| In order to investigate the effects of different dietary energy and protein levels on linear fattening performance, two experiments were conducted:Experiment 1: Thirty Holstein bulls(180 kg) were randomly divided into three groups with ten Holstein bulls in each group. The three groups were provided different nutrition level diets: low energy and low protein level diet(group Ⅰ), medium energy and medium protein level diet(group Ⅱ), high energy and high protein level diet(group Ⅲ). The experiment lasted 362 d. The fattening experiment was divided into earlier and later stages with body weight of 400 kg. The breeding method was free-range. The results showed as follows: at the earlier stage of fattening, the later stage of fattening and the total fattening period, the average daily gain( ADG) in the group Ⅲ was the highest. At the earlier stage of fattening, there had no significantly difference between the three groups. At the later stage of fattening, compared with group Ⅰ and group Ⅱ, the ADG of group Ⅲ was increased by 20.65 %(P<0.05) and 1.83%(P>0.05). The ADG of group Ⅱ was increased by 18.48%(P<0.05) than that of group Ⅰ. The DMI/ADG of group Ⅲ was decreased by 18.26%(P>0.05) and 4.21 %(P>0.05) than that of group Ⅰ and group Ⅱ. Throughout the fattening period, compared with the group Ⅰ, the ADG in the group Ⅲ was significantly increased by 14.43%(P<0.05) and that in the group Ⅱ had an increasing trend(P>0.05), while the DMI/ADG in the group Ⅲ was decreased by 12.12% and 5.34%(P>0.05) than that in the group Ⅰ and group Ⅱ. The content of serum glucose and growth hormone in the group Ⅲ was increased by 25.77 % and 30.43%(P<0.05) than that of group Ⅰ and the amount of serum urea nitrogen in the group Ⅲ was significantly decreased(P<0.05) than that in the group Ⅰ, but no significant was found between group Ⅱ and group Ⅲ. With the increasing of dietary energy and protein levels, apparent digestibility of crude protein and crude fat was rising. With the increasing of energy and protein levels in diet, dressing percentage, beef production of carcass, net meat percentage and eye muscle area were improved, but there had no difference significantly(P>0.05). Compared with group Ⅰ and group Ⅱ, dressing percentage of group Ⅲ increased by 1.09 and 0.14 percentage points, beef production of carcass increased by 0.95 and 0.12 percentage points, net meat percentage increased by 1.41 and 0.19 percentage points, eye muscle area were increased by 6.37 % and 3.33 %. PH, drop loss, shear force and dehydration rate had no difference significantly(P>0.05)for each test group, but with the increasing of energy and protein levels in diet, p H showed an increasing trend, but drop loss and shear force were decreased. Compared with the group Ⅰ, water content of meat of group Ⅲwas decreased by 2.42% significantly, and the content of crude protein was increased by 9.68% significantly(P<0.05). The content of ether extract was significantly different(P<0.05) between group Ⅱ and group Ⅰ. With the increasing energy and protein levels in diet, SFA content in the longissimus muscle was decreased, whereas the amount of MUFA and PUFA were increased. Compared with group Ⅰ, saturated fatty acids(SFA) content of group Ⅲ decreased by 1.94 %(P<0.05) and polyunsaturated fatty acids(PUFA) content of group Ⅲ increased by 8.44 %(P<0.01) and 3.37 %(P<0.05). PUFA content of group Ⅱ increased by 4.91 %(P<0.05) than that of group Ⅰ. The C18:1n9c content of group Ⅲ increased 8.52 %(P<0.05) than group Ⅰ. The amount of EPA and DHA had no difference significantly, but they showed a rising trend.Experiment 2: 36 Holstein bulls(121 kg) were allocated into two groups, group Ⅰ and group Ⅱ. Each group had 18 Holstein bulls. The Holstein bulls were subjected to a 440-d experimental period. In order to further study the high dietary energy and protein levels on linear fattening performance and meat quality of Holstein bulls, the energy and protein level of group Ⅰ of trial two was approximate to that of group Ⅲ of trial one. The groupⅡ of trial two continued to improve the level of dietary energy and protein and used different breeding method to determine the appropriate level of energy and protein. The fattening experiment was divided into earlier and later stages with body weight of 400 kg. At the earlier stage of fattening, the breeding method was free-range. These bulls were tethered at later stage of fattening. The results showed that: at the earlier stage of fattening, the ADG in the Group Ⅱwas significantly increased by 7.34%(P<0.05) than that in the group Ⅰ, whereas the DMI/ADG of group was decreased than that in the group Ⅱ Ⅰ. At the later stage of fattening, the DMI/ADG of group was increased than that Ⅱ of group Ⅰ(P>0.05). Throughout the fattening period, the ADG of group Ⅱwas significantly increased by 5.83%(P>0.05) than that in the group Ⅰ, whereas the DMI/ADG of group Ⅱwas decreased by 3.11%(P>0.05)than that of group Ⅰ. The apparent digestibility of crude protein, crude fat, neutral washing fiber, acid washing fiber, calcium and phosphorus of group were higher, but there was no significant difference between group and group Ⅱ ⅠⅡ. The glutamic-oxalacetic transaminease content, The glutamic-pyruvic transaminease content, growth hormone content and tetraiodothyronine content of group Ⅱ were increased by 8.27%, 13.85%, 6.70% and 1.26%(P<0.05) than that of group Ⅰ, respectively. The amount of blood urea nitrogen was decreased by 12.22%(P<0.01). The different dietary nutrition levels had no effects on dressing percentage, beef production of carcass and net meat percentage. With the increasing of dietary energy and protein levels, p H, drop loss, shear force and dehydration rate were decreased, but the amount of crude protein and ether extract were increased(P>0.05). Compared with group Ⅰ, The p H, drop loss, shear force and dehydration rate of group Ⅱwere decreased by 2.34%, 12.97%, 18.30% and 3.38% at 72 h, respectively. The amount of crude protein and ether extract were increased by 4.95% and 8.55%.The breed benefit of group Ⅱ increased by 0.98 yuan/day/head than that of group Ⅰ. The total breed benefit of group Ⅱ increased by 431.20 yuan/head than that in the group Ⅰ. Therefore, the improvement of dietary energy and protein levels could promote the growth of Holstein bulls, improve the quality of meat and increase the economic benefits.To comprehensive analyze the ADG, DMI/ADG, dressing percentage, net meat percentage and economic benefit of two trials, the energy and protein level of group Ⅲ in trial one was fit for the fattening for bulls and the ADG of the whole period was 1.1kg, the DMI/ADG was 6.38, dressing percentage was 53.75%, net meat percentage 44.56%. NEmf and IDCP requirement for fattening Holstein bulls is calculated as: NEmf(MJ/d/head)= 0.59 W0.75(kg)+2.87ADG(kg), R2=0.9247; IDCP(g/d/head)= 2.65 W0.75(kg)+202.03 ADG(kg),(R2=0.8929). |
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