Effects of different feeding regimes applied during rearing of dairy calves

Abstract

Metabolic programming is defined as an early stimulus with long term effect. In dairy cows, feeding in the preweaning period has long term effects on later milk production. However, the influence on metabolic and endocrine changes is not fully clarified. The aim of this thesis was to investigate the influence of different feeding regimen on performance data and metabolic and endocrine variables in dairy calves and around the first lactation. Special attention was directed to insulin sensitivity and adiponectin, an adipokine with insulin sensitizing properties. However, its concentration and changes with age were unknown in calves. To characterize the effects of colostrum feeding and of different feeding intensities before weaning, samples from different trials were used; In Manuscript I, twenty dairy calves fed with colostrum and then restrictively with milk replacer (MR; 130 g/L, 6 L/d) for 110 d post natum (p.n.) were studied. In addition, calves receiving either colostrum (n = 7) or formula (n = 7) until d 4 p.n., and calves born either at term (n = 7) or preterm (n = 7) receiving their first colostrum only at 24 h p.n. were included. Blood and milk samples were taken and adiponectin was measured by an in-house developed ELISA and by Western blot to assess the different molecular weight forms. In Manuscripts II, the influence of different feeding regimen on performance including milk yield in the first lactation was investigated; in Manuscript III, the animal trial from manuscript II was extended to assess metabolic and endocrine variables. The experiment comprised dairy calves fed at 3 different regimen until d 25 p.n. (MR restricted, n = 20; MR ad libitum (ad lib), n = 17; whole milk (WM) ad lib, n = 20) and observed thereafter until d 110 p.n. The female calves (n = 28) were further pursued in their first pregnancy from 3 months ante partum until 10 weeks post partum. Blood samples were taken in regular intervals. During calfhood, glucose tolerance tests and insulin tolerance tests (only male calves) were done and liver biopsies were taken. Performance data like body weight, average daily gain, food and energy intake, milk yield were recorded and economic outcomes were calculated. The postpartal increase in adiponectin serum concentrations depended on colostrum intake suggesting a transfer of colostral adiponectin to the calves’ circulation. The different feeding regimen yielded differences in the metabolic and endocrine variables as well as the performance data but these were not sustained at later age. Around the first lactation the metabolic and endocrine variables were not different, albeit the heifers from in the WM-ad lib group had numerically greater milk yields thus compensating the higher costs during the rearing period. The present thesis provides information about the circulating adiponectin concentrations in dairy calves and about the effects of different feeding regimen on performance and endocrine and metabolic variables in blood.