BOARD-INVITED REVIEW: Efficiency of converting digestible energy to metabolizable energy and reevaluation of the California Net Energy System maintenance requirements and equations for predicting dietary net energy values for beef cattle

Bioactive metabolites of Asparagopsis stabilized in canola oil completely suppress methane emissions in beef cattle fed a feedlot diet

Asparagopsis taxiformis (Asparagopsis) has been shown to be highly efficacious at inhibiting the production of methane (CH4) in ruminants. To date, Asparagopsis has been primarily produced as a dietary supplement by freeze-drying to retain the volatile bioactive compound bromoform (CHBr3) in the product. Steeping of Asparagopsis bioactive compounds into a vegetable oil carrier (Asp-Oil) is an alternative method of stabilizing Asparagopsis as a ruminant feed additive. A dose-response experimental design used 3 Asp-Oil-canola oil blends, low, medium, and high Asp-Oil which provided 17, 34, and 51 mg Asparagopsis derived CHBr3/kg dry matter intake (DMI), respectively (in addition to a zero CHBr3 canola oil control), in a tempered-barley based feedlot finisher diet, fed for 59 d to 20 Angus heifers (five replicates per treatment). On four occasions, live weight was measured and CH4 emissions were quantified in respiration chambers, and blood, rumen fluid, and fecal samples were collected. At the end of the experiment, all animals were slaughtered, with carcasses graded, and samples of meat and edible offal collected for testing of consumer sensory qualities and residues of CHBr3, bromide, and iodide. All Asp-Oil treatments reduced CH4 yield (g CH4/kg DMI, P = 0.008) from control levels, with the low, medium, and high Asp-Oil achieving 64%, 98%, and 99% reduction, respectively. Dissolved hydrogen increased linearly with increasing Asp-Oil inclusion, by more than 17-fold in the high Asp-Oil group (P = 0.017). There was no effect of Asp-Oil treatment on rumen temperature, pH, reduction potential, volatile fatty acid and ammonia production, rumen pathology, and histopathology (P > 0.10). There were no differences in animal production and carcass parameters (P > 0.10). There was no detectable CHBr3 in feces or any carcass samples (P > 0.10), and iodide and bromide residues in kidneys were at levels unlikely to lead to consumers exceeding recommended maximum intakes. Overall, Asp-Oil was found to be safe for animals and consumers of meat, and effective at reducing CH4 emissions and yield by up to 99% within the range of inclusion levels tested.

Review: Harnessing extant energy and protein requirement modeling for sustainable beef production

Numerous mathematical nutrition models have been developed in the last sixty years to predict the dietary supply and requirement of farm animals' energy and protein. Although these models, usually developed by different groups, share similar concepts and data, their calculation routines (i.e., submodels) have rarely been combined into generalized models. This lack of mixing submodels is partly because different models have different attributes, including paradigms, structural decisions, inputs/outputs, and parameterization processes that could render them incompatible for merging. Another reason is that predictability might increase due to offsetting errors that cannot be thoroughly studied. Alternatively, combining concepts might be more accessible and safer than combining models' calculation routines because concepts can be incorporated into existing models without changing the modeling structure and calculation logic, though additional inputs might be needed. Instead of developing new models, improving the merging of extant models' concepts might curtail the time and effort needed to develop models capable of evaluating aspects of sustainability. Two areas of beef production research that are needed to ensure adequate diet formulation include accurate energy requirements of grazing animals (decrease methane emissions) and efficiency of energy use (reduce carcass waste and resource use) by growing cattle. A revised model for energy expenditure of grazing animals was proposed to incorporate the energy needed for physical activity, as the British feeding system recommended, and eating and rumination (HjEer) into the total energy requirement. Unfortunately, the proposed equation can only be solved iteratively through optimization because HjEer requires metabolizable energy (ME) intake. The other revised model expanded an existing model to estimate the partial efficiency of using ME for growth (kg) from protein proportion in the retained energy by including an animal degree of maturity and average daily gain (ADG) as used in the Australian feeding system. The revised kg model uses carcass composition, and it is less dependent on dietary ME content, but still requires an accurate assessment of the degree of maturity and ADG, which in turn depends on the kg. Therefore, it needs to be solved iteratively or using one-step delayed continuous calculation (i.e., use the previous day's ADG to compute the current day's kg). We believe that generalized models developed by merging different models' concepts might improve our understanding of the relationships of existing variables that were known for their importance but not included in extant models because of the lack of proper information or confidence at that time.

ASAS-NANP symposium: mathematical modeling in animal nutrition-Making sense of big data and machine learning: how open-source code can advance training of animal scientists

Advancements in precision livestock technology have resulted in an unprecedented amount of data being collected on individual animals. Throughout the data analysis chain, many bottlenecks occur, including processing raw sensor data, integrating multiple streams of information, incorporating data into animal growth and nutrition models, developing decision support tools for producers, and training animal science students as data scientists. To realize the promise of precision livestock management technologies, open-source tools and tutorials must be developed to reduce these bottlenecks, which are a direct result of the tremendous time and effort required to create data pipelines from scratch. Open-source programming languages (e.g., R or Python) can provide users with tools to automate many data processing steps for cleaning, aggregating, and integrating data. However, the steps from data collection to training artificial intelligence models and integrating predictions into mathematical models can be tedious for those new to statistical programming, with few examples pertaining to animal science. To address this issue, we outline how open-source code can help overcome many of the bottlenecks that occur in the era of big data and precision livestock technology, with an emphasis on how routine use and publication of open-source code can help facilitate training the next generation of animal scientists. In addition, two case studies are presented with publicly available data and code to demonstrate how open-source tutorials can be utilized to streamline data processing, train machine learning models, integrate with animal nutrition models, and facilitate learning. The National Animal Nutrition Program focuses on providing research-based data on animal performance and feeding strategies. Open-source data and code repositories with examples specific to animal science can help create a reinforcing mechanism aimed at advancing animal science research.

A review of the effect of nutrient and energy restriction during late gestation on beef cattle offspring growth and development

Changes in the environment, including nutritional changes, can influence fetal and postnatal development of the offspring, which can result in differences in growth, metabolism, reproduction, and health later in life. In beef cattle research on energy and protein restriction during late gestation appears to be contradictory. Therefore, in this review, we will examine the nutrient requirements recommended for this period. We are summarizing contradictory data on effects on offspring performance with possible explanations of the reason for why the data seems contradictory. We will finish by discussing some areas that we consider important for further research to increase the knowledge on how maternal nutrition influences offspring development. In particular, suggestions are provided on the need for more accurately measuring nutrient and energy supply and use and the impact on subsequent epigenetic effects. This will improve understanding of nutritional effects during gestation on offspring performance.

Protein Supplementation as a Nutritional Strategy to Reduce Gastrointestinal Nematodiasis in Periparturient and Lactating Pelibuey Ewes in a Tropical Environment

The study was carried out to evaluate the effect of energy and protein supplementation on parasitological and hematological response during peripartum and lactation of productive and non-productive Pelibuey ewes in a tropical environment. Forty-eight Pelibuey ewes aged 3–5 years and with a body weight of 31 ± 5 kg were used. Four groups of 12 ewes, including non-pregnant and productive ewes, were formed. A factorial treatment design was formulated, where two levels of energy (low, 9.6 MJ/kg, n = 24; and high, 10.1 MJ/kg, n = 24) and two levels of protein (high, 15% crude protein in diet, n = 24; and low, 8% crude protein in diet, n = 24) were studied. Fecal and blood samples were collected to determine the fecal egg count (FEC) of gastrointestinal nematodes (GIN), packed cell volume (PCV) and peripheral eosinophil (EOS) count. These variables were rearranged with respect to the lambing date in a retrospective study. The high dietary protein level had a significant effect on reducing the FEC and increasing the PCV of ewes during lactation, in comparison with animals fed with the low protein level. Differences in the study variables were attributed to physiological stage. Lactating ewes showed the highest FEC values (2709 ± 359 EPG), the lowest PCV values (21.9 ± 0.7%) and the lowest EOS (0.59 ± 0.6 Cells × 10³ µL). It is concluded that high levels of dietary protein improve the hematological response and reduce the FEC in Pelibuey ewes under grazing conditions. The non-pregnant ewes maintained some resilience and resistance to GIN infection compared to productive ewes.

Intake, performance, and feeding behavior of Holstein and Holstein × Gyr heifers grazing intensively managed tropical grasses during the rainy season

Holstein × Gyr and Holstein are the primary dairy breeds used in tropical systems, but when rearing under pasture, feed intake, behavior, and performance might differ between them. This study aimed to evaluate the voluntary intake, nutrient digestibility, performance, and ingestive behavior of Holstein and Holstein × Gyr (½ Holstein × ½ Gyr) heifers managed in a rotational system of Guinea grass (Panicum maximum Jacq. cv. Mombaça). The experiment was conducted during the summer season throughout four periods of 21 d. Two 8-heifers (four Holstein and four Holstein × Gyr) groups, averaging 258.6 ± 24.79 kg and 157.1 ± 24.99 kg BW, were used. Each group grazed a separate set of 16 paddocks, and all heifers received a concentrate supplement daily. Heifers were weighed at the beginning and end of the experiment. Fecal, forage and concentrate samples were evaluated for their DM, CP, crude fat, ash, NDF, and indigestible NDF. Feeding behavior was evaluated through 24 h of live observation for 48 h of each experimental period. Grazing, ruminating, resting, and intake of concentrate times were recorded, and rumination criteria, bout criteria, mealtime, meal frequency, and meal duration were calculated. There was no difference in total dry matter intake (DMI), but forage DMI of Holstein × Gyr was 11.70 % greater than the Holstein heifers. The Holstein × Gyr heifers had greater NDF intake and feed efficiency tended to show greater CP and NDF digestibilities, consequently, they had greater average daily gain (ADG). Holstein grazed less than Holstein × Gyr heifers in the afternoon. Ruminating time was 18.43 % lower for Holstein than Holstein × Gyr heifers, and rumination criteria (i.e. longest non-feeding interval within a rumination event) were greater for Holstein heifers. Holstein heifers presented more prolonged rumination bouts and resting time than Holstein × Gyr heifers. Holstein × Gyr can ingest and ruminate greater amounts of fibrous material, and Holstein heifers needed to spend more time ruminating the cud. Overall, even though the behavior was not markedly different between breeds, rearing young Holstein heifers in tropical pasture conditions is less suitable than Holstein-Gyr because of their lower ADG. Therefore, this management condition seems appropriate for Holstein × Gyr but inappropriate for Holstein dairy heifers.

Reduction of Enteric Methane Emissions in Heifers Fed Tropical Grass-Based Rations Supplemented with Palm Oil

Vegetable oils have been shown to reduce enteric methane (CH4) production by up to 20%. However, when the level of incorporation exceeds the threshold of 70 g/kg DM, dry matter intake (DMI) and nutrient digestibility may be reduced. The objective of this study was to determine the effects of the incorporation of three levels of palm oil (PO) on enteric CH4 emissions, rumen fermentation and apparent digestibility in heifers fed low-quality grass. Four rumen-cannulated heifers (Bos taurus × Bos indicus) were randomly assigned to four treatments: control (CON) and three increasing PO levels: 20, 40 and 60 g/kg in a 4 × 4 Latin square design with four periods of 22 days (14 days of adaptation to the ration), 5 days of feces and rumen fluid sampling (day 18, 4 h postprandial) and the last 3 days for measurements of CH4 in respiration chambers. With the exception of CP (p = 0.04), starch (p = 0.002) and EE (p < 0.001), the intake of nutrients was not affected by the inclusion of PO (p > 0.05). The apparent digestibility (AD) of nutrients was not affected by the inclusion of PO (p > 0.05), except for starch, which reduced its AD as the PO level was increased (p < 0.05). The gross energy intake was higher in PO-containing rations (p = 0.001), on the other hand, the digestible energy intake was similar between treatments (p > 0.05). In situ ruminal digestion kinetics and the potential degradability remained unchanged (p > 0.05), however, the effective degradability decreased with the inclusion of PO in the rations (p < 0.05). The ruminal pH and molar proportions of acetic, isovaleric and valeric acid were not different between treatments (p > 0.05). The ruminal concentration of propionic acid increased as the PO level increased, reaching its highest molar proportion with 60 g/kg PO (p < 0.05), however, the acetic/propionic ratio and the molar proportions of butyric acid and isobutyric acid decreased as the PO level increased (p < 0.05). The total daily CH4 production was lower in diets containing 20, 40 and 60 g/kg PO compared to the CON diet (p < 0.001). The production of CH4 per kg DMI and DOMI was greater (p < 0.05) for the CON diet compared to all three rations containing PO. The emission intensity, Ym, energy lost as CH4, emission factor (EF) and kg CO2 eq/year were reduced as an effect of the inclusion of PO (p < 0.05). Based on the results obtained, it is concluded that the incorporation of PO in cattle rations has the potential to reduce enteric methane emissions by 4% for every 10 g/kg PO in the ration, without affecting DMI, apparent digestibility or the consumption of digestible nutrient fractions.

Feeding a high energy finishing diet upon arrival to high-risk feedlot calves: effects on health, performance, ruminal pH, rumination, serum metabolites, and carcass traits

This study evaluated the impacts of feeding a high-energy finishing diet during both the receiving and finishing period compared with a lower-energy receiving diet with adaptation to the finishing diet on health, performance, serum chemistry, ruminal pH, rumination, and carcass characteristics of high-risk feedlot cattle. Five truck-load blocks of steers (n = 101) and bulls (n = 299) were used in a generalized complete block design and randomly assigned to receive: 1) finishing diet for the entire feeding period (FIN) or 2) receiving diet for the first 56 d, followed by a transition to the finishing diet (REC). All cattle were fed ad libitum and consumed the same diet by day 74. A subset of cattle (n = 48) was randomly selected to quantify ruminal pH, temperature, and rumination time. Ultrasound images were collected on days 0, 74, and 146 to determine fat thickness over the 12th rib and rump, and carcass characteristics were determined after slaughter. Cattle fed FIN had less (P < 0.01) dry matter intake (DMI) from days 0 to 74, but DMI did not differ (P = 0.80) after day 74. From days 0 to final, DMI was 0.26 kg less for FIN compared with REC (P = 0.01). However, calculated metabolizable energy intake was not different from days 0 to 74 (P = 0.19), days 74 to final (P = 0.80), or overall (P = 0.78). Body weight (BW) on day 74 was greater (P < 0.01) and final BW tended to be greater (P = 0.10) for FIN compared with REC. Cattle consuming FIN had greater (P < 0.01) average daily gain and increased (P < 0.01) gain:feed from days 0 to 74. There were no differences (P ≥ 0.31) in health outcomes. On day 74, FIN had greater (P = 0.04) fat thickness over the rump and rib but did not differ (P ≥ 0.52) on day 146. Carcasses of FIN had greater (P = 0.04) hot carcass weight with no difference (P ≥ 0.11) in ribeye area, 12th rib fat thickness, yield grade, or quality grade. There was no difference (P = 0.18) in liver abscess rate. There was a diet × day interaction for blood urea nitrogen (P = 0.02) such that concentration decreased from days 0 to 28 in both treatments, but was less on day 28 for FIN. Ruminal pH was greater on days 2 and 61 and rumination time was less from days 0 to 28 for FIN (diet × day interaction; P < 0.01). Overall, these results suggest that providing a finishing diet fed ad libitum to high-risk calves upon arrival may be a viable alternative to a low-energy receiving diet.

The Energy Requirement for Maintenance of Nellore Crossbreds in Tropical Conditions during the Finishing Period

This study determined the energy requirement for maintenance of purebred Nellore cattle and its crossbreds using data from a comparative slaughter trial in which animals were raised under the same plane of nutrition from birth through slaughter and born from a single commercial Nellore cow herd. Seventy-nine castrated steers (361 ± 54 kg initial BW) were used in a completely randomized design by age (22 months ± 23 days of age) with four genetic groups (GG): Nellore (NL), ½ Angus x ½ Nellore (AN), ½ Canchim x ½ Nellore (CN), and ½ Simmental x ½ Nellore (SN). The experimental design provided ranges in ME intake, BW, and ADG needed to develop regression equations to predict NEm requirements. Four steers of each GG were slaughtered to determine the initial body composition. The remaining 63 steers were assigned to different nutritional treatments (NT) by GG; ad libitum or limit-fed treatments (receiving 70% of the daily feed of the ad libitum treatment of the same GG). Full BW was recorded at birth, weaning, 12, 18, and 22 months. In the feedlot, steers were fed for 101 days a diet containing (DM basis) 60% corn silage and 40% concentrate. No difference of age at weaning (P = 0.534) and slaughter (P = 0.179 and P = 0.896, for GG and NT, respectively) were observed. AN steers were heavier at weaning weight, yearling weight and had higher EBW (P = 0.007, P = 0.014 and P < 0.001, respectively) in comparison to NL, CN, and SN. There were no interactions (P > 0.05) between GG and NT for any variable evaluated. When fed ad libitum, AN steers had higher daily MEI (Mcal/d; P < 0.001) in comparison to NL, CN, and SN. On a constant age basis, differences were observed on body composition (P < 0.05) between GG. The slope (P = 0.600) and intercept (P = 0.702) of the regression of log HP on MEI were similar among GG. Evaluating at the same age and the same frame size, there were no differences in NEm requirement between Nellore and AN (P = 0.528), CN (P = 0.671), and SN (P = 0.706). The combined data indicated a NEm requirement of 86.8 kcal/d/kg 0.75 EBW and a MEm requirement had a common value of 137.53 kcal/d/kg 0.75 EBW. The km and kg values were similar among GG (P > 0.05 and P > 0.05, respectively) and were on average 63.2 and 26.0%, respectively. However, although not statistically different, the NEm values from NL showed a decrease in NEm of 5.76% compared to AN steers.

Predicting Metabolizable Energy from Digestible Energy for Growing and Finishing Beef Cattle and Relationships to Prediction of Methane

Reliable predictions of metabolizable energy (ME) from digestible energy (DE) are necessary to prescribe nutrient requirements of beef cattle accurately. A previously developed database that included 87 treatment means from 23 respiration calorimetry studies has been updated to evaluate the efficiency of converting DE to ME by adding 47 treatment means from 11 additional studies. Diets were fed to growing-finishing cattle under individual feeding conditions. A citation-adjusted linear regression equation was developed where dietary ME concentration (Mcal/kg of dry matter [DM]) was the dependent variable and dietary DE concentration (Mcal/kg) was the independent variable: ME = 1.0001 × DE – 0.3926; r² = 0.99, root mean square prediction error [RMSPE] = 0.04, and P < 0.01 for the intercept and slope. The slope did not differ from unity (95% CI = 0.936 to 1.065); therefore, the intercept (95% CI = −0.567 to −0.218) defines the value of ME predicted from DE. For practical use, we recommend ME = DE – 0.39. Based on the relationship between DE and ME, we calculated the citation-adjusted loss of methane, which yielded a value of 0.2433 Mcal/kg of dry matter intake (DMI; SE = 0.0134). This value was also adjusted for the effects of DMI above maintenance, yielding a citation-adjusted relationship: CH₄, Mcal/kg = 0.3344 – 0.05639 × multiple of maintenance; r² = 0.536, RMSPE = 0.0245, and P < 0.01 for the intercept and slope. Both the 0.2433 value and the result of the intake-adjusted equation can be multiplied by DMI to yield an estimate of methane production. These two approaches were evaluated using a second, independent database comprising 129 data points from 29 published studies. Four equations in the literature that used DMI or intake energy to predict methane production also were evaluated with the second database. The mean bias was substantially greater for the two new equations, but slope bias was substantially less than noted for the other DMI-based equations. Our results suggest that ME for growing and finishing cattle can be predicted from DE across a wide range of diets, cattle types, and intake levels by simply subtracting a constant from DE. Mean bias associated with our two new methane emission equations suggests that further research is needed to determine whether coefficients to predict methane from DMI could be developed for specific diet types, levels of DMI relative to body weight, or other variables that affect the emission of methane.

Modifying the National Research Council weight gain model to estimate daily gain for stockers grazing bermudagrass in the southern United States

The energy requirements, feed intake, and performance of grazing animals vary daily due to changes in weather conditions, forage nutritive values, and plant and animal maturity throughout the grazing season. Hence, realistic simulations of daily animal performance can be made only by the models that can address these changes. Given the dearth of simple, user-friendly models of this kind, especially for pastures, we developed a daily gain model for large-frame stockers grazing bermudagrass sCynodon dactylon (L.) Pers.], a widely used warm-season perennial grass in the southern United States. For model development, we first assembled some of the classic works in forage-beef modeling in the last 50 yr into the National Research Council (NRC) weight gain model. Then, we tested it using the average daily gain (ADG) data obtained from several locations in the southern United States. The evaluation results showed that the performance of the NRC model was poor as it consistently underpredicted ADG throughout the grazing season. To improve the predictive accuracy of the NRC model to make it perform under bermudagrass grazing conditions, we made an adjustment to the model by adding the daily departures of the modeled values from the data trendline. Subsequently, we tested the revised model against an independent set of ADG data obtained from eight research locations in the region involving about 4,800 animals, using 30 yr (1991-2020) of daily weather data. The values of the various measures of fit used, namely the Willmott index of 0.92, the modeling efficiency of 0.75, the R2 of 0.76, the root mean square error of 0.13 kg d-1, and the prediction error relative to the mean observed data of 24%, demonstrated that the revised model mimicked the pattern of observed ADG data satisfactorily. Unlike the original model, the revised model predicted more closely the ADG value throughout the grazing season. The revised model may be useful to accurately reflect the impacts of daily weather conditions, forage nutritive values, seasonality, and plant and animal maturity on animal performance.

Effects of corn processing and cattle size on total tract digestion and energy and nitrogen balance

This study used 18 calves (295 ± 29 kg) and 18 yearlings (521 ± 29 kg) fed whole, cracked, or steam-flaked corn (SFC) to evaluate nutrient digestion and energy balance across different types of processed corn and sizes of cattle. Cattle were fed a diet comprised of 75% corn (dry matter [DM]-basis) from whole, cracked, or SFC to 2.5-times maintenance energy requirements. Subsequently, cattle were placed in individual stanchions, and urine and feces were collected together with measures of gas production via indirect calorimetry. Data were analyzed using the MIXED procedure of SAS. There was no interaction between corn processing and cattle size (P ≥ 0.40). Time spent ruminating (min/d) and rumination rate (min/kg DM intake [DMI]) were not affected by corn processing or cattle size. The eating rate (min/kg DMI) was faster (P < 0.01) for yearlings compared with calves. Total tract starch digestion was greatest (P = 0.01) for cattle fed SFC (97.5%), intermediate in cattle fed cracked (92.4%), and least in cattle fed whole corn (89.5%). Dietary digestible energy and metabolizable energy (Mcal/kg DMI) were greater (P ≤ 0.05) for cattle fed SFC compared with cracked or whole. A greater proportion of digestible energy was lost to heat production (P = 0.01) in cattle fed whole corn compared with cracked and tended to be greater (P = 0.08) in cattle fed SFC than cracked. Conversion of digestible energy to metabolizable energy in this study was more closely related to a dynamic model used to estimate metabolizable energy of feeds to dairy cows than to a linear model used to predict metabolizable energy of feeds to beef cattle. If library estimates of net energy for maintenance are correct, then retained energy (Mcal/d) should have been similar between each type of processed corn; however, retained energy was greater (P < 0.01) for cattle fed cracked compared with whole corn and tended to be greater (P = 0.06) compared with SFC. Yet, observed amounts of net energy based on measures of retained energy were not different (P ≥ 0.60) between cracked and SFC. Nitrogen balance was not affected (P ≥ 0.30) by corn processing or cattle size, although cattle fed cracked had numerically greater (P ≤ 035) N retention. These data indicate that physical processing of corn provides greater net energy to cattle in comparison to whole corn.

Development of a model to predict dietary metabolizable energy from digestible energy in beef cattle

Understanding the utilization of feed energy is essential for precision feeding in beef cattle production. We aimed to assess whether predicting the metabolizable energy (ME) to digestible energy (DE) ratio (MDR), rather than a prediction of ME with DE, is feasible and to develop a model equation to predict MDR in beef cattle. We constructed a literature database based on published data. A meta-analysis was conducted with 306 means from 69 studies containing both dietary DE and ME concentrations measured by calorimetry to test whether exclusion of the y-intercept is adequate in the linear relationship between DE and ME. A random coefficient model with study as the random variable was used to develop equations to predict MDR in growing and finishing beef cattle. Routinely measured or calculated variables in the field (body weight, age, daily gain, intake, and dietary nutrient components) were chosen as explanatory variables. The developed equations were evaluated with other published equations. The no-intercept linear equation was found to represent the relationship between DE and ME more appropriately than the equation with a y-intercept. The y-intercept (-0.025 ± 0.0525) was not different from 0 (P = 0.638), and Akaike and Bayesian information criteria of the no-intercept model were smaller than those with the y-intercept. Within our growing and finishing cattle data, the animal's physiological stage was not a significant variable affecting MDR after accounting for the study effect (P = 0.213). The mean (±SE) of MDR was 0.849 (±0.0063). The best equation for predicting MDR (n = 106 from 28 studies) was 0.9410 ( ± 0.02160) +0.0042 ( ± 0.00186) × DMI (kg) - 0.0017 ( ± 0.00024) × NDF(% DM) - 0.0022 ( ± 0.00084) × CP(% DM). We also presented a model with a positive coefficient for the ether extract (n = 80 from 22 studies). When using these equations, the observed ME was predicted with high precision (R2 = 0.92). The model accuracy was also high, as shown by the high concordance correlation coefficient (>0.95) and small root mean square error of prediction (RMSEP), <5% of the observed mean. Moreover, a significant portion of the RMSEP was due to random bias (> 93%), without mean or slope bias (P > 0.05). We concluded that dietary ME in beef cattle could be accurately estimated from dietary DE and its conversion factor, MDR, predicted by the dry matter intake and concentration of several dietary nutrients, using the 2 equations developed in this study.

Developing Equations for Converting Digestible Energy to Metabolizable Energy for Korean Hanwoo Beef Cattle

Simple Summary

The available energy in feedstuff represents the largest proportion of the total cost for intensive beef production. Therefore, the energy content of feeds must be known before diet formulation. The determination of digestible energy (DE) and metabolizable energy (ME) values by animal experiments is both time-consuming and costly. Predictive equations to estimate the ME from DE can be useful for feed ingredient evaluations and diet formulations. A range of regression equations were developed in the present study, taking into consideration the gender and body weights of the animals, as well as the feed nutrients, to predict the relationship between the DE and ME. An evaluation of these equations suggested predicting the ME value based on ME = 0.9215 × DE − 0.1434 (R² = 0.999). The generation of these predictive equations represents a step towards updating the ME:DE default conversion factor value of 0.82 adopted from the National Research Council to meet the ME requirements of beef cattle in Korea. The new recommended predictive equation enables the adjustment of the nutrient requirements, thus enhancing animal productivity and maximising the economic return for beef farmers.

Abstract

This study was performed to update and generate prediction equations for converting digestible energy (DE) to metabolizable energy (ME) for Korean Hanwoo beef cattle, taking into consideration the gender (male and female) and body weights (BW above and below 350 kg) of the animals. The data consisted of 141 measurements from respiratory chambers with a wide range of diets and energy intake levels. A simple linear regression of the overall unadjusted data suggested a strong relationship between the DE and ME (Mcal/kg DM): ME = 0.8722 × DE + 0.0016 (coefficient of determination (R²) = 0.946, root mean square error (RMSE) = 0.107, p < 0.001 for intercept and slope). Mixed-model regression analyses to adjust for the effects of the experiment from which the data were obtained similarly showed a strong linear relationship between the DE and ME (Mcal/kg of DM): ME = 0.9215 × DE − 0.1434 (R² = 0.999, RMSE = 0.004, p < 0.001 for the intercept and slope). The DE was strongly related to the ME for both genders: ME = 0.8621 × DE + 0.0808 (R² = 0.9600, RMSE = 0.083, p < 0.001 for the intercept and slope) and ME = 0.7785 × DE + 0.1546 (R² = 0.971, RMSE = 0.070, p < 0.001 for the intercept and slope) for male and female Hanwoo cattle, respectively. By BW, the simple linear regression similarly showed a strong relationship between the DE and ME for Hanwoo above and below 350 kg BW: ME = 0.9833 × DE − 0.2760 (R² = 0.991, RMSE = 0.055, p < 0.001 for the intercept and slope) and ME = 0.72975 × DE + 0.38744 (R² = 0.913, RMSE = 0.100, p < 0.001 for the intercept and slope), respectively. A multiple regression using the DE and dietary factors as independent variables did not improve the accuracy of the ME prediction (ME = 1.149 × DE − 0.045 × crude protein + 0.011 × neutral detergent fibre − 0.027 × acid detergent fibre + 0.683).

Animals selected for postweaning weight gain rate have similar maintenance energy requirements regardless of their residual feed intake classification

Data of comparative slaughter were used to determine Nellore bulls' net energy requirements classified as efficient or inefficient according to residual feed intake (RFI) and selection lines (SL). Sixty-seven Nellore bulls from the selected (SE) and control (CO) lines of the selection program for postweaning weight gain were used. The animals underwent digestibility trials before being submitted to the finishing trial. Sixteen bulls were slaughtered at the beginning of the finishing trial, and their body composition was used as the baseline for the remaining animals. For body composition determinations, whole empty body components were weighed, ground, and subsampled for chemical analyses. Initial body composition was determined with equations developed from the baseline group using shrunk body weight, fat, and protein. The low RFI (LRFI) and CO animals had a lower dry matter (DMI) and nutrient intake (P < 0.05) than high RFI (HRFI) and SE animals, without alterations in digestibility coefficients (P > 0.05). During the finishing trial, DMI remained lower for LRFI and CO animals. Growth performance was similar between RFI classes, except for empty body weight gain that tended to be higher for LRFI than HRFI (P = 0.091). The SE animals had less fat content on the empty body (P = 0.005) than CO. Carcasses tended to be leaner for LRFI than HRFI (P = 0.080) and for SE than CO (P = 0.066) animals. LRFI animals retained more energy (P = 0.049) and had lower heat production (HP; P = 0.033) than the HRFI ones. Retained energy was not influenced by SL (P = 0.165), but HP tended to be higher for SE when compared to CO (P = 0.075) animals. Net energy requirement for maintenance (NEm) was lower for LRFI than HRFI (P = 0.009), and higher for SE than CO (P = 0.046) animals. There was an interaction tendency between RFI and SL (P = 0.063), suggesting that NEm was lower for LRFI+CO than HRFI+CO (P = 0.006), with no differences for SE (P = 0.527) animals. The efficiency of ME utilization for maintenance (km) of LRFI and HRFI animals were 62.6% and 58.4%, respectively, and for SE and CO were 59.0% and 62.1%, respectively. The breeding program for postweaning weight has not improved feed efficiency over the years, with RFI classification not being a promising selection tool for SE animals. Classification based on RFI seems to be useful in animals that have not undergone the breeding program, with LRFI animals having lower energy requirements than the HRFI ones.

The effects of the forage-to-concentrate ratio on the conversion of digestible energy to metabolizable energy in growing beef steers

Metabolizable energy (ME) is calculated from digestible energy (DE) using a constant conversion factor of 0.82. Methane and urine energy losses vary across diets and dry matter intake (DMI), suggesting that a static conversion factor fails to describe the biology. To quantify the effects of the forage-to-concentrate ratio (F:C) on the efficiency of conversion of DE to ME, 10 Angus steers were used in a 5 × 5 replicated Latin square. Dry-rolled corn was included in experimental diets at 0%, 22.5%, 45.0%, 67.5%, and 83.8% on a dry matter (DM) basis, resulting in a high F:C (HF:C), intermediate F:C (IF:C), equal F:C (EF:C), low F:C (LF:C), and a very low F:C (VLF:C), respectively. Each experimental period consisted of a 23-d diet adaption followed by 5 d of total fecal and urine collections and a 24-h gas exchange collection. Contrasts were used to test the linear and quadratic effects of the F:C. There was a tendency (P = 0.06) for DMI to increase linearly as F:C decreased. As a result, gross energy intake (GEI) increased linearly (P = 0.04) as F:C decreased. Fecal energy loss expressed as Mcal/d (P = 0.02) or as a proportion of GEI (P < 0.01) decreased as F:C decreased, such that DE (Mcal/d and Mcal/kg) increased linearly (P < 0.01) as F:C decreased. As a proportion of GEI, urine energy decreased linearly (P = 0.03) as F:C decreased. Methane energy loss as a proportion of GEI responded quadratically (P < 0.01), increasing from HF:C to IF:C then decreasing thereafter. The efficiency of DE to ME conversion increased quadratically (P < 0.01) as F:C decreased, ranging from 0.86 to 0.92. Heat production (Mcal) increased linearly (P < 0.04) as F:C decreased but was not different as a proportion of GEI (P ≥ 0.22). As a proportion of GEI, retained energy responded quadratically (P = 0.03), decreasing from HF:C to IF:C and increasing thereafter. DM, organic matter, and neutral detergent fiber digestibility increased linearly (P < 0.01) and starch digestibility decreased linearly (P < 0.01) as the F:C decreased. Total N retained tended to increase linearly as the proportion of concentrate increased in the diet (P = 0.09). In conclusion, the efficiency of conversion of DE to ME increased with decreasing F:C due to decreasing methane and urine energy loss. The relationship between DE and ME is not static, especially when differing F:C.

Energy and protein requirements of Holstein × Gyr crossbred heifers

Nutrient requirements in cattle are dependent on physiological stage, breed and environmental conditions. In Holstein × Gyr crossbred dairy heifers, the lack of data remains a limiting factor for estimating energy and protein requirements. Thus, we aimed to estimate the energy and protein requirements of Holstein × Gyr crossbred heifers raised under tropical conditions. Twenty-two crossbred (½ Holstein × ½ Gyr) heifers with an average initial BW of 102.2 ± 3.4 kg and 3 to 4 months of age were used. To estimate requirements, the comparative slaughter technique was used: four animals were assigned to the reference group, slaughtered at the beginning of the experiment to estimate the initial empty BW (EBW) and composition of the animals that remained in the experiment. The remaining animals were randomized into three treatments based on targeted rates of BW gain: high (1.0 kg/day), low (0.5 kg/day) and close to maintenance (0.1 kg/day). At the end of the experiment, all animals were slaughtered to determine EBW, empty body gain (EBG) and body energy and protein contents. The linear regression parameters were estimated using PROC MIXED of SAS (version 9.4). Estimates of the parameters of non-linear regressions were adjusted through PROC NLIN of SAS using the Gauss-Newton method for parameter fit. The net requirements of energy for maintenance (NEm) and metabolizable energy for maintenance (MEm) were 0.303 and 0.469 MJ/EBW0.75 per day, respectively. The efficiency of use of MEm was 64.5%. The estimated equation to predict the net energy requirement for gain (NEg) was: NEg (MJ/day) = 0.299 × EBW0.75 × EBG0.601. The efficiency of use of ME for gain (kg) was 30.7%. The requirement of metabolizable protein for maintenance was 3.52 g/EBW0.75 per day. The equation to predict net protein requirement for gain (NPg) was: NPg (g/day) = 243.65 × EBW-0.091 × EBG. The efficiency of use of metabolizable protein for gain (k) was 50.8%. We observed noteworthy differences when comparing to ME and protein requirements of Holstein × Gyr crossbred heifers with other systems. In addition, we also observed differences in estimates for NEm, NEg, NPg, kg and k. Therefore, we propose that the equations generated in the present study should be used to estimate energy and protein requirements for Holstein × Gyr crossbred dairy heifers raised in tropical conditions in the post-weaning phase up to 185 kg of BW.

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.

Effects of diet type on nutrient utilization and energy balance in drylot heifers1

Feeding cattle in intensified settings allows cow-calf producers to decrease their reliance on grazed forage and utilize alternative feedstuffs. During times of intense management, diet type may alter energy utilization. Fourteen pregnant MARC III heifers (405 ± 44 kg BW) were used in a 180 d experiment to determine effects of diet type on nutrient and energy utilization. Heifers were randomly assigned to one of two treatments, a forage diet (FOR; 2.10 Mcal metabolizable energy [ME]/kg; 95.75% forage) or a concentrate diet (CONC; 2.94 Mcal ME/kg; 71% concentrate), and individually fed to meet maintenance energy requirements (0.135 Mcal ME/kg BW0.75). The CONC diet contained dry-rolled corn, corn stalks (10.16 cm grind size), soybean meal, corn silage (approximately 45% corn grain; stored in a plastic bag), dicalcium phosphate, urea, and a premix pellet; FOR contained alfalfa hay (harvested at mid-bloom), corn silage, dicalcium phosphate, and a premix pellet. Measurements of energy intake and digestibility were measured over a 4-d period on days 116, 172, and 235 of gestation. Using portable headbox calorimeters, measurements of O2, CO2, and CH4 gases were collected over a period of 24 h. Data were analyzed in a completely randomized design with diet as fixed effect. Dry matter and organic matter digestibility were greater for CONC than FOR (P < 0.01). Intake of gross energy (GE) and digestible energy (DE) were greater for FOR (P < 0.01), but by design, ME intake was not different between treatments (P = 0.26). Energy lost as methane (% of GE intake) was not different between treatments (P = 0.49). The ratio of ME to DE was greater for CONC (86.8 vs. 82.8; P = 0.01) than FOR. Heat production relative to ME was not different between treatments (P = 0.85). Maternal tissue energy did not differ and was 1.2 Mcal/d for CONC and 0.9 Mcal/d for FOR (P = 0.73). Greater nitrogen (N) consumption was observed for FOR (192.2 g/d) than CONC (134.0 g/d; P < 0.01), and retained N was greater for FOR than CONC (P < 0.01) on days 116 and 235 of gestation. Neither concentrate-based or forage-based diets affected body condition score (P = 0.26). Heifers fed concentrate-based diets retained more energy in part because they had larger calves, but this energy was not recovered in maternal tissue.

Nitrogen metabolism and protein requirements for maintenance of growing Red Norte bulls

Dietary protein adjustments can reduce environmental impact and economic losses in production systems. However, we lack information regarding nitrogen (N) metabolism and protein requirements for maintenance of crossbred animals such as Red Norte breed, precluding a precise dietary management. The objective was to evaluate the effect of increasing dietary CP levels (9%, 11%, 13%, 15% and 17%) on intake, digestibility and N balance, as well as to estimate the metabolizable protein requirements for maintenance (MPm) of growing Red Norte bulls. Thirty five animals averaging 280 ± 4.0 kg BW were fed during 45 days in a 60 : 40 forage : concentrate ratio diet in which the last 5 days were used for the digestibility trial. Intakes of CP and non-fibrous carbohydrates (NFCs) and feed efficiency linearly increased (P < 0.05) as CP levels increased, while DM, NDF, nitrogen efficiency use and ether extract were not influenced by CP levels (P > 0.05). Digestibilities of DM, organic matter, ether extract, NFC and CP as well as metabolizable energy intake linearly increased (P < 0.05), and true digestibility of CP was not affected (P > 0.05) by treatments. Urinary N and retained N linearly increased (P < 0.05) with the increase in dietary N. The MPm were estimated as 4.46 g/BW0.75 and the efficiency of use of MPm was 0.673. In conclusion, obtained MPm requirements of growing Red Norte bulls are greater than the values reported in literature for Zebu cattle and dietary CP levels of 15% and 17% exhibited great responses for growing Red Norte cattle. However, a cost-benefit evaluation should be done before its use.

What is the digestibility and caloric value of different botanical parts in corn residue to cattle?1

Two experiments were conducted to measure rates of ruminal disappearance, and energy and nutrient availability and N balance among cows fed corn husks, leaves, or stalks. Ruminal disappearance was estimated after incubation of polyester bags containing husks, leaves or stalks in 2 separate ruminally cannulated cows in a completely randomized design. Organic matter (OM) that initially disappeared was greatest for stalks and least for husks and leaves (P < 0.01), but amounts of NDF that initially disappeared was greatest for husks, intermediate for stalks, and least for leaves (P < 0.01). Amounts of DM and OM that slowly disappeared were greatest in husks, intermediate in leaves, and least in stalks (P < 0.01). However, amounts of NDF that slowly disappeared were greatest in leaves, intermediate in husks, and least in stalks (P < 0.01). Rate of DM and OM disappearance was greater for leaves, intermediate for husks and least for stalks, but rate of NDF disappearance was greatest for stalks, intermediate for leaves, and least for husks (P < 0.01). Energy and nutrient availability in husks, leaves, or stalks were measured by feeding ruminally cannulated cows husk-, leaf-, or stalk-based diets in a replicated Latin square. Digestible energy lost as methane was less (P = 0.02) when cows were fed leaves in comparison to husks or stalks, and metabolizable energy (Mcal/kg DM) was greater (P = 0.03) when cows were fed husks and leaves compared with stalks. Heat production (Mcal/d) was not different (P = 0.74) between husks, leaves, or stalks; however, amounts of heat produced as a proportion of digestible energy intake were less (P = 0.05) among cows fed leaves in comparison to stalks or husks. Subsequently, there was a tendency (P = 0.06) for net energy available for maintenance from leaves (1.42 Mcal/kg DM) to be greater than stalks (0.91 Mcal/kg DM), and husks (1.30 Mcal/kg DM) were intermediate. Nitrogen balance was greater when cows were fed leaves, intermediate for husks, and least for stalks (P = 0.01). Total tract digestion of NDF was greater (P < 0.01) for husks and leaves compared with stalks. Husks had greater (P = 0.04) OM digestibility in comparison to stalks, and leaves were intermediate. Apparently, greater production of methane from husks in comparison to leaves limited amounts of energy available for maintenance from husks even though total-tract nutrient digestion was greatest when cows were fed husks or leaves.

Effects of dietary exogenous fibrolytic enzymes on ruminal fermentation characteristics of beef steers fed high- and low-quality growing diets1

The effects of dietary pretreatment with fibrolytic enzyme-based cocktail were evaluated in 2 studies: (1) in vitro true digestibility; and (2) intake, digestibility, feeding behavior, and ruminal fermentation of beef steers fed growing diets. For the in vitro assessment, the ruminal inoculum was collected from 2 steers (BW = 543 ± 45 kg; 4-h after feeding; growing diets) and enzymes included or not (Trichoderma reesei fermentation extract; 0.75 µL/g of substrate DM). Within in vitro batches (n = 4), 12 substrates were incubated and in vitro true nutrient digestibility was evaluated. For study 2, 5 ruminally cannulated beef steers (BW = 520 ± 30 kg) were used in a 5 × 4 unbalanced Latin square using a 2 × 2 factorial arrangement of treatments: (a) diet quality (high = HQ; and low = LQ) and (b) enzyme inclusion (0 or 0.75 mL/kg of diet DM). Steers were fed ad libitum during four 21-d periods consisting of 14-d of adaptation and 7-d of collections. An enzyme × substrate was observed (P < 0.01), in which DM, OM, and NDF disappearance of sorghum grain increased with enzymes addition. Addition of enzymes increased (P < 0.01) ADF digestibility for all substrates. No diet quality × enzyme (P ≥ 0.18) was observed for intake variables in study 2. Enzyme-fed steers increased (P ≤ 0.05) intake of DM, digestible DM, NDF, and ADF compared with steers not fed fibrolytic enzymes. Addition of enzyme did not affect (P ≥ 0.28) apparent total tract digestibility of beef steers. Steers fed HQ diets consumed more (P ≤ 0.04) DM, digestible DM and OM, and less (P ≤ 0.03) total and digestible fiber than steers fed LQ diets. Ruminal pH average decreased (P = 0.01) for steers fed HQ or enzyme-fed diets compared with other treatments. A tendency (P = 0.06) toward improved total VFA was observed on enzyme-fed steers with HQ diets, but not for LQ diets. The molar proportion of ruminal propionate increased (P = 0.01) when steers were fed enzyme. Steers fed HQ diets had greater (P < 0.01) propionate and valerate molar proportions, lower (P < 0.01) acetate and acetate:propionate ratio than steers fed LQ diets. In vitro methane and total gas production were not affected (P ≥ 0.50) by dietary treatments. Fibrolytic enzymes positively affected digestion of multiple roughage sources commonly fed to cattle and might have additional benefit when used on unprocessed sorghum grain. Fibrolytic enzymes in beef cattle growing diets stimulated intake and generated positive impacts on ruminal fermentation.

Relationships between digestible energy and metabolizable energy in current feedlot diets

It is commonplace that metabolizable energy (ME) is calculated from digestible energy (DE) as DE × 0.82. However, recent published literature suggests that the relationship between DE and ME is variable depending on the type of diet used, and is typically > 0.90 when high-concentrate diets are fed. Literature means were compiled from 23 respiration calorimetry studies where total fecal and urine collections were conducted and gaseous energy was measured. The relationship between experimentally observed and predicted ME (DE × 0.82) was evaluated using these previously reported treatment means. Additionally, a previously published linear regression equation for predicting ME from DE was also evaluated using a residual analysis. Published (Hales, K. E., A. P. Foote, T. M. Brown-Brandl, and H. C. Freetly. 2017. The effects of feeding increasing concentrations of corn oil on energy metabolism and nutrient balance in finishing beef steers. J. Anim. Sci. 95:939-948. doi:10.2527/jas.2016.0902 and Hemphill, C. N., T. A. Wickersham, J. E. Sawyer, T. M. Brown-Brandl, H. C. Freetly, and K. E. Hales. 2018. Effects of feeding monensin to bred heifers fed in a drylot on nutrient and energy balance. J. Anim. Sci. 96:1171-1180. doi:10.1093/jas/skx030) and unpublished data (K. E. Hales, unpublished data) were used to develop a new equation for estimating ME from DE (megacalories/kilogram [Mcal/kg] of DM; ME = -0.057 ± 0.022 DE² + 1.3764 ± 0.1197 DE - 0.9483 ± 0.1605; r ² = 0.9671, root mean square error = 0.12; P < 0.01 for intercept, P < 0.01 for linear term, and P < 0.01 for quadratic term). To establish a maximum biological threshold for the conversion of DE to ME, individual animal data were used (n = 234) to regress the ME:DE on DE concentration (1.53 to 3.79 Mcal DE/kg). When using experimentally derived data and solving for the first derivative, the maximum biological threshold for the conversion of DE to ME was 3.65 Mcal DE/kg. Additionally, the quadratic regression (equation 1) was used to predict ME from a wide range of DE (1.8 to 4.6 Mcal/kg). The ME:DE ratio was then calculated by dividing predicted ME by DE. The maximum biological threshold for the conversion of DE to ME was estimated by solving for the first derivative and was 3.96 Mcal DE/kg. In conclusion, this review suggests that the relationship between DE and ME is not static, especially in high-concentrate diets. The equation presented here is an alternative that can be used for the calculation of ME from DE in current feedlot diets, but it is not recommended for use in high-forage diets. The maximization of ME in current diets, maximum biological threshold, occurs between 3.65 and 3.96 Mcal DE/kg in the diet, which based on these data is approximately 3.43 to 3.65 Mcal/kg of ME consumption.

Can net energy values be determined from animal performance measurements? A review of factors affecting application of the California Net Energy System

The California Net Energy System (CNES) can reliably project performance of feedlot cattle based on three factors: expected dry matter intake (DMI), some index of degree of maturity of cattle linked to body composition (fat and protein content), and an estimate of the net energy (NE) content of the diet. The CNES allowed feedlot managers to monitor growth and efficiency of individual pens of cattle. Through assigning distinct values for net energy for maintenance (NEm) vs. net energy for gain (NEg) of the metabolizable energy (ME) present in feeds, the CNES enables valid economic comparisons among feedstuffs, an appraisal not feasible based on total digestible nutrients or digestible energy (DE) values. Because NEm and NEg are linked mathematically to ME, the CNES also allows performance-adjusted ME (paME) value of diets to be calculated from observed DMI and growth or carcass measurements. Compared with other productivity measures (e.g., average daily gain and gain-to-feed ratio) that are confounded with and affected by DMI, the CNES logically separates production responses by cattle into two factors-DMI and ME of the diet. This enables research scientists or cattle producers to appraise responses within these two factors independently. In feeding studies, means of paME values were related closely to ME values of diets calculated from the ME of diet ingredients. But unlike ME values projected from diet analyses, paME estimates are affected by environmental conditions (e.g., season, weather, animal interactions, stress, nutritional history and deficiencies, associative effects of feeds, imprecise feed management, and animal healthfulness and disorders). These factors typically overestimate ME intake or increase energy requirements, both of which decrease energetic efficiency. By comparing paME with ME values calculated from diet composition, logical reasons behind performance responses to and quantitative benefits from feed additives, grain processing, hormone implants, and animal management can be appraised. Considering the evolution in cattle types, management and marketing conditions, and changes in diet ingredients and processing that have occurred during the past 50 yr, updating by a skilled committee to correct certain anomalies within the CNES as currently being applied seems appropriate. Developing simplified spreadsheets could help users evaluate their own dietary and management conditions and assure that the CNES continues to be widely applied by the feedlot industry within the United States and worldwide.

Applying the California net energy system to growing goats

The aim of this review is to describe the main findings of studies carried out during the last decades applying the California net energy system (CNES) in goats. This review also highlights the strengths and pitfalls while using CNES in studies with goats, as well as provides future perspectives on energy requirements of goats. The nonlinear relationship between heat production and metabolizable energy intake was used to estimate net energy requirements for maintenance (NE_m). Our studies showed that NE_m of intact and castrated male Saanen goats were approximately 15% greater than female Saanen goats. Similarly, NE_m of meat goats (i.e., >50% Boer) was 8.5% greater than NE_m of dairy and indigenous goats. The first partial derivative of allometric equations using empty body weight (EBW) as independent variable and body energy as dependent variable was used to estimate net energy requirements for gain (NE_g). In this matter, female Saanen goats had greater NE_g than males; also, castrated males had greater NE_g than intact males. This means that females have more body fat than males when evaluated at a given EBW or that degree of maturity affects NE_g. Our preliminary results showed that indigenous goats had NE_g 14% and 27.5% greater than meat and dairy goats, respectively. Sex and genotype also affect the efficiency of energy use for growth. The present study suggests that losses in urine and methane in goats are lower than previously reported for bovine and sheep, resulting in greater metabolizable energy:digestible energy ratio (i.e., 0.87 to 0.90). It was demonstrated that the CNES successfully works for goats and that the use of comparative slaughter technique enhances the understanding of energy partition in this species, allowing the development of models applied specifically to goat. However, these models require their evaluation in real-world conditions, permitting continuous adjustments.

Contribution of nutrient fluxes to the evolution of the net energy systems, example of the INRA feeding system for beef cattle

Energy feeding systems define energy as a whole, but progress made to define metabolizable energy (ME) as the sum of the metabolizable nutrients produced by digestion and available for tissue metabolism in a wide range of nutritional situations opens the way to quantitatively model and predict nutrient fluxes between and within tissues and organs and improve predictions of energy use. This review addresses the contribution of nutrient flux concepts and data to the evolution of the Institut de la Recherche Agronomique (INRA) energy feeding system for growing and fattening cattle and evaluates the outcomes on the net energy (NE) requirements. It summarizes recent progress made to quantitatively predict nutrient fluxes both at digestive and visceral levels. It reviews how nutrient flux concepts and results were introduced in the recently updated INRA feeding system, resulting in improvements in the accuracy of the revised digestible energy (DE) and ME value of diets. The use of an independent database showed that for diets fed to fattening cattle, DE and ME concentrations were downgraded for low-energy-dense diets and upgraded for high-energy-dense diets. We are also showing that compared with its previous version, the updated INRA system improves the quantitative relationship between ME supply and flows of metabolizable nutrients. Evidence is provided on how measured nutrient fluxes at portal level were used to evaluate the predicted flows of metabolizable nutrients. This review then revisits the NE values of diets for fattening cattle as defined by the INRA feeding system and not updated yet. Using an independent database and at similar ME intake, carcass composition was shown to be linearly related to the energy density of diets for fiber-rich diets but not for concentrate-rich diets, suggesting that the efficiency of energy utilization of ME into NE is not linearly related to differences in the composition of the gain. Accounting for the balance of metabolizable nutrients or their proxies in models used to predict carcass composition from ME intake can improve predictions. Overall partitioning aggregated energy fluxes into their subcomponent nutrient fluxes in a more physiological approach offers promising perspectives for the evolution of NE feeding systems.

Effects of timing of weaning on energy utilization in primiparous beef cows and post-weaning performance of their progeny1

Early weaning is used to minimize cow nutrient requirements in situations where feed inputs are scarce or expensive. For many years, maintenance energy requirements have been assumed to be 20% greater in lactating compared with non-lactating beef cows. While not well established, maintenance energy requirements are thought to be greatest in primiparous cows and to decline with age. Consequently, early weaning primiparous cow-calf pairs should improve overall efficiency, particularly in situations where mid-to-late lactation forage or feed nutritive value is low. The objective of this study was to determine the biological efficiency of early weaning and maintenance energy requirements of lactating versus non-lactating primiparous cows. Experiments were conducted in two consecutive years using 90 primiparous cows and their calves (48 in yr 1, 42 in yr 2). Pairs were randomly assigned to one of the six pens (8 pairs/pen yr 1, 7 pairs/pen yr 2) and pens were randomly assigned to 1 of 2 treatments; (1) early weaning (130 d ± 15.4; EW, n = 6) and (2) traditional weaning (226 d ± 13.1; TW, n = 6). Late lactation cow and calf performance and feed consumption were measured for 92 d (yr 1) and 100 d (yr 2). Cows were limit-fed to meet maintenance requirements, while calves were offered ad libitum access to the same diet in a creep-feeding area. Calves were not allowed access to the cows' feed. Cow feed intake, body condition score, body weight (BW), milk yield and composition, and calf body weight gain and creep feed intake were recorded. After accounting for lactation and retained energy, there was a trend for greater maintenance energy requirements of lactating primiparous cows (P = 0.07). From the early weaning date to traditional weaning date, calf average daily gain (ADG) was greater (P < 0.01) for TW calves. Feed and energy efficiency of the pair was improved for the TW system (P < 0.01). Greater ADG were reported for EW calves during the stocker period (P = 0.03), but there were no differences during the finishing period (P > 0.40). At harvest, BW was greater (P = 0.02) and gain to feed ratio tended (P = 0.06) to be improved for TW calves. The increased TW calf performance offset the additional maintenance costs of their lactating dams, resulting in the TW system converting total feed energy to kilograms of calf BW gain more efficiently.

ASN-ASAS SYMPOSIUM: FUTURE OF DATA ANALYTICS IN NUTRITION: Mathematical modeling in ruminant nutrition: approaches and paradigms, extant models, and thoughts for upcoming predictive analytics1,2

This paper outlines typical terminology for modeling and highlights key historical and forthcoming aspects of mathematical modeling. Mathematical models (MM) are mental conceptualizations, enclosed in a virtual domain, whose purpose is to translate real-life situations into mathematical formulations to describe existing patterns or forecast future behaviors in real-life situations. The appropriateness of the virtual representation of real-life situations through MM depends on the modeler's ability to synthesize essential concepts and associate their interrelationships with measured data. The development of MM paralleled the evolution of digital computing. The scientific community has only slightly accepted and used MM, in part because scientists are trained in experimental research and not systems thinking. The scientific advancements in ruminant production have been tangible but incipient because we are still learning how to connect experimental research data and concepts through MM, a process that is still obscure to many scientists. Our inability to ask the right questions and to define the boundaries of our problem when developing models might have limited the breadth and depth of MM in agriculture. Artificial intelligence (AI) has been developed in tandem with the need to analyze big data using high-performance computing. However, the emergence of AI, a computational technology that is data-intensive and requires less systems thinking of how things are interrelated, may further reduce the interest in mechanistic, conceptual MM. Artificial intelligence might provide, however, a paradigm shift in MM, including nutrition modeling, by creating novel opportunities to understand the underlying mechanisms when integrating large amounts of quantifiable data. Associating AI with mechanistic models may eventually lead to the development of hybrid mechanistic machine-learning modeling. Modelers must learn how to integrate powerful data-driven tools and knowledge-driven approaches into functional models that are sustainable and resilient. The successful future of MM might rely on the development of redesigned models that can integrate existing technological advancements in data analytics to take advantage of accumulated scientific knowledge. However, the next evolution may require the creation of novel technologies for data gathering and analyses and the rethinking of innovative MM concepts rather than spending resources in collecting futile data or amending old technologies.

Effects of feeding monensin to bred heifers fed in a drylot on nutrient and energy balance

The objective of this study was to determine if feeding monensin would improve diet digestion, energy and nitrogen balance in bred heifers receiving a limit-fed corn stalk-based diet. Sixteen pregnant Meat Animal Research Center (MARC) III composite heifers were used in a 161-d completely randomized design. Heifers were randomly assigned to one of two treatments, no monensin (CON) or 150 mg/d monensin (MON), with eight heifers in each treatment group. Heifers were limit-fed a corn stalk-based diet at 100% of MEm requirements. Effects of monensin on energy and nitrogen balance were determined via total fecal and urine collections and open-circuit respiration calorimetry. Total fecal and urine collection occurred on d 14, 42, and 161 of monensin feeding, and calorimetry measurements were made on d 0, 3, 14, 28, 42, and 161 of monensin feeding. DMI was not different (P = 0.94) for CON and MON heifers and, by design, increased (P < 0.01) from d 14 to d 161 of the trial to account for increasing fetal growth requirements. No differences (P = 0.91) in GE intake were observed between CON and MON heifers, and DE and ME intakes did not differ (P > 0.58) with monensin inclusion. DM, OM, NDF, and ADF digestion did not differ (P > 0.52) between treatments. Fecal, methane, urinary, and heat energy losses were not different (P > 0.16) for MON and CON heifers. Methane production was not different between treatments when expressed as daily liters of methane (P = 0.40); however, MON heifers produced 7% less (P = 0.03) methane per day than CON heifers when expressed as liters of methane produced on a metabolic body weight (MBW) basis. Furthermore, monensin had no effect (P = 0.36) on overall retained energy (RE). Nitrogen intake and excretion was not different (P > 0.13) between treatment groups. Results of this experiment indicate that adding monensin to limit-fed, corn stalk-based diets may not have a large effect on the energy and nitrogen balance of confined heifers.

Comparative effects of grain source on digestion characteristics of finishing diets for feedlot cattle: steam-flaked corn, barley, wheat, and oats

Twelve Holstein steers (454 ± 32 kg) with cannulas in rumen and proximal duodenum were used in a generalized randomized block design to compare steam-flaked corn (SFC), barley (SFB), wheat (SFW), and oats (SFO) as grain sources (74% of diet dry matter, flake density = 0.31 kg L−1) on characteristics of digestion. Ruminal organic matter (OM) digestion was similar for SFC-, SFB-, and SFW-based diets, but lower for SFO. Ruminal microbial efficiency was greater for SFW and SFO. Given that the undegradable intake protein (UIP) value of SFC is 57%, the comparative UIP values for SFB, SFW, and SFO were 39.8%, 36.1%, and 47.3%, respectively. Ruminal starch digestion was lower for SFC than the other flaked grains. Total-tract OM digestion and digestible energy were greatest for SFC, intermediate for SFB and SFW, and lowest for SFO. Given the net energy maintenance (NEm) value of SFC is 2.40 Mcal kg−1, the comparative NEm value for SFB, SFW, and SFO were 2.25, 2.36, and 2.17 Mcal kg−1, respectively. Steam flaking results in important modifications of small grains that appreciably affect their comparative feeding value. Current standards underestimates the NE value of SFB, SFW, and SFO, and overestimates the UIP values for SFB and SFO.

Estimating digestible energy values of feeds and diets and integrating those values into net energy systems

The California Net Energy System (CNES) used a combination of measured and tabular metabolizable energy (ME) values and changes in body composition gain to determine net energy requirements for maintenance and gain and their corresponding dietary concentrations. The accuracy of the CNES depends on the accuracy of the feed ME values. Feed or diet ME values can be measured directly but are expensive and require specialized facilities; therefore, most ME values are estimated from digestible energy (DE) values, which are often estimated from the concentration of total digestible nutrients (TDN). Both DE and TDN values are often from tables and not based on actual nutrient analysis. The use of tabular values eliminates important within-feed variation in composition and digestibility. Furthermore, the use of TDN to estimate DE does not account for important variation in the gross energy value of feeds. A better approach would be to estimate DE concentration directly from nutrient composition or in vitro (or in situ) digestibility measurements. This approach incorporates within-feed variation into the energy system and eliminates the issues of using TDN. A widely used summative equation based on the commonly measured feed fractions (ash, crude protein, neutral detergent fiber, and fat) has been shown to accurately estimate DE concentrations of many diets for cattle; however, deficiencies in that equation have been identified and include an overestimation of DE provided by fat and an exaggerated negative effect of intake on digestibility. Replacing the nonfiber carbohydrate term (which included everything that was not measured) in the equation with measured starch concentration and residual organic matter (i.e., nonfiber carbohydrate minus starch) should improve accuracy by accounting for more variation in starch digestibility. More accurate estimates of DE will improve the accuracy of ME values, which will ultimately lead to more accurate NE values.

Effects of active dry yeast on ruminal pH characteristics and energy partitioning of finishing steers under thermoneutral or heat-stressed environment

The objective of this trial was to determine the effects of supplementing active dried yeast (ADY) in the diets of finishing steers on energy and nitrogen metabolism and ruminal pH characteristics under thermoneutral (TN) or heat-stressed (HS) conditions. Eight British cross steers received 1 of 2 treatments (TRT) [either a control finishing diet (CON) or supplemented with 3 g/d of ADY] under 1 of 2 temperatures [TEMP: TN = 18 ± 0.55 °C and 20 ± 1.2% relative humidity (RH) or HS = 35 ± 0.55 °C and 42 ± 6.1% RH]. Steers were orally administered an indwelling rumen pH and temperature recording bolus. Data collection occurred for 48 consecutive hours inside 2 calorimetry chambers. Data were analyzed as a 4 × 8 Latin rectangle design with fixed effects of TRT and TEMP and random effects of steer and period. There were no TRT × TEMP interactions for metabolism or calorimetric measurements (P ≥ 0.1510). In vivo DM digestibility (DMD) was greater for ADY-fed steers than for CON-fed steers (77.1% vs. 75.3%, respectively; P = 0.0311). No TRT (P = 0.3032) or TEMP (P = 0.1833) effect was observed for nitrogen retention. Energy partitioning suggested DE and ME (Mcal/kg) were greater for ADY-fed steers than for CON-fed steers (P = 0.0097 and P = 0.0377, respectively). Steers under HS had reduced DMI but greater DMD than TN steers (77.1% vs. 75.3%, respectively; P = 0.0316) and greater CH4 per unit of DM (8.53 vs. 6.47 g/kg, respectively; P = 0.0145). Although DE was greater for HS than TN (3.16 vs. 3.06 Mcal/kg, respectively; P = 0.0123), heat production energy (HE) tended to be greater for HS than TN (18.1 vs. 17.0 Mcal/d, respectively; P = 0.0743), resulting in a less retained energy (0.412 vs. 0.100 Mcal/kg; P = 0.0147). There was a tendency for an interaction of mean ruminal pH (P = 0.1279) where pH of ADY-fed steers was greater than pH of CON-fed steers under TN conditions (5.81 vs. 5.57, respectively), but not under HS conditions (5.37 vs. 5.41, respectively). Duration (DUR) and area under the curve (AUC) for pH > 5.6 had similar tendencies; under TN conditions, the DUR and AUC for pH > 5.6 in ADY-fed steers were greater than in CON-fed steers (P = 0.0726 and P = 0.0954, respectively), but under HS conditions, there was no difference between ADY and CON. We conclude that supplementing ADY in the diets of finishing steers improved DMD, DE, ME, and mean ruminal pH under TN conditions, but not in extreme HS conditions likely due to reduced DMI and greater HE requirements.

Energy costs of feeding excess protein from corn-based by-products to finishing cattle

The increased use of by-products in finishing diets for cattle leads to diets that contain greater concentrations of crude protein (CP) and metabolizable protein (MP) than required. The hypothesis was that excess dietary CP and MP would increase maintenance energy requirements because of the energy costs of removing excess N as urea in urine. To evaluate the potential efficiency lost, two experiments were performed to determine the effects of feeding excess CP and MP to calves fed a finishing diet at 1 × maintenance energy intake (Exp. 1) and at 2 × maintenance intake (Exp. 2). In each experiment, eight crossbred Angus-based steers were assigned to two dietary treatments in a switchback design with three periods. Treatments were steam-flaked corn-based finishing diets with two dietary protein concentrations, 13.8% CP/9.63% MP (CON) or 19.5% CP/14.14% MP (dry matter basis; ECP), containing corn gluten meal to reflect a diet with excess CP and MP from corn by-products. Each period was 27 d in length with a 19-d dietary adaptation period in outdoor individual pens followed by a 4-d sample collection in one of four open circuit respiration chambers, 2-d fast in outdoor pen, and 2-d fast in one of four respiration chambers. Energy metabolism, diet digestibility, carbon (C) and nitrogen (N) balance, oxygen consumption, and carbon dioxide and methane production were measured. At both levels of intake, digestible energy as a proportion of gross energy (GE) tended to be greater (P < 0.06) in ECP than in CON steers. Metabolizable energy (ME) as a proportion of GE tended to be greater (P = 0.08) in the ECP steers than in the CON steers at 2 × maintenance intake. At 1 × and 2 × maintenance intake, urinary N excretion (g/d) was greater (P < 0.01) in the ECP steers than the CON steers. Heat production as a proportion of ME intake at 1 × maintenance tended (P = 0.06) to be greater for CON than for ECP (90.9% vs. 87.0% for CON and ECP, respectively); however, at 2 × maintenance energy intake, it was not different (63.9% vs. 63.8%, respectively). At 1 × maintenance intake, fasting heat production (FHP) was similar (P = 0.45) for both treatments, whereas at 2 × maintenance intake, FHP tended to be greater (P = 0.09) by 6% in ECP than in CON steers. Maintenance energy requirements estimated from linear and quadratic regression of energy retention on ME intake were 4% to 6% greater for ECP than for CON. Results of these studies suggest that feeding excess CP and MP from a protein source that is high in ruminally undegradable protein and low in protein quality will increase maintenance energy requirements of finishing steers.

Effects of energy supplementation on energy losses and nitrogen balance of steers fed green-chopped wheat pasture I: Calorimetry

Cattle grazing wheat pasture in the southern Great Plains are sometimes fed an energy supplement; however, the benefits of supplementation on nutrient balance, energy metabolism, and greenhouse gas emissions have not been elucidated. Therefore, we used 10 British crossbred steers (206 ± 10.7 kg initial BW) in a respiration calorimetry study to evaluate the effects of energy supplementation on energy losses, N balance, and nutrient digestibility of steers fed green-chopped wheat forage. The study design was an incomplete replicated 4 × 4 Latin square with treatments in a 2 × 2 factorial arrangement. Steers ( = 8) were assigned to 1 of 2 BW blocks (4 steers per block) with dietary factors consisting of 1) no supplementation (CON) or supplemented with a steam-flaked corn-based energy supplement (that also contained monensin sodium) at 0.5% of BW daily (SUP) and 2) NEm intakes of 1 times (1x) or 1.5 times (1.5x) maintenance. Wheat forage was harvested daily and continuously fed as green-chop to steers during the 56-d study. There were no differences ( ≥ 0.32) between CON and SUP for OM (78.3 vs. 80.7%, respectively) or NDF (68.3 vs. 64.8%, respectively) digestibility. At the 1.5x level of intake, there was no difference ( ≥ 0.16) in energy lost in feces (4.27 vs. 3.92 Mcal/d) or urine (0.58 vs. 0.55 Mcal/d), heat production (8.69 vs. 8.44 Mcal/d), or retained energy (3.10 vs. 3.46 Mcal/d) between supplementation treatments. Oxygen consumption (1,777 vs. 1,731 L/d; = 0.67) and CO production (1,704 vs. 1,627 L/d; = 0.56) of CON and SUP steers, respectively, were not different; however, SUP steers tended to have ( = 0.06) lower CH production (115 vs 130 L/d) than CON steers. Methane, as a proportion of GE intake, was similar for CON (6.87%) and SUP (6.07%; = 0.18), as was the ME:DE ratio ( = 0.24; 86.3% for CON and 87.9% for SUP). Fractional N excretion in urine and feces, as a proportion of total N excreted ( ≥ 0.84) or N intake ( ≥ 0.63), was not different between treatments. Calculated NEm and NEg values for CON were 1.76 and 1.37 Mcal/kg DM, respectively, whereas the NEm and NEg values for the SUP treatment were 2.32 and 1.61 Mcal/kg DM, respectively. Calculated NE values for steers fed additional energy were approximately 17.5% greater than the expected difference in energy content. This was probably the result of the inconsistent response at the 1x DMI level. Under these circumstances, energy supplementation did appear to enhance NEm and NEg value of the supplemented wheat forage diet.

Recent advances in estimating protein and energy requirements of ruminants

Considerable efforts have been made in gathering scientific data and developing feeding systems for ruminant animals in the past 50 years. Future endeavours should target the assessment, interpretation and integration of the accumulated knowledge to develop nutrition models in a holistic and pragmatic manner. We highlight some of the areas that need improvement. A fixed metabolisable-to-digestible energy ratio is an oversimplification and does not represent the diversity of existing feedstock, but, at the same time, we must ensure the internal consistency and dependency of the energy system in models. For grazing animals, although data exist to compute energy expenditure associated with walking in different terrains, nutrition models must incorporate the main factors that initiate and control grazing. New equations have been developed to predict microbial crude protein (MCP) production, but efforts must be made to account for the diversity of the rumen microbiome. There is large and unexplained variation in the efficiency of MCP synthesis (9.81–16.3 g MCP/100 g of fermentable organic matter). Given the uncertainties in the determination of MCP, current estimates of metabolisable protein required for maintenance are biased. The use of empirical equations to predict MCP, which, in turn, is used to estimate metabolisable protein intake, is risky because it establishes a dependency between these estimates and creates a specificity that is not appropriate for mechanistic systems. Despite the existence of data and knowledge about the partitioning of retained energy into fat and protein, the prediction of retained protein remains unsatisfactory, and is even less accurate when reported data on the efficiency of use of amino acids are employed in the predictive equations. The integrative approach to develop empirical mechanistic nutrition models has introduced interconnected submodels, which can destabilise the predictability of the model if changed independently.