Relationships among early lactation milk fat depression, cattle productivity and fatty acid composition on intensive dairy farms in Northern Italy

An observational study was conducted on three northern Italy Holstein dairy herds to evaluate the impact of milk fat depression (MFD, defined as milk fat lower than 3.2) on milk production and fatty acids (FA) composition in order to investigate the practical consequences and the possible origin of this phenomenon. The diet composition and the individual milk production and composition, were monitored during the first six months of lactation. Two virtual groups were created in each farm on the basis of the milk fat levels observed during the first two months of lactation (higher or lower than 3.2). Individual milk samples were taken from 16 animals /group/farm for composition and fatty acid analysis. The diet of Farm A, characterized by the highest average prevalence of MFD (33.1%), showed the highest acidogenic attitude (high NFC, low NDF, low peNDF8). The milk fat level differed significantly per group over time in all farms. Cattle with MFD showed tendentially lower energy corrected milk output and greater concentrations of C12:0÷C15:0, C18:1trans10, total polyunsaturated, total odd chain (OCFA), total n-6 as well as OCFA/branched chain fatty acids, and C18:1trans10/C18:1trans11 ratios. Farm A milk fat showed higher values of C12:0, C13:0, C14:0 and C15:0. It appears that MFD cattle are characterized by lower mammary energy output and a milk FA profile similar to cattle fed acidogenic diets, thus suggesting an alteration in the rumen fermentation patterns, as occurs in acidotic cattle