Influence of dietary starch contents on milk composition of Friesian cows in early lactation

Abstract

The aim of this research was to evaluate the effect of the modification of diet starch content on milk composition and on its nitrogen and mineral fractions. Ten Italian Friesian primiparous cows were randomly assigned to two groups and fed a basal total mixed ration, (BSD, basal starch diet, 24.9% starch/DM) until 42 days in milking (DIM). At 43 DIM, 5 animals (control group, CTR) continued to receive the same ration and the remaining 5 cows (experimental group, EXP) were fed a low starch diet (LSD, 21.0% starch/DM) until 65 DIM, followed by a high starch diet (HSD, 28.3% starch/DM) 66 to 85 DIM. From 86 DIM until 94 DIM, cows of the EXP group returned to the BSD. Milk samples were collected at 37, 50, 60, 70, 80, 94 DIM. Starch intake was lower for EXP at DIM 50, 60 and higher at 70 and 80 DIM (P < 0.01). Milk yield and fat corrected milk (FCM) did not vary between groups and times of sampling, but HSD caused a significant (P < 0.05) reduction of milk fat in the EXP animals. NPN and MUN contents were affected by dietary treatments at 80 DIM (P < 0.05), being higher in CTR and lower in EXP group in comparison to their basal values (37 DIM). The αs1-casein percentages at 80 and 94 DIM increased in the EXP but not in the CTR group, and a marked decrease of αs2- casein percentage for the EXP group at 94 DIM was observed (P < 0.05). Milk sodium content decreased at 80 and 94 DIM and the sodium to potassium ratio was reduced after the return to the basal diet in the EXP group (94 DIM), indicating that dietary starch variations can be involved in the control of epithelium integrity of mammary gland in early lactation.