Milk acidity is an important indicator reflecting the f […]
Milk acidity is an important indicator reflecting the freshness of the milk. The national standard stipulates that the acidity of raw milk and finished liquid milk is 12-18oT. If it exceeds this range, it is considered unqualified. The milk that has just been extruded has an acidity of 16-18oT, which is considered to be low acidity below 16oT, and the acidity of the microorganism increases as the fermentation progresses. Because milk acidity is one of the indicators for milk collection, the farm pays great attention to the stability of milk acidity. In addition to the effects of microbial growth, dairy cow's acidity, individual and feeding management factors also have a certain impact on acidity. The following factors affect the acidity of milk by Freezing iqf of manufacturers:
As the number of lactating days increases, the probability of acidity also shifts from the higher acidity zone to the lower acidity zone, ie, the acidity is slightly lower than that of the previous lactation. The acidity of colostrum is higher, the average value of colostrum in secondary extrusion is 0.44%, the second average is 0.26%, and the third is 0.21%, which gradually decreases in the first 15-20 days of lactation. The acidity of the whole lactation gradually decreased, and the acidity decreased significantly during the early lactation. From the second month to the seventh month, the acidity was relatively stable.
When the yield is low, the ratio of low acidity is large, and when the milk yield is high, the ratio of high acidity is large. Therefore, when the yield of dairy cows is from the peak of lactation to the low lactation, the acidity tends to decrease. When the protein rate is low, the ratio of low acidity is large; when the protein is high, the ratio of high acidity is large.
Dietary nutritional imbalance: The protein content in the diet is too high or the quality is poor, but the energy is insufficient, which leads to the low efficiency of the use of ammonia by the microorganisms in the rumen, and excessive ammonia enters the blood, causing the blood to be alkaline. Insufficient dry matter intake and lack of nutrition in dairy cows' diets result in low acidity of raw milk.
Acid-base balance disorder: When the rumen pH is lower than 6, ammonia is present in an ionic state and rarely absorbed into the blood through the rumen mucosa. However, when the concentration of ammonia ions in the rumen is too large and the pH exceeds 6.5, the rate of absorption of ammonia rapidly increases. In order to increase milk production, dairy farmers often increase the amount of concentrate feed and add a large amount of NaHCO3 to prevent acidosis, but the pH in the rumen increases, the ammonia absorption rate increases, the ammonia in the rumen increases, and the blood ammonia content increases. The partial pressure of CO2 reflects the blood-salt acid-base balance of dairy cows. In summer, cows are in a state of heat stress, the frequency of respiration increases, the amount of CO2 exhaled is higher than the amount formed in the body, and the partial pressure of CO2 in the blood is reduced, causing decomposition of carbonic acid in the blood, resulting in Respiratory acidosis, blood pH rise, resulting in reduced milk acidity.
Dietary anion and cation difference (DACD) refers to the main action (Na+, K+, Ca2+, Mg2+) millimoles and main anions (Cl-, S2- and PO43- per kilogram or per hundred grams of dry matter in the diet). The difference between millimoles. Studies have shown that the pH, urine pH, and HCO3- concentration in the blood of dairy cows increase with the increase of DCAD in the diet. With the increase of dietary DACD, the intake of Na+ also increases, so the glomerular filtration The concentration of Na+ in the decontamination also increased, and Na+ increased from the renal tubules and exchanged with H+ to promote the secretion of H+ by renal tubular epithelial cells, which promoted the reabsorption of carbonate, resulting in blood pH and The concentration of bicarbonate increases, and the extracellular fluid of cows tends to change in alkaline
Due to the influence of the physical and bacterial numbers and virulence of dairy cows, the inflammatory process of tissues is aggravated, the vascular permeability is increased, the body regulates by itself, and a large number of white blood cells ooze out, which causes the number of somatic cells to increase sharply, with the increase of inflammatory reaction. The pH gradient difference between blood and milk is reduced, resulting in a gradual increase in the pH of the milk, which tends to a blood value of 7.4 and a low milk acidity.