Effect of live weight gain of steers during winter grazing: II. Visceral organ mass, cellularity, and oxygen consumption

Two experiments were conducted to examine the effect of BW gain during winter grazing on mass, cellularity, and oxygen consumption of splanchnic tissues before and after the feedlot finishing phase. In each experiment, 48 fall-weaned Angus x Angus-Hereford steer calves were assigned randomly to one of three treatments: 1) high rate of BW gain grazing winter wheat (HGW), 2) low rate of BW gain grazing winter wheat (LGW), or 3) grazing dormant tallgrass native range supplemented with 0.91 kg/d of a 41% CP supplement (NR). At the end of winter grazing, four steers were selected randomly from each treatment for initial slaughter to measure organ mass, cellularity, and oxygen consumption. All remaining steers were placed into a feedlot and fed to the same backfat end point (1.27 cm). Six steers were selected randomly from each treatment for final organ mass, cellularity, and oxygen consumption. Initial empty BW (EBW) was greatest (P < 0.001) for HGW, intermediate for LGW, and least for NR steers in both Exp. 1 and 2 (355 > 263 > 207 +/- 6.5 kg and 337 > 274 > 205 +/- 8.7 kg, respectively). For both experiments, the initial total gastrointestinal tract (GIT; g/kg of EBW) proportional weight was greater (P < 0.05) in NR steers than in LGW, and LGW steers had greater (P < 0.05) initial GIT proportional weight than HGW steers. Proportional weight of total splanchnic tissues (TST; g/kg of EBW) did not differ (P < 0.19) among treatments. Initial duodenal RNA concentration and RNA:protein were greater (P < 0.02) in LGW than in HGW steers, and NR steers were intermediate. Initial in vitro liver O2 consumption was greater (P < 0.09) in HGW and LGW than in NR steers (34.5 > 16.9 mL/min), whereas initial small intestinal oxygen consumption was greater (P < 0.01) in LGW than in HGW and NR steers (12.1 > 5.2 mL/min). Ruminal papillae oxygen consumption did not differ (P < 0.55) among treatments. The rate of decrease of GIT (g x g EBW(-1) x d(-1)) during finishing was greater in NR than in HGW and LGW steers in both Exp. 1 and 2, but mesenteric fat (g x g EBW(-1) x d(-1)) increased for NR steers, resulting in a similar (P < 0.75) increase in TST across the finishing period for all treatments. Similar rates of increase in TST across the finishing phase corresponded with similar rates of live and carcass weight gain among treatments. Our data support the hypothesis that increased visceral organ mass increases maintenance energy requirements of growing cattle.     

Influence of Bos indicus crossbreeding and cattle age on apparent utilization of a high-grain diet

Ten Bos indicus x MARC III (initial BW = 303 +/- 25 kg) and 10 MARC III (initial BW = 322 +/- 16 kg) steers were used in a 2 x 2 factorial design to determine whether cattle age or Bos indicus crossbreeding influence site of digestion of a high-grain diet. Initially, five Bos indicus x MARC III and five MARC III steers were fitted with duodenal cannulas and adapted to a 95% concentrate diet that was offered for ad libitum consumption for a 237-d feeding period (calves). During the feeding period, duodenal and fecal samples were collected during 4-d periods beginning on d 14, 67, 137, and 228. The remaining 10 steers were fed a forage-based diet for a targeted daily gain of .6 to .7 kg for 210 d (yearlings). Following this period, yearling steers were duodenally cannulated and adapted to the 95% concentrate diet. Yearling steers had ad libitum access to feed for 165 d, and samples were collected during 4-d periods beginning on d 13, 42, 102, and 159. Dry matter intake was 9.8 and 7.6 kg/d and daily gain was 1.35 and 1.16 kg in yearlings and calves, respectively. Apparent OM digestion in the stomach was greater (P < .01) in yearlings than in calves. In contrast, postruminal disappearance as a percentage of OM intake was greater (P = .05) in calves than in yearlings. Duodenal flows of total N, microbial N, nonmicrobial N, and total amino acids and total tract N digestibility were not affected (P > .05) by age or Bos indicus crossbreeding. Fecal N excretion was greater (P < .01) in yearlings than in calves. Results of this experiment suggest little effect of Bos indicus influence on utilization of a high-grain diet. However, more feed is digested in the rumen of yearlings than of calves consuming a high-grain diet.     

Effect of live weight gain of steers during winter grazing: III. Blood metabolites and hormones during feedlot finishing

Two experiments were conducted using 48 Angus x Angus-Hereford steers in each experiment to determine the effect of previous winter grazing BW gain on jugular concentrations of metabolites and hormones during feedlot finishing. In each experiment, steers were randomly assigned to one of three treatments: 1) high rate of BW gain grazing winter wheat (HGW), 2) low rate of BW gain grazing winter wheat (LGW), or 3) grazing dormant tallgrass native range (NR) with 0.91 kg/d of a 41% CP (DM basis) supplement. Steers grazed for 120 or 144 d in Exp. 1 and 2, respectively. Plasma and serum were collected from all steers before placement into a feedlot, and six or seven times during finishing in Exp. 1 and 2, respectively. In Exp. 1, before steers entered the feedlot, concentrations of insulin, triiodothyronine (T3), and thyroxine (T4) were greater (P < 0.05) in HGW than in LGW or NR steers, and concentrations of IGF-I and plasma urea-N were greater (P < 0.05) in steers that grazed wheat pasture than in NR steers. In Exp. 2, concentrations of glucose, T3, T4, and IGF-I were greater (P < 0.05) in steers that grazed wheat pasture than NR steers. In Exp. 1 (P < 0.19) and 2 (P < 0.86), glucose concentration did not differ among treatments during finishing. In Exp. 1, insulin concentration across days on feed was greater for HGW than LGW steers, which were greater than for NR steers (treatment x day interaction, P < 0.03). In Exp. 2, insulin concentration increased (P < 0.001) as days on feed increased. Concentrations of IGF-I were greater in steers that had grazed wheat pasture, whereas the increase in IGF-I with increasing days on feed was greater for NR steers (treatment x day interaction, P < 0.003). Concentrations of T3 and T4 during finishing were greater (P < 0.001) in HGW and LGW than in NR steers in Exp. 1. In Exp. 2, T4 concentration also differed (P < 0.009) among treatments (HGW > LGW > NR). In Exp. 2, final concentration of glucose was greater (P < 0.01) in NR than in HGW and LGW steers, and serum insulin concentration was greater (P < 0.04) in NR than LGW steers. Final concentrations of T3 (P < 0.01) and T4 (P < 0.004) were greater in NR than in HGW steers. Our data show that previous BW gain can affect blood metabolites and hormones in steers entering the feedlot. However, lower concentrations of T3, T4, and IGF-I in steers when they entered the feedlot did not inhibit the growth response of previously restricted steers.     

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.     

Effect of live weight gain of steers during winter grazing: I. Feedlot performance, carcass characteristics, and body composition of beef steers

Two experiments were conducted to examine the effect of previous BW gain during winter grazing on subsequent growth, carcass characteristics, and change in body composition during the feedlot finishing phase. In each experiment, 48 fall-weaned Angus x Angus-Hereford steer calves were assigned randomly to one of three treatments: 1) high rate of BW gain grazing winter wheat (HGW), 2) low rate of BW gain grazing winter wheat (LGW), or 3) grazing dormant tallgrass native range (NR) supplemented with 0.91 kg/d of cottonseed meal. Winter grazing ADG (kg/d) for HGW, LGW, and NR steers were, respectively, 1.31, 0.54, 0.16 (Exp. 1) and 1.10, 0.68, 0.15 (Exp. 2). At the end of winter grazing, four steers were selected randomly from each treatment to measure initial carcass characteristics and chemical composition of carcass, offal, and empty body. All remaining steers were fed a high-concentrate diet to a common backfat end point. Six steers were selected randomly from each treatment for final chemical composition, and carcass characteristics were measured on all steers. Initial fat mass and proportion in carcass, offal, and empty body were greatest (P < 0.001) for HGW, intermediate for LGW, and least for NR steers in both experiments. Live BW ADG and gain efficiency during the finishing phase did not differ (P = 0.24) among treatments, but DMI (% of mean BW) for NR and LGW was greater (P < 0.003) than for HGW steers. Final empty-body composition did not differ (P = 0.25) among treatments in Exp. 1. In Exp. 2, final carcass and empty-body fat proportion (g/kg) was greater (P < 0.03) for LGW and NR than for HGW steers. Accretion of carcass fat-free organic matter was greater (P < 0.004) for LGW than for HGW and NR steers in Exp. 1, but did not differ (P = 0.22) among treatments in Exp. 2. Fat accretion in carcass, offal, and empty body did not differ (P = 0.19) among treatments in Exp. 1, but was greater (P < 0.05) for LGW and NR than for HGW steers in Exp. 2. Heat production by NR steers during finishing was greater (P < 0.02) than by HGW steers in Exp. 1 and 2. Differences in ADG during winter grazing and initial body fat content did not affect rate of live BW gain or gain efficiency during finishing. Feeding steers to a common backfat thickness end point mitigated initial differences in carcass and empty-body fat content. However, maintenance energy requirements during finishing were increased for nutritionally restricted steers that were wintered on dormant native range.     

Effects of Delaying Implant and Programmed Rate of Gain on Performance and Carcass Characteristics of Yearling Beef Steers

Ninety-six steers (average BW = 335 ± 36 kg) were allotted in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Factors were 1) implant on d 1 or no implant and 2) ad libitum access to feed on d 1 or programmed-fed for a target BW gain of 1.4 kg/d during the first 62 d of the feeding period. On d 63, all steers were implanted with Revalor-S® (Hoechst Roussel Vet, Overland Park, KS) and provided ad libitum access to feed until harvest. From d 63 to 116, ADG and gain efficiency (g gain/kg DMI) for steers programmed-fed to gain slowly were greater (P<0.05) than those for steers fed to gain rapidly during the first 62 d of the trial. Restricting feed intake to limit ADG during the first 62 d of the finishing period increased ADG during the remaining portion of the finishing period. Gain efficiency was increased (P=0.097) throughout the entire finishing period by limiting ADG during the first 62 d of the experiment. Steers implanted twice and fed to gain rapidly had the least fat in the 9th to 11th rib section; steers with a delayed implant and programmed-fed to gain slowly had the most fat in this same section. In this experiment, no significant interactions occurred except for fat weight in the 9th to 11th rib sections, although steers implanted on d 1 and fed to gain rapidly tended to have fewer days on feed.     

Use of soybean hulls as a replacement for dry rolled corn in beef cattle feedlot receiving diets

Consecutive receiving studies were used to evaluate the replacement of starch (dry rolled corn; DRC) with a nonforage fiber source (soybean hulls; SBH) on performance, mineral, and blood metabolite status of newly arrived feedlot steer calves. Steers in yr 1 (Y1; 9 pens/diet, 8 to 10 animals/pen) and yr 2 (Y2; 6 pens/diet, 9 to 10 animals/pen) were blocked by weaning management, and then stratified by BW and randomly assigned to pens. Pens were randomly assigned to an oat silage-based diet containing starch (HS) from DRC or digestible fiber (HF) from SBH. Diets were formulated for 12% CP (DM basis) and to meet or exceed NRC (1996) nutrient requirements for Ca, P, and vitamins A and E. Mineral status was assessed in Y1 only via liver biopsies and serum samples collected on d 3 and 28. Mineral concentrations on d 28 were compared using d 3 concentrations as a covariate. Glucose, NEFA, and plasma urea N status were assessed in Y2 only via blood collections on d 0, 3, 7, 14, 28, and 59. Morbidity (<10%) and mortality rates were not different (P > 0.10) between treatments across years. Daily BW gain was similar (P > 0.10) between treatments both during the receiving period and cumulatively across years. Overall, feed intake was greater (P = 0.007) for steers fed HF compared with steers fed HS in Y1, but was not different in Y2 (P = 0.13). Steers consuming the HS diet tended (P = 0.07) to have better BW gain efficiency in Y1 only. Across years, BW gain efficiency and ADG were similar between treatments (P > 0.10), although DMI was greater for steers fed HF (P = 0.003). Based on 2 yr of performance, the calculated ME content of SBH was estimated at 92.5% of the ME value of DRC (2.74 vs. 2.96 Mcal/kg, respectively). Mineral concentrations on d 28 were similar (P > 0.10) for most minerals assayed. There was a steeper (P = 0.005) decline in hepatic Cu concentrations early in the feeding period for steers fed HF, resulting in decreased (P = 0.001) d 28 hepatic concentrations. Hepatic Mn was greater (P = 0.003) in steers fed HF on d 28 as a result of greater (P = 0.006) Mn accumulation during the initial 28 d on feed. Blood metabolites in Y2 (using d 0 values as a covariate) were similar (P > 0.10) across treatments, except for reduced (P = 0.025) plasma urea N concentrations on d 7 and greater (P = 0.050) NEFA concentrations on d 28 for steers fed HS. These studies indicate that the use of SBH in receiving diets can support BW gain similar to the use of DRC.     

Season-Long vs Intensive-Early Stocking with Growing Cattle Grazing Bermudagrass Pasture

Our objective was to compare the performance of weaned steer calves managed with intensive-early stocking (IES; 12.4 steers per ha for 70 d) or season-long stocking (SLS; 6.2 steers per ha for 140 d) with and without supplementation (2 × 2 factorial). Beginning on May 15, 90 steers (BW = 217 ± 0.8 kg) were randomly assigned to one of 12 common bermudagrass (Cynodon dactylon [L.] Pers.) pastures (0.81 ha each) fertilized with 168 kg of nitrogen/ha. One of the following four treatments was randomly applied to three pastures: i) SLS plus no supplement, ii) SLS plus 0.45 kg/steer of ground corn daily, iii) IES plus no supplement, and iv) IES plus 0.45 kg/steer of ground corn daily. Steers on IES were lighter (P=0.01) than SLS steers on d 70. By d 140, SLS steers supplemented with corn were 33 kg heavier (P=0.02) than nonsupplemented steers. When using SLS, corn increased the BW gain 0.5 kg/kg of corn fed; however, when IES was used, there was no benefit from corn supplementation. Total BW gain/ha did not differ (P>0.17) among treatments, but SLS with corn supplementation could have the potential to produce more BW gain/ha compared to the other treatments. Grazing systems did not affect feedlot ADG (P>0.53), but IES (175 d on feed) steers did have a higher (P<0.01) feedlot total BW gain than the SLS steers (154 d on feed). Using IES positively affected (P<0.08) dressing percentage and longissimus area compared to SLS; however, these differences in carcass characteristics were probably the result of the longer feeding period.     

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.     

Season-Long vs Intensive-Early Stocking with Growing Cattle Grazing Bermudagrass Pasture

Our objective was to compare the performance of weaned steer calves managed with intensive-early stocking (IES; 12.4 steers per ha for 70 d) or season-long stocking (SLS; 6.2 steers per ha for 140 d) with and without supplementation (2 x 2 factorial). Beginning on May 15, 90 steers (BW = 217 ± 0.8 kg) were randomly assigned to one of 12 common bermudagrass (Cynodon dactylon [L.] Pers.) pastures (0.81 ha each) fertilized with 168 kg of nitrogen/ ha. One of the following four treatments was randomly applied to three pastures: i) SLS plus no supplement, ii) SLS plus 0.45 kg/steer of ground corn daily, iii) IES plus no supplement, and iv) IES plus 0.45 kg/steer of ground corn daily. Steers on IES were lighter (P=0.01) than SLS steers on d 70. By d 140, SLS steers supplemented with corn were 33 kg heavier (P=0.02) than nonsupplemented steers. When using SLS, corn increased the BW gain 0.5 kg/kg of corn fed; however, when IES was used, there was no benefit from corn supplementation. Total BW gain/ha did not differ (P>0.17) among treatments, but SLS with corn supplementation could have the potential to produce more BW gain/ ha compared to the other treatments. Grazing systems did not affect feedlot ADG (P>0.53), but IES (175 d on feed) steers did have a higher (P<0.01) feedlot total BW gain than the SLS steers (154 d on feed). Using IES positively affected (P<0.08) dressing percentage and longissimus area compared to SLS; however, these differences in carcass characteristics were probably the result of the longer feeding period.     

Effects of phase feeding of protein on performance, blood urea nitrogen concentration, manure nitrogen:phosphorus ratio, and carcass characteristics of feedlot cattle

Two experiments with a randomized complete block design were conducted to determine the effects of phase feeding of CP on performance, blood urea nitrogen (BUN), manure N:P ratio, and carcass characteristics of steers fed in a feedlot. In Exp. 1, 45 crossbred steers (initial BW = 423 +/- 3.3 kg) were individually fed a diet formulated to contain 13.0% CP (DM basis) for 62 d. On d 63, the dietary CP was maintained at 13.0% or formulated to contain 11.5 or 10.0% CP until slaughter. Actual CP values were 12.8, 11.8, and 9.9%, respectively. Reducing the CP concentration of the diet did not affect ADG of steers from d 62 to 109 (P = 0.54) or over the 109-d feeding period (1.45, 1.50, and 1.49 kg/d for 13.0, 11.5, and 10.0% CP, respectively; P = 0.85). No differences (P > 0.12) among treatments were detected for BUN concentrations on d 0, 62, or 109. Gain:feed, DMI, and carcass characteristics did not differ among treatments (P > 0.10). In Exp. 2, 2 trials were conducted using 184 (initial BW = 406 +/- 2.6 kg) and 162 (initial BW = 342 +/- 1.9 kg) crossbred steers. Data from the 2 trials were pooled for statistical analysis, and trial effect was added to the statistical model. Steers were fed a diet formulated to contain 13.0% CP until reaching approximately 477 kg. When the average BW of the pen was 477 kg, diets were maintained at 13.0% CP or reduced to contain 11.5 or 10.0% CP. Actual CP values were 12.4, 11.5, and 9.3% CP for treatments 13.0, 11.5, and 10.0% CP, respectively. Reducing the CP content of the diet did not affect ADG after the diet changed (P = 0.16) or throughout the finishing period (P = 0.14). Immediately before slaughter, steers fed the 13.0% CP diet had greater (P < 0.001) BUN concentrations than steers fed the 11.5 and 10.0% CP diets. Carcasses from cattle fed the 11.5% CP diet had greater (P = 0.02) fat thickness than the 13.0 and 10.0% CP treatments, whereas carcasses from cattle fed 13.0% CP had greater (P = 0.004) marbling scores than steers fed the 11.5 or 10.0% CP diets. Other carcass characteristics, DMI, and G:F did not differ (P > 0.10) among treatments. The N:P ratio was increased with the 10.0% CP diet (P = 0.02) compared with the 11.5 or 13.5% CP treatments; however, manure composition did not differ (P > 0.10) among treatments. These results indicate that reduced CP concentration during the finishing period does not affect feedlot performance but can improve the N and P relationship in the manure.     

Effects of feeding polyclonal antibody preparations on rumen fermentation patterns, performance, and carcass characteristics of feedlot steers

In a previous study, preparations of polyclonal antibodies (PAP) against Fusobacterium necrophorum (PAP-Fn) or Streptococcus bovis (PAP-Sb) were successful in decreasing ruminal counts of target bacteria and increasing ruminal pH in steers fed high-grain diets. The objective of this study was to evaluate the effects of feeding PAP-Fn or PAP-Sb on performance, carcass characteristics, and ruminal fermentation variables of feedlot steers. In Exp. 1, during 2 consecutive years, 226 or 192 Angus and Angus crossbred steers were fed a high-grain diet containing either PAP-Sb or PAP-Fn, or both. When measured on a BW basis, steers fed only PAP-Sb had a greater G:F (P < 0.05) than those fed no PAP. Nevertheless, when both PAP were fed, feed efficiency was similar (P > 0.10) to steers fed no PAP or only PAP-Sb. Steers receiving PAP-Fn (alone or in combination with PAP-Sb) had a decreased (P < 0.05) dressing percentage. Steers receiving PAP-Fn (alone or in combination with PAP-Sb) had a decreased severity of liver abscess (P < 0.05). No differences (P > 0.10) were observed in any other carcass characteristics. In Exp. 2, sixteen ruminally cannulated Angus crossbred steers (BW = 665 +/- 86 kg) were fed a high-grain diet containing either PAP-Sb or PAP-Fn, or both. Feeding only PAP-Fn or PAP-Sb for 19 d decreased (P < 0.05) ruminal counts of S. bovis when compared with steers fed both or no PAP. The ruminal counts of F. necrophorum in steers fed PAP-Fn alone or in combination with PAP-Sb were decreased by 98% (P < 0.05) after 19 d, when compared with the counts in control steers. Mean daily ruminal pH was greater (P < 0.05) in steers fed both PAP when compared with feeding either or no PAP. Ruminal pH in the first 4 h after feeding was greater (P < 0.05) for steers receiving PAP-Fn alone or in combination with PAP-Sb. Steers receiving either PAP alone or in combination had less (P < 0.05) ruminal NH(3)-N concentrations in the first 4 h after feeding when compared with those of control steers. Polyclonal antibody preparations against S. bovis were effective in enhancing G:F of steers fed high-grain diets, but dressing percentage was decreased. Mechanisms of enhancement of G:F remain unknown but may be related to changes in ruminal counts of target bacteria and associated effects on ruminal fermentation products.     

Effect of source and amount of energy and rate of growth in the growing phase on performance and carcass characteristics of early- and normal-weaned steers

One hundred eighty-four Angus x Simmental steers (initial BW 161.7 +/- 3.4 kg) were used to determine whether different sources and amounts of energy in the growing phase could extend the growth curve and maintain high amounts of intramuscular fat deposition in early-weaned steers. Steers were allotted by source, age, and BW to one of four growing-phase (119 to 259 d of age) regimens. For three regimens, steers were weaned at 119 d of age and either 1) fed (DM basis) a 50% grain diet ad libitum (ALC); 2) limit-fed a 70% grain diet to achieve a gain of 0.8 kg/d from 119 to 192 d of age, and 1.2 kg/d from 193 to 259 d of age (LFC); or 3) fed a 60% haylage diet ad libitum from 119 to 192 d of age, and a 25% haylage diet ad libitum from 193 to 259 d of age (ALF). For the fourth regimen, steers were normal-weaned at 204 d of age and fed a silage diet from 205 to 259 d of age (NW). From 260 d of age to slaughter, all steers consumed a 70% grain (DM basis) diet. Limit-fed and ALF steers spent the most, and NW the least amount of time (P < 0.01) in the feedlot to achieve a target fat depth of 1.27 cm. Ad libitum-fed steers were the youngest (331 d), and NW the oldest (383 d) at slaughter (P < 0.01). Overall ADG was greatest for ALC and least for NW steers (P < 0.01). Overall, ALF steers consumed the most DM (P < 0.01). While in the feedlot, LFC and ALC steers were more efficient in converting feed to BW gain (P < 0.01) than ALF and NW steers. Normal-weaned had the least and ALC the greatest (P < 0.01) fat depth at 260 d of age. Consequently, NW steers produced the heaviest, and ALC the lightest (P < 0.01) carcasses at slaughter. Normal-weaned steers had the largest, and ALC and LFC steers had the smallest longissimus muscle area (P < 0.06). Growing phase dietary treatments did not affect (P > 0.20) yield grade. Marbling score did not differ (P > 0.35), but laboratory analysis revealed that ALC steers had the lowest percentage of fat (P < 0.02) in the longissimus muscle. Shear force was greatest (P < 0.08) for steaks from ALC and LFC steers, and least for steaks from ALF and NW steers. Feeding steers the ALC diet from 119 to 260 d of age hastened physiological maturity, decreased marbling scores, and decreased muscle tenderness compared with forage feeding (ALF, NW). Limit-feeding a high-grain diet also hastened physiological maturity and decreased muscle tenderness but did not decrease marbling scores. Source and amount of energy affected partitioning of fat deposition.     

Effect of rotating monensin plus tylosin and lasalocid on performance, ruminal fermentation, and site and extent of digestion in feedlot cattle

Two trials were conducted to evaluate the effects of ionophore rotation programs on performance and digestion by feedlot cattle. A 90% concentrate diet was fed with treatments of no ionophore (C), 33 mg lasalocid/kg diet daily (L), 29 mg monensin plus 11 mg tylosin/kg diet daily (MT), and daily (D) and weekly (W) rotation of L and MT. In Trial 1, feedlot performance of 200 crossbred steers (average initial BW 296 kg) was evaluated during a 133-d period. In Trial 2, four crossbred steers (average initial BW 376 kg) fitted with ruminal, duodenal and ileal cannulas were used in a 4 x 4 Latin square design to evaluate treatment effects (excluding W) on ruminal fermentation and site and extent of digestion. In Trial 1, daily rotation of L and MT improved (P less than .10) feed:gain ratio compared with other treatment groups, but daily feed intake did not differ (P greater than .10) among treatments. Daily gain was greater (P less than .10) for steers fed D than for those fed C or MT, but not different from that of steers fed L or W. Carcass measurements did not differ (P greater than .10) among treatments. In Trial 2, ruminal molar proportions of butyrate and valerate were decreased (P less than .07) by MT and D compared with C and L. Proportions of other VFA, ammonia concentrations and ruminal pH did not differ among treatments. Ionophore treatments did not affect site or extent of digestion of OM, starch or N; no differences among treatments were observed for efficiency of microbial protein synthesis. Although daily rotation of L and MT improved performance of growing-finishing feedlot steers, this improvement was not attributable to alterations in ruminal fermentation, or in site or extent of nutrient digestion.     

Pilocarpine and digestive efficiency in beef cattle fed a high-concentrate diet

The effect of pilocarpine HCl, a parasympathetic muscarinic agonist, on digestive characteristics was evaluated in growing beef steers fed a high-grain diet. Oral doses of 0, 2 or 4 mg/kg BW were administered daily to each of eight steers immediately prior to offering an 88% concentrate: 12% hay diet in this three-period crossover design (19 d/period). Treatments did not improve digestibilities of dry matter, organic matter and nitrogen, ruminal liquid volume and fractional dilution rate, body weight gain or feed efficiency. Although daily voluntary feed intake was not altered by treatment (P = .25), there was a dose-dependent slowing of the rate at which feed was consumed (P less than .01). Also, ruminal fluid pH was increased with increasing dose (5.36, 5.55 and 6.11 respectively; P = .10). These observations indicate that the digestive improvements due to pilocarpine reported to occur in mature, nongrowing cattle consuming a high-forage diet are not observed in growing steers fed a production-type diet.     

Effects of rate of gain during winter on subsequent grazing and finishing performance

Sixty mixed British breed yearling steers (237 kg) were used each year for 2 yr to study the effects of rate of gain during the winter on subsequent pasture and finishing performance. Winter gains of .28, .38 and .50 kg/d (P less than .05) were established for the low, medium and high gain treatments, respectively. Daily gain of steers on pasture was reduced (P less than .01) 81 g for each 100-g increase in winter daily gain. No differences in BW were observed among the treatment groups after grazing summer pasture. Wintering performance did not affect finishing performance. Daily gains during the finishing period increased slightly as pasture gain decreased due to increased feed intake, but efficiency was not altered. These data suggest that within this range of ADG during the winter and under the conditions of this study, it was not beneficial to winter cattle for an ADG more than .28 kg/d.     

The effect of zeranol on live weight gain, feed intake and carcass composition of steers during compensatory growth

To evaluate the effect of zeranol implants in steers on compensatory ++growth, 80 steer calves (9 mo of age; 200 kg) were fed at two feeding levels (RO = 9.2 MJ ME/kg DM; R1 = 6.9 MJ ME/kg DM) for 119 d (Period 1). During Period 2, steers were full-fed to 400 kg BW with (Z1) or without (ZO) zeranol implants. Ten steers were slaughtered at the end of Period 1 to estimate carcass composition. Differences of 100 kg in BW were achieved by restriction in Period 1. Subsequent to restriction, cumulative ADG remained greater (P less than .05) up to the 24th wk of recuperation and implants increased (P less than .001) BW gain by 31% and 24% for RO and R1, respectively. The average daily energy intake (ME/W(.75) in Period 2 was similar for all treatments. Feed conversion was improved by 21.5% (P less than .05) by implants. At the end of Period 2 the R1ZO had 8.6 kg less muscle (P less than .001), 2.9 kg less bone (P less than .001) and 5.9 kg more fat (P less than .05) than the ROZO. In comparison, the carcasses of the implanted animals did not show significant differences (P greater than .05) due to restriction. Carcass daily gains were increased by previous restriction (P less than .01) and implants (P less than .05). Zeranol increased daily live weight gain and feed conversion in animals in continuous growth as well as in those observed in compensatory growth an tended to eliminate a tendency for higher content of fat in carcasses of nonimplanted animals making compensatory growth.     

Effects of DL-malate on ruminal metabolism and performance of cattle fed a high-concentrate diet.

To determine the effects of DL-malate on ruminal metabolism, four steers equipped with ruminal cannulas were fed an 80% rolled grain (75% corn:25% wheat) diet twice daily with a DMI equal to 2.0% of BW (485+/-24.8 kg). DL-Malate was infused into the rumen on two consecutive days in 500 mL of phosphate buffer to provide 0, 27, 54, or 80 g of DL-malate/d. Ruminal pH linearly increased (P < .01) with DL-malate concentration and was greater (P < .01) for DL-malate than for the control steers (6.07 vs 5.77). DL-Malate treatment linearly decreased (P < .10) total VFA and tended to linearly increase (P = .10) acetate concentration. Propionate, butyrate, and L-lactate concentrations and acetate:propionate ratio were not affected (P > .10) by DL-malate. Three finishing studies were conducted to determine the effects of feeding DL-malate on growth rate and feed efficiency. In a 98-d experiment, 33 crossbred steers were randomly allotted in a Calan gate feeding system to three DL-malate levels (0, 40, and 80 g/d). Steers (initial weight = 367+/-4.5 kg) were fed a rolled corn-based diet twice daily. After 84 d on feed, gain efficiency (gain:feed) tended to improve with more DL-malate (linear, P < .10) and was 8.1% greater (P < .05) for DL-malate than for the control. The ADG linearly increased (P < .05) with more DL-malate and was 8.6% greater (P = .10) for DL-malate than for the control. After 98-d on feed, ADG was linearly increased (P = .09) by DL--malate, and the greatest increase occurred with 80 g of DL-malate. In the second performance study, 27 Angus steers were randomly allotted in a Calan gate feeding system to three DL-malate concentrations (0, 60, and 120 g/d). Steers (initial weight = 432+/-4.6 kg) were fed diets used in the first finishing study twice daily, but DL-malate was included during the 10-d step-up period. During the 10-d step-up period, feed efficiency and ADG linearly increased (P = .01) with more DL-malate. DL-Malate had little effect on steer and heifer performance or plasma constituents in a 113-d finishing study. Collectively, these results suggest that feeding DL-malate to cattle consuming high-grain diets alleviates subclinical acidosis, and it improved animal performance in two finishing studies.     

Circulating ghrelin and leptin concentrations and growth hormone secretagogue receptor abundance in liver, muscle, and adipose tissue of beef cattle exhibiting differences in composition of gain

Data from species other than cattle indicate that ghrelin and GH secretagogue receptor (GHS-R) could play a key role in fat deposition, energy homeostasis, or glucose metabolism by directly affecting liver and adipose tissue metabolism. Beef steers (n = 72) were used to test the hypothesis that plasma ghrelin and leptin concentrations and abundance of the GHS-R in liver, muscle, and adipose tissues differ in steers exhibiting differences in composition of gain. At trial initiation (d 0), 8 steers were slaughtered for initial carcass composition. The remaining 64 steers were stratified by BW, allotted to pen, and treatment was assigned randomly to pen. Steers were not implanted with anabolic steroids. Treatments were 1) a low-energy (LE) diet fed during the growing period (0 to 111 d) followed by a high-energy (HE) diet during the finishing period (112 to 209 d; LE-HE) or 2) the HE diet for the duration of the trial (1 to 209 d; HE-HE). Eight steers per treatment were slaughtered on d 88, 111, 160, and 209. Carcass ninth, tenth, and eleventh rib sections were dissected for chemical composition and regression equations were developed to predict compositional gain. Liver, muscle, and subcutaneous adipose tissues were frozen in liquid nitrogen for subsequent Western blotting for GHS-R. Replicate blood samples collected before each slaughter were assayed for ghrelin and leptin concentrations. When compared at a common compositional fat end-point, the rate of carcass fat accretion (g·kg of shrunk BW(-1)) was greater (P < 0.001) in HE-HE steers whereas the rate of carcass protein accretion (g·kg of shrunk BW(-1)) was less (P < 0.001) compared with LE-HE steers. When compared at a common compositional fat end-point, plasma leptin, ghrelin, and insulin concentrations were greater (P < 0.05) for HE-HE compared with LE-HE steers. Abundance of the GHS-R, to which ghrelin binds, increased over time in liver and adipose tissue but did not differ as a result of treatment. Plasma ghrelin concentrations were increased for cattle continuously fed the HE diet as they became increasingly fatter; however, abundance of the GHS-R in liver, muscle, and subcutaneous adipose tissue was not different between treatment groups. The role of ghrelin in cattle metabolism warrants further investigation as it could have a significant effect on composition of BW gain, feed efficiency, and metabolic disorders such as ketosis and fatty liver.     

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.