NEm Requirement Research Articles

133 Feeding Behavior of High-Risk Steers Newly Received for Backgrounding

Abstract There is a need to understand the feeding behavior ontogeny of newly received high-risk steers. Understanding how calves learn to eat out of a bunk will facilitate the implementation of management practices that expedite this process and allow animal managers to exploit this information to monitor individual animal health. To address this knowledge gap, the feeding behavior of high-risk steers that were received for backgrounding was quantified and characterized using electronic feedbunks in this context. To create this paradigm, crossbred steers (n = 20) were purchased in two groups (Group: n = 64 steers; Group 2: n = 56 steers) from a local auction market, transported 800 km to the Prairie Research Unit in Prairie, MS, and immediately weighed (shrunk body weight, BW). Steers were purchased according to research unit space availability. Therefore, purchases occurred 133 days apart. The subsequent day, steers were ranked by shrunk BW (227 ±.3 kg) and allocated to 1 of 8 drylot pens (n = 8 steers/pen) with two GrowSafe automated feeding systems per pen. Steers were fed a total mixed ration ad libitum for a 28-day period and steer BW was recorded on d 0, 2, 6, 10, 13, 21 and 28. Daily feeding behavior [e.g., meal duration (sec), intake (g/d), meal frequency (count/d), bunk visit frequency (count/d), head down duration (sec), maximum non-feeding interval (NFI,s), ratio of head down duration to bunk visit duration)] were calculated using Meal Criterion Calculation Software. The impact of time on feeding behavior and performance was analyzed using a mixed linear model (PROC MIXED). To determine when steers had established consistent dry matter intake (DMI), consistency was defined as when the DMI of a steer remained within one standard deviation of the 7-day average DMI of the steer. Latency to first bunk attendance (d), first feed consumption, attainment of NEm requirement, and latency (d) to establish consistent feed intake levels were analyzed using a generalized linear mixed model (PROC GLIMMIX) for binomial data. Steer BW increased across days (P < 0.01), whereas average daily gain was.48 ± 0.4 kg/d. All feeding behaviors changed across days (P < 0.01). Meal and bunk visit (duration and frequency), meal intake (mean and sum), head down duration, and maximum NFI increased over time. All steers visited the bunk and consumed their first meal by day 4 (P < 0.01). All steers achieved NEm requirements by day11 (P < 0.01). These results quantify the acclimation period of steers to a new environment and characterizes the learning and development of novel modes of eating. These results inform the development of behavioral expectations for newly received high-risk calves that can be used to monitor cattle health, understand cattle perception, and promote cattle welfare.

90 Evaluating the Difference between Formulated Dietary net Energy Values and net Energy Values Determined from Growth Performance and Estimates of Shrunk Body Weight Gain in Finishing Beef Cattle

Abstract The California Net Energy System (CNES) was developed more than 50 yr ago and partitions energy into NEm and NEg, both of which can be calculated for feedstuffs as a cubic function of dietary ME. Recovered energy (i.e., NEg) can be calculated from NEm requirements, dry matter intake (DMI), and shrunk body weight gain (SWG). Thus, if body composition can be reliably estimated relative to maturity, SWG and DMI can be used to calculate performance-adjusted net energy values using a quadratic solution. Likewise, SWG can be predicted from 13.91 × RE0.9116 x EQSBW-0.6837. Evaluating observed vs. predicted values of NEm, NEg, and SWG enables nutritionists to better understand differences in maintenance energy requirements, efficiency of energy use, associative or antagonistic effects of feedstuffs, nutrient deficiencies, and environmental factors. Our objective was to use feedlot performance and carcass data from numerous pens of cattle fed at two locations to identify potential weaknesses in the CNES equations by evaluating factors affecting residuals between calculated dietary NEm and NEg values based on NASEM (2016) tabular values and performance based NEm and NEg values. With adjustments to address beef industry changes, the CNES will continue to maintain functionality in practical beef production.

Energy requirements of Holstein, Gyr, and Holstein × Gyr crossbred heifers using the respirometry technique

We aimed to determine the energy requirements for maintenance and gain of 18 prepubertal dairy heifers of three breed compositions (BC; Holstein, Gyr, and Holstein × Gyr). Diets were formulated for gains of 0, 400, and 800 g/day, corresponding to 1.0×, 1.5×, and 2.0× maintenance, respectively. Each dairy BC had six animals with an initial body weight (iBW) of 219.8 ± 32 kg, 215.8 ± 33 kg, and 228.3 ± 33 kg for Holstein, Gyr, and Holstein × Gyr, respectively. The experiment was designed as a completely randomized design in a factorial scheme 3 × 3 [three BC and three feeding levels (FL)]. Digestibility and metabolism assays were performed to determine energy losses through feces and urine. Heat production was determined using the continuous measurement of oxygen consumption, carbon dioxide production, and methane emissions in respiration chambers. Energy requirements for maintenance (NEm) were calculated based on the relationship between heat production (HP) and metabolizable energy intake (MEI). The efficiency of use of metabolizable energy for maintenance (km) was obtained from the ratio between NEm and metabolizable energy requirements for maintenance. The net energy requirements for growth (NEg) were estimated from the model RE = β0 × EBW0.75 × EBGβ1, where RE is the retained energy (Mcal/day), EBW is empty body weight (kg0.75), and EBG is the empty body gain (kg/day). The efficiency of use of metabolizable energy for gain (kg) was estimated as the slope of the regression between RE and MEI for gain. Gyr heifers presented NEm 15% lower (98 kcal/kg of BW0.75) than HG crossbred animals. Holstein and crossbred heifers had similar NEm, 102 and 112 kcal/kg of BW0.75, respectively. The km was 0.71, 0.74, and 0.75 for HG, Holstein, and Gyr, respectively. Net energy requirement for gain (NEg) did not differ across BC, and a single equation was fit for all BC: RE = 0.069 × BW0.75 × BGW0.852. A single kg of 0.65 was observed for all three BC. Breed composition affected the energy requirements for maintenance and the energy partition, and those differences should be considered when estimating requirements for Gyr, Holstein × Gyr crossbred, and Holstein heifers.

Effect of feeding method on nutrient utilization and cow performance in limit-fed cow-calf systems.

Delivery of limit-fed, complete rations requires significant capital investment, and creates logistical challenges for producers. Deconstruction and separate delivery of roughage and concentrate portions of diets may decrease feeding cost. Two experiments were conducted to evaluate the potential of separately limit-feeding roughage and concentrate. In Experiment 1, 4 ruminally cannulated steers (371 ± 12 kg bodyweight) were used in a 4 × 4 Latin square to evaluate the effects of time of concentrate delivery in deconstructed diets. Intake was restricted to 80% of predicted NEm requirements of a diet consisting of wheat straw (35%), cracked corn (29%), and distillers’ grains (27%) formulated to contain 1.58 Mcal NEm/kg. Treatments were: concentrate fed 2 h prior to wheat straw (–2S), concentrate and wheat straw fed as total mixed ration (TMR), concentrate fed 2 h after wheat straw (+2S), and concentrate fed 12 h after wheat straw (+12S). In Experiment 2, 95 mid- to late-gestation cows (503 ± 151 kg) were used in a 112-d trial to evaluate feeding system on cow performance. Cows were assigned to 1 of 12 pens. Treatments were limit-fed the complete diet from Experiment 1 (TMR), fed roughage and concentrate portions of the deconstructed TMR 12 h apart (SEP), and ad libitum bermudagrass hay (HAY). Bodyweight (BW), BCS, and back fat measures were collected every 28 d. In Experiment 1, treatment did not affect DM or OM digestion (P ≥ 0.88), rate of particulate passage (P ≥ 0.55), or ruminal DM fill (P ≥ 0.19). Fill averaged 3.8 kg DM. Nadir of ruminal pH occurred 4–8 h after concentrate was delivered, but mean ruminal pH was not different among treatments (P = 0.22) ranging from 6.4 to 6.6 for +2S and 12S, respectively. In Experiment 2, treatment did not affect final BW (518 kg; P = 0.72) or final BCS (5.6; P = 0.67), but limit-fed strategies tended (P = 0.06) to have greater final RE (137.1, 98.9, and –14.6 Mcal for TMR, SEP, and HAY, respectively). Delivering forage and concentrate separately did not change digestion, and timing of concentrate delivery had only minor effects on ruminal fermentation. Limit-feeding a TMR or separate delivery of roughage and concentrate sustained cow performance compared to ad libitum hay consumption.

PSII-6 Performance based NEm requirement adjustment for heifers fed during winter months in eastern South Dakota compared to the Texas panhandle

Abstract Crossbred beef heifers [n = 96; initial shrunk BW=238 kg (SD 21.5)] were used in a completely randomized design to evaluate climatic effects on feedlot heifer growth and efficiency. The study was conducted from November 8, 1991 to May 11, 1992. Heifers were assembled into groups at the Ruminant Nutrition Center (RNC) in Brookings, SD. One group (TX; n = 48) was shipped to New Deal, Texas and fed on slatted-concrete floors, and the second group (SD; n = 48), was shipped half-way to Texas, returned to the RNC, and fed on solid-concrete floors. Transit distance was 1,530 km. Pen was the experimental unit (6 to 8 head·pen-1); diets, health management, and implant programs were normalized across locations. The finishing diet was fed from d 33 to 185 at both locations and the energetics assessment was for the period from d 60 to 185. There were 18 d below -7.8°C and 102 d below 5°C in SD. Transit shrink, estimated empty body fat % (EBF), BW adjusted to 28% EBF (AFBW), and DMI did not differ (P ≥ 0.10). Heifer ADG was 18% greater (P < 0.05) in TX (1.40 vs. 1.16 ± 0.037 kg). Observed vs. predicted dietary energy differed (P ≤ 0.05), for NEm (0.97 vs. 0.87 ± 0.013) and NEg (0.97 vs. 0.84 ± 0.016) for TX and SD, respectively. Using calculated diet energy values based upon TX heifer performance as a reference, relative adjustments to metabolic rate were calculated. The estimated metabolic rate was elevated (P < 0.05) for SD heifers (0.077 vs. 0.101 ± 0.0031 Mcal/MBS). These results indicate that heifers fed in South Dakota had a 31% increase in metabolic rate when compared to heifers fed in the Texas panhandle. More of these types of assessments are needed to improve projection and tracking models used in precision cattle feeding.

Estimation of the net energy value of barley for finishing beef steers1

The objective of this study was to identify barley grain characteristics measured by laboratory procedures that could be used to predict barley energy content for finishing beef steers. Twenty-eight different barley genotypes were evaluated including 18 cultivars and 10 experimental lines. Laboratory analysis of barley samples included bulk density, particle size, N, ADF, starch, and ISDMD (in situ DM disappearance after 3 h of ruminal incubation). Animal performance data (BW, DMI, ADG, steer NEm, and NEg requirements) were collected from 26 feedlot experiments conducted in Montana and Idaho during a 10-yr period and were used to estimate barley NEm and NEg content. A total of 80 experimental units were available with each experimental unit being a diet mean from an individual feedlot experiment. Fifty-eight of the 80 experimental units were randomly selected and used in the development data set and the remaining 22 experimental units were used in the validation data set. Forward, backward, and stepwise selection methods were used to identify variables to be included in regression equations for NEm using PROC REG of SAS. Barley samples in the model development data set represented a wide range in concentrations (DM basis): N (1.6% to 2.8%), ISDMD (25.7% to 58.7%), ADF (3.6% to 8.0%), starch (44.1% to 62.4%), particle size (1,100 to 2,814 µm), and bulk density (50.8 to 69.4 kg/hL). The barley grain characteristics of particle size, ISDMD, starch, and ADF were the most important variables in six successful models (R 2 = 0.48 to 0.60; P = 0.001). The six prediction equations gave mean predicted values for NEm ranging from 1.99 to 2.05 Mcal/kg (average 2.04 Mcal/kg; 0.45% CV). The mean actual NEm values from animal performance trials ranged from 1.75 to 2.48 Mcal/kg (average 2.03 Mcal/kg; 6.5% CV). The mean bias or difference in predicted vs. actual values ranged from -0.001 to 0.005 Mcal/kg. Barley NEg values calculated from animal performance ranged from 1.13 to 1.78 Mcal/kg (average 1.39 Mcal/kg; 8.4% CV). Average predicted barley NEm and NEg were 0.02 and 0.01 Mcal/kg less, respectively, than the 2.06 Mcal/kg NEm and 1.40 Mcal/kg NEg reported by NRC. Barley NE can be predicted from simple laboratory procedures which will aid plant breeders developing new feed varieties and nutritionists formulating finishing rations for beef cattle.

Meta-analysis of the energy and protein requirements of hair sheep raised in the tropical region of Brazil.

The objective of this study was to estimate, through mathematical models, energy and protein requirements for maintenance and gain of hair sheep raised in the tropical region of Brazil. To determine the equation parameters, a meta-analysis of seven independent experiments of nutrient requirements was performed, comprising a total of 243 experimental units (animals), which were conducted under tropical conditions, using hair sheep in growing and finishing phases and endowed of the following quantitative data for each animal: body weight (BW), empty body weight (EBW), average daily gain (ADG), empty body gain (EBG), heat production (HP), metabolizable energy intake (MEI), retained energy (RE), metabolizable protein intake (MPI) and body protein content. The regression equations generated were as follows: for Net Energy for maintenance, (NEm ):LogHP(MJEBW-0.75day-1)=-0.6090(±0.07470)+0.5149(±0.07216)×MEI(MJEBW-0.75day-1); for NetEnergy for gain, (NEg ): LogRE(MJEBW-0.75day-1)=0.03084(±0.05334)+0.8455(±0.04355)×LogEBG(kg/day); for Metabolizable Protein for maintenance,(MPm ): MPI(g/day) =24.8470 (±7.3646)+560.28 (±99.6582)×EBG(kg/day) ; for Net Protein for gain, (NPg ): NPg(kg/day)=0.1941×EBW(kg)-0.1058. The NEm requirement was 0.246MJEBW-0.75 day-1 . The metabolizable energy for maintenance requirement was 0.391MJEBW-0.75 day-1 . Considering an ADG of 100g, the NEg requirement ranged from 0.496 to 1.701MJ/day for animals with BW ranging from 10 to 40kg respectively. The efficiencies of use of the metabolizable energy for maintenance and gain were 0.63 and 0.36 respectively. The MPm requirement was 3.097gEBW-0.75 day-1 . Considering an ADG of 100g, the NPg requirement ranged from 12.4 to 10.5g/day for animals with BW ranging from 10 to 40kg respectively. The total metabolizable energy and protein requirements were lower than those reported by the NRC and AFRC systems. Thus, our results support the hypothesis that nutrient requirements of hair sheep raised in tropical regions differ from wool sheep raised in temperate regions. Therefore, the use of the equations designed in this study is recommended.

Evaluation of production efficiencies among primiparous suckler cows of diverse genetic index at pasture

This study aimed to determine estimates of production efficiency among primiparous suckler cows of diverse genetic merit (GM) for the national Irish maternal index. Data from 82 heifers of diverse GM across two different replacement strategies (suckler (S) or dairy (D) sourced) were available. Milk yield, grass dry matter intake, cow BW and body condition score (BCS) were recorded. The maternal index had no significant effect on any parameters investigated, whereas S cows were 86 kg heavier in BW, had a 0.33 greater BCS and 0.6 UFL greater NEM requirement compared with D beef crossbred (F1) cows. The F1 produced 2.2 kg/day more milk and had greater lactation energy requirements (0.8 UFL) than S. The F1 produced 0.48 kg milk per 100 kg BW and 0.15 kg more milk per unit intake. An interaction between GM and cow origin (CO) showed that F1 low merit cows consumed an additional 1 kg DM than F1 high, and that S high merit cows produced 1.5 kg less milk than their S low counterparts resulting in a 0.5 UFL greater energy requirement for milk production for S low. The F1 high merit cows produced 0.12 kg more milk per unit intake than F1 low cows, whereas S low cows produced 0.12 kg less milk per unit intake than S high. The F1 low cows consumed 0.17 kg more DM per unit BW than F1 high. Thus, genetic selection for maternal traits has not resulted in differences in production efficiency traits, however CO differences were observed.

Short-term energy restriction during late gestation of beef cows decreases postweaning calf humoral immune response to vaccination.

Our objectives were to evaluate the pre- and postweaning growth and measurements of innate and humoral immune response of beef calves born to cows fed 70 or 100% of NEm requirements during the last 40 d of gestation. On d 0 (approximately 40 d before calving), 30 multiparous Angus cows pregnant to embryo transfer (BW = 631 ± 15 kg; age = 5.2 ± 0.98 yr; BCS = 6.3 ± 0.12) were randomly allocated into 1 of 10 drylot pens (3 cows/pen). Treatments were randomly assigned to pens (5 pens/treatment) and consisted of cows limit-fed (d 0 to calving) isonitrogenous, total-mixed diets formulated to provide 100 (CTRL) or 70% (REST) of daily NEm requirements of a 630-kg beef cow at 8 mo of gestation. Immediately after calving, all cow-calf pairs were combined into a single management group and rotationally grazed on tall fescue pastures (6 pastures; 22 ha/pasture) until weaning (d 266). All calves were assigned to a 40-d preconditioning period in a drylot from d 266 to 306 and vaccinated against infectious bovine rhinotracheitis, bovine viral diarrhea virus (BVDV), , and spp. on d 273 and 287. Blood samples from jugular vein were collected from cows on d 0, 17, and 35 and from calves within 12 h of birth and on d 266, 273, 274, 276, 279, and 287. By design, REST cows consumed less ( ≤ 0.002) total DMI, TDN, and NEm but had similar CP intake ( = 0.67), which tended ( = 0.06) to increase BW loss from d 0 to calving, than CTRL cows (-1.09 vs. -0.70 ± 0.14 kg/d, respectively). However, gestational NEm intake did not affect ( ≥ 0.30) plasma concentrations of cortisol, insulin, and glucose during gestation and BCS at calving as well as postcalving pregnancy rate, BW, and BCS change of cows. Calf serum IgG concentrations and plasma concentrations of haptoglobin and cortisol at birth as well as calf pre- and postweaning BW and ADG did not differ ( ≥ 0.15) between calves born to REST and CTRL cows. However, calf postweaning overall plasma concentrations of cortisol; plasma haptoglobin concentrations on d 274, 276, and 279; and serum BVDV-1a titers on d 306 were less for REST calves than for CTRL calves ( ≤ 0.05). Hence, a NEm restriction to 70% of daily requirements during the last 40 d of gestation had minimal effects on cow precalving growth and did not affect postcalving cow growth and reproductive performance. However, it decreased postweaning vaccination-induced humoral immunity, inflammatory, and physiological stress responses of calves.

Intake, apparent digestibility, and nutrient requirements for growing Nellore heifers and steers fed two levels of calcium and phosphorus

Nutrient apparent digestibility, intake, performance, microbial efficiency, and energy and protein requirements for growing Nellore heifers and steers were evaluated, fifty animals were used, 32 Nellore heifers and 18 Nellore steers. Four animals of each gender used as baseline reference animals were slaughtered at the beginning of the experiment. Four animals from each gender were fed at MAIN receiving 11g/kgBW, whereas 10 steers and 24 heifers were assigned to the ADLIB group. The ADLIB heifers were divided further into 4 groups according to the dietary treatment: (1) Ca and P fed at their proposed requirements (CaPR) with a 50:50 roughage:concentrate (R:C) diet, (2) CaPR with a 70:30 R:C diet, (3) 43% of their proposed requirements for Ca and 80% of their requirements for P (CaPL) with a 50:50 R:C diet, and (4) CaPL with a 70:30 R:C diet. The ADLIB and MAIN steers were fed CaPR with a 50:50 R:C diet. Half of the ADLIB steers and heifers were slaughtered at day 50; the other ADLIB animals were slaughtered after 100 days of the feeding period, whereas all MAIN animals were slaughtered at day 100. Total feces and urine were collected from all animals for 72h prior to slaughter. After slaughter, EBW was measured. The NEm and MEm requirements were estimated by exponentially relating heat production with metabolizable energy intake; NEg was estimated from EBW and EBG. The NPg was estimated from EBG and RE. Dry matter digestibility and the apparent absorption and retention of Ca and P were similar across Ca and P treatments. Final body weight, and consequently ADG, was greater (P<0.05) for heifers receiving the high concentrate compared to the low concentrate diet, but dietary Ca and P concentration did not affect (P>0.05) performance. The NEm and MEm requirements were 294 and 496kJ/kgEBW0.75, respectively. Net protein for maintenance was 1.28g/kgBW0.75 and NEg and NPg were estimated from the following equations: NEg=0.222×EBW0.75×EBG0.6263 and NPg=137.53×EBG−0.038×RE, respectively. Under the conditions of this experiment, reducing the dietary concentrations of Ca and P had no significant impact on intake, digestibility, or performance of growing Nellore heifers and steers.

Energy requirements of Dorper crossbred ewe lambs1

The ME and NE requirements of Dorper crossbred ewe lambs grown from 35 to 50 kg BW were assessed in a comparative slaughter trial. Thirty-five ewe lambs (33.5 ± 0.6 kg BW) of F1 crosses of purebred Dorper and thin-tailed Han sheep were used: 7 lambs were slaughtered at the start of the trial to provide baseline measures of body composition and 7 lambs were fed ad libitum and slaughtered when they reached 43 kg BW to provide intermediate measures of body composition. The remaining 21 lambs were divided into 3 groups of 7 lambs each and fed a pelleted mixed diet (concentrate:roughage = 44:56, DM basis) for ad libitum intake or 65 or 45% of ad libitum intake. All 3 groups were slaughtered when the ad libitum group reached 50 kg BW. Total body energy, N, fat, ash, and moisture content were measured. In a separate trial, 15 ewe lambs (39.5 ± 0.7 kg BW) of F1 crosses of purebred Dorper and thin-tailed Han sheep were housed in metabolism cages to evaluate the ME value of the diet at each of the 3 levels of feed intake. In vivo methane production was measured by open-circuit respirometry along with the collection of all feces and urine. The daily NEm requirement of the ewe lambs was 280 kJ/kg metabolic BW (BW(0.75)) or 292 kJ/kg metabolic shrunk BW (SBW(0.75)), whereas the daily ME requirement for maintenance was 418 kJ/kg BW(0.75) or 437 kJ/kg SBW(0.75), with a partial efficiency of ME utilization for maintenance of 0.67. The NEg requirement ranged from 1.37 to 3.94 MJ/d for ADG from 100 to 250 g BW, and the partial efficiency of ME utilization for gain was 0.44. The NE and ME requirements of Dorper × thin-tailed Han crossbred ewe lambs were lower than the recommendations of the United States' nutritional system.

BEEF SPECIES SYMPOSIUM: Potential limitations of NRC in predicting energetic requirements of beef females within western U.S. grazing systems1,2

Assessment of beef cow energy balance and efficiency in grazing-extensive rangelands has occurred on a nominal basis over short time intervals and has not accounted for the complexity of metabolic and digestive responses; behavioral adaptations to climatic, terrain, and vegetation variables; and documentation of the effects of nutrient form and supply to grazing cattle. Previous research using pen-fed cows demonstrated differences (P < 0.01) in efficiency of weight change ranging from 135 to 58 g/Mcal ME intake. Furthermore, variation in efficiency of ME use for tissue energy gain or loss ranged from 36% to 80%. In general, energy costs for maintenance, tissue accretion, and mobilization were greatest in Angus-based cows, intermediate in Brahman- and Hereford-based cows, and least in dairy-based cows. The most efficient cattle may reflect the types that are successful in semiarid grazing environments with low input management. Successful range cattle systems are likely the result of retention of animals that best adapted to the grazing environment and thus were potentially more efficient. Animals exposed to a variety of stressors may continually adapt, so energy expenditure is reduced and may tend to depart from the modeled beef cow in the 1996 NRC Beef Cattle Requirements. Critical factors comprising cow lifetime achievement, including reproductive success, disease resistance, and calf weaning weight, may be driven by cow total energy utilization in energy-limiting environments. Therefore, energy adjustments for adapted cattle within these landscapes and seasonal BW changes can alter seasonal NEm requirements. Evaluated studies indicate that in static grazing environments, NRC prediction fitness was improved compared with predictions from dynamic systems where cattle were influenced less by management and more by environmental conditions. Preliminary herd analyses cast doubt on the accuracy of NRC BCS descriptions representing NEm requirements of adapted females utilizing semiarid rangelands. Possible gaps are proposed that could be the basis for prediction inaccuracies. A more complete understanding of mechanisms contributing to productivity in the field than the current model predicts will improve future models to better simulate energetic accountability and subsequent female performance.

Influence of monensin and lauric acid distillate or palm oil on in vitro fermentation kinetics and metabolites produced using forage and high concentrate substrates

Two in vitro experiments were conducted to evaluate the interactions of monensin with lauric acid distillate (LAD) or palm oil (PO) in forage and concentrate diets on 24h in vitro rumen fermentation characteristics. Two Holstein steers, each surgically fitted with a ruminal cannula, consuming 0.50 alfalfa cubes and 0.50 cracked corn-based concentrate at 1.75×NEm requirements were used as rumen fluid donors. For both experiments in vitro gas production was measured in a completely random design with a 3×2×3 factorial treatment structure. Factors were diet [control (no substrate), forage (alfalfa), and high concentrate (corn)], 3μg/ml of monensin (±), and LAD (0, .05 and 0.10 of the substrate, Exp. 1) or PO (0, .05 and 0.10 of the substrate, Exp. 2). Gas production was affected by diet (P<0.001), and decreased (P<0.001) for monensin addition in both experiments. Gas production had a diet×monensin interaction (P<0.01). Lauric acid distillate and PO addition did not influence gas production. Degradation rate also responded with a diet×monensin interaction (P<0.01) and lag time had only a diet effect (P=0.001) in both in vitro experiments. Both the degradation rate and lag time were not affected by a monensin×fat (LAD or PO) interaction. Monensin addition reduced total volatile fatty acid concentration across all 3 substrates (control, alfalfa and high concentrate). Monensin addition decreased acetate:propionate (P<0.001) and increased the propionate proportion (P<0.001). Butyrate proportion had a diet×monensin interaction (P<0.01) as butyrate proportion was increased with monensin for the alfalfa but decreased for the concentrate substrate. Ammonia concentration was reduced (P<0.01) by monensin on all substrates and was slightly higher (P<0.01) for the alfalfa substrate compared with control and concentrate. Lauric acid distillate or PO addition did not influence fermentation metabolites in the present study. In addition, a monensin by LAD or PO interaction was not observed for the metabolites. Methane production and the methane proportion to total gas production had a diet×monensin interaction (P<0.01). The methane proportion was decreased quadratically (P=0.028) with LAD addition, whereas PO addition linearly increased (P=0.014) the methane proportion; both of these effects were small. Meanwhile, monensin by LAD or PO interactions were not observed for methane concentration and proportion. In conclusion, the combinations of monensin and LAD or PO in forage and high concentrate diets had no interactions on in vitro fermentation kinetics and end product production.

Eating a high fiber diet during pregnancy increases intake and digestibility of a high fiber diet by offspring in cattle

Experiences early in life influence preferences for the forages which animals eat as adults, but little is known about how such experiences affect forage intake and digestibility. We hypothesized that experience with high fiber (HF) diets in utero enables cattle to better utilize HF diets by enhancing intake and digestibility of HF diets. We exposed cows to either HF or low fiber (LF) diets from October 20 until parturition on March 15. The HF diet was primarily ammoniated wheat straw (AWS), while the LF diet was mainly grass hay (700g/kg orchardgrass and 300g/kg meadow bromegrass). The two diets were iso-net energy (NEm), isonitrogenous, and similar in mineral and vitamin contents, but they varied 10-fold in neutral detergent soluble carbohydrates. Following weaning, the 8mo old calves from mothers fed HF or LF diets during pregnancy were fed AWS and a high fiber supplement, and dry matter (DM) intake and digestibility were measured during the last half of a 40d experiment (i.e., 26d adaptation, 14d measured DM intake, 5d measured DM digestibility). Intake (5.6 versus 5.3kg/d; P=0.04) and digestibility (545 versus 523g/kg; P=0.03) of AWS were higher for calves fed HF than for those fed LF diets. As a result, digestible DM intake of AWS was higher for HF than LF (3.1 versus 2.8kg/d; P<0.01). Calves fed HF diets ate more straw as a proportion of their diet than did calves fed LF (733 versus 723g/kg; P=0.05). Total digestible DM intake (i.e., AWS+supplement) was higher for calves fed HF than LF diets (4.7 versus 4.4kg/d; P<0.01), as was total diet DM digestibility (613 versus 600g/kg; P=0.07). Calves were weighed at the conclusion of the DM intake and digestibility measurement periods, and then fed an AWS/processed wheat middlings diet for an addition 28d to determine daily gain. Collectively, increases in intake and digestibility affected body weight gains such that HF diet fed calves numerically gained more than LF fed calves even during this short period (0.45 versus 0.41kg/d; P=0.13). Higher DDM intake is likely important for pregnant cows and their offspring which winter for many months under extensive range conditions on dormant forages where their NEm requirements are marginally satisfied. These effects on offspring, further magnified by experiences with their mothers early in life, make cows and their progeny better adapted to using dormant forages during winter.

Effect of dietary corn silage inclusion on visceral organ mass, cellularity, and the protein expression of ATP synthase, Na+/K+-ATPase, proliferating cell nuclear antigen and ubiquitin in feedlot steers

Twenty-four steers (initial body weight = 535 ± 5.0 kg) predominately of Angus breeding were used to determine the effect of dietary corn silage inclusion [20, 40, 60, or 80% of dry matter (DM)] on visceral mass, cellularity, and the protein expression of ATP synthase, Na+/K+-ATPase, proliferating cell nuclear antigen (PCNA) and ubiquitin. Steers were fed at similar energy levels (2.1 × NEm requirement). There were no significant treatment effects on specific visceral organ weights. Hepatic Na+/K+-ATPase expression linearly increased (P = 0.01) and ruminal Na+/K+-ATPase expression linearly decreased (P = 0.01) with increasing corn silage inclusion. Hepatic PCNA expression was quadratically affected (P = 0.05) with a decrease when corn silage inclusion increased from 20 to 60%, and an increase when corn silage inclusion increased from 60 to 80%. Renal ATP synthase (P = 0.02) and ubiquitin expression (P = 0.01) were quadratically affected in a similar pattern with an increase when corn silage inclusion increased from 20 to 60%, and a decrease when corn silage inclusion increased from 60 to 80%. These results indicate that different dietary corn silage inclusions, at similar dietary energy intake, may alter rumen, liver, and kidney energy expenditure, at least in part, through changes in specific metabolism rather than mass. Key words: Corn silage inclusion, visceral organ mass, cellular energy metabolism, steer

Expression of system N protein mRNA, but not system A or L, is upregulated by ileal epithelia of growing beef cattle in response to increased luminal supply of energy but not amino acids

To complete our in vivo study of how basal expression profiles of 20 amino acid (AA) transporter genes respond to increases in luminal supply of substrates or energy in the small intestine, total RNA was extracted from duodenal (D), jejunal (J), and ileal (I) epithelia of 18 ruminally and abomasally catheterized Angus steers (BW ? 260 kg) fed an alfalfa‐cube based diet at 1.3× NEm requirement and infused for 14 to 16 d with either (n = 6) water (basal) or corn starch hydrolysate (20% ME intake) into rumen (increased microbial AA) or abomasum (increased glucose/energy). The effect of infusion treatments on expression of mRNA encoding systems A (ATA1, 2, 3), N (SN1, 2), and L (LAT1, 2) neutral AA transporters was evaluated by real‐time RT‐PCR methodoloy. Basal expression of all mRNA but ATA3 differed (P = 0.06) among D, J, and I: ATA1, D=J&gt;I; ATA2, D=J, D=I, J&gt;I; SN1, D&gt;J=I; SN2, J&gt;D=I; LAT1, D=J&gt;I; LAT2, D=J, J=I, D&lt;I. Increased luminal AA or energy supply did not affect (P &gt; 0.15) the mRNA content of these neutral AA transporters except that expression of SN1 and SN2 mRNA by I was increased (P = 0.08) 57 and 51%, respectively, with increased luminal energy supply. This latter finding suggests that luminal energy supply may limit I expression of SN1 and SN2 mRNA. This study was funded by a USDA‐ARS Special Cooperative Agreement Grant.

Pancreatic mass, cellularity, and α-amylase and trypsin activity in feedlot steers fed diets with increasing corn silage inclusion

Twenty-four yearling beef steers (initial BW = 535 ± 5.0 kg), predominately of Angus breeding, were used in a randomized complete block design to determine the effect of dietary inclusion of corn silage on pancreatic cellularity, mass, and α-amylase and trypsin activity. Using calan gates, steers were individually fed diets containing 20, 40, 60, or 80% corn silage (DM basis) with the rest of the diet made up of concentrate. Diets were formulated to maintain a constant CP:ME (g Mcal-1) and were fed at 2.1 × NEm requirement. After 28 d on treatment, the two heaviest steers from each treatment were slaughtered per week and pancreata collected. Pancreatic weight (g and g kg-1 BW) and content (kU and U kg-1 BW) of α-amylase activity did not differ among dietary treatments. Concentration (U g-1) of pancreatic α-amylase decreased (P = 0.03) with increasing corn silage inclusion. Pancreatic DNA and RNA content (g and mg kg-1 BW) increased linearly (P ≤ 0.04) with increasing corn silage inclusion. The content of pancreatic trypsin activity responded cubically (P = 0.03). These data indicate that increasing corn silage inclusion does not influence total pancreatic α-amylase activity and that cell number may influence pancreatic α-amylase concentration. Key words: Beef cattle, pancreas, α-amylase, trypsin, forage, concentrate

Basal Expression of Nucleoside Transporter mRNA Differs Among Small Intestinal Epithelia of Beef Steers and Is Differentially Altered by Ruminal or Abomasal Infusion of Starch Hydrolysate1,2

In ruminants, microbial-derived nucleic acids are a major source of N and are absorbed as nucleosides by small intestinal epithelia. Although the biochemical activities of 2 nucleoside transport systems have been described for cattle, little is known regarding the regulation of their gene expression. This study was conducted to test 2 hypotheses: (1) the small intestinal epithelia of beef cattle differentially express mRNA for 3 concentrative (CNT1, 2, 3) and 2 equilibrative (ENT1, 2) nucleoside transporters (NT), and (2) expression of these NT is responsive to small intestine luminal supply of rumen-derived microbes (hence, nucleosides), energy (cornstarch hydrolysate, SH), or both. Eighteen ruminally and abomasally catheterized Angus steers (260±17kg of BW) were fed an alfalfa cube-based diet at 1.33× NEm requirement. Six steers in each of 3 periods were blocked by BW (heavy vs. light). Within each block, 3 steers were randomly assigned to 3 treatments (n=6): ruminal and abomasal water infusion (control), ruminal SH infusion/abomasal water infusion, or ruminal water infusion/abomasal SH infusion. The dosage of SH infusion amounted to 20% of ME intake. After a 14-or 16-d infusion period, steers were slaughtered, and duodenal, jejunal, and ileal epithelia were harvested for total RNA extraction and the relative amounts of mRNA expressed were determined using real-time RT-PCR quantification methodologies. All 5 NT mRNA were found expressed by each epithelium, but their abundance differed among epithelia. Specifically, jejunal expression of all 5 NT mRNA was higher than that by the ileum, whereas jejunal expression of CNT1, CNT3, and ENT1 mRNA was higher, or tended to be higher, than duodenal expression. Duodenal expression of CNT2, CNT3, and ENT2 mRNA was higher than ileal expression. With regard to SH infusion treatments, ruminal infusion increased duodenal expression of CNT3 (67%), ENT1 (51%), and ENT2 (39%) mRNA and ileal expression of CNT3 (210%) and ENT2 (65%) mRNA. Abomasal infusion increased (54%) ileal expression of ENT2 mRNA and tended to increase (50%) jejunal ENT2 mRNA expression. This study has uniquely characterized the pattern of NT mRNA expression by growing beef cattle and found that the mRNA abundance for CNT3, ENT1, and ENT2 in small intestinal epithelia can be increased by increasing the luminal supply of nucleotides (CNT3, ENT1, ENT2) or glucose (ENT2).

Exigência de energia de mantença e composição corporal e do ganho de vacas de corte adultas de três grupos genéticos confinadas

Neste trabalho, foram estimadas as exigências de mantença de energia líquida (ELm) e metabolizável (EMm) e as mudanças na composição corporal e no ganho de vacas adultas não-gestantes e não-lactantes confinadas. Foram utilizadas 36 vacas, 12 Nelore (NEL), 12 F1 Pardo-Suíço-Nelore (PSN) e 12 F1 Red Angus-Nelore (RAN). As alterações na composição corporal dos animais durante o período experimental foram estimadas utilizando-se a técnica do abate comparativo: quatro animais de cada grupo genético foram alocados, aleatoriamente, nos tratamentos abate inicial (AI), alimentação restrita (AR) e alimentação ad libitum (AL). Os animais AR receberam, no período experimental, níveis de proteína e energia 15% acima da mantença e os AL, ração ad libitum, para ganho de 1,1 kg/dia. Os animais AI foram abatidos no início do experimento e os AR e AL 120 dias depois. Em todos os animais abatidos, foram estimadas as proporções corporais dos tecidos muscular, adiposo e ósseo, além dos conteúdos corporais de proteína, gordura e energia. Na estimação da ELm e da EMm, foram empregados modelos linear e não-linear. Os grupos genéticos não diferiram quanto às exigências de ELm e EMm, expressas em peso vivo em jejum (kcal/kg0,75/dia PVJ). Quando utilizados os modelos linear e não-linear, os valores de ELm encontrados foram de 80,7 e 83,6 kcal/kg0,75/dia PVJ e os de EMm, 109,9 e 128,0 kcal/kg0,75/dia PVJ, respectivamente. Os conteúdos de proteína por unidade de peso corpo vazio (PCVZ) e do ganho (GPCVZ) não diferiram entre os grupos genéticos, porém, os animais NEL apresentaram maior concentração de gordura e energia por kg PCVZ e GPVCZ para mesmo peso vivo.

Effect of nutrient restriction on calpain and calpastatin content of skeletal muscle from cows and fetuses.

Calpains are crucial for the degradation of myofibrillar proteins in muscle. Calpastatin is a specific inhibitor of calpains. The objective of this study was to elucidate the effect of nutrient restriction on the activity of calpains and calpastatin in the skeletal muscle of both cows and fetuses. Beginning 30 d after conception, 20 cows were fed either a control diet consisting of native grass hay fortified with vitamins and minerals at recommendations for a mature cow to gain 0.72 kg/d or half the vitamins and minerals and millet straw at 68.1% of NEm requirements. Cows were slaughtered on d 125 of gestation, and the LM was sampled at the 12th rib for calpain and calpastatin measurement. When comparing the muscle samples from nutrient-restricted and control cows, no difference in the activity of calpain I and II was observed; however, there was a significant difference (P < 0.05) in calpastatin activity. Muscle samples from control cows had greater calpastatin content than those of nutrient-restricted cows (P < 0.05); in contrast, the calpastatin content of fetal muscle was greater in fetuses gestated by nutrient-restricted cows than those of control cows (P < 0.05). Further, there were three calpastatin isoforms of 125, 110, and 70 kD detected in fetal muscle, whereas only the110-kD isoform was detected for cow muscle. These results indicate that the activity of the calpain system in skeletal muscle is mainly controlled through the expression of calpastatin. Alternating the calpastatin content in muscle and thereby modulating calpain activity may provide a mechanism for the maintenance of fetal muscle growth during nutrient restriction, whereas skeletal muscle loss in cows is upregulated.