Effect of wheat adaptation strategies on rumen parameters and dry matter intake of late lactation dairy cows

Abstract

The effects of a major dietary change on ruminal fluid pH, volatile fatty acid (VFA), lactate and ammonia concentrations, dry matter intake (DMI) and milk yield were measured in 32 dairy cows in late lactation. All cows were initially fed 100% lucerne hay cubes and were then gradually introduced to a diet with wheat comprising 40% of total dry matter (DM) and lucerne hay cubes, the remainder. Wheat was gradually substituted for lucerne via one of four strategies, (1) in six small increments (each 6.7% of total DM) over 6 days; (2) in six small increments (each 6.7% of total DM) over 11 days; (3) in three large increments (each 13.3% of total DM) over 6 days; or (4) in three large increments (each 13.3% of total DM) over 11 days. The introduction of wheat in six small increments resulted in a lower daily minimum ruminal fluid pH (pH 5.95) when compared with using three large increments (pH 6.05). Despite this difference none of the treatments exhibited a ruminal fluid pH that would have compromised ruminal function, nor were there differences in DMI (19.7 kg DM/cow.day) or milk yield (16.0 kg/cow.day). Additionally, there were no differences between ruminal fluid VFA, lactate or ammonia concentrations. It is speculated that the properties of the lucerne cubes, including a high buffering capacity, helped the ruminal contents resist the pronounced declines in pH often seen with the fermentation of large amounts of wheat. Under the conditions of this experiment the wheat adaptation strategies used did not lead to any critical differences in rumen parameters. These results suggest that changes to rumen function are driven not only by the characteristics of the concentrate being introduced but also by those of the forage.