Effects of dry matter intake and metabolisable energy density on the concentrations of insulin-like growth factor-I (IGF-I) and blood metabolites in pasture-fed dairy cows

Abstract

Blood metabolites including glucose, NEFA, BHB and urea could be used as indicators of nutritional or energy balance in an animal. The plasma concentrations of IGF-1 may also be a sensitive measure of dietary changes. The relationship between IGF-I and the above metabolites in the blood, and their potential in monitoring dietary effects in 32 pasture-fed Holstein-Friesian cows in early lactation were investigated in a 5-wk study. The cows were randomly assigned to four dietary sub-groups and fed one of 4 rations varying in dry matter (DM) and metabolizable energy (ME) concentration (LL: 16.6 kg DM and 174 MJ ME; HL: 17.3 kg DM and 181 MJ ME; LH: 15.4 kg DM and 183.1 MJ ME; HH: 17.9 kg DM and 213.3 MJ ME, with the first letter indicating DM and the second ME). The four rations consisted of pasture, hay and pelleted cereal grain. Plasma IGF-I concentrations were positively associated with glucose (R = 0.587; P<0.01) but negatively associated with BHB (R = - 0.588; P<0.01) and urea (R = -0.372; P<0.05) concentrations at d 35. The relationship between IGF-1 and NEFA concentration was not statistically significant (R = 0.007: P.00.05) at d 35. ME density had grater influence on the proportional changes in blood IGF-1, glucose, BHB and urea concentrations, than changes associated with DM intake. Plasma IGF-I had a higher R2 estimate in its model than any other metabolite at d 14 (R2 = 0.528) and d 35 (R2 = 0.649) of the study, except for BHB at d 35 (R2 = 0.708). The changes in IGF-1 with diet were over a greater range than with the other metabolites, and were indicative of a stronger association of IGF-I with dietary changes.