Response of Cows to a Reduction in Dietary Crude Protein from 17% to 13% During Early Lactation

Four treatments involving 48 multiparous cows (12 per group) were compared during wk 0 to 19 postpartum. Treatments involved decreasing dietary crude protein from 17% to 13% at the 5th, 10th, or 15th wk postpartum or leaving on the 17% diet throughout. Treatment means across periods for milk yields, solids-corrected-milk, dry matter intake, crude protein intake, and milk fatty acids of chain length less than or equal to palmitoleic acid, adjusted by covariance, in orders listed were 27.4, 28.0, 29.1, 29.5 kg; 23.2, 25.1 26.4, 26.8 kg; 19.0, 19.7, 20.4, 20.6 kg; 2.65, 2.98, 3.31, 3.44 kg; 59.83, 63.72, 62.74, 64.55%. There were linear increased as duration on 17% diet increased. The effect of decreasing dietary protein percent was greatest for the change at 5 wk postpartum. Milk fat, protein, and lactose percentages were not affected by treatment. Protein disappearance from nylon bags inserted in rumen fistulated steers was more rapid on 17% than 13% crude protein rations, but ration dry matter disappearance did not differ between rations.