The effect of concentrate crude protein concentration and replacing imported feed ingredients with locally grown cereals and faba bean on milk production and nitrogen utilization in grazing dairy cows

Concentrate feeds with a lower CP concentration are an effective means of reducing nitrogen (N) excretion from grazing dairy cows.Typically, imported feedstuffs such as soybean meal and maize are included in concentrate feeds to increase the protein and fermentable carbohydrate concentration of the diet.However, both the EU and Ireland have committed to becoming climate neutral by 2050, which will require greater use of locally sourced feed ingredients that have a lower carbon footprint.The objective of this experiment was to investigate the effects of (1) decreasing the protein concentration of concentrate supplementation, and (2) replacing imported feed ingredients with locally sourced cereals and faba beans (Vicia faba) on milk production over the main grazing season, and DMI and N excretion in latelactation, of grazing dairy cows.A randomized complete block experiment was carried out from May -October over a 2-year period.In total, 105 (n = 35) spring-calving Holstein Friesian dairy cows were blocked on parity, and balanced on DIM, milk production, and BCS.Cows were then randomly assigned to one of 3 concentrate treatments offered at varying rates according to DIM.Concentrate treatments consisted of a 12% CP concentrate formulated using locally sourced barley, oats and faba beans (LS12); a 12% CP concentrate (IF12) or a 14% CP concentrate (IF14) both formulated using ingredients of any origin, generally imported, including barley, maize, beet pulp and soybean meal.Cows were offered a basal diet of grazed pasture.Dry matter intake and N partitioning were measured once in late-lactation each year (188 17.6 DIM).Reducing concentrate CP from 14% to 12% did not affect milk yield or milk composition.Similarly, replacing imported feed ingredients with locally sourced feedstuffs did not affect overall milk yield or milk composition.Cumulative milk yield (kg) and milk solids yield (fat + protein kg) were not affected by treatment (P > 0.05).However, there was a significant reduction in energy corrected milk for cows offered LS12 during the first 10 weeks of the experiment compared with IF14 (-1.52 kg/d).In late-lactation, cows offered LS12 had a significantly higher pasture DMI and N intake compared with IF12.Cows offered IF14 also had a higher N intake compared with IF12.Both LS12 and IF14 had significantly reduced N utilization efficiency in late-lactation compared with IF12, likely due to increased N intake without a concurrent increase in milk production.Results from this experiment show that a 12% CP concentrate, formulated using either imported or locally sourced feed ingredients, can be offered to grazing dairy cows without negatively impacting milk production during the main grazing season.