Metabolizable Protein Requirements For Maintenance Research Articles

PSIV-A-4 Effect of late gestational nutrient restriction on locomotor activity of beef heifers

Abstract The objective of this study was to determine the effects of nutrient restriction on locomotor behavior during late gestation. Fall-calving crossbred beef heifers were moved to 3.7 × 15.8 m partially-covered pens and individually-fed 100% (control; n = 13) or 70% (nutrient restricted; n = 13) 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 fed in Calan gates and supplemented to meet targeted nutritional planes. IceQube accelerometers (iceRobotics, Edinburgh, UK) were placed on the left hind fetlock between d 158 and 168 of gestation to determine standing time, lying time, step count, number of lying bouts, and motion index. Daily behavior data were averaged for 5 distinct periods (period 1: IceQube placement to d 180 of gestation; period 2: d 181 to 201 of gestation; period 3: d 202 to 222 of gestation; period 4: d 223 to 243 of gestation; and period 5: 244 to 264 of gestation). Days in which animals were moved from their pens were excluded from the data set, resulting in an average of 17.2 ± 2.35 d per period. Data were analyzed with fixed effects of nutritional plane, period, and their interaction in the model. Maternal sire and day of treatment initiation were included as covariates. The number of lying bouts was affected (P = 0.02) by the nutritional plane × period interaction. Within period, there was no effect (P ≥ 0.20) of nutritional plane on lying bouts. Lying bouts in control heifers decreased (P = 0.008) from period 1 to 2, whereas lying bouts in nutrient restricted heifers decreased (P = 0.002) from period 1 to 2 before increasing (P = 0.02) again from period 2 to 3. Motion index and step count were affected (P ≤ 0.05) by nutritional plane, where both were greater in control heifers. Motion index and step count were affected (P < 0.001) by period, while standing time and lying time tended to be affected (P ≤ 0.09) by period. Motion index and step count decreased (P < 0.001) between periods 1 and 2 and periods 3 and 4 but increased (P ≤ 0.004) between periods 2 and 3 and periods 4 and 5. Standing time decreased (P = 0.02), while lying time increased (P = 0.02), between periods 3 and 4. These data suggest that nutrient restricted heifers may have reduced locomotor behavior in late gestation compared with control heifers. Throughout all periods of gestation, control heifers took more daily steps and had a greater motion index, suggesting that nutrient availability in late gestation may directly impact locomotor behavior of beef heifers.

PSIV-A-7 Effects of late gestational nutrient restriction of beef heifers on small intestinal crypt depth in neonatal calves

Abstract We hypothesized that late gestational nutrient restriction would impair small intestinal development in neonatal calves, including crypt cell depth and proliferation. Fall-calving crossbred beef heifers [body weight (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; n = 12) of NASEM metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Calves were removed from their dams immediately post-calving and fed artificial colostrum and milk replacer relative to body weight until euthanasia at 48.7 ± 0.4 h of age. The gastrointestinal tract was removed, and proximal jejunum samples were dissected from each calf and immersion-fixed in 10% neutral buffered formalin. Tissues were embedded in paraffin blocks and cut into 5-µm sections that were mounted on glass slides. Slides were incubated with Ki-67 (marker of nuclear proliferation) and counterstained with Hematoxylin using an autostainer. Images were taken at 5× magnification using an upright microscope. QuPath software was used to measure crypt depth, starting at the base of the crypt region and ending at the furthest cluster of Ki-67 positive cells, perpendicular to the base of the mucosa. For each calf, 10 crypt depth measurements were taken from 4 images, resulting in 40 crypt depth measurements that were averaged. Nutritional plane was a fixed effect in the model, and maternal sire, date of study initiation, and calf sex (when P < 0.25) were considered covariates. We previously reported that calves born to nutrient restricted dams weighed less (P ≤ 0.05) at birth and 48 h than calves born to control dams. Small intestinal mass tended to be less (P = 0.11) in offspring of nutrient restricted dams but was not affected (P = 0.58) when expressed relative to body weight. Calves born to nutrient restricted dams also tended to have less (P = 0.11) small intestinal mass relative to brain weight. Maternal nutrient restriction did not affect (P = 0.95) jejunal crypt depth. Additionally, crypt depth relative to body weight was not affected (P = 0.20) by nutrient restriction. Although crypt depth was not affected, further analysis of proliferation and morphology will help to understand the relationship between maternal nutrient restriction and small intestine development in neonatal calves.

PSIV-14 Effects of Maternal Nutrient Restriction During Late Gestation on Expelled Cotyledonary Mrna Expression in Primiparous Beef Females

Abstract To determine the effects of late gestational nutrient restriction on expelled cotyledonary mRNA expression, fall-calving Hereford × Simmental-Angus heifers [single-sired; BW: 451 ± 28 (SD) kg; BCS: 5.4 ± 0.7] bred to a single sire were allocated by fetal sex and expected calving date to receive either 100% (control; CON; n = 12) or 70% (nutrient restricted; NR; n = 11) of NASEM metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth. Beginning on d 160 of gestation, heifers were individually fed chopped sorghum sudan hay (1.74 Mcal ME/kg, 6.69% CP, 72.0% NDF; DM basis) and based on individual intakes, supplemented to meet targeted nutritional planes. Calving was observed for all females and placentas were collected at natural expulsion. Immediately after collection (average: 4.5 h post-calving; range: 2.3 to 12.1 h post-calving), 2 representative cotyledons on the ipsilateral side were cleaned with phosphate buffered saline, and cotyledonary tissue was flash frozen. Total RNA was extracted, and RT-qPCR was performed for mRNA expression of glucose transporters (SLC2A1, SLC2A3, SLC2A4), a fructose transporter (SLC2A5), amino acid transporters (SLC1A1, SLC3A2, SLC7A1, SLC7A5, SLC7A8, SLC38A2), angiogenic factors/receptors (VEGFA, NOS3, FLT1, KDR, GUCY1B3), and pregnancy-associated glycoprotein 2 (PAG2). Relative mRNA expression was analyzed with nutritional plane, treatment initiation date, time to cotyledon sampling, and calf sex (when P < 0.25) as fixed effects. We have previously reported that total uterine blood flow during late gestation was not affected (P ≥ 0.20) by nutritional plane or the nutritional plane × day of gestation interaction. Post-calving, NR dams were 64 kg BW less (P < 0.001) and 2.0 BCS less (P < 0.001), but calf birth weight was not affected (P = 0.72) by nutritional plane. Contralateral placental dry weight tended to be less (P = 0.07) in NR dams, but total placental weight was not affected (P = 0.86) by late gestational nutritional plane. Cotyledonary relative mRNA expression of SLC2A3 and SLC38A2 was greater (P ≤ 0.05) and relative expression of SLC2A1, SLC2A4, and NOS3 tended to be greater (P ≤ 0.07) in NR dams compared with CON. Late gestational nutritional plane did not affect (P ≥ 0.13) cotyledonary relative mRNA expression of FLT1, GUCY1B3, KDR, PAG2, SLC1A1, SLC2A5, SLC3A2, SLC7A1, SLC7A5, SLC7A8, and VEGFA. In summary, first parity beef females who experienced late gestational nutrient restriction maintained uterine blood flow and placental mass and had 4 nutrient transporters and 1 angiogenic factor upregulated in cotyledons, all which likely contributed to their conservation of fetal growth.

71 Effects of Late Gestational Nutrient Restriction on Calf pre-Weaning Growth, Backgrounding and Feedlot Performance, and Carcass Composition

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 metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from day 160 of gestation to calving. Post-calving, all females were fed chopped tall-fescue hay supplemented to meet lactational nutrient requirements in Calan gates to constrain diets of calves to milk only until day 147, then pen-fed in drylots until weaning at day 242 ± 3 (SD). Post-weaning, calves were fed a tall fescue hay-based backgrounding diet in the same large drylots for 53 ± 12 d, then moved to partially covered pens with GrowSafe feeding systems in 2 groups and fed a corn-based feedlot diet (formulated to be 18.3% CP, 1.21 Mcal NEg/kg, DM basis; 89% DM) for 255 ± 3 d (similar days on feed rather than carcass endpoint). Cattle were harvested in a commercial plant, and camera carcass grading was performed. Data were analyzed with maternal treatment, calving date, and calf sex (when P < 0.25) as fixed effects; feedlot group was included for feedlot and carcass measures. We previously reported that birth weight was not affected (P = 0.72), but NR decreased (P < 0.04) milk production by 15%. Calves born to NR dams had reduced ADG from birth to day 147 (P = 0.02), day 147 to weaning (P = 0.08), and birth to weaning (P = 0.003), resulting in NR calves having 13% lighter (P = 0.004) weaning weight. Backgrounding ADG was not affected (P = 0.80) by maternal treatment; thus, feedlot entry BW was 11% less (P = 0.009) in NR calves. On day 28, 56, 84, and 112 on feed, NR calves weighed less (P ≤ 0.09) than control. Final BW was not affected (P = 0.91) by maternal treatment. Feedlot ADG was greater for NR calves from day 168 to slaughter (P = 0.02) and the overall feeding period (P = 0.03), but not before day 168 on feed (P ≥ 0.22). Calves born to NR dams had less (P = 0.02) dressing percentage, but improved (P = 0.02) yield grade and backfat thickness. Hot carcass weight, ribeye area, marbling score, and KPH were not affected (P ≥ 0.26) by maternal treatment. Percent prime, yield grade ≤ 2, and yield grade ≥ 4 were not affected (P ≥ 0.29) by maternal treatment. Overall, late gestational nutrient restriction decreased growth pre-weaning but increased late finishing growth, without affecting backgrounding or early feedlot growth. These cattle had leaner carcasses after similar days on feed, suggesting that late gestational nutrient restriction altered growth patterns or body composition.

70 Nutrient Restriction During Late Gestation Alters Maternal Circulating Amino Acid Concentrations in Primiparous Beef Females

Abstract We hypothesized that maternal circulating AA concentrations would be reduced by late gestational nutrient restriction, indicating less available nutrients for transport by the uteroplacenta to the growing fetus. Fall-calving Hereford-SimAngus heifers [single-sired; BW: 451 ± 28 (SD) kg; BCS: 5.4 ± 0.7] bred to a single sire were allocated by fetal sex and expected calving date to receive either 100% (control; CON; n = 12) or 70% (NR; n = 13) of NASEM metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from day 160 of gestation to calving. Heifers were individually fed chopped sorghum sudan hay (1.74 Mcal ME, 6.66% CP, 72.0% NDF; DM basis) and based on individual intakes, supplemented to meet targeted nutritional planes. Jugular blood samples were obtained on days 159 (Pre-treatment), 202, and 244 of gestation, and 1 h post-calving to determine serum concentrations of the 20 common AA (except cysteine), 1-methyl histidine, and 3-methyl histidine. Gestational and post-calving AA were analyzed separately with nutritional plane, treatment initiation date, and calf sex (when P < 0.25) as fixed effects. Gestational AA included day and nutritional plane x day using repeated measures. We have previously reported that dam BCS was less (P ≤ 0.04) by day 202 of gestation and dam BW was less (P ≤ 0.01) by day 223 of gestation for NR dams. Post-calving, NR dams were 64 kg BW and 2.0 BCS lless (P < 0.001), but calf birth weight was not affected (P = 0.72) by nutritional plane. Histidine, lysine, and methionine were greater (P ≤ 0.03) in NR dams on day 202 of gestation. Tryptophan and valine were less (P ≤ 0.05) while methionine and total AA tended to be less (P ≤ 0.08) on day 244 of gestation in NR dams. Aspartic acid, glutamic acid, and tyrosine were less (P ≤ 0.03), but 3-methyl histidine was greater (P ≤ 0.01) on days 202 and 244 of gestation in NR dams. 1-methyl histidine was greater (P ≤ 0.05) at all 3 gestational timepoints but leucine was less (P = 0.03) in NR dams during gestation. Post-calving, glutamic acid, leucine, and valine were less (P ≤ 0.04), and methionine, threonine, tryptophan, tyrosine, and total AA tended to be less (P ≤ 0.10) in NR dams. Histidine, 1-methyl histidine, 3-methyl histidine, and serine were greater (P ≤ 0.03) in NR dams post-calving. In summary, late gestational nutrient restriction reduced total maternal circulating AA and altered the maternal serum AA profile, but calf birth weight was not affected. Individual AA that were greater or unaffected in NR dams were likely indicative of body protein catabolism occurring to meet nutrient requirements.

Maternal nutrient restriction during late gestation reduces vigor and alters blood chemistry and hematology in neonatal beef calves.

Fall-calving primiparous beef females [body weight: 451 ± 28 (SD) kg; body condition score: 5.4 ± 0.7] were individually-fed either 100% (control; CON; n = 13) or 70% (nutrient restricted; NR; n = 13) of metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from day 160 of gestation to parturition. Calves were reared naturally by their dams and monitored for latency times from birth to first sternal recumbency, attempt to stand, and stand; vigor scores were assigned at 2, 5, 10, and 20min of age. Rectal temperatures and jugular blood were obtained at 0 (pre-suckling), 6, 12, 24, and 48h of age, and blood chemistry, hematology, cortisol, and insulin were determined. Data were analyzed with fixed effects of late gestational nutritional plane (single data point) or nutritional plane, hour, and their interaction (data over time, repeated measures). Calving date was a fixed effect; calf sex was included when P < 0.25. We previously reported that late gestational nutritional plane did not affect gestation length or calf size at birth, but calving assistance and fetal malpresentations occurred more often in NR. Nutritional plane did not affect (P = 0.65) duration of parturition, but calves born to NR dams had slower times to attempt to stand (P = 0.09), slower times to stand (P = 0.02), and had poorer 20min vigor scores (P = 0.05). Serum immunoglobulin G and A concentrations at 48h were greater (P ≤ 0.03) for NR calves. Rectal temperature of NR calves was less (P = 0.02) at 0h, but greater (P = 0.04) at 24h compared with CON. Circulating glucose, non-esterified fatty acids, triglycerides, cortisol, and insulin were not affected by nutritional plane (P ≥ 0.18). Total protein and globulin from 6 to 48h were greater (P ≤ 0.02) in NR calves. Calves from NR dams had greater (P < 0.08) gamma-glutamyl transferase at 6, 12, and 48h. Serum aspartate aminotransferase was greater (P ≤ 0.07) from 0 to 24h and creatine kinase was greater (P ≤ 0.04) from 6 to 24h in NR calves. At 0h, potassium was greater (P = 0.03) in NR calves. Calves born to CON had greater chloride (P = 0.08; main effect), sodium (P ≤ 0.09) from 0 to 48h, and anion gap (P = 0.02) at 6h. Hematocrit from 6 to 24h and red blood cells and hemoglobin at 6 and 12h were greater (P ≤ 0.09) in CON calves. These data indicate that nutrient restriction during late gestation resulted in less vigorous calves with more indicators of trauma in early life.

Late gestational nutrient restriction in primiparous beef females: nutrient partitioning among the dam, fetus, and colostrum during gestation.

Fall-calving primiparous crossbred beef females [body weight (BW): 451 ± 28 (SD) kg; body condition score (BCS): 5.4 ± 0.7] were allocated by fetal sex and expected calving date to receive either 100% (control; CON; n = 13) or 70% (nutrient restricted; NR; n = 13) of metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from day 160 of gestation to calving. Heifers were individually-fed chopped poor quality hay and supplemented to meet targeted nutritional planes based on estimated hay intakes. Dam BW, BCS, backfat, and metabolic status were determined pre-treatment, every 21 d (BW and metabolic status) or 42 d (BCS and backfat) during gestation, and post-calving. At birth, calf BW and size were measured, and total colostrum from the most full rear quarter was collected pre-suckling. Data were analyzed with nutritional plane, treatment initiation date, and calf sex (when P < 0.25) as fixed effects. Gestational metabolites included day and nutritional plane × day as repeated measures. During late gestation, CON dams gained (P < 0.01) maternal (non-gravid) BW and maintained (P ≥ 0.17) BCS and backfat, while NR dams lost (P < 0.01) maternal BW, BCS, and backfat. Circulating glucose, urea N, and triglycerides were less (P ≤ 0.05) in NR dams than CON at most late gestational timepoints after treatment initiation. Circulating non-esterified fatty acids were greater (P < 0.01) in NR dams than CON. Post-calving, NR dams weighed 63.6 kg less (P < 0.01) and were 2.0 BCS less (P < 0.01) than CON. At 1 h post-calving, NR dams had less (P = 0.01) plasma glucose and tended to have less (P = 0.08) plasma triglycerides than CON. Nutrient restriction did not affect (P ≥ 0.27) gestation length, calf birth weight, or calf size at birth. Colostrum yield was 40% less (P = 0.04) in NR dams than CON. Protein and immunoglobulin concentrations were greater (P ≤ 0.04), but free glucose and urea N concentrations were less (P ≤ 0.03), in colostrum of NR dams than CON. Colostrum total lactose, free glucose, and urea N were less (P ≤ 0.03) in NR dams than CON, but total protein, triglycerides, and immunoglobulins were not affected (P ≥ 0.55). In summary, beef heifers experiencing late gestational nutrient restriction prioritized partitioning nutrients to fetal growth and colostrum production over maternal growth. During undernutrition, fetal and colostral nutrient demands were largely compensated for by catabolism of maternal tissue stores.

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 &amp;lt; 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 &amp;lt; 0.001) from 1 to 36 h. Total triglycerides and MUN decreased (P &amp;lt; 0.001) from 1 to 12 h, before total MUN increased (P &amp;lt; 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 &amp;lt; 0.25), and date of study initiation were covariates. Post-calving, NR dams were 62 kg BW and 2.1 BCS less (P &amp;lt; 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.

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.

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.

342 Effects of Maternal Nutrient Restriction During Late Gestation on Primiparous Dam Performance and Fetal Growth

Abstract To determine the effects of late gestational nutrient restriction (NR) on heifer performance, fetal growth, and calving difficulty, single-sired fall-calving Hereford-SimAngus heifers (BW: 451 ± 28 [SD] kg; BCS: 5.4 ± 0.7) bred to a single sire were allocated by fetal sex and expected calving date to either 100% (control; CON; n = 12) or 70% (n = 13) of NASEM net energy and metabolizable protein requirements for maintenance, pregnancy, and growth. Beginning on d 160 of gestation, heifers were individually fed chopped sorghum sudan hay (1.74 Mcal ME, 6.66% CP, 72.0% NDF; DM basis) and based on individual intakes, supplemented to meet targeted nutritional planes. Dam BW, BCS, and backfat (BF) were determined pre-treatment, every 21 d (BW) or 42 d (BCS and BF) during treatments, and post-calving. At birth, calf BW and size (length, heart girth, abdominal girth, flank girth, cannon circumference, cannon length, shoulder height, and ribeye area) were measured. Data were analyzed with treatment, treatment initiation date, and calf sex (when P &amp;lt; 0.25) as fixed effects. Dam BW tended to be less (P = 0.09) and BCS was less (P = 0.04) at d 202 of gestation for NR dams. Dam BW, BCS, and BF were less (P ≤ 0.01) in NR dams for the remainder of gestation. Post-calving, NR dams weighed 64 kg less (P ≤ 0.01) than CON, with a BCS of 3.6 ± 0.1. Nutrient restriction did not affect (P ≥ 0.27) calf gestation length, BW, or size. Calf BW as % post-calving dam BW tended to be greater (P = 0.09) for NR calves. Fetal presentation was normal for all CON births, while 23.1% of NR dams had fetal malpresentation (P = 0.12). In the current study, NR dam BW and BCS were sacrificed during late gestation without altering fetal growth trajectory.

PSI-14 Effects of maternal nutrient restriction during late gestation on neonatal beef calf serum chemistry and complete blood cell count

Abstract To determine effects of late gestational nutrient restriction (NR) on neonatal blood chemistry and hematology, 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. Calf jugular blood was obtained at 0 (pre-suckling), 6, 12, 24, and 48 h postnatally to determine serum chemistry and complete blood cell count. Data were analyzed with fixed effects of treatment, hour, and their interaction, using repeated measures. Calving date was a fixed effect; calf sex was included when P &amp;lt; 0.25. The treatment x hour interaction (P &amp;lt; 0.10) affected total protein, globulin, gamma-glutamyl transferase (GGT), aspartate aminotransferase (AST), creatinine, creatine kinase, red blood cells (RBC), hemoglobin, hematocrit, sodium, anion gap, and potassium. Total protein and globulin at 6 to 48 h were greater (P ≤ 0.02) in NR calves. Calves from NR heifers had greater (P &amp;lt; 0.08) GGT at 6, 12, and 48 h and greater (P ≤ 0.07) AST at 0 to 24 h. Creatinine at 24 h and creatine kinase at 6 to 24 h were greater (P &amp;lt; 0.04) in NR calves. Hematocrit from 6 to 24 h and RBC and hemoglobin at 6 and 12 h were greater (P ≤ 0.09) in CON calves. Sodium from 0 to 48 h and anion gap at 6 h were greater (P &amp;lt; 0.09) in CON calves. Calves from NR heifers had greater (P = 0.03) 0 h potassium. Treatment affected chloride, which was greater (P = 0.08) in CON calves. These data indicate calves born to nutrient restricted heifers may experience more trauma at calving but have improved passive transfer.

Determination of energy and protein requirements of preweaned dairy calves: A multistudy approach

The first studies concerning nutrient requirements for preweaned dairy calves were from the 1920s and 1930s; however, few studies were published in the following decades. We aimed to determine energy and protein requirements of preweaning Holstein and Holstein × Gyr dairy calves in a multistudy meta-regression. We used a database composed of individual measurements of 166 preweaned male calves (138 submitted to treatments and 28 used as the reference group) from 4 studies that used the methodology of comparative slaughter. Animals with less than 15/16 of Holstein genetic composition were considered crossbred Holstein × Gyr, whereas other animals were considered Holstein. Net energy requirements for maintenance (NEM) were determined by the regression between heat production and metabolizable energy intake (MEI). The metabolizable energy requirements for maintenance were calculated by the iterative method, and the efficiency of use of metabolizable energy for maintenance was obtained by NEM divided by the metabolizable energy requirements for maintenance. Net energy requirements for gain (NEG) were estimated using a regression of the retained energy (RE) as a function of empty body weight (EBW) and empty body gain (EBG). The efficiency of use of metabolizable energy for gain was estimated by the regression of RE as a function of MEI, but with partitioning the MEI into MEI from liquid feed and MEI from starter feed. Additionally, the effect of a liquid feed (milk or milk replacer) was tested on the slope of the regression. The metabolizable protein requirements for maintenance (MPM) were estimated using the intercept of the regression between the metabolizable protein intake (MPI) and average daily gain. The MPM was determined as the ratio between the intercept and the metabolic body weight. Net protein requirements for gain (NPG) were estimated by the regression between retained protein, EBG, and RE. The efficiency of use of metabolizable protein for gain was estimated by the regression of the retained protein as a function of MPI, but with partitioning the MPI into MPI from liquid feed and MPI from starter feed. Additionally, the effect of a liquid feed (milk or milk replacer) was tested on the regression slope. Breed did not influence any of the nutrient requirements' estimates. The NEM was estimated as 70.2 kcal/metabolic body weight per day. The efficiency of use of metabolizable energy for maintenance observed was 66%. The NEG was estimated by the equation NEG = 0.0901 × EBW0.75 × EBG0.9539. The efficiency of use of metabolizable energy for gain was estimated as 57.6, 49.3, and 41.2% for milk, milk replacer, and starter feed, respectively. The MPM was estimated as 4.22 g/EBW0.75 per day, and the NPG was determined by the equation: NPG = 30.06 × EBG + 70.98 × RE. The efficiency of use of metabolizable protein for gain was estimated as 71.9, 59.2, and 44.4% for milk, milk replacer, and starter feed, respectively. We concluded that no differences were observed in energy and protein requirements between Holstein and Holstein × Gyr crossbred cows. The efficiencies of use of metabolizable energy and protein are greater for milk when compared with milk replacer and starter feed. Therefore, we propose that the equations generated herein should be used to estimate energy and protein requirements of preweaned Holstein and Holstein × Gyr crossbred dairy calves raised under tropical conditions.

Metabolizable Protein: 2. Requirements for Maintenance in Growing Saanen Goats.

This study aimed to estimate the protein requirements for the maintenance of growing Saanen goats of different sexes from 5 to 45 kg of body weight (BW) using two methods and applying a meta-analysis. For this purpose, two datasets were used. One dataset was used to evaluate the effects of sex on the protein requirements for maintenance using the comparative slaughter technique. This dataset was composed of 185 individual records (80 intact males, 62 castrated males, and 43 females) from six studies. The other dataset was used to evaluate the effects of sex on the protein requirements for maintenance using the N balance method. This dataset was composed of 136 individual records (59 intact males, 43 castrated males, and 34 females) from six studies. All studies applied an experimental design that provided different levels of N intake and different levels of N retention, allowing the development of regression equations to predict the net protein requirement for maintenance (NPM) and the metabolizable protein (MP) requirements for maintenance (MPM) in Saanen goats. The efficiency of MP use for maintenance (kPM) was computed as NPM/MPM. The efficiency of MP use for gain (kPG) was calculated using the equation of daily protein retained against daily MP intake above maintenance. A meta-analysis was applied using the MIXED procedure of SAS, in which sex was considered a fixed effect, and blocks nested in the studies and goat sex were considered as random effects. The NPM did not differ between sexes, irrespective of the approach used. The daily NPM estimated was 1.23 g/kg0.75 BW when using the comparative slaughter technique, while it was 3.18 g/kg0.75 BW when using the N balance technique for growing Saanen goats. The MPM estimated was 3.8 g/kg0.75 BW, the kPM was 0.33, and the kPG was 0.52. We observed that the NPM when using the comparative slaughter technique in growing Saanen goats is lower than that recommended by the current small ruminant feeding systems; on the other hand, the MPM was similar to previous reports by the feeding systems. Sex did not affect the protein requirements for maintenance and the efficiencies of use of metabolizable protein.

Nutrient requirements and evaluation of equations to predict chemical body composition of dairy crossbred steers.

ObjectiveObjectives were to estimate energy and protein requirements of dairy crossbred steers, as well as to evaluate equations previously described in the literature (HH46 and CS16) to predict the carcass and empty body chemical composition of crossbred dairy cattle.MethodsThirty-three Holstein×Zebu steers, aged 19±1 months old, with an initial shrunk body weight (BW) of 324±7.7 kg, were randomly divided into three groups: reference group (n = 5), maintenance level (1.17% BW; n = 4), and the remaining 24 steers were randomly allocated to 1 of 4 treatments. Treatments were: intake restricted to 85% of ad libitum feed intake for either 0, 28, 42, or 84 d of an 84-d finishing period.ResultsThe net energy and the metabolizable protein requirements for maintenance were 0.083 Mcal/EBW0.75/d and 4.40 g/EBW0.75, respectively. The net energy (NEG) and protein (NPG) requirements for growth can be estimated with the following equations: NEG (Mcal/kg EBG) = 0.2973(±0.1212) ×EBW0.4336(±0.1002) and NPG (g/d) = 183.6(±22.5333)×EBG−2.0693(±4.7254)×RE, where EBW, empty BW; EBG, empty body gain; and RE, retained energy. Crude protein (CP) and ether extract (EE) chemical contents in carcass, and all the chemical components in the empty body were precisely and accurately estimated by CS16 equations. However, water content in carcass was better predicted by HH46 equation.ConclusionThe equations proposed in this study can be used for estimating the energy and protein requirements of crossbred dairy steers. The CS16 equations were the best estimator for CP and EE chemical contents in carcass, and all chemical components in the empty body of crossbred dairy steers, whereas water in carcass was better estimated using the HH46 equations.

Nitrogen metabolism and protein requirements for maintenance of growing Red Norte bulls

Dietary protein adjustments can reduce environmental impact and economic losses in production systems. However, we lack information regarding nitrogen (N) metabolism and protein requirements for maintenance of crossbred animals such as Red Norte breed, precluding a precise dietary management. The objective was to evaluate the effect of increasing dietary CP levels (9%, 11%, 13%, 15% and 17%) on intake, digestibility and N balance, as well as to estimate the metabolizable protein requirements for maintenance (MPm) of growing Red Norte bulls. Thirty five animals averaging 280 ± 4.0 kg BW were fed during 45 days in a 60 : 40 forage : concentrate ratio diet in which the last 5 days were used for the digestibility trial. Intakes of CP and non-fibrous carbohydrates (NFCs) and feed efficiency linearly increased (P < 0.05) as CP levels increased, while DM, NDF, nitrogen efficiency use and ether extract were not influenced by CP levels (P > 0.05). Digestibilities of DM, organic matter, ether extract, NFC and CP as well as metabolizable energy intake linearly increased (P < 0.05), and true digestibility of CP was not affected (P > 0.05) by treatments. Urinary N and retained N linearly increased (P < 0.05) with the increase in dietary N. The MPm were estimated as 4.46 g/BW0.75 and the efficiency of use of MPm was 0.673. In conclusion, obtained MPm requirements of growing Red Norte bulls are greater than the values reported in literature for Zebu cattle and dietary CP levels of 15% and 17% exhibited great responses for growing Red Norte cattle. However, a cost-benefit evaluation should be done before its use.

Energy and protein requirements for Nellore steers estimated with the deuterium oxide marker

The aim of this study was determine the energy and protein requirements for maintenance and gain of Nellore steers. Thirty six Nellore steers with a average weight and age of 359±13 kg and 20 months at the beginning of the trial were individually fed for 56. The steers were fed the same diet (76.43% TDN and 13.62% CP) in three levels of dry matter (DM) intake, ad libitum, 75 g DM/kg BW0.75 and 60 g DM/kg BW0.75. The initial and final body composition was estimated with the marker deuterium oxide that allowed repeated water estimate in the same animal. Deuterium in blood samples was analyzed by mass spectrometry. The effects of intake levels, comparison of intercept and slope among feeding level, and equations were evaluated by the analysis of variance, adopting P&lt;0.05 as a significant level. The net energy for maintenance was 75 kcal/kg EBW0.75 or 70 kcal/kg BW0.75. The net energy for gain for steers with 350 to 450 kg weight was 5.1 to 6.1Mcal. The efficiency of energy utilization for maintenance, km, was 0.7492 and for weight gain, kg, was 0.3404. The metabolizable protein requirement for maintenance was 4.32 * BW0.75 and the net protein for gain was estimated with the equation NPg = (254.68*EBWG) €“ (29.38*RE). The technique of deuterium oxide marker used to estimate energy and protein requirement for maintenance and weight gain at Nellore steers confirm the hypothesis presented in NRC, that NEm is lower than the requirement for taurine cattle. On the other hand, the reverse was true for the NP requirement for maintenance and for weight gain. We consider that indirect method using D2O for estimate body composition in zebu cattle was suitable to determine nutrient requirements.