Comparison of concentrate feeding strategies for growing dairy bulls.

摘要

A 2 x 3 factorial design with 53 Finnish Ayrshire bulls was used to study the effects of level and allocation regime of concentrate on performance and carcass quality of growing dairy bulls. The concentrate was given at low (L) or high (H) level and the respective concentrate dry matter (DM) allocations were 39 or 74 g/kg0.60 live weight (LW), respectively. The concentrate allocation regimes within both concentrate levels were steady (SR), and increased (IR) or decreased (DR) during the later part of the growing period. Grass silage was offered for ad libitum intake. The bulls were slaughtered at LW of 550 kg. Increased allowance of concentrate decreased silage intake (P < 0.001) but total DM intake (DMI) increased (P < 0.05). Decrease in silage DMI per kg increase of concentrate DMI was 0.81. Concentrate allocation regime tended to decrease DMI (P < 0.10) when IR and DR were compared to SR. There was no effect of the level of concentrate on the efficiency of microbial N synthesis in the rumen estimated by urinary purine derivative excretion. Microbial N synthesis per day increased (P < 0.05) as a result of increased DMI. Increased concentrate level increased LW gain (LWG) from 1059 to 1158 g/d (P < 0.01). Growth rate response was 73 g/day per 1 kg concentrate DMI. The LWG in the late part of growing period decreased slightly in SR and dramatically in DR, but was maintained in IR, as a response to changes in concentrate allocation in DR and IR. Concentrate level did not affect the growth patterns. When the total growing period was observed, concentrate allocation regimes did not affect LWG. Increased concentrate intake shortened the growing period by 29 days (P < 0.05) but concentrate allocation regime did not affect it. Increased concentrate level tended to increase carcass fatness (P < 0.10) and concentrate allocation decreased (P < 0.01) it when IR and DR were compared to SR. Concentrate level or concentrate allocation regime did not affect dressing proportion or carcass conformation. The results of this study confirm that increasing concentrate allowance is a possible method to increase growth rate and shorten the growing period of dairy bulls, but it also increases carcass fatness. The responses to concentrate allocation regime demonstrate the great ability of growing bulls to adapt to different kinds of feeding regimes without decreasing the production and may also reduce carcass fatness