Composition of natural milk in cats and dogs

Immediately after parturition, the dam produces a special type of milk called colostrum. Colostrum is vitally important for the provision of passive immunity to newborn puppies and kittens. Passive immunity is provided in the form of immunoglobulins and other immune factors that are absorbed across the intestinal mucosa of the newborns. Most of these factors are large, intact proteins. Once absorbed into the body, these factors offer protection from a number of infectious diseases.

In such species such as humans, rats, rabbits and guinea pigs, a significant proportion of p√Ęssive immunity is acquired in utero. In contrast, puppies and kittens, like pigs, horses and ruminant species, obtain the greatest proportion of maternally derived antibodies through the colostrum. These differences are due to the types of placentas found in different species, and they reflect the number of placental layers the antibodies must transverse to reach developing fetuses. The dog and cat have an endotheliochorial placenta consisting of four layers, which allows only about 10% to 20% of passive immunity to be transferred in utero. Therefore, for puppies and kittens, the major proportion of passive immunity is acquired after birth via the colostrum.

In older neonates and adult animals, normal digestive processes would result in the complete digestion of the immunological compounds found in colostrum, making them unavailable to the body as immune mediators. However, the intestinal mucosa of newborn dogs and cats is capable of absorbing intact immunoglobulins provided by colostrum. The time during which the newborn’s gastrointestinal tract is permeable to the intact immunoglobulins in colostrum is very short. The term closure refers to the change in the gastrointestinal tract’s absorptive capacity that precludes further absorption of large, intact proteins. The mechanisms behind closure are not fully understood, but they appear to be related to the increasing levels of circulating insulin that appear after the initiation of suckling. This limits the ability of the neonatal intestine to absorb intact proteins to about the first 48 hours of life. Therefore, it is vitally important that newborn puppies and kittens receive adequate colostrum as soon as possible within the first 1 to 2 days afeter birth.

In addition to the immunological benefits of colostrum, the volume of fluid ingested immediately after birth contributes significantly to postnatal circulating volume. It is believed that a lack of adequate fluid intake shortly after birth may contribute to circulatory failure in newborns. Water turnover is also very high in newborn puppies and kittens, necessitation a consistent fluid intake to maintain normal blood volume throughout the neonatal period. For this reason, the volume of milk produced by a bitch or queen is as important as its nutrient content.

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