Extent of processing of barley grain did not affect productivity of lactating dairy cows

The objective of this experiment was to evaluate effects of extent of processing of barley grain on productivity of lactating dairy cows. The barley grain (Metcalf variety; 168 g/kg neutral detergent fiber assayed with a heat stable amylase and expressed exclusive of residual ash (aNDFom); 68.3 kg/hL in test weight) was either finely or coarsely steam-rolled. The Processing indices were 0.825 ± 0.007 and 0.687 ± 0.003 (mean ± standard deviation) for coarsely steam-rolled barley grain (CR) and finely steam-rolled barley grain (FN), respectively. Sixty Holstein cows (191 ± 10.6 days in milk; 643 ± 10.8 kg body weight) were used in a cross-over design with 14 d periods. The experimental diets contained either CR or FN at 384 g/kg of dietary dry matter. The in situ starch disappearance was greater for FN compared with CR, but the extent of processing barley grain did not affect productivity of dairy cows in this study; neither dry matter intake, milk yield, milk energy output, nor milk fat concentration was affected by treatments. Although, statistically significant differences were observed for some production parameters, the magnitude of the differences between treatments was not large enough to be of practical importance. Animal responses in milk yield and milk fat concentration were similar among cows varying in pre-trial milk yield; treatment effects were not observed even for high producing cows. It is speculated that barley grain with low aNDFom concentration requires less processing with marginal benefits from more extensive processing. Effects of extent of processing barley grain have been extensively evaluated for beef cattle, but little is known for the effects on productivity of dairy cows. The interaction between extent of processing and quality of the grain prior to processing warrants further investigation.