Effects of isoenergetic supplementation as water use mitigation strategy on water footprint and health of nursing bull calves.

Sustainable livestock systems focus on mitigating natural resource use such as water. Dietary management strategies can significantly reduce the water footprint of livestock animals; however, animal health is of concern when animals reduce water intake due to subacute dehydration. To evaluate potential consequences of this nutritional management intervention, a total of 23, 60 ±â€…3 days old nursing Holstein bull calves, weighing 94.7 ±â€…12.07 kg, were distributed in a completely randomized design and received one of three diets. Control was a basal diet composed of a non-medicated milk replacer (milk replacer; n = 7), and the additional two diets, were composed of the same non-medicated milk replacer in addition to either lipid [n = 8; milk replacer + menhaden fish oil (3 %)] or soluble carbohydrate [n = 8; milk replacer + corn starch (7%) isoenergetic to fat group] supplements. Animals were offered ad libitum mineral mix and water, as well as 120 g/day of a composite mix of dried microbrewery's spent grains. Data were analyzed as linear and generalized linear mixed models with diet as a fixed effect and animal as random utilizing R studio (R Core Team, 2021, Vienna, Austria; SAS Inst., Cary, NC). Within supplementation groups, lipid supplemented calves had the highest lymphocyte (63.24 vs 57.69 counts/100 lymphocytes; P < 0.033), and lowest neutrophil counts (29.3 vs 35.3 counts/100 lymphocytes; P < 0.047). Supplementation significantly increased total serum protein (P = 0.001) and skin moisture (P < 0.011), with carbohydrate group having the highest skin moisture (5.30 vs 3.99; P < 0.047). Supplementation also decreased fecal fluidity scores (P < 0.001) with no significant change in serum electrolytes (P > 0.256). No significant differences were found amongst treatments for the ingestive behavior (P > 0.338). The carbohydrate-supplemented calves significantly decreased all daily water footprints compared to the control and fat-supplemented groups: blue a 47.55 L decrease, (P < 0.001), green a 265.62 L decrease (P = 0.005), and gray a 55.87 L decrease (P = 0.009) water footprint, as well as total water footprint (369.04 L, P = 0.004). Our results indicate the potential to maintain animal performance while increasing water use efficiency through diet supplementation tailored to mitigate water use, without adverse effects on animal health.

Effect of live yeast supplementation on energy partitioning and ruminal fermentation characteristics of steers fed a grower-type diet in heat-stress conditions.

The objective of this trial was to determine the influence of live yeast supplementation (LY), environmental condition (ENV), and their interaction (TRT) on energy partitioning, nitrogen metabolism, and ruminal fermentation dynamics of steers receiving a grower-type diet. The effects of LY and ENV were investigated using a 2 × 2 crossover design that spanned five periods. Eight Angus-crossbred steers were randomly split into pairs and housed in four outdoor pens outfitted with an individualized feeding system. Animals were limit-fed a grower diet (DIET) at 1.2% shrunk body weight (SBW) with no live yeast supplementation (NOY) or a grower diet top-dressed with 10 g LY/d for 14 d (1.2 × 1012 CFU/d). On days 13 and 14, animals were subjected to one of two ENV conditions, thermoneutral (TN; 18.4 ± 1.1 °C, 57.6 ± 2.8% relative humidity [RH]) or heat stress (HS; 33.8 ± 0.6 °C, 55.7 ± 2.7% RH), in two side-by-side, single-stall open-circuit, indirect respiration calorimetry chambers. Data were analyzed using a random coefficients model. Carryover effects were examined and removed from the model if not significant. Gross (GE), digestible, metabolizable, heat, and retained energies were not influenced by DIET, ENV, or TRT (P ≥ 0.202). Gaseous energy, as a percentage of GE, tended to increase during HS (P = 0.097). The only carryover effect in the study was for oxygen consumption (P = 0.031), which could be attributed to the tendency of NOY (P = 0.068) to have greater oxygen consumption. DIET, ENV, or TRT (P ≥ 0.154) had no effects on total animal methane or carbon dioxide emissions. Similarly, DIET, ENV, or TRT (P ≥ 0.157) did not affect ruminal pH, redox, protozoa enumeration, ruminal ammonia concentrations, and acetate-to-propionate ratio. Propionate concentrations were the greatest in animals in TN conditions receiving LY (P = 0.034) compared to the other TRT. This effect is mirrored by TN-LY tending to have greater acetate concentrations (P = 0.076) and total VFA concentrations (P = 0.065). Butyrate concentrations tended to be greater for animals fed LY (P = 0.09). There was a tendency for LY to have elevated numbers of Fusobacterium necrophorum (P = 0.053). Although this study lacked effects of LY on energy partitioning, nitrogen metabolism, and some ruminal parameters during HS, further research should be completed to understand if LY is a plausible mitigation technique to enhance beef animals' performance in tropical and sub-tropical regions of the world.

About 70% of global beef production is located in tropical and sub-tropical regions. With elevated temperatures and significant humidity, these regions impose heat stress on beef animals. Heat stress is the main antagonist to ruminant production as it decreases dry matter intake and digestion and increases energy expenditure due to the animal's need for thermoregulation. Supplementation of live yeast products has proven efficacious at improving ruminal fermentation dynamics. This study sets out to determine if live yeast supplementation to animals in heat stress conditions can positively affect energy partitioning, nitrogen metabolism, and ruminal parameters. Additionally, this study models the ruminal performance after exposure to heat stress or live yeast supplementation. This study identified several interesting in vitro dynamics of previously stressed- or supplemented rumen fluid. Although there were a lack of effects for live yeast supplementation on energy partitioning, nitrogen metabolism, and some ruminal parameters during heat stress, further research should be completed in order to understand if live yeast supplementation is a plausible mitigation technique to enhance the performance of beef animals reared in tropical and sub-tropical regions of the world.

Technical note: Evaluation of sampling methods for methane concentration from in vitro fermentation.

The objectives of this multipart study were 1) to assess the efficacy of sampling methods of methane concentration ([CH4]) of headspace gas produced during in vitro gas production (IVGP) fermentation, 2) to verify whether headspace [CH4] sampled from an exetainer has the same [CH4] as the headspace of IVGP bottles, 3) to measure relative humidity (RH) within an IVGP bottle, and 4) to compare [CH4] on a dry-gas (DG) basis when accounting for water vapor pressure (Pw). The original IVGP protocol recommends placing bottles on ice (0 °C) for 30 min to stop fermentation (ICE). A laboratory protocol recommends placing the bottles in the refrigerator (4 to 6 °C) to slow fermentation for 48 h and subsequently allowing the bottles to return to ambient temperature before sampling (FRIDGE). This study evaluated the previous methods against a direct sampling of the headspace gas after incubation (DIRECT). Rumen inoculum from four rumen-cannulated beef steers was combined and homogenized before incubating the fermentable substrate of ground alfalfa hay. After 48 h of IVGP incubation, each bottle was randomly assigned to a treatment protocol. The pressure (P), volume (V), and temperature (T) of headspace gas in each bottle were recorded. Headspace gas was then thoroughly mixed, and 12 mL gas was removed into an evacuated exetainer for [CH4] sampling via gas chromatography (EXET; Objective 1). Eight bottles from ICE and FRIDGE were randomly selected to follow EXET, whereas the remaining bottles had [CH4] directly measured from their headspace (BOTT; Objective 2). Five diets of differing feed composition and nutrient densities were used with a blank to test the RH of the IVGP slurry (Objective 3). Using RH, [CH4] was transformed to a DG basis to account for Pw (Objective 4). Statistical analysis was completed using a random coefficients model. There were no differences between EXET and BOTT (P = 0.28). The RH of the IVGP slurry was 100% (P = 1.00), confirming that IVGP gas is saturated with water vapor. The P, V, and T differed among treatments (P < 0.01). The [CH4] of DIRECT, ICE, and FRIDGE were different (P < 0.01). Dry-gas P, V, and [CH4] differed among treatments (P < 0.01). As the methods differ in their assessment of [CH4], there is no clear recommendation. Instead, to present a more accurate [CH4], P, V, and T should be measured when sampling headspace gas and equations presented should be used to remove volume inflation due to water vapor and present [CH4] on a DG basis.

Greenhouse gas emissions (GHG) from ruminant production equate to 81% of total global livestock supply chain emissions, with 51% originating from beef cattle production. Traditional in vivo estimation methods of methane (CH4), a highly scrutinized greenhouse gas, are timely and costly. In vitro gas production (IVGP) methods can accurately describe CH4 emission patterns from the rumen but tend to overestimate quantities. Additionally, in vivo estimation methods present CH4 on a dry-gas basis, whereas in vitro do not. In vitro methods utilize a gas chromatography machine to estimate CH4. Laboratory constraints can impose deviations to a strict IVGP protocol. This multi-objective study evaluates three treatment methods of IVGP bottles to understand whether discrepancies exist in CH4 estimation when deviating from the published protocol. To estimate CH4 from IVGP more accurately and provide a more comparable number to in vivo methods, this study also evaluates environmental conditions within an IVGP bottle to formulate a system of equations to calculate CH4 on a dry-gas basis. This study found that the treatment method of the IVGP bottle had an impact on CH4 estimation, and the developed equations should be utilized to produce more comparable estimates.

Characterization of body composition and liver epigenetic markers during periods of negative energy balance and subsequent compensatory growth in postpubertal beef bulls.

This study aimed to characterize the effects of dietary restriction and subsequent re-alimentation on body composition and hepatic gene expression of epigenetic markers of DNA methylation, RNA m6A methylation, and histone acetylation in the liver of postpubertal beef bulls. Twelve Angus × Hereford crossbred bulls (n = 6, 23 ± 0.55 mo [young bulls], 558 ± 6.1 kg; and n = 6, 47 ± 1.2 mo [mature bulls], 740 ± 30.5 kg) were submitted to two dietary regimes per offering of the same hay: low plane of nutrition (90 d) and compensatory growth (90 d). Each animal acted as its own control and were fed Beardless wheat (Triticum aestivum) hay and mineral mix during the trial. Statistical analyses were performed using SAS 9.4 following a pre-post repeated measures design. Bulls in negative energy balance (NEB) decreased (P < 0.001) empty body weight (EBW; 23.1% [-139.1 kg]), empty body fat (EBF; 39.8% [-85.4 kg]), and empty body protein (EBP; 14.9% [-13.5 kg]) and fully recovered at the end of the trial. Body fat accounted for 77.1% of daily changes in body energy status, whereas body protein accounted for only 22.9% (P < 0.001). Relative abundance of epigenetic markers transcripts was analyzed via qPCR. Bulls at NEB tended (P ≤ 0.097) to increase gene expression of epigenetic markers of RNA m6A methylation (METTL14, VIRMA, and WTAP) and increased (P ≤ 0.050) the gene expression of epigenetic markers of DNA methylation (DNMT3A) and histone-acetylation (SIRT3 and SIRT7). Young bulls had a tendency (P ≤ 0.072) of higher RNA m6A methylation, VIRMA, and WTAP than mature bulls. Effect of diet × age interaction was not detected (P ≥ 0.137) for METTL14, VIRMA, WTAP, DNMT3A, SIRT3, or SIRT7. Younger bulls tended to have greater RNA m6A methylation levels than mature bulls, indicating that, while contemporaneously fed the same diet during periods of undernourishment followed by compensatory growth, age has an impact on this epigenetic mechanism. In conclusion, metabolic status seems to carry a greater impact on regulating bovine hepatic epigenetic mechanisms that modulate gene transcription, such as DNA methylation and histone acetylation, than on epigenetic mechanisms that regulate gene translation, such as RNA m6A methylation. During periods of undernourishment followed by compensatory growth, body fat pools appear to change more dynamically and are easily detected having a greater impact on epigenetic markers that modulate hepatic gene transcription rather than translation.

Epigenetics refers to heritable modifications that regulate gene expression without altering DNA sequence, hence, acting on top of the genes. Epigenetic markers change in response to stressors such as environmental factors, nutritional challenges, among other overlooked players that altogether could drastically impair animal performance. During periods of undernourishment followed by fast weight gain, dynamic changes in body composition, especially fat, appear to trigger an increased action of such physiological markers that modulate hepatic gene expression. Findings of this study unveil epigenetic metabolic pathways that deserve further investigation for proper quantification of potential consequences of metabolic stress on the liver of bovines that suffer significant loss of body weight followed by recovery. The alterations at the molecular level shown in this study provide a picture of silent metabolic changes that have not been detected previously in liver metabolism studies of cattle. Therefore, the impact of nutritional management and metabolic stress may be greater than previously expected and differently controlled than previously assumed.

Sperm DNA 5-methyl cytosine and RNA N6-methyladenosine methylation are differently affected during periods of body weight losses and body weight gain of young and mature breeding bulls.

Aiming to characterize the effects of nutritional status on epigenetic markers, such as DNA 5-methyl cytosine (mC) methylation and RNA N6-methyladenosine (m6A) methylation, of bovine sperm, 12 Angus × Hereford crossbred breeding bulls were submitted to nutritional changes for a period of 180 d: no change in body weight (BW) (phase 1 = 12 d), BW loss (phase 2 = 78 d), and BW gain (phase 3 = 90 d) in a repeated measures design. Animals were fed Beardless wheat (Triticum aestivum) hay and mineral mix. Statistical analyses were performed using SAS 9.4 (SAS Inst., Cary, NC). Higher levels of RNA m6A (P = 0.004) and DNA methylation (P = 0.007) of spermatic cells were observed at phase 2 compared with phase 1. In phase 3, sperm RNA m6A methylation levels continued to be higher (P = 0.004), whereas the DNA of sperm cells was similar (P = 0.426) compared with phase 1. Growing bulls had a tendency (P = 0.109) of higher RNA m6A methylation levels than mature bulls. Phase 2 altered scrotal circumference (P < 0.001), sperm volume (P = 0.007), sperm total motility (P = 0.004), sperm progressive motility (P = 0.004), total sperm count (P = 0.049), normal sperm (P < 0.001), abnormal sperm (P < 0.001), primary sperm defects (P = 0.039), and secondary sperm defects (P < 0.001). In phase 3, bulls had scrotal circumference, sperm volume, sperm motility, sperm progressive motility, total sperm count, normal and abnormal spermatozoa, and primary and secondary spermatozoa defects similar to phase 1 (P > 0.05). Serum concentrations of insulin-like growth factor-1 and leptin decreased during phase 2 (P = 0.010), while no differences (P > 0.05) were detected between phases 3 and 1; growing bulls tended (P = 0.102) to present higher leptin levels than mature bulls. Specific for mature bulls, DNA methylation was positively correlated with leptin concentration (0.569, P = 0.021), whereas for young bulls, DNA methylation was positively correlated with abnormal spermatozoa (0.824, P = 0.006), primary spermatozoa defect (0.711, P = 0.032), and secondary spermatozoa defect (0.661, P = 0.052) and negatively correlated with normal spermatozoa (-0.824, P = 0.006), total sperm count (-0.702, P = 0.035), and sperm concentration (-0.846, P = 0.004). There was no significant correlation (P > 0.05) between RNA m6A and hormones and semen traits. In conclusion, the nutritional status of breeding bulls alters epigenetic markers, such as DNA methylation and RNA m6A methylation, in sperm, and the impact of change seems to be age dependent. These markers may serve as biomarkers of sperm quality and fertility of bulls in the future. Detrimental effects on sperm production and seminal quality are observed at periods and places when and where environmental and nutritional limitations are a year-round reality and may carry hidden players that may influence a lifetime of underperformance.

Technical Note: The comparison of pH and redox potential in different locations in the reticulo-rumen of growing beef steers supplemented with different levels of quebracho extract.

Rumen acidosis is a common metabolic disorder occurring when organic acid production exceeds clearance capacity, reducing ruminal pH. The occurrence of acidosis has been directly correlated to the ratio of concentrate to forage in the diet. However, rates of substrate fermentation and acid absorption vary at different locations in the reticulo-rumen. The objective of this study was to determine the pH and redox potential (Eh) in different locations of the reticulo-rumen using 16 ruminally cannulated steers (309 ± 43 kg) receiving different supplementation levels of quebracho extract (QT; Schinopsis balansae) within a grower type diet (CP: 13.4%; total digestible nutrients [TDN]: 70.4%; and ME: 2.55 Mcal/kg, dry matter [DM] basis). Animals were randomly assigned to one of four dietary treatments: QT at 0%, 1%, 2%, and 3% of DM (QT0, QT1, QT2, and QT3, respectively), containing about 0%, 0.7%, 1.4%, and 2.1% of condensed tannins (CT), DM basis, respectively. Animals were adapted to the basal diet for 12 d before being introduced to predetermined treatments for 4 weeks (wk), with diets provided twice daily to allow ad libitum intake. Weekly measurements of ruminal fluid pH and Eh were taken 4 h post-feeding using a portable pH meter with two probes (pH and redox) in four locations of the reticulo-rumen (reticulum, cranial sac, dorsal sac, and ventral sac). Data were analyzed using a random coefficients model with the pen as a random effect and wk as repeated measures, with DM intake included as a covariate. There was no interaction among treatments, location, and wk (P ≥ 0.882) on reticulo-ruminal pH. Overall, ruminal pH was lower for QT0 and QT1 compared to QT3 (P < 0.001). The pH in the reticulum was greater than those of the ventral and dorsal sacs (6.05 vs. 5.94, 5.89, respectively; P ≤ 0.001) but similar to cranial sac (6.00). Reticular pH was positively correlated with the ruminal locations (≥0.78; P < 0.001). The linear equation to estimate ruminal mean pH using reticulum pH had an intercept and slope different from zero (P ≤ 0.04), but CT (% DM) was not different from zero (P = 0.15), root mean square error of 0.15, and R2 of 0.778: 0.723 (±0.36) + 0.857 (±0.059) × reticulum pH + 0.033 (±0.023) × CT. The Eh was lower for QT0 in week 1 than all other treatments (P < 0.001). We concluded that reticulo-ruminal pH differs among locations in the rumen regardless of QT supplementation level and days on feed, with reticular pH being the highest.

The influence of extended supplementation of quebracho extract to beef steers consuming a hay diet on digestion, ruminal, and blood parameters.

The addition of natural plant secondary compounds to ruminant feed has been extensively studied because of their ability to modify digestive and metabolic functions, resulting in a potential reduction in greenhouse gas emissions, among other benefits. Condensed tannin (CT) supplementation may alter ruminal fermentation and mitigate methane (CH4) emissions. This study's objective was to determine the effect of quebracho CT extract [QT; Schinopsis quebracho-colorado (Schltdl.) F.A. Barkley & T. Meyer] within a roughage-based diet on ruminal digestibility and kinetic parameters by using the in situ and in vitro gas production techniques, in addition to blood urea nitrogen (BUN) and ruminal (volatile fatty acid [VFA], NH3-N, and protozoa count) parameters. Twenty rumen-cannulated steers were randomly assigned to four dietary treatments: QT at 0%, 1%, 2%, and 3% of dry matter (DM; QT0: 0% CT, QT1: 0.70% CT, QT2: 1.41% CT, and QT3: 2.13% CT). The in situ DM digestibility increased linearly (P = 0.048) as QT inclusion increased, whereas in situ neutral detergent fiber digestibility (NDFD) was not altered among treatments (P = 0.980). Neither total VFA concentration nor acetate-to-propionate ratio differed among dietary treatments (P = 0.470 and P = 0.873, respectively). However, QT3 had lower isovalerate and isobutyrate concentrations compared with QT0 (P ≤ 0.025). Ruminal NH3 and BUN tended to decline (P ≤ 0.075) in a linear fashion as QT inclusion increased, suggesting decreased deamination of feed protein. Ruminal protozoa count was reduced in quadratic fashion (P = 0.005) as QT inclusion increased, where QT1 and QT2 were lower compared with QT0 and QT3. Urinary N excretion tended to reduce in a linear fashion (P = 0.080) as QT increased. There was a treatment (TRT) × Day interaction for in vitro total gas production and fractional rate of gas production (P = 0.013 and P = 0.007, respectively), and in vitro NDFD tended to be greater for QT treatments compared with no QT inclusion (P = 0.077). There was a TRT × Day interaction (P = 0.001) on CH4 production, with QT3 having less CH4 production relative to QT0 on day 0 and QT2 on days 7 and 28. Feeding QT up to 3% of the dietary DM in a roughage-based diet did not sacrifice the overall DM digestibility and ruminal parameters over time. Still, it is unclear why QT2 did not follow the same pattern as in vitro gas parameters. Detailed evaluations of amino acid degradation might be required to fully define CT influences on ruminal fermentation parameters and CH4 production.

Nutritional Aspects of Ecologically Relevant Phytochemicals in Ruminant Production.

This review provides an update of ecologically relevant phytochemicals for ruminant production, focusing on their contribution to advancing nutrition. Phytochemicals embody a broad spectrum of chemical components that influence resource competence and biological advantage in determining plant species' distribution and density in different ecosystems. These natural compounds also often act as plant defensive chemicals against predatorial microbes, insects, and herbivores. They may modulate or exacerbate microbial transactions in the gastrointestinal tract and physiological responses in ruminant microbiomes. To harness their production-enhancing characteristics, phytochemicals have been actively researched as feed additives to manipulate ruminal fermentation and establish other phytochemoprophylactic (prevent animal diseases) and phytochemotherapeutic (treat animal diseases) roles. However, phytochemical-host interactions, the exact mechanism of action, and their effects require more profound elucidation to provide definitive recommendations for ruminant production. The majority of phytochemicals of nutritional and pharmacological interest are typically classified as flavonoids (9%), terpenoids (55%), and alkaloids (36%). Within flavonoids, polyphenolics (e.g., hydrolyzable and condensed tannins) have many benefits to ruminants, including reducing methane (CH4) emission, gastrointestinal nematode parasitism, and ruminal proteolysis. Within terpenoids, saponins and essential oils also mitigate CH4 emission, but triterpenoid saponins have rich biochemical structures with many clinical benefits in humans. The anti-methanogenic property in ruminants is variable because of the simultaneous targeting of several physiological pathways. This may explain saponin-containing forages' relative safety for long-term use and describe associated molecular interactions on all ruminant metabolism phases. Alkaloids are N-containing compounds with vast pharmacological properties currently used to treat humans, but their phytochemical usage as feed additives in ruminants has yet to be exploited as they may act as ghost compounds alongside other phytochemicals of known importance. We discussed strategic recommendations for phytochemicals to support sustainable ruminant production, such as replacements for antibiotics and anthelmintics. Topics that merit further examination are discussed and include the role of fresh forages vis-à-vis processed feeds in confined ruminant operations. Applications and benefits of phytochemicals to humankind are yet to be fully understood or utilized. Scientific explorations have provided promising results, pending thorough vetting before primetime use, such that academic and commercial interests in the technology are fully adopted.

Comparison of in situ techniques to evaluate the recovery of indigestible components and the accuracy of digestibility estimates.

Indigestible components, including indigestible dry matter (iDM) and indigestible neutral detergent fiber (iNDF), play an integral role as internal markers for determining ruminal kinetics and digestibility estimations. However, the accuracy of internal markers is dependent upon the incubation technique utilized as bag type (BT) and incubation length (IL) can be significant sources of error. Previous studies have primarily focused on iDM and iNDF as digestibility markers, but few studies have compared digestibility estimates to those of acid detergent insoluble ash (ADIA). Therefore, our objective was to investigate the effect of BT (F57, F58, and Dacron) and IL (288 and 576 h) on iDM and iNDF residues, DM and NDF digestibilities, and fecal recoveries when using in situ incubations. Additionally, we evaluated the accuracy of digestibility estimates when using iDM, iNDF, and ADIA. For iDM and iNDF, feed residues demonstrated a BT × IL interaction (P < 0.01). However, fecal residues were only influenced by the main effects of BT and IL (P < 0.01), with the F58 BT and 288-h IL having the greatest residues for both iDM and iNDF. The variation in residues was greatly reduced when using iNDF compared with iDM. Fecal recovery estimates most closely approximated 100% recovery when utilizing ADIA and iDM using the F57 × 576 h incubation method (P < 0.01), although recovery was overestimated for all incubation combinations. Fecal NDF recovery estimates better represented the excretion profiles when the F57 × 576 h combination was used with iDM as the internal marker (P < 0.01). Estimates of DM and NDF digestibility were the most accurate when utilizing ADIA (P < 0.01) relative to all other treatments. Our results indicate that the proper methodological application is specific to the purpose of the inferences. When evaluating fecal recoveries and digestibility, ADIA or iDM with F57 at 576-h in situ incubation provides the greatest accuracy.

Inclusion of quebracho tannin extract in a high-roughage cattle diet alters digestibility, nitrogen balance, and energy partitioning.

Condensed tannins (CT) might improve animal and system-level efficiency due to enhanced protein efficiency and reduced CH4. This study evaluated the impact of quebracho tannin (QT) extract fed at 0%, 1.5%, 3%, and 4.5% of dry matter (DM), within a roughage-based diet on apparent digestibility of DM, organic matter (OM), fibrous fractions, and N retention and energy partitioning of growing steers (236 ± 16 kg BW). A Latin rectangle design with eight animals and four periods was used to determine the whole-animal exchange of CO2, O2, and CH4 as well as the collection of total feces and urine over a 48-h period, using two open-circuit, indirect calorimetry respiration chambers. Following the removal of steers from respiration chambers, rumen inoculum was collected to determine ruminal parameter, including volatile fatty acids (VFA) and ammonia. Animals were fed a 56.5% roughage diet at 1.7% BW (dry matter basis). Dry matter and gross energy intakes were influenced by the level of QT inclusion (P ≤ 0.036). Digestibility of DM, OM, and N was reduced with QT inclusion (P < 0.001), and fiber digestibility was slightly impacted (P > 0.123). QTs altered the N excretion route, average fecal N-to-total N ratio excreted increased 14%, and fecal N-to-urinary N ratio increased 38% (P < 0.001) without altering the retained N. Increased fecal energy with QT provision resulted in reduced dietary digestible energy (DE) concentration (Mcal/kg DM; P = 0.024). There were no differences in urinary energy (P = 0.491), but CH4 energy decreased drastically (P = 0.007) as QT inclusion increased. Total ruminal VFA concentration did not differ across treatments, but VFA concentration increased linearly with QT inclusion (P = 0.049). Metabolizable energy (ME) was not affected by the QT rate, and the conversion efficiency of DE-to-ME did not differ. Heat energy decreased (P = 0.013) with increased QT provision likely due to changes in the DE intake, but there was no difference in retained energy. There were no differences for retained energy or N per CO2 equivalent emission produced (P = 0.774 and 0.962, respectively), but improved efficiency for energy retention occurred for 3% QT. We concluded that QT provided up to 4.5% of dry matter intake (about 3.51% of CT, dry matter basis) does not affect N and energy retention within the current setting. Feeding QT reduced energy losses in the form of CH4 and heat, but the route of energy loss appears to be influenced by the rate of QT inclusion.

Assessment of in situ techniques to determine indigestible components in the feed and feces of cattle receiving supplemental condensed tannins1.

Reliable assessments of indigestible dietary components are required when using internal markers to estimate diet digestibility and determine the potentially digestible portion of the fiber. The lack of a standardized methodology and understanding of how antinutritional factors influence indigestible residues can result in erroneous estimates with inconsistent variation across trials and among studies. Previous studies have detailed suitable bag porosity and sample size (SS) with incubation length (IL) varying from 96 to 504 h, with many assuming that 288-h IL yields truly indigestible components. Recent studies have primarily investigated the variation that exists among feedstuffs, but most have failed to account for possible effects of secondary compounds. Using 2 similar concentrate diets, one of which contained supplemental condensed tannins (CT), we investigated the effect of bag type (BT; 10 and 25 µm), SS (20 and 40 mg/cm2), and IL (288 and 576 h) on in situ indigestible DM (iDM) and neutral detergent fiber (iNDF) residues of feed and feces, and resultant DM and NDF digestibilities. There were no 3-way interactions (P > 0.05), but 2-way interactions were present for iDM and iNDF residues with BT × SS influencing the control (no CT) ration (P < 0.01), SS × IL impacting feed containing CT (P < 0.01), and BT × IL affecting both feedstuffs (P ≤ 0.01). For the control diet, only BT × SS affected DM and NDF digestibilities. Whereas the CT diet did not demonstrate any significant interactions for digestibilities. Values of iDM were largely influenced by contamination that varied greatly based on intrinsic factors associated with the bag and incubation duration. The presence of CT influenced iDM and iNDF to varying degrees due to possible trapping of CT-substrate complexes. For the control diet, the use of 25-µm bags resulted in lower fecal recoveries relative to the 10 µm (P < 0.01). However, there appears to be a dynamic relationship among BT, SS, and IL within respective diets and sample types that can affect indigestible components and resultant digestibility estimates. Based on simulations from these data, the sample size required to attain 90% power when utilizing 2 incubation animals exceeds the triplicate and quadruplicate replications commonly utilized. Further emphasizing the necessity for a more complete understanding of incubation dynamics to design biologically and statistically valid investigations.