Intrajugular Infusion Research Articles

Somatic and anxiety-like behaviors in male and female rats during withdrawal from the non-selective cannabinoid agonist WIN 55,212–2

Synthetic cannabinoids are associated with higher risk of dependence and more intense withdrawal symptoms than plant-derived Δ9-tetrahydrocannabinol (THC). Avoidance of withdrawal symptoms, including anxiogenic effects, can contribute to continued cannabinoid use. Adult male and female Long-Evans rats were given escalating doses of WIN 55,212–2 (WIN) via twice daily intrajugular infusions. Precipitated withdrawal was elicited with SR 141716 (rimonabant) 4 h after the final infusion. Global withdrawal scores (GWS) were compiled by summing z-scores of observed somatic behaviors over a 30-min period with locomotor activity simultaneously collected via beam breaks. Rimonabant precipitated withdrawal in female and male rats at 3 or 10 mg/kg, respectively, but the individual behaviors contributing to GWS were not identical. 3 mg/kg rimonabant did not impact locomotor behavior in females, but 10 mg/kg decreased locomotion in male controls. Spontaneous withdrawal observed between 6 and 96 h after the final infusion was quantifiable up to 24 h following WIN administration. Individual behaviors contributing to GWS varied by sex and time point. Males undergoing spontaneous withdrawal engaged in more locomotion than females undergoing withdrawal. Separate groups of rats were subjected to a battery of anxiety-like behavioral tests (elevated plus maze, open field test, and marble burying test) one or two weeks after WIN or vehicle infusions. At one week abstinence, sex-related effects were noted in marble burying and the open field test but were unrelated to drug treatment. At two weeks abstinence, females undergoing withdrawal spent more time grooming during marble burying and performed more marble manipulations than their male counterparts. WIN infusions did not impact estrous cycling, and GWS scores were not correlated with estrous at withdrawal. Collectively, these results show qualitative sex differences in behaviors contributing to the behavioral experience of cannabinoid withdrawal supporting clinical findings from THC.

Whole-body urea kinetics and functional roles of urea transporters and aquaporins in urea secretion into the rumen in sheep fed diets varying in crude protein content and corn grain processing method.

The objectives were to determine the effects of dietary crude protein (CP) content and corn grain processing on whole-body urea kinetics and the functional roles of urea transporter-B (UT-B) and aquaporins (AQP) in serosal-to-mucosal urea flux (Jsm-urea) in ovine ruminal epithelia. Thirty-two Rideau-Arcott ram lambs were blocked by bodyweight into groups of 4 and then randomly allocated within blocks to 1 of 4 diets (n = 8) in a 2 × 2 factorial design. Dietary factors were CP content (11% [LP] vs. 16% [HP]) and corn grain processing (whole-shelled [WSC] vs. steam-flaked [SFC] corn). Whole-body urea kinetics and N balance were determined using 4-d continuous intrajugular infusions of [15N15N]-urea with concurrent collections of urine and feces with four blocks of lambs (n = 4). After 23 d on diets, lambs were killed to collect ruminal epithelia for mounting in Ussing chambers to determine Jsm-urea and the measurement of mRNA abundance of UT-B and AQP. Serosal and mucosal additions of phloretin and NiCl2 were used to inhibit UT-B- and AQP-mediated urea transport, respectively. Lambs fed HP had a greater (P < 0.01) N intake (29.4 vs. 19.1g/d) than those fed LP; however, retained N (g/d or % of N intake) was not different. As a % of N intake, lambs fed SFC tended (P = 0.09) to have a lower N excretion (72.2 vs. 83.5%) and a greater N retention (27.8 vs. 16.6%) compared to those fed WSC. Endogenous urea-N production (UER) was greater in lambs fed HP compared to those fed LP (29.9 vs. 20.6g/d; P = 0.02), whereas urea-N secreted into the gut (GER; g/d) and urea-N used for anabolic purposes (UUA; g/d) were similar. Lambs fed LP tended (P = 0.05) to have greater GER:UER (0.78 vs. 0.66) and UUA:GER (0.23 vs. 0.13) ratios, and a greater Jsm-urea (144.7 vs. 116.1 nmol/[cm2 × h]; P = 0.07) compared to those fed HP. Lambs fed SFC tended to have a lower NiCl2-insensitive Jsm-urea (117.4 vs. 178.4 nmol/[cm2 × h]; P = 0.09) and had a lower phloretin-insensitive Jsm-urea (87.1 vs. 143.1 nmol/[cm2 × h]; P = 0.02) compared to those fed WSC. The mRNA abundance of UT-B (0.89 vs. 1.07; P = 0.08) and AQP-3 (0.90 vs. 1.05; P = 0.07) tended to be lower in lambs fed SFC compared to those fed WSC. Overall, reducing CP content tended to increase the GER:UER ratio with no changes in the expression or function of UT-B and AQP. Although corn grain processing had no effects on GER, feeding SFC increased the portion of urea secretion into the rumen that was mediated via UT-B and AQP.

Tibetan sheep require less energy intake than small-tailed Han sheep for N balance when offered a low protein diet

Tibetan sheep are indigenous to the Qinghai-Tibetan Plateau and graze natural pasture all year round; small-tailed Han sheep were introduced to the plateau, are raised mainly in feedlots and graze natural pasture only in summer. A low energy intake could have a negative effect on N utilization and N balance in ruminants. We hypothesized that Tibetan sheep require less energy for N balance and utilize N more efficiently than Han sheep when offered a low protein and low energy diet. To test this hypothesis, we examined the effect of dietary energy on whole-body N retention and urea kinetics in Tibetan (47.7 ± 2.46 kg BW) and Han (46.2 ± 3.42 kg BW) sheep. Diets were formulated to be low in crude protein (˜7%) with different metabolizable energy levels (6.73, 7.65, 8.57 and 9.49 MJ/kg). Urea kinetics were determined using continuous intrajugular infusion of 15N15N-urea for 72 h. N retention was greater (P < 0.01) in Tibetan than in Han sheep and increased linearly with increasing energy intake (P < 0.001). Tibetan sheep maintained a positive N balance on all dietary energy levels, whereas Han sheep were in a negative N balance at the lowest energy intake. To achieve a N balance of zero, Tibetan sheep required 0.28 MJ/kg0.75, whereas Han sheep required 0.33 MJ/kg0.75 per day. Fecal N excretion was less (P < 0.05) for Tibetan than for Han sheep. Plasma urea concentrations tended to be greater in Tibetan than in Han sheep (P < 0.10), but urinary urea excretion was lower in Tibetan sheep at the lowest energy diet (linear dietary energy × breed; P < 0.05). As energy intake increased, urinary N decreased linearly (P < 0.001) and microbial N production increased linearly (P < 0.001). Urea entry rate and gastrointestinal tract entry rate were greater in Tibetan than in Han sheep (P < 0.01). Urinary purine derivatives excretion, microbial N production, and the portion of microbial N that originated from recycled urea were greater in Tibetan than in Han sheep (P < 0.01). Renal urea reabsorption rate was greater in Tibetan than in Han sheep (P < 0.05) and increased linearly with dietary energy level (P < 0.05). We concluded that: 1) Tibetan sheep were better able to cope with low N diets when energy intake was low; and 2) when N intakes are low, N utilization is improved by supplemental energy.

Efficiency of rumen microbial protein synthesis in cattle grazing tropical pastures as estimated by a novel technique

The efficiency of microbial protein synthesis (EMPS) in cattle grazing a range of tropical pasture types was examined using a new method of intra-jugular infusion of chromium–EDTA to estimate urinary excretion of purine derivatives. Seven pasture types were studied in south-eastern Queensland, Australia, over a 13-month period. These included native tropical grass (C4) pasture (major species Heteropogon contortus and Bothriochloa bladhii) studied in the early wet, the wet–dry transition and the dry season; introduced tropical grass (C4) pasture (Bothriochloa insculpta) in the mid-wet season; two introduced tropical legume species (C3; Lablab purpureus and Clitoria ternatea); and the temperate-grass (C3) pasture, ryegrass (Lolium multiflorum). There was a large range in EMPS across pasture types, with a range of 26–209 g microbial crude protein per kilogram digestible organic matter intake (DOMI). Estimated rumen-degradable protein (RDP) supply (42–525 g/kg DOMI) was the major factor associated with EMPS across the range of pasture types studied. EMPS in steers grazing all tropical grass pastures was low (&amp;lt;130 g/kg DOMI) and limited by RDP supply. Negative linear relationships (P &amp;lt; 0.05) between EMPS and concentrations of both neutral detergent fibre and acid detergent fibre in extrusa were evident. However, non-fibre carbohydrate in extrusa, total non-structural carbohydrate concentration in plucked pasture leaf, rumen fluid and particle dilution rate, protozoal concentration in rumen fluid and rumen fluid pH were not correlated with EMPS. It was concluded that EMPS was well below 130 g microbial crude protein per kilogram DOMI when cattle grazed unfertilised, tropical grass pastures in south-eastern Queensland and that RDP was the primary limiting nutrient. High EMPS was associated with a very high RDP, vastly in excess of RDP requirements by microbes.

Effects of dietary crude protein and rumen-degradable protein concentrations on urea recycling, nitrogen balance, omasal nutrient flow, and milk production in dairy cows

The objective of this study was to determine how interactions between dietary crude protein (CP) and rumen-degradable protein (RDP) concentrations alter urea-nitrogen recycling, nitrogen (N) balance, omasal nutrient flow, and milk production in lactating Holstein cows. Eight multiparous Holstein cows (711±21kg of body weight; 91±17d in milk at the start of the experiment) were used in a replicated 4×4 Latin square design with a 2×2 factorial arrangement of dietary treatments and 29-d experimental periods. Four cows in one Latin square were fitted with ruminal cannulas to allow ruminal and omasal sampling. The dietary treatment factors were CP (14.9 vs. 17.5%; dry matter basis) and RDP (63 vs. 69% of CP) contents. Dietary RDP concentration was manipulated by including unprocessed or micronized canola meal. Diet adaptation (d 1–20) was followed by 8d (d 21–29) of sample and data collection. Continuous intrajugular infusions of [15N15N]-urea (220mg/d) were conducted for 4d (d 25–29) with concurrent total collections of urine and feces to estimate N balance and whole-body urea kinetics. Proportions of [15N15N]- and [14N15N]-urea in urinary urea, and 15N enrichment in feces were used to calculate urea kinetics. For the low-CP diets, cows fed the high-RDP diet had a greater DM intake compared with those fed the low-RDP diet, but the opposite trend was observed for cows fed the high-CP diets. Dietary treatment had no effect on milk yield. Milk composition and milk component yields were largely unaffected by dietary treatment; however, on the low-CP diets, milk fat yield was greater for cows fed the low-RDP diet compared with those fed the high-RDP diet, but it was unaffected by RDP concentration on the high-CP diets. On the high-CP diets, milk urea nitrogen concentration was greater in cows fed the high-RDP diet compared with those fed the low-RDP diet, but it was unaffected by RDP concentration on the low-CP diets. Ruminal NH3-N concentration tended to be greater in cows fed the high-CP diet compared with those fed the low-CP diet, and it was greater in cows fed the high-RDP diet as compared with those fed the low-RDP diet. Nitrogen intake and both total N and urea-N excretion in urine were greater for cows fed the high-CP diet compared with those fed the low-CP diet. However, N balance and urinary excretion of purine derivatives were unaffected by dietary treatment. Urea-N entry rate (UER) was greater in cows fed the high-CP diet compared with those fed the low-CP diet; however, UER was unaffected by dietary RDP concentration. The proportion of urea-N recycled to the gastrointestinal tract (as a percentage of UER) was greater in cows fed the low-CP diet compared with those fed the high-CP diet. In summary, reducing dietary CP concentration decreased urinary N excretion but had no effect on milk yield, thus resulting in an overall improvement in milk N efficiency.

A comparison of nitrogen utilization and urea metabolism between Tibetan and fine-wool sheep.

To study metabolic adaptation to harsh foraging conditions, an experiment was conducted to characterize and quantify N utilization efficiency and urea metabolism in Tibetan and fine-wool sheep fed 4 levels of dietary N (11.0, 16.7, 23.1, and 29.2 g N/kg DM) in 2 concurrent 4 × 4 Latin square designs. Urea kinetics were determined using continuous intrajugular infusions of 15N15N-urea. Urinary excretions of total N and urea N increased linearly (P < 0.001) with dietary N and were not different between breeds (P ≥ 0.37). Fecal N excretion increased with dietary N for Tibetan sheep but not for fine-wool sheep (linear dietary N × breed; P < 0.05). Nitrogen retention (both amount per day and percentage of N intake) increased with increasing dietary N concentration (P < 0.001), and the rates of increase were greater in fine-wool than in Tibetan sheep (linear dietary N × breed and cubic dietary N × breed; P < 0.05). In Tibetan sheep, N retention as a percentage of intake was greatest for diets containing 16.7 g N/kg DM, whereas it was maximal for fine-wool sheep when the diet contained 23.1 g N/kg DM. Urea N entry rate, urea N recycled to the gastrointestinal tract (GIT), and urea N returned to the ornithine cycle all increased with dietary N (P < 0.05), and all were greater in Tibetan than fine-wool sheep for the 11.0 g N/kg DM diet but were greater in fine-wool than Tibetan sheep for the diet with 29.2 g N/kg DM (linear dietary N × breed; P < 0.05). Urea N excreted in feces, both amount and fraction of GIT entry rate, was less in Tibetan than fine-wool sheep for the 11.0 and 16.7 g N/kg DM diets but similar for diets with 23.1 or 29.2 g N/kg DM (linear dietary N × breed; P < 0.01). For the lowest-protein diet, the fraction of urea N production recycled to the GIT was greater in the Tibetan than fine-wool sheep (88% vs. 82%), but for the diet with 29.2 g N/kg DM it was greater for fine-wool than Tibetan sheep (46% vs. 39%; linear dietary N × breed; P < 0.05). Plasma urea N increased more rapidly in response to increasing dietary N concentration for fine-wool sheep than for Tibetan sheep (linear dietary N × breed; P < 0.05). Urea tubular load and the amount and percentage of urea reabsorbed by the kidney were greater in Tibetan than fine-wool sheep (P < 0.05). These results suggest that Tibetan sheep have mechanisms that allow them to utilize N more efficiently than the fine-wool sheep when dietary N is inadequate.

Urea kinetics and nitrogen balance and requirements for maintenance in Tibetan sheep when fed oat hay

Tibetan sheep inhabit the Qinghai-Tibetan Plateau, an area characterized by sparse vegetation of low protein content much of the year. Consequently, we predicted that their N requirements for maintenance would be low. To test our prediction, we determined urea kinetics, N balance and requirements for maintenance in five growing wethers (43.0±2.3kg live weight). A 4×4 Latin square design was used with 4 levels of oat hay intakes (0.3, 0.5, 0.7, and 0.9×voluntary intake), in which each period lasted for 21 days. Urea kinetics was determined using a continuous intrajugular infusion of 15N15N-urea. There was a linear increase in faecal N excretion, urinary N elimination and N retention (P<0.01) with an increase in feed intake. From the regression equation generated between daily N retention and daily N intake, the estimated N requirements for maintenance were 0.50g/kg BW0.75 per day, that is, only 66% of the amount recommended by NRC for growing sheep of its size. However, it should be noted that the NRC values were for sheep without marked feed restriction. Urea-N entry rate (UER), gastrointestinal tract (GIT) entry rate (GER), return to ornithine cycle (ROC) and faecal urea-N excretion all increased linearly (P<0.01) with an increase in DMI. The ratio of UER to apparent digestible N intake increased linearly from 1.53 to 2.99 with a decrease in feed intake. The proportion of UER that entered the gut did not differ (P>0.05) among intakes and ranged between 0.52 and 0.61. GER used for anabolism decreased (P<0.01) from 0.45 to 0.28, whereas GER to ROC increased linearly (P<0.01) from 0.51 to 0.68 with increasing DMI. Glomerular filtration rate increased (P<0.05) with increasing DMI, but urinary creatinine excretion and plasma urea-N concentrations remained constant (P>0.05). The proportion of renal urea-N reabsorbed increased linearly with a decrease in DMI (P<0.05) while GIT urea-N clearance was always higher than kidney urea-N clearance. The low N requirements demonstrated by the Tibetan sheep supported our prediction. The increase in renal urea-N absorption rate with a decrease in nitrogen and feed intake, the greater ratios of UER to apparent digestible N intake and the greater GIT urea-N clearance to kidney urea-N clearance, regardless of N intake explain, at least in part, how Tibetan sheep cope with low nitrogen intake.

Effects of intrajugular glucose infusion on feed intake, milk yield, and metabolic responses of early postpartum cows fed diets varying in protein and starch concentration

Effects of glucose infusion on feed intake, milk production, and metabolic responses of early postpartum cows fed diets varying in starch and protein concentration were evaluated by utilizing a randomized complete block design with a 2 × 2 factorial arrangement of treatments. Twenty-four multiparous Holstein cows were blocked by body condition score and 305-d mature-equivalent milk yield and randomly assigned at calving to 1 of 4 treatments. Treatments were continuous intrajugular infusion of glucose (GI) or isotonic saline (SI), and diets containing high starch, low crude protein (HSLP) or high crude protein, low starch (HPLS) concentrations. Treatments were initiated at the first scheduled feeding following parturition and lasted 12 d. The GI reduced cumulative dry matter intake and tended to reduce daily dry matter intake and meal size for HPLS but not HSLP compared with SI. The GI increased cumulative milk yield by 39 kg/12 d compared with SI by increasing it for HSLP but not HPLS. The HPLS treatment tended to increase loss of body condition from 0.65 to 0.82 body condition score units/12 d compared with HSLP. Consistent with this, HPLS increased plasma concentrations of nonesterified fatty acids, β-hydroxybutyrate, liver triglyceride, milk fat concentration and yield, 3.5% fat-corrected milk, and milk urea nitrogen compared with HSLP. Overall, the GI-HPLS treatment reduced feed intake by reducing meal size. The GI-HPLS may have reduced meal size by the independent or additive effects of (1) decreasing hepatic gluconeogenesis and promoting oxidation of acetyl coenzyme A (CoA), (2) elevated plasma nonesterified fatty acids from HPLS increasing the pool of acetyl CoA available to be oxidized, and (3) the HPLS diet increasing urea synthesis, which also provides the tricarboxylic acid cycle intermediate fumarate to promote oxidation of acetyl CoA.

Effects of prepartum 2,4-thiazolidinedione on insulin sensitivity, plasma concentrations of tumor necrosis factor-α and leptin, and adipose tissue gene expression

Administration of peroxisome proliferator-activated receptor gamma (PPARγ) ligands, thiazolidinediones (TZD), to prepartum dairy cattle has been shown to improve dry matter intake and decrease circulating nonesterified fatty acids (NEFA) around the time of calving. The objective of this work was to elucidate mechanisms of TZD action in transition dairy cattle by investigating changes in plasma leptin, tumor necrosis factor-α (TNFα), the revised quantitative insulin sensitivity check index (RQUICKI), and adipose tissue gene expression of leptin, PPARγ, lipoprotein lipase (LPL), and fatty acid synthase (FAS). Multiparous Holstein cows (n=40) were administered 0, 2.0, or 4.0mg of TZD/kg of body weight (BW) by intrajugular infusion once daily from 21d before expected parturition until parturition. Plasma samples collected daily from 22d before expected parturition through 21d postpartum were analyzed for glucose, NEFA, and insulin. Plasma samples collected on d −14, −3, −1, 1, 3, 7, 14, and 49 relative to parturition were also analyzed for leptin and TNFα. Adipose tissue was collected on d 7 before expected parturition from a subset of cows, and gene expression was examined via quantitative real-time PCR. A tendency for a treatment by time effect on plasma leptin prepartum was observed such that values were similar on d −14 but cows receiving 2.0mg/kg of BW of TZD tended to have lower circulating leptin as calving approached. Postpartum leptin tended to be increased linearly (2.3, 2.4, and 2.5±0.1ng/mL for 0, 2.0, and 4.0mg/kg treatments, respectively) in cows that received TZD prepartum. Plasma TNFα increased linearly (2.6, 3.7, and 4.0±0.1 pg/mL) in response to TZD treatment and decreased through the first week postpartum. Calculation of RQUICKI 1/[log(glucose)+log(insulin)+log(NEFA)] suggested altered insulin sensitivity in cows administered TZD that may depend on day relative to calving. Administration of TZD increased adipose tissue expression of PPARγ mRNA (11.0, 13.3, and 12.8±1.9). Administration of TZD had a quadratic effect on gene expression of leptin (16.2, 10.7, and 17.4±1.6) and no effect on LPL expression, and expression of FAS was lower for TZD-treated cows than for controls (8.2, 4.2, and 6.1±1.8, respectively). Results imply altered expression and plasma concentrations of leptin, increased plasma TNFα concentrations, and increased expression of PPARγ in adipose tissue as potential mechanisms for the effects of TZD administration on transition dairy cattle.

Dietary Ca concentration to minimize the risk of hypocalcaemia in dairy cows is affected by the dietary cation–anion difference

The objective of this study was to determine whether dietary Ca concentration affects the ability to maintain Ca homeostasis in non-lactating non-pregnant dairy cows fed diets differing in dietary cation–anion difference (DCAD). Eight non-lactating non-pregnant multiparous Holstein cows (594 ± 80.3 kg body weight; 34.5 ± 11.4 month old) were fed diets Low or High in DCAD (−64 vs. 82 mequiv./kg dry matter, respectively) in combinations with Low or High dietary Ca concentration (3.0 vs. 9.1 g/kg of dry matter, respectively) in a duplicated 4 × 4 Latin square design with 14-d periods. On d 14 of each period, cows were subjected to an EDTA challenge that consists of an intra-jugular infusion of EDTA solution to decrease blood Ca concentration. In this protocol, the time required to recover to 90% of the pre-challenge blood Ca concentration was determined as recovery time. During the EDTA challenge, mean blood bicarbonate concentration was lower for cows fed Low-DCAD diets although mean blood pH was not affected by treatment, indicating that cows fed Low-DCAD diets had mild compensated metabolic acidosis. Feeding High-Ca diet shortened the recovery time (106 vs. 134 min; P=0.04) when DCAD was low, while Low-Ca diet shortened the recovery time (125 vs. 159 min; P=0.02) when DCAD was high. These results suggest that the optimum dietary Ca concentration to minimize the risk of hypocalcaemia in dairy cows is likely different depending on the DCAD value.

Feeding sunflower oil to partially defaunate the rumen increases nitrogen retention, urea-nitrogen recycling to the gastrointestinal tract and the anabolic use of recycled urea-nitrogen in growing lambs

The objective of the present study was to delineate how interactions between feeding sunflower oil (SFO) to partially defaunate the rumen and altering dietary ruminally fermentable carbohydrate may alter urea-N kinetics and N metabolism in lambs. In a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments, four Suffolk ram lambs (61·5 (se 4·0) kg) were used. Treatments were 0 ( - SFO) v. 6 % (+SFO) SFO and dry-rolled barley (DRB) v. pelleted barley (PB). N balance was measured over 4 d, with concurrent measurement of urea-N kinetics using continuous intra-jugular infusions of [(15)N(15)N]urea. Feeding SFO decreased (P = 0·001) ruminal protozoa and NH3-N concentrations. Urinary N excretion was lower (P = 0·003), and retained N was higher (P = 0·002) in +SFO lambs compared with - SFO lambs. Endogenous production of urea-N (urea-N entry rate; UER) was similar across treatments. Urea-N transfer to the gastrointestinal tract (GIT) (GIT entry rate; GER), expressed as absolute amounts (16·4 v. 13·1 g/d) or as a proportion of the UER (0·693 v. 0·570), its anabolic use (9·0 v. 6·0 g/d) and microbial N supply (14·6 v. 10·9 g/d) were higher (P ≤ 0·001) in +SFO lambs compared with -SFO lambs. As a proportion of the UER, GER was higher, whereas urinary urea-N loss was lower, in lambs fed PB compared with those fed DRB (P = 0·01). In summary, feeding SFO increased urea-N recycling to the GIT and microbial non-NH(3)-N supply, thus providing new evidence that the improved efficiency of N utilization in partially defaunated ruminants could be partly mediated by an increase in urea-N recycling.

Effect of feeding fat or intrajugular infusion of glucagon-like peptide-1 and cholecystokinin on dry matter intake, digestibility, and digesta rate of passage in growing wethers1

A cause and effect relationship between glucagon-like peptide 1 (7, 36) amide (GLP-1) and cholecystokinin (CCK) and DMI regulation has not been established in ruminants. Three randomized complete block experiments were conducted to determine the effect of feeding fat or infusing GLP-1 or CCK intravenously on DMI, nutrient digestibility, and Cr rate of passage (using Cr(2)O(3) as a marker) in wethers. A total of 18 Targhee × Hampshire wethers (36.5 ± 2.5 kg of BW) were used, and each experiment consisted of four 21-d periods (14 d for adaptation and 7 d for infusion and sampling). Wethers allotted to the control treatments served as the controls for all 3 experiments; experiments were performed simultaneously. The basal diet was 60% concentrate and 40% forage. In Exp. 1, treatments were the control (0% added fat) and addition of 4 or 6% Ca salts of palm oil fatty acids (DM basis). Treatments in Exp. 2 and 3 were the control and 3 jugular vein infusion dosages of GLP-1 (0.052, 0.103, or 0.155 µg•kg of BW(-1)•d(-1)) or CCK (0.069, 0.138, or 0.207 µg•kg of BW(-1)•d(-1)), respectively. Increases in plasma GLP-1 and CCK concentrations during hormone infusions were comparable with increases observed when increasing amounts of fat were fed. Feeding fat and infusion of GLP-1 tended (linear, P = 0.12; quadratic, P = 0.13) to decrease DMI. Infusion of CCK did not affect (P > 0.21) DMI. Retention time of Cr in the total gastrointestinal tract decreased (linear, P < 0.01) when fat was fed, but was not affected by GLP-1 or CCK infusion. In conclusion, jugular vein infusion produced similar plasma CCK and GLP-1 concentrations as observed when fat was fed. The effects of feeding fat on DMI may be partially regulated by plasma concentration of GLP-1, but are not likely due solely to changes in a single hormone concentration.

Effects of partial ruminal defaunation on urea-nitrogen recycling, nitrogen metabolism, and microbial nitrogen supply in growing lambs fed low or high dietary crude protein concentrations1

Urea-nitrogen recycling to the gastrointestinal tract (GIT), N metabolism, and urea transporter-B (UT-B) mRNA abundance in ruminal epithelium were evaluated in partially defaunated (PDFAUN) and faunated (FAUN) growing lambs fed 2 levels (10%, low, or 15%, high) of dietary CP (DM basis). Four Suffolk ram lambs (43.9 +/- 1.4 kg initial BW) were used in a 4 x 4 Latin square design with 27-d periods. Sunflower oil was fed (6%; DM basis) as an anti-protozoal agent. Nitrogen balance was measured from d 22 to 26, with concurrent measurement of urea-N kinetics using continuous intrajugular infusions of [(15)N(15)N]-urea. Feeding sunflower oil decreased (P < 0.01) total ruminal protozoa by 88%, and this was associated with a decrease (P < 0.01) in ruminal ammonia-N concentrations. Endogenous production of urea-N (UER; 26.1 vs. 34.6 g/d) and urea-N loss in urine (UUE; 10.1 vs. 15.7 g/d) were less (P < 0.01), and urea-N entering the GIT (GER; 16.0 vs. 18.9 g/d) tended to be less (P = 0.06) in PDFAUN as compared with FAUN lambs. However, as a proportion of UER, GER was greater (P < 0.01) and the proportion of recycled urea-N that was utilized for anabolism (i.e., UUA) tended to be greater (P = 0.09) in PDFAUN lambs. Partial defaunation increased (P < 0.01) microbial N supply. The UER, GER, and UUE were greater (P < 0.01) in lambs fed the high diet. However, as a proportion of UER, GER and its anabolic use were greater (P < 0.01) in lambs fed the low diet. The expression of UT-B mRNA in PDFAUN lambs was numerically greater (by 20%; P = 0.15) compared with FAUN lambs. In summary, results indicate that part of the mechanism for improved N utilization in defaunated ruminants is an increase in the proportion of endogenous urea-N output that is recycled to the GIT, thus potentially providing additional N for microbial growth.

Effects of prepartum 2,4-thiazolidinedione on metabolism and performance in transition dairy cows

Thiazolidinediones (TZD) are potent synthetic ligands for peroxisome proliferator-activated receptor-γ that have been shown previously to reduce plasma nonesterified fatty acids and increase peripartal dry matter intake (DMI) in dairy cows. Data from Holstein cows (n = 36) entering their second or greater lactation were used to determine whether late prepartum administration of TZD would affect periparturient metabolism, milk production, and ovarian activity. Cows were administered 0, 2.0, or 4.0mg of TZD/kg of BW by intrajugular infusion once daily from 21 d before expected parturition until parturition. Plasma samples were collected daily from 22 d before expected parturition through 21 d postpartum and twice weekly from wk 4 through 9 postpartum. In response to increasing TZD dosage, plasma nonesterified fatty acid concentrations decreased linearly during the postpartum period (d 0 to +21: 348, 331, 268±31μEq/L, respectively). Plasma concentrations of glucose were highest in cows administered 4.0mg of TZD/kg of BW during the peripartum and postpartum periods (d −7 to +7: 57.9, 57.8, 61.1±0.8 mg/dL and d 0 to +21: 51.6, 49.3, 54.7±1.1 mg/dL, respectively). Plasma concentrations of β-hydroxybutyrate were increased during the peripartum period by TZD administration (9.6, 9.9, 10.2±0.3 mg/dL) but were not affected during the postpartum period. Plasma insulin was not affected by treatment during any time period. Postpartum liver triglyceride content was decreased linearly (11.0, 10.4, 4.2±1.6%) and glycogen content was increased linearly (2.16, 2.38, 2.79±0.19%) by prepartum TZD administration. Prepartum TZD administration linearly increased DMI during the peripartum period (d −7 to +7: 16.1, 17.2, 17.3±0.5 kg/d). Cows administered TZD prepartum maintained higher postpartum body condition scores than control cows (wk 1 through 9: 2.77, 2.89, 3.02±0.05). There was no effect of prepartum TZD on milk yield; however, yields of 3.5% fat-corrected milk (52.2, 54.6, 48.0±1.6 kg/d) and most other milk components were decreased in cows that received 4.0mg of TZD/kg of BW prepartum. Prepartum TZD administration linearly decreased the number of days to first ovulation (29.3, 28.3, 19.0±3.6 d). These results suggest that prepartum administration of TZD improves metabolic health and DMI of periparturient dairy cows and may decrease reliance on body fat reserves during early lactation.

Urea metabolism in beef steers fed tall fescue, orchardgrass, or gamagrass hays1,2

Two experiments were conducted to assess effects of endophyte treatments (Exp. 1), forage species (Exp. 2), and supplementation (Exp. 2) on urea production, excretion, and recycling in beef steers. Infusion of (15,15)N-urea and enrichment of urea in urine samples were used to calculate urea-N entry and recycling to the gut. Acceptably stable enrichment of (15)N-urea in urine was obtained after 50 h of intrajugular infusion of (15,15)N-urea, indicating that valid data on urea metabolism can be obtained from steers fed forages twice daily. After adjustment by covariance for differences in N intake among treatments in Exp. 1, steers fed endophyte-infected tall fescue had less (P<0.10) urea-N entry, recycling to the gut, and return of recycled urea-N to the ornithine cycle than those fed endophyte-free or novel endophyte-infected tall fescue. However, urea-N urinary excretion or return to the gut was similar among endophyte treatments when expressed as a proportion of urea-N entry. Urea-N entry and return to the gut in Exp. 2 was similar in steers fed gamagrass or orchardgrass hay after adjustment by covariance for differences in N intake. Less (P<0.01) urinary excretion, expressed as grams per day or as a proportion of urea-N entry, with gamagrass than with orchardgrass was associated with faster in vitro NDF-N digestion with gamagrass. Supplementation of gamagrass or orchardgrass with 1.76 kg/d of readily fermentable fiber and starch decreased urea entry (P<0.06) and urinary excretion of urea (P<0.01). Interactions between hay source and supplement reflected a greater response to supplementation for steers fed orchardgrass than for those fed gamagrass. After adjustment for differences among treatments in N supply, results of both experiments support the concept of improved N use in response to increased carbohydrate fermentability in the rumen, due either to inherent differences in forage fiber or to supplementation with readily fermentable carbohydrate (starch or fiber). Closer coordination of ruminal fermentation of carbohydrate and N sources provided greater and more efficient capture of dietary N as tissue protein in forage-fed steers.

Bioluminescence imaging to monitor the in vivo distribution of administered mesenchymal stem cells in acute kidney injury

Effective and targeted delivery of cells to injured organs is critical to the development of cell therapies. However, currently available in vivo cell tracking methods still lack sufficient sensitivity and specificity. We examined, therefore, whether a highly sensitive and specific bioluminescence method is suitable to noninvasively image the organ distribution of administered mesenchymal stem cells (MSCs) in vivo. MSCs were transfected with a luciferase/neomycin phosphotransferase construct (luc/neo-MSC). Bioluminescence of these cells was measured (charge-coupled device camera) after treatment with luciferin, showing a linear increase of photon emission with rising cell numbers. To track these cells in vivo, groups of mice were injected with 1 x 10(5) luc/neo-MSCs/animal and imaged with bioluminescence imaging at various time points. Injection of cells in the suprarenal aorta showed diffuse distribution of cells in normal animals, whereas distinct localization to the kidneys was observed in mice with ischemia- and reperfusion-induced acute kidney injury (AKI). Intrajugular infusion of MSCs demonstrated predominant accumulation of cells in both lungs. In animals with AKI, detectable cell numbers declined over time, as assessed by bioluminescence imaging and confirmed by PCR, a process that was associated with low apoptosis levels of intrarenally located MSCs. In conclusion, the described bioluminescence technology provides a sensitive and safe tool for the repeated in vivo tracking of infused luc/neo-MSCs in all major organs. This method will be of substantial utility in the preclinical testing and design of cell therapeutic strategies in kidney and other diseases.

Effect of chronic growth hormone and hyperinsulinemic euglycemia on endogenous glucose production and utilization in periparturient dairy cows

Twenty-one periparturient Holstein cows were used to assess the effects of chronic intramuscular growth hormone (GH) and hyperinsulinemic euglycemia (HE) on glucose rate of appearance (Ra) into plasma. Cows were administered intramuscular GH (40 mg) or saline (CTL) daily for 96 h beginning either 25 d prepartum (GH, n=5; CTL, n=6) or 5 d postpartum (GH, n=6; CTL, n=4). Glucose Ra into plasma was determined using tracer methodologies on d 4 of treatment during basal condition and again during a period of HE. The period of HE was initiated immediately after the basal period and lasted for 4 h. It involved a 2 μg*kg−1 infusion of bovine insulin with maintenance of glycemia within 10% of the pre-insulin baseline by intrajugular infusion of exogenous glucose. The HE decreased endogenous glucose Ra to a greater extent postpartum than it did prepartum (P<0.001). Chronic GH increased endogenous glucose Ra (P=0.03); however there were no interactions of GH with physiological state (pre- vs. postpartum) or degree of suppression of endogenous Ra by HE. The amount of exogenous glucose needed to maintain euglycemia during HE was not affected by GH (P≥0.20). In conclusion, there were no interactions of chronic GH with insulin relative to glucose metabolism. However, insulin did have differential effects on glucose metabolism during the pre-and postpartum periods. Project funded by internal sources.

Interactions Between Barley Grain Processing and Source of Supplemental Dietary Fat on Nitrogen Metabolism and Urea-Nitrogen Recycling in Dairy Cows

The objective of this study was to determine the effects of methods of barley grain processing and source of supplemental fat on urea-N transfer to the gastrointestinal tract (GIT) and the utilization of this recycled urea-N in lactating dairy cows. Four ruminally cannulated Holstein cows (656.3±27.7kg of BW; 79.8±12.3 d in milk) were used in a 4×4 Latin square design with 28-d periods and a 2×2 factorial arrangement of dietary treatments. Experimental diets contained dry-rolled barley or pelleted barley in combination with whole canola or whole flaxseed as supplemental fat sources. Nitrogen balance was measured from d 15 to 19, with concurrent measurements of urea-N kinetics using continuous intrajugular infusions of [15N15N]-urea. Dry matter intake and N intake were higher in cows fed dry-rolled barley compared with those fed pelleted barley. Nitrogen retention was not affected by diet, but fecal N excretion was higher in cows fed dry-rolled barley than in those fed pelleted barley. Actual and energy-corrected milk yield were not affected by diet. Milk fat content and milk fat yield were higher in cows fed dry-rolled barley compared with those fed pelleted barley. Source of supplemental fat did not affect urea-N kinetics. Urea-N production was higher (442.2 vs. 334.3g of N/d), and urea-N entering the GIT tended to be higher (272.9 vs. 202.0g of N/d), in cows fed dry-rolled barley compared with those fed pelleted barley. The amount of urea-N entry into the GIT that was returned to the ornithine cycle was higher (204.1 vs. 159.5g of N/d) in cows fed dry-rolled barley than in pelleted barley-fed cows. The amount of urea-N recycled to the GIT and used for anabolic purposes, and the amounts lost in the urine or feces were not affected by dietary treatment. Microbial nonammonia N supply, estimated using total urinary excretion of purine derivatives, was not affected by diet. These results show that even though barley grain processing altered urea-N entry into the GIT, the utilization of this recycled urea-N for microbial production was unaffected as the additional urea-N, which entered the GIT was returned to ureagenesis.

Effects of barley grain processing and dietary ruminally degradable protein on urea nitrogen recycling and nitrogen metabolism in growing lambs1

The objective of this study was to determine how interactions between dietary ruminally degradable protein (RDP) level and ruminally fermentable carbohydrate (RFC) alter urea N transfer to the gastrointestinal tract (GIT) and the utilization of this recycled urea N in rapidly growing lambs fed high-N diets. Four Suffolk ram lambs (34.8 +/- 0.5 kg of BW) were used in a 4 x 4 Latin square design with 21-d periods and a 2 x 2 factorial arrangement of dietary treatments. The dietary factors studied were 1) dry-rolled vs. pelleted barley as the principal source of RFC and 2) dietary levels of RDP of 60 vs. 70% (% of CP). All diets contained 28.8 g of N/kg of DM. Experimental diets were composed of 80% concentrate mixture and 20% barley silage (DM basis) and were fed twice daily at 0900 and 1700 as total mixed rations. Nitrogen balance was measured from d 15 to 20, and urea N kinetics were measured from d 15 to 19 using intrajugular infusions of [(15)N(15)N]-urea. Nitrogen intake (P = 0.001) and fecal (P = 0.002) and urinary (P = 0.03) N excretion increased as dietary RDP level increased, but the method of barley processing had no effect. Feeding dry-rolled compared with pelleted barley (P = 0.04) as well as feeding 60% RDP compared with 70% RDP (P = 0.04) resulted in a greater N digestibility. Whole-body N retention was unaffected (P >/= 0.74) by dietary treatment. Dietary treatment had no effect on endogenous production of urea N and its recycling to the GIT; however, across dietary treatments, endogenous production of urea N (45.8 to 50.9 g/d) exceeded N intake (42.3 to 47.9 g/d). Across dietary treatments, 30.6 to 38.5 g/d of urea N were recycled to the GIT, representing 0.67 to 0.74 of endogenous urea N production; however, 0.64 to 0.76 of urea N recycled to the GIT was returned to the ornithine cycle. In summary, although dietary treatment did not alter urea N kinetics, substantial amounts of hepatic urea N output were recycled to the GIT under the dietary conditions used in this study, and additional research is required to determine how this recycled urea N can be efficiently captured by bacteria within the GIT.

Comparison of Blood Glucose Concentrations After Administration of a Glucose Solution via the Jugular Vein and Portal Vein in Cows

The goals of the present study were to determine whether the infusion of a glucose solution into the portal vein is tolerated in cows and whether the glucose concentration differs after administration of glucose into the jugular vein and portal vein. Fifteen healthy Swiss Braunvieh cows were used. An indwelling catheter was placed in both jugular veins and a balloon-tipped indwelling catheter with a diameter of 2 mm was placed in the portal vein under the guidance of ultrasonography. Three cows received 500 ml of 20% glucose solution over 60 min via the left jugular vein. Three other cows received the same solution over 60 min via the portal vein. Blood samples were collected from the right jugular vein before and for 24 h after the infusion of glucose for the determination of the concentrations of glucose and bilirubin and the activities of glutamate dehydrogenase, sorbitol dehydrogenase and gamma-glutamyl transferase. Infusion via the portal vein did not result in abnormalities in the general condition of the cows or increases in the concentration of bilirubin or the activities of liver enzymes. The blood glucose concentration increased to the same extent after both intraportal and intrajugular infusion. Over a 12-h period, three cows received 10 l of 20% glucose solution via the left jugular vein and three others received the same solution over a 12-h period via the portal vein. Blood samples were collected from the right jugular vein before and for 30 h after the start of infusion. Infusion via the portal vein did not affect the general condition of the cows or the activities of the liver enzymes. There was no significant difference in the blood glucose concentration between the two groups throughout the study.