Abstract: The aim of this study was to evaluate the effect of daily supplementation of a devitalized strain of Saccharomyces cerevisiae on milk yield and composition of Friesian-Holstein lactating cows. Average Days In Milk (DIM) and Body Weight (BW) of cows were 98±24 days and 619±13.2 kg. Prior to the experiment, the effects of the yeast culture added to the diet were investigated in 2 in vitro experiments. In the first experiment, 6 samples of rumen fluid were used to determine the DM, CP and NDF degradability (IVDMD, IVCPD, IVNDFD) of Total Mixed Ration (TMR) at 0 and 48 h with the addition of 0 g (Y0) and 1 g (Y1) of yeast culture. In the second experiment, free, total and microbial ATP production were used for the evaluation of microbial activity in rumen fluids after 0, 8, 24 and 48 h incubation. In the 4 weeks trial, 10 multiparous cows were assigned to a Control diet (C) and 10 to the experimental diet (YC = C+35 g/cow/day of yeast culture). TMR on a Dry Matter (DM) basis consisted of corn silage (42.3%), ryegrass hay (14.1%), corn meal (22.1%), soybean meal (17.9%) and a mineral/vitamins mix (3.6%). Crude Protein (CP) and ENl were 14.6% and 1.56 Mcal kg-1 DM, respectively. Cows were individually fed once daily and milked at 7 and 19 h. In vitro experiments showed that the addition of 1 g YC to the rumen fluid increased IVCPD and IVNDFD after 48 h of incubation but did not influence IVDMD. Free, total and microbial ATP values showed a continuous decrease during the 48 h of the trial but the addition of YC proved to be effective in slowing the decrease. Milk yield (31.9 and 33.4 kg day-1, for the C and YC group), 4% fat corrected milk (FCM: 30.3 and 31.7 kg day-1) and energy corrected milk (ECM: 32.9 and 34.5 kg day-1) were significantly different between groups. Dry Matter Intake (DMI), milk fat and protein percentage were similar in both groups. Feed efficiency (ECM kg-1 DMI) was higher in YC group than in C.
R. Fortina, L.M. Battaglini, F. Opsi, S. Tassone, M. Renna and A. Mimosi, 2011. Effects of Inactivated Yeast Culture on Rumen Fermentation and Performance of Mid-Lactation Dairy Cows. Journal of Animal and Veterinary Advances, 10: 577-580.