The exact colostrum composition of carnivores is not extensively known, and data reported in the literature are characterized by high variability
[23][1]. Considering calories, the colostrum energy is nearly equally provided by proteins (50% of colostral calories) and by lipids (40% of colostral calories), and the energy concentration (kcal/mL) is similar in colostrum and in milk, but the pattern during lactation differs slightly between bitches and queens
[6][2]. In dogs, the energy value progressively decreases by 20% during the two first weeks postpartum, whereas in queens, it rapidly drops (−30% over the first 3 days) and then increases progressively over the whole lactation period
[22,23,24][3][1][4]. Considering carbohydrates, lactose represents, as in other animal species, the principal sugar source, although its concentration in bitch and cat milk is about 30% lower if compared to cows’ milk. The lactose concentration in queen and bitch colostrum was 29.9 g/L and 16.6 g/L, and approximately 35–42 g/L in mature milk
[22,23][3][1]. Lactose is the only glucose source for a puppy during the first month of life, as the pancreatic activity of amylase is practically nonexistent and, therefore, other carbohydrates cannot be digested. The digestion of lactose remains constant up to two months of age, and then, there is a sharp decline in intestinal lactase. This sharp decline is responsible for outbreaks of diarrhea in patients over 2–3 months of age who are given a large amount of milk
[25][5]. Vitamin E is required to protect the newborn against oxidative stress and vitamin A is fundamental for growth and development. Furthermore, colostrum of livestock animals was found to contain higher concentrations (approximately 80% more in cows’ milk) of vitamins A and E compared to mature milk
[24][4]. Vitamin A is essential for cellular differentiation, vision, skin health and protein synthesis. A lack of vitamin A causes depression of immune function, mainly cell-mediated function, and alteration of nonspecific defenses. Vitamin A deficiency can lead to metaplasia and keratinization in skin and mucous membranes
[26][6]. Vitamin D is essential for blood calcium regulation through intestinal absorption, which is fundamental for bone development, and is also implicated in a properly functioning immune system. Vitamin D must be supplemented with the diet since puppies and kittens cannot convert dehydrocholesterol in the skin to a more active form of vitamin D
[27][7]. In addition to calcium absorption, in the intestine, vitamin D also acts on phosphate absorption, influencing bone growth, mineralization and remodeling
[28][8]. Calcium-phosphorus ratio is generally stable over time in a bitch’s colostrum and milk (1.5) and rises from colostrum to milk in queens
[23][1]. The micronutrient content of colostrum strongly contributes to puppies’ and kittens’ health and growth.