The effects of energy source and level of digestible undegradable protein in concentrates on silage intake and performance of lactating dairy cows offered a range of grass silages

The effects of energy source and level of digestible undegraded protein (DU P) in concentrates on silage intake and performance of lactating dairy cote s, offered one of a range of grass silages differing in digestibility and i ntake characteristics, were evaluated in a partially balanced change-over d esign experiment involving 48 cows. Four silages were prepared using differ ing management practices prior to and during ensiling. All silages were tre ated with an inoculant additive. For silages A, B, C and D, dry matter (DM) concentrations were 199, 320, 313 and 223 (s.e. 4.6) g/kg, pH values 3.82, 4.03, 4.03 and 5.27 (s.e. 0.056), ammonia nitrogen (N) concentrations 58, 122, 66 and 356 (s.e. 13.2) g/kg total N and in vivo DM apparent digestibil ities 0.77, 0.75, 0.60 and 0.60 (s.e. 0.013) respectively. When offered as the sole diet to 12 dairy cotes in a partially balanced change-over design experiment, silage DM intakes were 14.7, 14.7, 12.7 and 10.5 (s.e. 0.36) kg /day respectively for silages A, B, C and D. Six concentrates containing th ree starch concentrations, each at two levels of DUP, were formulated to ha ve similar concentrations of crude protein, metabolizable energy (ME) and f ermentable ME. For the low and high starch concentrates and low and high le vels of DUP, starch concentrations were 22.5 and 273 g/kg DM and DUP levels were 44 and 60 g/kg DM respectively. Silages were offered ad libitum suppl emented with 10 kg fresh concentrate per head per day. For silages A, B, C and D, DM intakes were 10.8, 11.2, 10.7 and 9.1 (s.e. 0.26) kg/day and milk yields 29.0, 27.6, 27.1 and 25.7 (s.e. 0.69) kg/day respectively. With the exception of milk protein concentration there were no significant (P > 0.0 5) silage type by concentrate energy source and/or level of DUP interaction s on silage intake, milk output or composition. Concentrate energy source h ad no effect (P > 0.05) on silage DM intake, the yields of milk, fat, prote in or fat plus protein or milk fat concentration. However, increasing starc h concentration increased milk protein concentration (P < 0.001), urinary a llantoin concentration (P < 0.01) and diet apparent digestibility (P < 0.00 1). Altering concentrate DUP level had no effect (P > 0.05) on silage DM in take, yields of milk, protein, fat or fat plus protein, milk fat concentrat ions or diet apparent digestibility. Increasing the level of DUP decreased milk protein (P < 0.05) concentration. It is concluded that with silages of varying digestibility, fermentation and intake characteristics, there were no concentrate energy source and/or level of DUP by silage type interactio ns on silage intake, milk yield or composition, ol diet apparent digestibil ity with the exception of a silage type by concentrate level of DUP interac tion on milk protein concentration. With out-of-parlour feeding of concentr ates the results of the present study suggest that there is no evidence to justify the formulation of concentrates differing in energy source or level of DUP to complement individual silage types.