PROTEIN DEGRADABILITY AND CALCIUM SALTS OF LONG-CHAIN FATTY-ACIDS IN THE DIETS OF LACTATING DAIRY-COWS - PRODUCTIVE RESPONSES

Our objective was to evaluate the effect of excessive intake of rumina lly degradable crude protein [11.1 and 15.7% of dietary dry matter (DM )] and supplemental fat (Ca salts of long-chain fatty acids at 0 or 2. 2% of dietary DM) on the productive performance of lactating Holstein cows (n = 45) during the first 120 d postpartum The main N sources wer e soybean meal and urea in the diets with high concentrations of degra dable protein versus a combination of vegetable and animal by-product feedstuffs in the diets with less degradable protein. Cows fed the die ts with excess degradable protein had slower rates of increase in DM i ntake (DMI) and milk production, had lower plasma insulin and greater plasma glucose and urea concentrations, and lost more than twice the b ody weight of cows fed the diets with less degradable protein. Supplem ental fat in the highly degradable protein diet reduced the loss of bo dy condition, stimulated DMI, and reduced concentrations of plasma non esterified fatty acids early postpartum compared with the highly degra dable protein diet without added fat. Without affecting DMI, supplemen tal fat stimulated milk production (2 kg/d) starting at 3 wk postpartu m. During early lactation, DMI and milk production were sensitive to t he degree of ruminal degradability of protein and energy supplementati on in the form of fat.