Biochemical and biological characterizations and ribotyping of Actinomyces pyogenes and Actinomyces pyogenes-like organisms from liver abscesses in cattle

Actinomyces pyogenes is the second most frequently encountered pathogen, next only to Fusobacterium necrophorum, in liver abscesses of feedlot cattle. Ninety-one isolates, presumptively identified as A. pyogenes, isolated from liver abscesses of cattle were studied. Biochemical characteristics determined by the API 20 Strep kit were similar to those reported previously for A. pyogenes isolated from other infections, except that 18% of isolates hydrolyzed esculin. Nine isolates that resembled A. pyogenes in morphology and in certain biochemical characteristics, but fermented mannitol and/or raffinose, were called A. pyogenes-like (APL) organisms. The five antimicrobial agents, bacitracin, chlortetracycline, oxytetracycline, tylosin, and virginiamycin were inhibitory to all strains of A. pyogenes and APLs. Generally, APL organisms had higher mean hemolytic and leukotoxic activities than A. pyogenes. All isolates of A. pyogenes and APLs produced proteases and neuraminidases. Ribotyping with endonucleases, including BstEII, ClaI, EcoRI, EcoRV, HaeIII, MboI, PvuII, SalI, and SmaI alone or in combinations, showed considerable genetic heterogeneity in both A. pyogenes and APLs. No specific ribopattern characteristic of each group was observed with any of the endonucleases used. The origin of A. pyogenes and APLs and the relative importance of APLs in causing liver abscesses in feedlot cattle are not known.     

Liver abscesses in feedlot cattle.

Liver abscesses in feedlot cattle result from aggressive grain-feeding programs and are influenced by a number of dietary and management factors. They have a major economic impact on the feedlot industry because of liver condemnation and reduced animal performance and carcass yield. Ruminal lesions resulting from acidosis usually are accepted as the predisposing factors. Generally, control of liver abscesses in feedlot cattle has depended on the use of tylosin, which reduces abscess incidence by 40% to 70%. However, new methods and products for liver abscess control are needed. Corn milling by-products that are less fermentable may aide in the quest for cattle production techniques that lead to lower usage of antimicrobials. A vaccine is also commercially available.     

The prevalence and economic significance of liver disorders and contamination in grain-fed and grass-fed cattle

SUMMARY Livers were examined from 5,647 grain-fed and 621 grass-fed cattle of similar breed, age and weight, killed at a Queensland abattoir in 1980–81. The prevalences of disorders found in grain-fed cattle were liver abscesses 5.6% and 11.1% (after 80 and 120 days in the feedlot), telangiectasis 8.4%, Echinococcus granulosis 3.3%, Fasciola hepatica 0.4%, unclassified lesions 7.4%, and contamination 3.2%. In grass-fed cattle liver abscesses were 0.2%, telangiectasis 1.0%, E. granulosis 18.9%, F. hepatica 5.4%, unclassified lesions 6.5%, and contamination 1.0%. Liver abscess disease was the main cause of loss in grain-fed cattle and the mean carcase weight of affected steers was 298kg±42kg, compared wiith 308kg±40kg in non-affected (p 0.01). Liver weights of grain-fed and grass-fed cattle were highly significantly correlated with carcase weights (r - 0.78 and 0.49 respectively). Total losses were $2.25 per head in grain-fed steers and $0.90 in grass-fed steers.     

Bacterial flora of liver abscesses in feedlot cattle fed tylosin or no tylosin.

Bacterial flora of liver abscesses from cattle fed tylosin or no tylosin and susceptibilities of the predominant bacterial isolates to tylosin and other antimicrobial compounds were determined. Abscessed livers were collected at slaughter from cattle originating from feedlots that had fed tylosin (n = 36) or no tylosin (n = 41) for at least 2 yr, and segments of livers with one or two intact abscesses were transported to the laboratory. Abscesses were cultured for anaerobic and facultative bacteria. Fusobacterium necrophorum, either as single culture or mixed with other bacteria, was isolated from all abscesses. The incidence of subsp. necrophorum, as part of the mixed infection, was lower (P < .05) in the tylosin group than in the no-tylosin group (33 vs 61%). However, the incidence of Actinomyces pyogenes was higher (P < .01) in the tylosin group than in the no-tylosin group (53 vs 10%). Totals of 119 F. necrophorum and 21 A. pyogenes isolates were used for determinations of susceptibilities to bacitracin, oxytetracycline, chlortetracycline, lasalocid, monensin, tylosin, tilmicosin, and virginiamycin. The minimum inhibitory concentrations (MIC) of antibiotics were determined with a broth microdilution method. The mean MIC of tylosin for F. necrophorum and A. pyogenes were not different between isolates from tylosin and no-tylosin groups. We concluded that continuous feeding of tylosin did not induce resistance in F. necrophorum or A. pyogenes. Also, the higher incidence of mixed infection of F. necrophorum and A. pyogenes in liver abscesses of tylosin-fed cattle suggests a potential synergistic interaction between the two organisms in causing liver abscesses.     

Effects of dietary zilpaterol hydrochloride on feedlot performance and carcass characteristics of beef steers fed with and without monensin and tylosin

A feedlot experiment was conducted under commercial conditions in the Texas Panhandle using 3,757 feedlot steers (average of 94 steers/pen) to evaluate the effects of feeding zilpaterol hydrochloride with or without monensin and tylosin on feedlot performance and carcass characteristics. The experiment was conducted using a randomized complete block design. Treatments were arranged as a 2 (no zilpaterol vs. zilpaterol) x 2 (monensin and tylosin withdrawn vs. monensin and tylosin fed during the final 35 d on feed) factorial. Steers were fed for a total of 161 to 167 d, and treatments were administered during the final 35 d that cattle were on feed. When included in the diet, zilpaterol, monensin, and tylosin were supplemented at 8.3, 33.1, and 12.2 mg/kg (DM basis), respectively. Zilpaterol was included in the diet for 30 d at the end of the finishing period and withdrawn from the diet for the last 5 or 6 d cattle were on feed. Cattle were harvested and carcass data collected. There were no zilpaterol x monensin/tylosin interactions (P >or= 0.12) for ADG or G:F. Feeding zilpaterol increased ADG (P < 0.001) by 0.20 kg and G:F (P < 0.001) by 0.029 kg/kg during the last 35 d on feed. Likewise, when feedlot variables were measured throughout the entire 161- to 167-d feeding trial, ADG (3.4%; P < 0.001) and G:F (3.9%; P < 0.001) were increased. Feeding zilpaterol increased (P < 0.001) dressing percent and HCW and decreased (P < 0.001) total liver abscess rate compared with controls. In addition, zilpaterol increased (P < 0.001) LM area by an average of 8.0 cm(2). There was a zilpaterol x monensin/tylosin interaction (P = 0.03) for marbling score. Zilpaterol decreased (P < 0.001) marbling score regardless of monensin and tylosin treatment, although withdrawal of monensin and tylosin for 35 d decreased marbling to a greater extent (31 vs. 17 degrees). Zilpaterol decreased (i.e., improved; P < 0.001) calculated yield grade regardless of monensin and tylosin treatment, but feeding zilpaterol in combination with the withdrawal of monensin and tylosin for 35 d decreased calculated yield grade to a greater extent (0.49 vs. 0.29) compared with the zilpaterol, monensin, and tylosin combination treatment (zilpaterol x monensin/tylosin interaction, P = 0.03). Results suggest that monensin and tylosin can be withdrawn from the diet during the zilpaterol feeding period (final 35 d on feed) with minimal effect on animal performance, although feeding zilpaterol in combination with monensin and tylosin seemed to moderate effects on carcass quality.     

Factors affecting in-transit shrink and liver abscesses in fed steers

Live weight loss (shrink) and liver conditions (abscesses) were determined on 3,570 crossbred steers of predominantly British breeding over a 5-yr period. Starting in November 1979, steers were placed on feed at bimonthly intervals and provided one of three housing treatments: no shelter, access to overhead shelter or confinement. All steers were implanted with Synovex during the first 3 yr and Compudose the last 2 yr and fed a diet consisting of high-moisture corn grain, which provided 85% of the energy, and corn silage, along with a protein, vitamin and mineral supplement. Cattle were processed into beef after a feeding period of approximately 160 d. Year affected shrink (P less than .001), and month on feed and housing type tended to alter shrink. Cattle marketed during summer and fall and those outside without overhead shelter tended to shrink more. Year, month on feed and housing type affected liver condition (P less than .01). Cattle started on feed in November and January and cattle housed in confinement or outside without overhead shelter had higher incidences of liver abscesses and slower average daily gains (P less than .01). Daily gains for steers with normal and abnormal livers were not different (P greater than .19) for any month started on feed or housing treatment. These results indicate that under the conditions of this study a 2 or 3% weight loss should be expected during the marketing of finished steers and a 16% incidence of liver abscesses should be anticipated, with some modification of the latter due to time of year and housing. The presence of liver abscesses at the time of processing steers into beef did not reduce feedlot performance.     

Evaluation of the Ability of Implants Containing a Pellet of Tylosin Tartrate (Component® with Tylan®) to Prevent Implant Site Abscesses Under Field Conditions

Five studies were conducted to evaluate the ability of growth-promoting implants containing a pellet of tylosin tartrate [Component®(Ivy Animal Health, Overland Park, KS) with Tylan® (Elanco Animal Health, Indianapolis, IN)] to prevent implant site abscesses in feedlot cattle. Component® with Tylan® implants contain an additional pellet with 29 mg tylosin tartrate as a local antibacterial. Component® with Tylan® was used in heifers and steers and was tested as the initial implant, administered on arrival at the feedlot, or as a re-implant, administered later during the feeding period. Cattle implanted with Component® with Tylan® had or tended to have fewer implant site abscesses. Both incidence and severity of defects were lower; the incidence of missing implants was reduced to nearly zero with Component® with Tylan®. In three studies in which performance was measured, Component® with Tylan® tended (P=0.07 in Study 2, P=0.06 in Study 4, and P=0.09 in Study 5) to improve ADG, and it improved (P=0.03) feed conversion efficiency in the only study in which it was measured (Study 4). Differences in hot carcass weights (HCW) with Component® with Tylan® (3.0, 2.7, and 2.4 kg in Study 2, 4, and 5, respectively) were also observed. Results of implant site evaluations conducted in feedyards as part of a quality assurance program confirm the research results regarding implant site abscesses.     

Effects of timing and duration of dietary vitamin A reduction on carcass quality of finishing beef cattle

Two feedlot studies were conducted to investigate the timing and duration of supplemental vitamin A withdrawal from feedlot cattle (Bos taurus) diets to reduce intramuscular adipose tissue vitamin A concentration and improve carcass quality. In Exp. 1, Angus crossbred steers (n = 84, BW = 211 ± 4 kg) were allotted to 4 treatments: no supplemental vitamin A for 227 d, no supplemental vitamin A for 112 d followed by 115 d of supplemental vitamin A, supplemental vitamin A for 112 d followed by no supplemental vitamin A for 115 d, or supplemental vitamin A for 227 d. In Exp. 2, Angus crossbred steers (n = 80, BW = 210 ± 5 kg) were allotted to 4 treatments: early weaning with or without supplemental vitamin A, and traditional weaning with or without supplemental vitamin A. In both experiments, serum vitamin A concentrations were greatest (P < 0.05) 56 d after cattle were weaned and placed in the feedlot, regardless of feedlot dietary vitamin A concentration. Hepatic vitamin A stores were dramatically decreased (P < 0.05) in the first 56 d and remained depressed as long as steers were not supplemented with vitamin A. At the end of the finishing period, vitamin A concentrations were less in intramuscular than subcutaneous adipose tissue. Growth was not affected by finishing cattle without supplemental dietary vitamin A (P > 0.10). Dietary vitamin A supplementation did not affect USDA yield grades. However, in Exp. 2, cattle without supplemental vitamin A had greater (P < 0.001) ether extractable lipid in the LM. Ether extractable lipid in the LM or marbling scores were enhanced when intramuscular adipose tissue vitamin A concentration was reduced in response to feeding diets without supplemental vitamin A.     

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.     

Effects of tylosin on concentrations of Fusobacterium necrophorum and fermentation products in the rumen of cattle fed a high-concentrate diet.

OBJECTIVE: To determine effects of tylosin on ruminal concentrations of Fusobacterium necrophorum and fermentation products in cattle during rapid adaptation to a high-concentrate diet. ANIMALS: 6 steers fitted with ruminal cannulas. PROCEDURE: Steers were assigned randomly to 2 treatment groups and switched from a 0 to an 85% concentrate diet during a 4-day period. Cattle received this diet, with or without tylosin (90 mg/steer/d), for 4 weeks. Samples of ruminal contents were collected daily beginning 2 days before the treatment protocol and in the first week of concentrate feeding. Four subsequent samples were collected at weekly intervals. Concentration of F. necrophorum in samples was determined, using the most-probable-number technique. Ruminal pH and concentrations of volatile fatty acids (VFA), lactate, and ammonia also were determined. All steers received both treatments separated by 4 weeks (cross-over design), during which time they were fed alfalfa hay only. RESULTS: In control steers, concentration of F. necrophorum increased in response to the high-concentrate diet. Tylosin-fed steers had lower concentrations of F. necrophorum than control steers at all times during concentrate feeding. However, ruminal pH and concentrations of lactate, VFA, and ammonia did not differ between treatment groups. CONCLUSIONS AND CLINICAL RELEVANCE: Tylosin caused a significant reduction in ruminal concentrations of F. necrophorum during rapid adaptation to a high-concentrate diet but had no effect on fermentation products. The reduction in ruminal concentration of F. necrophorum helps explain the reduction in prevalence of hepatic abscesses reported in tylosin-fed feedlot cattle.     

Feeding Holstein steers from start to finish.

Holstein beef has become a significant segment of the feedlot industry. Holstein steers typically enter the feedlot at a lighter body weight, require more pen space per animal, and are in the feedlot for longer periods of time than beef breeds. The only real differences in carcass characteristics are the lower dressing percentage and the smaller rib eye area, which can be increased with anabolic implants and the use of beta-agonists. Holsteins are typically fed higher roughage concentrations. Fat concentrations can also be increased to offset the lower energy diets. Protein requirements do not appear to be different from beef cattle, although Holstein steers weighing from 300 to 700 lb should be fed plant protein sources (eg, soybean meal).     

Effect of monensin and tylosin on average daily gain, feed efficiency and liver abscess incidence in feedlot cattle

Fourteen trials were conducted to evaluate the effects of feeding monensin at 33 ppm alone, tylosin at 11 ppm alone and the two feed additives in combination on the average daily gain, average daily feed intake, feed:gain ratio and the incidence of liver abscesses in feedlot cattle. Monensin reduced feed intake and improved feed efficiency (P less than .05), and had no effect on average daily gain. Tylosin improved average daily gain (P less than .05) and had no effect on daily feed intake. The effect of tylosin on feed efficiency approached significance. The interaction of monensin and tylosin was nonsignificant for daily gain, daily feed intake and feed:gain ratio. Monensin had no effect on liver abscess incidence, while tylosin reduced abscess incidence from 27 to 9%.     

Effects of forage and protein source on feedlot performance and carcass traits of Holstein and crossbred beef steers.

Fifty-eight Holstein and 58 crossbred beef steers were individually fed one of four isonitrogenous diets to evaluate the effects of forage source (corn silage and alfalfa haylage) and protein source (soybean meal and fish meal) on feedlot performance. Phase 1 diets (up to 354 kg of BW) were 40% forage and 60% concentrates and were fed for 70 to 136 d (depending on diet and breed group). Phase 2 diets (354 kg of BW until slaughter) were 20% forage and 80% concentrates and were fed for 127 to 150 d (depending on diet and breed group). Slaughter end points were .6 cm of 12th rib fat for Holsteins and 1.0 cm of rib fat for crossbreds using real-time ultrasonic estimates. The steers were fed for a maximum of 330 d each year. Forage source was a significant component of variation for most growth, efficiency, and carcass traits. Holstein and crossbred steers fed alfalfa haylage had significantly lower average daily gain, feed efficiency, dressing percentage, and empty body fat and required more days on feed to reach slaughter end points, but had higher total feed energy intake available for production. Steers fed corn silage diets had significantly greater energetic efficiency (P less than .05) than those fed alfalfa haylage, due to increased use of ME to produce fat in the carcass. Protein type did not influence gain, feed or energetic efficiency, energy intake, or most carcass traits. A significant protein system x forage source interaction among the four diets was detected for crossbred steers fed corn silage and fish meal, for which there was significantly greater feed conversion with lower energy intake above maintenance, possibly due to better fiber digestion and(or) amino acid flow to the lower tract. Alfalfa haylage plus soybean meal diets decreased (P less than .05) the percentage of Holsteins grading USDA Choice or higher. These results indicate that corn silage, because of greater energy concentration, was a more desirable forage in feedlot diets composed of less than or equal to 40% forage and that protein type (soybean meal and fish meal) in growing diets is not an important factor in feedlot performance or carcass traits of Holstein or crossbred steers that are fed these diets.     

Leptin as a predictor of carcass composition in beef cattle

Our objective was to determine if serum concentrations of leptin could be used to predict carcass composition and merit in feedlot finished cattle. Two different groups of crossbred Bos taurus steers and heifers were managed under feedlot conditions near Miles City, MT. The first group consisted of 88 1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise composite gene combination steers (CGC) harvested at the ConAgra processing facility in Greeley, CO. The second group (Lean Beef Project; LB) consisted of 91 F2 steers and heifers born to Limousin, Hereford, or Piedmontese by CGC F1 cows crossed to F1 bulls of similar breed composition and harvested at a local processing facility in Miles City, MT. Blood samples were collected approximately 24 h before harvest (CGC) or approximately 3 d before and at harvest (LB). No differences in serum concentrations of leptin were detected (P > 0.10) between Hereford, Limousin, or Piedmontese F2 calves nor between LB steers and heifers. Positive correlations (P < 0.01) existed between serum leptin and marbling score (r = 0.35 and 0.50), fat depth measured between the 12th and 13th rib (r = 0.34 and 0.46), kidney, pelvic, and heart fat (KPH) (r = 0.42 and 0.46), and quality grade (r = 0.36 and 0.49) in CGC and LB cattle, respectively. Serum leptin was also positively correlated with calculated yield grade for CGC steers (r = 0. 19; P = 0. 10) and LB cattle (r = 0.52; P < 0.01). Longissimus area was not correlated with serum leptin in CGC steers (r = 0.12; P > 0.10). However, a negative correlation existed between longissimus area and serum leptin in the LB cattle (r = -0.45; P < 0.01). Serum concentrations of leptin were significantly associated with carcass composition (marbling, back fat depth, and KPH fat) and quality grade in both groups of cattle studied and may provide an additional indicator of fat content in feedlot cattle.     

Characteristics of various fibrolytic isozyme activities in the rumen microbial communities of Japanese Black and Holstein Friesian cattle under different conditions

Rumen microorganisms produce various fibrolytic enzymes and degrade lignocellulosic materials into nutrient sources for ruminants; therefore, the characterization of fibrolytic enzymes contributing to the polysaccharide degradation in the rumen microbiota is important for efficient animal production. This study characterized the fibrolytic isozyme activities of a rumen microbiota from four groups of housed cattle (1, breeding Japanese Black; 2, feedlot Japanese Black; 3, lactating Holstein Friesian; 4, dry Holstein Friesian). Rumen fluids in all cattle groups showed similar concentrations of total volatile fatty acids and reducing sugars, whereas acetic acid contents and pH were different among them. Predominant genera were commonly detected in all cattle, although the bacterial compositions were different among cattle groups. Zymograms of whole proteins in rumen fluids showed endoglucanase activities at 55 and 57 kDa and xylanase activity at 44 kDa in all cattle. Meanwhile, several fibrolytic isozyme activities differed among cattle groups and individuals. Treponema, Succinivibrio, Anaeroplasma, Succiniclasticum, Ruminococcus, and Butyrivibrio showed positive correlations with fibrolytic isozyme activities. Further, endoglucanase activity at 68 kDa was positively correlated with pH. This study suggests the characteristics of fibrolytic isozyme activities and their correlations with the rumen microbiota.     

Effects of a Tylosin Tartrate Pellet Added to Cattle Growth Implants on the Incidence of Implant Site Abscesses

The antibacterial effects of tylosin tartrate, added to a cattle growth implant, were evaluated in terms of prevention of implant site abscess formation. An implant site abscess induction model was developed to create implant site abscesses reliably in test animals. This model was then used to test the ability of tylosin tartrate, added as a separate compressed pellet to Component® brand implants (Ivy Animal Health, Overland Park, KS), to reduce implant site abscess incidence in animals expected to develop an ear abscess. Abscesses were induced in all cattle at implanting (d 0). Implant sites were observed on d 6, 10, 16, 21, 28, and 35 post-implantation to determine the presence and severity of an abscess. Three steer implant formulations and two heifer implant formulations, each with and without the tylosin tartrate pellet, were tested. The overall implant site abscess rate was 94.1% in animals that did not receive a tylosin tartrate pellet and 4.2% in animals that received a tylosin tartrate pellet. For each implant at each implant site observation, abscess rate was significantly less (P<0.002) in steers or heifers treated with the tylosin tartrate pellet. Results show that a significantly lesser percentage of ear implant site abscesses are induced if a tylosin tartrate pellet is added to the implant.     

Feeding strategies for managing heat load in feedlot cattle

Eighty-four Bos taurus crossbred steers were used to investigate effects of level and duration of limit-feeding feedlot cattle in a hot environment. Pens (four/treatment) of steers (seven/pen) were fed feedlot finishing diets and randomly assigned to the following treatments: 1) restricted to approximately 75% of feed consumed when offered ad libitum for 21-d duration (RES21); 2) restricted to approximately 75% of ad libitum for 42-d duration (RES42); and 3) feed offered ad libitum (ADLIB). Tympanic temperatures (TT) were measured via thermistors placed in the ear canal and attached to data loggers. Restricting feed intake for both 21- and 42-d reduced tympanic temperature when compared with ADLIB treatment groups under hot environmental conditions. Temperature reductions exceeded 0.5 degrees C (P < 0.05) depending on time of day. The reduced tympanic temperature is likely due to a reduction in metabolic heat load and/or a concurrent reduction in metabolic rate. Within respective periods, no differences (P > 0.05) were found among treatments for panting or bunching score. However, different proportions of cattle were found to be bunching and panting with ADLIB cattle displaying a greater number of bunched steers that were panting when compared with the other groups. When averaged across diet treatments, dark-colored cattle had the greatest percentage of cattle showing moderate to excessive panting, while light-colored cattle displayed the least panting under thermoneutral climatic conditions. Under hot (mean daily temperature-humidity index >74) conditions, dark-colored cattle tended to bunch more (P = 0.073) and pant more (P < 0.01) than light-colored cattle. Mean TT were 0.2 to 0.6 degrees C (P < 0.05) greater for dark- vs light-colored cattle under hot conditions. Limit-feeding feedlot cattle during early summer is a successful tool for enhancing animal comfort by alleviating the combined effects of high climatic and metabolic heat load.     

Strategies to reduce feedlot cattle heat stress: effects on tympanic temperature

Three experiments were conducted to evaluate the effect of different management strategies on body temperature of feedlot steers finished in the summer months. In Exp. 1, 24 crossbred steers were chosen to assess the effect of altered feed intake and feeding time on tympanic temperature (TT) response. Managed feeding (MF) treatments were applied for 22 d only and provided 1) ad libitum access to feed at 0800 (ADLIB), 2) feed at 1600 with amount adjusted so that no feed was available at 0800 (BKMGT), 3) feed at 1600 at 85% of predicted ad libitum levels (LIMFD). During heat stress conditions on d 20 to 22 of MF, LIMFD and BKMGT had lower (P < 0.05) TT than ADLIB from 2100 through 2400. A carryover effect of limit-feeding was evident during a severe heat episode (d 36 to 38) with LIMFD steers having lower (P < 0.05) TT than ADLIB. In Exp. 2, TT were obtained from 24 crossbred steers assigned to three treatments, consisting of no water application (CON), water applied to feedlot mound surfaces from 1000 to 1200 (AM) or 1400 to 1600 (PM). From 2200 to 0900 and 1200 to 1400, steers assigned to morning sprinkling treatment had lower (P < 0.05) TT than steers assigned to afternoon sprinkling treatment. In Exp. 3, 24 steers were utilized in a 2 x 2 factorial arrangement of treatments with factors of feeding time [0800 (AMF) and 1400 (PMF)] and sprinkling (WET and DRY). Tympanic temperatures were monitored under hot environmental conditions on d 30 to 32 and 61 to 62. A feeding time x sprinkling interaction (P < 0.001) was evident on d 30 to 32, although AMF/DRY steers had the highest (P < 0.05) TT. On d 61 to 62, TT of PMF steers was higher (P < 0.05) than AMF between 1500 to 1800. Use of sprinklers can effectively reduce TT of feedlot cattle, whereas shifting to an afternoon vs morning feeding time was most beneficial when bunks were empty several hours prior to feeding.     

Associations between immune competence phenotype and feedlot health and productivity in Angus cattle

Genetic strategies aimed at improving general immune competence (IC) have the potential to reduce the incidence and severity of disease in beef production systems, with resulting benefits of improved animal health and welfare and reduced reliance on antibiotics to prevent and treat disease. Implementation of such strategies first requires that methodologies be developed to phenotype animals for IC and demonstration that these phenotypes are associated with health outcomes. We have developed a methodology to identify IC phenotypes in beef steers during the yard weaning period, which is both practical to apply on-farm and does not restrict the future sale of tested animals. In the current study, a total of 838 Angus steers, previously IC phenotyped at weaning, were categorized as low (n = 98), average (n = 653), or high (n = 88) for the IC phenotype. Detailed health and productivity data were collected on all steers during feedlot finishing, and associations between IC phenotype, health outcomes, and productivity were investigated. A favorable association between IC phenotype and number of mortalities during feedlot finishing was observed with higher mortalities recorded in low IC steers (6.1%) as compared with average (1.2%, P < 0.001) or high (0%, P = 0.018) IC steers. Disease incidence was numerically highest in low IC steers (15.3 cases/100 animals) and similar in average IC steers (10.1 cases/100 animals) and high IC steers (10.2 cases/100 animals); however, differences between groups were not significant. No significant influence of IC phenotype on average daily gain was observed, suggesting that selection for improved IC is unlikely to incur a significant penalty to production. The potential economic benefits of selecting for IC in the feedlot production environment were calculated. Health-associated costs were calculated as the sum of lost production costs, lost capital investment costs, and disease treatment costs. Based on these calculations, health-associated costs were estimated at AUS$103/head in low IC steers, AUS$25/head in average IC steers, and AUS$4/head in high IC steers, respectively. These findings suggest that selection for IC has the potential to reduce mortalities during feedlot finishing and, as a consequence, improve the health and welfare of cattle in the feedlot production environment and reduce health-associated costs incurred by feedlot operators.