Physiology of lactation in cattle

Cow’s milk is one of the most consumed foods in the world because of its high nutritional value. Besides, due to its composition, it is considered the most nutritious food source for mammals including humans. For cows to produce milk, many physiological components are needed, which we will summarize here.

It should be noted that the ruminant industry has managed to genetically select some breeds of cattle more specialized in milk production. For this reason, some breeds produce more than others. It is also well known that the composition of milk among the different bovine breeds can have significance differences.

Anatomy of the mammary gland

The functional unit of the mammary glands corresponds to the alveoli. These are the fundamental units in the secretion of milk from the gland. The breast alveoli develop embryologically from the layer of the ectoderm, the same that gives rise to systems such as the skin and the nerves. Also, next to these, the nipples are developed which are the connection between the outside with the internal milk secretory system.

The passage between milk formation and distribution is made possible by the connection between the alveoli and the nipple. In cows, the nipples have an opening where the milk drains.

Cows have developed specialized milk storage structures called cisterns. The cisterns are located in the ventral part of the gland and all the ducts reach these. The function of cisterns is to store large quantities of milk before milking.

Cows have two pairs of mammary glands, that is, four glands in total. All this structure described above is called udder.

Due to the large milk production in the cows, they have developed anatomical mechanisms specialized in supporting the weight of the udder. This task is performed by the internal suspensory ligament and the lateral suspensory ligament. This suspension system must support the weight of the udder that can even reach 25 Kg just before milking. Occasionally, some abnormalities in this suspensory system can lead to udder problems.

Physiology of milk production

Milk must be first developed in the cow to be secreted through the mammary gland. The ovaries will increase the production of estrogen and progesterone. The production of growth hormones and adrenal corticosteroids is also increased. All these hormonal components are responsible for the proliferation of the udder tubular system. Besides, progesterone and prolactin are the hormones that promote the development of the alveoli.

However, this development in puberty is partial. The cow must be pregnant to fully develop the mammary gland. Then, the secretion of milk can be evidenced in the last part of the gestation thanks to the increase of prolactin.

Several mechanisms regulate milk production in cows. One of these mechanisms is regulated by prolactin. When the nipple is stimulated by the calf or milking system, dopamine is blocked in the brain. This increases the production of prolactin, which is responsible for the mobilization of milk to the nipple.

Another important mechanism in milk production in cows is constant stimulation. If a cow lasts more than 16 hours without milking, the stimulus decreases, and it will start to stop producing milk. The stimulation in the nipple generates contraction of the alveoli. When there is a milking or suction stimulus, these nerve signals travel to the hypothalamus where dopamine is blocked. When this hormone is blocked, prolactin is released and the vasoactive intestinal peptide facilitates the production of milk.

Composition of the milk

The most important component of cow’s milk is fat as a source of energy. This fat is vital for the young animals due to this nutritional value as it provides a considerable energy contribution.

On the other hand, lactose is the main carbohydrate present in mammalian milk. Lactose is composed of glucose and galactose.

Regarding proteins, the main one is casein, which contains essential amino acids. Milk is also an important source of calcium, phosphorus, riboflavin (Vitamin B12), Vitamin A, and Vitamin B1 (Thiamine).

All these nutritional aspects make milk one of the most complete foods in the world. However, for its production the intestinal and liver health in the cow must be ensured. It is recognized that among the non-genetic factors most involved in breastfeeding is cow feeding. Not only should you ensure a complete and balanced diet with all the nutrients, but maintain the health of the intestine as it is where all these are absorbed.

On the other hand, the liver plays an important metabolic role for animals, assimilating, breaking down and storing nutrients. In addition, it is the main detoxifying organ. If a healthy state of the liver is ensured, a quality milk production will also be obtained

The colostrum

Milk formed before birth is called colostrum. In this process, there is a concentration of several and essential substances, including antibodies. Besides, due to the type of bovine placentation, the transference of immunoglobulins from the cow to the fetus is not significant. Therefore, the way the mother transfers immunoglobulins to the fetus is through colostrum.

Newborns should consume milk in less than 24 hours to be able to absorb these immunoglobulins by the digestive system. The main immunoglobulins of colostrum are IgA, IgM and IgG. If the time is longer, the intestinal epithelium will prevent the passage of these important proteins and the newborn will be unprotected. It should be noted that the colostrum of the cow also has compounds such as lysozymes, lactoferrin, and lactoperoxidase which have antibiotic effects.

Colostrum stands out for its high composition in fats, vitamins, and proteins. On the contrary, its proportion of carbohydrates is low.

Breastfeeding

The cow starts breastfeeding with the production of colostrum that will last a few days. Afterward, the colostrum will disappear, giving rise to the common milk. That is, as the days go by, milk will change in its composition and appearance. About 3 to 4 weeks after starting breastfeeding, the cow has its peak milk production.

The breastfeeding period lasts approximately 305 days. After this period, the cow enters the so-called “dry period” where the cow will not produce milk. In the dry period, the udder is left to rest and recover, preparing for the next production period. To achieve the dry period, the cow should not be milked which inhibits production.

Diseases of the mammary gland

Mastitis is the main disease of the mammary gland. Besides, subclinical and clinical mastitis are the pathologies that have the greatest incidence in dairy cattle farms.

There are various guidelines to mitigate the impact of mastitis, such as:

1. Identify mastitis-causing pathogenic micro-organisms
2. Identify and reduce predominant reservoirs
3. Identify and limit risk factors for transmission
4. Promoting cow defense mechanisms
5. Ensure good nipple condition
6. Implement Good Livestock Practices focused on milking
7. Reduce herd stress
8. Implement a rigorous milking hygiene plan
9. Review and maintenance of automatic milking systems
10. Frequent diagnostic tests for subclinical mastitis

Other measures that can be implemented and further explanation of mastitis can be read in : Bovine mastitis: a worldwide disease

CONCLUSIONS

Milk is one of the most complete foods in the world. The physiological mechanisms that regulate its production in cows are complex and extensive. There are several cascades and hormonal cycles in the cow’s body that favor the start or end of breastfeeding. It is of great value for the producer to understand these physiological cycles to favor the different stages of production.

References:

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