Supplementation of dried distillers grains with solubles to beef cows consuming low-quality forage during late gestation and early lactation.

Three experiments were conducted to evaluate supplementation of dried distillers grains with solubles (DGS) to spring-calving beef cows (n = 120; 541 kg of initial BW; 5.1 initial BCS) consuming low-quality forage during late gestation and early lactation. Supplemental treatments included (DM basis) 1) 0.77 kg/d DGS (DGSL); 2) 1.54 kg/d DGS (DGSI); 3) 2.31 kg/d DGS (DGSH); 4) 1.54 kg/d of a blend of 49% wheat middlings and 51% cottonseed meal (POS); and 5) 0.23 kg/d of a cottonseed hull-based pellet (NEG). Feeding rate and CP intake were similar for DGSI and POS. In Exp. 1, cows were individually fed 3 d/wk until calving and 4 d/wk during lactation; total supplementation period was 119 d, encompassing 106 d of gestation and 13 d of lactation. Tall-grass prairie hay (5.6% CP, 50% TDN, 73% NDF; DM basis) was fed for ad libitum intake throughout the supplementation period. Change in cow BW and BCS during gestation was similar for DGSI and POS (-5.0 kg, P = 0.61 and -0.13, P = 0.25, respectively) and linearly increased with increasing DGS level (P < 0.01). Likewise, during the 119-d supplementation period, BW and BCS change were similar for DGSI and POS (-72 kg, P = 0.22 and -0.60, P = 0.10) and increased linearly with respect to increasing DGS (P < 0.01). The percentage of cows exhibiting luteal activity at the beginning of breeding season (56%, P = 0.31), AI conception rate (57%, P = 0.62), or pregnancy rate at weaning (88%, P = 0.74) were not influenced by supplementation. In Exp. 2, 30 cows from a separate herd were used to evaluate the effect of DGS on hay intake and digestion. Supplementation improved all digestibility measures compared with NEG. Hay intake was not influenced by DGS (P > 0.10); digestibility of NDF, ADF, CP, and fat linearly increased with increasing DGS. In Exp. 3, milk production and composition were determined for cows (n = 16/treatment) of similar days postpartum from Exp. 1. Daily milk production was not influenced by supplementation (6.3 kg/d, P = 0.25). Milk fat (2.1%) and lactose (5.0%) were not different (P > 0.10). Milk protein linearly increased as DGS increased (P < 0.05) and was greater for DGSI compared with POS. Similar cow performance was achieved when cows were fed DGS at the same rate and level of CP as a traditional cottonseed meal-based supplement. Increasing amounts of DGS did not negatively influence forage intake or diet digestibility.

Supplemental energy and extruded-expelled cottonseed meal as a supplemental protein source for beef cows consuming low-quality forage.

Three experiments were conducted to evaluate the efficacy of supplemental energy and extruded-expelled cottonseed meal (ECSM; 30.6% CP; 44% NDF, 10.2% fat; DM basis) as a protein supplement (SUP) to spring-calving beef cows (n = 96; 535 kg initial BW; 5.4 initial BCS) consuming low-quality forage during late gestation and early lactation. Supplementation of ECSM was compared with 2 traditional cottonseed meal-based SUP. For all experiments, SUP provided equal CP. On a DM basis, SUP included 1) a blend of 76% wheat middlings and 18% solvent-extracted cottonseed meal (WMCSM); 2) solvent-extracted cottonseed meal (CSM); and 3) delinted, extruded-expelled cottonseed meal (ECSM). In Exp. 1, cows were individually fed SUP 3 d/wk until calving and 4 d/wk during lactation; total SUP period was 95 d. Tall-grass prairie hay (4.4% CP; 74% NDF; DM basis) was provided during the SUP period. Changes in cow BW during gestation (P = 0.23), over the SUP period (P = 0.27), and over the 301-d experiment (P = 0.56) were similar. Changes in BCS were similar during gestation (P = 0.78), over the SUP period (P = 0.95) and over the 301-d experiment (P = 0.37). Calf birth weights (P = 0.21) and BW at weaning (P = 0.76) were not different. Percentage of cows exhibiting luteal activity at the beginning of breeding season (P = 0.59), AI conception rate (P = 0.71), and pregnancy rate at weaning (P = 0.88) were not different. In Exp. 2, 18 cows in early lactation from Exp. 1 were used to determine the effect of SUP on hay intake and digestion. Hay intake tended (P = 0.10) to be greater for CSM than ECSM. Intake of OM and DM was greater for WMCSM (P 0.10). Similarly, 24-h milk production was not different (P = 0.25). Neither greater energy intake of cows consuming WMCSM nor greater fat intake of cows consuming ECSM influenced cow performance measures or calf weaning weight. Cow response to SUP with ECSM compared with traditional cottonseed meal-based SUP indicates that ECSM is a viable source of supplemental protein for beef cows consuming low-quality forage.

In situ ruminal degradation characteristics of by-product feedstuffs for beef cattle consuming low-quality forage.

Eight ruminally cannulated steers (BW = 753 +/- 48 kg) were used to evaluate in situ N, NDF, and DM degradation characteristics of by-product feeds and their application for beef cows consuming low-quality forage. Experimental feedstuffs included (DM basis) 1) extruded-expelled cottonseed meal (ECSM; 33% CP and 55% NDF), 2) extruded-expelled cottonseed meal with linters (ECSML; 25% CP and 41% NDF), 3) dried distillers grains with solubles (DGS; 33% CP and 36% NDF), 4) solvent-extracted cottonseed meal (CSM; 43% CP and 29% NDF), and 5) a blend of 76% wheat middlings with 18% CSM (WMCSM; 23% CP and 40% NDF). Steers were fed chopped prairie hay (4.8% CP, 69% NDF; DM basis) ad libitum and received 0.38 kg/100 kg of BW of WMCSM daily. In situ degradation kinetics of N, NDF, and DM components included the following fractions: A (immediately soluble), B (potentially degradable), and C (undegradable). Calculated rumen degradable protein (RDP) for ECSM was the greatest among all feedstuffs (83.8%; P < 0.01), which was composed of a large A fraction of N (41%). Similar RDP values were observed for DGS and ECSML (50.7 and 50.9%, respectively, P = 0.93). The B fraction N for ECSML was large (88.9%); however, most of this was unavailable for ruminal degradation. The amount of RDP in CSM and WMCSM was similar (78.2 and 73.5%, respectively; P = 0.12) though the A fraction of N was greater for WMCSM compared with CSM (P < 0.01). Degradability of NDF was greatest (P < 0.01) for DGS (67.4%) and was similar (P = 0.48) for WMCSM and CSM (54.5 and 57.0%, respectively). The least degradability of NDF was calculated for ECSM (29.3%; P < 0.01), attributed to greater lignin content (13.3%, DM). Degradability of DM was greatest (P < 0.01) for CSM and WMCSM (63.7 and 59.4%, respectively) and least (P < 0.01) for ECSM (36.5%) and ECSML (40.6%). Ruminal N degradation characteristics of ECSM were similar to more traditional supplements containing CSM and WMCSM. The RDP for ECSML and DGS N was less compared with other feedstuffs, indicating these feeds may need to be blended with other ingredients containing greater concentrations of degradable N, particularly in situations in which forage RDP is low.

Effect of feedlot management system on response to ractopamine-HCl in yearling steers.

Two experiments evaluated the effects of conventional and natural feedlot management systems (MS) on ractopamine-HCl (RAC) response in yearling steers. Feedlot performance, carcass characteristics, skeletal muscle gene expression, and circulating IGF-I concentrations were measured. The conventional system included a combined trenbolone acetate and estradiol implant, Revalor-S (IMP), as well as monensin-tylosin feed additives (IA). Treatments were arranged in a 2 x 2 factorial and included: 1) natural (NAT): no IMP-no IA, no RAC; 2) natural plus (NAT+): no IMP-no IA, RAC; 3) conventional (CON): IMP-IA, no RAC; and 4) conventional plus (CON+): IMP-IA, RAC. In Exp. 1, one hundred twenty crossbred steers (initial BW = 400 +/- 26 kg) were allotted randomly to treatment in a randomized complete block design (BW was blocking criteria); pen was the experimental unit. In Exp. 2, twenty-four individually fed crossbred steers (initial BW = 452 +/- 25 kg) were used in a randomized complete block design (BW was blocking criteria) and assigned to the same treatments as Exp. 1, with 6 steers/treatment. In Exp. 2, serum was harvested on d 0 and 31 and within the 28-d RAC feeding period, at d 0, 14, and 28. Longissimus biopsy samples were taken on d 0, 14, and 28 of the RAC feeding period for mRNA analysis of beta-adrenergic receptors and steady-state IGF-I mRNA. In Exp. 1, ADG, G:F, final BW, and HCW were greatest for CON+ (P < 0.01). During the final 37 d, RAC increased ADG (P = 0.05) and increased overall G:F (P = 0.02). Marbling score was reduced (P = 0.02), and yield grade was improved with RAC (P = 0.02), but RAC did not affect dressing percentage (P = 0.96) or HCW (P = 0.31). In Exp. 2, MS x RAC interactions were detected in ADG and G:F the last 28 d, overall ADG and overall G:F, final BW, and HCW (P < 0.01). Dressing percentage, yield grade, and marbling score were not altered by MS or RAC (P > 0.10). Circulating IGF-I concentration was increased on d 31 by the conventional MS, and concentration was greater throughout the study than NAT steers (P < 0.01). Circulating IGF-I concentrations were not changed by RAC (P = 0.49). Abundance of beta(1)-AR mRNA tended to increase (P = 0.09) with RAC, but RAC did not affect beta(2)-AR, beta(3)-AR, or IGF-I mRNA (P > 0.40). Management system did not affect beta(1)-AR, beta(2)-AR, beta(3)-AR, or IGF-I mRNA (P > 0.18), yet a trend (P = 0.06) for MS x RAC for beta(2)-AR mRNA was detected. These results indicate that response to RAC is affected by feedlot management practices.

Response to ractopamine-hydrogen chloride is similar in yearling steers across days on feed.

Yearling steers (n = 2,552; 314 kg of initial BW) were used to evaluate the effects of ractopamine-HCl (RAC) and days on feed on performance, carcass characteristics, and skeletal muscle gene expression in finishing steers. Treatment groups included serial slaughter dates of 150, 171, or 192 d on feed. Within each slaughter date, steers either received RAC (200 mg/steer) daily for the final 28 d or were not fed RAC. All steers were initially implanted with Revalor-IS and were reimplanted with Revalor-S after 75 d on feed. At slaughter, muscle samples from the semimembranosus were collected for mRNA analysis of the beta-adrenergic receptors (beta-AR). Ractopamine administration increased (P < 0.05) ADG, G:F, and HCW and increased (P = 0.08) LM area. Ractopamine did not affect the dressing percentage, USDA yield grade, or quality grade (P > 0.3). There was no change in overall feed intake across the entire feeding period; however, feed intake was increased during the 28-d period during which the steers were fed RAC (P < or = 0.05). Greater days on feed decreased (P < 0.05) ADG, G:F, DMI, and the number of yield grade 1 and 2 carcasses. Also, greater days on feed increased (P < 0.05) HCW, dressing percentage, and the number of prime and choice carcasses, as well as the number of yield grade 4 and 5 carcasses. Increasing days on feed decreased (P < 0.05) the abundance of beta(1)-AR and beta(3)-AR mRNA and increased (P < 0.05) the abundance of beta(2)-AR mRNA in skeletal muscle samples obtained at slaughter. Ractopamine had no effect (P > 0.10) on the abundance of beta(1)-AR or beta(3)-AR mRNA, but tended (P = 0.09) to increase beta(2)-AR mRNA. Additional time-course studies with primary muscle cell cultures revealed that advancing time in culture increased (P < 0.001) beta(2)-AR mRNA but had no effect (P > 0.10) on beta(1)-AR or beta(3)-AR mRNA. We conclude that days on feed and RAC are affecting beta-AR mRNA levels, which could, in turn, impact the biological response to RAC feeding in yearling steers.