Metabolizable Protein Requirements Research Articles

76 Does supplemental protein and rumen-protected methionine improve performance and digestibility during late-gestation in beef cows?

Abstract Methionine (MET) is likely the first limiting amino acid in low-protein forages fed to beef cattle during late-gestation. Therefore, the objective of this study was to determine if supplemental protein and rumen-protected MET improve cow performance and apparent tract digestibility (TTD) during late-gestation. This study used 147 late-gestation Angus crossbred cows and heifers in a 3x2 factorial arrangement for dietary treatments. The cattle were randomly assigned to one of six diets formulated to 90, 100 or 110% of metabolizable protein (MP) requirements (NRC, 2016), with (without) 9 g/d of rumen-protected MET (MetaSmart, Adisseo Inc.). These diets were fed for approximately 8 wks before calving. All data was analyzed as a randomized block design using SAS 9.4 PROC GLIMMIX procedure. Cows fed at 90% MP requirements lost body weight (BW), while cows fed at 100% and 110% MP requirements maintained and (or) gained BW over the trial (P = 0.02). Similarly, cows fed at 90% MP requirements lost more pregnancy corrected BW than cows fed at 100% and 110% MP requirements (P = 0.01). However, supplemental MET did not affect body weight gains (P > 0.07). Cows and heifers fed at 90% MP requirements had reduced TTD for crude protein compared to cattle fed to 110% MP requirements (P < 0.001), MET supplementation did not impact TTD (P > 0.20). Additionally, cattle fed at 90% MP requirements had increased serum cholesterol and reduced urea concentrations compared to cows fed to 100% and 110% MP requirements (P < 0.0001). MET supplementation increased serum concentrations for glucose, isoleucine, leucine, lysine, serine, threonine and valine (P < 0.02). Calf birth weights were not significantly impacted by dietary treatment (P > 0.31). Feeding cows above their MP requirements may improve late-gestation performance and CP digestibility. Supplemental MET may increase amino acid utilization but did not improve beef cow performance or digestibility parameters measured in late-gestation.

393 Beef cow antepartum glucose-insulin kinetics are altered by overfeeding metabolizable protein during late gestation and influenced by test-day relative to calving

Abstract The objective of this study was to determine whether antepartum glucose-insulin kinetics were affected when primiparous Hereford-cross heifers were fed diets containing 100 (CON; n = 10) or 133% (HMP; n = 11) of their metabolizable protein requirements from d -55.3 ± 3.7 until parturition. Intravenous glucose tolerance tests (IVGTT) were performed on d -5.4 and -7.1 ± 1.3 (CON and HMP, respectively; P = 0.34) by collecting baseline (-10 min) plasma, infusing 1.36 g glucose/kg BW0.75 via a jugular catheter, and subsequently sampling plasma for analysis of glucose and insulin. Data were analyzed with PROC GLIMMIX as a randomized block design with the fixed effects of diet, time (minute), and diet × time, considering cow (block) as a random effect. Pearson correlations were performed for IVGTT variables and test-day relative to parturition. Differences and trends were declared at P < 0.05 and 0.05 ≤ P < 0.10, respectively. Basal glucose was 13.5% greater (P = 0.048) and basal insulin tended to be 28.8% greater (P = 0.068) for HMP than CON heifers. Plasma glucose (-10 to 120 min) was greater (P = 0.047) for HMP than CON, whereas insulin was not (P = 0.54). Glucose and insulin were respectively elevated (time: P < 0.001) at 0 and 5 and 5 to 20 min and both equilibrated to baseline by 90- and 120-min. Diet × time tended to affect (P = 0.061) the glucose:insulin ratio. Test-day was correlated with time-to-max insulin (ρ = 0.60, P = 0.006), insulin clearance rate (ρ = 0.48, P = 0.027), and glucose area-under-the-curve (ρ = -0.47, P = 0.031). Time relative to calving can influence antepartum glucose-insulin kinetics. Oversupplying metabolizable protein increased baseline glucose and insulin and glucose throughout the IVGTT. Antepartum beef cattle may have altered energy partitioning that is responsive to protein consumption.

398 Effects of protein level and supplemental methionine in late-gestation on colostrum quality and passive immunity transfer in beef cattle

Abstract The objective of this study was to evaluate the influence of metabolizable protein (MP) level and supplemental rumen-protected methionine (RPM) on colostrum quality and passive immunity transfer from beef cows fed during late-gestation. One hundred and forty-seven pregnant Angus crossbred cows and heifers were randomly assigned to one of six dietary treatments based on a 3 x 2 factorial arrangement. Diets included feeding to 90%, 100% and 110% MP requirements (NRC, 2016), offered with (without) 9 g/d of RPM. Cattle were individually fed a partially mixed ration (60% haylage/40% straw for cows; 70% haylage/30% straw for heifers) with supplements top-dressed daily for approximately 56 d prior to calving. Immediately after calving, a colostrum sample was collected from each dam for analysis of milk components, total protein, and IgG concentrations. Two d post-calving, serum samples were collected from each calf for analysis of total protein and IgG concentrations. A refractometer was used to estimate total protein as a preliminary estimate of the transfer of maternal IgG and total IgG concentrations were later determined using Radial Immunodiffusion (RID). Data were analyzed as a completely randomized block design using Proc GLIMMIX in SAS. Level of MP, RPM, and their interaction did not influence concentrations of fat, protein, BHB or SCC in colostrum (P ≥ 0.12). Supplementation of RPM decreased concentrations of MUN (45.92 vs. 54.51 ±3.17 mg/dl; P = 0.04), but did not change IgG (14.66 vs. 15.90 ±0.87 g/dl; P = 0.29). While MP level during gestation did not affect total protein or IgG concentrations in calf serum (P ≥ 0.64), providing supplemental RPM decreased total protein (5.79 vs. 6.33 ±0.13 g/dl; P = 0.002) and IgG concentrations in calf serum (3.44 vs. 4.30 ±0.25 g/dl; P = 0.01). These results suggest that providing supplemental methionine for beef cows during gestation may alter colostrum quality and decrease serum protein and IgG in offspring.

394 Exploring the relationships between cow-calf management systems as affected by protein/methionine nutrition during gestation on the performance of cow-calf pairs prior to weaning

Abstract A three-way factorial arrangement was used to assess impacts of protein/methionine nutrition during gestation and two lactational management systems on performance of cow-calf pairs pre-weaning. 140 crossbred beef cows were managed in drylot and randomly assigned to one of six nutritional treatments during the third trimester of gestation. Cows were fed to meet 110% (HP), 100% (MP), or 90% (LP) of metabolizable protein requirements for late-gestation (NRC, 2016), with(without) rumen-protected methionine (RPM) for 8 weeks prior to parturition. Post-partum, cow-calf pairs were managed in drylot (DL) and fed ad libitum, a ration formulated to meet lactational nutrient requirements, or rotationally grazed on pasture (PAS). Cow body weights (BW) and body condition scores (BCS) and calf BW were recorded at regular intervals. All data were analyzed using PROC GLIMMIX (SAS v9.4). HP cows were heaviest at calving (P = 0.02), but calf birthweight was unaffected by gestational nutrition (P > 0.19). Gestational nutrition did not impact cow conception rate (CR), or calf BW and ADG (P > 0.17). Lactational management system (PAS, DL) did not affect cow BCS or CR (P > 0.13), but impacted cow and calf BW and ADG. PAS calves were heavier, had greater ADG, and heavier weaning BW than DL calves (P < 0.02). This came at the expense of BW loss throughout lactation and lower ADG for PAS cows, versus BW gains and greater ADG for DL cows (P < 0.0001). An interaction between protein level and RPM supplementation was present for cow BW at calving and weaning, and BW change throughout lactation (P < 0.04), with tendencies for interactions for cow ADG and BCS (P < 0.09). Overall, prepartum protein/methionine supplementation did not affect calf performance prior to weaning, but may have affected cow performance during lactation. Rotationally grazing cow-calf pairs on pasture improved pre-weaning calf gains, but reduced cow gains throughout lactation.

344 Protein supplementation during gestation enhances offspring growth performance of Wagyu sired but not Angus sired cattle

Abstract Wheat straw based diets are commonly fed to pregnant cows in Pacific Northwest, which may not meet protein requirements, but its impact on growth performance of offspring is unclear. Angus is the most common breed in this region while Wagyu is gaining popularity due to enhanced meat quality. The interaction between maternal nutrition and breed on growth performance of calves was examined. Angus cross cows (621 ± 73kg) were selected and randomly allotted to two groups and inseminated with either Angus or Wagyu semen. At 185 days of pregnancy, cows in each group were further separated into two-subgroups: control diet (CON, n = 21) received 85 % of the NRC metabolizable protein requirement, and protein supplemented group (SUPP, n = 21) received 108 % of requirement until calving. Then, cows and calves were moved to pastures and the cow calf pairs grazed rangeland. After weaning, calves were backgrounded, finished, and harvested at a body weight of 576.5 ± 16.6 kg. There were no differences between CON and SUPP in birth weight. However, SUPP increased 205 days adjusted weaning weight of Wagyu progeny (P < 0.01) and average daily gain (ADG) during the period of birth to weaning (P < 0.05) compared to calves from cows fed the CON diet. Moreover, Angus progeny had higher 205 days adjusted weaning weight (P < 0.01) and ADG during birth to weaning than Wagyu fed SUPP diet (P = 0.056). In both treatments, Angus gained weight faster and showed higher weight before finishing than Wagyu (P < 0.05). Angus had higher harvest weight (P < 0.01) and maternal protein supplementation tended to increase the dressing percent (P = 0.06). In conclusion, maternal protein supplementation enhanced growth performance of Wagyu but not Angus cattle, and Angus grew faster than Wagyu sired cattle. (Supported by USDA-NIFA grants 2015-67015-23219/2016-68006-24634 to MD)

274 Improved beef quality and yield in Wagyu compared to Angus sired cattle unaffected by protein supplementation during the late gestation

Abstract Maternal nutrition during the late gestation affects marbling fat in offspring. Wagyu cattle are well known for their very high marbling with more unsaturated fatty acid contents, but they grow slower than Angus cattle. The interaction between maternal diet and breed on marbling fat development is unclear. To examine, Angus cows (621 ± 73kg) were selected and separated into two groups, bred with either Angus or Wagyu semen. During the last 90 d of gestation, cows in each group were further separated and received either a low protein diet (85% of the NRC metabolizable protein requirement), which mimics the protein intake common in Northwestern region when fed a wheat straw based diet, or a high protein diet (108% NRC requirement). All progeny were managed together and harvested at a final body weight of 576.5± 16.6 kg. For Wagyu sired offspring, marbling score and quality grade was higher than Angus (P < 0.01), and also had higher Ribeye area (P = 0.07). The marbling scores were higher for the low protein diet for all except Wagyu steers. No difference was detected in KPH fat and the yield grade was higher for Wagyu sired cattle than Angus (P < 0.01). In both diets, Angus offspring showed higher shear force (P < 0.05). When grouped according to sex, higher marbling was observed in heifers (P < 0.01). No difference was found in cooking yield, drip loss, but Wagyu sired offspring had thicker back fat than Angus (P < 0.01). Within the high protein diet, Wagyu beef had higher linoleic acid content compared to Angus (P < 0.05). In conclusion, Wagyu sired cattle had better quality and yield compared to Angus sired, and protein supplementation during the late gestation had no major effect on beef quality. (Supported by the USDA-NIFA grants 2015-67015-23219/2016-68006-24634 to MD)

Energy and protein requirements of woolless sheep under tropical conditions

The objective of this study was to determine the energy and protein requirements for maintenance and weight gain of growing woolless sheep and, in addition, to estimate the shrunk body weight (SBW) and empty body weight (EBW) of the animals according to their body weight (BW) in the fed state. Data from 150 animals from three comparative slaughter experiments with confined castrated sheep averaging 5 ± 0.96 months of age and similar BW (20.74 ± 2.99 kg) were used. Three models were evaluated to estimate EBW from SBW: linear, linear with intercept and non-linear. The following requirements were estimated: net energy for maintenance (NEm), metabolizable for maintenance (MEm), net energy for gain (NEg), efficiency of use of metabolizable energy for gain, metabolizable protein requirement for maintenance (MPm), net protein requirement for gain (NPg), and efficiency of use of metabolizable protein for gain (k). Fasting losses corresponded to 6.18% of BW and the better model to establish the relationship between SBW and EBW was nonlinear. The NEm and MEm were 70.44 and 109.34 kcal/kg EBW0.75/day, respectively. For NEg, the adjusted model was based on the ratio of the energy retained as a function of the EBW and the desired empty body weight gain (EBG). Considering two lambs weighing 15 kg and 30 kg with a daily gain of 100 g, the estimated NEg is 181 and 360 kcal/kg EBW0.75/day, respectively. The estimated kg was 0.407. For MPm, the value of 3.19 g/kg EBW0.75/day was estimated. The estimated NPg for animals of 15 and 30 kg, with the same gain rate was 13.13 and 13.61 g/day, respectively, which corresponds to the protein concentration in gain of 170 and 161 g/kg EBG, and efficiency of use of the metabolizable protein for gain ranging from 0.66 to 0.41. The nutritional requirements of woolless sheep did not follow the standards assumed by the international feeding systems, except for the energy requirements for maintenance and efficiency of use of the metabolizable energy for maintenance, which did not differ. The losses represented by the gastrointestinal tract (GIT) after fasting and slaughtering periods are higher in woolless sheep compared to those presented by the international feeding systems.

Energy and nitrogen balance of dairy cattle as affected by provision of different essential amino acid profiles at the same metabolizable protein supply

Amino acid composition of metabolizable protein (MP) is important in dairy cattle diets, but effects of AA imbalances on energy and N utilization are unclear. This study determined the effect of different AA profiles within a constant supplemental MP level on whole-body energy and N partitioning in dairy cattle. Five rumen-fistulated Holstein-Friesian dairy cows (2.8 ± 0.4 lactations; 81 ± 11 d in milk; mean ± standard deviation) were randomly assigned to a 5 × 5 Latin square design in which each experimental period consisted of 5 d of continuous abomasal infusion followed by 2 d of rest. A total mixed ration consisting of 58% corn silage, 16% alfalfa hay, and 26% concentrate (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 by individual cow. Abomasal infusion treatments were saline (SAL) or 562 g/d of essential AA delivered in 4 profiles where individual AA content corresponded to their relative content in casein. The profiles were (1) a complete essential amino acid 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). The experiment was conducted in climate respiration chambers to determine energy and N balance in conjunction with milk production and composition, digestibility, and plasma constituents. Compared with SAL, infusion of EAAC increased milk, protein, and lactose yield, increased energy retained as body protein, and did not affect milk N efficiency. Total N intake and urine N output was higher with all AA infusions relative to SAL. Compared with EAAC, infusions of GR1+ILV and GR1+ALT produced the same milk yield and the same yield and content of milk fat, protein, and lactose, and had similar energy and N retention. Milk N efficiency was not different between EAAC and GR1+ILV, but was lower with GR1+ALT compared with EAAC, and tended to be lower with GR1+ALT compared with GR1+ILV. Infusion of ILV tended to decrease dry matter intake compared with the other AA infusions. Milk production and composition was not different between ILV and SAL. Compared with EAAC, infusion of ILV decreased or tended to decrease milk, protein, and lactose yields and milk protein content, and increased milk fat and lactose content. Milk N efficiency decreased with ILV compared with SAL, EAAC, and GR1+ILV. Milk urea concentration was not affected by essential amino acid (EAA) infusions. Plasma urea concentration did not differ between EAAC and SAL, tended to increase with ILV and GR1+ILV over SAL, and increased with GR1+ALT compared with EAAC and SAL. In conclusion, removing Arg, Lys, and Thr or removing Ile, Leu, and Val from a complete EAA profile when the total amount of EAA infused remained constant did not impair milk production, but milk N efficiency decreased when Ile, Leu, and Val were absent. Infusion of only Ile, Leu, and Val decreased milk protein yield and content and reduced milk N efficiency compared with a complete EAA profile.

335 Metabolizable protein requirement of lightweight beef calves

Abstract The objective was to assess the metabolizable protein (MP) requirements of lightweight beef steers. The 2016 Beef Cattle Nutrient Requirements Model (BCNRM) prediction of MP requirements in lightweight beef steers (less than 250 kg) is limited by available performance data in beef calves. Fall born Angus × Simmental crossbred steers (n = 172; BW = 153 kg) were weaned at 70 d of age (± 26 d), backgrounded 73 d, implanted with Component TE-IS, blocked by BW as light (96–163 kg) or heavy (163–215 kg), and assigned to one of four treatments for 56 d. Treatment diets provided MP at: 0.59 (MP1), 0.69 (MP2), 0.85 (MP3), and 0.91 kg per d (MP4) based on observed DMI. Energy was similar across all treatments at 2.14 Mcal/kg ME. Shrunk body weights were collected on d 0 and 56 to estimate performance. Dry matter intake was affected (P < 0.01) by treatment and increased (linear; P < 0.01) with greater provision of MP. As a percent of shrunk body weight, DMI averaged 2.8% and tended (linear; P = 0.07) to increase with MP. Based on observed DMI, ADG for MP1, MP2, MP3, and MP4 was predicted using the BCNRM at 1.15, 1.55, 1.99, and 1.98 kg, respectively. Observed ADG increased quadratically (P = 0.01) with MP1, MP2, MP3, and MP4 gaining 1.86, 2.13, 2.3, and 2.3 kg, respectively. Final BW increased (quadratic; P = 0.02) with greater MP as MP1, MP2, MP3, and MP4 were 258, 273, 282, and 284 kg, respectively. Gain:feed increased quadratically (P = 0.04) with observed values for MP1, MP2, MP3, and MP4 being 0.323, 0.357, 0.359, and 0.360, respectively. Steer ADG response exceeded BCNRM predictions by 29%. Data suggest MP requirements of lightweight beef steers (BW = 213 kg) are 0.85 kg per d to achieve 2.3 kg ADG when fed a 2.14 Mcal/kg ME diet.

Effects of jugular infusions of isoleucine, leucine, methionine, threonine, and other amino acids on insulin and glucagon concentrations, mammalian target of rapamycin (mTOR) signaling, and lactational performance in goats

The supply and profile of absorbed AA may affect milk protein synthesis through hormonal changes and mammalian target of rapamycin (mTOR) signaling pathways; and Ile, Leu, Met, and Thr (ILMT) are the 4 AA that have been reported to have the greatest effect on mammary mTOR signaling. The extent to which ILMT and the other remaining AA (RAA) differ in their effects on milk protein synthesis needs to be systematically investigated. In this study, 5 lactating goats, averaging 120 ± 10 d in milk, fitted with jugular vein and carotid artery catheters, were fasted for 24 h, followed by intravenous infusions of a mixture containing AA and glucose for 8 h in a 5 × 5 Latin square design. The AA mixtures were formulated according to the profile of casein. The amounts of AA infused were calculated based on supplies of AA when metabolizable protein (MP) was at requirement (MR). Treatments were an infusate containing glucose without AA (NTAA); an infusate containing 3 × the MR of Ile, Leu, Met and Thr (3F0R); and infusates containing 3F0R plus 1, 2, or 3 × MR of RAA (3F1R, 3F2R, and 3F3R, respectively) according to amounts provided when fed to meet MP requirements for maintenance and lactation for each goat. Milk, arterial blood, and mammary tissue samples were collected immediately after halting the infusion. Relative to NTAA, supplementation of ILMT tended to increase milk protein production and plasma glucose concentrations, and increased milk and lactose production, but had no effects on production or content of milk fat. Graded supplementation of RAA tended to quadratically affect production of milk and lactose. Arterial glucose and glucagon concentrations decreased linearly, and plasma insulin concentrations decreased quadratically with increased RAA. Mammary p70-S6K1 phosphorylation was decreased by addition of ILMT compared with NTAA but increased linearly with increased RAA infusion. Furthermore, EIF4EBP1 gene expression was much lower for 3F-treated goats than for the NTAA treatment. Both MTOR and RPS6KB1 gene expressions were decreased quadratically with increased RAA supply. These results suggested that short-term milk protein yield tended to be increased by elevated ILMT availability, and this trend was not explained by variations in mammary mTOR signaling or pancreatic hormone secretions, whereas graded increase of RAA in combination with ILMT appeared to regulate the efficiency of conversion of glucose to lactose in a manner not involving milk protein production.

Mammary gland metabolite utilization in response to exogenous glucose or long-chain fatty acids at low and high metabolizable protein levels

We investigated mammary gland metabolism in lactating dairy cattle in response to energy from glucogenic (glucose; GG) or lipogenic (palm olein; LG) substrates at low (LMP) and high (HMP) metabolizable protein levels. According to a 6 × 6 Latin square design, 6 rumen-fistulated second-lactation Holstein-Friesian dairy cows (97 ± 13 d in milk) were abomasally infused with saline (LMP-C); isoenergetic infusions (digestible energy basis) of 1,319 g/d glucose (LMP-GG), 676 g/d palm olein (LMP-LG), or 844 g/d essential AA (EAA; HMP-C); or isoenergetic infusions of 1,319 g/d glucose + 844 g/d EAA (HMP-GG) or 676 g/d palm olein + 844 g/d EAA (HMP-LG). Each experimental period consisted of 5 d of continuous infusion followed by 2 d of rest. A total mixed ration (42% corn silage, 31% grass silage, and 27% concentrate on a dry matter basis) formulated to meet 100 and 83% of net energy and metabolizable protein requirements, respectively, was fed at 90% of ad libitum intake by individual cow. Arterial and venous blood samples were collected on d 5 of each period. Infusing GG or LG at the HMP level did not affect milk yield or composition differently than at the LMP level. Neither GG nor LG infusion stimulated milk protein or lactose yield, but fat yield tended to decrease with GG and tended to increase with LG. Infusion of GG increased arterial plasma concentrations of glucose and insulin and decreased concentrations of β-hydroxybutyrate (BHB), nonesterified fatty acids, long-chain fatty acids (LCFA), total AA, EAA, and group 2 AA. Infusion of LG increased arterial triacylglycerides (TAG) and LCFA but did not affect EAA concentrations. Compared with the LMP level, the HMP level increased arterial concentrations of BHB, urea, and all EAA groups and decreased the concentration of total non-EAA. Mammary plasma flow increased with GG and was not affected by LG or protein level. Uptake and clearance of total EAA and group 2 AA were affected or tended to be affected by GG × AA interactions, with their uptakes being lower and their clearances higher with GG, but only at the LMP level. Infusion of LG did not affect uptake or clearance of any AA group. The HMP level increased uptake and decreased clearance of all EAA groups and decreased non-EAA uptake. Infusion of GG tended to increase mammary glucose uptake, and tended to decrease BHB uptake only at the LMP level. Infusion of LG increased mammary uptake of TAG and LCFA and increased or tended to increase clearance of TAG and LCFA. We suspect GG increased mammary plasma flow to maintain intramammary energy and AA balance and stimulated lipogenesis in adipose, accounting for depressed arterial BHB and group 2 AA concentrations. Mammary glucose uptake did not cover estimated requirements for lactose and fat synthesis at the HMP level, except during HMP-GG infusion. Results of this study illustrate flexibility in mammary metabolite utilization when absorptive supply of glucogenic, lipogenic, and aminogenic substrate is increased.

Influence of maternal protein restriction in primiparous heifers during mid- and/or late-gestation on meat quality and fatty acid profile of progeny

The objective of this study was to evaluate the influence of metabolizable protein (MP) restriction in mid- and/or late-gestation on meat quality characteristics of progeny. Heifers were assigned to 2 levels of dietary protein (control [CON], 102% of MP requirements; or restricted [RES], 80% of MP requirements) at 2 stages of gestation (mid-gestation [MID] and late-gestation [LATE]) in a Balaam's Design crossover treatment structure resulting in 4 treatment combinations (CON-CON, CON-RES, RES-CON, RES-RES). A carryover effect of MID MP treatment on LATE CON indicated CON-CON steaks were more tender (P < .001) than RES CON. Mid-gestation restriction resulted in progeny with increased (P < .05) carcass water, soft tissue moisture, and decreased soft tissue fat percentage compared with progeny from dams receiving MID CON. Reduced maternal MP also differentially influenced the fatty acid profiles of progeny. Results suggest it is possible for progeny to overcome a moderate gestational MP restriction with minimal impacts on carcass composition or meat characteristics.

Effects of crude protein and undegradable intake protein on growth performance, nutrient utilization, and rumen fermentation in growing Thai-indigenous beef cattle

The objective of this study was to investigate growth performance, nutrients apparent digestibility, nitrogen utilization, rumen fermentation, and rumen microorganism of growing Thai-indigenous beef cattle receiving different levels of crude protein (CP) and undegradable intake protein (UIP) diets. Eighteen healthy growing Thai-indigenous beef cattle were used in a 2 × 3 factorial randomized complete block design (RCBD). There were six treatments: two levels of CP (10% and 12% of dry matter (DM)) and three levels of UIP (15%, 25%, and 35% of CP). The results indicated that dry matter intake (DMI) and average daily gain (ADG) increased linearly (P < 0.01) with increasing UIP level. The apparent digestibility of DM, organic matter (OM), acid detergent fiber (ADF), and neutral detergent fiber (NDF); rumen fermentation parameters; microbes counts; and microbial nitrogen synthesis (MNS) were unaffected (P > 0.05) by CP and UIP levels. The nitrogen (N) intake and N retained increased linearly (P < 0.01) with increasing UIP level. Specifically, the metabolizable protein (MP) requirement of 1g/kg BW0.75 gain was 0.34g MP/kg BW0.75; the 10% dietary CP of DM was able to meet animals' normal nutrition requirements and 6.5% DIP of DM can provide adequate N source for the requirement of rumen microbe growth in. Collectively, it was indicated that the supplemental level of 10% CP and the ratio of UIP to DIP was 35:65 in diets shown the best growth performance for growing Thai-indigenous beef cattle under the conditions in the current study.

Predicting post-absorptive protein and amino acid metabolism

ABSTRACT Sustainable production of adequate quantities of food to support a growing human population is a worldwide goal. Under current feeding conditions in the United States, dairy cattle convert dietary nitrogen to milk nitrogen with 25% efficiency. The remaining 75% is excreted, which contributes to air and water quality problems and reduces economic performance of the industry. Efficiency could be improved to 29% if protein was given to just meet current NRC requirements. Additional improvements may be achievable, but only with improved knowledge of amino acid (AA) requirements. The current metabolizable protein requirement model overestimates true requirements due to lack of knowledge of AA supply and requirements and to intrinsic limitations in system data and assumptions. Existing protein supply models based on passage and degradation rates are biased, which undermines predictions of AA supply. The use of an equation driven solely by protein solubility of each ingredient in the diet with no consideration of the effects of passage rate yielded unbiased predictions with significant improvements in precision. However, this still leaves a problem in predicting the AA composition of the ruminally undegraded protein (RUP). Current models generally assume that RUP AA composition equals the parent ingredient composition, but assessments of RUP AA composition indicate that this is false. Thus, bias is being introduced into predictions of the absorbed AA supply, which hampers derivation of estimates of AA digestion and absorption from the small intestine. Emerging isotope-based methods hold promise in allowing assessment of AA availability from individual ingredients in vivo, which will allow construction of a database of true ingredient AA bioavailabilities. These efforts will eventually allow development of more robust predictions of AA supply. On the AA requirement side, numerous data indicate that the efficiency of metabolizable protein use for lactation is variable and maximally 45%, whereas most models assume an efficiency of 65% or greater. The efficiencies of individual AA are centered on the protein efficiency value with those lower in efficiency, likely being provided in large excess. A better representation of the use efficiency of individual AA would allow improvements in overall animal N efficiency. Variable efficiency is driven by regulatory mechanisms that control protein synthesis in response to the supply of energy and individual AA and circulating concentrations of hormones and these drivers act independently and additively. Under this theory, protein synthesis can respond to nutrients other than the one identified as most limiting. Reflecting this regulation in our requirement models will allow better prediction of AA efficiency and enable construction of diets that minimize excess of individual AA by optimizing the energy and hormonal signals to improve N efficiency. Models of such an interacting system have been developed and shown to be superior in performance to models based on current paradigms.

Energy and nitrogen partitioning in dairy cows at low or high metabolizable protein levels is affected differently by postrumen glucogenic and lipogenic substrates

This study tested the effects of energy from glucogenic (glucose; GG) or lipogenic (palm olein; LG) substrates at low (LMP) and high (HMP) metabolizable protein levels on whole-body energy and N partitioning of dairy cattle. Six rumen-fistulated, second-lactation Holstein-Friesian dairy cows (97 ± 13 d in milk) were randomly assigned to a 6 × 6 Latin square design in which each experimental period consisted of 5 d of continuous abomasal infusion followed by 2 d of rest. A total mixed ration consisting of 42% corn silage, 31% grass silage, and 27% concentrate (dry matter basis) was formulated to meet 100 and 83% of net energy and metabolizable protein requirements, respectively, and was fed at 90% of ad libitum intake by individual cow. Abomasal infusion treatments were saline (LMP-C), isoenergetic infusions (digestible energy basis) of 1,319 g/d of glucose (LMP-GG), 676 g/d of palm olein (LMP-LG; major fatty acid constituents are palmitic, oleic, and linoleic acid), or 844 g/d of essential AA (HMP-C), or isoenergetic infusions of 1,319 g/d of glucose + 844 g/d of essential AA (HMP-GG) or 676 g/d of palm olein + 844 g/d of essential AA (HMP-LG). The experiment was conducted in climate respiration chambers to determine energy and N balance in conjunction with milk production and composition, nutrient digestibility, and plasma constituents. Infusion of GG and LG decreased dry matter intake, but total gross energy intake from the diet plus infusions was not affected by GG or LG. Furthermore, GG or LG did not affect total milk, protein, or lactose yields. Infusing GG or LG at the HMP level did not affect milk production differently than at the LMP level. Infusion of GG stimulated energy retention in body tissue, increased plasma glucose and insulin concentrations, decreased lipogenic metabolites in plasma, and decreased milk fat yield and milk energy output. Nitrogen intake decreased and milk N efficiency increased in response to GG, and N retention was not affected. Infusion of LG tended to increase metabolizable energy intake, increased milk fat yield and milk energy output, increased plasma triacylglycerides and long-chain fatty acid concentrations, and had no effect on energy retention. Infusion of LG decreased N intake but did not affect milk N efficiency or N retention. Compared with the LMP level, the HMP level increased dry matter intake, gross and metabolizable energy intake, and total milk, fat, protein, and lactose yields. Milk energy output increased at the HMP level, and protein level did not affect total energy retention. Heat production increased at the HMP level, but only when GG and LG were infused. The HMP level increased N intake, milk N output, and plasma urea concentration, tended to increase N retention, and decreased milk N efficiency. Regardless of protein level, GG promoted energy retention and improved milk N efficiency, but not through increased milk protein yield. Infusion of LG partitioned extra energy intake into milk and had no effect on milk N efficiency.

Nitrate improves ammonia incorporation into rumen microbial protein in lactating dairy cows fed a low-protein diet

Generation of ammonia from nitrate reduction is slower compared with urea hydrolysis and may be more efficiently incorporated into ruminal microbial protein. We hypothesized that nitrate supplementation could increase ammonia incorporation into microbial protein in the rumen compared with urea supplementation of a low-protein diet fed to lactating dairy cows. Eight multiparous Chinese Holstein dairy cows were used in a crossover design to investigate the effect of nitrate or an isonitrogenous urea inclusion in the basal low-protein diet on rumen fermentation, milk yield, and ruminal microbial community in dairy cows fed a low-protein diet in comparison with an isonitrogenous urea control. Eight lactating cows were blocked in 4 pairs according to days in milk, parity, and milk yield and allocated to urea (7.0 g urea/kg of dry matter of basal diet) or nitrate (14.6 g of NO3-/kg of dry matter of basal diet, supplemented as sodium nitrate) treatments, which were formulated on 75% of metabolizable protein requirements. Nitrate supplementation decreased ammonia concentration in the rumen liquids (-33.1%) and plasma (-30.6%) as well as methane emissions (-15.0%) and increased dissolved hydrogen concentration (102%), microbial N (22.8%), propionate molar percentage, milk yield, and 16S rRNA gene copies of Selenomonas ruminantium. Ruminal dissolved hydrogen was positively correlated with the molar proportion of propionate (r = 0.57), and negatively correlated with acetate-to-propionate ratio (r = -0.57) and estimated net metabolic hydrogen production relative to total VFA produced (r = -0.58). Nitrate reduction to ammonia redirected metabolic hydrogen away from methanogenesis, enhanced ammonia incorporation into rumen microbial protein, and shifted fermentation from acetate to propionate, along with increasing S. ruminantium 16S rRNA gene copies, likely leading to the increased milk yield.

Predicting milk protein responses and the requirement of metabolizable protein by lactating dairy cows

The objective of this study was to develop a modeling framework to predict milk protein yield responses to varying metabolizable protein (MP) supplies and to determine the requirement of MP by lactating dairy cows. The logistic curve was used to model milk protein yield while accounting for a variable efficiency of MP utilization and between-study variability. Models were developed with databases from 2 recently published meta-analyses and based on either total MP supply or MP supply available for milk production. All models provided reasonable fit to data, with root mean square prediction error ranging from 18 to 20% of the average milk protein yield. The estimated horizontal asymptotes were 1.17 (posterior SD = 0.02) and 1.55 (posterior SD = 0.06) in the 2 databases, suggesting that the limiting milk protein yield, as MP supply increases, converges to 1.17 or 1.55 kg/d in the environments determined by the 2 databases. The observed efficiencies ranged from 0.75 to 0.18 when total MP supply was used as the denominator and above 1 to 0.24 when the MP supply available for milk production was used as the denominator. The predicted efficiencies were in good agreement with the data, decreasing nonlinearly with the MP supply. The MP requirement was calculated with a function constructed with the inverse of the logistic model and modified at regions of maximum marginal efficiency and minimum second derivative. This strategy assumes that the MP solution, or the MP needed to predict a given protein yield in the fitted logistic curve, determines the MP requirement for maintenance and lactation. Requirements calculated with the independent variable as total MP supply refer to the total requirement of maintenance plus lactation, whereas the requirement from models based on MP supply available for milk production are referent to the MP required only for lactation. The requirements were, on average, slightly smaller than the ones predicted by the current Northern American feeding system for dairy cows at lower protein yields and greater than currently recommended at high yields.

Maintenance and growth requirements in male and female hair lambs

An experiment was conducted to evaluate the energy and protein requirements of intact male, castrated male and female Morada Nova lambs. The animals were distributed in a completely randomized 3×3 factorial design with three sexes (15 intact males, 16 castrated males and 16 females) and three levels of dietary restriction (ad libitum, 30% and 60% feed restriction) with an initial body weight (BW) of 14.50±0.89kg. Four animals per sex were slaughtered at the start of the trial as a baseline group. When the mean BW in the ad libitum treatment reached 28kg, at day 120 of the experiment, all lambs were slaughtered. For all sexes, the net energy requirement for maintenance was 73.0kcal/kg0.75 empty body weight (EBW)/d (P=0.17). The metabolizable energy efficiency for maintenance (km) was 0.58. The metabolizable energy efficiency utilization for gain (kg) was 0.36; 0.25 and 0.28 for intact males, castrated males and females, respectively. The net energy requirement for gain (NEg) differed (P<0.01) between sexes. The NEg was 0.191, 0.198 and 0.276Mcal/kg0.75 EBW/d for intact males, castrated males and females, respectively, with a BW of 20kg and a body weight gain (BWG) of 100g. The net and metabolizable protein requirements for maintenance obtained for lambs were 1.06g/kg0.75 BW/d (P=0.78) and 3.46g/kg0.75 BW/d (P=0.39), respectively. The net protein for gain (NPg) differed (P<0.01) between sexes. For animals weighing 20kg and with an average daily gain of 100g/d, NPg was 7.08, 7.11 and 6.78g/d for intact males, castrated males and females, respectively. The net energy and protein requirements for maintenance of Morada Nova lambs slaughtered between 15 and 28kg did not vary by sex. The net energy for gain increases and the net protein for gain decreased with the increase in body weight in hair lambs.

Energy and protein requirements for maintenance of Southern Yellow cattle fed a corn silage or straw-based diet

Abstract The objective of this study was to estimate the net energy and net protein requirements for maintenance (NEm and NPm) of Southern Yellow cattle in China. A database involving 175 cattle with body weight (BW) ranging from 211 to 454 kg was obtained from a series of calorimetry experiments. The diets offered to cattle consisted of proportionately corn-soybean meal concentrate and roughage containing corn silage, rice straw and wheat straw. Linear regression equations of the logarithm of heat production (HP) and retained energy (RE) against metabolizable energy intake (MEI) were developed to predict the maintenance requirements for metabolizable energy (MEm) and NEm. The combined data indicated that the MEm and NEm were 522 and 348 MJ/kg0.75 of BW d−1, respectively. In addition, the partial efficiency of use of ME for maintenance was 0.66, and the partial efficiency for growth was 0.51. Similarly, there was also a linear relationship between retained nitrogen (RN) and nitrogen intake (NI). The pooled data provided a NPm of 2.63 g/kg0.75 of BW d−1 and a metabolizable protein requirement for maintenance (MPm) of 3.93 g/kg0.75 of BW d−1 for Southern Yellow cattle. In conclusion, our estimate of NEm was extremely similar to the value of the AFRC nutritional system, whereas it was slightly greater than that recommended by the NRC nutritional system. Additionally, the MPm value obtained in the current study was in agreement with the NRC recommendation.

Net protein and metabolizable protein requirements for maintenance and growth of early-weaned Dorper crossbred male lambs

BackgroundDorper is an important breed for meat purpose and widely used in the livestock industry of the world. However, the protein requirement of Dorper crossbred has not been investigated. The current paper reports the net protein (NP) and metabolizable protein (MP) requirements of Dorper crossbred ram lambs from 20 to 35 kg BW.MethodsThirty-five Dorper × thin-tailed Han crossbred lambs weaned at approximately 50 d of age (20.3 ± 2.15 kg of BW) were used. Seven lambs of 25 kg BW were slaughtered as the baseline animals at the start of the trial. An intermediate group of seven randomly selected lambs fed ad libitum was slaughtered at 28.6 kg BW. The remaining 21 lambs were randomly divided into three levels of dry matter intake: ad libitum or 70% or 40% of ad libitum intake. Those lambs were slaughtered when the lambs fed ad libitum reached 35 kg BW. Total body N and N retention were measured.ResultsThe daily NP and MP requirements for maintenance were 1.89 and 4.52 g/kg metabolic shrunk BW (SBW0.75). The partial efficiency of MP utilization for maintenance was 0.42. The NP requirement for growth ranged from 12.1 to 43.5 g/d, for the lambs gaining 100 to 350 g/d, and the partial efficiency of MP utilization for growth was 0.86.ConclusionsThe NP and MP requirements for the maintenance and growth of Dorper crossbred male lambs were lower than the recommendations of American and British nutritional systems.