Forage Dry Matter Intake Research Articles

Effect of Supplementation Plans and Frequency on Performance and Metabolic Responses of Grazing Pregnant Beef Heifers

Our objective was to evaluate the effects of protein supplementation frequency and supplementation plans during gestation on productive performance and metabolic responses of grazing super-precocious Nellore heifers. Thirty-five pregnant Nellore heifers were used in a completely randomized design in a 2 × 2 factorial arrangement with an additional control group. The factors were the following: 1. Frequency of supplementation: (a) Daily (seven times per week), (b) Infrequent (three times per week); 2. Supplementation plans: (a) Constant, (b) Increasing. A control group with no supplementation was included. Two digestibility trials were carried out on the 40th and 130th experimental days. Productive performance and body composition were evaluated in the prepartum and postpartum periods. Blood samples were collected at −114, −113, −15, −14, +15, +30, and +45 days relative to calving for measuring metabolic status. Supplementation (daily and infrequent) increased the intake of total dry matter (DM) (p ≤ 0.004), average daily gain (p < 0.001), and body weight at calving (p = 0.008) at prepartum. However, frequency or supplementation plan did not alter (p > 0.17) the intake of total DM and forage DM. There was an effect (p ≤ 0.02) of the supplementation plan on subcutaneous thickness fat in the prepartum period and albumin and non-esterified fatty acid concentrations (p < 0.004) in the postpartum period. Nonetheless, frequency and supplementation plans did not affect (p ≥ 0.10) heifers’ productive performance during the postpartum period. In conclusion, protein supplementation frequency and supplementation plan during beef heifers’ gestation do not negatively impact their productive performance or metabolic responses.

96 Using greenhouse gas flux to estimate forage dry matter intake in ad libitum fed replacement heifers

Abstract An accurate estimate of feed intake is a critical component in determining individual animal feed efficiency. However, existing feed intake measurement systems are not designed for unprocessed, dry forage diets. Open-circuit gas flux technology measures enteric gas emissions for cattle in a pasture-based setting. If a significant relationship exists between feed intake and gas emissions, this system could be used to rank grazing cattle for forage intake and forage utilization efficiency. Our objective was to develop prediction equations to estimate forage dry matter intake using gas flux and performance data. Angus and Angus x Hereford heifers [n = 71; initial body weight (BW) 329.5 ± 31.1 kg] were used over 3 yr to measure intake, gain, and gas flux. All heifers were subject to a 21-d adaptation and 71-d intake test using individual intake technology (SmartFeed; C-Lock Rapid City, SD) with a stocking rate of 3.3 heifers per feeder. Throughout the study, heifers were fed a long-stem, unprocessed, grass hay diet (≥ 10.8% CP, 2.0 Mcal ME, and 56% TDN) with ad libitum access to a salt/mineral supplement. The GreenFeed system (C-Lock Rapid City, SD) was used to monitor oxygen (O2) consumption (means ± SD; 3364.4 ± 374.8 g/d), methane (CH4; 181.4 ± 24.3 g/d) and carbon dioxide (CO2) production (4,965.3 ± 494.5 g/d). Body weights were collected every 14 d, and average daily gain (ADG) was calculated by regressing BW on day of study. The phenotypic correlations of forage DMI with CO2, CH4, O2, and heat production (HP) were 0.72, 0.66, 0.74, and 0.74, respectively. Average daily gain and midpoint metabolic BW combined with the estimate of daily HP, O2, or CO2 accounted for 60% of the variation in forage DMI. These results suggest that forage intake can be predicted using performance data in conjunction with the GreenFeed gas quantification system.

195 Effect of selection for growth and maternal influence on crossbred Angus heifer development

Abstract This multiyear experiment was designed to determine the effects of sire yearling weight (YW) and maternal influence (MILK) expected progeny differences (EPD) on production and fertility of beef replacement heifers. Sires were classified as moderate (< 50th percentile) or high for YW EPD (122 ± 29; from 79 to 172) and as low (< 50th percentile) or high for MILK EPD (27 ± 8; from 5 to 40). Fall-born (n = 214) and spring-born (n = 207) heifers were enrolled in the study. Birth weight (BW), weaning weight (WW), and YW of the heifers were measured. In addition, reproductive tract score (RTS), dry matter intake (DMI), and average daily gain (ADG) while consuming an unprocessed grass hay diet were determined in a subsample of enrolled heifers. Neogen Igenity Beef scores (NIBS) were also run on this subset. Pregnancy rate and conception rate at fixed timed artificial insemination (FTAI) were also determined. Adjusted BW, WW and YW and RTS were analyzed using the GLIMMIX procedure of SAS (9.4, SAS Institute Inc., Cary, NC), with YW and MILK EPD as fixed effects and year of birth as random effect. Effects of sire YW and MILK classification on the likelihood of pregnancy and successful FTAI were also analyzed using the GLIMMIX procedure of SAS. Pearson correlation coefficients between independent and dependent variables were obtained using the CORR procedure of SAS. Sire MILK EPD had no effect (P ≥ 0.13) on the body weight of fall- or spring-born heifers. However, fall-born heifers were 0.12 kg and 0.34 kg heavier (P = 0.06 and 0.001, respectively) per unit increase in sire YW EPD at weaning and yearling time, respectively. There was no effect of sire YW EPD on fall-born heifer DMI as percentage of body weight (DMI % BOW; P = 0.74) nor ADG (P = 0.90) while consuming the low-energy diet. Spring-born heifers had significantly greater (all, P ≤ 0.001) adjusted BW, WW, and YW (0.02, 0.23 and 0.37 kg per unit increase in sire YW EPD, respectively. Reproductive tract score was strong and negatively correlated (P ≤ 0.001) with DMI % BOW. Heifer YW NIBS were moderate and positively correlated (P < 0.001) with ADG. There was a tendency (P = 0.09) for a weak and negative correlation between residual feed intake genetic scores and DMI % BOW. Sire genetic merit for yearling growth was transmitted to replacement heifers. However, neither ADG, nor unprocessed forage DMI % BOW was influenced by genetic potential for growth during this study. Further research is needed to assess the benefits of using genomic profile of heifers for maternal, performance and carcass traits, alongside sire EPDs, when selecting and developing beef replacement heifers.

What the hay: predicting equine voluntary forage intake using a meta-analysis approach

To properly formulate diets, the ability to accurately estimate feed intake is critical as the amount of feed consumed will influence the amount of nutrients delivered to the animal. Inaccurate intake estimates may lead to under- or over-feeding of nutrients to the animal. Individual differences in equine forage intake are well-known, but predictive equations based on animal and nutritional factors are not comprehensive. The objective of the present study was to consolidate the current body of knowledge in the published literature on voluntary forage DM intake (VFDMI) in equines and conduct a meta-analysis to identify driving factors, sources of heterogeneity, and develop predictive equations. Therefore, a systematic literature search was applied and identified 61 publications which met the inclusion criteria. From each study, the outcomes of interest (e.g., forage intake), diet composition (e.g., forage information, nutrient composition), and animal factors (e.g., sex, age, breed, BW, exercise level) were extracted. Forage intake was analyzed as two different outcome variables: (1) VFDMI in kg/d and (2) VFDMI in g/kg BW. Linear mixed model analysis treating study as a random effect was applied, using a backward−stepping approach to identifying potential driving variables for VFDMI (both units) where all terms have P < 0.1. The best fitting models for VFDMI included similar factors (also across kg/d and g/kg BW) such as forage quality (i.e., neutral detergent fiber or CP content), forage type (i.e., grass, legume, or mixed), the animals’ size category (i.e., horses vs ponies), and some management factors (i.e., pasture access). As anticipated, forage intake increased when higher quality forages were fed (i.e., lower neutral detergent fiber or higher CP), potentially due to improved digestibility. Additionally, VFDMI increased as BW increased but ponies increased their VFDMI more per every kg increase in BW compared to horses. Lastly, pasture access (i.e., grazing) may influence VFDMI such that pastured animals consume less than stalled animals, possibly due to the time it takes to graze forage. In conclusion, equations to predict equine VFDMI with high accuracy and precision (concordance correlation coefficient = 0.82 – 0.95; root mean squared error RMSE = 0.82–5.49) were developed which could be applied in practice by equine nutritionists or owners and managers. The results of this meta-analysis confirm that animal traits and forage quality have a significant impact on the VFDMI of equines and should be accounted for when formulating diets to ensure nutritional requirements are met.

The effects of feeding liquid or pelleted formulations of Asparagopsis armata to lactating dairy cows on methane production, dry matter intake, milk production and milk composition

Asparagopsis armata has been reported to have strong antimethanogenic effects when fed to dairy cows. The aim of this study was to evaluate the effect of a liquid and a pelleted formulation of A. armata when fed to lactating dairy cows as a supplemental feed twice daily at milking on i) enteric methane emissions, milk yield and dry matter intake (DMI), and ii) presence of halogenated compounds in milk, urine, faeces, and blood. Forty lactating, multiparous, Holstein-Friesian cows (117 ± 20.2 days in milk) were randomly allocated one of four treatments; 1) CON1: basal diet plus liquid supplement without A. armata, 2) AA1: basal diet plus liquid supplement with A. armata, 3) CON2: basal diet plus pellet supplement without A. armata, and 4) AA2: basal diet plus pellet supplement with A. armata. The liquid and pelleted supplements were offered twice daily for 34 days. Supplements were offered with a grain mix during each milking. The basal diet consisted of vetch hay ad libitum and 6.15 kg dry matter (DM)/d of a grain mix fed as 3.07 kg DM in the dairy per milking. Cows given the AA1 treatment received 298 mg bromoform per day while cows on the AA2 treatment received 293 mg bromoform per day. Individual forage DMI were measured daily via electronic monitoring of individual cows at the feed bins. Methane emissions were measured using the modified sulphur hexafluoride tracer technique on the last 5 days of the experiment. Feeding the A. armata formulations showed no effect on total DMI, forage DMI, concentrate DMI or milk yield. Methane production (g CH4/d), methane yield (g CH4/kg DMI) and methane intensity (g CH4/kg energy corrected milk) were reduced by about 20 % for both the liquid and the pelleted A. armata formulations. Feeding the A. armata formulations led to increased bromoform concentrations in milk (∼2.0 µg/L) but were well below the limit for safe consumption (100 µg/L). It is concluded that both formulations were effective in reducing enteric methane emissions and that milk from cows fed these A. armata formulations is safe for human consumption.

362 The Influence of Supplemental Protein Level on the Intake, Digestion, and Metabolism of Beef Cattle Consuming Low-Quality, High-Fiber Roughages

Abstract Two studies were conducted to evaluate the influence of graded levels of supplemental protein on the intake, digestion, ruminal fermentation, and metabolism of beef cows consuming low-quality forage base diets (6% CP and 74% NDF). For both studies, 15 ruminally cannulated cows (4/5 yrs age, 803 and 757 kg = avg BW for study 1 and 2, respectively) were stratified by BW and, within stratum, randomly assigned to three supplemental treatment groups (n = 5). In study 1, cows were assigned to the following treatments: 1) control, no supplement; 2) 0.25 % BW of a 20% CP supplement; and 3) 0.25 % BW of a 40% supplement. Both supplements were composed of soybean meal and ground corn with the composition adjusted to hit the target CP level. In study 2, cows were assigned to the following alfalfa pellet supplement treatments: 1) control, no supplement; 2) 0.20 % BW of alfalfa pellets, and 3) 0.40 % BW of alfalfa pellets. In study 1, forage intake, DM fill, liquid fill and total tract digestibility were not influenced by supplemental treatment (P ≥ 0.49). However, total DM intake increased linearly (P = 0.02) with increasing supplemental protein, with the 40% CP supplemented cows consuming 39% more DM than control cows. No treatment differences (P ≥ 0.97) were observed for heart rate or surface temperature just before feeding (hour 0) nor 5 hours post-feeding averaging 46.0 bpm, 15.3°C, and 35.2°C, respectively. In study 2, both forage intake and total intake increased linearly (P ≤ 0.02) with increasing amounts of supplemental alfalfa. Cattle supplemented alfalfa pellets at 0.4% of BW had 33 and 71% greater forage and total DM intake compared with non-supplemented control cows, respectively. In contrast, there were no treatment effects (P ≥ 0.11) on DM fill and total tract digestibility averaging 15.73 kg and 44.99%, respectively. In contrast, liquid fill tended to increase (P = 0.08) linearly with increasing levels of supplemental alfalfa. Heart rate nor surface temperature prior to feeding and 5-hours post feeding were influenced (P ≥ 0.83) by the addition of supplemental alfalfa averaging 51.91 bpm, 15.05°C and 31.75°C, respectively. In summary, overall total DM intake was enhanced with the addition of supplemental protein, however, only modest effects were observed in ruminal fill and total tract digestion. Additionally, heart rate and surface body temperatures were not influenced by supplemental treatments under the conditions of these studies.

PSI-17 Use of Sunn Hemp as Forage for Early-Weaned Beef Calves

Abstract Sunn hemp (Crotalaria juncea) has been widely used as cover crop in the USA and due to superior biomass accumulation and nutritive value, there is interest from producers to use sunn hemp as forage for livestock. However, sunn hemp has pyrrolizidine alkaloids, which can affect animal performance. The objective of this study was to evaluate the effects of feeding sunn hemp hay to early-weaned beef calves in a dry lot in Florida. The experiment was conducted at the UF/IFAS Range Cattle Research and Education Center, Ona, FL from April to May 2021 (42 d). Treatments were calves receiving sunn hemp or stargrass (Cynodon nlemfuensis) hay distributed in a randomized complete block design with 12 replicates. Calves were supplemented with concentrate at 1.3% BW daily (18% CP and 78% TDN). Twenty-four Angus crossbred calves were weaned with 90 ± 14 kg BW and grazed annual ryegrass (Lolium multiflorum) with 1% BW concentrate supplementation for approximately 60 d. Subsequently, calves were randomly distributed and assigned to experimental units (pen) on 14 April 2021 with initial BW of 184 ± 10 kg. ‘Ubon’ sunn hemp hay was harvested approximately 49 d after seeding when 75% of the plants were initially flowering. Ground hay was fed daily targeting 10% refusals, and the initial CP and in vitro digestible organic matter concentrations of sunn hemp and stargrass hay were 9 and 48%, and 9 and 47%, respectively. The average concentration of pyrrolizidine alkaloids from sunn hemp hay was 58 μg/g DM. Early-weaned calves receiving stargrass had a tendency to have greater ADG than sunn hemp (0.5 vs. 0.4 kg/d, P = 0.09), and had greater forage DM intake (1.2 vs. 1.0% BW, P &amp;lt; 0.01) and total DM intake (2.5 vs. 2.3% BW, P &amp;lt; 0.01). Conversely, diets with sunn hemp had greater in vivo DM digestibility than stargrass (68 vs. 62%, P = 0.04). There was no difference between treatments on parasite egg count (mean = 45 eggs/3 g feces, P = 0.25) and coccidia egg count (log10 eggs/g feces, P = 0.35). Early-weaned calves receiving sunn hemp consumed 0.25 g pyrrolizidine alkaloids/d; however, there was no detectable amount (&amp;lt; 0.05 μg/g DM) of pyrrolizidine alkaloids in the feces. The presence of pyrrolizidine alkaloids in sunn hemp may be the potential cause of decreased early-weaned calves forage intake and animal performance.

Performance of dairy cows offered either zero-grazed grass or grass silage prepared from the same sward

Daily harvesting of fresh grass for housed livestock when its nutritive value is high (Zero-grazing) is a labour-intensive process which requires a consistent supply of grass at the optimum growth stage. An alternative approach which may save on labour and require less time spent on grassland management each day, involves harvesting and ensiling herbage on a number of occasions (every 4 weeks approximately) during the growing season when it is at the same nutritive value as herbage used for zero-grazing. This study examined the impact of these two approaches to dairy cow performance. Thirty-six mid-lactation Holstein-Friesian dairy cows were offered either zero-grazed fresh grass (ZG), or grass silage (SIL) prepared from the same sward harvested at a similar growth stage, over a single season. Fresh grass was harvested daily and offered to ZG cows for a 12-week period. During this period, the same sward was harvested once weekly and ensiled in round bales. Following a five-week ensilage period, the silage was offered to cows on SIL for a 12-week period. All cows were also offered 8.0 kg concentrate per day. Zero-grazed grass and grass silage had a mean metabolisable energy content of 11.0 and 11.3 MJ/kg DM, respectively. Mean forage DM intake (DMI) and total DMI were greater for cows on ZG (P < 0.001) compared to SIL, with intakes during weeks 8–12 of the experiment lower with SIL compared to ZG (P < 0.001). Cows on ZG had a higher milk yield, milk protein concentration, milk fat plus protein yield and energy-corrected milk (ECM) yield (P < 0.001) than cows on SIL. With the exception of milk yield (where the difference was primarily observed during weeks 8–12 of lactation), these differences were observed most weeks during the study period. Milk fat concentration was unaffected by treatment (P > 0.05). Milk of cows on ZG had higher concentrations of total monounsaturated fatty acids (P < 0.001), total polyunsaturated fatty acids (PUFAs, P < 0.001) but lower concentrations of saturated fatty acids (SFAs, P < 0.001) compared to cows on SIL. Diet had no effect on cow BW or condition score. This study has shown that when harvested from the same sward, milk yield and ECM yield were improved when cows were offered zero-grazed grass compared to grass silage. This difference in performance was likely due to the lower forage intake observed with the grass silage-based diet.

Behavioural compensation of extruded urea level and the effects of supplementation presencefor finished lambs in tropical grass pastures

The objective was to investigate how different levels of soybean meal replacement with extruded urea (EU) in sheep supplementation affected pasture characteristics (Brachiaria spp.), consumption, ingestive behavior and animal performance. Sixty Texel crossbred lambs were randomly divided between treatments: 0, 6, 12, 18 and 24 g of 100 kg−1 body weight (BW) EU supplement under continuous stocking in Brachiaria spp. The animals receiving a supplement in the proportion of 24 g 100 kg−1 BW from the EU had the highest pasture height (39.5 cm) as compared with other treatments. The levels of replacement of soybean meal by the EU had no effect on the supply of forage, forage accumulation rate or structural characteristics. The forage dry matter intake (DMI) as percentage of BW and metabolic BW were adjusted to quadratic equations, and the minimum levels of DMI in relation to BW (1.5 %) and metabolic (55.6 g DM/kg0.75) were estimated at 10 g and 9.4 g 100 kg−1 BW of the EU, respectively. The grazing time of the lambs decreased linearly (P = 0.006) by 4.88 min for each increase in the EU level. In contrast, as EU levels in lamb supplementation increased, the time taken to consume the supplement and the bite rate increased by 4.38 min and 0.28 bites/minutes, respectively. The average daily gain increased linearly up to 18 g 100 kg−1 BW (146 g/day) (P = 0.034). For lambs finishing in Brachiaria spp., the EU can be used in place of soybean meal up to 18 g 100 kg-1 BW without altering animal performance, consumption, or the structural characteristics of the pasture.

Benefits of barley straw as a forage for dairy calves before and after weaning

The aim of this study was to assess the potential consequences on calf intake, performance, behavior, ruminal microbiome, and ruminal epithelium development of combining the inclusion of chopped barley straw and alfalfa hay during the pre- and post-weaning periods keeping concentrate to forage ratio constant among dietary treatments. Forty-five Holstein calves (44 ± 5.7 kg of BW and 3 ± 1.5 d of age) individually penned were blocked by body weight (BW) and randomly assigned to a common pellet concentrate fed ad libitum along with one of following forage feeding strategies: barley straw before and after weaning (SS), barley straw before and alfalfa hay after weaning (SA), or alfalfa hay before and after weaning (AA). All calves received the same milk replacer regimen. Forage was supplied in a separated bucket at the rate of 7.5% (preweaning) and 15% (postweaning) of total solid feed intake of the previous day. Feed intake and BW were recorded daily and weekly, respectively. Rumen samples were obtained via a stomach tube at 53, 66, and 87 d and were composite in 3 samples of 5 animals each for subsequent rumen microbiome analysis. A rumen epithelium sample was taken by endoscopy at 90 d to assess gene expression of occludin, claudin-4, NHE1, NHE3, MCT1, MCT4, IL6, and TGFß1. Data were analyzed with a mixed-effects model accounting for the fixed-effects of block, forage, week of study, and their interaction, and calf as a random effect. The type of forage fed did not affect concentrate feed, forage, or total DM intake before weaning. However, SA and AA calves consumed less concentrate feed and SA calves grew at a lower rate after weaning than SS calves. Expression of the gene coding for MCT1 in the rumen epithelium was greatest in SS among treatments. Rumen microbiome did not differ among treatments, while the relative abundance of Acidaminococcus and Selenomas genera increased, while Alloprevotella, Bifidobaterium, Olsenella and Succiclasticum genera decreased with age. In conclusion, feeding barley straw before and after weaning was more effective than feeding alfalfa hay in promoting concentrate feed intake after weaning and fostering an increase in the expression of MCT1 in the rumen epithelium.

Comparison of imputation methods for missing production data of dairy cattle

Nowadays, vast amounts of data representing feed intake, growth, and environmental impact of individual animals are being recorded in on-farm settings. Despite their apparent use, data collected in real-world applications often have missing values in one or several variables, due to reasons including human error, machine error, or sampling frequency misalignment across multiple variables. Since incomplete datasets are less valuable for downstream data analysis, it is important to address the missing value problem properly. One option may be to reduce the dataset to a subset that contains only complete data, but considerable data may be lost via this process. The current study aimed to compare imputation methods for the estimation of missing values in a raw dataset of dairy cattle including 454 553 records collected from 629 cows between 2009 and 2020. The dataset was subjected to a cleaning process that reduced its size to 437 075 observations corresponding to 512 cows. Missing values were present in four variables: concentrate DM intake (CDMI, missing percentage = 2.30%), forage DM intake (FDMI, 8.05%), milk yield (MY, 15.12%), and BW (64.33%). After removing all missing values, the resulting dataset (n = 129 353) was randomly sampled five times to create five independent subsets that exhibit the same missing data percentages as the cleaned dataset. Four univariate and nine multivariate imputation methods (eight machine learning methods and the MissForest method) were applied and evaluated on the five repeats, and average imputation performance was reported for each repeat. The results showed that Random Forest was overall the best imputation method for this type of data and had a lower mean squared prediction error and higher concordance correlation coefficient than the other imputation methods for all imputed variables. Random Forest performed particularly well for imputing CDMI, MY, and BW, compared to imputing FDMI.

33 Supplementation Level Effects on Early-Weaned Beef Calves Receiving Annual Ryegrass

Abstract The objective of this study was to evaluate the effects of concentrate supplementation levels on performance and DM intake of early-weaned beef calves consuming annual ryegrass (Lolium multiflorium). The experiments were conducted at the UF/IFAS Range Cattle Research and Education Center, Ona, FL from January to May 2022. In experiment 1, treatments were two levels of concentrate supplementation (0.75% or 1.0% of BW) distributed in a randomized complete block design with four replicates. Concentrate was fed daily and had 18% CP and 78% TDN. Thirty-two Angus crossbred calves were weaned with 90 ± 14 kg BW at 76 ± 10 d of age and allocated to 1 of 8 annual ryegrass pastures (experimental units; 0.3 ha/pasture; 4 calves/pasture) with a continuous and fixed stocking rate. Herbage mass and nutritive value were estimated every 14 d and calves were weighed every 28 d. There was no difference in herbage mass (mean = 1.300 kg DM/ha; P = 0.44; SE = 0.46), herbage allowance (mean = 0.86 kg DM/kg LW; P = 0.66; SE = 0.03), CP (mean = 24.4%; P = 0.46; SE = 0.78), and in vitro digestible organic matter (mean = 77%; P = 0.49; SE = 1) concentration between treatments. There was a treatment × month interaction on ADG and the interaction occurred because calves receiving 1% BW had greater ADG than 0.75% BW in April (1.0 vs. 0.8 kg/d; P = 0.04; 0.03) but there were no differences between treatments in February, March, and May. In experiment 2, treatments were supplementation with 0.75% or 1.0% BW concentrate distributed in a complete randomized design with seven replicates. Fourteen steers calves (166 ± 17 kg BW) from experiment 1 were maintained in the same treatment, transferred to a drylot (1 steer/pen), and evaluated for forage and total DM intake, and in vivo DM digestibility. Ground annual ryegrass hay (11% CP, 58% IVDOM) was offered and adjusted to allow 10% refusals. There was no difference in forage DM intake (mean = 1.8 kg DM/d; P = 0.3; SE = 0.06) between treatments but calves receiving 1.0% BW had greater total DM intake (2.7 vs. 2.5 kg DM/d; P = 0.05; SE = 0.06) and in vivo DM digestibility (77 vs. 75%; P &amp;lt; 0.01; SE = 0.53) than 0.75% BW. Decreasing concentrate supplementation level from 1.0 to 0.75% BW may be a viable management practice to reduce cost of developing early weaned beef calves grazing annual ryegrass.

83 Effect of a Saccharomyces cerevisiae fermentation product on intake and digestion in young horses undergoing exercise training

Young growing horses subjected to exercise have greater dietary requirements than horses at maintenance necessitating the delivery of a more nutrient dense diet. Inclusion of a grain concentrate in the total daily ration achieves this goal but also may put the young horse at risk of digestive disorders and reduced forage utilization. As such, the objective of this study was to determine if a dietary S. cerevisiae fermentation product (SCFP; TruEquine C, Diamond V) could influence nutrient utilization in young horses being introduced to grain concentrate feed and if the response was dose dependent. Thirty Quarter horse yearlings (561 ± 15.8 d of age and 371 ± 24.4 kg BW) were adapted to a 14% CP grain concentrate feed (Nutrena SafeChoice Original formulated without microbial ingredients), fed at 1% of BW as fed to meet or slightly exceed nutrient requirements for yearling horses undergoing light to moderate work and allowed ad-libitum access to Coastal bermudagrass (Cynodon dactylon) hay (67.8% NDF) and fresh water. Horses were stratified by age, BW, and sex and randomly assigned to one of 3 levels of SCFP: 0, 46, or 92 mg/kg BW divided evenly and top-dressed onto the grain concentrate meal at 12 h intervals. After 14 d of adaptation, intake and total fecal production were measured overa 4-d period. Horses were housed in individual 3.7 × 3.7 m stalls and allowed 1 h of exercise in individual 3.7 × 7.4 m runs daily during the collection period. All statistical analyses were performed in SAS 9.4 using PROC MIXED with the model containing treatment and horse included as the random variable. There was no significant treatment difference for any measure of intake (P ≥ 0.33); forage DM intake averaged 6.14 kg/d, total DM intake averaged 9.60 kg/d, and total digestible organic matter intake averaged 4.97 kg/d. There was a tendency for improved DM digestibility (P = 0.09) with supplementation (56.3 and 56.8% for 46 and 92 mg/kg BW, respectively) compared with no supplementation (54.2%). Supplementation of SCFP resulted in no significant differences (P ≥ 0.15) in organic matter (OM) or NDF digestibility. There were no differences in any indicator of nutrient digestibility between the low and high level of SCFP supplementation. An observed tendency for improved DM digestibility with SCFP supplementation suggests further research is warranted.

Effects of frequency of concentrate supplementation on performance of early-weaned beef calves consuming annual ryegrass

The objectives of this study were to evaluate the growth performance during a grazing period (experi- ment 1) and forage intake and apparent in vivo digestibil- ity (experiment 2) of early-weaned beef calves consuming annual ryegrass (Lolium multiflorum) and supplemented with concentrate either daily or 3 times weekly. The experiment was con- ducted in Ona, Florida. Treatments consisted of similar weekly concentrate amounts (1% of BW × 7 d) divided into equal amounts and then offered daily (7×) or 3 times weekly (3×) to early-weaned beef calves consuming annual ryegrass pastures from d 0 to 84 (experiment 1) and annu- al ryegrass hay in drylot from d 84 to 105 (experiment 2). From d 0 to 84, reducing the frequency of concentrate supplementation did not influ- ence herbage mass, herbage allowance, or nutritive value of annual ryegrass pastures, or calf ADG, BW, or plasma concentrations of glucose and urea N. The overall forage DM intake was 15% less for 3× versus 7× calves (1.51 vs. 1.78% of BW, respectively). Total DM intake did not differ between 3× and 7× (2.63 vs. 2.73% of BW, respec- tively), whereas in vivo apparent digestibility decreased for 3× versus 7× (85.3 vs. 86.5%, respectively). Reducing frequen- cy of concentrate supplementation from daily to 3 times weekly did not affect overall growth performance of early- weaned beef calves consuming annual ryegrass and can successfully be implemented to reduce feeding costs.

Effects of stage of maturity at harvest of cereal crops on biomass and quality, estimated forage dry matter intake, beef cow performance, and system economics

The objective of this study was to evaluate the effects of maturity at harvest of cereal crops on biomass, quality, cow performance, and economics. In each of 3 yr, a 48-ha field was divided into 3 paddocks (16 ha per treatment) and seeded to either barley (Hordeum vulgare CDC Maverick, 135 kg/ha), oat (Avena sativa CDC 29 SO1, 135 kg/ha), or triticale (Triticosecale Taza, 135 kg/ha). Half of each field (8 ha) was swathed at either soft dough (SDo) or hard dough (HDo) stage for grazing. Each year, 120 dry pregnant beef cows (631 kg) were randomly allocated to 1 of 6 replicated (n = 2) paddocks for 90, 106, and 88 d in yr 1, 2, and 3, respectively. Triticale had 19 and 23% greater total yield than oat and barley, respectively. Barley CP was greater (P < 0.05; 10.9%) than oat (9.3%) or triticale (9.8%) at HDo stage. The animal unit months (AUM) per hectare were greater for HDo (11.5 ± 0.8 AUM/ha) than SDo (9.15 ± 0.8 AUM/ha) stage. Cow ADG was greater (P = 0.01) for barley (0.61 kg/d) compared with triticale (0.39 kg/d). Total crop cost averaged Can$426, Can$437, and Can$458/ha for oat, barley, and triticale, respectively. The HDo stage had Can$0.40 lower dollars per cow per day in-field costs (P = 0.02) than the SDo stage and 10% (Can$26.25 per cow/d) lower feeding costs (P = 0.02) over 3 yr. Delaying harvest to hard dough can increase yield and reduce feeding costs without affecting cow performance.

4 Developing a Dry Matter Intake Prediction Equation for Grazing Animals based on Real-Time Enteric Emissions Measurements

Abstract Cattle dry matter intake (DMI) is an essential component of calculating cattle stocking rates, determining nutrient requirements, and evaluating grazing efficiency. Cattle DMI and digestion of forages impact enteric greenhouse gas (CO2e) emissions. Enteric emissions include methane (CH4) and carbon dioxide (CO2), that are eructated by ruminants. The amount of methane produced is affected by consumption, quality, and type of feedstuffs. Intake of grazing animals varies on environmental factors and physiological stage. Additionally, increased GHG levels indicate energy loss during the rumen fermentation process. However, there may be a silver lining to enteric GHG emissions to predict DMI of grazing animals since they are highly correlated with DMI and forage composition. There is limited data on the relationship of DMI and GHG on extensive rangeland systems. Obtaining data for beef cattle DMI and enteric emissions on forage-based diets similar to extensive rangelands is needed to develop an equation capable of predicting DMI for grazing cattle. Therefore, our objective was to determine the relationship between CH4, CO2, oxygen (O2), and hydrogen (H2) emissions and DMI of dry beef cows to develop a mathematical model that predicts grazing DMI from enteric emissions. The predictive equation or precision system model (PSM; Menendez et al., 2022) was developed using data from two feeding trials that were conducted using GreenFeed, SmartFeed Pro, and SmartScale (C-Lock Inc. Rapid City, SD). This study was conducted at the SDSU Cottonwood Field Station (Cottonwood, SD). The two feeding trials consisted of dry beef cows (n=10) receiving low (8% CP) or high (15% CP) quality grass hay using a 14-day adaptation period and a 14-day period of data collection. Regression, artificial neural network, and dynamic-mechanistic models were developed using these data and assessed to identify a model that accurately and precisely predicts forage DMI for dry beef cows on pasture. Model evaluation of the machine learning algorithms used a training, testing, and cross-validation scheme to determine model accuracy. Evaluation of mechanistic models used the Model Evaluation System (MES; Tedeschi, 2006) to measure accuracy (mean bias, Cb, RMSEP), precision (R2, MEF, CCC), and screening for systematic errors. This study successfully integrated three precision technologies which improve research capabilities on extensive rangeland systems through precision enhanced data collection. Deploying a precision-based DMI algorithm enhances research-based capabilities to manage range beef cattle on an individual level by more precisely setting stocking rates, providing supplementation, and evaluating individual animal efficiency; ultimately leading to lower cost, optimized resources, and enhanced environmental sustainability. Further, the enteric emissions data collected fills a gap for missing GHG data of dry beef cows in maintenance phase in semi-arid western South Dakota rangelands.

Feeding behavior of post-weaned crossbred steers supplemented in the dry season of the year.

The objective of this study was to evaluate the feeding behavior of grazing steers supplemented in the dry season of the year. Thirty-two castrated crossbred (½ Holstein-Zebu) steers with an average initial weight of 378 ± 7.54kg, aged 14months, were distributed into four treatment groups in a completely randomized design with eight replicates. The animals were managed in an area covered with a pasture of Brachiaria brizantha cv. Marandu, in a rotational grazing system. The supplement was formulated so that the animals in the different treatment groups would ingest the same amount of crude protein (CP) daily. Thus, the treatments consisted of increasing levels of supplementation, based on the animals' body weight (BW), as the protein content of the supplement was reduced. The following treatments (dry matter basis) were tested: T2, supplement at 0.2% BW, with 50% CP; T4, supplement at 0.4% BW, with 25% CP; T6, supplement at 0.6% BW, with 16.67% CP; and T8, supplement at 0.8% BW, with 12.5% CP. Forage dry matter intake decreased linearly (P < 0.05), characterizing a substitution effect. The increasing supplementation levels influenced the animals' feeding behavior, especially grazing time, total feeding time, number of grazing bouts, and number of bites per day, which showed a positive quadratic response (P < 0.05), and rumination time, number of rumination bouts, number of cuds ruminated per day, and number of chews per ruminated cud, which exhibited a negative quadratic behavior (P < 0.05). Dry matter and neutral detergent fiber (NDF) feed efficiencies and dry matter and NDF rumination efficiencies responded quadratically (P < 0.05). In conclusion, concentrate supplementation at up to 0.8% BW improves the feeding behavior of grazing steers in terms of the intake of concentrate supplement and forage as well as the feed and rumination efficiencies.

Different fat sources in supplements for beef cattle at pasture.

We investigated the consequences of fat supplementation (free oil and rumen-protected oil) on the nutrient intake and digestion of beef cattle at pasture. Five rumen-cannulated Nelore bulls, with a median body weight (BW) of 467.8 ± 32.8kg and an age of 26months, were distributed in a Latin square design (5 × 5). The treatments were as follows: WF, no additional fat; PA, rumen-protected palm oil; PS, rumen-protected soybean oil; SO, soybean-free oil and CO, free corn oil. Nutrient intake and digestibility, ruminal pH and ammonia (NH3-N), serum urea and nitrogen balance were analysed. The supplements with different oil sources did not alter (P > 0.05) the intake and digestibility of dry matter (DM), forage DM intake (DM), organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), neutral detergent fibre-corrected ash and protein (apNDF), nonfibre carbohydrates (NFC) or total digestible nutrients (TDN) compared to WF. An increase (P < 0.05) in the intake and digestibility of EE was observed with the inclusion of fat, independent of the source. No differences were observed between WF and other supplements with regard to ruminal parameters (pH and NH3-N) (P > 0.05) and serum urea (P > 0.05). The nitrogen balance was not affected by the fat source (P > 0.05). Supplementation of grazing beef cattle (2g/kg BW) with free oil (130g/kg DM supplement) or rumen-protected oil (160g/kg DM supplement) did not interfere with nutrient intake and digestibility.

340 Relationship of Retained Energy in Lactating Beef Cows to Maintenance Energy Requirement and voluntary Feed Intake

Abstract This study’s objective was to determine the relationship between retained energy, lactation maintenance energy requirement (MER), and dry period voluntary feed intake (VOL) in beef cows. Twenty-four mature fall-calving Angus cows were used in an 82-d study during lactation to establish maintenance energy requirements followed by a voluntary feed intake study after weaning. During the lactation MER experiment, cows were housed in 2 drylot pens and limit-fed a mixed hay/concentrate diet (17.8% CP, 2.6 Mcal/kg ME, DM basis) individually once per d in a stall barn. Cows were adapted to the diet and feeding management for the first 16 d. Subsequently, cows were weighed and feed allowance adjusted at 14-d intervals to achieve BW and BCS stasis. Milk yield and composition were determined on d – 10, 49, and 77 using a milking machine. Retained energy was calculated as average daily maternal tissue energy change plus average daily milk energy yield. During the post-weaning VOL experiment, cows were provided ad libitum access to a grass hay diet for 41 d (8.15% CP, 1.8 Mcal/kg ME, DM basis) using five individual feed intake monitoring units (SmartFeed, C-Lock, Inc). Each one unit increase in metabolizable energy intake, kcal/kg BW0.75 was associated with a 0.86 ± 0.28 kcal/kg BW0.75 increase in total retained energy (P = 0.005). Using this partial efficiency coefficient, ME required for maintenance declined by 0.80 ± 0.11 kcal ME/kg BW0.75 for each additional kcal net energy retained/kg BW0.75 (P &amp;lt; 0.0001). There was no relationship between lactation-period retained energy and post-weaning VOL forage dry matter intake. The present study results contradict previous reports suggesting that maintenance requirements increase with increasing productivity.

Effects of different supplement amounts on dry matter intake, milk production and milk composition of high-producing Lacaune dairy ewes

In general, dairy sheep are fed in large groups that receive the same diet based on the average group milk yield (MY), which is increased by approximately 15% and 25% to cover the energy and protein requirements respectively of part of the high-producing ewes, according to the French INRA system recommendations. Despite this, some of the highest producing ewes are still underfed, especially in terms of energy. This experiment was designed to measure the effect of increasing the amount of energy supplement on milk yield, milk composition and forage intake. Three groups of 16 multiparous Lacaune dairy ewes (DIM mean ± SD: 40 ± 1.5) producing 3.4 ± 0.29 L/d, were balanced in terms of MY, milk composition, body weight (BW: 74.7 ± 8.43 kg) and body condition score (BCS: 2.7 ± 0.26). During three periods of three weeks (P1, P2, P3), groups were fed a basal diet based on a mixture of herbage silages and good quality hay (173 g CP/kg DM) offered ad libitum. A protein concentrate was offered at a constant level (0.34 ± 0.034 kg DM/d/ewe) to cover initial protein requirements. Barley grain was offered at three average levels (kg DM/d/ewe): medium (M, 0.478), high (H, 0.667) or very high (vH, 0.883). The three groups (MMH, MHH, MvHH) received the corresponding amount of barley in the three successive periods: in P1, 0.485 for the three groups, in P2, 0.470 for MMH, 0.672 for MHH and 0.883 for MvHH, and in P3, 0.661 for the three groups. Forage and concentrate dry matter intake were measured each week over five days; milk yield and composition (total fat, protein and urea content) were measured once a week; and BW and BCS were measured every two weeks. Modifying the amount of concentrate (P2, P3) gave no significant (P<0.05) difference between groups for MY, milk composition, BW or BCS. In P2, increasing the level of barley led to a high substitution effect with a decrease of the forage dry matter intake. In P3, increasing or decreasing the amount of barley moderately decreased or increased the forage. Taking into account the whole experimental period (P1-P3), increasing the level of barley did not improve (P>0.05) MY, but slightly increased (P<0.05) BW and BCS. In conclusion, increasing the amount of energy of high-producing dairy ewes fed high-quality forage ad libitum, reduces the forage intake, did not improve MY or change milk composition, but increases BW and BCS.