Interannual variation of forage quantity and quality driven by precipitation events influence beef livestock production systems within the Southern and Northern Plains and Pacific West, which ...combined represent 60% (approximately 17.5 million) of the total beef cows in the United States. The beef cattle requirements published by the NRC are an important tool and excellent resource for both professionals and producers to use when implementing feeding practices and nutritional programs within the various production systems. The objectives of this paper include evaluation of the 1996 Beef NRC model in terms of effectiveness in predicting extensive range beef cow performance within arid and semiarid environments using available data sets, identifying model inefficiencies that could be refined to improve the precision of predicting protein supply and demand for range beef cows, and last, providing recommendations for future areas of research. An important addition to the current Beef NRC model would be to allow users to provide region-specific forage characteristics and the ability to describe supplement composition, amount, and delivery frequency. Beef NRC models would then need to be modified to account for the N recycling that occurs throughout a supplementation interval and the impact that this would have on microbial efficiency and microbial protein supply. The Beef NRC should also consider the role of ruminal and postruminal supply and demand of specific limiting AA. Additional considerations should include the partitioning effects of nitrogenous compounds under different physiological production stages (e.g., lactation, pregnancy, and periods of BW loss). The intent of information provided is to aid revision of the Beef NRC by providing supporting material for changes and identifying gaps in existing scientific literature where future research is needed to enhance the predictive precision and application of the Beef NRC models.
Eighteen steers (268±16
kg) were used in an intake and digestion study (experiment 1), and six ruminally cannulated steers (459±33
kg) were used in a ruminal fermentation study (experiment 2) to ...evaluate sources of nonprotein nitrogen (NPN) in cooked molasses blocks supplemented to cattle fed prairie hay ad libitum. Treatments for experiment 1 were: (1) control (no block); (2) 60% CP block with 83% of the CP from urea (UREA block); and (3) 60% CP block with 42% of the CP from urea and 42% from feed-grade biuret (UREA/BIURET block). Treatments for experiment 2 were the UREA and UREA/BIURET blocks. Blocks were fed once daily at 0.125% of body weight as small pieces that allowed rapid consumption. Experiment 1 lasted 21 days with 15 days for adaptation. In experiment 2, samples of ruminal fluid and blood were collected 3, 7, 14 and 21 days after initiation of treatments. Ruminal fluid samples were collected at 0, 1, 2, 4, 6, 8, 12 and 16
h and blood samples 5
h after feeding blocks. In experiment 1, intakes of forage OM, NDF and CP tended to increase (
P<0.08); intakes of total (forage plus block) OM, NDF and CP increased (
P≤0.05) by 28, 23 and 95%, respectively; and intakes of digestible OM, NDF and CP increased (
P<0.01) by 52, 47 and 202%, respectively, when either UREA or UREA/BIURET blocks were fed. Apparent total tract digestibilities of OM, NDF and CP also increased (
P<0.01) with block supplementation. Intakes and digestibilities were similar between the UREA and UREA/BIURET blocks. In experiment 2, ruminal ammonia and VFA concentrations and plasma urea concentrations were lower (
P<0.05) for steers fed the UREA/BIURET block than those fed the UREA block. Supplementation with cooked molasses blocks containing high levels of NPN increased intake and digestion of prairie hay, but replacing half of the nitrogen from urea with biuret had little effect on those parameters.
Summary
Effects of glycine (Gly) and B‐vitamins on sulphur amino acid (AA) utilization were studied in growing steers maintained under conditions where methionine (Met) was first limiting. Conditions ...were generated by limit feeding a diet low in ruminally non‐degraded protein and abomasally infusing an AA mixture limiting in Met. Retained N tended (p = 0.07) to improve when steers received 10 mg folate, 10 mg vitamin B6, and 0.10 mg vitamin B12 daily. Hepatic vitamin B12 (p = 0.08) and folate (p = 0.05) concentrations increased with vitamin supplementation. In another trial, factorial treatments were 2 or 5 g/day l‐Met and 0 or 50 g/day Gly infused abomasally. Retained N increased (p < 0.05) in response to Met, and responses were numerically larger in the presence of supplemental Gly. In a different trial, factorial treatments were 0 or 2.4 g/day l‐cysteine (Cys) and 0 or 40 g/day Gly. Retained N was not affected by Cys in the absence of Gly, but was increased by Cys when Gly was supplemented (interaction, p = 0.01). B‐vitamin status may affect sparing of Met by Cys. Supplemental Gly improved responses to supplemental Met and Cys.
The effects of supplemental methionine (Met), supplied abomasally, on the activities of methionine synthase (MS), cystathionine synthase (CS) and betaine-homocysteine methyltransferase (BHMT) were ...studied in growing steers. Six Holstein steers (205 kg) were used in a replicated 3 × 3 Latin square experiment. Steers were fed 2.6 kg dry matter daily of a diet containing 83% soybean hulls and 8% wheat straw. Ruminal infusions of 180 g/d acetate, 180 g/d propionate, 45 g/d butyrate, and abomasal infusion of 300 g/d dextrose provided additional energy. An amino acid mixture (299 g/d) limiting in Met was infused into the abomasum to ensure that nonsulfur amino acids did not limit growth. Treatments were infused abomasally and included 0, 5 or 10 g/d L-Met. Retained N (20.5, 26.9 and 31.6 g/d for 0, 5 and 10 g/d L-Met, respectively) increased (P < 0.01) linearly with increased supplemental Met. Hepatic Met, vitamin B-12, S-adenosylmethionine and S-adenosylhomocysteine were not affected by Met supplementation. Hepatic folates tended (P = 0.07) to decrease linearly with Met supplementation. All three enzymes were detected in hepatic tissue of our steers. Hepatic CS activity was not affected by Met supplementation. Hepatic MS decreased (P < 0.01) linearly with increasing Met supply, and hepatic BHMT activity responded quadratically (P = 0.04), with 0 and 10 g/d Met being higher than the intermediate level. Data from this experiment indicate that sulfur amino acid metabolism may be regulated differently in cattle than in other tested species.
Liver abscesses in feedlot cattle are a major economic, welfare, and production concern to the cattle feeding industry. Severe liver abscesses (LA) reduce ADG by as much as 0.20 kg, DMI by 5%, ...trimming loss by 0.43%, carcasses grading choice by 7%, and HCW by 36 kg. In processing facilities, LA introduce operational and food safety concerns. These include a reduction in processing efficiency, lost time as a result of line stoppages, and offal condemnation in addition to the consumer risk associated with LA contamination of edible meat. Tylosin phosphate, a macrolide antibiotic, has been shown to reduce LA by 75% and level of Fusobacterium Necrophorum in the rumen by 80 to 90%. During this initial observational study, a total of 83 feedlot pens (each individual feed yard exceeding 40,000 head capacity) within three geographical regions (Arizona, Colorado, and the Texas Panhandle) were sampled. Feedlot pen data were collected within 1 wk before harvest and cattle were traced to the packing plant. Every third rumen and its matching liver were tagged (if condemned only). Rumens were scored for consolidation, scars, moderate and acute lesions, and a sample was taken. Livers were scored based on an adaptation of the Elanco Liver Check scoring system. Holstein cattle had a greater (P < 0.05) percentage of LA than beef breeds (30.3 vs. 20.0%). Additionally, Holstein cattle had 11% severe LA (A+) compared with 4% for beef breeds (P < 0.05). No geographical difference (P ≥ 0.10) were detected for liver abscess prevalence and averaged 23, 25, and 26% for the Texas Panhandle, Arizona, and Colorado regions, respectively. Liver abscess rate and severe LA (A+) incidence differed between feedlots (P < 0.05) with within feedlot variation. A correlation was observed for LA% and days on feed (R2 = 0.22; P = 0.04) and for LA % and breed (R2 = 0.29; P = 0.01). No correlation was observed between LA percentage and tylosin phosphate, and between LA percentage and rumen lesions (P ≥ 0.10). These data indicated no association between LA and rumen damage as a result of acidosis. Rumen lesions averaged 12.2%, of which 9.3% were consolidated, 2.4% scar tissue, and the remainder moderate and acute lesions. This study justifies further investigation of feedlot soil and manure as the source of LA causing pathogens to evaluate the within feedlot variation observed for in LA percentage in cattle.
This study evaluated if excess protein decreases performance and carcass quality of finishing cattle fed diets with or without ractopamine hydrochloride (RH). Heifers were assigned to 48 pens in a ...randomized complete block design and pens of cattle were randomly assigned to 3 protein and 2 RH (0 vs. 400 mg/day) treatments. Protein treatments were steam-flaked corn-based diets containing 13.9% CP, 8.8% RDP, and 5.0% RUP (CON), 20.9% CP, 13.4% RDP, 6.1% RUP (High RDP), or 20.9% CP, 9.1% RDP, 10.4% RUP (High RUP). Cattle were weighed at initiation of RH and at shipping. No RH x CP interactions (P ≥ 0.11) occurred for performance or carcass traits. Excess CP did not affect (P ≥ 0.12) final BW or ADG. Carcass-adjusted final BW and ADG tended to be greater (P = 0.06) for cattle receiving High RDP than High RUP and CON. Water intake, DMI, G:F, and carcass-adjusted G:F were not different (P ≥ 0.12) among CP treatments. Hot carcass weight tended to be greater (P = 0.06) for cattle receiving High RDP than High RUP and CON. Dressing percentage was lower (P < 0.01) for cattle fed High RUP than High RDP and CON. Marbling score, 12th rib fat depth, LM area, and yield grade were not different (P ≥ 0.16) among CP treatments. Heifers receiving High RUP tended to have lower (P = 0.10) KPH than CON. Percentage choice tended to be greater (P = 0.09) for heifers receiving High RDP vs. High RUP. Water and DMI were not different (P ≥ 0.36) for RH vs. no RH. Cattle receiving RH had greater (P < 0.01) final BW, ADG, carcass- adjusted final BW, and carcass-adjusted ADG, and lower (P < 0.01) G:F and carcass-adjusted G:F compared with no RH. Hot carcass weights were greater (P < 0.01) and dressing percentage tended to be greater (P = 0.09) for cattle receiving RH, while marbling score was not affected (P = 0.11) by RH. Twelfth-rib fat depth tended to be lower (P = 0.08), and KPH was lower (P = 0.02) for RH vs. no RH. The LM area was greater (P = 0.03) for cattle receiving RH vs. no RH. Excess CP does not negatively impact performance or carcass traits of finishing cattle, and no interactions between CP and RH suggest that CP requirements are not affected by RH.
The objective of this study was to evaluate the effects of monensin and protein supplementation and their interaction on intake, apparent digestion, and ruminal fermentation variables in cattle ...consuming low-quality forage.
Four ruminally cannulated cows (637 ± 24 kg of BW) were used in a 4 × 4 Latin square design. Treatments were arranged as a 2 × 2 factorial: (1) monensin (0 or 200 mg∙cow−1∙d−1) and (2) protein (0 or 0.64 kg∙cow−1∙d−1 CP). Day 1 through 4 of each period, animals were fed only low-quality forage, d 5 through 14 allowed for treatment adaptation, and d 15 through 20 were for sample collection. Data were analyzed using the MIXED procedure of SAS 9.4 (SAS Institute Inc.).
Neither a monensin × protein interaction nor a monensin effect (P ≥ 0.30) was observed for any intake or digestion variable measured. In contrast, protein treatment increased (P < 0.01) all measures of intake. Protein increased (P < 0.01) OM digestibility, total digestible OM intake, and total digestible NDF intake but had no effect (P = 0.13) on NDF digestibility. A monensin × protein interaction (P = 0.33) or monensin effect (P = 0.34) were not observed for total VFA concentration, but protein increased (P < 0.01) total VFA concentration. A tendency for monensin × protein interaction was observed for the acetate:propionate ratio (P = 0.06) and molar percentage of propionate. Monensin increased (P < 0.01) molar percentage of propionate but had no effect (P = 0.21) on acetate.
Although monensin altered ruminal VFA profiles, providing monensin to cows consuming a low-quality-forage diet provided no benefits in forage intake or digestion.
PDF
