[Effect of feeding on the energy balance and fertility in dairy cows]

The effect of two different feeding regimes on energy metabolism and fertility was studied in dairy cows. The cows were divided according to the type of feed into a hay-urea and a silage group. Ketone body levels in blood were used as indicators of energy balance. Intake of dry matter and of energy was lower in the silage group than in the hay-urea group. The energy balance had almost equilibrated in the hay-urea group at 50 days p.p., in contrast to that of the silage group. The ketone body levels were lower in the hay-urea group than in the silage group in early lactation. The cows in the hay-urea group had a shorter interval from calving to first insemination and to conception than those in the silage group. Low energy level in the late puerperal period had an adverse effect on fertility. The higher the level of ketone bodies at day 50 p.p., the lower the fertility of the cows is likely to be.