Growth performance and economic impact of Simmental fattening bulls fed dry or corn silage-based total mixed rations.

Bull-fattening diets in Europe and most developed countries around the world have traditionally been based on corn silage, starch-rich, and high-energy/ high-protein supplemental feeds. The impact of climate change on crop yields feed availability, and price volatility, requires new and adapted feeding strategies, including for fattening bulls. Therefore, the objective of this study was to compare the growth performance and economic impact of a representative, conventional corn silage-based (CONVL) total mixed ration, and a dry (DRY) total mixed ration (TMR) fed to Simmental bulls. For nine months (272 days), 24 bulls (215 ± 10 kg BW) were randomly assigned to one of two TMR feeding groups (n = 12 per group). The DRY-TMR was primarily characterised by the nutrient fibre source, exclusively based on straw and other by-products. The diets were formulated and balanced based on the Cornell Net Carbohydrate and Protein System. After 272 days of fattening, bulls were slaughtered. Feed intake, average daily gain (ADG)/DM intake (DMI) ratio, and nutrient intake were affected by treatment, time, and their interaction (P < 0.05). The treatment affected neither acid detergent lignin intake nor starch intake. Compared with CONVL bulls, animals fed DRY-TMR consumed more non-fibre carbohydrates and rumen undegradable neutral detergent fibre, showing lesser dry and fresh matter intake and less metabolisable energy and physically effective neutral detergent fibre intake. Despite differences in nutrient intake (P < 0.05), particle size distribution between the two diets and growth performance were not different (P = 0.45). Simmental bulls in both treatment groups reached target weight in a shorter time due to high ADG of 1.87 kg (DRY-TMR) and 1.84 kg (CONVL). Both treatments achieved a positive profit margin (598 ± 28 €/bull). While total income per bull and dressing percentage did not differ between treatments, the substantially higher feed costs (P < 0.01) of the DRY-TMR resulted in a higher (P = 0.04) income over feed cost in favour of the CONVL treatment group. Despite the higher feed cost of DRY compared with CONVL diets, the better ADG/DMI ratio (P < 0.01) of DRY-TMR contributed to lower absolute feed quantity requirements during the fattening period. Due to the positive profit margin and high ADG results, DRY-TMR solutions for fattening bulls based on straw and by-products can be considered a promising alternative feeding strategy.