Adjusting the ration of cows before calving in terms of calcium and energy is very important due to the significant increase in the need of calcium in cattle during calving.
One of the things that is of the highest importance when adjusting the ration of cows before calving is adjusting the ration according to the significant increase in the calcium requirement of the animal at the time of calving. A large amount of calcium is needed to produce milk because milk contains approximately 1.21 grams (in Holstein cows) and 1.45 grams (in Jersey cows) of calcium per kilogram of milk produced.
Why should you pay attention to the calcium in the cow’s diet before calving?
Calcium is an essential mineral that contributes to bone strength, muscle function, immune system function and many other vital processes. If the body faces calcium deficiency, the performance of these processes will be limited. Lack of total blood calcium is called clinical or subclinical hypocalcemia. In clinical hypocalcemia (milk fever), the total concentration of calcium in the blood serum is less than or equal to 5.5 mg/dL. In subclinical hypocalcemia, the total concentration of calcium in the blood serum is less than or equal to 8.5 mg/dL.
Milk fever can also lead to death if not treated quickly, while subclinical hypocalcemia is associated with a high risk of other metabolic abnormalities in newborn cows such as ketosis, uterine infection, udder displacement, and placental abruption. In addition, subclinical hypocalcemia affects a higher percentage of the herd than milk fever (65% vs. 2%) and is difficult to diagnose because no obvious symptoms are observed in cows. The total cost of subclinical hypocalcemia includes reduced milk production and treatment of related diseases. This is because a higher percentage of the herd will suffer from subclinical hypocalcemia and it will be more costly to the cow than clinical hypocalcemia.
In 1991, researchers at the University of Wisconsin linked the prevalence of hypocalcemia directly to prenatal dietary calcium. So that they believed that the amount of 1.6% calcium (based on dry matter) has the highest risk and recommended that calcium in the diet should be less or more than this amount to reduce the risk. This finding confirmed important recommendations to limit dietary calcium intake below maintenance requirements (less than 40 grams per day) to stimulate parathyroid hormone secretion. Although this approach was effective in preventing milk fever, keeping calcium intake low is a major challenge. This approach has made it possible to prevent the occurrence of hypocalcemia by using an acidogenic diet before birth.
Important ration anions are: chlorine, sulfur and phosphorus. Important cations include sodium, potassium, calcium and magnesium. The anion-cation difference is calculated by subtracting the weight equivalency (molecular weight divided by the ion charge) of anions from the weight equivalency of cations. Diets whose cations are more than their anions or have a positive anion-cation balance are known as alkaline diets. In other words, diets whose cations are less than their anions or have a negative anion-cation balance are known as acidogenic diets.
What is an acidogenic diet?
Acidogenic diet reduces the pH of urine and blood. In most cases, the use of sulfate anions and chloride supplementation reduces the anion-cation difference (DCAD) of the diet. Feeding acidogenic diets puts cows in a state of compensated metabolic acidosis. In this situation, the cow’s body adjusts to changes in dietary minerals using a natural buffering mechanism controlled by the kidney. In this way, with the help of changing blood calcium concentration, due to calcium absorption from bones and increased intestinal absorption, more calcium enters the blood, both of which are controlled by parathyroid hormone. This mechanism leads to increased calcium efflux and prepares the calcium regulatory systems for the postpartum response. On the other hand, with the help of the kidney, it maintains calcium homeostasis before delivery. Compensated metabolic acidosis increases the secretion of parathyroid hormone and the sensitivity of bone and kidney tissues to parathyroid hormone.
These rations increase the metabolism of vitamin D in the body. The reason is that acidic rations cause the absorption of calcium from the bones of the body. Now this cow, which is close to giving birth, after giving birth, the amount of calcium in the body decreases again with the secretion of milk, so to compensate for this The action and prevention of bone fractures after childbirth should increase vitamin D metabolism.
Effect of diet acidity level
All adjusted acidogenic diets do not prevent metabolic acidosis to the same extent. Two of the most common approaches to feeding acidogenic diets include feeding “fully acidified” and “partially acidified” diets.
A “partially acidified” approach (in which urine pH is maintained in the range of 6 to 7) generally achieves a DCAD of 0 to 5 mEq per 100 g of DM and may help prevent hypocalcemia. be clinically effective. In the “fully acidified” approach (in which the pH of the urine is maintained in the range of 5.5 to 6), DCAD is generally maintained in the range of -10 to -15 milliequivalents per 100 grams of dry matter and in the prevention of clinical hypocalcemia and significantly reducing the prevalence of subclinical hypocalcemia is effective.
Total acidification or partial acidification of DCAD can be highly variable due to forage and other feed ingredients as well as environmental and management factors. Urine pH is the most basic tool to determine the appropriate amount of ration DCAD.
Many anionic supplements can be used to achieve a completely acidified diet, but all of them do not sufficiently maintain the dry matter consumed by pre-calving cows, which leads to the uniformity of urine pH during the day. This is an important point to consider when choosing an acidogenic supplement.
Recent research from Cornell University has shown the benefits of eating a fully acidified acidogenic diet. The results of the research showed that decreasing the pH of urine before calving leads to an increase in the consumption of animal feed after calving and milk production, while it has the least effect on the consumption of animal feed before calving.
Dietary energy regulation
It is necessary that the pre-fresh ration contains a higher concentration of energy, usually the most economical way to meet this need is NFC.
NFC levels in pre-fresh rations need to be higher for 3 different reasons:
1- Propionate (a volatile fatty acid that is mainly produced from NFC fermentation) increases the length of rumen villi. Ruminal villi are finger-like protrusions that absorb volatile fatty acids from the rumen, stimulating the growth of villi before calving increases the absorption of volatile fatty acids after calving. Volatile fatty acids are used as an energy source for cattle, and propionate is especially needed to reduce ketosis. Removing stomach acids is also important for controlling stomach acidosis.
2- Higher levels of NFC help the adaptation of rumen microbes to the lactation diet. Increasing the growth of NFC-fermenting microbes before calving reduces the occurrence of acidosis and feed-related problems when a cow calves and consumes a diet with more NFC.
3- Propionate is used to obtain energy from body fat and reduce ketosis. NFC levels during the pre-fresh period should increase to 32 to 33 percent of dry matter. In a normal diet, this amount is equal to 3.6 to 4.5 kilograms of added seeds. In the diet of Dosha cows, it is important to include a mixture of NFC sources. Some of them are fermented quickly (such as sugars and corn with high moisture) and some of them are fermented more slowly (such as corn flour), this increases the digestion of NFC, the number of rumen bacteria and the amount of microbial protein available for use by the gut.
The rumen should be stimulated with a diet with a higher energy concentration to lengthen the rumen papillae. This increases the absorption level of volatile fatty acids. Since cows receive high energy rations after calving, the change of microbial population should also occur.
Adding food supplements to animal feed
Adding 500 to 700 grams of calcium propionate (or its equivalent commercial supplement) in pre-fresh diets provides a higher dose of propionate, which reduces acute and chronic ketosis. Liver propionate is used to convert acetate from mobilized fat into energy instead of converting acetate to ketones.
Niacin is a water-soluble vitamin produced by rumen microbes. The need for niacin, especially during the transition period, is more than what is produced in the rumen. Niacin can help the liver in the metabolism of fats, and therefore adding 6 to 12 grams of niacin to the diet can reduce blood ketone levels.
Choline is a water-soluble vitamin that, like niacin, is produced by rumen microbes. As with niacin, researchers now believe that rumen microbes cannot make enough choline to meet all of the cow’s needs, especially during the transition period. Choline is present in a part of the cell wall structure, especially cell membranes. Choline is involved in the use of fats and their transfer from the liver in the form of lipoproteins, but with very low density (VLDL). Of course, choline is especially vital for cows during the transition period to help them clear the liver of accumulated fat to prevent fatty liver syndrome. Rumen bacteria break down most of the choline in the diet consumed by cows. Therefore, the added choline should be fed in a protected form against the rumen.