Effects of altering energy and protein supply to dairy cows during the dryperiod. 1. Intake, body condition, and milk production

We used 48 Holstein-Friesian cows to investigate the effects of altering en ergy and protein supply to dry cows. Cows were fed one of three diets for 6 wk prior to parturition: (a) a 60:40 (DM basis) mixture of grass silage wi th barley straw ad libitum; (b) grass silage ad libitum; or (c) 0.5 kg/d of prairie meal with grass silage ad libitum. The standard lactation diet was a flat-rate allocation of concentrates and grass silage ad libitum. We eva luated dry-period diets using four dry fistulated cows; rumen pH remained h igh (mean = 6.6) and ammonia concentrations followed N intake. The inclusio n of straw reduced apparent ruminal digestion of OM, N, and NDF as well as microbial protein yield, though microbial yield per unit of OM apparently d igested in the rumen remained unchanged. Voluntary intake of forage was red uced by the inclusion of straw, while the inclusion of prairie meal had lit tle effect. The decline in intake as calving approached was lower with the silage and straw mix diet. There were large differences in the BW change ov er the final 5 wk of the dry period, although the opposite effect was seen in early lactation, and differences in BW and body condition score were sma ll by lactation wk 22. Despite the substantial differences in nutrient supp ly and effects on body reserves, there was little effect of dry-period diet on subsequent performance. Lower forage intakes and yields of protein and lactose were confined to the first month of lactation for cows previously o ffered straw.