transfer achieving serum IgG concentrations of 10 mg/mL or greater at 24 to 48 hours is associated with reduced risk for morbidity and mortality.25-27

The Nonimmunological Benefits of Colostrum

Provision of adequate good-quality colostrum results in improved daily weight gain and feed conversion efficiency both pre and post weaning, although the effect of this on joining dates and age at first calving varies between studies.^27-31 Calves receiving larger volumes of colostrum at birth have been shown to require less veterinary input in the preweaning period.²⁸ An increased volume of colostrum fed followed by a higher plane of milk nutrition can significantly increase the average daily weight gain during the first 80 days of life compared to calves fed a lower volume of colostrum followed by the same plane of milk nutrition.

Both serum IgG at 24 to 48 hours and the provision of adequate good-quality colostrum have been associated with increased milk production in the first and second lactations.^28,33 There may not be a direct cause-and-effect relationship between serum IgG and future milk production but rather an indirect relationship in that calves with adequate IgG can develop more efficient metabolic systems, which in turn could contribute to future milk production.

Growth factors and hormones in colostrum and milk have been shown to enhance the development of tissues in the gastrointestinal tract of other species.³⁴ The effect of such bioactive factors in colostrum and milk on the development of specific tissues and/or physiologic functions in the neonate is called the “lactocrine hypothesis.”³⁵ This maternal program­ming is an example of epigenetics in that the dam continues to influence the development of the neonate even after parturi­tion has occurred.

of specific tissues.,

The factors present in colostrum that are likely to influence long-term outcomes include IGF-1, IGF-2, insulin, GH, epidermal growth factor, leptin, and prolactin.³⁸ It is unknown whether all of these factors are absorbed by the gastrointestinal tract of the newborn calf, but studies have shown that serum IGF-1 levels are higher in calves fed colostrum compared to those deprived of colostrum.³⁹ This may be due to increased endogenous production of IGF-1 as a result of increased intake of energy and protein in colostrum, as opposed to direct absorption of IGF-1 itself.

Lactose intake is insufficient to maintain plasma glucose concentrations, and colostrum feeding increases plasma glucose, most likely due to stimulation of gluconeogenesis. Newborn calves are deficient in vitamin A and have a low lactoferrin status. Both are found in elevated quantities in colostrum compared with milk. Lactoferrin is an iron-binding glycoprotein that is a potent antimicrobial factor in the milk cistern and in the alimentary tract of newborn animals. Digestive functions develop during fetal life and undergo the largest morphological and functional changes during the first 48 hours of extrauterine life under the influence of IGF-1, lactoferrin, and other bioactive substances, many of which are present in significantly higher concentration in colostrum than milk. These factors are key regulators in the development of the gastrointestinal tracts of bovine neonates, including stimulation of mucosal and sub­mucosal growth, brush border enzymes, intestinal DNA synthesis, increased duodenal villus size, and apoptosis; protein synthesis and degradation; and digestion and absorption. They also exert systemic effects outside the gastrointestinal tract on metabolism and endocrine systems, vascular tone and hemo­stasis, activity and behavior, and systemic growth.^40-42