Effect of quebracho condensed tannin extract on fecal gas flux in steers.

Naturally occurring gaseous by-products of ruminant production-carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O)-can negatively affect the environment. Along with enteric fermentation, manure on pasture is among the most significant contributors to non-CO2 emissions. Condensed tannins, a group of naturally occurring phenolic compounds, can alter the route of nutrient excretion and interact with microbes, suggesting they are a plausible feed additive for reducing excreta gas emissions. We evaluated how quebracho (Schinopsis balansae) tannin extract fed at 0, 15, 30, and 45 g kg-1 of dry matter (DM) within a roughage-based diet affected fecal gas emissions at multiple locations (College Station and Stephenville, TX) during two periods corresponding to winter and spring. During both periods, CO2 , CH4 , and N2 O fluxes were determined using the vented-static chamber methodology over 39 d, and cumulative emissions were calculated. A random coefficients model with animal nested within dietary treatment and period as the random factor was analyzed by location due to the presence of collinearity with soil parameters within periods. Daily CO2 flux was influenced by soil moisture and temperature (r = .34; P < .01), whereas CH4 and N2 O were associated with soil moisture. Cumulative gas production confirmed a dietary effect for CO2 and gross CO2 equivalent at the College Station site (P ≤ .001), demonstrating a linear reduction as quebracho inclusion increased. Variance partitioning indicated that dietary treatment and seasonal period likely influenced animal digestive and metabolic parameters. Within specific environments, quebracho supplementation may assist in reducing fecal gas emissions.

Responses in the rumen microbiome of Bos taurus and indicus steers fed a low-quality rice straw diet and supplemented protein.

Bos indicus typically perform better than Bos taurus when consuming a low-quality diet; however, the response to supplementation is generally greater in B. taurus. The underlying mechanisms supporting these responses have not been fully elucidated. Characterization of differences in rumen prokaryotic populations and their functional role in the two subspecies may provide additional insight. Ten cannulated steers (5 Angus and 5 Brahman) were used in concurrent 5 × 5 Latin squares. Animals were offered ad libitum access to rice straw (4.7% CP). Treatments consisted of an unsupplemented control diet and two levels (50 or 120 mg N/kg BW) of isonitrogenous supplements (30% CP), that were either high (H; 74%) or low (L; 26%) in undegradable intake protein. Rumen samples were collected at 0 and 4 h postfeeding and separated into liquid and solid fractions. Rumen bacterial taxa were sequenced utilizing a Roche 454 platform based on the 16s rRNA gene. At 97% sequence similarity, 97,826 operational taxonomic units were identified, which included 24 phyla, 108 families, and 255 genera. Analysis included SAS PROC mixed model, QIIME, and PICRUSt. Across all samples, Bacteroidetes and Firmicutes accounted for 65% and 28% of total bacterial abundance, respectively. The families Prevotellaceae (P = 0.05) and Ruminococcaceae (P = 0.004) and the genera Prevotellaceae (family; P = 0.003) within the phyla Bacteroidetes differed significantly in relative abundance with added protein when compared to the control. Consistent differences in the relative abundance of family and genus taxa between B. indicus and B. taurus suggest roles the symbiotic rumen microbiome may have in the capacity of B. indicus to utilize low-quality forage over a range of supplement types and levels including (Prevotella, Ruminococcus [family], Sphingobacteriaceae [family], Bacteroidales [order], Pontibacter, Bacteroides, Succiclasticum, Barnesiella, and Xylanibacter). Overall bacterial community diversity differences across parameters were limited. Rice straw is recalcitrant to bacterial digestion because of high levels of silica in the epidermis making this straw more resistant to bacterial attachment. Thus, this analysis represents the bacterial diversity and function of the rumen under conditions depleted CP, recalcitrant fiber matrix and restricted digestibility which appear to limit the microbial population to those capable of attaching and digesting complexed structural carbohydrates, resulting in reduced plasticity, and more evenness in diversity across parameters.

Influence of short-term dietary starch inclusion on the equine cecal microbiome.

The objective of this study was to determine bacterial community profiles of the equine cecum in response to abrupt inclusion of varying levels of dietary starch. Seven cecally cannulated Quarter Horse geldings (497 to 580 kg) were used in a crossover design with two 28-d periods and a 28-d washout between each. Horses were randomly assigned to dietary treatments consisting of a commercial concentrate offered as fed at either 0.6 (low starch [LS]) or 1.2% BW (high starch [HS]) daily that was divided into 2 meals at 12-h intervals. Prior to the start of each period, horses were allowed ad libitum access to coastal bermudagrass () hay. Concentrate was fed on d 1 with no adaptation. Cecal fluid was collected on d 1 at h 0 and at 3, 6, 9, and 12 h relative to the initial concentrate meal on d 1. Additional samples were collected 6 h after feeding on d 2, 3, and 7 of each period. Cecal contents were used to determine pH and VFA concentrations and extract microbial DNA. The V4 through V6 region of 16S rRNA gene was amplified using PCR and sequenced on the Roche 454 FLX platform. Sequence analysis was performed with QIIME, and data were analyzed using the MIXED procedure of SAS. Cecal pH tended to decrease ( = 0.09) in horses fed HS in the first 12 h after the first concentrate meal and remained lower ( ≤ 0.05) the following 7 d. Total VFA were greater ( ≤ 0.05) in horses fed HS in the initial 12 h and 7 d after addition of concentrate. Species richness determined using the Chao1 index was unchanged ( > 0.20) over the initial 12 h and decreased ( = 0.01) over 7 d for both treatments. Community diversity determined using the Shannon index tended to decrease ( = 0.06) over the 7 d. Relative abundances of Paraprevotellaceae were greater ( ≤ 0.05) in HS in the first 12 h. Over 7 d, relative abundances of Paraprevotellaceae, Veillonellaceae, and Succinivibrionaceae were greater ( ≤ 0.05) in HS compared with LS. Abrupt and short-term exposure to dietary starch does alter cecal fermentation and microbial community structure in horses, but the impact on horse health is unknown.

Metagenomic Analysis of the Rumen Microbiome of Steers with Wheat-Induced Frothy Bloat.

Frothy bloat is a serious metabolic disorder that affects stocker cattle grazing hard red winter wheat forage in the Southern Great Plains causing reduced performance, morbidity, and mortality. We hypothesize that a microbial dysbiosis develops in the rumen microbiome of stocker cattle when grazing on high quality winter wheat pasture that predisposes them to frothy bloat risk. In this study, rumen contents were harvested from six cannulated steers grazing hard red winter wheat (three with bloat score "2" and three with bloat score "0"), extracted for genomic DNA and subjected to 16S rDNA and shotgun sequencing on 454/Roche platform. Approximately 1.5 million reads were sequenced, assembled and assigned for phylogenetic and functional annotations. Bacteria predominated up to 84% of the sequences while archaea contributed to nearly 5% of the sequences. The abundance of archaea was higher in bloated animals (P < 0.05) and dominated by Methanobrevibacter. Predominant bacterial phyla were Firmicutes (65%), Actinobacteria (13%), Bacteroidetes (10%), and Proteobacteria (6%) across all samples. Genera from Firmicutes such as Clostridium, Eubacterium, and Butyrivibrio increased (P < 0.05) while Prevotella from Bacteroidetes decreased in bloated samples. Co-occurrence analysis revealed syntrophic associations between bacteria and archaea in non-bloated samples, however; such interactions faded in bloated samples. Functional annotations of assembled reads to Subsystems database revealed the abundance of several metabolic pathways, with carbohydrate and protein metabolism well represented. Assignment of contigs to CaZy database revealed a greater diversity of Glycosyl Hydrolases dominated by oligosaccharide breaking enzymes (>70%) in non-bloated samples. However, the abundance and diversity of CaZymes were greatly reduced in bloated samples indicating the disruption of carbohydrate metabolism. We conclude that mild to moderate frothy bloat results from tradeoffs both within and between microbial domains due to greater competition for substrates that are of limited availability as a result of biofilm formation.

Changes in feeding behavior patterns and dry matter intake before clinical symptoms associated with bovine respiratory disease in growing bulls.

Methods to improve accuracy of preclinical detection of bovine respiratory disease (BRD) are needed to reduce the economic impact of this disease, improve animal welfare, and promote more judicious use of antimicrobials in beef cattle. The objectives of this study were to retrospectively characterize time-series deviations in DMI and feeding behavior patterns preceding the display of observed clinical symptoms associated with BRD and to identify those feeding behavior traits that would be most predictive of BRD. The study was conducted with 231 seed stock bulls (391 ± 55 kg initial BW) representing 5 breeds that were housed in a facility equipped with GrowSafe feed bunks at a commercial bull-test facility. All bulls were vaccinated against standard viral and bacterial pathogens before and on arrival at the facility. Daily DMI and feeding behavior traits (frequency and duration of bunk visit events, head-down duration, variance of nonfeeding intervals, and time to approach feed bunk following feed-truck delivery) were measured for 70 d with a GrowSafe system. During a 10-d period from Day 28 to 37 of the trial, 30 bulls were administered antimicrobial therapy for clinical symptoms of BRD (rectal temperatures > 39.5°C). All remaining bulls ( = 201) were administered metaphylactic therapy on Day 38 of the trial in response to an acute decrease in feed intake. A retrospective analysis was conducted using a 2-slope broken-line regression model to identify inflection points in DMI and feeding behavior traits relative to onset of illness. The bulls were separated into 2 cohort groups based on observed clinical illness ( = 30) or those metaphylactically treated ( = 201), with the 2-slope broken-line regression model applied separately to each cohort. The model-detected inflection points for DMI were 6.8 and 3.8 d before observed clinical illness and metaphylactic treatment, respectively, and the reductions in DMI from detected inflection points to the day of observed clinical illness and day of metaphylactic treatment were 39.3 and 49.8%, respectively. Furthermore, the model-detected inflection points for individual feeding behavior traits ranged from 1.3 to 14.2 d before observed clinical illness and from 3.8 to 12.6 d before metaphylactic treatment. Results from this study demonstrate the potential value of electronic behavior-monitoring systems to improve the sensitivity and specificity of preclinical detection of BRD in feedlot cattle.

Effect of postextraction algal residue supplementation on the ruminal microbiome of steers consuming low-quality forage.

Cattle consuming low-quality forages (LQF) require protein supplementation to increase forage utilization via ruminal fermentation. Biofuel production from algal biomass results in large quantities of postextraction algal residue (PEAR), which has the potential to elicit LQF utilization responses similar to cottonseed meal (CSM); however, its effect on ruminal bacterial communities is unknown. Five ruminally and duodenally cannulated Angus steers in a 5 × 5 Latin square had ad libitum access to oat straw diets. Treatments were infused ruminally and consisted of an unsupplemented control; PEAR at 50, 100, and 150 mg N/kg BW; and CSM at 100 mg N/kg BW. Ruminal samples were collected 4 h after supplementation on d 14 of each period and separated into solid and liquid fractions. Each sample was extracted for genomic DNA, PCR amplified for the V4 to V6 region of the 16S rRNA, sequenced on the 454 Roche pyrosequencing platform, and analyzed using the QIIME pipeline. Weighted UniFrac analysis and Morisita-Horn index demonstrated different community composition between liquid and solid fractions. Measures of richness including observed operational taxonomic units (OTU) and abundance coverage estimator metric decreased with greater PEAR provision (P ≤ 0.09). There were 42 core microbiome OTU observed in all solid fraction samples while the liquid fraction samples contained 30 core OTU. Bacteroidetes was the predominant phylum followed by Firmicutes in both fractions, which together characterized more than 90% of sequences. Relative abundance of Firmicutes increased with PEAR supplementation in the liquid fraction (linear, P = 0.02). Among Firmicutes, Lachnospiraceae, Ruminococcaceae, and Clostridiaceae families increased in the liquid fraction with greater PEAR supplementation (linear, P ≤ 0.03). Prevotella represented over 25% of sequences in all treatments, and relative abundance decreased in the solid fraction with increasing PEAR provision (linear, P = 0.01). Fibrobacter and Treponema decreased in the liquid fraction with increasing PEAR (linear, P < 0.10). Results suggest PEAR supplementation increased forage utilization by increasing members of Firmicutes within the liquid fraction of the rumen microbiome.

Longitudinal shifts in bacterial diversity and fermentation pattern in the rumen of steers grazing wheat pasture.

Grazing steers on winter wheat forage is routinely practiced in the Southern Great Plains of the US. Here, we investigated the dynamics in bacterial populations of both solid and liquid ruminal fractions of steers grazing on maturing wheat forage of changing nutritive quality. The relationship between bacterial diversity and fermentation parameters in the liquid fraction was also investigated. During the first 28 days, the wheat was in a vegetative phase with a relatively high crude protein content (CP; 21%), which led to the incidence of mild cases of frothy bloat among steers. Rumen samples were collected on days 14, 28, 56 and 76, separated into solid and liquid fractions and analyzed for bacterial diversity using 16S pyrotag technology. The predominant phyla identified were Bacteroidetes (59-77%) and Firmicutes (20-33%) across both ruminal fractions. Very few differences were observed in the rumen bacterial communities within solid and liquid fractions on day 14. However, by day 28, the relatively high CP content complemented a distinct bacterial and chemical composition of the rumen fluid that was characterized by a higher ratio (4:1) of Bacteroidetes:Firmicutes and a corresponding lower acetate:propionate (3:1) ratio. Further, a greater accumulation of biofilm (mucopolysaccharide complex) on day 28 was strongly associated with the abundance of Firmicutes lineages such as Clostridium, Ruminococcus, Oscillospira and Moryella (P<0.05) in the fiber fraction. Such changes were diminished as the CP concentration declined over the course of the study. The abundance of Firmicutes was noticeable by 76 d in both fractions which signifies the development of a core microbiome associated with digestion of a more recalcitrant fiber in the mature wheat. This study demonstrates dynamics in the rumen microbiome and their association with fermentation activity in the rumen of steers during the vegetative (bloat-prone) and reproductive stages of wheat forage.

Effect of increasing amounts of postextraction algal residue on straw utilization in steers.

Algal biomass has been identified as a third-generation biofuel. Significant quantities of the coproduct postextraction algal residue (PEAR) remain after lipid extraction. After extraction, PEAR is concentrated in protein (17.9% CP on a DM basis and 32.5% CP on an ash-free basis), suggesting it may be an alternative to cottonseed meal (CSM) as a protein supplement. Our objectives were to determine the optimal level of PEAR supplementation to steers consuming straw and to compare the effects of PEAR supplementation on straw utilization and N metabolism with an isonitrogenous level of CSM. Five steers (198.2 ± 6.1 kg of BW), in a 5 × 5 Latin square, had ad libitum access to oat straw (80% NDF and 4.5% CP on a DM basis). Treatments were infused ruminally once daily and included no supplemental protein (CON); PEAR at 50, 100, and 150 mg N/kg BW; and CSM at 100 mg N/kg BW. Provision of PEAR increased total digestible OM intake (TDOMI) quadratically (P = 0.01) from 0.9 (CON) to 1.6 kg/d (100 mg N/kg BW of PEAR). Organic matter digestibility (OMD) increased quadratically (P < 0.01) with supplementation and was maximized (55% OMD) at 50 mg N/kg BW of PEAR. At isonitrogenous levels of PEAR and CSM, TDOMI was similar (P = 0.13) as was OMD (P = 0.50). Negative N balance was observed for all treatments except PEAR provided at 100 or 150 mg of N/kg BW. Nitrogen balance was quadratic (P < 0.01) with the greatest retention (1.84 g N/d) occurring at 100 mg N/kg BW of PEAR. There were no differences (P ≥ 0.22) between isonitrogenous PEAR and CSM supplementation in measurements of ruminal ammonia or VFA concentrations. Straw utilization was maximized when PEAR was provided at 100 mg N/kg BW. Our observations suggest cattle provided PEAR utilize straw in a manner similar to those supplemented CSM, indicating PEAR has potential to substitute for CSM as a protein supplement in forage-based operations.

Validation of a system for monitoring feeding behavior in beef cattle.

The objective of this study was to evaluate the use of an electronic radio-frequency-identification-based system (GrowSafe System Ltd., Airdrie, Alberta, Canada) to measure feeding behavior traits in beef cattle fed a high-grain diet. Feeding behavior data were recorded by the GrowSafe system and time-lapse video using 10 heifers over a 6-d period. Observed bunk visit (BV) and meal event data (frequency and duration) were compared with electronic feeding behavior data generated by the GrowSafe system at 5 parameter settings (MPS; 30, 60, 100, 150, and 300 s), which are used to define the maximum duration between consecutive electronic identification recordings to initiate a subsequent BV event. A random coefficient model was used to compare video and electronic data using orthogonal contrasts. Video data were regressed on the electronic feeding behavior data to obtain an estimate of precision (r(2)) and other statistical estimates, including mean square error of prediction and concordance correlation coefficient, to access the adequacy of the electronic system predictions. The variation in MPS values affected BV data, but not meal event data. Electronic meal frequency and duration data were not different (P > 0.50) from observed values, and were not affected by electronic MPS values. The optimal MPS value for prediction of BV and meal event frequency and duration traits was 100 s. Our evaluation indicated the GrowSafe system 4000E was able to predict BV and meal event data when the 100-s MPS was used to analyze the feeding behavior data.

In vitro bacterial growth and in vivo ruminal microbiota populations associated with bloat in steers grazing wheat forage.

The role of ruminal bacteria in the frothy bloat complex common to cattle grazing winter wheat has not been previously determined. Two experiments, one in vitro and another in vivo, were designed to elucidate the effects of fresh wheat forage on bacterial growth, biofilm complexes, rumen fermentation end products, rumen bacterial diversity, and bloat potential. In Exp. 1, 6 strains of ruminal bacteria (Streptococcus bovis strain 26, Prevotella ruminicola strain 23, Eubacterium ruminantium B1C23, Ruminococcus albus SY3, Fibrobacter succinogenes ssp. S85, and Ruminococcus flavefaciens C94) were used in vitro to determine the effect of soluble plant protein from winter wheat forage on specific bacterial growth rate, biofilm complexes, VFA, and ruminal H2 and CH4 in mono or coculture with Methanobrevibacter smithii. The specific growth rate in plant protein medium containing soluble plant protein (3.27% nitrogen) was measured during a 24-h incubation at 39 degrees C in Hungate tubes under a CO2 gas phase. A monoculture of M. smithii was grown similarly, except under H2:CO2 (1:1), in a basal methanogen growth medium supplemented likewise with soluble plant protein. In Exp. 2, 6 ruminally cannulated steers grazing wheat forage were used to evaluate the influence of bloat on the production of biofilm complexes, ruminal microbial biodiversity patterns, and ruminal fluid protein fractions. In Exp. 1, cultures of R. albus (P < 0.01) and R. flavefaciens (P < 0.05) produced the most H2 among strains and resulted in greater (P < 0.01) CH4 production when cocultured with M. smithii than other coculture combinations. Cultures of S. bovis and E. ruminantium + M. smithii produced the most biofilm mass among strains. In Exp. 2, when diets changed from bermudagrass hay to wheat forage, biofilm production increased (P < 0.01). Biofilm production, concentrations of whole ruminal content (P < 0.01), and cheesecloth filtrate protein fractions (P < 0.05) in the ruminal fluid were greater on d 50 for bloated than for nonbloated steers when grazing wheat forage. The molecular analysis of the 16S rDNA showed that 2 different ruminal microbiota populations developed between bloated and nonbloated animals grazing wheat forage. Bloat in cattle grazing wheat pastures may be caused by increased production of biofilm, resulting from a diet-influenced switch in the rumen bacterial population.

Effects of condensed tannins supplementation level on weight gain and in vitro and in vivo bloat precursors in steers grazing winter wheat.

Research was conducted to determine the effects of level of supplementation with quebracho condensed tannins (CT) on in vitro ruminal fluid gas production, in vivo ruminal fluid protein fractions, bloat dynamics, and ADG of steers grazing winter wheat. Two experiments were conducted to 1) enumerate the effect of ruminal fluid from steers fed quebracho CT (0, 1, and 2% CT/kg of DMI) on in vitro gas and methane production from minced fresh wheat forage; and 2) quantify the influence of CT supplementation on ruminal protein characteristics, biofilm complexes, bloat potential, and ADG of steers grazing wheat pasture. Eighteen ruminally cannulated steers (386 +/- 36 kg of BW) were randomly allocated to 1 of 3 treatments that included a control (water infusion) and 2 CT treatment levels (1 or 2% CT/kg of DMI). Treatments were administered daily (63 d) through the rumen cannula as pre-mixes with warm water (approximately 30 degrees C). Rumen contents were collected 2 h postinfusion (at 1030 to 1130) on d 0, 20, 40, 50, and 60. Bloat was visually scored daily for 5 d each wk. In Exp. 1, supplementation of CT decreased the rate of in vitro gas production in a dose-dependent response. In Exp. 2, ADG increased (P < 0.04) at both levels of CT supplementation. Mean bloat score across stage of growth and replicates decreased linearly with increasing CT supplementation; bloat scores were greater (P < 0.001) for the vegetative than for the reproductive stage of plant growth. Biofilm production and rumen fluid protein fractions varied among CT treatments and stage of growth. Addition of CT reduced the severity of bloat, principally through reducing microbial activities, biofilm production, and ruminal gas production. Quebracho CT is potentially a value-added supplement that can decrease the impacts of frothy bloat and increase BW gains in stocker cattle-wheat systems.

Wheat pasture bloat dynamics, in vitro ruminal gas production, and potential bloat mitigation with condensed tannins.

The aim of this study was to determine the effect of winter wheat (Triticum aestivum L.) forage growth stage, forage allowance, time of day, and commercial condensed tannins (CT) on steer bloat dynamics and in vitro ruminal gas production. Twenty-six crossbreed steers (Angus x Hereford x Salers; average initial BW = 194 +/- 26 kg) were used. Wheat forage allowances were either 18 kg (high forage allowance) and 6 kg (low forage allowance) of DM/(100 kg BW.d). In each bloat observation period, fresh wheat forage samples were hand-clipped to ground level in all study pastures for nutrient and in vitro ruminal gas production analyses. In vitro ruminal gas accumulation was measured at 0, 1, 2, 3, 4, 5, 6, and 12 h. Commercial CT was added at 0, 10, 15, and 20 mg of CT/g of DM. Bloat was scored once per week on two consecutive days at 0800 and 1500 during the vegetative stage and once every 2 wk during the reproductive stage of wheat development. Mean bloat score was calculated for each steer by time of day, stage of plant growth, and forage allowance. Bloat was detected in 65.8% of the observation periods. Average bloat scores were four and 2.5 times greater (P < 0.05) in cattle grazing at a high forage allowance than at a low forage allowance in the vegetative and reproductive growth phases of wheat, respectively. Rate of gas production was greater (P < 0.001) in the vegetative stage than in the reproductive stage. Steer bloat score was positively correlated with forage CP (r = 0.22; P < 0.05) and IVDMD (r = 0.32; P < 0.05). Rate of ruminal gas production was positively correlated (P < 0.01) to forage CP (r = 0.48), NPN (r = 0.40), soluble protein (r = 0.32), and IVDMD (r = 0.47). Conversely, negative correlations were found for forage DM (r = -0.20; P < 0.05), insoluble protein (r = -0.40), NDF (r = -0.69), and forage height (r = -0.49; P < 0.01) on the rate of ruminal gas production. Addition of CT at levels greater than 10 mg of CT/g of DM decreased (P < 0.05) the rate of in vitro ruminal gas and methane gas production after 5 h of incubation. Wheat pasture bloat is a complex disorder that varies across an array of forage and environmental conditions. Condensed tannins have the potential to decrease bloat by altering ruminal gas production and soluble protein digestibility from wheat forage.

Morbidity effects on productivity and profitability of stocker cattle grazing in the Southern Plains.

Effects of bovine respiratory disease (BRD) on stocker cattle systems are unknown under extensive rangeland environments. Three experiments were conducted to test the hypothesis that BRD-based morbidity is a major factor affecting the productivity and profitability of stocker cattle grazing Southern Plains rangelands. In Exp. 1 (658 male calves; average BW = 231 kg), 17% of the cattle were treated for BRD <8 d, 6% for 8 to 14 d, and 8% for >14 d. Morbid cattle had lower ADG than did healthy cattle (P < 0.10). Cattle requiring 14 d of pharmaceutical therapy gained less than cattle having <14 d therapy (P < 0.01). In Exp. 2, (279 steers and bulls; average BW = 216 kg), the ADG by steers (0.74 kg x animal(-1) x d(-1)) was greater (P < 0.05) than by bulls castrated after arrival (0.64 kg x animal(-1) x d(-1)). Castration after arrival led to a 13.5% loss in daily gain and a 10.3% loss in season-long gain. More (P < 0.05) bulls castrated after arrival (60%) were morbid compared with steers (28%). In Exp. 3, 633 heifers (average BW = 251 kg) were used to test the effects of morbidity on weight gain and reproduction. Heifers with lower initial weights exhibited increased (P < 0.05) morbidity. Heifers requiring two or more antibiotic treatments gained 0.03 kg/d less (P < 0.10) than did healthy heifers and had lower (P < 0.05) conception rates (66 vs. 81%). Conception rate in twice-treated heifers was 19% less than healthy heifers. Morbid heifers conceived 0.6 mo later (P < 0.05) than healthy heifers. Under the conditions of Exp. 1 and Exp. 2, morbidity decreased net returns 9.7 to 21.3% per animal. Adjusted gross returns per animal in Exp. 3 for replacement heifers were 3 to 7.8% less for morbid heifers.