Mammary gland : physiology and anatomy

Dry Period

The mammary gland of the dairy cow requires a nonlactating (dry) period prior to an impending parturition to optimize milk production in the subsequent lactation. This period is called the dry period, and it includes the time between halting of milk removal (milk stasis) and the subsequent calving. This period allows regenerating secretory tissue of mammary gland. In a 5-points notation scale for body condition score in dairy cows, the goal for ideal body condition score for the dry cow is 3.5. To achieve satisfactory health and performance early in the subsequent lactation condition score must fall between a minimum of 3 and a maximum of 4. Cows having a thin body condition at the end of lactation require a dry period to replenish their body supplies. Body fat can be utilized for milk production: 1 kg of body fat supplies energy to produce approximately 7 kg of milk. However, overconditioning may be detrimental, especially for heifers entering the dairy. A cow that is overconitioned at calving is also more susceptible to metabolic diseases, particularly ketosis.

The normal procedure to dry off a cow is to withdraw all grain and reduce the water supply several days before the start of the dry period. This drastically reduces the milk production during that time. Then milking is halted about 45 to 50 days before expected date of parturition. Infusion of the udder with antibiotics can help prevent infections that may occur in early involution. After milking is stopped intramammary pressure increases, milk products accumulate in the gland, and further milk secretion is inhibited. Sometimes if the udder becomes extremely congested, it may need to be re-milked. However, this practice stimulates further milk synthesis because intramammary pressure is reduced and pituitary hormones (oxytocin and prolactin) are released.

Pay attention during the dry period

  • There is an optimum length of dry period;

  • A dry period shorter than 40 days will decrease subsequent production (also long dry periods over 70 or 80 days will result in lowered production in the next lactation);

  • Changes occur in the mammary gland during the dry period which influence mammary cell proliferation and mammary function in the subsequent lactation.

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