Metabolizable Protein Requirements Research Articles

Protein requirements of hair sheep raised in warm areas: a multi-study approach

The protein requirements of hair sheep are a key factor in increasing profitability and decreasing the environmental impacts of nitrogen excretion. The objective of this study was to evaluate the protein requirements of hair sheep. A database with 382 individual records (269 intact and 113 castrated males) comprising information from 11 studies was used. The studies provided different levels of metabolisable protein intake (MPI) and of N retention, allowing the development of equations to predict the net protein (NP) and the metabolisable protein (MP) requirements. The efficiency of MP use for gain (kpg) was calculated using the equation of daily protein retained against daily MPI above maintenance. The efficiency of MP use for maintenance (kpm) was computed as the ratio between the NP for maintenance (NPm) and the MP for maintenance (MPm). The NPm (1.32 g/kg0.75 EBW) did not differ between sex. The kpm was 0.34, and the kpg was 0.25. The MPm estimated was 3.21 g/kg0.75 BW. Sex affects the protein requirements for gain (NPg). The protein requirements of hair sheep differ from those recommended by feeding systems for sheep. The equations provided herein may improve the optimisation of protein nutrition of sheep, thereby minimising the environmental impacts of sheep production.

326 Nutritional Grouping and Machine-Learning Techniques: Towards a Feed Efficiency Improvement in Beef Cattle Production

Abstract Nutritional grouping (NG) strategies have been proposed mainly in dairy cattle to improve economic efficiency (30-60$/cow per year) of dairy farmers. In dairy cattle, NG is made according to net energy (NE) requirements estimated from some animal variables (i.e., milk yield and dairy merit). However, NG has not been evaluated for beef cattle, likely because data are not readily available and existing protocols have been fixed for decades by the beef industry, such as allotting by body weight (BW): growing diet for 180 to 400-kg animals, and finishing diet for 400 to 550-kg animals. Therefore, we investigated an unsupervised machine learning (ML) technique in R to sort animals at the arrival according to their DM intake (DMI), NE and metabolizable protein (MP) requirements, estimated through INRA from BW and average daily gain. We utilized data from 77 growing Friesian steers allotted conventionally by BW (139±21.6 kg) in 4 pens, weighed every 3 weeks (n=9 weighings) during 190 days, and fed a high-energy diet (1.59 Mcal NE/kg DM and 89 g MP/kg DM). Results identified that estimated performances were significantly (P< 0.002) different between 3 groups made from ML and between 4 pens made from BW; however, ML groups presented a minor within-group variability of NE and MP requirements (-25%CV) than pens. We also regressed energy and protein intake minus their respective requirements by the duration of the experiment observing a better fitting (R2= 0.93 vs 0.80) when allotting animals by groups than by pens, which implicates better feed efficiency if diets were formulated according to requirements established by ML groups. We demonstrated that ML techniques could help the decision-making of beef farmers to better sort animals according to their requirements and not only by BW. The next step is to formulate rations according to animal requirements to improve efficiency.

79 Effects of Nutrient Restriction During Late Gestation of the First Parity on cow and Calf Performance During the Second Lactation

Abstract Fall-calving Herford-SimAngus heifers were individually fed either 100% (control; CON, n = 10) or 70% (nutrient restricted; NR, n = 12) of NASEM metabolizable energy and metabolizable protein requirements from d 160 of gestation to calving. Postpartum cows were individually fed 100% of energy and protein requirements until d 149 of lactation, then fed tall fescue hay or pasture as a single group through parity 2. Second parity cow performance and calf size were measured at birth, d 30, and d 60 post-calving. Single-quarter colostrum yield was collected pre-suckling. At d 30 and 60 of lactation, 4-hour milk yield was collected. Data were analyzed with the fixed effect of first parity nutritional plane, and calving or breeding date, calf sex, and calf sire (calf measures) were covariates. Milk yield included day and day x treatment (repeated measures). We previously reported that in parity 1, NR reduced (P ≤ 0.04) colostrum and milk yield, calf weaning weight, and dam weaning BCS. From calving to d 60 of parity 2, CON cows had greater (P ≤ 0.008) BCS and greater (P = 0.003) backfat on d 30. Additionally, CON cows had greater (P ≤ 0.002) BW compared with NR at d 30 and 60 of lactation. Calf size was not affected (P ≥ 0.17) by first parity nutritional plane except that cannon length at birth and d 60 tended (P ≤ 0.08) to be longer in CON calves. Colostrum and milk volume and weight were not affected (P ≥ 0.37) by first parity nutritional plane. Milk yield was greater (P ≤ 0.001) at d 30 than d 60. These data indicate that cow BW and energy reserves remained less in parity 2 when heifers experienced late gestational nutrient restriction, but calf size, colostrum yield, and milk yield were unaffected in the second parity.

PSII-A-5 Effects of Time Postpartum and Late Gestational Nutrient Restriction on Beef Heifer Colostrum

Abstract Our objectives were to determine changes in colostrum yield and composition across the 36 hours post-calving and effects of late gestational nutrient restriction (NR) on these changes. Fall-calving, crossbred beef heifers (BW: 472 ± 33 [SD] kg; BCS: 5.4 ± 0.5) were individually fed 100% (control; CON; n = 13) or 70% (NR; n = 13) of NASEM metabolizable energy and metabolizable protein requirements for maintenance, growth, and pregnancy from d 160 of gestation to parturition. Calves were removed from dams immediately post-calving and pre-suckling. Colostrum was hand-milked from all quarters at 1, 12, 24, and 36 h to determine total colostrum volume and weight. Colostrum protein, triglycerides, and milk urea nitrogen (MUN) concentration were analyzed using colorimetric assays on a UV-visible light microplate reader. Data were analyzed using fixed effects of treatment, hour, treatment × hour (repeated measures); calf sex, maternal sire, and treatment initiation date were covariates. Colostrum yield was affected (P < 0.02) by the treatment × hour interaction. Colostrum volume and weight were 28% less (P ≤ 0.03) for NR than CON at 1 h. For both treatments, colostrum volume and weight decreased (P ≤ 0.04) from 1 to 12 h, before increasing (P ≤ 0.02) from 12 to 36 h. Triglyceride concentration was greater (P = 0.03) in NR than CON. Both triglyceride concentration and total protein decreased (P ≤ 0.01) from 1 to 24 h. Protein concentration decreased (P < 0.001) from 1 to 36 h. Total triglycerides and MUN decreased (P < 0.001) from 1 to 12 h, before total MUN increased (P < 0.001) from 12 to 36 h and total triglycerides increased (P = 0.004) from 24 to 36 h. In conclusion, nutrient restriction may only affect colostrum yield at 1 h, and colostrum nutrient content decreases dramatically after the first milking.

298 Late Gestational Nutrient Restriction of Primiparous Beef Heifers Decreases Neonatal Calf Body Weight and Organ Mass

Abstract We hypothesized that late gestational nutrient restriction (NR) would decrease organ mass in neonatal calves. Fall-calving crossbred beef heifers (BW: 466 ± 30 [SD] kg; BCS: 5.4 ± 0.5) bred to a single sire were individually fed 100% (control; n = 10) or 70% (nutrient restricted; NR; n = 12) of NASEM metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Diets were based on chopped sorghum sudan hay and supplemented to meet targeted nutritional planes. Calves were removed immediately post-calving and fed colostrum and milk replacer relative to BW until euthanasia (48.7 ± 0.4 h of age) for organ mass determination. Nutritional plane was a fixed effect, and maternal sire, calf sex (when P < 0.25), and date of study initiation were covariates. Post-calving, NR dams were 62 kg BW and 2.1 BCS less (P < 0.001) than controls. Calf BW, liver, large intestine, omental/mesenteric fat, kidney, and heart weights were less (P ≤ 0.05) and carcass, rumen/reticulum/omasum, stomach complex, and total gastrointestinal tract weights tended to be less (P ≤ 0.09) in offspring from NR dams. Maternal nutrient restriction did not affect (P ≥ 0.11) weights of the small intestine, pancreas, abomasum, spleen, perirenal fat, adrenals, lungs, femur, and brain. Expressed per BW, lung weight was greater (P = 0.05), and brain and femur weight tended to be greater (P ≤ 0.10) in calves from NR dams, but other organ masses were unaffected (P ≥ 0.15). Expressed relative to brain weight, liver and large intestine weights were less (P ≤ 0.04) and carcass, total gastrointestinal tract, omental/mesenteric fat, and kidney weights tended to be less (P ≤ 0.08) in NR. In summary, late gestational NR decreased some organ masses in neonatal calves while sparing other tissues via asymmetric growth.

Essential amino acid profile of supplemental metabolizable protein affects mammary gland metabolism and whole-body glucose kinetics in dairy cattle.

This study investigated mammary gland metabolism and whole-body (WB) rate of appearance (Ra) of glucose in dairy cattle in response to a constant supplemental level of metabolizable protein (MP) composed of different essential AA (EAA) profiles. Five multiparous rumen-fistulated Holstein-Friesian dairy cows (2.8 ± 0.4 lactations; 81 ± 11 d in milk; mean ± standard deviation) were abomasally infused according to a 5 × 5 Latin square design with saline (SAL) or 562 g/d of EAA delivered in different profiles where individual AA content corresponded to their relative content in casein. The profiles consisted of (1) a complete EAA mixture (EAAC), (2) Ile, Leu, and Val (ILV), (3) His, Ile, Leu, Met, Phe, Trp, Val (GR1+ILV), and (4) Arg, His, Lys, Met, Phe, Thr, Trp (GR1+ALT). A total mixed ration (58% corn silage, 16% alfalfa hay, and 26% concentrate on a dry matter basis) was formulated to meet 100 and 83% of net energy and MP requirements, respectively, and was fed at 90% of ad libitum intake on an individual cow basis. Each experimental period consisted of 5 d of continuous abomasal infusion followed by 2 d of no infusion. Arterial and venous blood samples were collected on d 4 of each period for determination of mammary gland AA and glucose metabolism. On d 5 of each period, D-[U-13C]glucose (13 mmol priming dose; continuous 3.5 mmol/h for 520 min) was infused into a jugular vein and arterial blood samples were collected before and during infusion to determine WB Ra of glucose. Milk protein yield did not differ between EAAC, GR1+ILV, and GR1+ALT, or between SAL and ILV, and increased over SAL and ILV with EAAC and GR1+ILV. Mammary plasma flow increased with ILV infusion compared with EAAC and GR1+ILV. Infusion of EAAC tended to increase mammary gland net uptake of total EAA and decreased the mammary uptake to milk protein output ratio (U:O) of non-EAA compared with SAL. Infusion of ILV increased mammary net uptake and U:O of Ile, Leu, and Val markedly over all treatments. The U:O of total Ile, Leu, and Val increased numerically (25%) with GR1+ILV infusion compared with EAAC, and the U:O of total Arg, Lys, and Thr tended to decrease, primarily from decreased U:O of Lys. During GR1+ALT infusion, U:O of total Arg, Lys, and Thr was greater than that during EAAC infusion, whereas U:O of Ile, Leu, and Val did not differ from EAAC. Glucose WB Ra increased 16% with GR1+ALT over SAL, and increased numerically 8 and 12% over SAL with EAAC and GR1+ILV, respectively. The average proportion of lactose yield relative to glucose WB Ra did not differ across treatments and averaged 0.53. On average, 28% of milk galactose arose from nonglucose precursors, regardless of treatment. In conclusion, intramammary catabolism of group 2 AA increased to support milk component synthesis when the EAA profile of MP was incomplete with respect to casein. Further, WB and mammary gland glucose metabolism was flexible in support of milk component synthesis, regardless of absorptive EAA profile.

Review: Problems in determining metabolisable protein value of dairy cow diets and the impact on protein feeding

Accurate determination of dairy cow’s metabolisable protein (MP) requirements is essential for maximising milk yield and minimising N input in dairy production systems. The main objectives of feed evaluation systems are to predict accurately the nutritive value of feed resources and production responses to ingested nutrients. In recent years, protein evaluation systems have made progress in complexity but our analysis indicated that in comparison to simple MP models, or even models based on CP and metabolisable energy intake, new models have failed to improve milk protein yield predictions. Previous meta-analyses have indicated low marginal efficiencies for incremental CP intake even with high-quality feeds as protein supplements. Most current protein systems tend to overestimate MP supply from rumen undegradable protein and overlook the effects on rumen microbial protein synthesis. These findings suggest that there is scope for improving predictions of MP supply. This review highlights and discusses some evident problems in the current MP systems that may partly explain the modest progress achieved over the last few decades.

Influence of hempseed cake inclusion on growth performance, carcass characteristics, feeding behavior, and blood parameters in finishing heifers.

As the hemp industry continues to develop in the United States, there is an increasing interest in feeding byproducts of industrial hemp production to livestock. A completely randomized design experiment using crossbred finishing heifers (initial body weight [BW] ± SE = 494 ± 10 kg) was conducted to determine the effects of feeding hempseed cake in a corn-based finishing diet (10% forage) formulated to meet or exceed ruminally degradable and metabolizable protein requirements on growth performance, carcass characteristics, feeding behavior, and plasma parameters. Dietary treatments were the inclusion of 20% (dry matter [DM] basis) of dried corn distillers grains plus solubles (DDGS, n = 16) or hempseed cake (HEMP, n = 15). Cattle were housed in two pens, had ad libitum access to feed and water, and individual intakes and feeding behavior were monitored using the Insentec feeding system. Cattle were fed treatment diets for 111 d, and every 14 d BW were measured and blood samples were collected. Blood plasma was analyzed for glucose, urea nitrogen, and individual amino acids, and results were analyzed using repeated-measures analysis in SAS. Final BW, average daily gain, gain:feed, and hot carcass weight decreased (P ≤ 0.05) by 2.3%, 7.7%, 7.7%, and 2.6%, respectively, in heifers fed the HEMP diet than in heifers fed the DDGS diet. Net energy for maintenance and gain (Mcal/kg of feed, DM basis), estimated based on heifer intake and performance, were greater (P = 0.02) for the DDGS diet than for the HEMP diet. All other performance and carcass characteristics were not different (P ≥ 0.20) between treatments. Heifers fed the HEMP diet had greater (P < 0.05) plasma urea nitrogen concentration in samples from each collection day compared with heifers fed the DDGS diet, although there was a treatment-by-day interaction (P < 0.01) because of variability in the magnitude of treatment differences over time. Plasma glucose concentration was not influenced (P = 0.17) by dietary treatment. Plasma concentrations of total amino acids, nonessential amino acids, and essential amino acids were not different between treatments (P ≥ 0.09), although there were several interactions between treatment and day (P ≤ 0.04) for individual amino acids. These data suggest that hempseed cake has a lower net energy for maintenance and gain relative to DDGS when adequate metabolizable protein is supplied, while still providing adequate nutrition to support the acceptable performance of finishing cattle.

208 Nutrient Restriction During Late Gestation Alters Beef Heifer Colostrum Composition

Abstract We hypothesized that late gestational nutrient restriction of beef heifers would decrease nutrient partitioning to the mammary gland, resulting in less colostrum nutrient availability for neonatal calves. Fall-calving Hereford-SimAngus heifers (single-sired; BW: 451 ± 28 [SD] kg; BCS: 5.4 ± 0.7) bred to a single sire were individually fed 100% (control; n = 12) or 70% (nutrient restricted; NR; n = 13) of NASEM net energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Diets were based on chopped sorghum sudan hay (1.74 Mcal ME, 6.66% CP, 72.0% NDF; DM basis) supplemented to meet targeted nutritional planes. Calving was observed for all females, and total colostrum from one rear quarter was collected pre-suckling (50.5 ± 17 min [SD] postpartum). Colostrum nutrient composition was determined by colorimetric assays run on a UV-visible light microplate reader. Data were analyzed with treatment, calving date, and calf sex (when P &amp;lt; 0.25) as fixed effects. We have previously reported that single-quarter colostrum weight and volume were 40% less (P = 0.04) in NR compared with control heifers. Colostrum lactose concentration was not affected (P = 0.32) by treatment, but yield differences resulted in 46% less (P = 0.03) total single-quarter colostrum lactose in NR than control. Colostrum from NR heifers had 36% greater (P = 0.004) protein concentration than control, but greater colostrum yield of control heifers allowed for total protein to be unaffected (P = 0.57) by treatment. Nutrient restricted heifers had 23% less (P = 0.04) colostrum urea N concentration and 60% less (P = 0.01) total colostrum urea N than control. Late gestational nutrient restriction (P ≥ 0.59) did not affect colostrum triglyceride concentration or total. In summary, energy and protein restriction had disparate effects on nutrient partitioning to colostrum in primiparous beef females.

68 Late Gestational Nutrient Restriction Decreases Blood Flow to the Mammary Gland in Lactating Primiparous Beef Females

Abstract To determine the effects of late gestational nutrient restriction on mammary blood flow during lactation, fall-calving Hereford-SimAngus heifers (single-sired; BW: 451 ± 28 [SD] kg; BCS: 5.4 ± 0.7) bred to a single sire were individually-fed 100% (control; CON; n = 10) or 70% (NR; n = 13) of NASEM net energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Post-calving, all females were individually fed chopped tall fescue hay supplemented to meet lactational nutrient requirements in Calan gates. Transrectal color Doppler ultrasonography of both external pudendal arteries was conducted every 21 d from d 23 to 107 of lactation. Total mammary blood flow was calculated and hemodynamics from both sides averaged. Data were analyzed with fixed effects of nutritional plane, day of lactation, and their interaction, using repeated measures. Calving date and calf sex (if P &amp;lt; 0.25) were fixed effects, and Doppler angle of insonation was included in the model for flow-related variables. We have previously reported that CON cows had greater (P ≤ 0.003) BW, BCS, and backfat from calving to d 147 of lactation, and NR cows had 15% less (P &amp;lt; 0.04) milk yield. External pudendal artery pulsatility index tended to be greater (P = 0.06) and resistance index, peak systolic velocity, and cross-sectional area were greater (P ≤ 0.04) in CON cows. Heart rate was greater (P = 0.008), yet mammary blood flow was 19% less (P = 0.004) in NR cows. Mammary blood flow/cow BW and blood flow/milk yield were not affected (P ≥ 0.13) by nutritional plane. All hemodynamic variables were affected by day (P ≤ 0.04) except resistance index (P = 0.11). In summary, late gestational nutrient restriction decreased mammary blood flow similarly to the reduction observed in milk yield.

Oversupplying metabolizable protein during late gestation to beef cattle does not influence ante- or postpartum glucose-insulin kinetics but does affect prepartum insulin resistance indices and colostrum insulin content.

The objective of this study was to evaluate whether oversupplying metabolizable protein (MP) during late gestation influences glucose and insulin concentrations, and insulin resistance (IR) in late gestation and early lactation. Crossbred Hereford, first-lactation heifers were individually fed diets to supply 133% (HMP, n = 11) or 100% (CON, n = 10) of their predicted MP requirements for 55 ± 4 d (mean ± SD) prior to calving. All heifers received a common lactation ration formulated to meet postpartum requirements (103% MP and 126% ME). After feed was withheld for 12 h, cattle underwent an intravenous glucose tolerance test (IVGTT) on days -6.7 ± 0.9 and 14.3 ± 0.4 by infusing a 50% dextrose solution (1.36 g glucose/kg BW0.75) through a jugular catheter with plasma collected at -10, 0 (immediately after infusion), 5, 10, 15, 20, 25, 30, 45, 60, 75, 90, and 120 min, respective to the infusion. Glucose and insulin concentrations were assessed. Insulin resistance indices (homeostasis model of insulin resistance [HOMA-IR], quantitative insulin sensitivity check index [QUICKI], revised quantitative insulin sensitivity check index [RQUICK], and RQUICKI incorporating serum beta-hydroxybutyrate concentrations [RQUICKIBHB]) were calculated from measurements of serum non-esterified fatty acids and beta-hydroxybutyrate and plasma glucose and insulin concentrations on days -34 ± 4, -15 ± 4, 7 ± 1, 28 ± 3, 70 ± 3, and 112 ± 3. Colostrum samples were collected within an hour of calving (prior to suckling) and analyzed for insulin concentration. Data were analyzed as a randomized block design using the PROC GLIMMIX of SAS, accounting for repeated measurements when necessary. Baseline (-10 min) plasma glucose and insulin concentrations were elevated (P ≤ 0.038) for HMP heifers during the antepartum IVGTT, but not (P ≥ 0.25) during the postpartum IVGTT. Plasma glucose and insulin concentrations throughout the antepartum or postpartum IVGTT did not differ (P ≥ 0.18) by prepartum treatment, nor did other glucose and insulin IVGTT parameters (i.e., max concentration and time to reach max concentration, nadir values, clearance rates and half-lives, area-under-the-curve, and insulin sensitivity index; P ≥ 0.20). Antepartum IVGTT IR indices indicated that HMP heifers were more (P ≤ 0.011) IR than their counterparts. Similarly, the prepartum HOMA-IR was greater (P = 0.033) for HMP heifers, suggesting increased IR. Postpartum IR indices did not (P ≥ 0.25) indicate that prepartum MP consumption impacted postpartum IR. Colostrum insulin concentration was increased (P = 0.004) by nearly 2-fold for HMP relative to CON heifers. These data demonstrate that prepartum MP overfeeding alters baseline glucose-insulin concentrations in late-pregnant beef heifers and increases colostrum insulin content without having carry-over effects on postpartum glucose-insulin concentrations and IR.

Maternal metabolizable protein restriction during gestation affects the vascular function of maternal and fetal placental arteries in sheep

We hypothesized isocaloric diets low in protein would decrease the sensitivity of caruncular (CAR) and cotyledonary (COT) arteries compared to placental arteries from ewes receiving adequate metabolizable protein (MP) requirements. Pregnant ewes were fed one of three isocaloric dietary treatments that provided 60% (MP60), 80% (MP80), or 100% (MP100) of the MP requirements. Diets were fed from day 100–130 of gestation. In vitro dose response curves to bradykinin (BK), sodium nitroprusside (SNP), potassium chloride (KCl), and phenylephrine (PE) in CAR and COT arteries were performed. As MP decreased, the sensitivity to a low dose of KCl increased (P = 0.05) in the COT arteries. There was an overall treatment effect in the CAR and COT arteries for the BK dose response curve, where CAR arteries of MP80 ewes were more sensitive (P = 0.05) to BK compared with MP60 and MP100 ewes, and COT arteries of MP60 and MP80 ewes were more sensitive (P = 0.01) to BK compared with MP100 ewes. There were no treatment effects (P ≥ 0.09) on the SNP or PE dose response curves in CAR or COT arteries. The mechanism of the BK induced vasodilation needs to be elucidated. Moreover, MP restriction appears to alter placental vascular function, which could help explain the differences in nutrient flux previously reported.

Influence of Maternal Protein Restriction in Primiparous Beef Heifers during Mid- and/or Late-Gestation on Progeny Feedlot Performance and Carcass Characteristics.

Simple SummaryMaternal nutrient restriction in beef cows can impact developmental processes in the fetus, which may influence lifetime performance. If feed is limited, a maternal deficiency in protein and/or energy can occur. As a result, the fetus may receive inadequate levels of nutrients, potentially altering fetal development. In the present study, we evaluated the impact of a metabolizable protein restriction during mid- and/or late-gestation on progeny carcass characteristics. First-calf heifers were provided with a diet that either met their metabolizable protein requirements or caused an 80% restriction in metabolizable protein during mid- and/or late-gestation in a crossover design. Our results suggest that heifers catabolized lean body tissue, but not body fat stores, to overcome the metabolizable protein deficiency. However, restricting metabolizable protein in gestating heifers did not substantially influence the feedlot performance or carcass characteristics of their offspring. The restricted dams may have buffered their offspring from the metabolizable protein limitation during gestation.This study investigated the impacts of metabolizable protein (MP) restriction in primiparous heifers during mid- and/or late-gestation on progeny performance and carcass characteristics. Heifers were allocated to 12 pens in a randomized complete block design. The factorial treatment structure included two stages of gestation (mid- and late-) and two levels of dietary protein (control (CON); ~101% of MP requirements and restricted (RES); ~80% of MP requirements). Half of the pens on each treatment were randomly reassigned to the other treatment at the end of mid-gestation. Progeny were finished in a GrowSafe feeding system and carcass measurements were collected. Gestation treatment x time interactions indicated that MP restriction negatively influenced heifer body weight (BW), body condition score, and longissimus muscle (LM) area (p < 0.05), but not fat thickness (p > 0.05). Treatment did not affect the feeding period, initial or final BW, dry matter intake, or average daily gain of progeny (p > 0.05). The progeny of dams on the RES treatment in late gestation had a greater LM area (p = 0.04), but not when adjusted on a hot carcass weight basis (p > 0.10). Minimal differences in the animal performance and carcass characteristics suggest that the level of MP restriction imposed during mid- and late-gestation in this study did not have a significant developmental programming effect.

Interaction of early metabolizable protein supplementation and virginiamycin on feedlot growth performance and carcass characteristics of calf-fed Holstein steers.

One hundred sixty-eight Holstein steer calves (133.4 ± 7.9 kg) were used to evaluate the influence of virginiamycin (VM) supplementation on cattle growth performance and liver abscess incidence, and the effect of feeding 100% vs. 87% of metabolizable protein (MP) requirements during the initial 112 d on growth performance, efficiency of energy utilization, and carcass characteristics. Steers were balanced by weight and assigned to 28 pens (6 steers/pen). During the initial 112-d feeding period, dietary treatments consisted of two levels of MP (100% vs. 87% of expected requirements) supplemented with or without 22.5 mg/kg VM in a 2 × 2 factorial arrangement. There were no VM × MP supplementation interactions (P ≥ 0.14) on any of the parameters measured in both experiments. Calf-fed Holstein steers supplemented with VM increased (P ≤ 0.03) overall average daily gain (ADG), feed efficiency (G:F), observed/expected net energy (NE) values for maintenance and gain, and final body weight (BW). Cattle fed VM also increased (P ≤ 0.04) carcass weight, dressing percent, and longissimus muscle area. However, there was no effect (P ≥ 0.22) of VM supplementation on any other carcass characteristics. Calf-fed Holstein steers fed 100% MP requirements during the initial 112-d feeding period had greater (P ≤ 0.02) ADG, G:F, observed/expected NE values for maintenance and gain, and live BW compared with steers fed 87% of the expected MP requirements. However, there was no effect (P ≥ 0.17) of MP supply during the initial 112-d period on overall (342 d) growth performance measurements. The incidence of liver abscesses was low (averaging 7.7%) and not affected by dietary treatments. We conclude that, independent of MP supplies, supplemental VM enhances overall growth performance and efficiency of energy utilization of calf-fed Holstein steers.

Milk production and efficiency of utilization of nitrogen, metabolizable protein, and amino acids are affected by protein and energy supplies in dairy cows fed alfalfa-based diets

Alfalfa has a lower fiber digestibility and a greater concentration of degradable protein than grasses. Dairy cows could benefit from an increased digestibility of alfalfa fibers, or from a better match between nitrogen and energy supplies in the rumen. Alfalfa cultivars with improved fiber digestibility represent an opportunity to increase milk production, but no independent studies have tested these cultivars under the agroclimatic conditions of Canada. Moreover, decreasing metabolizable protein (MP) supply could increase N use efficiency while decreasing environmental impact, but it is often associated with a decrease in milk protein yield, possibly caused by a reduced supply of essential AA. This study evaluated the performance of dairy cows fed diets based on a regular or a reduced-lignin alfalfa cultivar and measured the effect of energy levels at low MP supply when digestible His (dHis), Lys (dLys), and Met (dMet) requirements were met. Eight Holstein cows were used in a double 4 × 4 Latin square design, each square representing an alfalfa cultivar. Within each square, 4 diets were tested: the control diet was formulated for an adequate supply of MP and energy (AMP_AE), whereas the 3 other diets were formulated to be deficient in MP (DMP; formulated to meet 90% of the MP requirement) with deficient (94% of requirement: DMP_DE), adequate (99% of requirement: DMP_AE), or excess energy supply (104% of requirement; DMP_EE). Alfalfa cultivars had no significant effect on all measured parameters. As compared with cows receiving AMP_AE, the dry matter intake of cows fed DMP_AE and DMP_EE was not significantly different but decreased for cows fed DMP_DE. The AMP_AE diet provided 103% of MP and 108% of NEL requirements whereas DMP_DE, DMP_AE, and DMP_EE diets provided 84, 87, and 87% of MP and 94, 101, and 107% of NEL requirements, respectively. In contrast to design, feeding DMP_EE resulted in a similar energy supply compared with AMP_AE, although MP supply has been effectively reduced. This resulted in a maintained milk and milk component yields and improved the efficiency of utilization of N, MP, and essential AA. The DMP diets decreased total N excretion, whereas DMP_AE and DMP_EE diets also decreased milk urea-N concentration. Reducing MP supply without negative effects on dairy cow performance is possible when energy, dHis, dLys, and dMet requirements are met. This could reduce N excretion and decrease the environmental impact of milk production.

335 Evaluation of Hempseed Cake on Cattle Performance, Carcass Characteristics and Feeding Behavior in Finishing Diets

Abstract As cannabinoid production continues to increase, there is increasing interest in feeding byproducts of industrial hemp production to livestock. An experiment using crossbred heifers (n = 31; initial BW= 494 kg, SE = 10) was conducted to determine the effects of feeding hempseed cake in a corn-based finishing diet (10% forage) formulated to meet or exceed ruminally degradable and metabolizable protein requirements on growth, performance, carcass characteristics, and feeding behavior. Heifers were assigned randomly to one of two treatments: 1.) diet containing 20% dried distillers grains plus solubles (CON, n = 16), or 2.) diet containing 20% hempseed cake (HEMP, n = 15) on a dry-matter basis. Cattle were housed in two pens, had ad-libitum access to feed and water, and individual intakes and feeding behavior were captured using the Insentec BV feeding system across the feeding period (111 d). Final BW was not different (P = 0.28) between CON (696 kg, SE = 12) and HEMP (683 kg, SE = 12) heifers. Dry matter intake was not different between treatments (P = 0.99), while CON cattle had improved ADG and feed efficiency (G:F; P ≤ 0.04) compared to HEMP cattle. Carcass characteristics were not different (P ≥ 0.20) between treatments for all parameters measured. Control and HEMP cattle were not different (P ≥ 0.34) for number of meals, time spent eating, number of visits to the bunk per day, meal size, or eating rate. Feeding hempseed cake reduced ADG and G:F while having no effect on other performance measures, carcass characteristics, or feeding behavior. Overall, these data suggest hempseed cake could be a viable alternative feed source for ruminants depending on availability and cost. Further understanding of hempseed cakes’ nutrient utilization is critical to determining this products viability as a feedstuff for cattle.

PSIII-23 Maternal metabolizable protein level and rumen-protected methionine impacts on beef steer progeny gene expression in muscle and liver

Abstract This experiment evaluated how maternal metabolizable protein level and rumen-protected methionine supplementation during late gestation impacts expression of genes associated with fetal programming in beef steer offspring. In a 3 x 2 factorial arrangement, 138 Angus crossbred cows were randomly assigned one of three metabolizable protein (MP) treatments (fed to meet 90, 100, or 110% of MP requirements), with(without) 9 g/d of rumen-protected methionine (MET; Smartamine®M, Adisseo Inc.). The isocaloric diets were fed for the last 8 weeks of gestation. Steer progeny (n = 51) were assigned to one of seven pens by weight and received a common corn-based grower diet (58% corn silage, 26% alfalfa haylage, 15% soybean meal) for 47 days, followed by a finisher diet (78% high moisture corn, 12% alfalfa haylage, 8% soybean meal) for 115 ±31.5 days until slaughter. At slaughter, samples of Sternomandibularis muscle and liver were collected and snap-frozen in liquid nitrogen for RNA isolation and analysis of gene expression for growth, myogenic, and adipogenic genes. Data were analyzed using PROC GLIMMIX in SAS, with maternal MP level and MET supplementation as fixed effects, and pen as a random effect. Exceeding maternal MP requirements increased expression of myogenic regulatory factor, myogenin (MYOG; 90% MP: 0.72, 100% MP: 0.94, and 110% MP: 1.00; SEM = 0.083, respectively; P = 0.02) in muscle from steer progeny at slaughter. Methionine supplementation decreased expression of pyruvate kinase (PKM; MET: 0.81, No MET: 1.16; SEM = 0.092; P = 0.02) in muscle, which is associated with lean tissue growth. Maternal nutritional treatment did not influence hepatic gene expression (P ≥ 0.06). These data suggest that maternal nutrition may impact progeny muscle development, while maintaining metabolic function of the liver.

352 A Century and a Half of Nitrogen and Protein Metabolism in Ruminants

Abstract By 1870, we knew plants and animals contained protein, and the participation of protein and urea in animal and human N metabolism was recognized. Nitrogen balance studies had been conducted, and the atomic theory was established. By 1900, research established the concepts of energy and protein metabolic interactions, the role for urea in ruminant metabolism, amino acids as constituents of protein molecules, and enzyme-catalyzed reactions. Research stations were publishing research results and feeding recommendations. By 1950, the concept of biological value was established, and we knew ruminal microorganisms use dietary NPN, degrade dietary protein, and form microbial protein as a source of amino acids for ruminant tissue protein. By 2000, hypothesis-driven, statistically valid experimental designs created quantitative information on metabolizable protein and essential amino acid requirements. Use of surgically altered animals, isotopically labelled molecules, and standardized laboratory analyses created quantitative information on ingestion, ruminal degradability of dietary protein, digestion, absorption, and metabolism of N-containing compounds. Research showed that ruminants respond to manipulation of postruminal amino acid supply. We had elucidated protein composition and structure, the role of protein turnover to determine the concentration of cellular proteins, and the quantitative significance of protein turnover to whole body protein metabolism. The internet and the advent of international symposia provided links among researchers around the globe. By 2020, proteomics and metabolomics enhanced description of underlying control mechanisms related to amino acid metabolism. Research quantified integration of amino acid supply and use among body tissues. Multidisciplinary research teams had created empirical and mechanistic models. Those models currently use or estimate rates and daily amounts of ruminal (in)degradability of dietary protein, ammonia production, urea recycling, microbial protein synthesis, postruminal protein digestion, metabolic fecal nitrogen, and amino acid absorption and metabolism. They predict use of metabolizable amino acids for maintenance, reproduction, postnatal growth, and lactation.

92 Maternal Nutrient Restriction of Primiparous Beef Heifers During Late Gestation Decreases Colostrum Yield and Reduces Calf Vigor

Abstract We hypothesized that late gestational nutrient restriction (NR) would reduce colostrum yield and impair offspring transition to postnatal life. Primiparous, fall-calving crossbred beef heifers (BW: 451 ± 28 [SD] kg; BCS: 5.4 ± 0.7) were individually-fed either 100% (control; CON; n = 12) or 70% (n = 13) of NASEM net energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to parturition. Delivery duration was determined as minutes from first fetal feet expulsion to birth. Calves were reared naturally by their dams and monitored for times from birth to first sternal recumbency, attempt to stand, and stand; vigor scores (1 = very weak, 5 = extremely vigorous) were assigned at 2, 5, 10, and 20 min of age. Total colostrum from one rear quarter was collected pre-suckling. Calf rectal temperatures were recorded at 0, 6, 12, 24, and 48 h postnatally. Data were analyzed with the fixed effects of treatment (single point) or treatment, hour, and their interaction (over time, using repeated measures). Date of calving was a fixed effect; calf sex was included when P &amp;lt; 0.25. Heifers fed CON had greater (P = 0.04) colostrum weight and volume than NR. Although gestational nutrition did not affect (P = 0.72) calf birth weight, calves born to CON heifers had faster (P = 0.02) times to stand and tended to have faster (P = 0.09) times to attempt to stand. Calves from CON heifers had greater (P = 0.05) 20 min vigor scores. Rectal temperatures at 0 h were greater (P = 0.02) in CON calves, but at 24 h were greater (P = 0.04) in NR calves. These data indicate that heifers nutrient restricted during late gestation have reduced colostrum yield and less vigorous calves, which may influence postnatal calf survival.

525 Late-Breaking: Late Gestational Nutrient Restriction of Primiparous Beef Heifers Decreases Milk Yield and Pre-weaning Calf Growth

Abstract Fall-calving Hereford-SimAngus heifers (single-sired; BW: 451 ± 28 [SD] kg; BCS: 5.4 ± 0.7) bred to a single sire were individually-fed 100% (control; CON; n = 12) or 70% (nutrient restricted; NR; n = 13) of NASEM net energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Post-calving, all females were limit-fed chopped tall-fescue hay supplemented to meet lactational nutrient requirements in Calan gates to constrain calves’ diets to milk only until d 147. Four-hour milk yields were measured 5 times; calf size was determined every 21 d. Data were analyzed with treatment, calving date, and calf sex (when P &amp;lt; 0.25) as fixed effects; day and day x treatment were included for milk yield. From calving to d 147, CON cows had greater (P ≤ 0.003) BW, BCS, and backfat, but NR cows gained more (P ≤ 0.004) BW, BCS, and backfat. Milk weight and volume was 15% less (main effect; P &amp;lt; 0.04) for NR cows. Calf size did not differ at birth (P ≥ 0.27). From d 42 to 147, calves born to NR dams had lower (P ≤ 0.02) BW. Heart, abdominal, and flank girths were less (P ≤ 0.07) for NR calves through d 147. Calf ribeye area tended to be less (P ≤ 0.11) in NR calves at d 42, 84, and 126. Nutrient restricted calves had less shoulder to rump length (d 63 to 147; P ≤ 0.08), shoulder height (d 63 to 126; P ≤ 0.02), cannon length (d 42 to 105 and 147; P ≤ 0.09), and cannon circumference (d 63 and 105 to 147; P ≤ 0.06). These data indicate that even when dams are fed to meet lactational requirements, milk yield and calf growth are reduced by late gestational nutrient restriction.