more data from sheep of different dairy breeds.It draws attention to the fact that no significant relationship was found between the number of somatic cells in the milk of both sheep and goats with all other components, except for the lactose content (MDL).

Conclusions
Milk fat is one of the most complex natural fats, which consist of approximately 400-500 fatty acids, the biosynthesis of which is a complex process consisting of many cellular processes and metabolic pathways [15].Sheep and goat milk tend to be richer in conjugated linoleic acid than cow's milk, probably due to the nature of the feeding system in which small ruminants are commonly raised [16].
There are various options for enriching the fatty acid composition of ruminant milk by changing the diet.
For example, it was noted that the fatty acid profile of the fatty phase of milk in animals consuming mainly green fodder has a higher content of mono-and polyunsaturated fatty acids [24,25].Also, some studies indicate that genetic polymorphism also has an effect on the fatty acid composition.So allele DGAT1 K232A is associated with the ratio of saturated and unsaturated fatty acids, as well as with the content of conjugated linoleic acid [26].
Additional introduction of fish oil and vegetable oils into the diet for ruminants can also, to a certain extent, affect the increase in the content of unsaturated fatty acids in milk.But at the same time, it can cause a depression of milk fat and a decrease in milk yield.
So, organizing the industrial production of both goat and sheep milk, one of the ways to improve the qualitative composition of milk can be the selection of animals based on the selection index, taking into account the identified relationships between the individual components of milk.

Table 1 .
Correlation coefficients between goat (top) and sheep (bottom) milk components