Digestibility, ruminal fermentation, ingesta kinetics and nitrogen utilisation in dairy cows fed diets based on silage of a brown midrib or a standard maize hybrid

The aim of the present experiment was to investigate an experimental brown midrib (Bm) maize hybrid in comparison with a control (Con) non-Bm maize hybrid on ruminal and total tract digestibility, ruminal fermentation, ruminal ingesta kinetics, nitrogen (N) utilisation and microbial efficiency. A total of six ruminally and duodenally cannulated German Holstein cows were used. Animals were fed diets of either 11.5kg dry matter (DM) of a Con or a Bm maize silage plus 4.1kg DM of concentrate. Ruminal and total tract digestibility of organic matter, neutral detergent fibre and acid detergent fibre did not differ between hybrids. Short-chain fatty acid concentrations and pH in the rumen were not affected, but ruminal mean retention time was lower for Diet Bm (Con: 45.4 +/- 2.39h; Bm: 40.6 +/- 2.39h; least squares means +/- standard error). Cows fed Diet Bm had greater efficiency of N utilisation (Con: 30.1 +/- 1.37%; Bm: 33.1 +/- 1.37%) and increased flow of microbial crude protein at the duodenum (MCPF) (Con: 7.0 +/- 0.37g/MJ metabolisable energy (ME); Bm: 8.1 +/- 0.37g/MJ ME). Thus, MCPF and utilisable crude protein at the duodenum (uCP) were greater for Diet Bm (MCPF - Con: 1117 +/- 52.1g/d; Bm: 1306 +/- 52.1g/d; uCP - Con: 1594 +/- 57.9g/d; Bm: 1807 +/- 57.9g/d) and ruminal N balance was lower for Diet Bm (Con: 98.7 +/- 8.92g/d; Bm: 65.6 +/- 8.92g/d). The present results show that the Bm maize hybrid might be advantageous for dairy cow nutrition with regard to N utilisation and MCPF. However, further research is necessary to draw more precise conclusions on the potential of Bm maize hybrids in general.