Methods of accounting and quality control of milk in dairy cattle breeding

To increase the productivity of livestock animals and improve the quality of milk, it is necessary to know the methods of recording, sampling, and analyzing the chemical composition of milk; possible adulteration, contamination, antibiotic content, and bacterial count. These issues become particularly important in connection with Russia's accession to the WTO and the need to produce competitive products.

Objective of the lesson. Learn to determine milk yield, average fat and protein content in milk, and the amount of milk fat and protein over 305 days or a shortened and completed lactation; graphically represent the dynamics of milk yield during lactation; calculate the amount of standard milk. Familiarize yourself with the appraisal and evaluation of cattle based on offspring quality.

Task 1. Learn to collect, preserve, and store an average milk sample for analysis.

Methodology. The collection of average milk samples for analysis is carried out during control milkings once a month (on commercial farms) or every ten days (on breeding farms). When milking cows into portable milk buckets, the sample is collected after milking the cow: after mixing the milk thoroughly and carefully using a "skimmer," it is immediately collected with a "sampler" by immersing it carefully vertically from top to bottom.

In pipeline milking systems, special devices are fixed at the point where milk enters the milk pipeline, through which a portion of the milk flow is automatically and gradually separated into the device's container. After milking the cow, the collected sample is poured into a separate container.

When milking in milking parlors with automatic systems, the milk sample is collected automatically after this function is enabled on the equipment.

Some modern milking equipment is equipped with automatic devices that allow for recording the amount of milk yielded during each milking and assessing milk quality. To do this, it is sufficient to press a button on the device, the screen of which displays the recording and assessment results, or (if computer programs, etc., are available) transmit the information to a computer specifically for the milked cow.

When collecting an average milk sample for analysis from daily yield, it is necessary to consider that milk quality in a cow changes throughout the day. Due to the fact that the amount of milk also varies during different milkings (especially with three-time milking), it is necessary to collect samples from each milking in proportion to the amount of milk yielded.

Example: a cow yielded 10 kg of milk in the morning, 8 kg at lunch, and 7 kg in the evening.

It is necessary to determine how many ml of sample should be taken from each 1 kg of milk yielded. Depending on the methods used and the number of quality indicators planned for the analysis, one can take from 2 to 10 ml from each kg of milk yielded.

If a 150–250 ml sample is required, 5 or 10 ml is taken from each kg of yield, i.e.

morning (10 kg × 5(10)) = 50 (100) ml lunch (8 kg × 5(10)) = 40 (80) ml evening (7 kg × 5 (10)) = 35 (70) ml

The three resulting samples are mixed and used for further analysis.

Samples should be stored at a temperature of 6–8°C for no more than four hours.

Formalin: Add 1–2 drops of formalin per 100 ml of milk; sample shelf life is 15 days. Disadvantage: formalin reacts with milk proteins, forming a dense compound, which makes it difficult to determine fat in milk.

Potassium dichromate (K2Cr2O7): 1 ml of 10% solution or 2 ml of 5% solution per 100 ml of milk. Sample shelf life is 10–12 days.

Hydrogen peroxide (H2O2): 2–3 drops of 30–33% solution per 100 ml. Sample shelf life is 8–10 days.

– fractional application of preservatives: add ½ of the dose immediately, and the remaining dose of the preservative after 2–3 hours;

– store preserved samples in a dark place at a temperature of 10°C.

Task 2. Conduct an organoleptic evaluation of milk.

Methodology. Organoleptic (sensory) analysis is a qualitative and quantitative assessment of the response of human senses to product properties. Qualitative assessment is expressed by a verbal description, and quantitative assessment is expressed in numbers and graphs.

Appearance and consistency. Pour milk or cream into a clean, dry Petri dish (about half its volume), place it on a white surface, and inspect. Milk (cream) should be opaque, white in color with a slightly yellowish tint. The whiteness and opacity are due to light-scattering fat globules and casein micelles; the fat and pigments give the milk and cream a yellow tint.

Consistency is assessed by pouring milk from one transparent colorless vessel into another similar vessel, then examining it carefully along the surface of the vessel. Raw cow's milk is a homogeneous, non-stringy, slightly viscous liquid without sediment. The consistency of milk (cream) is considered non-homogeneous if a layer of settled fat appears in it, the degree of compaction of which depends on the freshness of the milk (cream).

Smell, taste, and aroma. About 60 ml of milk is poured into a clean, dry 100 ml flask with a ground-glass stopper and heated in a water bath to 72°C. 30 s after reaching the target temperature, the flask with milk is cooled to a temperature of 35–39°C and analyzed. The smell of the milk is determined immediately after opening the flask, then 18–20 ml of milk is poured into a clean, dry cup to evaluate the taste.

The point-based evaluation of the smell, taste, and aroma of raw milk is carried out according to the following criteria provided in Table 1: Table 1 – Criteria for evaluating raw milk

Smell, taste, and aroma: Evaluation, points: Clean, pleasant. Taste is slightly sweet Excellent (5) Not sufficiently expressed, bland Good (4) Weak off-flavors and odors (feed,

Satisfactory (3) oxidized, lipolytic, unclean) Pronounced feed (including onion, garlic, wormwood), musty, and other Bad (2) off-flavors and odors Rancid, moldy, putrid. Bitter taste. Smell and taste of petroleum products, medicines, Very bad (1) detergents and disinfectants

Freshly drawn milk has a faint, pleasant odor that is difficult to characterize more precisely than with the term "milky"; the taste is pleasant, slightly sweetish-salty. The specific smell and taste of raw milk are determined by its chemical composition. Fat gives milk a delicate and pleasant taste, protein substances enhance the fullness of the taste sensation. Carbohydrates determine the sweetish taste (lactose is 6 times less sweet than sucrose), and mineral substances – a slight saltiness.

Task 3. Learn to determine the density of milk or cream.

Methodology. Milk density is the ratio of the mass of milk at a temperature of 20°C to the mass of an equal volume of water at 4°C (the temperature at which water has the greatest density).

Normal milk has a density in the range of 1027–1032 kg/m3, or 1.027–1.032 g/cm3. Sometimes it is convenient to express density in areometer degrees – 0A. The first two digits (1 and 0) are dropped from the density value.

Milk density is determined at a temperature of (20±5)°C. In cream or milk with high fat content, the density determination is carried out at a temperature of (20±2)°C.

Before determination, a milk sample with a volume of 250 or 500 cm3 (depending on the capacity of the cylinder) is thoroughly mixed and carefully poured along the wall into a dry cylinder, which should be held at a slight angle, to avoid the formation of foam. The cylinder is placed on a horizontal surface, and an areometer is carefully lowered into it to approximately the middle of the areometric scale, then it is left in a freely floating state. The areometer should not touch the walls of the cylinder.

The first reading of temperature and density is carried out 3 minutes after the areometer has stabilized. After that, the areometer is carefully lifted to the level of the ballast inside it and lowered again. After it stabilizes, a second density reading is taken. When taking readings, the eye must be at the level of the meniscus. The readings are taken from the upper edge of the meniscus with an accuracy of half a scale division.

If the milk sample had a temperature above or below 20°C during density determination, then the results must be adjusted to this temperature, i.e., the true density is determined.

By applying a correction (±0.2° A per degree of temperature). If the temperature is above 20°C, the correction is multiplied by the temperature difference and added; if it is below 20°C, it is subtracted.

Task 4. Learn to determine the fat content in milk and cream (sour cream)

The gravimetric (weight) Rose-Gottlieb method is used as an arbitration method, the most accurate one. Its essence lies in extracting milk fat from an ammonia-alcohol solution of milk with diethyl and petroleum ethers, evaporating the solvents, and weighing the residue (fat).

The acidic (butyrometric) Gerber method is the most common method for determining fat in milk and dairy products. The analysis is performed in a special device – a fat meter (butyrometer). The fat separates as a solid layer, and its volume is measured in the graduated part of the fat meter.

The essence of the method lies in isolating the fat in its pure form by freeing the fat globules from protein membranes. Concentrated sulfuric acid (H2SO4) is used as a protein solvent. As a result of the isometric reaction (the temperature rises to 70–75°C), a soluble complex compound of casein and sulfuric acid is formed with the calcium-caseinate-phosphate complex of milk. The excess acid forms isoamyl-sulfuric ester with isoamyl alcohol (C5H11OH), which promotes fat aggregation due to a decrease in surface tension at the interface between the fat and the non-fat phase. As a result, the membrane-free fat droplets stick together (aggregate) faster and more easily. The reaction is accelerated by centrifugation and heating.

Instrumental methods using automatic and semi-automatic devices:

– turbidimetric, based on the photometric measurement of the degree of light scattering by fat globules (light scattering by protein particles is eliminated by adding a special protein solvent).

Turbidimetric devices include the domestic digital fat analyzer TsZhM-1, Danish devices such as "Milko-Tester", and the Japanese fat analyzer "Milko-Checker". Measurement ranges from 0 to 10%, accuracy of determination – 0.06%, analysis time for one sample – 20–30 s.

– ultrasonic, based on measuring the speed of ultrasound propagation in milk at two different temperatures.

Several generations of analyzers have been created: the Pan-3 device (Estonia), FMU-1 (Ukraine), and new-generation analyzers "Laktan" and "Klever" (Russia).

The latest modification of the "Laktan 1-4" device (model 200) also allows for the determination of protein content. The measurement range for mass fraction of fat is from 0 to 20%, SNF (solids-non-fat) – from 6 to 12%, density – from 1.00 to 1.04 g/cm³.

– infrared radiation – based on measuring the degree of absorption of infrared radiation by milk components.

These analyzers include: devices manufactured by "Milko-Scan", English analyzers of the "Multispec" type, and the domestic device "Irma-11". These devices are also intended for complex monitoring of milk composition (fat, protein, lactose, water).

Methods for determining fat content in milk and cream

Precise monitoring of the fat content of raw materials allows for the accurate calculation of dairy farm economics and the adjustment of rations for the dairy herd. Milk quality directly affects its grade and final selling price. In practice, luminescent and acid methods of analysis are used to assess quality.

The primary arbitration method for determining fat remains the acid method using fat analyzers (butyrometers). Research is conducted in parallel using two devices, having previously marked them with a pencil on a special ground glass joint. This eliminates random measurement errors.

1. Using a dispenser, pour 10 cm³ of sulfuric acid into clean fat analyzers, being careful not to wet the neck of the device.
2. Slowly, along the wall, add 10.77 cm³ of the milk under study using a pipette, holding it at an angle to the neck. Do not mix the liquids at this stage and do not blow out the remaining milk from the pipette. Remove the pipette from the neck 3 seconds after it has emptied.
3. Add 1 cm³ of isoamyl alcohol using a dispenser. The level of the mixture should settle 1–2 mm below the base of the neck (if necessary, add a few drops of distilled water).
4. Close the fat analyzers with dry stoppers, wrap them in a napkin, and shake vigorously until the protein is completely dissolved, then invert at least 5 times.
5. Place the fat analyzers with stoppers facing down in a water bath at a temperature of (65±2) °C for 5 minutes.
6. Centrifuge the samples for 5 minutes by placing the fat analyzers into the centrifuge cups with the graduated part facing the center. Position the devices strictly symmetrically opposite each other.
7. Adjust the height of the fat column by moving the stopper so that it is in the graduated part of the scale, and place the fat analyzers back into the bath at (65±2) °C for 5 minutes with stoppers facing down.
8. Extract the fat analyzer, hold it strictly vertically at eye level, and read the measurement at the lower point of the fat column meniscus with an accuracy of up to the smallest graduation.

For determining fat in cream, the algorithm of actions remains the same, but the sample preparation differs. The parameters for preparing components for both types of analysis are given below.

Parameter / Component	Whole milk analysis	Cream analysis
Volume or weight of product	10.77 cm³ milk	5 g cream (+ 5 cm³ distilled water)
Volume of sulfuric acid	10 cm³	10 cm³
Volume of isoamyl alcohol	1 cm³	1 cm³
Required mixture level in fat analyzer	1–2 mm below the base of the neck	4–5 mm below the base of the neck
Type of fat analyzer used	Standard milk	Cream (type 1–40)

If there is an odd number of fat analyzers being analyzed, a balancing device must be placed in the centrifuge. It is filled with water instead of milk, sulfuric acid, and isoamyl alcohol in the same proportions. This is necessary to prevent the centrifuge rotor from wobbling and to avoid equipment damage.

Determination of dry matter: drying and calculation method

Dry matter content determines the total nutritional value of milk. To monitor humidity and dry residue, the classic thermogravimetric drying method or express calculation using formulas are used. Accurate data helps to timely detect the falsification of raw materials with water and to assess the quality of the feed base.

• Water bath temperature — 65±2 °C
• Holding time in the bath — 5 minutes
• Drying temperature — 102±2 °C
• Initial drying time — 2 hours
• Mass of sand in the weighing bottle — 20–30 g

The thermogravimetric method is based on weighing a sample before and after moisture evaporation at a temperature of 102±2 °C. This temperature regime allows for the complete removal of water without destroying the dry components of milk. To ensure uniform heating of the sample, auxiliary materials are used: clean river sand, double gauze, clarified butter, or paraffin.

Procedure for determining dry matter using the oven drying method:

1. Dry a glass weighing bottle with 20–30 g of sand and a glass rod at 102±2 °C for 30–40 minutes, cool in a desiccator, and weigh.
2. Using a pipette, pour 10 cm³ of milk into the weighing bottle, cover with a lid, and weigh again.
3. Thoroughly mix the milk with the sand using the glass rod and place the open weighing bottle in a drying oven at 102±2 °C for 2 hours.
4. Close the weighing bottle with the lid, cool in a desiccator for 40 minutes, and weigh (the rod remains inside at all times).
5. Repeat the drying cycles for 1 hour followed by cooling and weighing until the difference between two weighings is 0.001 g or less.

The moisture content (W, in %) is calculated using the formula:

W = ((m₁ - m₂) / m₁) × 100

where m₁ is the mass of the sample before drying (g), and m₂ is the mass of the sample after drying (g).

The dry matter content (S, in %) is calculated using the formula:

S = ((m₁ - m₀) / (m - m₀)) × 100

where m₁ is the mass of the weighing bottle with sand, rod, and sample after drying (g), m₀ is the mass of the weighing bottle with sand and rod (g), and m is the mass of the weighing bottle with sand, rod, and sample before drying (g).

In production conditions, it is permitted to quickly determine the content of dry matter (S) and solids-non-fat (SNF) using empirical formulas:

• S = (4.9 × F + D) / 4 + 0.5
• SNF = F / 5 + D / 4 + 0.76

where S is dry matter (%).

The next important stage in assessing raw material quality on the farm is determining the protein content in milk.

Determination of protein and lactose content in milk

Milk proteins are casein, globulin, and albumin. The yield of cheese, cottage cheese, and other protein products during processing depends directly on their concentration. To monitor the quality of raw materials, farms use laboratory and calculated methods.

• Average protein content in milk — 3.2%
• Share of casein in total protein — about 82%
• Standard lactose content in milk — 4.7–4.8%
• Freezing point of pure milk — about –0.545 °C
• Density decrease for every 10% of added water — by 3 °A

The following methods are used to determine the mass fraction of protein:

• Kjeldahl method. This is the basic arbitration method. A milk sample is digested in a Kjeldahl flask with sulfuric acid, and the amount of protein is calculated from the volume of released nitrogen (in the form of ammonia), which is determined by titration.
• Colorimetric method. Based on the ability of proteins to bind acidic dyes at a pH below the isoelectric point. After removing the precipitate, the optical density of the remaining solution is measured, and the mass fraction of protein is found using an empirical formula.
• Formal titration method. Formalin is added to react with the amino groups of the protein, which leads to the formation of methylamino acid and an increase in titratable acidity. The amount of protein is judged by the increase in this acidity.
• Refractometric method. Analysis is conducted on AM-2 or IRF-464 refractometers. The method records the difference in the refractive index of light passing through whole milk and serum obtained after precipitating casein with calcium chloride.
• Calculated method. Based on the stable ratio of milk components (protein : lactose : ash as 9 : 13 : 2). The calculation is performed using the formula: Pm = 0.075 × Fm + 0.098 × A + 0.085, where Pm is the protein content (%) and Fm is the mass fraction of fat (%). The coefficients 0.075, 0.098, and 0.085 are empirical.

Lactose (milk sugar) is a disaccharide consisting of glucose and galactose. It provides all the microbiological fermentation processes during the production of fermented milk products and cheeses. Lactose content is determined by chemical (iodometric, Bertrand method) or physical (refractometric, spectrophotometric, polarimetric) methods.

• Iodometric method (arbitration). Based on the oxidation of reducing sugars (lactose and glucose) by iodine in an alkaline medium. The mass fraction of sugar is found by the difference between the amount of iodine taken and the amount unused, which is titrated with sodium thiosulfate.
• Refractometric method. Allows for the rapid determination of lactose in milk serum using devices such as AM-2, IRF, RL, or RLP. The method evaluates the ability of protein-free serum to refract light depending on the sugar concentration.

Monitoring Milk Authenticity and Detecting Adulteration

Only raw milk obtained from healthy cows, to which nothing has been added and from which no natural components have been removed, is considered natural. Any intentional alteration of the raw material composition is considered adulteration. In practice, the most common issues encountered are dilution with water, skimming (or the addition of skimmed milk), and double adulteration.

To detect adulteration, the parameters of the suspicious batch are compared with a stable sample—a standard from the same herd. For analysis, it is necessary to know the density, fat content, total solids, and solids-non-fat (SNF) in both samples.

The degree of adulteration can be estimated by the change in total solids in relation to the stable sample. The main types of adulteration and their impact on total solids are presented in the table.

Type of adulteration	Change in total solids content
Addition of water	Decreases
Skimming or addition of skimmed milk	Slightly decreases
Double adulteration (addition of water and skimmed milk)	Decreases

The degree of adulteration is calculated using formulas by comparing the fat content (Fc and Ff) and SNF (SNFc and SNFf) of the stable and test samples. For double adulteration, the indicator D (content of water or skimmed milk) is also taken into account. Dilution with water is indirectly judged by density: every 10% of added water reduces milk density by approximately 3° A.

The most accurate production method for detecting water in milk is measuring the freezing point (cryoscopic point) using a Beckman apparatus. In pure milk, the freezing point is stable and is about –0.545 °C. When diluted with water, this indicator rises and approaches zero.

Cryoscopic point of milk (freezing point), °C	Amount of added water, %
–0.53	3.63
–0.47	14.54
–0.41	24.45

Monitoring Milk Dilution with Water and Calculating Livestock Productivity

Adding water to milk is a common method of adulteration, which directly reduces the density and nutritional value of the raw material. The exact percentage of extraneous moisture can be determined by the change in the freezing point of the raw material using the cryoscopy method. Natural milk freezes at a lower temperature than pure water, and any dilution shifts this point closer to zero degrees.

Freezing point, °C	Added water, %	Freezing point, °C	Added water, %	Freezing point, °C	Added water, %
–0.52	5.45	–0.46	16.36	–0.40	27.27
–0.51	7.27	–0.45	18.18	–0.39	29.09
–0.50	9.09	–0.44	20.00	–0.38	30.90
–0.49	10.90	–0.43	21.84	–0.37	32.72
–0.48	12.72	–0.42	26.63	–0.36	34.54

For rapid detection of contamination by untreated water from wells or open water bodies, a qualitative reaction for nitrates is used. Pure cow's milk and tap water do not contain nitric acid salts. The presence of nitrates in the sample clearly indicates that the raw material has been diluted with water from natural sources.

1. Measure about 2 cm³ of acid into a clean test tube.
2. In another test tube, pour 2 cm³ of the milk to be tested and add 1 drop of formalin to it.
3. Carefully pour the prepared milk into the test tube with the acid along the wall so that the liquids form two immiscible layers.
4. Evaluate the result: the appearance of a blue-violet ring at the interface of the layers confirms the presence of nitrates in the milk.

In addition to monitoring the quality of raw materials, it is necessary to maintain regular records of individual livestock productivity on the farm. This allows for timely culling, calculating feeding standards, and evaluating the breeding value of the herd. Basic calculations are based on data from regular test milkings.

1. Measure the cow's daily milk yield during the test milking.
2. Multiply the resulting daily yield by 10 days (a decade) to determine the decadal yield.
3. Add the indicators of three decades sequentially to calculate the animal's monthly milk yield.

Based on the monthly data obtained, the cow's total milk yield for 305 days of lactation or for the entire period until the dry-off is calculated. Additionally, the gross production of milk fat and protein in kilograms is determined. This data makes it possible to objectively evaluate the average percentage of fat and protein in milk, both for individual animals and on average for the group.