EFFECT OF PREPARTUM AND POSTPARTUM DIETARY ENERGY ON GROWTH AND LACTATION OF PRIMIPAROUS COWS

Sixty-seven Holstein replacement heifers (19 mo) were fed a standard ( 59.7% TDN) or a high energy (69.3% TDN) diet until parturition. After parturition, primiparous cows were fed either 0 or 2.8% supplemental t allow for 150 d in a 2 x 2 factorial arrangement with prepartum treatm ents. High energy prepartum increased BW (693.5 vs. 663.7 kg) and body condition scores (3.72 vs. 3.55) at calving. Increased energy density of the diet prepartum did not affect milk yield or composition. Suppl emental dietary fat postpartum increased milk yield approximately 1.5 kg/d, but the response was not observed until 7 wk postpartum. Heifers fed the standard diet prepartum and higher DMI than other treatments. Heifers fed high energy prepartum and supplemental fat postpartum los t the greatest BW and body condition from 1 to 5 wk postpartum. Heifer s fed high energy diets prepartum had higher concentrations of blood N EFA, BHBA, and liver triglycerides. Increases in BW and body condition scores at calving above approximately 660 kg and 3.5, respectively, d o not enhance lactation performance. When 2.8% supplemental fat was fe d to primiparous cows, milk yield improved approximately 1.5 kg/d afte r wk 7 of lactation.