Milk production and protein utilization in high producing dairy cows fed a low CP diet based on cereals and roughage only : a full lactation study

Abstract: A feeding trial investigating the effect of a concentrate diet consisting only of cereals on milk production, protein utilization and nitrogen efficiency was conducted on Swedish dairy cows. 13 SRB and 12 SH cows were randomly assigned to one of two groups: group 1 was fed a concentrate feed (Cereal), mainly consisting of barley (36%), wheat (34%), oats (25%) as well as molasses (2%) and a mineral and vitamin mix (3%), whereas group 2 had access to both Cereal and a protein rich concentrate feed (Prot) based mainly on soya bean (51%) and rapeseed cake (28%). A high quality grass silage (energy 11.4 MJ ME, CP 14.8%) was fed ad libitum, and during summer months the cows were kept on pasture, where the pasture allowance was sufficient for maintaining the production level. The cows were fed according to Swedish regulations for organic production. Milk production data as well as BCS and LW were obtained for the entire lactation, whereas blood samples and urine spot samples were collected for the first three months of lactation. Total CP content in the feed ratio was 14.0% and 16.4% for group 1 and 2, respectively. Group 1 had lower CP and energy intake, whereas the total intake and starch intake did not differ between the groups. The concentrate intake was higher in group 2 at all stages of lactation, whereas the roughage intake was higher in group 1 in mid-lactation. Total ECM production over the whole lactation did not differ between the groups, being 9760 and 9706 kg for group 1 and 2, respectively. Daily milk yield did not differ between the two groups either, being 30.5 kg/day and 31.7 kg/day for group 1 and 2, respectively. Neither did the daily ECM yield, milk fat nor protein concentrations differ between the groups. The lactose content in milk was higher in group 1 (4.78%) compared to group 2 (4.71%). When MY and ECM were grouped by early, mid and late lactation stage, group 2 achieved higher daily MY in early lactation while group 1 had higher ECM yields in late lactation. N-efficiency was higher in group 1 (36.5%) compared to group 2 (32.0%). Milk urea concentration was lower in group 1 (3.85 vs. 4.27 mmol/l), as was the daily UUN excretion (66.08 vs. 150.58 g/d). Plasma histidine concentration differed between the groups, being 34.96 and 47.7 nmol/ml in group 1 and 2, respectively. All in all, the results obtained in this study indicates that high producing dairy cows can be fed with a diet consisting only of silage and cereal concentrate without any significant reductions in production levels. Further, an increased nitrogen efficiency as well as a more persistent lactation can be seen as a beneficial effect of the used diet and the reduced CP content in the dairy cow diet.