The Influence of Active Immunization Against Adrenocorticotropin Hormone on Galactopoiesis in Merino Ewes

Abstract

Background: Chronic active adrenocorticotropin hormone (ACTH) immunization of ewes (with a previous history of immunization) resulted in elevated titres of antibody against ACTH, which induced a reduction in circulating levels of cortisol. Objectives: The aim of the present study was to investigate: a) the influence of active immunization against ACTH on milk production of the ewe as assessed by milk intake of the lamb measured with two different methods, b) whether the stimulation of levels of β -end and α-MSH in the circulation can result in a similar increase in the expression of these peptides in the milk of the lactating ewe, thereby producing a milk with high analgesic properties. Materials and Methods: Ten primiparous Merino ewes (4-5 years old) during their first 5 weeks of lactation were used in the experiment. Milk intake of each lamb can be used to give the ewe’s milk yield per unit time, and this can be used for secretion of peptides over time. This was determined by two different techniques: the deuterium oxide method and the weigh-suck-weigh method. β -end, α-MSH and cortisol were measured in blood samples and β-end, α-MSH in milk samples using RIAs (Radio Immune Assay). Results: Plasma β-end and α-MSH in ACTH-immune animals increased to 3 and 38-fold respectively, although the level of α-MSH is most likely exaggerated by the presence of α-MSH antibodies in the ACTH immune plasma, as α-MSH comprises the N-terminal 13 amino acids of ACTH. Antibodies also were detected in the plasma of lambs of immune ewes after birth, at levels, which were comparable to those measured in the ewes during the period of colostrum production and thereafter decreased to much lower levels by the end of the experiment. Plasma β-end and α-MSH in the lambs of immune ewes were significantly higher than those measured in the lambs of control ewes. Conclusions: The immunization procedure had no effect on feed intake, live weight gain and milk production of ewes nor was the growth rate or milk intake of the lambs altered. The expression of β-end and α-MSH in milk was also unaffected by the high concentrations of these hormones in the circulation of immune ewes.