Milk protein yield and mammary metabolism are affected by phenylalanine deficiency but not by threonine or tryptophan deficiency.

Efficient milk protein synthesis requires that the essential AA be presented to the mammary gland in the right amount and proportion to maximize protein synthesis and minimize losses. This study investigated the effects of individual AA deficiencies on cow productivity, mammary metabolism, and glucose whole-body rate of appearance. Five Holstein cows were used in a 5 × 5 Latin square design trial with 10-d periods. Treatments were abomasal infusions of (1) water (CTL); (2) complete AA mixture (TAA); (3) TAA without Phe (No-Phe); (4) TAA without Thr (No-Thr); and (5) TAA without Trp (No-Trp). Each treatment was compared with TAA. Treatment did not affect milk, fat, or lactose yields. Arterial concentrations of Phe, Thr, and Trp decreased with their respective deletions by 60, 76, and 69%. In response to the decreased arterial supply of the deleted AA, mammary plasma flow significantly increased by 55% with No-Thr but did not increase with No-Phe or No-Trp. Mammary uptake of Phe was reduced by No-Phe, accompanied by a reduced milk protein yield; uptakes of Thr and Trp were not affected by their respective deletions, and milk protein yield did not decrease with these treatments. Deletion of Phe tended to reduce its mammary uptake relative to milk output (U:O), accompanied by an increased U:O of Tyr, but deletion of Thr and Trp did not affect the U:O of the corresponding AA. Plasma urea-N concentration was lower with CTL and tended to be higher with No-Phe. Arterial concentrations and mammary uptake of acetate, ß-hydroxybutyrate, glucose, and lactate were unaffected by treatment. Treatment had no effect on glucose rate of appearance at the whole-body level. Lactose output as a percentage of glucose whole-body rate of appearance was not affected by treatment. Overall, the study indicated that a deficiency of Phe negatively affected productivity and mammary metabolism but that a deficiency of Thr or Trp did not.

Evaluation of on-farm tools for colostrum quality measurement.

The objectives of this study were to determine the immunoglobulin G (IgG) content of colostrum on Alberta dairy farms and to determine which on-farm tool, the colostrometer or the Brix refractometer, was more highly correlated with IgG content as determined by radial immunodiffusion (RID). Colostrum samples (n=569) were collected between February and July 2012 from 13 commercial dairy farms in central Alberta, with herds ranging in size from 60 to 300 lactating cows. Immunoglobulin G content was determined directly by RID and indirectly by a colostrometer (specific gravity) and Brix refractometer (total solids). The Spearman correlation was used for the colostrometer and Brix refractometer data. According to RID analysis, 29.1% of the colostrum samples contained <50 mg/mL IgG. Concentrations ranged from 8.3 to 128.6 mg/mL IgG, with a median of 65.1 mg/mL. Third or greater parity cows had higher colostral IgG content (69.5±1.98 mg/mL) than second parity (59.80±2.06 mg/mL) or first parity (62.2±1.73 mg/mL) cows. The colostrometer data were more highly correlated with RID results (r=0.77) than were the Brix refractometer data (r=0.64). Specificity and sensitivity were determined for the colostrometer and Brix refractometer compared with a cut-point of 50 mg/mL IgG as determined by RID. The highest combined value for sensitivity and specificity occurred at 80 mg/mL for the colostrometer (84.1 and 77.0%, respectively) and 23% Brix (65.7 and 82.8%, respectively). This study indicates that although the colostrometer data are better correlated with true IgG values, the user-friendly Brix refractometer is a more specific tool to detect colostrum of adequate quality.

Exclusion of dietary sodium bicarbonate from a wheat-based diet: effects on milk production and ruminal fermentation.

Milk production, rumen fermentation, and whole-tract apparent nutrient digestibility in response to feeding 20% steam-rolled wheat with or without sodium bicarbonate were evaluated in 12 Holstein cows averaging 165±16 DIM. Cows were fed 1 of 2 isoenergetic and isonitrogenous diets containing either 0 or 0.75% sodium bicarbonate on a DM basis for 21 d in a crossover design. Rumen fluid samples were obtained 18 times during the last 2 d of each period, and fecal samples were collected on 12 occasions from d 18 to 21 of each period. Removal of sodium bicarbonate from the diet did not affect DMI (21.0 kg/d), yields of milk (30.8 kg/d), or milk components (1.16, 1.01, and 1.40 kg/d for fat, protein, and lactose, respectively). Whole-tract apparent digestibility of DM, CP, ADF, and NDF did not differ between the 2 treatments (75.3, 76.6, 67.2, and 63.6%, respectively). The mean rumen pH was 6.24 and was not affected by excluding sodium bicarbonate from the diet. Rumen NH3-N (12.31 mg/dL) and lactic acid (3.63 mM) concentrations were not different, whereas total volatile fatty acids concentration tended to increase when sodium bicarbonate was present in the diet (110 vs. 116 mM). However, average concentrations of the individual volatile fatty acids, as a proportion of total volatile fatty acids, were not affected by treatment. In conclusion, dairy cow diets can include up to 20% steam-rolled wheat without the need for added sodium bicarbonate as long as the diets are formulated to meet the fiber requirements of the cow.

Deletion of arginine from an abomasal infusion of amino acids does not decrease milk protein yield in Holstein cows.

This study was undertaken to determine if a limited supply of Arg would alter milk and milk protein yields, as well as mammary uptake of AA and energetic substrates. Six lactating Holstein cows (199 ± 5 d in milk) were used in a replicated 3 × 3 Latin square balanced for residual effects with 14-d periods. The diet was formulated to supply 100% of the National Research Council net energy requirement and 72% of the metabolizable protein requirement. The treatments were randomly distributed as abomasal infusions of (1) water (CTL), (2) a mixture of essential AA (EAA) excluding Arg (ARG-), or (3) a mixture of EAA including Arg (ARG+). The profile of EAA in the infusates was the same as that found in casein with the exception that methionine was increased to maintain a 3:1 ratio of digestible lysine:methionine (total dietary+infusion). Milk protein yield was increased by the ARG+ compared with the CTL treatment and deletion of Arg in the infusate (ARG-) did not impair this response. Deletion of Arg from the EAA mixture decreased the mammary uptake of Arg relative to that of the CTL treatment, and although the uptake:output ratio decreased from 2.52 (ARG+) to 2.12 (ARG-), it was still largely in excess of Arg secretion in milk protein. Otherwise, Arg deletion did not affect any of the measured parameters (no significant difference between ARG- and ARG+) except Arg and urea arterial concentrations. In support of the increased yields of milk protein and lactose, mammary uptake of the group 2 AA (Ile, Leu, Lys, and Val) increased and the uptake:output ratio tended to increase from 1.04 to 1.23. The mammary uptake:milk protein output ratio was not different from 1 and not different among treatments for the group 1 AA (His, Met, Phe+Tyr, Trp). Mammary uptake of energetic substrates did not vary across treatments, although milk lactose yield increased with the ARG+ treatment relative to CTL. These results indicate that deletion of Arg has minimal effects on milk and milk component yields when the remaining EAA are supplied in sufficient amounts despite decreased mammary Arg uptake and that group 2 AA seem to be involved in the mammary gland to support the lactose yield response to EAA infusion.

Peripartum responses of dairy cows to prepartal feeding level and dietary fatty acid source.

This experiment was conducted to investigate the effect of feeding level and oilseed supplementation during the close-up dry period on energy balance (EB), hepatic lipidosis, metabolic status, and productivity in early lactation. Seventy-seven Holstein cows were blocked according to parity and expected calving date and then assigned randomly to 1 of 6 treatments in a 2 × 3 factorial allocation with 2 feeding levels: ad libitum (AL) or 30% feed restriction (FR), and 3 dietary fatty acid sources: canola seed, linola seed, or flaxseed at 8% of dietary dry matter (DM), to enrich the rations with oleic, linoleic, or linolenic acids, respectively during the last 4 wk of gestation. After parturition, all cows were fed a common lactation diet. Cows fed AL lost less body weight (-2.9 vs. -6.0%) and body condition score (+0.67 vs. -2.30%), and consequently were in more positive EB (+4.6 vs. -0.3 Mcal) during the prepartum period than cows subjected to FR. Postpartum, FR cows lost less body weight (-9.7 vs. -12.4%) and experienced less severe negative EB (-4.5 vs. -7.0 Mcal) than AL cows. Cows fed AL had higher plasma insulin (6.8 vs. 4.4 µIU/mL) and lower nonesterified fatty acid concentrations (436 vs. 570 mEq/mL) during the close-up period than cows subjected to FR. Cows fed AL tended to have lower liver glycogen content in early lactation than cows subjected to FR (4.4 vs. 2.9 % of DM) [corrected], but had similar triglyceride content (13.1 ± 1.2 µg/g of DM). Fatty acid source did not influence response variables. In conclusion, eliminating intake depression by FR during the close-up period had positive carryover effects on EB and metabolic status during early lactation, but feeding linoleic and linolenic acids via unprotected oilseeds only had negligible effects on peripartum responses.

Starch source and content in postpartum dairy cow diets: effects on plasma metabolites and reproductive processes.

The objective of this study was to examine the effects of dietary starch source and content in the immediate postpartum period on plasma metabolites and hormones and ovarian follicular development. One of 3 diets was fed in a randomized block design to 40 cows from calving until 70 d in milk. The diets contained 45% alfalfa silage (AS), 45% barley silage (BS), or 41% barley silage and 4% supplemental starch (SS) on a dry matter basis. All diets contained 45% barley-based concentrate and 10% alfalfa hay. Resulting starch levels were 25.2, 23.3, and 26.7% for AS, BS, and SS, respectively. Body condition was scored every other week and dry matter intake and milk yield were recorded daily. Milk samples were obtained weekly and blood samples were taken at calving and then every other week to determine concentrations of glucose, insulin, insulin-like growth factor-1, ß-hydroxybutyrate, and nonesterified fatty acids. Transrectal ultrasonography was performed twice per week from 7 d after calving until first ovulation or 62 d in milk in all cows. For a subset of 7 AS-, 8 BS-, and 9 SS-fed cows, a complete estrous cycle was monitored for ovarian dynamics, and blood samples were collected every second day for progesterone and estradiol. Luteinizing hormone pulsatility was also determined (5 cows/treatment) approximately 15 d postcalving. Treatment had no effect on body condition score, dry matter intake, blood metabolites, milk yield, or milk fat and protein contents, but BS-fed cows had significantly higher levels of milk urea nitrogen compared with SS cows. Cows fed SS (31 d) tended to have a shorter interval from calving to first ovulation than cows fed AS (43 d) or BS (38 d). The incidence of double first ovulations was higher in cows fed SS (46%) compared with those fed BS (0%). Treatment had no effect on LH pulse frequency or amplitude, ovarian dynamics, or progesterone and estradiol concentrations during the observed estrous cycle. Energy balance did not differ among cows fed the 3 diets. Overall, dietary starch source and concentration had little effect on productivity or metabolic status of postpartum cows.

Changes in production and mammary metabolism of dairy cows in response to essential and nonessential amino acid infusions.

This study was undertaken to increase our understanding of the need of the mammary gland for the different types of AA and how the mammary gland alters its metabolism in response to a variable AA supply. Eight lactating Holstein cows (61+/-4 DIM) were used in a replicated 4 x 4 Latin square balanced for residual effects with 14-d periods. The diet was formulated to supply 100% of the net energy requirement and 72% of the metabolizable protein requirement. The 4 treatments were 1) abomasal infusions of water, 2) essential AA at 359 g/d, 3) nonessential AA at 356 g/d, and 4) essential AA at 359 g/d+nonessential AA at 356 g/d (total of 715 g/d). The infusates had the same AA profile as casein with the exception that Met was increased to maintain a 3:1 ratio of digestible Lys to Met and because of solubility limitations all the Tyr was replaced by Phe and part of the Glu was replaced by Gln. Milk yield and milk protein yield were increased by the essential AA treatments compared with the other treatments. Mammary uptake of beta-hydroxybutyrate plus lactate tended to increase with the essential AA treatments, whereas glucose mammary uptake tended to be higher with the nonessential AA treatments. With the essential AA treatments, the mammary uptake:milk protein output ratio for the group 1 AA (His, Met, Phe, Trp, and Tyr) did not differ from 1 but tended to increase; the ratio for the group 2 AA (Ile, Leu, Lys, and Val) did increase, significantly exceeding unity when essential AA were infused. These results indicate that the mammary gland alters differently its uptake of both AA and energy-yielding nutrients in response to the amount and profile of AA presented to it and that even under situations of protein deficiency nonessential AA supplementation does not enhance milk and milk protein synthesis.

Effects of increasing amounts of dietary wheat on performance and ruminal fermentation of Holstein cows.

Twelve second-lactation Holstein cows were used in a replicated Latin square design to examine the effects of dietary wheat on lactation performance, ruminal fermentation, and whole-tract nutrient digestibility. Cows were randomly assigned to 1 of 3 diets containing 0, 10, and 20% steam-rolled wheat on a dry matter basis at the expense of steam-rolled barley. Cows were fed and milked twice daily. Six of the cows were ruminally cannulated, and rumen fluid samples were obtained from these cows 18 times during the last 2 d of each period. Treatment did not affect dry matter intake (20.9 kg/d) or yields of milk (36.1 kg/d) or milk components (1.25, 1.10, and 1.67 kg/d for fat, protein, and lactose, respectively). Fat percentage was not different among the treatments but protein content of the milk was reduced by the wheat treatments, and was lower when 10% wheat was included in the diet versus 20%. Cows fed wheat had lower ruminal pH (6.36 vs. 6.44) and greater NH(3)-N (11.49 vs. 8.10 mg/dL) and total volatile fatty acids (121 vs. 113 mM) concentrations than cows not fed wheat. The acetate:propionate ratio was lower for cows fed wheat than for those not fed wheat (3.21 vs. 3.36), but was not different between cows fed 10% versus 20% wheat. Wheat feeding did not alter whole-tract apparent digestibility of dry matter, crude protein, acid detergent fiber, and neutral detergent fiber. Results of this study show that up to 20% steam-rolled wheat can be included in the diet of dairy cows without compromising production or causing subacute ruminal acidosis if adequate fiber is provided and the diets are properly formulated and mixed.

Reproductive performance of dairy cows is influenced by prepartum feed restriction and dietary fatty acid source.

The objective of this study was to determine the effects of feed restriction and source of dietary fatty acids during the close-up dry period on postcalving reproductive performance of dairy cattle. Thirty-four days before expected calving, pregnant Holstein cows (n = 72; parity 1 to 5) were randomly assigned to 1 of 6 treatments. Treatments were ad libitum (AL) or 24% feed restriction (FR) in combination with 1 of 3 oilseed supplements at 8% of diet dry matter: canola, linola, or flax to enrich the rations with oleic, linoleic, or linolenic fatty acids, respectively. After calving, cows were fed a common lactation diet that contained no oilseeds. Measurements of uterus, corpus luteum, and follicles were obtained by ultrasonography twice weekly from 7 +/- 1 d after calving until the first ovulation. Cows (n = 66) were subjected to timed artificial insemination (TAI), and pregnancy was determined 32 d later. Feed-restricted cows had lower dry matter intake and lost more body weight prepartum. Energy balance (Mcal/d) was negative in FR cows prepartum but they had a less severe negative energy balance postpartum. The dietary source of fatty acid did not affect energy balance. Cows fed AL had a higher incidence of uterine infections (10/37 vs. 2/35) but tended to have fewer ovarian cysts (2/37 vs. 7/35) than FR cows. Mean (+/-SE) interval from calving to uterine involution did not differ among dietary treatments (26.8 +/- 1.8 d). Interval from calving to first ovulation was longer in cows fed canola than in those fed either linola or flax (34.7 +/- 3.1 vs. 23.7 +/- 3.2 and 21.0 +/- 3.1 d, respectively). A greater percentage of cows fed AL conceived to the first TAI (47.1 vs. 18.8) and tended to have fewer mean days open (157 +/- 10.8 vs. 191 +/- 10.1) than cows fed FR. In summary, FR cows had a lower incidence of uterine infections, but they were less fertile as reflected by a lower percent pregnancy to first TAI and increased days open. Cows fed diets enriched in linoleic or linolenic fatty acids had a lesser incidence of ovarian cysts and ovulated sooner with no effect on energy balance or fertility.

Differences in splanchnic metabolism between late gestation and early lactation dairy cows.

In the transition from the pre- to postcalving state, the demands on the cow increase from support of gestation to high rates of milk production. This extra demand is met partly by increased intake but may also involve altered metabolism of major nutrients. Six multiparous Holstein cows were used to monitor changes in net fluxes of nutrients across the portal-drained viscera and liver (splanchnic tissues) between late gestation and early lactation. Blood samples were obtained simultaneously from the portal, hepatic, and subcutaneous abdominal veins and the caudal aorta 18 d before expected calving and 21 or 42 d after calving. On the day of blood sampling and the 3 d preceding sampling, cows were fed every 2 h. The precalving (1.63 Mcal of net energy for lactation/kg and 1,326 g of metabolizable protein/d) and postcalving (1.72 Mcal of net energy for lactation/kg and 2,136 g of metabolizable protein/d) diets were based on corn silage, alfalfa hay, and corn grain. Dry matter intake increased postcalving. Net splanchnic release of glucose increased postpartum because of tendencies for both increased portal absorption and net liver release. Increased removal of lactate, rather than AA, contributed to the additional hepatic gluconeogenesis. Although portal absorption of AA increased with intake at the onset of lactation, hepatic removal of total AA-N tended to decline. This clearly indicates that liver removal of AA is not linked to portal absorption. Furthermore, net liver removal relative to total liver inflow even decreased for Gly, His, Met, Phe, and Tyr. Together, these data indicate that in early lactation, metabolic priority is given to direct AA toward milk protein production rather than gluconeogenesis, in cows fed a corn-based ration.

Determining the IgG concentrations in bovine colostrum and calf sera with a novel enzymatic assay.

BACKGROUND: Immune protection in newborn calves relies on a combination of the timing, volume and quality of colostrum consumed by the calf after birth. Poor quality colostrum with inadequate immunoglobulin concentration contributes to failed transfer of passive immunity in calves, leading to higher calf morbidity and mortality. Therefore, estimating colostrum quality and ensuring the transfer of passive immunity on farm is of critical importance. Currently, there are no on-farm tools that directly measure immunoglobulin content in colostrum or serum. The aim of this study was to apply a novel molecular assay, split trehalase immunoglobulin G assay (STIGA), to directly estimate immunoglobulin content in dairy and beef colostrum and calf sera, and to examine its potential to be developed as on-farm test. The STIGA is based on a split version of trehalase TreA, an enzyme that converts trehalose into glucose, enabling the use of a common glucometer for signal detection. In a first study, 60 dairy and 64 beef colostrum and 83 dairy and 84 beef calf sera samples were tested with STIGA, and the resulting glucose production was measured and compared with radial immunodiffusion, the standard method for measuring immunoglobulin concentrations. RESULTS: Pearson correlation coefficients between the methods were determined and the sensitivity, specificity, and accuracy of the test were calculated for different colostrum quality and failed transfer of passive immunity cut-off points. The correlations of the STIGA measured by colorimetric enzymatic reaction compared to radial immunodiffusion for dairy and beef colostrum were 0.72 and 0.73, respectively, whereas the correlations for dairy and beef sera were 0.9 and 0.85, respectively. Next, STIGA was tested in a blinded study with fresh colostrum and serum samples where the correlation coefficient was 0.93 and 0.94, respectively. Furthermore, the performance of STIGA followed by glucometer readings resulted in correlations with radial immunodiffusion of 0.7 and 0.85 for dairy and beef colostrum and 0.94 and 0.83 for dairy and beef calf serum. CONCLUSIONS: A split TreA assay was validated for measurement of the immunoglobulin content of colostrum and calf sera using both a lab-based format and in a more user-friendly format compatible with on-farm testing.

Hepatic lipid metabolism in transition dairy cows fed flaxseed.

Thirty-three Holstein cows averaging 687 kg of body weight were allotted 6 wk before the expected date of parturition to 11 groups of 3 cows blocked within parity for similar calving dates to determine the effects of feeding different sources of fatty acids on blood parameters related to fatty liver and profile of fatty acids in plasma and liver. Cows were fed lipid supplements from 6 wk before the expected date of parturition until d 28 of lactation. Cows within each block were assigned to 1 of 3 isonitrogenous and isoenergetic dietary supplements: control with no added lipids (CO); unsaturated lipids supplied as whole flaxseed (FL; 3.3 and 11.0% of the dry matter in prepartum and postpartum diets, respectively); and saturated lipids supplied as Energy Booster (EB; 1.7 and 3.5% of the DM in prepartum and postpartum diets, respectively). Diets EB and FL had similar ether extract concentrations. Multiparous cows fed EB had lower dry matter intake and milk production, higher concentrations of nonesterified fatty acids and beta-hydroxybutyrate in plasma and triglycerides (TG) and total lipids in liver, and lower concentrations of plasma glucose and liver glycogen than those fed FL and CO. Production of 4% fat-corrected milk was similar among treatments. Multiparous cows fed FL had the highest liver concentrations of glycogen on wk 2 and 4 after calving and lowest concentrations of TG on wk 4 after calving. Liver C16:0 relative percentages in multiparous cows increased after calving whereas those of C18:0 decreased. Relative percentages of liver C16:0 were higher in wk 2 and 4 postpartum for multiparous cows fed EB compared with those fed CO and FL; those of C18:0 were lower in wk 4 postpartum for cows fed EB compared with those fed CO and FL. Liver C18:1 relative percentages of multiparous cows increased after calving and were higher in wk 4 for cows fed EB compared with those fed CO and FL. The inverse was observed for liver C18:2 relative percentages. In general, diets had more significant effects on plasma concentrations of nonesterified fatty acids, beta-hydroxybutyrate, and glucose and liver profiles of fatty acids, TG, total lipids, and glycogen of multiparous than primiparous cows. These data suggest that feeding a source of saturated fatty acids increased the risk of fatty liver in the transition cow compared with feeding no lipids or whole flaxseed. Feeding flaxseed compared with no lipids or a source of saturated fatty acids from 6 wk before calving could be a useful strategy to increase liver concentrations of glycogen and decrease liver concentrations of TG after calving, which may prevent the development of fatty liver in the transition dairy cow.

Effect of glutamine supplementation on splanchnic metabolism in lactating dairy cows.

The suggestion that glutamine (Gln) might become conditionally essential postpartum in dairy cows has been examined through increased postruminal supply of Gln. Net nutrient flux through the splanchnic tissues and mammary gland was measured in 7 multiparous Holstein cows receiving abomasal infusions of water or 300 g/d of Gln for 21 d in a crossover design. Milk yield increased significantly (by 3%) in response to Gln supplementation, but the 2.4% increase in milk protein yield was not statistically significant. Glutamine treatment had no effect on portal or hepatic venous blood flows. Net portal appearance of Gln and Glu was increased by Gln supplementation, accounting for 83% of the infused dose with, therefore, only limited amounts available to provide additional energy to fuel metabolism of the portal-drained viscera. The extra net portal appearance of Gln was offset, however, by a corresponding increase in hepatic removal such that net Gln splanchnic release was not different between treatments. Nonetheless, the Gln treatment resulted in a 43% increase in plasma Gln concentration. Infusions of Gln did not affect splanchnic flux of other nonessential amino acids or of essential amino acids. Glutamine supplementation increased plasma urea-N concentration and tended to increase net hepatic urea flux, with a numerical increase in liver hepatic O2 consumption. There were no effects on glucose in terms of plasma concentration, net portal appearance, net liver release, or postliver supply, suggesting that Gln supplementation had no sparing effect on glucose metabolism. Furthermore, mammary uptake of glucose and amino acids, including Gln, was not affected by Gln supplementation. In conclusion, this study did not support the hypothesis that supplemental Gln would reduce glucose utilization across the gut or increase liver gluconeogenesis or mammary glutamine uptake to increase milk protein synthesis.

Effects of dietary supplements of folic acid and vitamin B12 on metabolism of dairy cows in early lactation.

The present experiment was undertaken to determine the effects of dietary supplements of folic acid and vitamin B12 given from 3 wk before to 8 wk after calving on lactational performance and metabolism of 24 multiparous Holstein cows assigned to 6 blocks of 4 cows each according to their previous milk production. Supplementary folic acid at 0 or 2.6 g/d and vitamin B12 at 0 or 0.5 g/d were used in a 2 x 2 factorial arrangement. Supplementary folic acid increased milk production from 38.0 +/- 0.9 to 41.4 +/- 1.0 kg/d and milk crude protein yield from 1.17 +/- 0.02 to 1.25 +/- 0.03 kg/d. It also increased plasma Gly, Ser, Thr, and total sulfur AA, decreased Asp, and tended to increase plasma Met. Supplementary B12 decreased milk urea N, plasma Ile, and Leu and tended to decrease Val but increased homocysteine, Cys, and total sulfur AA. Liver concentration of phospholipids was higher in cows fed supplementary B12. Plasma and liver concentrations of folates and B12 were increased by their respective supplements, but the increase in plasma folates and plasma and liver B12 was smaller for cows fed the 2 vitamins together. In cows fed folic acid supplements, supplementary B12 increased plasma glucose and alanine, tended to decrease plasma biotin, and decreased Km of the methylmalonyl-coenzyme A mutase in hepatic tissues following addition of deoxyadenosylcobalamin, whereas it had no effect when cows were not fed folic acid supplements. There was no treatment effect on plasma nonesterified fatty acids as well as specific activity and gene expression of Met synthase and methylmalonyl-coenzyme A mutase in the liver. Ingestion of folic acid supplements by cows fed no supplementary B12 increased total lipid and triacylglycerols in liver, whereas these supplements had no effect in cows supplemented with B12. The increases in milk and milk protein yields due to folic acid supplements did not seem to be dependent on the vitamin B12 supply. However, when vitamin B12 was given in combination with folic acid, utilization of the 2 vitamins seems to be increased, probably more so in extrahepatic tissues. Metabolic efficiency seems also to be improved as suggested by similar lactational performance and dry matter intake for cows fed supplementary folic acid but increased plasma glucose and decreased hepatic lipids in cows fed folic acid and vitamin B12 together.

Effect of postruminal glutamine supplementation on immune response and milk production in dairy cows.

Seventeen multiparous Holstein cows were used to examine the effect of an increased duodenal supply of Gln on immune function and production. Cows received continuous abomasal infusions of water (control: n = 8) or 300 g/d of Gln (n = 9) for 21 d starting within 48 h of calving. There were nonsignificant increases in milk and milk protein yields in response to Gln supplementation. Glutamine treatment had no effect on plasma glucose, nonesterified fatty acids (NEFA), or beta-hydroxybutyrate (BHBA) concentrations but did tend to increase plasma urea N concentration. The Gln treatment resulted in an increase of 108 microM in the plasma Gln concentration. Total essential AA concentrations decreased with the Gln treatment, whereas total nonessential AA concentrations were unaffected. T Lymphocyte proliferation did not differ between the control and Gln-treated cows. Treatment had no effect on the relative abundance of CD8 T cells but did increase the abundance of CD4 T cells. Cytokine production, as measured by IFN-gamma concentration determined in vitro in concanavalin-A-stimulated peripheral blood mononuclear cells, was similar between the treatments. Over the first 3 wk following calving, Gln supplementation had limited effects on milk production, metabolic parameters, and immune function.

Triennial Lactation Symposium: Mammary metabolism of amino acids in dairy cows.

Although in dairy cows the mammary gland (MG) is the major net user of essential AA (EAA) supply, milk protein synthesis from absorbed EAA is not a straightforward process. Early studies identified 2 groups of EAA based on different pattern of mammary utilization: group 1 [Met, Phe (+Tyr), Trp], where MG uptake was similar to secretion in milk protein, and group 2 (Arg, Ile, Leu, Lys, Thr, and Val), where uptake exceeded milk protein output. This review examines the validity of this classification under variable protein supply through a meta-analysis, with the outcomes then explained with studies in which the fates of individual EAA were monitored using isotope approaches. For the meta-analysis, the Fick principle, based on stoichiometric transfer of Phe+Tyr uptake to milk protein, was used to estimate mammary plasma flow across all studies. This approach was judged acceptable because doubling Phe supply did not result in mammary oxidation of Phe+Tyr and either limited or no contribution of peptides to Phe and Tyr mammary supply could be detected. The AA content of proteins synthesized by the MG was estimated from milk protein composition, and the uptake-to-output ratio (U:O) for individual AA was re-calculated based on these assumptions. Analysis of individual samples by isotopic dilution resulted in reduced variance compared with analysis on pooled samples performed with an AA analyzer. Globally, the U:O of His and Met is maintained close to unity under variable protein supply. The group 2 AA could be subdivided. First, the U:O for group "2v" AA (Ile, Leu, Val, and Lys) is greater than 1 and varied with protein supply. Accordingly, the increased U:O of Leu, induced by duodenal casein infusion, led to extra-mammary Leu oxidation. Decreasing Lys supply decreased Lys U:O and the associated transfer of N to non-EAA, mainly to Glx, Asx, Ser, and Ala. Second, the U:O of group "2nv" AA, Arg and Thr, does not vary with protein supply. The Arg U:O averages 2.5, whereas the Thr U:O, albeit averaging 1.2, does not differ from unity. Excess of both these AA is probably directed toward the synthesis of non-EAA rather than energy supply. Overall, the ability of the MG to use excess EAA-N supply offers alternative sources of N and C for energy provision, lactose synthesis and non-EAA synthesis. The latter function spares dietary non-EAA for other necessary processes, such as gluconeogenesis and energy supply, in other tissues to support lactation.

Fenugreek (Trigonella foenum-graecum L.) as an alternative forage for dairy cows.

Fenugreek is a novel forage crop in Canada that is generating interest as an alternative to alfalfa for dairy cows. To evaluate the value of fenugreek haylage relative to alfalfa haylage, six, second lactation Holstein cows (56 ± 8 days in milk), which were fitted with rumen cannulas (10 cm i.d., Bar Diamond Inc., Parma, ID, USA) were used in a replicated three × three Latin square design with 18-day periods. Diets consisting of 400 g/kg haylage, 100 g/kg barley silage and 500 g/kg concentrate on a dry matter (DM) basis were fed once daily for ad libitum intake. The haylage component constituted the dietary treatments: (i) Agriculture and Agri-Food Canada F70 fenugreek (F70), (ii) Crop Development Center Quatro fenugreek (QUAT) and (iii) alfalfa (ALF). DM intake (DMI), milk yield and milk protein and lactose yields were higher (P < 0.001) for cows fed ALF than fenugreek (FEN, average of F70 and QUAT). Milk fat of cows fed FEN contained lower concentrations of saturated, medium-chain and hypercholestrolemic fatty acids (FAs; P < 0.05) than that of cows fed ALF. Apparent total tract digestibility of DM and nutrients was not affected by treatments. Similarly, individual ruminal volatile FA concentrations and rumen pH (5.9) were not affected by treatments. Rumen ammonia-N concentration was higher for FEN than ALF (P < 0.001). Estimates of neutral detergent fiber (NDF) passage rate (P < 0.05) and NDF turnover rate (P < 0.001) in the rumen were higher for ALF than FEN. Our results suggest that although the digestibility of the FEN diets was not different from that of the ALF diet, fenugreek haylage has a lower feeding value than ALF for lactating dairy cows due in part to lower DMI and subsequently lower milk yield.

Responses in mammary and splanchnic metabolism to altered lysine supply in dairy cows.

Lysine is usually taken up in excess by the mammary gland (MG) relative to milk protein output, allowing for mammary synthesis of non-essential (NE) amino acids (AA) from Lys-N. It is unclear whether this NEAA synthesis from Lys is obligate or whether more efficient use of Lys can be made under limiting conditions. Six multi-catheterized dairy cows received a basal diet low in protein plus an abomasal infusion of AA (560 g/day) with or without Lys (50.3 g/day), in a crossover design with 7-day periods. On day 7, all cows received a 7.5-h jugular infusion of [2-15N]lysine. Six blood samples were collected from arterial, portal, hepatic and mammary vessels at 45 min intervals. In addition, cows were milked at 6 and 7 h with the milk casein plus arterial and mammary plasma collected at 7 h analyzed for AA enrichment. Milk protein concentration and casein yield tended (P < 0.10) to decrease with Lys deletion, while Lys secretion in milk protein was lowered (P < 0.05). The addition of Lys in the AA mixture increased the net portal absorption of Lys by the amount infused, suggesting limited oxidation of this extra supply by the gut. Net liver flux of Lys was unaltered by treatment and, therefore, net splanchnic release of Lys reflected closely the amounts absorbed. For both treatments, however, post-liver supply was greater than mammary uptake, which exceeded milk output. Nonetheless, while Lys deletion decreased mammary uptake by 10.1 mmol/h, Lys in milk protein secretion was reduced by only 3.9 mmol/h. On a net basis, there was no evidence of the additional uptake of any other measured AA during the Lys deletion. The mammary uptake to output ratio of Lys decreased from 1.37 to 1.12, but still showed an excess with Lys deletion. The total amount of 15N in milk protein did not change with treatment but the distribution into AA was altered. In conditions that simulated normal feeding (Lys infused), 83% of the 15N was present as Lys, with Glx, Asx, Ser and Ala harvesting, respectively, 6.8%, 2.4%, 2.1% and 1.0%. With Lys depletion, N-transfers from Lys to other AA within the MG were still present, but rates were considerably lower. This would suggest that part, at least, of Lys catabolism in the MG is either needed or cannot be prevented completely, even at low supply of Lys. Such catabolism will provide N to support the synthesis of NEAA.

NIAID funds pediatric AIDS clinical trials group. National Institute of Allergy and Infectious Diseases.

AIDS: The National Institute of Allergy and Infectious Diseases (NIAID) has awarded 23 4-year grant programs to the Pediatric AIDS Clinical Trials Group, a national network that coordinates research projects. The money will support 21 trials, a data management center, and a new Coordinating and Operating Center. The restructured group's ability to conduct trials that address questions of high public health and scientific priority will be enhanced. As of February 1997, the group has initiated 60 trials, is currently recruiting patients for 27 studies, and has enrolled 10,867 participants.^ieng