Proportion of corn silage in diets of feedlot steers fed to achieve stepwise increases in growth.

Two experiments were conducted to investigate the effects of proportion of dietary corn silage during periods of feed restriction on performance of steers. In Exp. 1, Simmental x Angus steer calves (n = 107; initial BW = 273 +/- 3.8 kg) were allotted to 12 pens with eight or nine steers/pen and four pens/treatment. Periods of growth were 273 to 366 kg BW (Period 1), 367 to 501 kg BW (Period 2), and 502 to 564 kg BW (Period 3). In two of the dietary regimens, steers were given ad libitum access to feed throughout the experiment and were fed either a 15% corn silage diet in each period or an 85, 50, and 15% corn silage diet in Periods 1, 2, and 3; respectively. In the third feeding regimen, a programmed intake feeding regimen was used. Steers were fed a 15% corn silage diet in each period. However, feed intake was restricted to achieve a predicted gain of 1.13 kg/d in Period 1 and 1.36 kg/d in Period 2, and feed was offered for ad libitum consumption in Period 3. For the entire experiment, ADG was similar (P = 0.41) among treatments and feed efficiency was lower (P < 0.10) for steers in the corn silage regimen than for steers in the programmed intake and ad libitum regimens. In Exp. 2, Simmental x Angus steer calves (n = 106; initial BW = 233 +/- 2 kg) were allotted by BW to 12 pens (three pens/treatment) and fed in three periods similar to those described in Exp. 1. Four feeding regimens were investigated: 1) AL; steers were offered a 15% corn silage diet for ad libitum consumption in all three periods; 2) PI; DMI was programmed to achieve gains as described in Exp. 1; 3) CS-HLL; programmed intake as described above except diets contained 85, 15, and 15% corn silage in Periods 1, 2, and 3, respectively; and 4) CS-HIL; same feeding regimens as CS-HLL, except diets contained 85, 50, and 15% corn silage in Periods 1, 2, and 3, respectively. Steers were given ad libitum access to feed in Period 3. Overall ADG was lower (P < 0.05) for steers in the CS-HLL and CS-HIL feeding regimens than for steers in the AL and PI regimens; feed efficiency was greatest for steers in the PI regimen. Few effects of feeding regimen on carcass characteristics were observed.     

Effects of dietary crude protein concentration during periods of feed restriction on performance, carcass characteristics, and skeletal muscle protein turnover in feedlot steers.

In Exp. 1, 36 individually penned steers (initial BW = 294 +/- 3.8 kg) were used to determine effects of dietary CP percentage and programming gain on performance and carcass characteristics. Steers were fed to achieve a predicted gain of 1.13 kg/d for the first 84 kg of gain and 1.36 kg/d for the next 124 kg of gain and were offered feed for ad libitum consumption for the final 58 kg of gain before slaughter. In these three phases of growth, steers were fed diets, sequentially, with the following CP percentages: HHH (16, 13.5, and 12.5%), LHH (9, 13.5, and 13%), or LLL (9, 9, and 9%). When predicted gain was 1.13 kg/d, ADG was greater (P < 0.01) for steers in the HHH (1.09 kg/d) vs LHH and LLL (0.83 kg/d) systems. When predicted gain was 1.36 kg/d, ADG and gain efficiency were greatest (P < 0.01) for steers in the LHH system. Overall ADG and gain efficiency were greater (P < 0.01) for steers in the HHH (1.46 kg/d, 0.194) and LHH systems (1.38 kg/d, 0.190), compared with steers in the LLL (1.21 kg/d and 0.166) system. Carcass fat thickness was lower for steers in the LHH (0.74 cm) system than for steers in the LLL system (1.09 cm). In Exp. 2, 18 individually penned steers (initial BW = 225 +/- 5.8 kg) were either offered a 13% CP diet for ad libitum intake (AL) throughout the 134-d experiment or fed a high- (16% CP; PI-HH) or low- (10% CP; PI-LH) CP diet and fed to achieve a predicted gain of 1.13 kg/d for the first 85 d of the experiment. Steers in the PI-HH and PI-LH feeding regimens were then offered a 13% CP diet for ad libitum consumption from d 86 to 134. Fractional protein accretion rate was greater (P < 0.01) for steers in the PI-HH and PI-LH feeding regimens than for steers in the AL regimen at d 92, 106, and 120. Fractional breakdown and synthesis rates were not affected (P = 0.63) by feeding regimen. Increased ADG and gain efficiency of steers during compensatory growth periods may in part be due to greater fractional accretion rates of skeletal muscle protein.     

Effects of programmed growth rate and days fed on performance and carcass characteristics of feedlot steers.

Two experiments were conducted to investigate a feeding regimen in which a programmed amount of feed was offered daily to control growth rate of steers. In Exp. 1, steers (n = 107, 309 +/- 3 kg) were used to determine effects of offering ad libitum access to feed (AL) vs a programmed intake feeding regimen (PI) and the number of days steers were fed (168 vs 203) on performance and carcass characteristics. Steers in the programmed intake feeding regimen were fed to achieve a predicted gain of 1.13 kg/d for the first 78 kg of gain, 1.36 kg/d for the next 124 kg of gain, and were given ad libitum access to feed for the final 54 or 103 kg of gain before slaughter (for steers fed for 168 d or 203 d, respectively). Feed efficiency was greater (P < 0.02) for steers in the PI than for those in the AL feeding regimen (0.193 vs 0.183 kg gain/kg feed, respectively). From d 169 to 203, steers in the PI feeding regimen had greater (P < 0.06) ADG (1.60 vs 1.38 kg/d) and similar (P = 0.38) feed efficiency than steers in the AL regimen. In Exp. 2, steers (n = 96; 308 +/- 3 kg BW) were offered feed ad libitum throughout the experiment (AL) or were programmed to gain at a high (PI-H) or low (PI-L) growth rate. For the first 78 kg of gain, intake was restricted to achieve predicted gains of 1.13 kg/d (PI-L) or 1.25 kg/d (PI-H). For the next 124 kg of gain, intake was restricted to achieve predicted gains of 1.36 kg/d (PI-L) or 1.47 kg/d (PI-H). Feed was offered ad libitum for the final 58 kg of gain. Overall ADG was similar (P > 0.37) among feeding regimens despite lower DMI for the steers in the PI-L and PI-H feeding regimens than for those in the AL regimen. Feeding regimen did not affect (P < 0.22) carcass characteristics. Programmed intake feeding regimens sustained growth rate and feed efficiency for an extended period of time without detrimental effects on carcass characteristics.     

Responses to an estrogenic growth promoter in beef steers fed varying nutritional regimens

We investigated the influence of DM and(or) energy intake and dietary CP levels on the performance and nitrogen (N) retention of beef steers with and without growth promoter implants. In Exp. 1, four implanted (Synovex-S, 200 mg of progesterone plus 20 mg of estradiol benzoate) Angus steers and four Angus steers that were not implanted were assigned to concurrent 4 x 4 Latin squares. Initial BW averaged 296 kg. Each square consisted of moderate and moderately high DM intake treatments (4 and 6 kg/d) and low and adequate CP intake treatments (450 and 600 g/d) in a 2 x 2 factorial arrangement. Periods were 2 wk of adaptation, 5 wk of growth, and 1 wk of balance collection. Experiment 2 consisted of two replicates of 32 Hereford steers each (initial BW 324 kg). Each replicate was a 4 x 2 factorial in which steers were individually fed for 63 d. All steers had ad libitum access to a 60% corn-based concentrate diet containing either 7.9, 10.0, 12.1, or 14.6% CP (DM basis), and steers were either implanted or not implanted with Synovex-S. Experiment 3 was similar to Exp. 2 except that all steers (initial BW 315 kg) received a low-protein diet (7.6% CP) with calculated energy densities of either 1.86, 2.04, 2.22, or 2.42 Mcal ME/kg DM, and steers were limited to an equalized DM intake of 9.5 kg daily. In Exp. 1, gains for the low CP, moderate and moderately high DM intakes and the adequate CP, moderate and moderately high DM intakes were 240, 555, 208, and 730 g/d, respectively, for steers not implanted and 333, 643, 488, and 988 g/d, respectively, for implanted steers (SEM = 102 g/d). Respective values for retained N were .13, .18, .16, and .26 g/kg BW.75 and .13, .15, .22, and .29 g/kg BW.75 (SEM = .04 g/kg BW.75). Implant response was greater (CP x implant, P < .01) for both gain and retained N when adequate CP compared to low CP diets were fed. For Exp. 2, the lowest CP diet reduced ADG (.97 vs 1.27 kg/d) and efficiency of gain (100 vs 120 g gain/kg DM). Synovex-S was less effective in improving efficiency for the lowest protein diet than for the other diets (11.7 vs 20.2%). During Exp. 3, neither Synovex-S nor dietary energy influenced gain and efficiency. We concluded that adequate dietary protein is necessary to optimize the response to estrogenic growth promoters and that the low response under inadequate protein and energy intake is not improved by increasing the energy density of the diet.     

Effects of Restricted and Ad Libitum Intakes of Diets Containing Wheat Middlings During the Growing Phase on Performance and Carcass Composition of Early Weaned Steers

Three experiments were conducted to evaluate the effects of restricting the intake of 25% wheat middling diets during the growing phase on finishing phase performance and carcass composition of early weaned steers. In Exp. 1, early weaned Wagyu cross steers were used to compare effects of ad libitum (AL) intake vs restricted (RS; 75% AL) intake of a high concentrate diet. In Exp. 2, early weaned Continental cross steers were used to compare effects of AL intake vs RS intake of a high concentrate diet or hay for AL intake during the growing phase on finishing phase performance and carcass composition. In Exp. 3, early weaned Wagyu cross steers were used to evaluate the same treatments as Exp. 2. Steers were fed until they had ca. 1.0-cm subcutaneous fat cover. In Exp. 1, because steers fed for AL intake were leaner than RS-fed steers, backfat was used as a covariate for finishing phase performance and carcass composition. For Exp. 1, 2, and 3, steer performance for the finishing phase was adjusted to a common dressing percentage. In the growing phase of Exp. 1, steers fed AL gained 18.6% more (P<0.05) than RS-fed steers. However, feed efficiencies were similar for steers fed for AL intake and for RS-fed steers. In the finishing phase, ADG was similar for steers fed AL and for RS-fed steers. Steers fed AL tended (P<0.12) to be heavier at time of slaughter. During the growing phase of Exp. 2, steers fed high concentrate diets AL or RS gained more (P<0.01) than steers fed hay AL. Gain to feed ratio was higher (P<0.01) for AL steers than for steers fed hay AL. When growing and finishing phase performances were combined, steers fed AL had higher (P<0.01) daily gains than did steers fed hay AL. Also, feed efficiencies were improved (P<0.01) for steers fed AL and RS-fed steers more than for steers fed hay AL. Dressing percentages were higher (P<0.01) for steers fed AL and RS-fed steers when compared with steers fed hay AL. In Exp. 3, growing phase daily gains (P<0.04) and gain to feed ratio (P<0.03) were higher for steers fed AL and RS-fed steers than for steers fed hay AL. When growing and finishing phase performances were combined, steers fed for AL intake gained faster (P<0.03) than did steers fed hay AL. Feed efficiencies were improved (P<0.02) for steers fed AL and RS-fed steers compared with steers fed hay AL. Yield grades were higher (P<0.01) for AL steers than for steers fed hay AL.     

Effects of feeding growing cattle high-concentrate diets at a restricted intake on feedlot performance

Three trials were conducted to compare effects of restricted intake of high-concentrate diets vs ad libitum intake of corn silage diets during the growing phase on feedlot cattle performance. In Trial 1, 120 steers (initial BW, 246 kg) were fed 1) a corn silage-based diet ad libitum, 2) a high-moisture corn-corn silage-based diet with intake restricted to a level 20% less than that of the corn silage diet or 3) a high-moisture corn-based diet with intake restricted to a level 30% less than that of the corn silage diet. Steers fed the 20% restricted corn-corn silage-based diet tended (P = .07) to gain slower than those fed the corn silage or 30% restricted high-concentrate diet. Feed efficiency and diet digestibility were greatest for steers fed the 30% restricted-intake, high-concentrate diet (P less than .01). Performance of steers during the subsequent 118-d finishing period was not affected (P greater than .65) by source of energy during the growing period. In Trial 2, ADG of steers fed the 30% intake-restricted, high-concentrate diet was lower (P less than .01) than that of steers with ad libitum access to corn silage. During the 84-d growing period, steers fed supplemental blood meal had 8.3% greater gains and a 6% greater efficiency of feed use than those fed supplemental soybean meal (P less than .01). Monensin did not affect (P = .82) performance of steers fed 30% restricted-intake diets. During the 76-d finishing period, gains and feed conversion were improved (P less than .01) for steers fed the restricted-intake diet in the growing period compared with those given ad libitum access to corn silage. During the growing period in Trial 3, ADG of steers restricted-fed an all-concentrate diet were slightly greater (P less than .10) than ADG of those given ad libitum access to corn silage. Gains did not differ (P = .37) during the subsequent finishing period when steers were switched to 85 or 100% concentrate diets. We concluded that intake of all concentrate diets can be restricted to achieve gains equal to those of steers given ad libitum access to corn silage-based diets without detrimental effects on finishing performance.     

Effects of restricted and ad libitum intake of diets containing wheat middlings on site and extent of digestion in steers

A 5 x 5 Latin square design was used to determine the effects of restricted and ad libitum intake of diets containing wheat middlings on the site and extent of digestion compared to ad libitum intake of a corn-based diet and ad libitum intake of chopped alfalfa hay. Five ruminally and duodenally cannulated Angus steers (519 +/- 41.5 kg BW) were used to compare five dietary treatments. The five treatments were as follows: ad libitum access to a corn-based finishing diet (control), the control diet with 25 percentage units of the corn and soybean meal replaced with wheat middlings offered ad libitum (WM), the WM diet restricted to 75% of predicted ad libitum intake (RWM), the RWM diet with wheat middlings replaced with ammoniated wheat middlings (RNWM), and ad libitum access to a chopped alfalfa hay diet. Although RWM steers were fed to consume 75% of ad libitum intake, RWM steers consumed 15.5% less DM than WM. Steers fed ad libitum hay consumed 28.6, 31.7, and 37.2% less (P < 0.01) DM, OM, and nitrogen than RWM steers. No differences in apparent or true ruminal digestibility were observed among steers fed the control vs WM, WM vs RWM, RWM vs RNWM, or RWM vs hay diets. However, the steers fed the hay diet had 32.5, 33.4, and 36.9% lower (P < 0.01) apparent total tract digestibilities of DM, OM, and N than those fed the RWM diet. Average ruminal pH was lower (P < 0.01) for control steers than those fed the WM diet and for those fed RWM compared to the hay diet. The acetate:propionate ratio was higher for cattle fed hay vs the RWM diet. Microbial DM and OM flow to the small intestine was higher (P < 0.02) for steers fed the RWM diet than those fed the hay diet. In addition, bacterial N flow to the small intestine was higher (P < 0.01) for cattle receiving the RWM diet than the hay diet. Feeding diets containing 25 percentage units of wheat middlings at 75% ad libitum intake had no effect on ruminal digestibility.     

Effects of dry matter intake restriction on diet digestion, energy partitioning, phosphorus retention, and ruminal fermentation by beef steers

Two experiments were conducted to determine the effects of DMI restriction on diet digestion, ruminal fermentation, ME intake, and P retention by beef steers. In Exp. 1, twelve Angus x steers (average initial BW = 450 +/- 18 kg) were assigned randomly to 1 of 3 diets that were formulated to promote a 1.6-kg ADG at intake levels corresponding approximately to 100% (ad libitum, AL), 90% (IR90), or 80% (IR80) of ad libitum DMI. In Exp. 2, twelve crossbred steers (average initial BW = 445 +/- 56 kg) fitted with ruminal cannulae were randomly assigned to 1 of 2 diets that were formulated to promote a 1.6-kg ADG at AL or IR80. All diets delivered similar total NE, MP, Ca, and P per day. During both experiments, fecal DM output by IR80 was less (P /= 0.20) among treatments during both experiments, whereas P retention was similar (P >/= 0.46) among treatments during Exp. 1. Total VFA and the molar proportion of acetate of AL were greater (P 相似文献   

Effects of imposed feed intake variation on acidosis and performance of finishing steers.

Four metabolism and two finishing trials were conducted to determine the effects of imposed feed intake variation on acidosis and performance of finishing steers. In Metabolism Trial 1, four ruminally fistulated steers were limit-fed and subjected to either a constant amount of feed per day (C) or low intake variation of .7 kg/d (LV). No treatment differences were found for intake or measures of acidosis. Metabolism Trial 2 was conducted similarly to Metabolism Trial 1 with treatments of C and high intake variation of 1.4 kg/d (HV). Treatment HV increased (P < .05) acidosis, as indicated by the area of ruminal pH below 5.6. In Metabolism Trial 3, four steers were fed at ad libitum levels of intake and subjected to three levels of intake variation: ad libitum intake with no imposed intake variation (AL), LV of .7 kg/d, and HV of 1.4 kg/d. No treatment differences were found. In Metabolism Trial 4, six ruminally fistulated steers were fed at ad libitum levels and subjected to three levels of intake variation: AL, LV of .9 kg/d, and HV of 1.8 kg/d. Average ruminal pH increased (P < .05) and area of ruminal pH below 5.6 decreased (P < .05) as level of intake variation was increased. In Finishing Trial 1, 75 steers were assigned to eight pens and two treatments: AL or HV of 1.8 kg/d. Dry matter intake increased (P < .05) from AL to HV. Daily gain and gain/feed were not affected by treatment. In Finishing Trial 2, 94 steers were assigned to 12 pens and two treatments: AL or HV of 1.8 kg/d. No treatment differences were noted in DMI, daily gain, or gain/ feed. Therefore, results of these trials indicate that intake variation of up to 1.8 kg/d does not increase acidosis or decrease performance of finishing steers fed at ad libitum levels of intake.     

Growth performance, diet apparent digestibility, and plasma metabolite concentrations of barrows fed corn-soybean meal diets or low-protein, amino acid-supplemented diets at different feeding level

Two experiments, each with 36 barrows with high-lean-gain potential, were conducted to evaluate apparent nutrient digestibilities and performance and plasma metabolites of pigs fed corn-soybean meal diets (CONTROL) and low-protein diets. The low-protein diets were supplemented with crystalline lysine, threonine, tryptophan, and methionine either on an ideal protein basis (IDEAL) or in a pattern similar to that of the control diet (AACON). Amino acids were added on a true ileally digestible basis. The initial and final BW were, respectively, 31.5 and 82.3 kg in Exp. 1 and 32.7 and 57.1 kg in Exp. 2. In Exp. 1, the CONTROL and IDEAL diets were offered on an ad libitum basis or by feeding 90 or 80% of ad libitum intake. Pigs were fed for 55 d. In Exp. 2, the CONTROL, IDEAL, and AACON diets were offered on an ad libitum basis or by feeding 80% of the ad libitum intake. Pigs were fed for 27 d. Pigs fed the CONTROL diet had greater (P < 0.05) ADG and feed efficiency (G/F) than pigs fed the IDEAL (Exp. 1 and 2) and AACON diets (Exp. 2). As the level of feed intake decreased, ADG decreased (P < 0.05), but G/F tended to improve (P < 0.10) for pigs fed 90% of ad libitum in Exp. 1 and for pigs fed 80% of ad libitum in Exp. 2. In Exp. 1, the apparent total tract digestibilities of DM and energy were greater (P < 0.01) for pigs fed the IDEAL diet than for pigs fed the CONTROL diet. In Exp. 2, the apparent total tract digestibility of protein was greatest in pigs fed the CONTROL diet (P < 0.05) and was greater (P < 0.05) in pigs fed the AACON diet than in pigs fed the IDEAL diet. Plasma urea concentrations were lower in pigs fed the IDEAL diet than in pigs fed the CONTROL diet, regardless of feeding level. For pigs fed the CONTROL diet, plasma urea concentrations were lower when feed intake was 80% of ad libitum (diet level, P < 0.01). In summary, pigs fed the IDEAL and the AACON diets gained less and had lower plasma urea concentrations than pigs fed the CONTROL diet. Based on these data, it seems that the growth potential of pigs fed the IDEAL and AACON diets may have been limited by a deficiency of lysine, threonine, and(or) tryptophan and that the amino acid pattern(s) used was not ideal for these pigs.     

Excess crude protein for nongravid gilts

Twenty-five nongravid crossbred gilts (avg initial wt, 126 kg) were placed on either a high (38%) or a low (13%) crude protein (CP) diet and fed either at the rate of 1.82 kg/d or had ad libitum access to feed. In addition, a fifth group was pair-fed the 13% CP diet to the average intake of the gilts fed high CP ad libitum. The experimental period lasted 30 d. Corn-soybean meal diets were used and CP levels were varied by altering the corn:soybean meal ratio. Gain and gain/feed were reduced (P less than .01) in gilts fed 1.82 kg/d compared with the gilts fed ad libitum or pair-fed gilts. Gain (P less than .03) and feed intake (P less than .01) of gilts with ad libitum access to the 13% CP diet were higher than those of gilts with ad libitum access to the 38% CP diet. Gain/feed was not different (P greater than .10) between the two groups, however. Rate of gain and feed efficiency of gilts pair-fed the 13% CP diet were similar (P greater than .10) to those of gilts with ad libitum access to the 38% CP diet. Plasma total free amino acids, NH3 and total protein were not (P greater than .10) affected by treatment. Plasma urea-N and urinary total N, urea-N and orotic acid were increased (P less than .01) in gilts fed the high CP diet regardless of feed intake level. However, urinary NH3 was higher (P less than .01) in gilts fed the low-protein diet. These results indicate that excess dietary CP for nongravid gilts decreases gain and feed intake and has no effect on efficiency of feed utilization, but it increases plasma urea-N and urinary total N, urea-N and orotic acid.     

Influence of level of dietary protein or energy on effects of ractopamine in finishing swine.

The effect of ractopamine, a beta-adrenergic agonist, on growth, nutrient utilization, and carcass composition was studied in pigs fed either 18% CP, 12% CP, or 18% CP restricted (RES = 67% of ad libitum) diets. The 18 and 12% CP diets provided 3.52 and 3.68 Mcal of DE/kg, respectively. All pigs were fed a low-protein (12% CP) diet during pretreatment growth from 15 to 60 kg. Ractopamine at 20 or 30 ppm (30 ppm for RES pigs) in the diet was fed from 60 kg live BW until slaughter at 105 kg (9 pigs/treatment). No ractopamine treatment effect (P greater than .05) was observed for either daily gain or gain/feed, although gain/feed was improved by 8% in both of the ad libitum groups. Ractopamine treatment resulted (P less than .01) in an overall reduction of carcass lipid by 8%, an increase of carcass protein by 5%, and a 21% improvement in the efficiency of protein utilization; the greatest changes occurred in the pigs fed the 12% CP diet (-17%, +11%, and +32%, respectively). The ad libitum daily feed intake was 15% less for pigs fed the 12% CP diet than for those fed the 18% CP diet (P less than .01), and there was a 10% reduction in intake of both diets with the addition of ractopamine (P less than .05). Both carcass lipid and protein deposition seemed to be closely related to energy intake (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of dietary protein concentrations on performance and nitrogen repletion in stressed calves

Three trials were conducted to determine the influence of dietary CP concentration on health and performance of market-transport-stressed feeder calves (Exp. 1 and 2) and on repletion of nutrients lost during a 3-d feed and water deprivation period in steers fed at maintenance energy intake (Exp. 3). In Exp. 1 (84 calves) and 2 (256 calves), feeder calves averaging 184 kg were transported from Tennessee to Texas. In Exp. 1, calves were fed receiving diets containing either 12 or 16% CP. In Exp. 2, calves were fed diets containing 12 or 16% CP and .8 or 1.3% potassium in a 2 x 2 factorial arrangement of treatments. In Exp. 3, four Hereford steers averaging 253 kg were used in an N balance trial. Steers were deprived of feed and water for 3 d and then were limit-fed (1 x maintenance energy requirements) diets calculated to meet 100, 120, 140 or 160% of CP maintenance requirements for 14 d in a 4 x 4 Latin square design. In Exp. 1, calves fed the 16% CP diet had faster (P less than .05) daily gains and higher (P less than .10) feed consumption than calves fed the 12% CP diet during the first 14 d. In Exp. 2, calf performance was not affected by diet CP or K content. Calves fed the 16CP-1.3K diet had lower (P less than .10) mortality than calves on the remaining treatments. In Exp. 3, N balance and serum urea N increased linearly (P less than .05) with increasing dietary CP. Results of these studies are interpreted to indicate that the CP requirement (g/d) of market-transport-stressed feeder calves is similar to requirements of nonstressed calves; however, the CP concentration of the diet of stressed calves may need to be increased when feed intakes are low.     

Feedlot Diet Roughage Level for Hereford Cattle Exposed to Excessive Heat Load

In Exp. 1, six individually fed Hereford steers were exposed to hot (HOT) or thermoneutral (TNL) environmental conditions (ENV) while being adapted (stepped-up) to a finishing diet by decreasing roughage level from 55 to 10% of the diet DM over 17 d. Only at 10% roughage did heat exposure result in reduced (P<0.05) calculated ME intake (MEI) and measured DMI. In the TNL treatment group, pulse rates increased as MEI and diet energy density increased (P<0.05), whereas in the HOT treatment group, pulse rate tended to decline when MEI declined. Body temperature (BT) of steers increased under both TNL and HOT conditions. In Exp. 2, six individually fed feedlot steers were assigned in a replicated (n = 3) 2 × 3 factorial arrangement of treatments and exposed to HOT or TNL ENV, whereas the diet treatments were a 6% roughage diet fed ad libitum (HE), or 90% of ad libitum (RE), or a 28% roughage diet (HR) fed ad libitum such that MEI approximated the MEI of the RE group. Steers fed HR diets had lower (P<0.05) respiratory rate and BT than HE and RE fed steers. Steers fed RE diets had greater (P<0.05) water intake than HE fed steers when averaged across ENV. Lower BT (P<0.05) of cattle fed RE and HR would indicate MEI prior to exposure to excessive heat load (EHL) influences ability of cattle to cope with subsequent exposure to excessive heat load. Data also indicate that adapting cattle to high energy diets partially contributes to EHL.     

Effects of restricted versus conventional dietary adaptation on feedlot performance,carcass characteristics,site and extent of digestion,digesta kinetics,and ruminal metabolism

Three experiments were conducted to determine effects of restricting intake of the final finishing diet as a means of dietary adaptation compared with diets increasing in grain over a period of 20 to 22 d on overall cattle performance, carcass characteristics, digestibility, digesta kinetics, and ruminal metabolism. In Exp. 1, 84 Angus x Hereford yearling steers (initial BW = 418 +/- 29.0 kg) were fed for 70 d. Restricting intake during adaptation had no effect (P > 0.10) on overall ADG:DMI, but decreased (P < 0.05) DMI compared with ad libitum access to adaptation diets, which resulted from differences during the initial 28 d of the experiment. In Exp. 2, 150 mixed crossbred steer calves (initial BW = 289 +/- 22.9 kg) were fed for an average of 173 d. Restricting intake decreased (P < 0.01) overall daily gain (1.51 vs 1.65 kg/d) and DMI (8.68 vs 9.15 kg/d) compared with ad libitum fed steers; however, ADG:DMI was not influenced (P > 0.10) by adaptation method. Experiment three used eight ruminally and duodenally fistulated steers (initial BW = 336 +/- 20 kg) in a completely random design. Total tract digestibility, digesta kinetics and ruminal metabolism were determined. Restricting intake reduced (P < 0.10) daily DMI variation from d 1 through 7, 8 through 14, and 22 through 28 compared with ad libitum feeding of three adaptation diets. Restricted steers had reduced (adaptation method x period interaction, P < 0.05) intakes and fecal excretions of ADF and greater OM digestibilities on d 4 through 7, 11 through 14, and 18 through 21. Digesta kinetics and ruminal metabolism were generally not affected (P > 0.10) by adaptation method. Our results suggest that restricted-feeding of the final diet as a means of dietary adaptation can be used in finishing cattle with few problems from acidosis or related intake variation. In light-weight steers (Exp. 2), disruptions in intake during the adaptation period might have resulted in restriction for an extended period, which decreased (P < 0.01) hot carcass weight compared with calves fed ad libitum. Effects of limit feeding during the initial 28 d of the feeding period on site and extent of digestion, digesta kinetics, and ruminal metabolism were minimal, supporting few differences in performance across the finishing period for yearling cattle.     

Effect of source of energy and rate of growth on performance,carcass characteristics,ruminal fermentation,and serum glucose and insulin of early-weaned steers

Seventy-three crossbred steers (initial BW = 170.5 +/- 5.5 kg) from The Ohio State University (Exp. 1) and 216 crossbred steers (initial BW 135.4 +/- 4.4 kg) from the University of Illinois (Exp. 2) were used to determine the effect of source of energy and rate of growth on performance, carcass characteristics, and glucose and insulin profiles on early-weaned steers. Effects of the diets used in Exp. 1 and 2 on ruminal pH and VFA concentrations were quantified using ruminally fistulated steers (Exp. 3). Cattle were weaned at an average age of 119 d in all experiments and were allotted by age, BW, and breed to one of four diets: high-concentrate, fed ad libitum (ALCONC), high-concentrate fed to achieve a gain of either 1.2 kg/d (1.2CONC) or 0.8 kg/d (0.8CONC), or high-fiber, fed ad libitum (ALFIBER). At 218 d of age, all steers were placed on the ALCONC diet until slaughter. Steers were implanted with Compudose at the initiation of all experiments and with Revalor-S when they were estimated to be 100 d from slaughter. When steers in Exp. 1 averaged 181 and 279 d of age, serum samples were collected to determine glucose and insulin concentrations. Steers were slaughtered when a fat thickness of 1.27 cm was reached (Exp. 1) or after 273 d on feed (Exp. 2). In Exp. 1, days in the feedlot (P < 0.01) and age at slaughter (P < 0.01) were lowest for ALCONC and ALFIBER steers, and greatest for 0.8CONC steers. Overall, ADG was greatest for ALCONC and lowest for 0.8CONC steers; feed efficiency was lowest (P < 0.01) for ALFIBER steers. Final BW did not differ (P > 0.57) among treatments. At 181 and 218 d of age, serum insulin was increased (P < 0.10) and intramuscular fat percentage was greatest (P < 0.07), respectively, for ALCONC steers. In Exp. 2, overall ADG (P < 0.06) and final BW (P < 0.04) were greatest for ALCONC and lowest for 1.2CONC and 0.8CONC steers. Overall feed efficiency was greatest for 0.8CONC and lowest for ALFIBER (P < 0.01). Growing phase diet did not affect marbling score at 218 d of age or at slaughter (P > 0.81). In Exp. 3, differences in ruminal pH after feeding may have been a consequence of increasing acetate (ALFIBER), propionate (ALCONC), or a combination of VFA (0.8CONC and 1.2CONC), respectively (diet x time after feeding, P < 0.10). Controlling growth by limit-feeding a high-concentrate diet for only 100 d does not extend the growth curve of early-weaned steers or enhance intramuscular fat deposition at slaughter compared to ad libitum intake of a high-concentrate or high-fiber diet.     

Effect of intake level and alfalfa substitution for grass hay on ruminal kinetics of fiber digestion and particle passage in beef cattle

Two experiments were conducted to evaluate digestion kinetics of alfalfa (Medicago sativa L.) substitution for grass hay in beef cattle. In Exp. 1, forage combinations evaluated in situ consisted of 0% alfalfa-100% big bluestem (Andropogon gerardi Vitman), 25% alfalfa-75% big bluestem, 50% alfalfa-50% big bluestem, and 100% alfalfa-0% big bluestem. Nonlinear regression was used to determine the immediately soluble fraction A, the potentially degradable fraction B, the undegraded fraction C, and the disappearance rate of DM and NDF. Dry matter fraction A increased linearly (P = 0.03), and DM and NDF fraction B decreased linearly (P = 0.01) with increasing alfalfa substitution. Rate of DM and NDF disappearance increased linearly (P /= 0.23) on total tract apparent digestibility of all nutrients except CP. Steers fed orchardgrass plus alfalfa had 33% greater (P = 0.01) total tract apparent digestibility for CP than those fed orchardgrass alone. Lag time of DM and NDF disappearance was not affected (P >/= 0.20) by alfalfa supplementation or intake level. Rate of DM and NDF disappearance of orchardgrass was faster (P 相似文献   

Effect of diet composition and feed intake level on diet digestibility and ruminal metabolism in growing lambs.

Lambs (29 +/- 2.5 kg) were fed three diets at various intakes to determine whether diet composition or level of intake was reflected in changes in diet digestibility or ruminal fluid characteristics. In Exp. 1, a 90% concentrated, pelleted diet or a whole shelled corn diet with a pelleted protein supplement was fed at three levels of intake: ad libitum and 92.5 and 85% of ad libitum (n = 15). Exp. 2 compared the 90% concentrate diet with diets in which the energy density was diluted to 55 or 72.5% concentrate by including alfalfa hay as a possible method of restricting energy intake (n = 6). Lambs were adapted to diets for 13 d; feces were collected for 6 d and ruminal fluid was collected 0, 3, and 6 h after feeding on the day following fecal collection. Restricting intake in Exp. 1 did not affect DM digestibility or digestibility of CP or starch. Digestibility of ADF was increased (P less than .10) by restricting intake. Ruminal fluid pH, ammonia concentration and VFA concentrations were affected little by either restricted intake level. Digestibility of DM was 4% higher (P less than .001) and starch 5% higher (P less than .001) for the whole shelled corn diet than for the pelleted, high-concentrate diet. Ruminal pH of lambs fed the whole shelled corn diet was higher and fluctuated less than the ruminal pH of lambs fed the high-concentrate, pelleted diet. In Exp. 2, diet digestibility was reduced (P less than .01) and ruminal pH was increased (P less than .002) by addition of hay. Restricted feeding of lambs did not seem to increase diet digestibility or alter ruminal conditions.     

Body composition and tissue accretion rates of barrows fed corn-soybean meal diets or low-protein, amino acid-supplemented diets at different feeding levels

Two experiments, each with 39 high-lean-gain potential barrows, were conducted to evaluate the organ weights, body chemical composition, and tissue accretion rates of pigs fed corn-soybean meal diets (CONTROL) and low-protein diets supplemented with crystalline lysine, threonine, tryptophan, and methionine either on an ideal protein basis (IDEAL) or in a pattern similar to that of the control diet (AACON). Amino acids were added on a true ileally digestible basis. The initial and final BW were, respectively, 31.5 and 82.3 kg in Exp. 1 and 32.7 and 57.1 kg in Exp. 2, and pigs were fed for 55 and 27 d in Exp. 1 and 2, respectively. In Exp. 1, the CONTROL and IDEAL diets were offered on an ad libitum basis, or by feeding 90 or 80% of ad libitum intake. In Exp. 2, the CONTROL, IDEAL, and AACON diets were offered on an ad libitum basis, or by feeding 80% of the ad libitum intake. Three pigs were killed at the start of the experiments and three from each treatment were killed at the end of each experiment to determine body chemical composition. In both trials, the whole-body protein concentration (g/kg) and the accretion rates of protein (g/d) were greater (P < 0.05) for pigs fed the CONTROL than for pigs fed the IDEAL and AACON diets. In Exp. 1, pigs fed the CONTROL diet had a trend (P < 0.10) for greater water and lower lipid concentration and had greater (P < 0.05) water and ash accretion rates. Whole-body protein concentration was greatest (P < 0.05) in pigs fed at 80% of ad libitum, but protein, water, and ash accretion rates were greatest (P < 0.05) in pigs allowed ad libitum access to feed. In summary, pigs fed the IDEAL and the AACON diets had less protein in the body and lower protein accretion rates than pigs fed the CONTROL diet. It seems that reductions in protein deposition in pigs fed the IDEAL and AACON diets may have been due to a deficiency of one or more essential amino acids or possibly to increases in the NE for metabolic processes leading to increases in adipose tissue deposition.     

Effect of forage quality on digestion and performance responses of cattle to supplementation with cooked molasses blocks

We evaluated the effect of forage quality on response of cattle to supplementation with cooked molasses blocks. In Exp. 1, 175 heifers had ad libitum access to prairie hay (5.2% CP, DM basis). Treatments were a 2 x 3 factorial: supplementation with 0 or 1.96 kg/d of alfalfa DM, and supplementation with no cooked molasses block or with a low-protein or a high-protein cooked molasses block (14.4 and 27.5% CP, respectively, DM basis). There were no significant interactions between alfalfa and cooked molasses block for intake or gain. Forage intake and ADG were increased (P < 0.05) by alfalfa supplementation. Heifers fed high-protein cooked molasses blocks gained more (P < 0.05) weight than those fed low-protein cooked molasses blocks or no cooked molasses block. Heifers fed high-protein cooked molasses blocks ate more (P < 0.05) forage than those fed low-protein cooked molasses blocks, with heifers fed no cooked molasses block being intermediate. In Exp. 2, responses to cooked molasses blocks containing 33% CP (DM basis) were measured in 18 steers fed: 1) brome (8.4% CP), 2) alfalfa (19.2% CP), or 3) brome supplemented with 1.93 kg/d of alfalfa DM. Forages were available ad libitum. Forage DM intake was not affected by cooked molasses block and was greater (P < 0.05) for alfalfa than the alfalfa/brome mix, which in turn was greater (P < 0.05) than brome. Digestibility of DM was greater (P < 0.05) for alfalfa than brome or the alfalfa/brome mix and was not affected by cooked molasses block supplementation. Supplementation with cooked molasses blocks had only small effects on intake and digestion of medium- to high-quality forages, but it improved gains and feed efficiencies of heifers fed prairie hay ad libitum, with or without supplemental alfalfa.