The effect of concentrate supplementation type on milk production, dry matter intake, rumen fermentation, and nitrogen excretion in late-lactation, spring-calving grazing dairy cows

摘要

In Ireland, milk is primarily produced using a springcalvinggrass-based system, with the use of concentratesupplementation mainly when pasture availability andquality are reduced. In the autumn, when cows are inlate lactation, reduced pasture productivity results inreduced milk yield and altered milk composition. Nitrogenutilization efficiency also reduces as lactationprogresses. Concentrate supplementation has beenfound to increase milk production and reduce nitrogen(N) excretion, as high-N grass is usually replaced bya lower-N supplement; however, there is a paucity ofinformation with regard to the optimum type of supplementationin late lactation. Therefore, the objectiveof this research is to investigate the effect of differentconcentrate supplementation types, based on barley ormaize, on milk production, dry matter intake (DMI),rumen fermentation, and N excretion in late-lactation,spring-calving, grazing dairy cows. Thirty-six HolsteinFriesian dairy cows were blocked on days in milk (185DIM) and balanced for parity, pre-experimental milkyield, milk composition, and body condition score.Cows were randomly assigned to 1 of 3 dietary treatmentsin a randomized complete block design (n = 12).The 3 treatments consisted of a perennial ryegrassbasedpasture-only (PO) treatment and pasture pluseither of 2 supplementary concentrates, based on barley(PB) or maize (PM). The diets were fed for a 14-dacclimatization period and then for a further 63-d experimentalperiod. Cows offered PO had a lower dailymilk yield (15.1 kg) than PB (18.2 kg) or PM (16.8 kg).Similarly, PO had lower daily milk solids yield (1.46kg) than PB or PM (1.68 and 1.53 kg, respectively).Cows offered PB had a greater milk yield and higher fatand protein yields than those offered PM. Offering PBincreased total DMI (19.5 kg) compared with PO (17.7kg), and milk response to concentrates was also greaterfor PB compared with PM (1.21 vs. 0.71 kg of milk perkg of concentrate). Cows offered PB had increased Nin milk compared with PO. In conclusion, concentratesupplementation based on barley or maize resulted inincreased milk and milk solids yield compared with offeringPO. Cows offered barley had a greater responseto concentrates and increased milk and milk solids yieldin comparison to maize and showed increased N partitioningin milk compared with PO. A barley-basedconcentrate increased total DMI compared with PO.