SUPPLEMENTATION WITH PROTECTED LIPID AS A MEANS OF ALLEVIATING "SPRING PASTURE" INDUCED MILK FAT DEPRESSION

Abstract

Thirty-six lactating cows, after their first week on spring pasture, were subdivided into three groups of 12 cows each and assigned to one of three pelleted grain mixtures containing 0, 5 or 10% protected lipid. These grain mixtures were fed in the milking parlor at the rate of 1.0 kg/4.0 kg of milk yield for a period of 14 days and then the cows were switched to the next ration in the sequence. Milk yield and grain intake were recorded daily. Milk samples for fat, protein and lactose determinations were taken during the last week of the drylot feeding period, during the preliminary pasture period and on the last 2 days of each experimental period. The change in feeding system from drylot to pasture resulted in an average decrease of 0.65 and 0.10 percentage units in milk fat and lactose contents, respectively, and an increase of 0.27 of a percentage unit in protein content. Refusals of the grain mixture were greater (P < 0.05) but milk yields per kilogram of grain intake were higher (P < 0.05) for grain mixtures containing 10% protected lipid than for the control ration. Protected lipid was not effective in countering the milk fat depression caused by the onset of the spring grazing season. The feeding of protected lipid at the rate of 5 and 10% resulted in only a 10 and 27% recovery in total fat yield compared to cows fed the control ration.