Effects of bovine somatotropin and thyroid hormone status on hormone levels, body weight gain, and mohair fiber growth of Angora goats.

Forty-eight Angora goats (24 wethers and 24 doelings; 5 mo old; 16 +/- 0.5 kg initial BW) were used in an experiment with a 2 x 3 factorial treatment arrangement (n = 8) to evaluate effects of recombinant bovine somatotropin (bST) administration and thyroid hormone status (euthyroid, hypothyroid, and hyperthyroid) on hormone levels, ADG, and mohair fiber growth. The bST was a slow-release zinc-based suspension, with sustained delivery (100 microg/[kg BW x d]) over a 14-d period. Hyperthyroidism was maintained by daily treatment with thyroxine (T4; 150 microg/[kg BW x d]), and hypothyroidism was achieved by feeding 6 mg/(kg BW x d) of propylthiouracil. The experiment was conducted in July to September and consisted of a 2-wk pretreatment period and 8 wk of bST treatment. Goats were given ad libitum access to a diet with 15% CP and 2.54 Mcal/ kg ME (DM basis). Concentrations of T4 and T3 were greatest (P < 0.01) among treatments for hyperthyroid-bST and hyperthyroid-control (T4: 38.6 and 38.0 microg/dL; T3: 406 and 385 ng/dL, respectively); similar among euthyroid-control, euthyroid-bST, and hypothyroid-bST (T4: 11.1, 11.5, and 9.8 microg/dL, respectively; T3: 232, 252, and 226 ng/dL, respectively); and lowest (P < 0.01) for hypothyroid-control (T4: 5.1 microg/dL; T3: 144 ng/dL). Plasma concentration of insulin-like growth factor-I was greatest (P < 0.01) for euthyroid-bST (596 ng/mL) and hypothyroid-bST (618 ng/mL); however, concentration for hyperthyroid-bST was similar to those for euthyroid-control, hypothyroid-control, and hyperthyroid-control (188, 178, 187, and 191 ng/mL, respectively). Dry matter intake was greatest (P < 0.05) for euthyroid-bST (794 g/d), similar among hypothyroid treatments (693 and 703 g/d for control and bST, respectively) and euthyroid-control (681 g/d), and lowest for hyperthyroid groups (554 and 518 g/d for control and bST, respectively); ADG for hyperthyroid goats (11 g/d) was lower than with hypothyroidism and euthyroidism (72 and 73 g/d, respectively); and mohair fiber growth was greater (P < 0.01) for hyperthyroidism (0.133 g/[100 cm2 x d]) than for hypothyroid and euthyroid goats (0.102 and 0.104 g/[100 cm2 x d], respectively). Hyperthyroidism also increased mohair length growth rate by 15% and decreased fiber diameter by 7.8% (P < 0.01). These results demonstrate interactions between growth hormone administration and thyroid hormone status, although these influences had limited effects on ADG and mohair fiber growth.     

Effect of hypothyroidism on kinetics of metabolism of very-low-density lipoprotein in mares

OBJECTIVE: To compare kinetics of the metabolism of very-low-density lipoprotein (VLDL) apolipoprotein B (apoB) before and after thyroidectomy in mares. ANIMALS: 5 healthy adult mares. PROCEDURE: Thyroidectomy was performed in euthyroid mares. Kinetics of VLDL apoB metabolism were measured before and after thyroidectomy by use of a bolus IV injection of 5,5,5-2H3 (98%) leucine (5 mg/kg) and subsequent isolation of labeled amino acid from plasma and VLDL. Labeled leucine was quantified by use of gas chromatography-mass spectrometry. Production rate (PR), delay time, and fractional catabolic rate (FCR) were calculated for the 2 forms of equine VLDL, apoB-48 VLDL, and apoB-100 VLDL. Plasma lipid concentrations were measured, and VLDL composition was determined. RESULTS: Physical appearance of horses was not altered by thyroidectomy. Significantly lower mean blood concentrations of thyroid hormones and non-esterified fatty acids were detected following thyroidectomy. Mean percentage of free cholesterol in VLDL was significantly higher after thyroidectomy. Mean plasma VLDL concentration or kinetics of apoB-48 or apoB-100 were not significantly altered by thyroidectomy. Mean +/- SEM PR was significantly lower (8.70 +/- 1.61 mg/kg/d) and mean delay time significantly longer (1.58 +/- 0.12 hours) for apoB-48 VLDL in euthyroid mares, compared with values for thyroidectomized mares (16.15 +/- 2.24 mg/kg/d and 0.93 +/- 0.10 hours, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: Hypothyroidism did not significantly alter plasma VLDL concentrations or kinetics of VLDL apoB metabolism. Metabolism of apoB-48 VLDL differed significantly from that of apoB-100 VLDL in euthyroid mares.     

Effect of dietary fat on oral bioavailability of tepoxalin in dogs

A pharmacokinetic study was conducted to compare the oral bioavailability of tepoxalin and its pharmacologically active acid metabolite in fasted dogs and dogs fed either a low-fat or high-fat commercial diet. Using a cross-over design, six beagles were administered tepoxalin (10 mg/kg) intravenously (i.v.) and orally (p.o.) after being fed one of three diets (fasted, low-fat, or high-fat). Thereafter, blood samples were collected at frequent intervals, concentrations of tepoxalin and acid metabolite in plasma were determined by high performance liquid chromatography, and pharmacokinetic parameters were estimated. After i.v. dosing, the mean (+/-SD) half-life of elimination (t(1/2(beta))) was 2.45 +/- 1.47 h. After p.o. administration, plasma concentrations of acid metabolite were consistently higher than corresponding concentrations of the parent tepoxalin, indicating that tepoxalin is subject to a substantial first-pass effect. Mean (+/-SD) peak concentrations of tepoxalin were significantly higher after feeding of low-fat (1.08 +/- 0.37 microg/mL) and high-fat (1.19 +/- 0.29 microg/mL) diets than in fasted dogs (0.53 +/- 0.20 microg/mL), suggesting that feeding improves oral bioavailability.     

Effects of hypothyroidism and withholding of feed on plasma lipid concentrations,concentration and composition of very-low-density lipoprotein,and plasma lipase activity in horses

OBJECTIVE: To evaluate selected concentrations of blood lipids and lipase activities in euthyroid and hypothyroid horses deprived of feed for 96 hours. ANIMALS: 4 healthy adult mares and 4 thyroidectomized adult mares. PROCEDURE: Horses were deprived of feed for 96 hours. Blood samples were collected at 24-hour intervals and analyzed to determine concentrations of non-esterified fatty acid (NEFA), triglyceride (TG), total cholesterol (TC), and very-low-density lipoprotein (VLDL) as well as composition of VLDL. Plasma lipase activities were measured after feed was withheld for 96 hours and 12 days after resumption of feeding. RESULTS: Time significantly affected plasma NEFA, VLDL, TG, and TC concentrations in both groups of horses. During the 96-hour period, mean plasma concentrations of NEFA and VLDL increased 10-fold in euthyroid horses and increased 5-fold and 9-fold, respectively, in hypothyroid horses. Mean plasma TG concentrations increased 8-fold in both groups, and plasma TC concentrations significantly increased by 33 and 30%, respectively. Composition of VLDL was significantly affected by feed deprivation in euthyroid horses. Activities of lipoprotein lipase and hepatic lipase were significantly higher in feed-deprived horses. Activity of hepatic lipase was significantly lower in hypothyroid horses than in euthyroid horses. CONCLUSIONS AND CLINICAL RELEVANCE: Hypothyroidism did not significantly alter the magnitude of the response of blood lipids to feed deprivation. Thyroid hormones may reduce variability in blood lipid concentrations but do not determine susceptibility to hyperlipemia. Hypothyroidism does not appear to be a factor in the pathogenesis of hyperlipemia in horses.     

Diurnal variation of ghrelin, leptin, and adiponectin in Standardbred mares

Twelve Standardbred mares underwent blood sampling for 24 h to test the hypothesis that there is diurnal variation of humoral mediators of peripheral energy balance including active ghrelin, adiponectin, leptin, glucose, insulin, and cortisol. The experiment was conducted under acclimated conditions. Grass hay and pelleted grain were provided at 0730 and 1530. Plasma concentrations of active ghrelin and leptin concentrations both peaked (47.3 +/- 6.5 pg/ mL and 5.9 +/- 1.1 ng/mL, respectively; P < 0.05) at 1550, 20 min after feeding. Active ghrelin decreased (P < 0.05) to 28.9 +/- 4.5 pg/mL overnight. The nadir of leptin (4.6 +/- 0.9 ng/mL) occurred at 0650. Neither hormone showed variation (P > 0.05) after the morning feeding. Plasma glucose and insulin concentrations increased (P < 0.05) in response to feeding; however, the morning responses (glucose = 96.9 +/- 2.6 mg/dL; insulin = 40.6 +/- 7.3 uIU/mL) were greater (P < 0.05) than the afternoon responses (glucose = 89.9 +/- 1.8 mg/dL; insulin = 23.2 +/- 4.3 uIU/mL at 180 and 60 min after feeding, respectively). Cortisol concentrations increased (P < 0.05) during the morning hours, but did not respond to feeding, whereas adiponectin concentrations remained stable throughout the study. Hence, active ghrelin and leptin may be entrained to meal feeding in horses, whereas adiponectin seems unaffected. We concluded that there seems to be a diurnal variation in glucose and insulin response to a meal in horses. Furthermore, elevated glucose and insulin concentrations resulting from the morning feeding may be responsible for the increase in leptin concentration in the afternoon.     

Effects of rice bran oil on plasma lipid concentrations, lipoprotein composition, and glucose dynamics in mares

Plasma lipid concentrations, lipoprotein composition, and glucose dynamics were measured and compared between mares fed diets containing added water, corn oil (CO), refined rice bran oil (RR), or crude rice bran oil (CR) to test the hypothesis that rice bran oil lowers plasma lipid concentrations, alters lipoprotein composition, and improves insulin sensitivity in mares. Eight healthy adult mares received a basal diet fed at 1.5 times the DE requirement for maintenance and each of the four treatments according to a repeated 4 x 4 Latin square design consisting of four 5-wk feeding periods. Blood samples were collected for lipid analysis after mares were deprived of feed overnight at 0 and 5 wk. Glucose dynamics were assessed at 0 and 4 wk in fed mares by combined intravenous glucose-insulin tolerance tests. Plasma glucose and insulin concentrations were measured, and estimated values of insulin sensitivity (SI), glucose effectiveness, and net insulin response were obtained using the minimal model. Mean BW increased (P = 0.014) by 29 kg (range = 10 to 50 kg) over 5 wk. Mean plasma concentrations of NEFA, triglyceride (TG), and very low-density lipoprotein (VLDL) decreased (P < 0.001) by 55, 30, and 39%, respectively, and plasma high-density lipoprotein and total cholesterol (TC) concentrations increased (P < 0.001) by 15 and 12%, respectively, over 5 wk. Changes in plasma NEFA (r = 0.58; P < 0.001) and TC (r = 0.44; P = 0.013) concentrations were positively correlated with weight gain over 5 wk. Lipid components of VLDL decreased (P < 0.001) in abundance over 5 wk, whereas the relative protein content of VLDL increased by 39% (P < 0.001). Addition of oil to the basal diet instead of water lowered plasma NEFA and TG concentrations further (P = 0.002 and 0.020, respectively) and increased plasma TC concentrations by a greater magnitude (P = 0.072). However, only plasma TG concentrations and VLDL free cholesterol content were affected (P = 0.024 and 0.009, respectively) by the type of oil added to the diet. Mean plasma TG concentration decreased by 14.2 mg/dL over 5 wk in the CR group, which was a larger (P < 0.05) decrease than the one (-5.3 mg/dL) detected in mares that received water. Consumption of experimental diets lowered S(I), but glucose dynamics were not affected by oil supplementation. Addition of oil to the diet altered blood lipid concentrations, and supplementation with CR instead of water specifically affected plasma TG concentrations and VLDL free cholesterol content.     

Effects of short-term early gestational exposure to endophyte-infected tall fescue diets on plasma 3,4-dihydroxyphenyl acetic acid and fetal development in mares

Consumption of wild-type (toxic) endophyte-infected tall fescue (E+) by horses during late gestation is known to adversely affect pregnancy outcome; however, little is known of the potential disruptive consequences of E+ consumption by mares during the critical phases of placentation and fetal development in early pregnancy. The objective of this study was to evaluate the detrimental effects of feeding E+ to mares during early gestation. Mares (n = 12) paired by stage of gestation (d 65 to 100) were assigned to diets (six per diet) consisting of endophyte-free (E-) or E+ tall fescue seed (50% E- or E+ tall fescue seed, 45% sweet feed, and 10% molasses fed at 1.0% of BW/d). Mares also had ad libitum access to E+ or E- annual ryegrass hay, and were fed diets for 10 d. Following removal from the tall fescue diet on d 11, mares were placed on common bermudagrass pasture and monitored until d 21. Morning and evening rectal temperatures were recorded and daily blood samples were collected for progesterone and prolactin (PRL) analyses, whereas samples for 3,4-dihydroxyphenyl acetic acid (a catecholamine metabolite) analysis were collected on alternate days. For clinical chemistry analysis, blood samples were collected on d 0, 5, 10 and 21. Daily urine samples were collected for ergot alkaloid analysis, and ultrasonography was performed for presence of echogenic material in fetal fluids. Rectal temperatures (E+ 37.76+/-0.03; E- 37.84+/-0.03 degrees C) and serum PRL concentrations (E+ 14.06< or =0.76; E- 12.11+/-0.76 ng/mL) did not differ (P = 0.96) between treatments. Measuring the change in basal serum concentration from d 0 over time, progesterone concentrations did not differ (-0.64 +/-1.49 and -0.55+/-1.47 ng/mL for E+ and E- mares, respectively). There was no negative pregnancy outcome, and ultrasonography indicated no increase in echogenic material in fetal fluids. Plasma 3,4-dihydroxyphenyl acetic acid concentrations decreased (P < 0.05) in E+ compared with E- mares (2.1+/-0.14 and 4.4+/0.43 ng/mL, respectively). Urinary ergot alkaloid concentration was greater (P < 0.01) in mares consuming E+ compared with E- (532.12+/- 52.51 and 13.36+/-2.67 ng/mg of creatinine, respectively). Although no fetal loss was observed during the current study, elevated concentrations of urinary ergot alkaloid were consistent with depressed endogenous catecholamine activity, suggestive of an endocrine disruptive effect of hypothalamic origin.     

Effect of dietary fat and cholesterol level on growing pigs selected for three generations for high or low serum cholesterol at age 56 days.

Thirty-six female pigs selected for three generations for high (HS, n = 18) and low (LS, n = 18) serum cholesterol at 56 d of age were used to test the hypothesis that the two populations would respond differently to a high-fat, high-cholesterol diet (HD) and a low-fat, low-cholesterol diet (LD). The animals were four-way crosses (Chester White x Landrace x Large White x Yorkshire). All pigs were fed a standard corn-soybean meal starter diet from weaning (at 4 wk) to 8 wk of age and a grower diet from 8 to 12 wk of age. Initial serum total cholesterol concentration at 12 wk of age was higher (P less than .05) in HS than in LS pigs (94.6 vs 76.9 mg/dL, respectively). The effect of genetic background persisted throughout the 13-wk experiment (25 wk of age); there was no interaction between diet and genetic background in serum total cholesterol (final concentrations were 114.3 mg/dL in HS-HD; 107.0 mg/dL in HS-LD; 105.9 mg/dL in LS-HD; and 89.7 mg/dL LS-LD). Trends over time revealed significant effects of diet (P less than .01) and genetic background (P less than .01) on serum total cholesterol. There was no effect of genetic background on high-density lipoprotein-cholesterol concentration; high-density lipoprotein-cholesterol as a percentage of serum total cholesterol was similar for all groups: 43% for HS-HD, 48% for HS-LD, 42% for LS-HD, and 45% for LS-LD.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of supplemental lactoferrin on serum lactoferrin and IgG concentrations and neutrophil oxidative metabolism in Holstein calves

Lactoferrin (LF) is an iron-binding protein present in both colostrum and secondary granules of polymorphonuclear neutrophils (PMNs). We hypothesized that supplemental LF enhances neutrophil function in neonatal calves. Newborn calves were assigned to receive colostrum (C), colostrum + LF (CLF, 1 g/kg), or milk replacer + LF (MRLF, 1 g/kg). Serum (LF and IgG) and whole blood (neutrophil isolation) samples were obtained prior to treatment (day 0) and at 24 hours and 9 days of age. Serum IgG concentrations (mean +/- SD) in C, CLF, and MRLF calves at 24 hours were 1,911 +/- 994 mg/dL, 2,181 +/- 625 mg/dL, and 0 mg/ dL, respectively. Serum LF concentrations in C, CLF, and MRLF calves on day 0 were 324 +/- 334 ng/mL (range 0-863 ng/mL), 135 +/- 158 ng/mL (range 0-429 ng/mL), and 318 +/- 337 ng/mL (range 0-964 ng/mL), respectively. LF concentrations in C, CLF, and MRLF calves at 24 hours were significantly higher (P < .05), at 1,564 +/- 1,114 ng/mL (range 335-3,628 ng/mL, 2,237 +/- 936 ng/mL (range 31-3,287 ng/mL), and 3,189 +/- 926 ng/mL (range 1,736-4,120 ng/mL), respectively. Cytochrome c reduction in opsonized zymosan-treated or phorbol ester-treated cells was not significantly affected by supplemental LF provided at birth. Oral LF is absorbed in calves but does not alter PMN superoxide production and does not alter IgG absorption.     

Thyroid-stimulating hormone in adult euthyroid and hypothyroid horses

The purpose of this study was to validate a thyroid-stimulating hormone (TSH) assay in a model of equine hypothyroidism. Thyrotropin-releasing hormone (TRH) stimulation tests were performed in 12 healthy adult mares and geldings, aged 4 to greater than 20 years. before and during administration of the antithyroid drug propylthiouracil (PTU) for 6 weeks. Serum concentrations of equine TSH, total and free thyroxine (T4), and total and free triiodothyronine (T3) were measured. Before PTU administration, mean +/- standard deviation baseline concentrations of TSH were 0.40 +/- 0.29 ng/mL. TSH increased in response to TRH, reaching a peak concentration of 0.78 +/- 0.28 ng/mL at 45 minutes. Total and free T4 increased from 12.9 +/- 5.6 nmol/L and 12.2 +/- 3.5 pmol/L to 36.8 +/- 11.4 nmol/L and 23.1 +/- 5.9 pmol/L, respectively, peaking at 4-6 hours. Total and free T3 increased from 0.99 +/- 0.51 nmol/L and 2.07 +/- 1.14 pmol/L to 2.23 +/- 0.60 nmol/l and 5.78 +/- 1.94 pmol/L, respectively, peaking at 2-4 hours. Weekly measurements of baseline TSH and thyroid hormones during PTU administration showed that total and free T, concentrations fell abruptly and remained low throughout PTU administration. Total and free T4 concentrations did not decrease dramatically until weeks 5 and 4 of PTU administration, respectively. A steady increase in TSH concentration occurred throughout PTU administration, with TSH becoming markedly increased by weeks 5 and 6 (1.46 +/- 0.94 ng/mL at 6 weeks). During weeks 5 and 6 of PTU administration, TSH response to TRH was exaggerated, and thyroid hormone response was blunted. Results of this study show that measurement of equine TSH in conjunction with thyroid hormone measurement differentiated normal and hypothyroid horses in this model of equine hypothyroidism.     

Quantitative and qualitative assessment of milk production after pharmaceutical induction of lactation in the mare

The induction of lactation is performed in ruminants by steroidogenic impregnation, followed by drugs intended to increase prolactin secretion. The aim of this study was to induce lactation in barren mares and to evaluate milk production. Five treated and 5 control mares were used in June and September in year 1, and 12 mares were used in year 2. Mares were administered a vaginal pessary (500 mg altrenogest and 50 mg estradiol benzoate) for 1 week. The 2nd week, another sponge with 100 mg estradiol benzoate was administered, together with 50 mg/100 kg body weight (BW) sulpiride in oil (IM q12h). All mares were milked by hand. Drug treatment was stopped after I L was obtained. Milk production and composition and plasma prolactin concentration were measured. In year 2, the same steroid treatment was applied, but mares received sulpiride (n = 6) or domperidone (1.1 mg/kg PO q12h) (n = 6). A milking machine and oxytocin injections 1 minute before the start of milking were used. In year 1, all treated mares started milking within 1-5 days after sulpiride treatment. Mean daily milk production was 0.88 +/- 0.52 L/500 kg BW. Milk immunoglobulin G (IgG) contents increased in all mares (IgG concentration range, 14-92 g/L). Plasma prolactin increased during sulpiride treatment (range. 27.7 +/- 2.9 to 43.7 +/- 6.7 ng/mL [before] to 289.0 +/- 7.8 ng/mL during treatment, P < .001). In year 2, results were similar to those in year 1, with peak IgG concentrations ranging from 4.2 to 106.7 g/L and a larger daily milk production (3.13 +/- 0.75 with sulpiride and 3.45 +/- 0.51 L/500 kg BW with domperidone). In conclusion, lactation can be induced in mares within 2 weeks, and some mares produce good-quality colostrum.     

Plasma concentrations of thyroid hormone in steers treated with Synovex-S and 3,5,3'-triiodothyronine.

This experiment examined the effect of daily administration of 3,5,3'-triiodothyronine (T3) on plasma profiles of T3, thyroxine (T4), 3,3',5'-triiodothyronine (reverse T3; rT3) and thyrotropin (TSH) in beef steers in which protein accretion was increased by using implants of Synovex-S (SYN). Twenty-four Angus-Hereford steers (302 +/- 16 kg) were individually fed a diet of a corn-based concentrate and silage mixture for 56 d at equal energy intake per steer (ME/unit BW.75). A 2 x 2 factorial arrangement of treatments was used in which treatments were SYN ear implants (200 mg of progesterone and 20 mg of estradiol benzoate) or no implants and s.c. injections of T3 in polyethylene glycol (2 micrograms of T3/kg BW every 48 h) or no injections of T3. Blood samples were collected every 2 wk. Plasma T3 concentration during the experimental period was increased in T3-treated steers (3.0 +/- .1 vs 2.2 +/- .1 ng/mL, P < .01) and was decreased in SYN-implanted steers (2.4 +/- .1 vs 2.7 +/- .1 ng/mL, P < .01). Plasma T4 and rT3 concentrations were reduced (22 +/- 4 vs 75 +/- 2 and .04 +/- .01 vs .12 +/- .01 ng/mL, respectively, P < .01) in T3-treated steers. Concurrently, plasma TSH concentration was decreased in T3-treated steers (.37 +/- .01 vs .51 +/- .02 ng/mL, P < .02). Synovex-S increased BW gain (21.0%, P < .01) and protein gain (35.6%, P < .01) compared with that of nonimplanted steers. Body weight gain and protein gain were not affected by treatment with T3.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of short-term feed deprivation and melatonin implants on circadian patterns of leptin in the horse

Leptin is a protein hormone produced by adipose tissue that influences hypothalamic mechanisms regulating appetite and energy balance. In species tested thus far, including horses, concentrations of leptin increase as animal fat mass increases. The variables and mechanisms that influence the secretion of leptin are not well known, nor is it known in equine species how the secretion of leptin is influenced by acute alterations in energy balance, circadian patterns, and/or reproductive competence. Our objectives were to determine in horses: 1) whether plasma concentrations of leptin are secreted in a circadian and/or a pulsatile pattern; 2) whether a 48-h period of feed restriction would alter plasma concentrations of leptin, growth hormone, or insulin; and 3) whether ovariectomy and/or a melatonin implant would affect leptin. In Exp. 1, mares exposed to ambient photoperiod of visible light (11 h, 33 min to 11 h, 38 min), received treatments consisting of a 48-h feed restriction (RES) or 48 h of alfalfa hay fed ad libitum (FED). Mares were maintained in a dry lot before sampling and were tethered to a rail during sampling. Analyses revealed that leptin was not secreted in a pulsatile manner, and that mean leptin concentrations were greater (P < 0.001) in FED vs. RES mares (17.20 +/- 0.41 vs. 7.29 +/- 0.41 ng/mL). Plasma growth hormone was pulsatile, and mean concentrations were greater in RES than FED mares (2.15 +/- 0.31 vs. 1.08 +/- 0.31 ng/mL; P = 0.05). Circadian patterns of leptin secretion were observed, but only in FED mares (15.39 +/- 0.58 ng/mL for morning vs. 19.00 +/- 0.58 ng/mL for evening; P < 0.001). In Exp. 2, mares that were ovariectomized or intact received either a s.c. melatonin implant or a sham implant. Thereafter, blood was sampled at weekly intervals at 1000 and 1700. Concentrations of leptin in samples collected at 1700 were greater (P < 0.001) than in those collected at 1000 (28.24 +/- 1.7 vs. 22.07 +/- 1.7 ng/mL). Neither ovariectomy nor chronic treatment with melatonin affected plasma concentrations of leptin or the circadian pattern of secretion. These data provide evidence that plasma leptin concentrations in the equine are sensitive to acute changes in nutritional status and vary in a circadian pattern that is sensitive to fasting but not to melatonin treatment or ovariectomy.     

Effect of Experimental Hypothyroidism on Glomerular Filtration Rate and Plasma Creatinine Concentration in Dogs

Background: Hypothyroidism affects renal function in a manner opposite the effects of hyperthyroidism.
Objective: To evaluate the effects of experimentally induced hypothyroidism on glomerular filtration rate (GFR) and basal plasma creatinine concentration in dogs.
Animals: Sixteen anestrous, female dogs.
Methods: Hypothyroidism was induced by administration of ¹³¹I in 8 dogs, and 8 healthy euthyroid dogs acted as controls. Exogenous plasma creatinine clearance (an estimate of GFR) was measured in all dogs before (control period) and 43–50 weeks after induction of hypothyroidism (posttreatment period). Other pharmacokinetic parameters of creatinine were also determined.
Results: No significant difference was observed for basal plasma creatinine concentration and creatinine clearance between control and hypothyroid dogs in the control period. In the posttreatment period, mean ± SD creatinine clearance in the hypothyroid group (2.13 ± 0.48 mL/min/kg) was lower ( P < .001) than that of the control group (3.20 ± 0.42 mL/kg/min). Nevertheless, basal plasma creatinine concentrations were not significantly different between the hypothyroid and control groups (0.74 ± 0.18 versus 0.70 ± 0.08 mg/dL, respectively) because endogenous production of creatinine was decreased in hypothyroid dogs (22 ± 3 versus 32 ± 5 mg/kg/d, P =.001).
Conclusion and Clinical Importance: Hypothyroidism causes a substantial decrease in GFR without altering plasma creatinine concentrations, indicating that GFR evaluation is needed to identify renal dysfunction in such patients.     

Effects of birth weight and postnatal nutrition on neonatal sheep: III. Regulation of energy metabolism

This study investigated effects of birth weight and postnatal nutrition on regulation of energy metabolism in the neonatal lamb. Low (mean +/- SD 2.289 +/- 0.341 kg, n = 28) and high (4.840 +/- 0.446 kg, n = 20) birth weight male Suffolk x (Finnsheep x Dorset) lambs were individually reared on a liquid diet to grow rapidly (ad libitum fed, ADG = 337 g, n = 20) or slowly (ADG = 150 g, n = 20) from birth to live weights (LW) up to approximately 20 kg. At birth, small newborns had higher plasma concentrations of urea nitrogen (mean +/- SEM 8.31 +/- 0.25 vs 6.39 +/- 0.32 mM, P = 0.002) and somatotropin (ST, 49.1 +/- 17.0 vs 10.8 +/- 4.3 ng/mL, P = .045) and lower IGF-I (36.1 +/- 6.8 vs 157.7 +/- 21.8 ng/mL, P < 0.001) than large newborns. Plasma glucose (1.42 +/- 0.23 vs 2.63 +/- 0.95 mM, P = 0.147) and insulin (0.09 +/- 0.02 vs 0.13 +/- 0.06 ng/mL, P = 0.264) concentrations did not differ. Urea nitrogen concentration in plasma peaked and then declined rapidly in all lambs during the first week postpartum, and plasma ST declined on a body-weight-related basis from birth. During rearing to 20 kg LW, plasma insulin was higher in low- vs high-birth-weight lambs. Lambs fed ad libitum had greater plasma concentrations of glucose, urea nitrogen, insulin, and IGF-I compared to those fed a restricted diet (ADG = 150 g). The results suggest that during the early postpartum period, newborn lambs exhibit the fetal characteristic of high rates of amino acid oxidation. The results also support the notion that, at birth, low-birth-weight lambs are less mature than high-birth-weight lambs in aspects of metabolic and endocrine development, which may enhance their capacity to utilize amino acids for energy production and to support gluconeogenesis during the immediate postpartum period. Being small at birth also resulted in elevated plasma insulin concentrations when adequate nutriment to support moderate or rapid growth was provided postpartum, although it remains to be elucidated whether this more chronic effect persists in the longer term.     

Pigs weaned from the sow at 10 days of age respond to dietary energy source of manufactured liquid diets and exogenous porcine somatotropin

Previous research indicates that the neonatal pig does not alter feed intake in response to changes in the energy density of manufactured liquid diets. Also, the limited response of IGF-I to exogenous porcine ST (pST) previously observed in young pigs may be influenced by the source of dietary energy. Our objectives were to 1) determine the effect of a high-fat (HF; 25% fat and 4,639 kcal/kg ME; DM basis) or low-fat (LF; 2% fat and 3,481 kcal/kg ME; DM basis) manufactured liquid diet on pig performance; and 2) determine whether the limited response to exogenous pST in young pigs depends on the source of dietary energy. Two replicates of 60 pigs (n = 120; barrows and gilts distributed evenly), with an initial BW of 4,207 +/- 51 g, were weaned from the sow at 10 d of age and used in a randomized complete block design. Pigs were assigned by BW to one of six pens. Diets were formulated to provide a constant lysine:ME ratio and were fed on a pen basis for a duration of 9 d. On d 5, barrows and gilts within a pen were assigned randomly to receive either 0 or 120 microg of pST.kg BW(-1).d(-1) for 4 d. Pigs gained 336 +/- 9 g/d, which resulted in an ending BW of 7,228 +/- 120 g, regardless of dietary treatment (P > 0.15). Pigs fed the LF diet consumed 17% more DM per pen daily than pigs fed the HF diet (2,777 +/- 67 vs. 2,376 +/- 67 g/d, P < 0.01), but calculated ME intake did not differ between dietary treatments (P > 0.20). The G:F was 24% greater in HF- than in LF-fed pigs (P < 0.01). Plasma urea N concentrations were higher in the HF-fed pigs (11.0 +/- 0.6 mg/dL) than in pigs fed the LF diet (6.2 +/- 0.6 mg/dL; P < 0.05). Treatment with pST increased circulating IGF-I (P < 0.01) and decreased PUN (P < 0.01) concentration 32 and 25%, respectively, regardless of dietary treatment (P > 0.30). Circulating leptin averaged 1.8 +/- 0.1 ng/mL and was not affected by dietary treatment (P > 0.35) or pST (P > 0.40). These results suggest that the ST/IGF axis is responsive in the young pig and the increase in circulating IGF-I and growth is independent of the source of dietary energy. Also, young pigs respond to a lower energy density liquid diet with increased feed intake, without altering growth performance, apparently utilizing a mechanism other than circulating leptin.     

Endocrine responses in mares and geldings with high body condition scores grouped by high vs. low resting leptin concentrations

Previous observations from this laboratory indicated that horses with high BCS could have resting plasma leptin concentrations ranging from low (1 to 5 ng/mL) to very high (10 to 50 ng/mL). To study the possible interactions of leptin secretion with other endocrine systems, BCS and plasma leptin concentrations were measured on 36 mares and 18 geldings. From mares and geldings that had a mean BCS of at least 7.5, five with the lowest (low leptin) and five with the highest (high leptin) leptin concentrations were selected. Jugular blood samples were collected twice daily for 3 d from the 20 selected horses to determine average resting hormone concentrations. Over the next 12 d, glucose infusion, injection of thyrotropin-releasing hormone (TRH), exercise, and dexamethasone treatment were used to perturb various hormonal systems. By design, horses selected for high leptin had greater (P < 0.0001) leptin concentrations than horses selected for low leptin (14.1 vs. 2.8 +/- 0.92 ng/mL, respectively). In addition, mares had greater (P = 0.008) leptin concentrations than geldings. Horses selected for high leptin had lower (P = 0.027) concentrations of GH but higher (P = 0.0005) concentrations of insulin and thriiodothyronine (T3) than those selected for low leptin. Mares had greater (P = 0.0006) concentrations of cortisol than geldings. There was no difference (P > 0.10) in concentrations of IGF-1, prolactin, or thyroid-stimulating hormone (TSH). Horses selected for high leptin had a greater (P = 0.0365) insulin response to i.v. glucose infusion than horses selected for low leptin. Mares had a greater (P = 0.0006) TSH response and tended (P = 0.088) to have a greater prolactin response to TRH than geldings; the T3 response was greater (P = 0.047) in horses selected for high leptin. The leptin (P = 0.0057), insulin (P < 0.0001), and glucose (P = 0.0063) responses to dexamethasone were greater in horses selected for high leptin than in those selected for low leptin. In addition, mares had a greater (P < 0.0001) glucose response to dexamethasone than geldings. Cortisol concentrations were decreased (P = 0.029) by dexamethasone equally in all groups. In conclusion, differences in insulin, T3, and GH associated with high vs. low leptin concentrations indicate a likely interaction of these systems with leptin secretion in horses and serve as a starting point for future study of the cause-and-effect nature of the interactions.     

Administration of RRR‐α‐tocopherol to pregnant mares stimulates maternal IgG and IgM production in colostrum and enhances vitamin E and IgM status in foals

This study assessed the effect of a vitamin E supplement given to pregnant mares on immunoglobulins (Ig) levels in foals. In addition, the fatty acid (FA) content and composition of the mares’ milk was assessed. Milk α‐tocopherol concentrations were compared between pregnant Danish Warmblood mares (n = 17) given a daily oral supplement of 2500 international units (IU) RRR‐α‐tocopherol in the last 4 weeks of pregnancy and a group of unsupplemented mares (n = 17) receiving 170–320 IU vitamin E daily originating from the feed. Milk α‐tocopherol was higher in supplemented mares (36.7, 12.4 and 9.8 μmol/l respectively) in relation to control mares (13.1, 6.4 and 5.8 μmol/l on days 1, 2 and 3 respectively; p < 0.001). Milk IgG was higher on days 2 and 3 post‐partum (PP) in supplemented mares (1.03 and 0.73 mg/ml respectively) in relation to control mares (0.79 and 0.56 mg/ml respectively; p < 0.05). Milk IgM was higher on days 2 and 3 post‐partum (PP) in supplemented mares (0.19 and 0.17 mg/ml) in relation to control mares (0.13 and 0.11 mg/ml respectively; p < 0.05). Plasma α‐tocopherol in foals was higher from supplemented mares on days 1, 2 and 3 (5.7, 14.8 and 19.2 μmol/l respectively) in relation to foals from control mares (3.6, 6.1 and 7.6 respectively; p < 0.001). Foal plasma IgM was higher from supplemented mares on day 3 (0.50 mg/ml) in relation to foals from control mares (0.32 mg/ml; p < 0.001). The total FA content in milk was highest on day 1 (21.6 g FA/kg milk) in relation to days 2 and 3 (13.6 and 13.5 g FA/kg milk respectively; p < 0.001). In conclusion, a daily oral supplement of 2500 IU RRR‐α‐tocopherol increased α‐tocopherol content in mare milk and foal plasma, IgG and IgM in mare milk and IgM in foal plasma.     

Pharmacokinetics and endometrial tissue concentrations of enrofloxacin and the metabolite ciprofloxacin after i.v. administration of enrofloxacin to mares

Enrofloxacin was administered i.v. to five adult mares at a dose of 5 mg/kg. After administration, blood and endometrial biopsy samples were collected at regular intervals for 24 h. The plasma and tissue samples were analyzed for enrofloxacin and the metabolite ciprofloxacin by high-pressure liquid chromatography. In plasma, enrofloxacin had a terminal half-life (t(1/2)), volume of distribution (area method), and systemic clearance of 6.7 +/- 2.9 h, 1.9 +/- 0.4 L/kg, and 3.7 +/- 1.4 mL/kg/min, respectively. Ciprofloxacin had a maximum plasma concentration (Cmax) of 0.28 +/- 0.09 microg/mL. In endometrial tissue, the enrofloxacin Cmax was 1.7 +/- 0.5 microg/g, and the t(1/2) was 7.8 +/- 3.7 h. Ciprofloxacin Cmax in tissues was 0.15 +/- 0.04 microg/g and the t(1/2) was 5.2 +/- 2.0 h. The tissue:plasma enrofloxacin concentration ratios (w/w:w/v) were 0.175 +/- 0.08 and 0.47 +/- 0.06 for Cmax and AUC, respectively. For ciprofloxacin, these values were 0.55 +/- 0.13 and 0.58 +/- 0.31, respectively. We concluded that plasma concentrations achieved after 5 mg/kg i.v. are high enough to meet surrogate markers for antibacterial activity (Cmax:MIC ratio, and AUC:MIC ratio) considered effective for most susceptible gram-negative bacteria. Endometrial tissue concentrations taken from the mares after dosing showed that enrofloxacin and ciprofloxacin both penetrate this tissue adequately after systemic administration and would attain concentrations high enough in the tissue fluids to treat infections of the endometrium caused by susceptible bacteria.     

Effect of light intensity on circadian profiles of melatonin, prolactin, ACTH, and cortisol in pigs.

Eleven crossbred barrows were housed in environmentally controlled rooms with an 8-h photoperiod. Pigs in one room received control illumination of 113 1x (CON; n = 6), and pigs in the other room received intense illumination of 1,783 1x (INT; n = 5) fluorescent light. Pigs were given at least 20 d of exposure to the environment before blood samples were taken every 3 h for 48 h. Data were analyzed by split-plot analysis of variance. Except for prolactin, no treatment x time interactions were noted for the hormone profiles evaluated (P greater than .10). Pigs in INT had greater (P less than .05) concentrations of prolactin in serum than pigs in CON at every sampling time. Concentrations of ACTH and cortisol in plasma were similar for INT (33.9 +/- 3.2 pg/mL of ACTH and 24.4 +/- 3.4 ng/mL of cortisol, respectively) and CON (34.9 +/- 3.0 pg/mL of ACTH and 31.3 +/- 3.1 ng/mL of cortisol, respectively). Within the INT treatment, serum melatonin concentrations were more than doubled (P less than .05) during darkness (66.8 +/- 9.3 pg/mL) compared with during light (30.4 +/- 9.3 pg/mL); however, within the CON treatment, concentrations during light and darkness did not differ (38.4 +/- 9.3 pg/mL and 42.9 +/- 9.3 pg/mL, respectively). Results indicate that light of greater intensity is required to entrain circadian rhythms of melatonin in serum of pigs. Furthermore, pigs may respond to bright light with greater secretion of prolactin, even under constant duration of photoperiod.