Silages harvested at different stages of grass growth v. concentrate foodsas energy and protein sources in milk production

Four silages were prepared at 1-week intervals from a primary growth of tim othy-meadow fescue sward. They were offered to 32 Finnish Ayrshire cows and supplemented with 7 or 10 kg of concentrate containing 0 or 1.15 kg rapese ed meal (RSM). The basal concentrate consisted of barley, oats and molassed sugar-beet pulp (2 : 2 : I) and minerals. Diets were arranged 4 X 2 X 2 fa ctorially in a cyclic change-over experiment with four periods of 21 days e ach. Silages contained 739, 730, 707 and 639 g digestible organic matter (D valu e) per kg dry matter (DM) for harvests I, II, III and IV, respectively. All dietary factors had marked effects on the performance of the cows but gene rally interactions between treatments could not be detected. A decrease of 10 g/kg in silage D value decreased energy-corrected milk (ECM) production of the cows by 0.50 kg/day and silage DM intake by 0.162 kg/day. An increme nt of 1 kg concentrate DM decreased silage DM intake by 0.61 kg and yielded 0.55 kg more ECM per day. Inclusion of RSM into the concentrate increased daily ECM production by 1 7 kg and silage DM intake by 0.60 kg/kg RSM when substituting the basal concentrate. Milk yield and yields of milk constitue nts decreased curvilinearly with delayed date of harvest the difference bei ng greatest between the last two cuts and thus closely reflected the change s in silage D value. Milk protein concentration increased as apparent diges tibility (P < 0.001) and concentrate level in the diet increased (P < 0.001 ). Milk fat concentration was not affected by the dietary treatments. Marginal ECM production responses to estimated metabolizable energy (ME) in take were higher when intake was manipulated with the date of silage harves t (0.138 kg ECM per MJ additional ME) compared with increased concentrate f eeding (0.103); highest response was achieved by RSM feeding (0.244). Addit ional intake of calculated amino acids absorbed from the small intestine (A AT) manipulated by silage harvest time resulted in the highest marginal res ponse (0.59 g milk protein per 8 additional AAT), while increased concentra te feeding and inclusion of RSM were equal (0.50 v. 0.49, respectively). Im proving silage quality by earlier harvest resulted in higher milk yield, an d in greater efficiency in the use of increments of estimated ME and AAT th an was seen with increased concentrate feeding. Protein supplementation imp roved milk production irrespective of silage harvest date.