Milk yield and grazing behavior are influenced by the amount of concentrate but not the pregrazing pasture height offered to late-lactation grazing dairy cows

Abstract

In temperate regions of the world, such as southeastern Australia, the majority of dairy farms are pasture-based, with supplementary concentrates fed to cows in the parlor during milking to varying degrees based on location, season, and stage of lactation. Therefore, there is considerable variation between farms in the amount of pasture and concentrate fed. This experiment aimed to investigate the milk production, DMI, and grazing behavior of dairy cows offered pasture at different pregrazing pasture heights coupled with different amounts of concentrate. Thirty-six Holstein-Friesian dairy cows in late lactation were used in the 25-d experiment, during which there were two 6-d measurement periods. Six cows were randomly allocated to each of the 6 treatment combinations using a completely randomized design, balanced for DIM, and both BW and milk production based on data from the 7 d before the beginning of the experiment. The treatment combinations consisted of offering cows one of 2 pasture heights (10 or 14 cm, measured to ground level) and one of 3 amounts of concentrate (3, 5, or 7 kg DM/d). Pasture height did not influence milk yield or composition, but cows offered a higher pregrazing pasture height had increased pasture DMI (estimated using the n-alkane technique). Cows offered 7 kg DM of concentrate/d produced the greatest yields of milk but averaged a 4 kg DM/cow per d lower pasture DMI compared with cows offered 3 or 5 kg DM of concentrate/d. There was no difference in total daily eating time between any of the treatment groups, whereas total daily ruminating time was lowest for cows offered 7 kg DM of concentrate/d compared with cows offered 3 or 5 kg DM of concentrate/d. As pasture is generally the lowest-cost feed source on pasture-based farms, substituting pasture consumption for concentrate can reduce profit while also increasing postgrazing residuals, which affects subsequent pasture regrowth. Balancing concentrate feeding and pasture utilization in grazing-based dairy systems is an important principle for pasture-based dairy farms in temperate regions of the world.