Effects of primary growth compared to regrowth grass silage on feed intake, growth performance and carcass traits of growing bulls

The objective was to study the effects of primary growth vs. regrowth grass silage on intake, growth and carcass traits of growing bulls. In a feeding experiment, 30 bulls were offered a total mixed ration ad libitum. Two dietary treatments included either first or second cut grass silage (550 g kg(-1) dry matter) supplemented with rolled barley (435 g kg(-1) dry matter) and a mineral-vitamin mixture (15 g kg(-1) dry matter). Feed and energy intake as well as the live weight gain of the bulls decreased when the second cut silage was used instead of the first cut silage. No differences in carcass conformation or carcass fat score between the treatments were observed. Analysed chemical, digestibility or fermentation parameters of the silage samples did not explain the differences in feed intake. However, some second cut silage samples were found to contain mycotoxins (zearalenone, roquefortine C, mycophenolic acid and HT-2), but it is difficult to estimate whether this was the factor that affected feed intake in the present study.