Moallem, U., Institute of Animal Science, Agriculture Research Organization, Volcani Center, Bet Dagan 50250, Israel, Faculty of Agriculture, Hebrew University, Rehovot 76100, Israel
Folman, Y., Institute of Animal Science, Agriculture Research Organization, Volcani Center, Bet Dagan 50250, Israel
Sklan, D., Faculty of Agriculture, Hebrew University, Rehovot 76100, Israel

We allocated 39 high-yielding individually fed cows to three treatments: control, calcium soaps of fatty acids (CSFA) fed at 2.2% dry matter, and 500 mg of Zn-sometribove (bST) injected every 14 d from 10 to 150 d in milk (DIM). Production of fat corrected milk was increased by 3.0 kg/d in the CSFA group and by 5.4 kg/ d in the bST group. Energy balance was negative during the first 28 to 34 DIM in control and CSFA cows and during 59 DIM in bST-treated cows; minimum body weight, minimum body condition score, and DMI peak were reached 25-28 d later in the bST group. Dry matter intake (DMI) was significantly increased by bST, and during the first 3 wk of treatment the increase in DMI of the bST cows was 46% more than that of the controls. DMI was significantly correlated throughout the experimental periods with calculated energy expenditure in the control and CSFA groups, but only during 54 DIM in the bST group. Furthermore, commencement of the DMI decrease was correlated with the beginning of the decrease in milk production. Gross feed efficiency was significantly higher in the bST group than in the other groups. We concluded that treating high-yielding cows with bST early in lactation increased milk production at the expense of an extensive period of negative energy balance and body weight and body condition decreases despite an increase in DMI after bST treatment.