Uptake of Passive Immunity by the Compromized Newborn Animal

Circulating immunoglobulins constitute a key element in the host defence against environmental antigens. Before birth, the fetus is well protected from antigens by the protective barrier of the placenta. Just after birth, the newborn must be able to respond immunologically to a massive invasion of potentially harmful antigens and microorganisms from the surrounding environment. However, the innate immune defence is immature at the time of birth and some passive immunization from the mother is required until an active immune system is developed. Humans and certain other species are born with passive immunity in the form of maternal immunoglobulins transferred across the placenta before birth. In the large farm animals, the placenta does not allow transfer of maternal immunoglobulins before birth. The newborns from these species therefore depend entirely on the transmission of immunoglobulins from mother's colostrum transported across the small intestine immediately after birth. In the large farm animals, intestinal immunoglobulin absorption occurs mainly by a non-specific endocytosis of macromolecules, but the details of the absorption process and its cessation after 1–2 days of colostrum exposure ('intestinal closure') remains poorly understood. Little is known about both the feed and animal factors affecting the macromolecule absorptive capacity of the small intestine. This knowledge is important because a poor absorption of immunoglobulins from colostrum is known to increase neonatal disease susceptibility and mortality. The aim of this review is to provide information about the ability of the 'compromised newborn farm animal' to absorp colostral immunoglobulins. Stressful delivery, premature birth, fetal growth retardation and in vitro embryo production are factors that potentially lead to a compromised newborn animal. The available literature indicates that the ability of the small intestine to absorb macromolecules is severely reduced in response to premature birth and also negatively affected by some forms of metabolic and environmental stress after birth. The ability to take up immunoglobulins is also severely impaired, in both premature and term animals, if immunoglobulins are absorbed from diets other than mother's colostrum. On the other hand, fetal growth retardation, in vitro embryo production, or the birth process does not reduce the ability of the newborn intestine to absorb immunoglobulins from colostrum. Knowledge about both the diet- and animal-related factors which influence intestinal immunoglobulin uptake is important to improve the clinical care for both the normal and the 'compromized' newborn farm animal.