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* Texas Tech University, Lubbock 79409;
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Texas A&M Research and Extension Center, Amarillo 79106; and
and
West Texas A&M University, Canyon 79016
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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0.12) DMI, ADG, or G:F during the 35-d period, but the percentage of cattle treated once or more for bovine respiratory disease (BRD) was greater for control (P = 0.04) than for PTSF yeast heifers (24.0 vs. 13.78% respectively). In Exp. 3, 2 loads of beef heifers (180 heifers; average initial BW = 209.0 kg) that were not treated with antibiotic at the time of arrival processing were fed a 70% concentrate receiving diet and assigned the same 2 treatments as in Exp. 2. No differences (P > 0.72) were noted between treatments in ADG, DMI, and G:F for the 35-d receiving period, and BRD morbidity pooled across loads did not differ between treatments (40.2 vs. 33.1% for control vs. PTSF yeast). Providing PTSF yeast in an oral paste at the time of processing combined with the addition of 0.5 g of yeast·animal–1·d–1 in the diet had little effect on receiving period performance; however, it decreased BRD morbidity in heifers given florfenicol on arrival but was without effect on BRD morbidity in heifers that did not receive a prophylactic antibiotic.
Key Words: bovine respiratory disease • dry matter intake • feedlot beef cattle • florfenicol • Saccharomyces cerevisiae subspecies boulardii
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). Proper nutrition is essential for a healthy immune system, but low feed intake by highly stressed, lightweight cattle often makes it difficult to alter their nutrient status through dietary changes. Thus, finding methods to ensure adequate intake by such cattle is a potentially important means of improving their nutritional status and overall health in the feedlot. Feeding live, viable yeast or yeast cultures might provide a means to increase feed intake and improve health of newly received cattle (Cole et al., 1992; Zinn et al., 1999).
Responses to live yeast could interact with the manner in which newly received calves are treated after arrival. Lightweight cattle that are considered at high risk of BRD morbidity are often given a prophylactic antibiotic injection or fed antibiotics in the receiving diet (Duff et al., 2000). Factors associated with certain antibiotics (e.g., transfer of a strong antibiotic to the gut and its subsequent effects on the microbial population) might negatively affect feed intake. For example, Moseley et al. (2004) reported that healthy cattle injected with florfenicol had decreased DMI for up to 15 d compared with untreated controls. In human studies, Saccharomyces cerevisiae subspecies boulardii has been shown to decrease antibiotic-associated diarrhea (McFarland and Bernasconi, 1993).
Our objectives were 3-fold. First, we evaluated the effects of feeding Saccharomyces cerevisiae subspecies boulardii [ProTernative Stress Formula (PTSF) yeast, Ivy Natural Solutions, Overland Park, KS] on feed intake by healthy beef cattle given a dose of florfenicol. Second, we determined the effects of PTSF yeast on health and performance when added to practical diets for lightweight, newly received heifers treated with florfenicol at the time of arrival processing. Third, we evaluated the effects of PTSF yeast on health and performance of newly received heifers that were not treated with a prophylactic antibiotic.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Experiment 1
Pilot Study.
The pilot study was conducted to verify that a single injection of florfenicol (Nuflor, Schering-Plough Animal Health, Union, NJ) given s.c. in the neck would decrease feed intake by healthy beef steers. Ten beef steers (average BW = 391 ± 3.9 kg) were selected on the basis of BW from a larger group of 81 steers and were housed individually in concrete, partially slotted-floor pens (2.9 m wide x 5.6 m deep; 2.4 m of linear bunk space) at the Texas Tech University Burnett Center. These cattle had been fed a restricted quantity of a 65% concentrate diet (Table 1) for approximately 6 wk, and they were gradually increased to ad libitum intake of this diet over a period of 1 wk. After ad libitum intake was achieved, the diet was fed once daily at approximately 0800 in quantities sufficient to allow for 0.5 to 2.3 kg/d (as-fed basis) of orts. After 10 d, feed bunks were cleaned at 0700, and a 5-d baseline intake measurement period was initiated. Daily weights of the quantities of feed offered to each steer and the orts from the previous day’s feed delivery were weighed to the nearest 0.045 kg using an electronic platform balance (Ohaus Corp., Pine Brook, NJ). Diet samples collected when the feed was delivered to the feed bunks and daily samples of orts were analyzed for DM content by drying for approximately 22 h in a forced-air oven at 100°C. After the 5-d baseline measurement period, at approximately 0630, the feed bunks were cleaned and the orts were weighed. All 10 steers were weighed individually [Single-Animal Squeeze Chute (C & S, Garden City, KS) set on 4 load cells (Rice Lake Weighing Systems, Rice Lake, WI); the scale was calibrated with 454.5 kg of certified weights on the previous day]. At the time of weighing, 5 steers were injected s.c. in the neck (no more than 10 mL/site) with florfenicol at a rate of 40 mg/kg of BW, and 5 steers were injected with the same volume of sterile water (Vedco, St. Joseph, MO). After weighing and injection, the steers were returned to their respective pens and offered the same 65% concentrate diet they had received during the 5-d baseline period. Measurements of feed offered and orts continued for the next 6 d as described for the baseline period. At the end of the 6-d period, the steers were weighed individually at approximately 0730.
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As noted for the pilot study, 81 steers were available for use in the experiment, and the 60 steers of lightest BW (average BW = 383 ± 13.8 kg) were weighed individually. As before, these cattle had been previously fed restricted quantities of a 65% concentrate diet (Table 1
), and during the time the pilot study was conducted they were gradually increased to ad libitum consumption of this diet. The BW data were sorted from lightest to heaviest, and groups of 10 steers were assigned on the basis of BW to 6 blocks. Within block, steers were assigned randomly to treatments, beginning with the lightest pair in the block and proceeding to the heaviest pair. Treatments were then assigned randomly to the 2 pens within a block. Four days later, the 60 steers to be used in the experiment were sorted to their assigned pens (same type of pens as used in the pilot study).
The main study began 2 d after the steers were sorted to pens. The PTSF yeast treatment was applied by weighing (to the nearest 0.1 g using) 15 g (0.5 g/steer) of yeast, placing the weighed yeast into a 2.5-L glass bottle, adding 2 L of warm tap water, mixing, and pouring the contents of the bottle into a plastic sprinkler can. The residue in the glass bottle was rinsed into the sprinkler can with an additional 500 mL of tap water, after which the contents of the sprinkler can were poured over the feed (same 65% concentrate diet used in the pilot study; Table 1) as it was mixing in a mixer/delivery unit (84-8, Roto-Mix, Dodge City, KS). After approximately 3 min of mixing, the feed was delivered to the pens. Control pens received 2.5 L of tap water only, using the same procedures and another sprinkler can.
After 5 d, the feed bunks of all 12 pens were cleaned of any unconsumed feed, and orts were weighed and analyzed for DM content as described for the pilot study. Beginning at approximately 0700, each pen of steers was taken through a working chute, and an individual BW measurement (d 0) was obtained. Based on this BW measurement, each steer was injected s.c. in the neck (40 mg/kg of BW, with no more than 15 mL/injection site) with florfenicol. The BW was rounded to the nearest 22.6-kg increment to determine the dose. Steers were then returned to their pens, and treatment diets were fed as they had been for the previous 5 d.
During the next 7 d, the feed bunk for each pen was cleaned daily, and orts were weighed and dried in a forced-air oven at 100°C, as described for the pilot study. Diet samples were collected 3 times during this period and analyzed for DM. From d 8 through 21, feed bunks for all pens were managed to allow for a minimal accumulation of unconsumed feed, with orts weighed, sampled, and analyzed for DM content on a weekly basis. Diet samples were collected for DM analysis once each week from d 8 to 21. Composite samples of the 2 treatment diets fed during each week were analyzed by SDK Laboratories (Hutchinson, KS) for chemical components. Averaged over the 2 treatments, composition values (%, DM basis) were as follows: DM = 81.93; CP = 13.05; ADF = 19.58; ether extract = 4.40; Ca = 0.69; P = 0.24; and K = 1.14. All steers were weighed individually at approximately 0700 on d 21 to end the study.
Statistical Analyses.
For the pilot study, intake for the 6-d period after the injection of florfenicol or sterile water was analyzed as a completely random design with repeated measures using the MIXED procedure (SAS Inst. Inc., Cary, NC). The variance-covariance structure of the repeated measures (days after injection) was evaluated using autoregressive and compound symmetry structures, with homogenous or heterogeneous variance across days. A compound symmetry structure with homogeneous variance was found to provide the best fit. Because of random differences in initial BW, intake data were expressed relative to the average BW for the 6-d intake measurement period. Intake per unit of BW on the day before the beginning of the 6-d period also was included as a baseline covariate.
For the main study, pen BW and weekly DMI data were analyzed as a randomized complete block design using the MIXED procedure of SAS. Pen was the experimental unit, block was a random effect, and the residual was used to test for treatment effects. Daily intake data over the first 7 d after florfenicol injection were analyzed initially as a randomized complete block design with repeated measures using the MIXED procedure. Treatment and the treatment x day interaction were fixed effects, and block was considered random. As with the pilot study, different variance-covariance structures were evaluated, and the autoregressive covariance/heterogeneous variance structure provided the best fit. Because of the heterogeneous variance structure over days, and because fitting additional parameters associated with the heterogeneous structure might decrease the sensitivity for detecting treatment effects and treatment x day interaction, a subsequent analysis was conducted within each of the 7 d after florfenicol injection using the same model as for the BW and weekly DMI data.
Experiment 2
Receipt and Processing of Cattle.
Three loads of beef heifers were purchased from auction markets in Mississippi and shipped from Meridian, MS, on the evenings of 13 July, 10 August, and 8 September, 2005, respectively, arriving at the Burnett Center the next morning. Load 1 (91 heifers) was 14.5 h in transit, with a 3.07% shrink from a pay weight of 240.7 kg (average arrival BW = 233.3 kg). Cattle in load 1 were allowed access to water after unloading. Load 2 (93 heifers) was 13.75 h in transit, with a 6.08% shrink from a pay weight of 238 kg (average arrival BW = 223.5 kg). As with load 1, the cattle were allowed access to water after unloading. Load 3 (93 heifers) was 17 h in transit, with a 4.7% shrink from a pay weight 237.2 kg (average arrival BW = 226.1 kg). Heifers in load 3 were processed immediately after unloading (no access to water). Processing procedures and method of assignment to treatment that are described in the subsequent sections were consistent among the 3 loads.
Within 1 h of unloading, the heifers in each load were processed in the Burnett Center working facilities, which included: 1) placement of a uniquely numbered ear tag in the left ear; 2) an individual BW measurement; 3) vaccination (s.c.) with a modified live virus vaccine (Titanium 5, Agri-Labs, Des Moines, IA) and a clostridial bacterin-toxoid (Vision 7 with SPUR, Intervet, Millsboro, DE); 4) injection (i.m.) with 2 mL of vitamin A/D3 solution (Phoenix Pharmaceuticals, St. Joseph, MO; 500,000 IU of vitamin A and 75,000 IU of vitamin D3/mL); 5) deworming with 25 mL of moxidectin down the middorsal line (Cydectin, Ft. Dodge Animal Health, Overland Park, KS); 6) injection (s.c.) with florfenicol, with the dose determined to the nearest 4.5 kg of BW; and 7) assignment to treatment. The time required to process each load was approximately 2.5 to 3 h.
Procedures for Assignment of Cattle to Treatments.
The same 2 treatments used in Exp. 1 (control or PTSF yeast) were applied at the time of processing. Treatments were assigned by a coin toss before processing to establish the treatment for the first calf, after which the treatments were alternated between control and PTSF yeast. Yeast calves received an oral dose of a paste (applied via a caulking gun placed in the corner of the heifer’s mouth) containing PTSF yeast, to supply approximately 1 g of yeast/heifer. Control calves received an oral dose of an equivalent volume of water (applied in the corner of the mouth). After processing, heifers in the 2 treatment groups were housed in separate, temporary sorting pens until a sufficient number of each treatment (9 to 10 heifers per pen, depending on the total number in the load) had been processed to fill 2 soil-surfaced receiving pens (approximately 5.5 m x 30.5 m; 4.57 m of linear bunk space). After processing, each pair of control and PTSF yeast pens was moved to adjacent soil-surfaced pens. Each pair of pens within a load was considered a block, with blocks accounting for processing order and location in the feedlot.
Application of Treatments and Routine Feeding Procedures.
After processing and assignment to pens, heifers in each load were offered (as-fed basis) approximately 1.4 kg/heifer of long-stemmed, sorghum Sudangrass hay and 1.4 kg/heifer of the 65% concentrate receiving diet (Table 1). Heifers in the PTSF yeast treatment were fed 0.5 g·heifer–1·d–1 of PTSF yeast mixed in the receiving diet. The procedure to apply the yeast was the same as in Exp. 1, with control pens receiving water only. On d 21 after arrival, heifers in each load were switched to a 75% concentrate diet (Table 1). Diets were fed using the Roto-Mix delivery system described for Exp. 1, with a mixing order of control followed by PTSF yeast diets.
Additional BW measurements (same facilities and equipment as in Exp. 1) were collected for each load of heifers on d 14, 28, and 35 (end of the experimental period) after arrival. On d 14, heifers in each load were revaccinated with Titanium 5 (Agri-Labs) and implanted in the right ear with Ralgro (Schering-Plough Animal Health). Average daily gain was calculated (change in unshrunk BW divided by days in period) for the periods of d 0 to 14, d 0 to 28, and d 0 to 35.
Estimates of the approximate quantity of unconsumed feed and orts remaining in the feed bunk were made in each of the 10 pens/load from 0700 to 0730 daily. Adjustments to the feed delivery for each pen were made to ensure ad libitum access to feed. As noted previously, sorghum Sudangrass hay was fed after the cattle were processed, and hay feeding was continued at the rate of 0.91 to 1.4 kg (as-fed basis)/heifer daily for the first 6 (load 1) to 7 (loads 2 and 3) d after processing. Diet samples (and hay samples during the first week) were taken twice weekly from the feed bunks to determine the DM content for each load, as described for Exp. 1. Feed bunks were cleaned on d 7, 14, 21, 28, and 35, and orts were weighed and dried as in Exp. 1. The DMI of each pen during various periods of the study was calculated by subtracting the quantity of dry feed refusal at the end of each period from the total dietary DM delivered to each pen during that period. The number of animals housed per pen was multiplied by number of days in the weigh period to determine animal days, which were then divided into the corrected total DM delivered to the pen to obtain the average DMI/heifer.
Diet samples were ground to pass a 2-mm screen in a Wiley mill and analyzed for DM, CP, ADF, Ca, and P (Galyean, 1997) in the Texas Tech University Ruminant Nutrition Laboratory. Chemical composition (%, DM basis) for the hay was as follows: DM = 86.22; ash = 10.99; CP = 12.76; ADF = 32.81; Ca = 0.44; and P = 0.20. Similarly, composition of the 65% concentrate diet averaged over the 2 treatments and 3 loads was as follows: DM = 82.23; ash = 6.39; CP = 13.93; ADF = 26.04; Ca = 0.71; and P = 0.28, and composition of the 75% concentrate diet averaged over the 2 treatments and 3 loads was as follows: DM = 82.40; ash = 5.39; CP = 13.16; ADF = 21.51; Ca = 0.61; and P = 0.27.
Assessment and Treatment of Morbid Cattle.
Heifers in each load were monitored every morning for signs of morbidity from BRD. Signs included lethargy, anorexia, nasal and ocular discharge, and labored breathing. Heifers showing these signs were removed from their pen for a more thorough evaluation. Antimicrobial therapy was given when the rectal temperature of a heifer that had been pulled from the pen was 39.4°C, after which the heifer was returned to its pen. The antimicrobial therapy schedule was based on the number of times an animal was pulled for treatment. The first time an animal was treated, it received ceftiofur, crystalline-free acid, sterile suspension (Excede, Pfizer, Eaton, PA) at a rate of 1.5 mL/45.4 kg of BW given s.c. in the middle third of the posterior aspect of the ear. In addition to antibiotic treatment, heifers in the PTSF yeast treatment group were given an oral dose of a paste containing PTSF yeast (same as at arrival processing), whereas control heifers received an oral dose of an equal volume of water. Heifers that required a second treatment received tilmicosin phosphate (Micotil, Elanco Animal Health, Indianapolis, IN) at a rate of 1.5 mL/45.4 kg of BW given s.c. plus 2 mL/45.4 kg of BW (s.c.) of Penicillin G Benzathine and Penicillin Procaine G (150,000 units of each/mL, Aspen Veterinary Resources, Kansas City, MO). As with the first treatment, heifers received the oral paste or water at the time antibiotic therapy was given. Heifers requiring a third treatment were considered chronics and were removed from the experiment. During the experiment, 9 heifers either died or were removed as chronics [0 for load 1; 5 for load 2 (4 control heifers and 1 PTSF yeast heifer); and 4 for load 3 (4 control heifers)].
Statistical Analyses.
Performance data were analyzed using the MIXED procedure of SAS, with a model that included the fixed effect of treatment and the random effects of load, load x treatment, and block nested within load. Preliminary analyses of the data with load and load x treatment considered as fixed effects revealed no indication of load x treatment interactions (P = 0.12 to 0.97). Morbidity data were analyzed with the GLIMMIX procedure of SAS. The proportion of cattle in each pen that were treated 1 or more times for BRD was the dependent variable, with a model that included the fixed effect of treatment and the random effects of load, load x treatment, and block nested within load. A default logit link function with a binomial distribution was assumed. Percentages of morbidity by treatment were calculated with the MEANS procedure of SAS, and these values along with the odds ratio (odds of BRD for control vs. PTSF yeast) are reported. Because cattle with 2 or more treatments were infrequent in the data set (12.7% of total heifers treated), these data were not analyzed statistically. Morbidity data also were analyzed by load using a GLIMMIX model that included the fixed effect of treatment and the random effect of block.
Experiment 3
Receipt, Processing, and Assignment of Cattle to Treatments.
Two loads of heifers were ordered from a commercial order buyer (Vann-Roach Cattle Co., Fort Worth, TX). Load 1 (102 heifers; BW = 209.1 kg, SD = 15 kg) was received at the Texas Agriculture Experiment Station feedlot in Bushland, TX, on 15 May, 2006, and load 2 (98 heifers; BW = 208.6 kg, SD = 14.5 kg) was received on 26 May 2006. On arrival, heifers were identified with a uniquely numbered ear tag, and rectal temperature and initial BW were recorded. Heifers with a rectal temperature 40°C were administered 6.6 mg/kg of BW of Excede (Pfizer) s.c. in the middle one-third of the left ear. Heifers were placed into pens and fed approximately 1.3% of BW (DM basis) of a receiving diet (Table 1), which was fed for the entire trial. Ninety heifers per load were used in the study, so some heifers were removed from the pool of heifers available for use. Heifers were removed based on BW (light or heavy), temperament, or eye problems. If additional heifers needed to be removed after consideration of these reasons, they were selected randomly from the remaining pool. Heifers selected for the study were stratified by arrival BW and assigned randomly to pens that had previously been blocked by pen surface material (fly ash or clay) and assigned randomly to treatment. Only 1 heifer was treated on arrival in load 2, and this heifer was removed from the study pool. Heifers from load 1 were blocked so that heifers that had received Excede at the time of arrival were equally allocated across pens and treatments. Treatments with Excede at arrival were not included in the morbidity count for each pen; however, subsequent treatments for these heifers were included in the morbidity count.
After approximately 24 h of rest, the heifers were processed as follows: 1) s.c. injections in the neck of a modified live virus vaccine (Vista 5, Intervet) and a clostridial bacterin-toxoid with Haemophilus somnus (Vision 7, Intervet); 2) treatment with a combination of ivermectin and clorsulon (Ivomec Plus, Merial, Atlanta, GA) for parasite control; 3) horn tipping as needed; 4) individual BW measurement; and 5) sorting to assigned pens. Weights collected on arrival were used as initial BW for all performance calculations. On d 23 or 24 (loads 1 and 2, respectively), heifers were revaccinated with Vision 7, and individual BW were measured.
Application of Treatments and Routine Feeding Procedures.
Heifers were fed the receiving diet once daily in quantities sufficient to ensure ad libitum consumption. Feed bunks were evaluated daily at 0630 and feed allotted so that approximately 0.22 kg remained in the bunk each morning. When wet or stale feed remained in the bunk, orts were weighed, and a subsample was collected for DM determination. Orts were subtracted from the feed delivered on a DM basis to calculate DMI. Treatments were control and PTSF yeast, as described for Exp. 2. As before, the yeast treatment was added to the receiving diet by mixing the culture with approximately 2 L of warm water and sprinkling the mixture over the diet as it was mixing, with the solution being allowed to mix for approximately 3 min. Unlike Exp. 1 and 2, no water was added to the control diet. As in Exp. 2, the mixing order was the control diet followed by the PTSF yeast treatment diet. When possible, a clean-out load was fed to other cattle at the feedlot; otherwise, the mixer was cleaned by hand to eliminate cross contamination. Samples of dietary ingredients used during the experiment were analyzed by Servitech Laboratories (Amarillo, TX) for chemical components, with resulting average composition (%, DM basis) of DM = 78.80; CP = 17.56; ADF = 17.67; ether extract = 2.93; Ca = 0.90; P = 0.55; K = 1.69; and S = 0.29.
Assessment and Treatment of Morbid Cattle.
As described for Exp. 2, heifers were evaluated daily for signs of BRD. Heifers pulled for evaluation that had a rectal temperature 39.7°C received a s.c. injection of Excede (Pfizer) in the ear. Heifers that did not respond to Excede were given up to 2 s.c. injections of 5 mg/kg of BW of enrofloxacin (Baytril, Bayer Corp., Shawnee Mission, KS). Heifers with rectal temperatures <39.7°C but 39.2°C were treated similarly at the discretion of the personnel treating the cattle.
After 35 d, final BW were determined by limit feeding the heifers for 7 d at 1.5% of BW and weighing for 2 consecutive days. This approach was used to decrease variation in the final BW measurement associated with gut fill. Thus, this final, unshrunk BW measurement was used for the d-35 BW and combined with the DMI from d 0 to 35 to calculate G:F for the 35-d trial period.
Statistical Analyses.
Statistical analysis for morbidity data was conducted with the GLIMMIX procedure of SAS, with a binomial distribution and a logit link function as described for Exp. 2. The statistical analysis for performance data was conducted using the MIXED procedure of SAS as a randomized incomplete block design. Morbidity and performance data were analyzed with treatment, load, and the load x treatment interaction as fixed effects in the model statement. When little evidence for a load x treatment interaction existed (P > 0.20), load and the load x treatment interaction were considered random effects. For all analyses, degrees of freedom were corrected using the Satterwaite option.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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. As noted previously, average BW differed slightly between the 2 groups, so DMI was expressed as a percentage of BW. Both groups of cattle (sterile water and florfenicol) experienced a substantial drop in DMI from the values observed on the day before injection. On the day of injection, steers injected with florfenicol tended (P = 0.092) to have a lower DMI than steers injected with sterile water (15.6% decrease). The negative effect of florfenicol injection on DMI by healthy beef steers was further magnified on the day after injection, with a 22.2% decrease in DMI (P = 0.015) by steers injected with florfenicol compared with those injected with sterile water. From the day after injection onward, there were no significant differences in DMI between treatments, and cattle injected with florfenicol clearly reached equal intake with the controls by d 3 to 4 of the 6-d period.
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, who used healthy beef cattle in 2 crossover-design experiments. Cattle at 2 locations (1 in which cattle were fed in pens and 1 in which they were fed individually) were injected with ceftiofur crystalline free acid (s.c. at the base of the ear) or florfenicol (s.c. in the neck) or not treated. At both locations, injecting cattle with florfenicol decreased DMI compared with the untreated controls and those injected with ceftiofur, with effects lasting up to 15 d. In our case, effects of florfenicol on DMI were not evident beyond the day after injection. In addition, our results suggest that the process of handling and injecting the steers with saline or florfenicol decreased DMI, albeit the decrease was greater with florfenicol. Based on the results of the pilot study, we concluded that injecting florfenicol to impose a challenge in healthy steers would provide a valid model for evaluating the response in DMI to supplementation with PTSF yeast in the main study.
Main Study—Feed Intake after Injection with Florfenicol.
Dry matter intake during the 5-d period before the injection of florfenicol was essentially the same for the control and PTSF yeast groups (P = 0.544; data not shown). As in the pilot study, intake dropped substantially on the day of injection compared with the average of the 5-d period before injection, but DMI did not differ (P = 0.661) between treatments (Figure 2). Intake decreased further the day after injection (d 1 to 2), but again, treatments did not differ (P = 0.859). By the second day after injection (d 2 to 3), however, DMI began to increase for steers fed PTSF yeast, but it remained essentially unchanged for control cattle, with the difference approaching significance (P = 0.107). Similarly, for d 3 to 4, DMI was numerically but not significantly greater (P = 0.197) by cattle fed PTSF yeast compared with the control cattle. From d 4 through the remainder of the 7-d period, no differences were noted between treatments, although DMI was numerically greater by cattle supplemented with yeast on these days (Figure 2).
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Calves fed yeast culture generally had greater DMI than controls for several days after being inoculated with infectious bovine rhinotracheitis virus (Cole et al., 1992). Similarly, in lightweight calves subjected to weaning, fasting, refeeding, and fasting, adding 1 or 2% yeast culture to the diet tended to increase DMI for up to 4 wk after the stress (Phillips and VonTungeln, 1985). In contrast, Zinn et al. (1999) did not observe changes in DMI when lightweight steers were supplemented yeast culture. Our study involved the feeding of a live yeast product rather than yeast culture, and all cattle were injected with a strong antibiotic, which was not the case in previous studies with yeast culture. Saccharomyces cerevisiae subspecies boulardii has decreased antibiotic-associated diarrhea in humans (McFarland and Bernasconi, 1993), so the short-term DMI response we observed with PTSF yeast could well be related to the concurrent injection of florfenicol and might not occur in the absence of antibiotic therapy.
Experiment 2
Performance.
As noted previously, preliminary statistical analyses of the data were conducted with load considered as a fixed effect, which allowed testing the load x treatment interaction. Because these analyses revealed no indication of load x treatment interactions (P = 0.12 to 0.97), data were analyzed with load assumed to be a random effect, and results are presented averaged over the 3 loads (Table 2). With the exception of hay DMI (P = 0.01), no differences (P 0.12) were noted between treatments for performance. Hay was limit-fed, so the small difference in hay DMI (0.98 vs. 0.93 kg·heifer–1·d–1) for the control and PTSF yeast treatments, respectively) is difficult to explain and probably not of practical importance, likely reflecting very low variation in the measurement. Average daily gain did not differ between treatments, although numerical advantages for the PTSF yeast treatment were evident from d 0 to 14 and d 0 to 28; however, changes in ADG were somewhat inconsistent among the 3 loads (data not shown). Short-term changes in BW, for which changes in gut fill between measurements can have substantial effects on ADG, should be viewed cautiously.
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noted no differences in ADG by calves during the receiving period that were fed a microbial product that contained yeast plus various digestive enzymes. Moreover, this finding is consistent with previous studies (Adams et al., 1981; Cole et al., 1992; Zinn et al., 1999) in which no significant influence on ADG or feed efficiency was noted with the addition of yeast culture to receiving diets. In contrast, in finishing steers fed diets based on barley and potato processing residue, Hinman et al. (1998) reported greater ADG and improved G:F when yeast culture was supplemented (85 g·steer–1·d–1 for the first 28 d, followed by 28 g·steer–1·d–1 for the remainder of the 115-d feeding period). Similarly, Williams (1988) noted increased ADG by finishing steers supplemented with 0.375 or 0.75% yeast culture during the first 56 d of a 105-d feeding period. Whether results with yeast culture can be compared with live yeast, as was fed in the current study, is unknown. Recently, Galvao et al. (2005) evaluated the feeding of 0.5 g/d of Saccharomyces cerevisiae subspecies boulardii yeast added to milk replacer in Holstein calves with failure of passive transfer (based on serum IgG concentrations). Preweaning ADG and DMI tended (P < 0.10) to be increased by yeast, but performance after weaning of these calves was not affected by supplemental yeast. Treated calves had fewer (P < 0.05) days with diarrhea before weaning than control calves (Galvao et al., 2005). Further research is needed to fully describe the effects of live yeast on performance during the receiving and subsequent feeding periods, but present results suggest that feeding PTSF yeast would not have major effects on receiving period performance.
As noted in Exp. 1, when healthy beef steers fully accustomed to their diet and surroundings were injected with florfenicol, DMI decreased substantially from d 0 to 1 after florfenicol injection compared with the average of the 5-d period before injection. By the second day after injection, DMI began to increase for steers fed PTSF yeast, but it remained essentially unchanged for control cattle. Perhaps the numerically greater concentrate DMI by the newly received heifers fed PTSF yeast in Exp. 2 reflected effects of live yeast on intake associated with injection of florfenicol similar to those noted in Exp. 1. Nonetheless, it is likely that the marketing, transport, and processing stressors to which the heifers in Exp. 2 were subjected would have negatively affected their overall intake, thereby decreasing possible effects of florfenicol on DMI and decreasing the magnitude of any potential response to feeding PTSF yeast. Cole et al. (1992) reported that in feeder steers challenged intranasally with infectious bovine rhinotracheitis virus, feeding diets with 0.75% yeast culture tended to allow the calves to maintain a greater DMI and BW after the challenge than calves fed a control diet. In contrast, supplementing yeast culture to newly received steers did not affect DMI in the study of Zinn et al. (1999). Trends in the present data support the findings of Exp. 1 with healthy, heavier steers and suggest that PTSF yeast might stimulate intake by newly received cattle when they are given a strong antibiotic as a prophylactic measure at the time of arrival processing.
Morbidity.
Within loads, no differences (P = 0.21 to 0.28) were noted for the percentage of cattle treated 1 or more times for BRD (Table 3); however, a consistently smaller proportion of the cattle in the PTSF yeast treatment group was treated compared with those in the control group. Thus, when the data were analyzed across the 3 loads, the consistent response and the lack of load and load x treatment variance resulted in an (P = 0.04) increase in the percentage of control heifers treated once or more for BRD compared with PTSF yeast heifers (24.00 vs. 13.78%). The odds ratio was 1.99, indicating that control heifers were approximately twice as likely to be treated for BRD as were PTSF yeast heifers. Reasons for the effect of PTSF yeast on BRD morbidity are unknown; however, the previously noted trends for increased concentrate intake by these heifers might have contributed to (or perhaps reflected) their lower BRD morbidity compared with control heifers. A decrease in morbidity (48%) and in sick days (44%) was observed when 28.4 g/d of Diamond V XP yeast culture was supplemented to stressed calves by Zinn et al. (1999). In addition, Cole et al. (1992) reported that morbid stressed calves supplemented with XP yeast culture required fewer days of antibiotic treatment than controls. Krehbiel et al. (2003) observed decreased morbidity by 27.7% in cattle that received a microbial containing live cultures of Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus casei, and Streptococcus faecium at processing and throughout the receiving period (average = 30 d). McFarland and Bernasconi (1993) noted immunological responses to oral ingestion of S. boulardii in humans and in rats, with an increase in the mean number of erythrocytes, hemoglobin, leukocytes, and phagocytes, as well as increased disaccharidase activity within the intestinal mucosa. These observations might help explain how PTSF yeast affected morbidity in the present experiment, but further research is needed to understand more fully the potential mechanism(s) of action of yeast on BRD morbidity.
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There were no differences in initial BW (P = 0.74; Table 4). As noted previously, load 1 was revaccinated after 23 d, whereas load 2 was revaccinated after 24 d. No differences in ADG (P = 0.66) or G:F (P = 0.71) were detected at revaccination time (Table 4). Similarly, no differences in BW (P = 0.80), ADG (P = 0.78), or G:F (P = 0.72) were detected during the entire 35-d period (Table 4).
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). The lack of an intake response contrasts the trends for increased DMI observed in Exp. 2; however, the heifers used in Exp. 2 were administered florfenicol at the time of arrival processing, whereas heifers in Exp. 3 were not given an antibiotic on arrival. Moreover, the heifers in Exp. 3 had a relatively high DMI throughout the study, averaging approximately 2.0% of initial BW within the first 7 d and approximately 2.6% of BW during the overall study period compared with 1.8% of average BW for the overall 35-d receiving period for heifers in Exp. 2. Lightweight, stressed beef cattle often have low DMI, with an average for newly received calves of approximately 1.5% of BW during the first 14 d after arrival reported by Galyean et al. (1999).
The effects of the PTSF yeast and control treatments on BRD morbidity are shown in Table 5. There was a tendency (P = 0.16) for the PTSF yeast treatment to decrease the percentage of cattle treated for BRD from 35.0 to 20.0% in load 1, resulting in an odds ratio of 2.15. These data support the findings of Exp. 2, in which control heifers were 1.99 times more likely to be treated than heifers fed PTSF yeast. Nonetheless, there were no differences between treatments in proportions of cattle treated in load 2 (P = 0.81) and no differences when loads were pooled (P = 0.60). Based on the number of control cattle treated for each load (35.0 vs. 46.0% for loads 1 and 2, respectively), heifers in load 2 seemed to have been stressed to a greater degree than those in load 1. Although no statistical comparisons of loads were conducted, numerical differences in ADG (1.12 vs. 0.99 kg for loads 1 and 2, respectively) and G:F (0.184 vs. 0.168, respectively) would seem to support this observation. These data might suggest the potential for PTSF yeast to decrease morbidity in moderately stressed calves, with little or no effect in highly stressed calves when no antibiotic is administered on arrival.
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Footnotes |
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2 Corresponding author: michael.galyean{at}ttu.edu
Received for publication November 13, 2006. Accepted for publication January 19, 2007.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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