Pre- and postpartum metabolizable protein supply: II. Effects on plasma amino acids and markers of tissue mobilization in transition Holstein dairy cows.

The influence of diet composition on the degree of adipose and lean muscle mobilization and concentrations of circulating AA has been demonstrated during the transition period. Altering the MP supply might offer a strategy to control tissue mobilization and increase circulating AA availability, but the optimum supply of MP fed pre- and postpartum remains unknown. We investigated the effect of increasing the MP supply in the prepartum, postpartum, or both diets on plasma AA concentrations and ultrasound and circulating indicators of tissue mobilization. Multiparous Holstein cows (n = 96) were assigned to 1 of 4 treatment groups at 28 d before expected calving following a randomized block design. Prepartum diets were formulated to contain either a control (C; 85 g of MP/kg DM; 1,175 g of MP/d) or high (H; 113 g of MP/kg DM; 1,603 g of MP/d) level of estimated MP. From calving to 21 DIM, fresh diets were formulated to contain either a control (C; 104 g of MP/kg DM; 2,044 g of MP/d) or high (H; 131 g of MP/kg DM; 2,685 g of MP/d) level of estimated MP. To control the potential confounding effect of Met and Lys supply, diets were formulated to supply an equal amount at 1.24 and 3.84 g/Mcal of ME in both prepartum diets and 1.15 and 3.16 g/Mcal of ME in both postpartum diets, respectively. The combination of a pre- and postpartum diet resulted in 4 treatment groups: 1) CC (n = 23), 2) CH (n = 24), 3) HC (n = 22), and 4) HH (n = 23). A common lactation diet (113 g of MP/kg DM; 2,956 g of MP/d) was fed from 22 DIM to the end of the observation period at 42 DIM. Transcutaneous ultrasonography was used to determine the longissimus dorsi muscle diameter and backfat thickness. Concentrations of plasma AA, 3-methylhistidine (3MH), and creatinine were determined on a subset of cows (n = 60) using ultra-high-performance liquid chromatography and mass spectrometry. Treatment did not affect the longissimus dorsi muscle diameter from -14 to 21 d relative to calving, but the diameter was greater in CH compared with HH at 40 DIM. Backfat thickness and the ratio of 3MH to creatinine did not differ by treatment. Concentrations of EAA were greater at -13 d relative to calving in HH compared with CC and CH and at -6 d relative to calving EAA concentrations were higher in HC compared with CC. Cows fed the H diet postpartum had elevated EAA concentrations at 6 and 20 DIM compared with cows fed the C postpartum diet but EAA concentration did not differ at 40 DIM. Total NEAA concentrations were higher in CH compared with HC and HH at -6 d relative to calving, but NEAA concentration did not differ by treatment at -13, 6, 20, or 40 d relative to calving. In conclusion, increasing the supply of MP fed prepartum, postpartum, or both had minimal effects on tissue mobilization but influenced concentrations of plasma AA.

Pre- and postpartum metabolizable protein supply: I. Effects on feed intake, lactation performance, and metabolic markers in transition dairy cows.

The objective of this study was to investigate the effect of increasing MP supply in the prepartum, postpartum, or both diets on intake, performance, and metabolic indicators. Multiparous Holstein cows (n = 96) were assigned to 1 of 4 treatment groups at 28 d before expected calving following a randomized block design. Prepartum diets were formulated to contain either a control (C; 85 g of MP/kg DM) or high (H; 113 g of MP/kg DM) level of estimated MP. From calving to 21 DIM, diets were formulated to contain either a control (C; 104 g of MP/kg DM) or high (H; 131 g of MP/kg DM) level of estimated MP. To control the potential confounding effect of Met and Lys supply, diets were formulated to supply an equal amount at 1.24 and 3.84 g/Mcal of ME in both prepartum diets and 1.15 and 3.16 g/Mcal of ME in both postpartum diets, respectively. The combination of a pre- and postpartum diet resulted in 4 treatment groups: 1) CC (n = 23), 2) CH (n = 24), 3) HC (n = 22), and 4) HH (n = 23). A common lactation diet (113 g of MP/kg DM) was fed from 22 DIM to the end of the observation period at 42 DIM. Milk yield and DMI were collected daily, and plasma metabolic indicators (BHB, fatty acids [NEFA], urea nitrogen [PUN], and glucose) were determined twice weekly from -28 to 28 d relative to calving and once weekly from 29 to 42 DIM. Samples with BHB ≥1.2 mmol/L between 3 and 10 DIM were considered hyperketonemia events. Milk composition was determined weekly. Milk yield during 1 to 21 DIM was greater in HH (44.7 ± 1.0 kg/d) compared with CC (39.2 ± 1.0 kg/d) and HC (38.0 ± 1.0 kg/d) and milk yield in CH (42.4 ± 0.9 kg/d) was greater than HC, respectively. From 22 to 42 DIM, milk yield was greater in CH (53.3 ± 1.0 kg/d) and HH (54.1 ± 1.0 kg/d) compared with CC (49.6 ± 1.0 kg/d) and HC (49.3 ± 1.0 kg/d). Dry matter intake (% of BW) and concentrations of milk protein, fat, and total solids were not affected by treatment. Prepartum concentrations of PUN were greater in H compared with C. From 1 to 21 DIM, PUN concentrations were greater in CH and HH compared with CC and HC. From 1 to 21 DIM, glucose concentrations were lower in HH compared with HC and BHB were greater in CH and HH compared with HC. Concentrations of NEFA, as well as the number of hyperketonemia events did not differ by treatment during this time. From 22 to 42 DIM, concentrations of NEFA were greater in HH compared with HC and concentrations of BHB were greater in CH and HH compared with HC. Overall, feeding CH or HH increased lactation performance without altering intake or hyperketonemia events. Results from this study support formulating a fresh diet to reduce the negative MP balance during early lactation.

Effect of close-up metabolizable protein supply on colostrum yield, composition, and immunoglobulin G concentration and associations with prepartum metabolic indicators of Holstein cows.

The prepartum diet as well as individual metabolic status of the cow influences colostrum parameters. The objectives of this study were to 1) investigate the effect of increasing prepartum dietary MP supply on colostrum yield, composition, and immunoglobulin G (IgG) concentration, and 2) identify prepartum metabolic indicators associated with these outcomes. Multiparous Holstein cows (n = 96) were blocked by expected calving date and randomly assigned to 1 of 2 prepartum diets formulated to contain a control (CON; 85 g of MP/kg DM; 1,175 g of MP/d) or high (HI; 113 g of MP/kg DM; 1,603 g of MP/d) level of MP starting at 28 d before expected calving. Both prepartum diets were formulated to supply Met and Lys at an equal amount of 1.24 and 3.84 g/Mcal of metabolizable energy (ME), respectively. Metabolic indicators were determined in serum (albumin, glutamate dehydrogenase, cholesterol, aspartate transaminase, total protein, total bilirubin, and IgG) or plasma (Ca, glucose, fatty acids, BHB, and urea nitrogen) twice weekly in a subset of cows (n = 60). Colostrum was harvested at 3.6 ± 2.4 h from calving and yield as well as concentrations of IgG, fat, protein, and Ca were determined. Cows were retrospectively grouped based on the typical volume of colostrum needed for 2 colostrum meals (<6 or ≥ 6 kg), IgG concentration (<100 or ≥ 100 g/L), as well as the median concentrations of fat (<4.4 or ≥ 4.4%), protein (<16.5 or ≥ 16.5%), Ca (<0.21 or ≥ 0.21%), and total colostrum ME (<8.65 or ≥ 8.65 Mcal). Data were analyzed using mixed effects ANOVA, with repeated measures where applicable. Feeding HI tended to increase colostrum yield in cows entering parity 2 (9.4 vs. 7.2 ± 0.9 kg), but treatment did not affect yield from cows entering parity ≥3 (5.1 vs. 6.4 ± 1.0 kg). Supply of MP did not affect concentrations of IgG, fat, protein, or Ca. Cows that produced ≥ 6 kg vs. those producing <6 kg of colostrum had lower plasma concentrations of glucose. Metabolic indicators were not associated with IgG group. Colostrum fat ≥4.4% was associated with cows having lower prepartum concentrations of glucose, total protein, albumin, and aspartate transaminase activity. Colostrum protein ≥ 16.5% was associated with lower circulating serum IgG and elevated cholesterol. Elevated glucose as well as lower cholesterol and BHB concentrations were associated with colostrum Ca ≥ 0.21%. Further, higher albumin and fatty acids as well as lower glucose concentrations were associated with a greater colostrum energy output. In conclusion, increasing prepartum MP supply tended to increase colostrum yield in cows entering parity 2, but did not affect the composition or IgG concentration. The observed associations between metabolic indicators and colostrum parameters suggest that slight adjustment in metabolism during late gestation might be necessary to support colostrogenesis, but the causality of these relationships should be considered.

Invited review: Nutritional and management factors that influence colostrum production and composition in dairy cows.

Colostrum is a rich source of nutritional and non-nutritional components and is recognized as essential to transfer passive immunity to newborn calves. Because of the individual and seasonal variability in colostrum yield and composition, maintaining an adequate supply of high-quality colostrum year-round remains a challenge for commercial dairy producers. In this narrative review, we described the individual, seasonal, and herd-level variability of colostrum production and summarized the association between individual animal factors such as parity, sex of the calf, calf birth weight, as well as indicators of the cow's metabolic status and the yield and composition of colostrum. Further, we reviewed the current knowledge on the influence of prepartum nutrition and management strategies on colostrum production. Research on the metabolizable energy and protein supplied in the prepartum diet as well as on the inclusion and source of vitamins, minerals, and feed additives suggests prepartum nutrition influences the yield, quality, and composition of colostrum. Furthermore, the prepartum environment and dry period length remain influential factors in the production of colostrum. However, additional research is needed to understand the mechanisms by which prepartum nutrition and management affect colostrum production. Finally, time from calving to colostrum harvest and oxytocin administration as well as the current knowledge on the effect of heat treatment and colostrum storage strategies on colostral components were discussed. To conclude, we identify critical gaps in knowledge for future focus of investigation in colostrum research.

Effect of replacing a portion of inorganic chloride trace minerals with trace mineral amino acid complexes.

The objective was to determine whether replacing a portion of inorganic chloride trace minerals and cobalt carbonate in the diet with AA complexes of trace minerals and cobalt glucoheptonate will improve lactating cow performance, feed efficiency, and calf performance. In a clinical trial, 69 Holstein cows entering second lactation and greater were randomly assigned to 1 of 2 treatments, with the total dietary trace mineral concentration the same between treatments, starting 1 wk after dry off (50 to 57 d before expected parturition) until 154 d in milk (DIM): (1) an inorganic chloride trace mineral (ITM) blend consisting of Zn (75 mg/kg), Mn (65 mg/kg), and Cu (10 mg/kg) as hydroxychlorides and Co (1 mg/kg) as carbonate (n = 37) or (2) partial replacement of ITM with AA complexes of Zn (40 mg/kg), Mn (20 mg/kg), and Cu (3.5 mg/kg) and Co glucoheptonate (1 mg/kg; AATM; Availa-Dairy, Zinpro Corp.; n = 32). Dry matter intake (DMI) was recorded daily from enrollment through wk 8, and milk yields were recorded daily from calving through wk 22. Milk composition and body weights (BW) were collected weekly. Serum samples were analyzed for albumin (Alb), cholesterol (Chol), total bilirubin (Bili), aspartate aminotransferase (AST), haptoglobin, ß-hydroxybutyrate (BHB), and Ca. A liver health index (LHI) was calculated based on Bili, Chol, and Alb concentrations. A liver functionality index (LFI) was calculated to standardize changes in Alb, Chol, and Bili from 4 to 29 DIM. Greater LHI and LFI indicate better health status. Colostrum was analyzed for IgG and Brix, and calf serum was analyzed for IgG. Calf growth was monitored through 9 wk of age (AATM: n = 12, ITM: n = 10). Data were analyzed using SAS software with mixed effects models and repeated-measures analysis, when applicable. Survival analysis for pregnancy by 154 DIM was analyzed by Cox proportional and Kaplan-Meier hazards models. Disorder incidence was tested with Fisher's exact test. Prepartum DMI as a percent of BW was lower in cows fed AATM and not significant postpartum. Cows fed AATM produced more milk from wk 1 to 8 and from wk 1 to 22. Energy-corrected milk yield and colostrum measures did not significantly differ between treatments. A treatment by time interaction was seen for AST and BHB; cows fed AATM tended to have lower AST concentrations at 28 DIM and lower concentrations in BHB through 29 DIM, though not statistically significant. Cows fed AATM had greater LHI at 4 DIM. Haptoglobin, Ca, LFI, hazard of pregnancy, risk to first service, survival curves, or services per pregnancy did not significantly differ. Calf serum IgG and birth weight did not significantly differ between treatments. Calves from dams fed AATM had greater average daily gain than calves from dams fed ITM. Overall, cows fed AATM during the dry period and early lactation had improved postpartum performance and potential health improvements.

Epidemiology of bovine colostrum production in New York Holstein herds: Prepartum nutrition and metabolic indicators.

Colostrum yield and quality are influenced by prepartum nutrition and the metabolic status of the cow; however, data considering these associations on multiple dairy farms are limited. Our objective was to identify cow-level prepartum metabolic indicators, as well as farm-level nutritional strategies associated with colostrum yield and the indicator of colostrum quality, Brix %. A convenience sample of 19 New York Holstein dairies (median: 1,325 cows; range: 620 to 4,600 cows) were enrolled in this observational study. Records for individual colostrum yield and Brix % were collected by farm personnel between October 2019 and February 2021. Farms were visited 4 times, approximately 3 mo apart, to obtain feed samples of the prepartum diets, collect blood samples from 24 pre- and postpartum cows, respectively, and determine prepartum body condition score. Feed samples were submitted for analysis of chemical composition, and particle size was determined on-farm using a particle separator. Prepartum serum samples (n = 762) were analyzed for glucose and nonesterified fatty acid concentrations. Whole blood from postpartum cows was analyzed for herd prevalence of hyperketonemia (proportion of samples with ß-hydroxybutyrate ≥1.2 mmol/L). A cohort of primiparous (PP; n = 1,337) and multiparous (MPS; n = 3,059) cows calving ± 14 d of each farm visit were included in the statistical analysis. Animals calving in this period were assigned results for the close-up diet composition and herd prevalence of hyperketonemia collected from the respective farm visit. Greatest colostrum yield from PP and MPS cows was associated with moderate starch [18.6-22.5% of dry matter (DM)] and a moderate herd prevalence of hyperketonemia (10.1-15.0%). Greatest colostrum yield from MPS cows was associated with moderate crude protein (13.6-15.5% of DM) and a less severe negative dietary cation-anion difference (DCAD; >-8 mEq/100 g), whereas greatest colostrum yield from PP cows was associated with low crude protein (≤13.5% of DM). In addition, a moderate proportion of the diet with particle length ≥19 mm (15.3-19.1%) was associated with lowest colostrum yield from PP and MPS cows. Highest colostrum Brix % was associated with prepartum dietary factors of low neutral detergent fiber (≤39.0% of DM) and high proportion of the diet with particle length ≥19 mm (>19.1%). In addition, low starch (≤18.5% of DM) and low and moderate DCAD level (≥-15.9 mEq/100 g) were associated with greatest Brix % from PP cows, whereas moderate DCAD (-15.9 to -8.0 mEq/100 g) was associated with greatest Brix % from MPS cows. Prepartum serum nonesterified fatty acid concentration ≥290 µEq/L was associated with increased colostrum yield, but prepartum serum glucose concentration and body condition score were not associated with colostrum yield or Brix %. These data provide nutritional and metabolic variables to consider when troubleshooting colostrum production on farms.

Eucalcemia during lipopolysaccharide challenge in postpartum dairy cows: I. Clinical, inflammatory, and metabolic response.

Hypocalcemia induced by immune activation is a conserved response across mammalian species; however, administration of Ca is discouraged in other species as it is associated with increased morbidity and mortality. Early postpartum cows experience a decrease in circulating Ca concentration following acute inflammation. Corrective Ca therapy during the transition period, particularly in dairy cows experiencing acute disease, is common practice. However, the effect of Ca administration on the inflammatory response during acute immune activation is unknown. Our objective was to compare the clinical, inflammatory, and metabolic response to an intravenous (IV) lipopolysaccharide (LPS) challenge between postpartum cows infused, or not, with IV Ca to maintain eucalcemia. Cows (n = 14, 8 ± 1 d in milk) were enrolled in a matched-pair randomized controlled design to receive IV Ca (IVCa) or sterile 0.9% NaCl (CTRL) during an IV LPS challenge (0.040 or 0.045 µg of LPS/kg of body weight over 1 h). Ionized Ca (iCa) was monitored cow-side, and IV Ca infusion was adjusted in a eucalcemic clamp for 12 h following the start of LPS infusion. Cows were monitored during the 24 h following challenge and serial blood samples were collected to quantify concentrations of glucose, ß-hydroxybutyrate, nonesterified fatty acids, urea nitrogen, cytokines, acute-phase proteins, and cortisol. Blood iCa concentration decreased to 0.87 ± 0.03 mM in CTRL during challenge, and by design, iCa concentration was maintained within 3% of baseline in IVCa. Body temperature, heart rate, and respiratory rate were monitored for 24 h following the start of challenge and did not differ between groups. A treatment × time interaction was identified such that serum cortisol concentrations increased in both groups at 2 h but decreased to a greater extent at 6 h in IVCa compared with CTRL. Rumination time (min/h) over the first 12 h following challenge was greater in IVCa, but total rumination time in the 24 h following challenge did not differ from CTRL. Serum glucose and nonesterified fatty acid concentrations decreased, and ß-hydroxybutyrate and urea nitrogen concentrations increased over time, but did not differ between groups. Acute leukopenia occurred in both groups at 4 h before leukocytosis was observed at 24 h with total white blood cell counts returning to baseline within 72 h. Plasma concentrations of tumor necrosis factor (TNF) and interleukin-10 (IL-10) increased within 1 h following the start of challenge and did not differ between groups. Serum haptoglobin and serum amyloid A concentrations increased within the 24 h following challenge and were elevated through 72 h but did not differ between groups. Eucalcemia during the acute systemic inflammatory response did not alter the TNF or IL-10 cytokine response, or the acute-phase protein SAA and haptoglobin response in this LPS challenge model; however, eucalcemia was associated with a more rapid decline in cortisol response and greater rumination time in the first 12 h following challenge. We did not find evidence that eucalcemia exacerbated the inflammatory response in early postpartum cows, but Ca administration may alter the clinical response to acute systemic inflammation.

Eucalcemia during lipopolysaccharide challenge in postpartum dairy cows: II. Calcium dynamics.

Hypocalcemia induced by immune activation is a conserved response among mammals. Early postpartum cows will experience decreased circulating Ca concentrations following acute immune activation; however, the cause for decreased Ca concentration is unknown. Our objectives were to (1) describe Ca dynamics following an intravenous (IV) LPS challenge in early postpartum cows, and (2) compare inflammatory-induced changes in Ca dynamics between IV Ca-treated cows and control cows. Cows (n = 14, 8 ± 1 d in milk) were enrolled in a matched-pair randomized controlled design to receive IV Ca (IVCa) in a eucalcemic clamp for 12 h, or 0.9% NaCl (CTRL) following an IV LPS infusion (0.040 or 0.045 µg of LPS/kg of body weight over 1 h). During the 24 h following LPS infusion, circulating concentrations of parathyroid hormone and serotonin were measured, serum and urine samples were collected to calculate urinary fractional excretion of Ca (FECa), and fecal samples were collected to calculate Ca apparent digestibility (ADCa) using amylase-treated and ash-corrected undigested neutral detergent fiber after 240 h (uNDFom240) as an internal marker. Changes in Ca intake and milk Ca secretion were also quantified and compared with baseline values. Cows were fasted during challenge and dry matter intake was 20 ± 5% less than baseline values on the day of challenge and did not differ between groups. On the day of challenge, milk Ca concentration increased, but milk yield decreased such that total Ca secreted in milk did not change from baseline. Urine FECa was low overall, but an interaction of treatment and time was identified such that FECa increased in IVCa but decreased in CTRL. Concentrations of parathyroid hormone increased and serotonin decreased following challenge. Fecal dry matter decreased from baseline, but did not differ between 6, 12, and 24 h, and did not differ between groups. An interaction of treatment and time was identified for ADCa and apparent digestibility of dry matter such that digestibility was decreased in CTRL but not IVCa at 6 h. Acute immune activation induced hypocalcemia in CTRL, and although urinary Ca excretion was not a primary cause, it is unclear to what degree hypocalcemia was due to altered ADCa. Eucalcemia appeared to alter adaptations in Ca homeostasis during immune activation as FECa was increased in IVCa animals.

Epidemiology of bovine colostrum production in New York Holstein herds: Cow, management, and environmental factors.

Adequate supply of high-quality colostrum is essential for calf health. Colostrum production, at first milking, varies between animals and seasons, but herd-level and management associations with colostrum production have not been well described. Our objectives were to (1) describe colostrum production and colostrum handling practices and (2) to identify individual cow, herd management, and environmental factors associated with colostrum production. A convenience sample of 19 New York Holstein dairy farms (620 to 4,600 cows) were enrolled in this observational study to describe colostrum production and to evaluate cow, management, and prepartum environmental factors associated with colostrum yield and Brix %. Herd owners or managers were given a colostrum management questionnaire, and farm personnel recorded individual colostrum yield and Brix % for primiparous (PP; n = 5,978) and multiparous (MPS; n = 13,228) cows between October 2019 and February 2021. Temperature, relative humidity, and light intensity were measured by sensors placed in each farm's close-up dry cow pens for the entire length of the study. Median colostrum yield for each farm ranged from 2.5 to 7.6 kg for PP and 4.0 to 7.7 kg for MPS cows. Mean Brix % from each farm ranged from 22.2 to 27.9% for PP and 22.0 to 28.8% for MPS cows. Lowest colostrum yield from PP animals was associated with calf sex (female) and colostrum Brix % (≤22%). Greatest colostrum yield from MPS cows was associated with colostrum Brix % (≤22%), calf sex (twin), dry period length (>67 d), gestation length (283-293 d), an alive calf, second parity, previous lactation length (>344 d) and previous lactation 305-d mature equivalent milk yield (>13,091 kg), heat and humidity exposure area under the curve (AUC) 7 d before calving (>69.2 average temperature-humidity index per 30-min interval), and light intensity AUC 14 d before calving (>154.2 average lux per 15-min interval). Greatest colostrum Brix % from PP animals was associated with calf sex (male), an alive calf, and light intensity AUC 14 d before calving (≤64.0 average lux per 15-min interval). Greatest colostrum Brix % from MPS cows was associated with dry period length (>67 d), an alive calf, 305-d mature equivalent milk yield of previous lactation (≤15,862 kg), gestation length (274-282 d), colostrum yield (<6 kg), fifth or greater parity, and heat and humidity exposure AUC 7 d before calving (≤50.1 average temperature-humidity index per 30-min interval). Dairy producers can use this information to recognize the variation in colostrum production and alter colostrum management programs in anticipation of periods of low production or quality.

Lipopolysaccharide challenge following intravenous amino acid infusion in postpartum dairy cows: I. Production, metabolic, and hormonal responses.

Postpartum cows experience a nadir in energy and AA deficit early postpartum. At the same time, cows are challenged with inflammatory stimuli and often show heightened immune responsiveness, further increasing their metabolic needs during this critical time. This study investigated the response to a systemic inflammatory stimulus after a 4-d intravenous (IV) AA infusion designed to ameliorate the estimated metabolizable protein (MP) deficit in postpartum cows. Our objectives were to (1) describe the production and metabolic responses to early postpartum IV AA infusion, (2) determine the metabolic and hormonal responses to an acute IV lipopolysaccharide (LPS) challenge in early postpartum cows, and (3) compare these metabolic and hormonal responses between IV AA treated and control cows. Cows (n = 14, 4 ± 1 d in milk) were continuously IV infused for 4 d in a matched-pair randomized controlled design and received IV AA (IVAA) or 0.9% NaCl (CTRL). Treatment with IV AA consisted of 1 g/kg of BW per day of combined essential AA (EAA) and nonessential AA (NEAA). After infusion ended, cows were challenged IV with LPS (0.0625 µg/kg of BW over 1 h), and serial blood samples were collected to quantify AA, metabolite, and hormone concentrations. Amino acid infusion increased plasma EAA and NEAA concentrations and ameliorated the estimated MP deficit but not the metabolizable energy deficit in IVAA cows. Patterns of dry matter intake during infusion were different between groups. Milk yield and milk protein content and yield were unaffected, but IV AA was associated with increased milk fat content and yield of both de novo and preformed fatty acids. Before LPS infusion, plasma EAA and NEAA concentrations were greater in IVAA compared with CTRL. During LPS challenge, plasma AA concentrations decreased to a greater degree in IVAA than CTRL. Glucagon concentrations were greater and glucose concentrations lower in IVAA during challenge; however, previous AA infusion did not affect the time-dependent changes in concentrations of energy metabolites or glucoregulatory hormones. Plasma urea nitrogen concentration increased in both treatments following challenge, although the temporal pattern depended on treatment. Effects of AA infusion on milk fat response were pronounced and likely due to a combination of increased lipolysis and de novo milk fat synthesis. Despite differences in circulating concentrations of nutrients and hormones before challenge, metabolic responses to systemic inflammation did not differ between the 2 treatments. We conclude that AA infusion changed metabolic status and milk fat but did not appear to alter the metabolic response to subsequent systemic inflammation.

Lipopolysaccharide challenge following intravenous amino acid infusion in postpartum dairy cows: II. Clinical and inflammatory responses.

Amino acids (AA) are integral nutrients for a functioning immune system. Postpartum cows experience AA deficits early postpartum that may influence the response to immune activation. This study investigated the clinical and inflammatory responses to a systemic inflammatory stimulus after a 4-d intravenous (IV) AA infusion with a mix of essential and nonessential AA designed to ameliorate the estimated metabolizable protein deficit in early postpartum cows. Our objectives were (1) to describe the clinical and inflammatory response to an acute IV lipopolysaccharide (LPS) challenge in early postpartum cows, and (2) to compare these clinical and inflammatory responses between IV AA-treated and control cows. Cows (n = 14, 4 ± 1 d in milk) were continuously infused IV for 4 d in a matched-pair randomized controlled design and received 0.9% NaCl (CTRL) or IV AA (IVAA) to supply 1 g/kg of BW per day of combined essential and nonessential AA. After infusion ended, cows were challenged with IV LPS (0.0625 µg/kg of BW over 1 h), and serial blood samples were collected for complete blood cell counts and to quantify plasma cytokines and acute-phase proteins. Body temperature, heart rate, and respiratory rate were monitored for 24 h during challenge. During challenge, maximum body temperature was greater in IVAA (41.3 ± 0.20°C) than in CTRL (40.6 ± 0.19°C). In both groups, respiratory rate increased during the first 2 h following challenge, whereas heart rate first decreased over the first 2 h and then increased to reach a maximum at 4 h. Acute leucopenia occurred within 1 h of challenge in both groups before leukocytosis was observed at 24 h, with white blood cell counts returning to baseline values within 72 h. Plasma haptoglobin and serum amyloid A concentrations increased 3-fold and 4-fold in both groups and peaked at 48 and 24 h following challenge, respectively. Plasma concentrations of TNF-α and IL-10 increased within 1 h and peaked at 2 h following the start of challenge. Plasma IL-10 concentrations increased to a greater extent in CTRL compared with IVAA during challenge. Despite differences in IL-10 concentration, previous AA infusion did not alter the acute-phase protein response to LPS challenge. We conclude that AA infusion before systemic inflammatory challenge decreased the anti-inflammatory response but did not alter concentrations of other systemic markers of inflammation.