Cow-calf Systems Research Articles

255 Awardee Talk: Nutritional management to optimize cow-calf production in Southeast

Abstract Nearly one-half of beef cows in the United States are located in southern states where cow-calf operations predominate. Grazing management in cow-calf systems can be affected by environmental and seasonal conditions, often leading to nutrient deficiency, particularly during late gestation of beef females. Maternal nutrition during the last trimester of gestation can influence offspring development and health, and can be explored to optimize maternal and progeny performance. The objective of this presentation is to share nutritional and management strategies for pregnant beef cows and their long-term effects on offspring growth and physiology. Study 1 investigated the effects of timing of maternal protein supplementation during all last trimester of gestation (LATE84), only the first 42 d of last trimester of gestation (LATE42), or no prepartum supplementation (NOSUP) on offspring pre- and post-weaning performance. At weaning, LATE84 calves were the heaviest, followed by LATE42, and NOSUP (P ≤ 0.05). Steer serum parainfluenza-3 titers were greater (P = 0.03) for LATE42 vs. NOSUP and tended to be greater for LATE84 (P = 0.10) vs. NOSUP steers. Marbling and the proportion of steers grading choice were greater (P ≤ 0.04) for LATE42 vs. NOSUP, and intermediate for LATE84. Study 2 evaluated the effects of frequency of maternal protein supplementation on offspring pre-weaning growth. Cows received the same weekly amount of supplement (7 kg·cow⁻¹·wk⁻¹) but with different frequencies: once a week (1X), three times per week (3X), every day (7X), or no prepartum supplementation (NOSUP) during the last 80 d of gestation. At weaning, calves born from 7X cows were the heaviest (P ≤ 0.05), followed by 3X and 1X, which did not differ between them (P = 0.54), and NOSUP calves were the lightest (P ≤ 0.05). Study 3 evaluated the use of monensin supplementation during the last 77 d of gestation and its impacts on offspring performance. Treatments consisted of no prepartum supplementation (NOSUP), supplementation of dried distillers grains at 1 kg·cow⁻¹·d⁻¹ added with 0 (SUP) or 200 mg/d of monensin (SUPMO). At weaning, SUPMO calves were the heaviest (P ≤ 0.05), SUP intermediate, and NOSUP were the lightest. Experiment 4 consisted of pregnant heifers receiving the supplementation of 1 kg/d of soybean hulls dry matter added (BAC) or not (CON) with a Bacillus-based DFM mixture during late gestation (d 0 to 139) and early lactation (d 139 to 242). Post-weaning body weight gain and indicators of humoral immune response post-vaccination were greater for BAC vs. CON calves (P ≤ 0.05). Therefore, changing the time and frequency of supplementation, and the use of additives and probiotics during late gestation of beef females are effective alternatives to improve offspring pre- and post-weaning growth and immune response.

State of the art of the cow-calf systems in beef and dairy cattle (Bos taurus) operations in EU, USA, and Brazil from 1998 to 2023

Cow-calf systems represent a significant research area in animal husbandry, with differences depending on the final product (meat or milk). This study aimed to apply text mining and topic analysis on literature describing cow-calf systems in European, American, and Brazilian beef and dairy sectors between 1998 and 2023. Additionally, cow-calf contact (CCC) literature data was manually extracted. Our findings revealed the presence of 11 research areas among literature on cow-calf systems, with different priorities identified in the beef and dairy sectors. Beef industry mainly focused on animal proficiency and nutrition, while dairy on animal welfare and CCC, which showed a growing trend as emerging research topic, mostly in the EU. Current debates around calf welfare and EU's planned animal welfare legislation revision appeared to be driving the increasing interest in this topic. Studies in the beef sector were mainly localized in Brazil, showing that research in different contexts and species is important for CCC implementation. Manual data extraction showed considerable variation in the retained CCC documents regarding sample size, type of contact, methods and CCC duration. Learning about the varied CCC approaches used in beef and dairy farms in different locations, concentrating on their strengths and weaknesses, will help to develop novel solutions to global challenges. Adopting validated and robust indicators would help scientists and policymakers to monitor the system's quality. To improve CCC feasibility, match consumer demands, and move towards One Welfare and One Health, future research should focus on a variety of situations to overcome the current shortcomings.

Traditional cow-calf systems of the northern region of Santa Fe, Argentina: current situation and improvement opportunities

Traditional cow-calf systems of the northern region of Santa Fe, Argentina: current situation and improvement opportunities

The “how and why” of assessing micronutrient levels in beef cow-calf systems

Matching the nutritional resources of protein, energy, miner­als, trace minerals and vitamins to requirements of the beef cow at various times of the year is likely the most challenging aspect of meeting the production goals in a cow-calf production system. While each system will have different goals, commonly accepted goals are 95% of females pregnant in 60 days, 65% of the cows calving in the first 21 days, and a 90 % weaned calf crop based on number of cows exposed.18 If goals are not being met, the obvious question is “why?” and a careful evaluation of the entire system should be undertaken as many times these problems are multifactorial. It is not uncommon to find nutri­tion playing a significant role in these problems whether they be reproductive, neonatal health or weaning health (Figure 1).

Cow age, resilience and productivity of cow–calf systems

Context The energy availability for cow–calf systems is related to climate disturbances, and energy use is influenced by the age of the cows. Both factors determine the productivity and resilience of herds after climate disruption. Aims Identify the time needed for the herds composed of cows of a varying age to achieve resilience after energy restriction in the pre- and postpartum. Methods The resilience of systems was compared by deterministic dynamic simulation and herds were considered initially stable but different in (1) energy availability for all herd in the first year of production, namely at 50% (low, L), 75% (medium, M) of 100% (high, H) of the requirements according to the NRC (2000, 2016), with these energy levels being restricted to 60 days before and 60 days after the birth, and (2) the maximum age of the cull cow (lifetime, LT), namely 4 (LT4L, LT4M, LT4H), 6 (LT6L, LT6M, LT6H) of 11 (LT11L, LT11M, LT11H) years. From the second year, availability returned to meet the energy requirements of all animals. The availability of energy for the herd was simulated in natural and cultivated pasture. The productivity was determined as the relation between the kilograms of animals sold and the area used for production over a productive cycle. The system model was considered resilient when 95% of the standard productivity was reached (prior to energy restriction). Key results The time required to return to stability was 2 years in the LT6 and LT11, whereas LT4 required 3 years. Furthermore, LT6 had a higher productivity than did the other herds. The older the culled cow was, the greater was the change in the composition of the product commercialised. Conclusions Cows with an intermediate culling age allowed a sustainable intensification of the system, because they showed better productivity than did older cull cows. Furthermore, after climate disturbance, they presented more resilience than did younger cull cows. The level of energy restriction did not directly influence the time to resilience within each evaluated discard-age group. Implications Herds that culled females before reaching adult age are less resilient after disturbances, such as changes in climate or changes of any nature that interfere with reproductive rates.

266 Comparing the Prediction Accuracy of Models for Estimating DMI of Beef Heifers Using Surface Area, Volume, Body Measurements or Body Weight by the Elastic net Regularized Regression Method

Abstract Dry matter intake (DMI) remains one of the most variable and significant factors contributing to cost of production in cow-calf systems. Body weight (BW) has been used to estimate DMI of individual cattle as an alternative to measuring DMI, which is expensive, labor intensive, and not practically feasible in production environments. The objective of this study was to evaluate if calculated body measurements [volume (VL) 218 to 503 liters; frame score (FS) 2.1 to 7.5; surface area (SA) 4.02 to 7.12 m2) and direct body measurements (DBM: body length (BL) 89 to 136 cm; hip height (HH) 96 to 136 cm; hip width (HW) 33 to 52 cm; heart girth (HG) 149 to 191 cm; mid girth (MG) 177 to 234 cm; and flank girth (FG) 156 to 239 cm] could be used to estimate DMI of heifers as accurately as using BW (267 to 506 kg). Data from 300 heifers (9 breeds) collected over 4 years were used. Year was included in the model as a random effect. An elastic net model using the glmnet function of the R caret package was used. There were 206 training and 94 testing observations. The models were cross validated 10-fold with 5 repetitions. Models with the least minimum root mean square error and greatest median R-square (R2) values were selected as the best models. Model R2 ranged from 0.19 (SA) to 0.63 (BW), where DBM (0.40) and FS (0.43) performed similarly. As prior studies have suggested, BW in this study accounts for the greatest variation in DMI. However, calculated FS and ABM also explained some variation in DMI and more so than VL (0.22) and SA. These data indicate that FS and ABM could be used as alternatives in cases where BW records are not available to estimate DMI of heifers.

A conceptual model of cow-calf systems functioning on native grasslands in a subtropical region.

Cow-calf systems utilise grazing of native grasslands for beef cattle propagation and constitute the principal livestock activity in the Pampas and Campos areas. Cow-calf system sustainability is questioned because of their low production levels and negative environmental impact. Ecological intensification has been proposed as a way out that constitutes an alternative to dominant discourses based on increasing external-input use. There is, however, a considerable gap between the availability of scientific knowledge to promote the ecological intensification of cow-calf systems and farmers' practices. This gap between scientific knowledge availability and farmers' practices can be made explicit, and its consequences for systems performance can be explored through a conceptual model. Conceptual models are tools to build a systems view of the interactions among the production system's state variables, farm management, and resulting system performance. In this paper, we develop a conceptual model of cow-calf systems on native grasslands of the Pampas and Campos regions to support the diagnosis and redesign of farm systems towards ecological intensification. We apply the conceptual model to analyse cow-calf systems in Uruguay, drawing on a survey among 250 Uruguayan livestock farmers. Using the model, we show that in Uruguay, the level of implementation of strategic, tactical, and decision-supporting techniques is low. Consequently, most farms have poor control of the grazing intensity and timing of main events in the production cycle. This results in ample room to improve the productive and environmental performance of most cow-calf farms in Uruguay. We distinguished three broad types of cow-calf systems based on the degree of implementation of techniques, the evolution of state variables throughout the year, and productive indicators. These types imply different departure points and strategies for a sustainability transition process. The conceptual model designed in this paper may support the cow-calf systems sustainability transition in the context of co-innovation processes by aiding the interactive diagnosis and redesign of farm systems.

Failure of Passive Immunity Transfer Is Not a Risk Factor for Omphalitis in Beef Calves.

Omphalitis is the third most frequent disease in newborn calves after neonatal diarrhea and bovine respiratory disease (BRD), but limited data on the prevalence and risk factors are available in the literature. Failure of passive immunity transfer (FPIT) is recognized as a major risk factor for diseases and mortality in calves. However, the association between omphalitis and FPIT remains poorly described. To assess this association, 964 suckler beef calves from 22 farms were included in a longitudinal cohort study for 5 months. Each calf was examined twice (mean ages: 4.4 and 11.1 days old) to diagnose omphalitis through clinical examination and ultrasonographic evaluation (USE) if necessary. Measurements of the total solids percentage (TS-%Brix) and total protein (TP) were performed on the serum during the first visit to evaluate the calves' passive immunity status. FPIT (fair and poor) was defined as serum %Brix < 8.1 or TP < 5.1 g/dL; among calves with omphalitis, 14% had FPIT and among calves without omphalitis 12% had FPIT. The omphalitis prevalence was 32.3% in calves without any other disease (overall prevalence of 30.9%). No statistical association between the prevalence of omphalitis and FPIT was observed. Further research is needed to identify the risk factors and promote the prevention measures for omphalitis in cow-calf systems, such as calving difficulty, hygiene of housing, and navel disinfection.

O58 Energy efficiency of beef cattle in grazing production systems. II. Effect of herbage allowance on cow-calf systems

O58 Energy efficiency of beef cattle in grazing production systems. II. Effect of herbage allowance on cow-calf systems

BovCria: an application designed to assist breeders in the assessment of beef cattle herds

The aim of this study was to develop a technological tool in the form of a mobile application that provides functionalities for the easy calculation of reproductive and productive efficiency indices. This tool aims to assist breeders, technicians, and students of agricultural sciences in decision-making for the challenges faced in cattle production systems. The application was developed using the Android Studio development environment and the Dart programming language framework known as Flutter. The application's graphical interface follows Google guidelines in the Material Design documentation. The tool will provide a practical way to calculate recognized indexes of productive efficiency of cow-calf systems and provide information such as goals and management tips to help users achieve better results. The impact of the developed product is its use as an information platform, facilitating decision-making in the area of beef cattle production and as an efficient means of disseminating technologies generated by research institutions and popularizing science. Thus, the application is an accessible and comprehensible tool, providing a means of evaluating the technologies and management practices adopted in beef cattle farms.

Bioindicadores de estrés y evolución de peso de terneros provenientes de destete precoz e hiperprecoz

Early (60 – 70 days old) &amp; very early weaning (30 – 40 days old) are used to improve pregnancy in beef cow-calf systems. However, its application can affect the calves’ welfare. The aim of this work was to identify biomarkers levels &amp; average weight gain in early &amp; very early weaned calves. The animals were assigned to pens according to weaning age: very early weaned (40-d) &amp; early weaned (66-d). The weaning practice consisted of the daily supply of extruded food (26% crude protein &amp; 3 Mcal metabolizable energy). Live weight was registered at 14 days intervals. Blood samples were collected on the day of weaning (0) &amp; on days 2 &amp; 11 after. Red blood cells, hematocrit, hemoglobin, mean corpuscular value, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, white blood cells, total proteins, &amp; albumin were measured by complete blood count. Statistical analyzes were performed using the ANOVA ((Tukey Test, α = 0,05). Any calf lost weight; also, average weight gain was higher in early weaned calves. Most of the biomarkers presented normal values after the weaning stage (day 11). In this work, weaning at early ages didn`t affect animal welfare. These results are important in the beef cow-calf systems where are applied to improve the pregnancy rate.

Feed technologies and efficiency in cow-calf systems

This study was performed to evaluate the efficiency index of cow-calf systems, based on different feed technologies commonly employed in the Rio Grande do Sul state, southern Brazil. Hence, the efficiency of 35 cow-calf herds was evaluated by Data Envelopment Analysis (DEA). Data was collected by online survey and in-depth interviews, as well as data registers from the cow-calf systems, located in 31 municipalities. The analyzed indicators included rates of mortality, pregnancy, birth, and productivity. The feed technologies evaluated [...]

364 Comparison of Semi-Confined and Pasture-Based Fall Calving Beef cow Systems

Abstract Conversion of perennial grasslands to crop land in U.S. Northern Plains has resulted in a need to evaluate alternative management strategies for cow-calf production. A 3-yr study was conducted to compare beef cow/calf performance in two different August-calving cow systems. Multiparous beef cows (n = 318) were allocated to 8 replicates, and replicate was randomly assigned to drylot (DL) or pasture (PAST) treatments. From mid-gestation (March/April) until breeding (October), DL cows were limit-fed to meet requirements and PAST cow grazed perennial pasture. Feed resource during the 47-d breeding period (November/December) varied by year and treatment. However, pregnancy rates did not differ (P=0.72) between treatments within year. Both treatments went to corn residue at the time of weaning (late January) and grazed for 37 d. A treatment × year × time interaction (P&amp;lt;0.01) was observed for cow BW, BCS, and calf BW. In Year 1, cow BCS at pre-calving, breeding, and weaning was less (P&amp;lt;0.01) for DL (5.3) than PAST (6.2; 1 to 9 scale). Weaning weights in Year 1 were less (P&amp;lt;0.05) for DL (178 kg) than PAST (183 kg) calves. In Year 2, cow BCS was less (P&amp;lt;0.01) in DL (6.1) than PAST (6.7) at pre-calving and breeding, but did not differ (P=0.12) at weaning. At weaning in Year 2, calf BW of DL (212 kg) was greater (P&amp;lt;0.01) than PAST (201 kg). Like Year 2, DL cows in Year 3 had decreased (P&amp;lt;0.01) BCS at pre-calving compared with PAST (7.3 vs. 7.7). However, breeding BCS (6.8) did not differ (P=0.98). In Year 3, cow BCS at weaning was greater (P&amp;lt;0.01) for DL (7.1) than PAST (5.9) but calf BW at weaning did not differ (P=0.17). Cow and calf performance are not sacrificed in semi-confined cow-calf systems and are a reasonable alternative to traditional pasture systems.

Bioeconomic assessment of three ages at weaning in cow-calf systems

Early weaning is frequently used for the reestablishment of a cow's physiological conditions in situations of feed restriction and to increase the possibility of conception. However, studies on the systemic impacts of earlier weaning management are scarce, and bioeconomic assessments of beef calves weaned at 30 days of age have not been reported in the scientific literature. Therefore, this study aimed to perform a bioeconomic assessment of cow-calf systems with calves weaned at 30 (W30), 75 (W75), or 180 (W180) days of age. For this, a dynamic deterministic model was created based on a baseline scenario that used only W180, and thereafter the application of W30 and W75 was simulated. In the single application scenarios, W30 was applied only in year one in all cows (HA1), or only in primiparous cows (HP1), and W75 in all cows (EA1), or only in primiparous cows (EP1). In addition, successive application scenarios were simulated in which W30 and W75 were applied every year throughout eight years to intensify the system by increasing the number of dams. Thus, W30 was performed in all cows (HA8), primiparous (HP8), and W75 in all cows (EA8), or only in primiparous cows (EP8). The pregnancy rate breakpoint was simulated to determine which reduction in the pregnancy rate of conventional weaning systems would be necessary to justify the application of each single application scenario. The lowest gross margin per hectare, in the single application scenarios, was observed in the first year owing to the increase in weaning costs, and the highest gross margin per hectare in the second year due to a higher number of weaned calves. In year one, the highest gross margin per hectare was observed in EP1 and lowest in HA1. The pregnancy rate breakpoint for EP1 was 72.6%, whereas for HA1 was 42.3%. Intensification was observed in all successive application scenarios, but with GM/ha lower than CA8. Except for HA1 and HA8, all scenarios generated a positive gross margin per hectare. In conclusion, the single application of W30 only in primiparous and W75 in all cows and only in primiparous were economically viable. In addition, it is possible to intensify the system through consecutive applications of these technologies, although GM/ha was always lower than conventional weaning at 180 days of age. Therefore, adopting technologies that promote the rapid recovery of production and enable the reconstruction of the herd structure, such as W30 and W75, should be considered when unexpected weather events or sudden changes in culling policies occur.

Impacts of postpartum length at the initiation of the fixed-time artificial insemination protocol on pregnancy rates of Bos indicus beef cows.

The shortest interval between calving and initiation of fixed-time artificial insemination (FTAI) protocols recommended in Brazilian cow–calf systems is 30 d, based on research that characterized uterine involution and incidence of uterine disorders in Bos taurus females. Prevalence of uterine disorders such as subclinical endometritis is limited in Nelore (B. indicus) cows as early as 28 d after calving. We hypothesized that Nelore cows can receive an FTAI protocol as early as 20 d postpartum (DPP) and still experience satisfactory reproductive results. This study evaluated pregnancy rates in 5,258 Nelore cows (n = 1,703 primiparous and 3,555 multiparous) according to DPP at the initiation of the FTAI protocol. Cow body condition score (BCS) was recorded at FTAI, and pregnancy diagnosis was performed ~30 d after FTAI. Cows were ranked within parity by DPP at the initiation of the FTAI protocol and classified according to 5-d intervals (e.g., ≤15 DPP, 16 to 20 DPP, 21 to 26 DPP, until cows with ≥76 DPP). Data were analyzed within parity, using cow as experimental unit and orthogonal polynomial contrasts (linear, quadratic, or cubic) generated using the mean DPP of each DPP class. In both parities, cow BCS at FTAI decreased linearly (P ≤ 0.01) with the advance of DPP (e.g., 4.79, 4.00, and 3.73 in primiparous, and 4.95, 3.70, and 3.23 in multiparous cows classified as ≤15 DPP, 36 to 40 DPP, ≥76 DPP, respectively). The pregnancy rate to FTAI was affected quadratically (P < 0.01) by DPP for both parities. In primiparous cows, the pregnancy rate increased until 36 to 40 DPP (60%), remained near this level until 51 to 60 DPP, and then decreased with the advance of DPP, whereas cows classified as 21 to 25 DPP expressed satisfactory results (41.5%). In multiparous cows, the pregnancy rate increased until 46 to 50 DPP (70.8%), remained near this level until 56 to 60 DPP, and then decreased with the advance of DPP, whereas cows classified as 21 to 25 DPP also expressed satisfactory results (63.6%). Collectively, primiparous and multiparous Nelore cows evaluated herein experienced optimal pregnancy rates when the FTAI protocol was initiated within 30 to 60 DPP, although reasonable outcomes were observed when the FTAI protocol was initiated as early as 21 DPP. Hence, the interval between calving and initiation of the FTAI protocol can be shortened by 10 d in Nelore females and still yield acceptable pregnancy rates, which can be of great value to cows that calve immediately prior to or during the annual breeding season.

Selection effect for growth traits on energy requirements in beef Nelore steers.

Growth data of 77,372 Nelore steers were used to estimate the selection effect on energy requirements considering two beef production systems: cow-calf and slaughter cycles. All the animals had measures from 120days to 7years old. The parameters necessary to evaluate the selection effect on energy requirements were obtained by random regression analysis using Legendre polynomials. The models included additive direct and maternal effects, and animal and maternal permanent environmental effects as random terms. Contemporary group and dam age at calving (linear and quadratic effect) were included as fixed effects, and orthogonal Legendre polynomials of animal age (cubic regression) were considered random covariables. The coefficients from the model M3353_5 were used to calculate the genetic gains necessary to predict the increase in phenotypes. The selection was simulated for body weight (BW) and weight gain (WG) at different ages and energy requirements were calculated using NRC equations. The cost of feed was calculated for a cow-calf and slaughter cycle of production considering a system of Brachiaria decumbens pasture without supplementation. In slaughter system, the selection for weight of 365days of age is the best option. In cow-calf systems, the selection W120 is the best choice.

41 Genomic Approaches to Improving Forage-based Beef Cow Efficiency

Abstract In recent decades, the U.S. beef herd has seen massive gains in efficiency, driven by innovations in genetics, nutrition, reproduction, and resource management. Despite these advances, the industry remains under pressure to further reduce its environmental footprint. Perhaps the greatest opportunity to drive increases in sustainability is through targeted genetic improvement of forage-based cow-calf systems. While the industry has long focused on selecting for pre- and post-weaning performance, improvements in mature cow efficiency are more challenging to attain. One major impediment to directly selecting for cow efficiency is a lack of easily measured indicator phenotypes, leading some segments of the industry to focus exclusively on moderating mature size. The optimal solution to this problem will likely require a more complex understanding of the underlying biology of cow efficiency. As we consider how genomics might increase the environmental sustainability of forage-based beef production, we will need to focus on developing and measuring novel phenotypes and accounting for the complex interplay between an animal’s genetics, environment, and management. Using stochastic genetic simulations, we demonstrate the potential environmental and economic impacts of genetic selection for more efficient and well-adapted cows. We also describe possible solutions for measuring a cow’s efficiency on grass (e.g., forage intake to weaned calf pounds) that could be used to develop novel EPDs and economic selection indexes. Finally, we discuss the concept of precision genomic predictions that account for how genotypes interact with environmental stressors and management differences. We propose two potential solutions to address this concern: 1) Selecting robust cattle that perform well across all environments and management levels or 2) Developing precision predictions for precisely matching animals to their ideal production scheme.

The carbon footprint of beef cattle systems in the Southeast United States

Grasslands in the Southeast United States (SE US) cover 15.8 million ha and most of this area is dedicated to beef production systems. This region holds 6.3 million beef cows and 12.1 million cattle, including calves. Beef cattle systems in the SE US are mostly cow-calf based, and most of the greenhouse gas emission from cattle occurs during this phase (cow-calf) because of their forage-based diet. This review assessed the carbon footprint (C footprint) of beef cattle systems in the SE US and indicates possible ways to reduce it. Major emissions in beef cattle systems come from livestock enteric fermentation and greenhouse gases from excreta. Cow-calf systems in the SE US are typically low input, although they use some industrial fertilizers, machinery, and fossil fuel, which adds to the C footprint of the sector. There are opportunities to reduce the beef C footprint in the SE US by adopting climate-smart practices, including preservation of natural ecosystems that have potentially high carbon sequestration, afforestation, integration of forage legumes (and reduction of nitrogen fertilizer), use of slow-release fertilizers, and dietary interventions. In fact, depending on the level of adoption of some of these practices, it is possible to establish climate-neutral beef at the farm gate in the SE US. Beef is a key food for humans and has large economic effects. Development of climate-smart beef could create opportunities for a niche market that recognizes the environmental footprint of agricultural production and could incentivize producers to pursue those systems.

Cow–calf efficiency of beef cows grazing different herbage allowances of rangelands: hepatic mechanisms related to energy efficiency

Context Improvement in efficiency of energy utilisation of cow–calf systems could benefit beef production profitability and sustainability. Energy efficiency has been associated with mitochondrial function; therefore, hepatic mitochondrial function and oxidative stress could play a key role in energy efficiency of beef cows. Aim We evaluated the effect of two herbage allowances from rangelands (Campos biome) on cow–calf energy efficiency, hepatic mitochondrial density and function, and oxidative stress of purebred (Hereford and Aberdeen Angus) and reciprocal F1 crossbred beef cows. Methods Mature cows (n = 32) were used in a complete randomised block design with a factorial arrangement of herbage allowance (2.5 vs 4 kg dry matter/day; low vs high) and cow genotype (pure vs crossbred) over 3 years. At the end of the third year, cows were slaughtered at 190 ± 10 days postpartum. Liver was dissected and weighed, and samples were collected and snap-frozen pending analysis of mitochondrial density and oxidative stress markers. Estimated cow–calf energy efficiency was calculated by using total cow estimated metabolisable energy intake as input and calf energy retained at weaning as output. Key results Cow–calf energy efficiency was greater (P ≤ 0.07) for high than low herbage allowance and for crossbred than purebred cows. Mitochondrial density biomarkers (hepatic citrate synthase enzyme activity, citrate synthase mRNA, and mitochondrial:nuclear DNA ratio) were greater (P ≤ 0.03) for high than low herbage allowance. Plasma pro-oxidants and plasma antioxidant capacity were greater (P ≤ 0.07) for crossbred than purebred cows. Plasma oxidative stress index and expression of hepatic 4-hydroxynonenal protein adducts were affected (P ≤ 0.06) by herbage allowance × cow genotype interaction. Conclusion Greater cow–calf energy efficiency was associated with greater hepatic mitochondrial density without differences in mitochondrial function. Contrary to expectation, greater efficiency of crossbred than purebred cows was associated with increased hepatic oxidative damage, which probably reflects greater liver metabolic activity in crossbreds. Implications Herbage allowance and cow genotype affect cow–calf efficiency, hepatic mitochondrial function and oxidative stress markers. Greater efficiency of crossbred cows seems associated with increased hepatic oxidative damage.

Improving Beef Progeny Performance Through Developmental Programming

Maternal nutritional management during gestation appears to modulate fetal development and imprint offspring postnatal health and performance, via altered organ and tissue development and tissue-specific epigenetics. This review highlighted the studies demonstrating how developmental programming could be explored by beef producers to enhance offspring performance (growth, immune function, and reproduction), including altering cow body condition score (BCS) during pregnancy and maternal supplementation of protein and energy, polyunsaturated fatty acids (PUFA), trace minerals, frequency of supplementation, specific amino acids, and vitamins. However, this review also highlighted that programming effects on offspring performance reported in the literature were highly variable and depended on level, duration, timing, and type of nutrient restriction during gestation. It is suggested that maternal BCS gain during gestation, rather than BCS per se, enhances offspring preweaning growth. Opportunities for boosting offspring productive responses through maternal supplementation of protein and energy were identified more consistently for pre- vs. post-weaning phases. Maternal supplementation of specific nutrients (i.e., PUFA, trace minerals, and methionine) demonstrated potential for improving offspring performance, health and carcass characteristics during immunological challenging scenarios. Despite the growing body of evidence in recent years, the complexity of investigating developmental programming in beef cattle production is also growing and potential reasons for current research challenges are highlighted herein. These challenges include: (1) intrinsic difficulty of accurately measuring cow milk production multiple times in cow-calf systems; (2) larger focus on Bos taurus vs. Bos indicus breeds despite the predominance of Bos indicus-influenced beef breeds in tropical/subtropical environments and their specific, and sometimes opposite, physiological and performance outcomes compared to Bos taurus breeds; (3) limited focus on interaction between prenatal and postnatal management; (4) sex-specific outcomes following similar maternal nutrition during gestation; (5) greater focus on nutrient deficiency vs. excess; (6) limited implementation of immunological challenges; and (7) lack of multigeneration and longer periods of offspring evaluation. This review provides multiple evidence that such obstacles need to be overcome in order to significantly advance the scientific knowledge of developmental programming in beef cattle and promote global beef production.