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Leptin, a protein hormone secreted by adipocytes, plays an important role in energy homeostasis and regulation of body composition. We previously observed that acute feed restriction resulted in a rapid decline in concentrations of leptin in obese pony mares. This acute response prompted us to characterize the temporal changes in concentrations of leptin, GH, and insulin in obese pony mares during the transition between fed and feed-restricted conditions. Nine obese pony mares of mixed breed, previously maintained on fescue pasture, were randomly allotted to 2 groups. Treatments consisted of a 48-h feed restriction, a 48-h refeeding, and a 24-h feed restriction (RFR; n = 4), or 48 h of alfalfa hay ad libitum, a 48-h feed restriction, and a 24-h refeeding (FRF; n = 5). Blood samples were taken every 15 min during restriction and feeding transitions (0600 to 1400 on d 2 and 4), and every 30 min thereafter until 0830 of the following days (d 3 and 5). In the FRF treatment, plasma concentrations of leptin declined precipitously 6 h after the removal of feed (sample by treatment interaction; P < 0.01), and remained low and unresponsive to refeeding. Similarly, in the RFR group, plasma concentrations of leptin were initially low, and did not respond to feeding during the second (refeeding) sampling period. After feed restriction in each of the 2 treatment sequences, plasma insulin decreased and GH mean concentration, pulse frequency, pulse amplitude, and area under the curve increased (P < 0.05). Refeeding reversed these effects on insulin and GH. These data provide evidence that peripheral concentrations of insulin and GH are dynamically responsive to feed removal (decrease in insulin; increase in GH) and replacement (increase in insulin; decrease in GH), whereas leptin decreases in response to feed restriction but is slow to recover from a transient nutritional insult. Key words: equine, feed deprivation, growth hormone, leptin

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 [+ or -] 0.41 vs. 7.29 [+ or -] 0.41 ng/mL). Plasma growth hormone was pulsatile, and mean concentrations were greater in RES than FED mares (2.15 [+ or -] 0.31 vs. 1.08 [+ or -] 0.31 ng/mL; P = 0.05). Circadian patterns of leptin secretion were observed, but only in FED mares (15.39 [+ or -] 0.58 ng/mL for morning vs. 19.00 [+ or -] 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 [+ or -] 1.7 vs. 22.07 [+ or -] 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. Key Words: Equine, Feed Deprivation, Leptin, Melatonin

Four studies were designed to determine whether 1) tumor necrosis factor-[alpha] (TNF) and the Lipopolysaccharide (LPS) binding ligand, CD14, are produced by sheep adipose tissue; 2) nutritional reserves and/or short-term fasting affect circulating concentrations of TNF; 3) there is a relationship between TNF and metabolic factors in sheep; and 4) inflammation alters circulating concentrations of leptin. In Exp. 1 and 2, ewes were assigned, based on ultrasonic assessments of last-rib subcutaneous fat measurements to fat (fat thickness >1 cm; mean = 1.52 [+ or -] 0.03 cm) or thin (fat thickness 0.39). In Exp. 4, wethers were injected with LPS. Blood samples were collected every 15 min for 8 h following injection. Plasma concentration of leptin was not altered by LPS (P > 0.20). These results provide evidence: 1) of TNF-like immunoreactivity within fat tissue; 2) that elements within fatty tissues have CD14 that may allow adipocyte function to be directly affected by LPS; 3) that plasma concentrations of leptin are not altered by LPS treatment; and 4) that circulating concentrations of TNF are elevated with obesity in sheep. Key Words: Fat, Leptin, Lipopolysaccharides, Receptors, Sheep, Tumor necrosis factor.

In the current study, we hypothesized that diets high in linoleic acid would increase conjugated linoleic acid (CLA) tissue content, reduce adiposity and leptin production, and result in an increase in the age at puberty in heifers. Heifers were weaned and blocked by body weight (heavy, n = 10, and light, n = 10) and allocated randomly within block to receive isocaloric and isonitrogenous diets with either added fat (HF, n = 10) or no added fat (C, n = 10) from 4 mo of age until post-pubertal slaughter. Whole sunflower seed (55% oil; 70% linoleic acid) was used as the fat source in HF diets and provided 5% added fat from the start of the study until heifers weighed 250 [+ or -] 8 kg, at which time added fat was increased to 7% of dry matter until slaughter. Body weights were recorded weekly, and blood samples were collected weekly for total cholesterol and hormone analyses. Puberty was confirmed based on serum concentrations of progesterone and ultrasonographic confirmation of corpora lutea. Heifers were slaughtered at 325 [+ or -] 10 d of age, and longissimus muscle between the 9th and 11th rib was collected and analyzed to estimate carcass composition. Subcutaneous and kidney, pelvic, and heart fat were collected at slaughter for fatty acid analyses. The HF heavy group tended (P < 0.10) to reach puberty later than all other groups, and one HF light heifer did not reach puberty during the study. Linoleic acid and cis-9, trans-11 CLA tissue contents were higher (P < 0.03) in HF heifers than controls, but neither total carcass fat nor percentage of dry matter differed by dietary group, although the percentage of protein tended (P < 0.10) to be lower in HF heifers. Mean serum concentrations of leptin did not differ due to diet; however, leptin increased (P < 0.01) linearly as puberty approached. Circulating concentrations of growth hormone and insulin-like growth factor I increased or remained relatively constant between wk 2 to 10 of feeding, and then declined (P < 0.01) until the onset of puberty. Serum IGF-I was lower (P < 0.01) in heifers receiving the HF diet. Mean serum concentrations of insulin and total cholesterol increased (P < 0.01) with time in both groups, but only total cholesterol was increased by the HF diet (P < 0.05). Results indicate that diets high in linoleic acid fed to growing beef heifers beginning early in life have little or no effect on total carcass fat, circulating leptin, or age at puberty despite measurable increases in CLA accumulation. Key Words: Cattle, Conjugated Linoleic Acid, Fat, Leptin, Puberty

Obesity has been a major concern in the horse industry for many years, and the recent discovery of leptin and leptin receptors in numerous nonequine species has provided a basis for new approaches to study this problem in equine. The objectives were to: 1) clone a partial sequence of the equine leptin and leptin receptor genes so as to enable the design of primers for RTPCR determination of leptin and leptin receptor gene presence and distribution in tissues, 2) develop a radio-immunoassay to quantify peripheral concentrations of leptin in equine, 3) determine if peripheral concentrations of leptin correlate with body condition scores in equine, and 4) determine if changing body condition scores would influence peripheral concentrations of leptin in equine. In Experiment 1, equine leptin (GenBank accession number AF179275) and the long-form of the equine leptin receptor (GenBank accession number AF139663) genes were partially sequenced. Equine leptin receptor mRNA was detected in liver, lung, testis, ovary, choroid plexus, hypothalamus, and subcutaneous adipose tissues using RT-PCR. In Experiment 2, 71 horses were categorized by gender, age, and body condition score and blood samples were collected. Sera were assayed for leptin using a heterologous leptin radio-immunoassay developed for equine sera. Serum concentrations of leptin increased in horses with body condition score (1 = thin to 9 = fat; r = 0.64; P = 0.0001). Furthermore, serum concentrations of leptin were greater in geldings and stallions than in mares (P = 0.0002), and tended to increase with age of the animal (P = 0.08). In Experiment 3, blood samples, body weights, and body condition scores were collected every 14 d from 18 pony mares assigned to gain or lose weight over a 14-wk interval based on initial body condition score. Although statistical changes (P = 0.001) in body condition scores were achieved, congruent statistical changes in peripheral concentrations of leptin were not observed, likely due to the small range of change that occurred. Nonetheless, serum concentrations of leptin tended to be greater in fat-restricted mares than in thin-supplemented mares (P = 0.09). We conclude that leptin and leptin receptors are present in equine tissues and that peripheral concentrations of leptin reflect a significant influence of fat mass in equine. Key Words: Body Condition, Horses, Leptin

Circulating concentrations of leptin and IGF-I, leptin gene expression, and serum binding of [[sup.125]I]ovine leptin in cattle during pubertal development, as well as leptin gene expression and circulating concentrations of leptin during the estrous cycle and different calendar seasons, were investigated. Multivariate regression analysis was utilized to evaluate temporal changes in BW, leptin mRNA, and serum concentrations of IGF-I and leptin normalized to the week of puberty (Exp. 1). Body weight accounted for most of the variation associated with the onset of puberty in the full regression model ([R.sup.2] = 0.99; P < 0.01). However, serum leptin was closely related to changes in BW (r = 0.85; P < 0.02) and in the absence of BW was most predictive of pubertal onset ([r.sup.2] = 0.73; P < 0.01). Mean concentrations of leptin increased (P < 0.0001) linearly from 16 wk before until the wk of pubertal ovulation in yearling heifers reaching sexual maturation from early spring to midsummer. Leptin mRNA transformed to a percent of the value at puberty increased (P < 0.02) as puberty approached, but serum leptin and leptin mRNA values were not well correlated. We found no evidence of leptin-binding proteins in serum of developing heifers. Combined mean serum concentrations of IGF-I (ng/mL) during periods III and IV (-9 wk to wk of puberty; 216.6 [+ or -] 9) were 21% higher (P < 0.0001) than combined mean concentrations of IGF-I during periods I and II (-19 to wk of puberty; 193 [+ or -] 10). In mature heifers and cows (Exp. 2), serum leptin tended to decrease (P = 0.10) during the late luteal/early follicular phase of the estrous cycle, which corresponded to a reduction (P < 0.03) in adipocyte leptin gene expression. In mature ovariectomized cows, serum concentrations of leptin increased (P < 0.001) by 34% from early winter to the summer solstice and remained unchanged throughout the remainder of the year (Exp. 3). Results from these studies indicate that marked increases in both circulating leptin and leptin gene expression occur in developing heifers during pubertal development and are associated with increases in serum IGF-I and BW. Seasonal effects on circulating leptin observed in mature cows from winter to summer could also plausibly account for a portion of the prepubertal rise in serum leptin observed in heifers. Key Words: Estrous Cycle, Gene Expression, Heifers, Leptin, Puberty, Seasons

Understanding mechanisms that regulate growth and reproduction are important for improving selection strategies in cattle. In this study, Angus, Brangus, and Brahman bulls (n = 7 per breed) of similar age were selected from a group of 65 weanlings. Bulls were evaluated after weaning (i.e., ~ 6 mo of age) for 112 d for serum concentrations of metabolic hormones and glucose, growth, and reproductive traits. Performance data and blood sera were collected on d 0, 28, 56, 84, and 112. Sera were also collected in periods from d 50 to 59 (56D) and 103 to 112 (112D). Angus bulls were heavier (P < 0.05) throughout the study than Brahman bulls and were heavier than Brangus bulls on d 56, 84, and 112. Initial and final BW for Angus, Brangus, and Brahman bulls were 292.7, 260.6, and 230.4 and 468.3, 435.6, and 350.7 [+ or -] 12 kg, respectively. Conversely, Brahman bulls had greater hip height (P < 0.05) than Brangus, and Brangus were taller (P < 0.05) than Angus. Angus bulls had the greatest (P < 0.05) scrotal circumference (SC) and Brahman bulls the least. Mean SC across days was 31.5, 29.7, and 25.0 [+ or -] 0.6 cm for the three respective breeds. Serum testosterone was greater (P < 0.01) in Angus and Brangus bulls (10.0 and 8.9 [+ or -] 1.4 ng/mL) than in Brahman bulls (4.0 [+ or -] 1.4 ng/mL) throughout the study. After d 112, 100, 86, and 57% of the Angus, Brangus, and Brahman bulls passed a breeding soundness exam (P - 0.51). Serum concentrations of IGF-I and leptin were greater (P [less than or equal to] 0.06) in Angus bulls on d 56, 84, and 112 than in Brangus and Brahman bulls. Serum concentrations of GH (P < 0.08) and glucose (P < 0.03) were greater in Brangus bulls than in Angus or Brahman bulls throughout the study. Prediction analyses suggested that serum concentrations of leptin could be used to predict (P [less than or equal to] 0.08) BW and SC ([R.sup.2] > 0.82) in the 56D and 112D periods among these breeds. Leptin was also useful in predicting (P [less than or equal to] 0.09) serum concentrations of GH and testosterone in the 112D period ([R.sup.2] > 0.32). Residual correlation analyses with the effect of breed removed suggested that leptin was correlated (r [greater than or equal to] 0.53, P < 0.05) with both SC and serum testosterone. Angus and Brahman cattle differ in phenotype, level of adiposity, and rate of sexual development. Data herein suggest that these characteristics could be due to varying mechanisms by which metabolic hormones such as leptin, GH, and(or) IGF-I are regulated. Key Words: Bovidae, Breeds, Bulls, Growth, Leptin, Reproduction

Leptinis an adipocyte-derived hormone that suppresses feed intake and increases energy expenditure. Leptin is also involved in regulating body temperature. Thus, the presence of leptin in milk, which can be absorbed through the gut of neonates immediately after birth, may aid in the survival of neonates born in cold weather. Our objectives were to determine the temporal relationship between concentrations of leptin in postpartum ewe blood serum and ewe milk serum, and to determine whether ewe blood and milk serum leptin concentrations were correlated with concentrations of leptin in lamb blood serum in their offspring. Approximately 1 wk before the expected date of lambing, blood samples, weights, and body condition scores (BCS; 0 to 5 scale) were collected from 27 mixed-parity ewes. Following parturition, ewe blood and milk samples were collected within 2 h of parturition (d 0), 12 h (d 0.5) and 24 h (d 1) after parturition, again on d 5, and weekly thereafter until d 47. Lambs were blood-sampled and weighed within 2 h of parturition (d 0), bled daily until d 5, and bled and weighed weekly thereafter to d 47. Prior to lambing, ewe blood serum leptin was positively correlated with congruent BCS ([r.sup.2] = 0.10, P = 0.06), but not weight (P = 0.14). Following parturition, ewe blood serum leptin was positively correlated with BCS, weight, and milk serum leptin ([r.sup.2] = 0.14, P < 0.0001, [r.sup.2] = 0.12, P < 0.0001, and [r.sup.2] = 0.028, P = 0.04). Leptin in milk serum was correlated with ewe weight ([r.sup.2]=0.05, P = 0.007) but not ewe BCS (P = 0.7); however, concentrations of leptin in both ewe blood and milk serum varied with day of lactation (P = 0.0001), being maximal within 24 h of parturition and declining to nadir concentrations by d 5. Leptin in lamb serum was correlated with milk serum leptin, ([r.sup.2] = -0.05; P = 0.001), but not ewe blood serum leptin (P= 0.5). Concentrations of leptin in lamb serum increased from birth to d 5 and declined thereafter to nadir concentrations by d 19. Elevated concentrations of leptin in milk during the early stages of lactation may provide a mechanism for thermoregulation, satiation, and homeostatic endocrine control in the neonate. Key Words: Ewes, Lambs, Leptin, Milk

Beef production systems in the desert southwest require replacement females that are physiologically and behaviorally adapted to high temperature and low forage quality. To learn about potential use of differing breeds, Angus, Brahman, and Brangus heifers (n = 8/breed) of similar age were randomly selected from a group of 85 weanlings. Heifers were fed an alfalfa-corn-based diet (14.9 CP and 75% TDN) and evaluated for 78 d for differences in metabolic hormones and growth and reproductive performance. Angus heifers were heavier (P < 0.05) than Brahman and Brangus heifers throughout the study. Initial and final BW for Angus, Brahman, and Brangus heifers were 313, 247, 287, and 421, 332, 392 10 kg. Despite Angus and Brangus heifers exhibiting greater ADG than Brahman, no differences were observed in DMI when expressed per unit of BW. Brahman heifers did have greater hip height (P < 0.05) than Angus or Brangus, but Angus heifers had 55% more back fat than Brahman and 27% more than Brangus (P < 0.01) at the end of the study. In parallel, serum concentrations of the adipose derived hormone leptin were greater (P < 0.05) in Angus (4.4 0.2) than in Brangus and Brahman heifers (3.1 and 2.9 0.2) throughout the study. Partial correlation analyses with the effect of breed removed, revealed that serum concentrations of leptin were positively associated with back fat (r = 0.30, P < 0.05) and body condition score (r = 0.27, P < 0.05). Conversely, serum concentrations of GH (P < 0.13) and glucose (P < 0.05) tended to be greater in Brahman heifers relative to Angus and Brangus, whereas serum concentrations of IGF were greater (P < 0.05) in Brangus and Brahman compared with Angus heifers throughout the study. Puberty was observed in 75% of the Angus, 75% of the Brangus and 0% of Brahman heifers during the study. Then, after a 90-d breeding season, 100% of the Angus, 75% of the Brangus, and 12% of the Brahman heifers were pregnant ([chi square]; P < 0.05). Metabolic hormones such as GH and leptin are known to be involved in puberty in most mammals. Data herein, suggest that these varying hormone concentrations could help explain some of the differences that occur in the rate of reproductive development between various breeds of Bos indicus and Bos taurus cattle. Key Words: Leptin, Breeds, Heifer

Twelve crossbred steers (initial BW=227kg) were used in a replicated 3X3 Latin square design to determine the effect of a 16% CP soybean meal based diet (CON), 16% CP bloodmeal diet (BM), or 12% CP soybean meal diet+arginine-HCl (protected in a wax matrix) (ARG) on serum hormone, plasma amino acid (PAA), and protein retention levels. Steers were housed in a thermoneutral chamber with continuous lighting and weighed prior to the initiation of each period to adjust DM intake to 2% of BW. The study design consisted of a 7d adaptation period followed by 4d total fecal and urine collection. Jugular catheters were inserted into the steers on d 12 and blood was collected every 15 min for 8 h on d 13. ADG did not differ among treatments and averaged 0.74 kg/d. Nitrogen intake was lower (P Key Words: Ruminant, Endocrine, Protein

Leptin, a protein hormone secreted by adipocytes, acts as a metabolic signal potentially regulating growth, reproduction, and metabolism. The objective of the current study was to characterize the secretion of leptin before parturition and at weaning in sows. Lactation imposes significant nutritive and metabolic demands, and it was hypothesized that leptin levels would reflect this demand. Approximately 150 mixed parity sows from a large commercial farm were bled and ultrasounded 2 to 4 d before farrowing (d 111 of gestation; before parturition) and again on the day of weaning (at weaning). Radioimmunoassay was used to determine serum concentrations of leptin. Backfat thickness and loin eye area were determined via real-time ultrasound. Leptin concentrations were lower at weaning than before parturition (3.2 [+ or -] .174 vs. 4.92 [+ or -] .169 ng/ml; P [less than or equal to] 0.001). Separate regression analyses of serum concentrations of leptin before parturition and at weaning on back fat thickness and loin eye area on congruent days revealed a linear relationship between leptin and back fat before parturition (P [less than or equal to] 0.001; regression coefficient = 4.95 [+ or -] 1.17). Loin eye area before parturition and at weaning and backfat thickness at weaning were not related to serum leptin concentrations, even though backfat thickness and loin eye area also decreased during lactation (P [less than or equal to] 0.001). This work demonstrates that leptin levels are related to body fat in sows prior to parturition, with leptin levels decreasing from parturition to weaning. This decrease may be associated with the change in pregnancy status and/or the nutritive demands of lactation. The lack of relationship between leptin and backfat at weaning may also reflect the influence of factors other than adipose mass on leptin secretion. The impact of reduced serum leptin following lactation is unknown. However, because serum leptin is associated with reproductive performance in other species, post-lactation leptin levels may be a significant metabolic cue influencing subsequent reproductive performance. Key Words: Sow, Leptin, Reproduction

Fat supplemented diets are fed to performance horses as a means of increasing energy density and performance potential. Use of traditional concentrate rations as a means of increasing energy density predisposes the horse to maladies such as colic, laminitis, and developmental orthopedic diseases. Adding fat to growing horse rations is an option but is not widely implemented. Our objective was to determine if feeding a fat-added diet vs. a control diet to growing yearling mares would affect growth and body compositional parameters as assessed via body weight, plasma leptin levels, and body condition scores (BCS). Eight yearling mares (348 [+ or -] 19 kg) were paired by initial body weight and fed either a high fat (HF) diet or a control (C) diet at 0.8% of their body weight per day. The diets were fed as two daily meals for 8 wk. In addition to the concentrate, all horses were allowed ad libitum access to pasture and water. Diets contained equivalent amounts of protein (14%) and fiber (11.5%). The HF diet contained 16% fat from stabilized rice bran and soybean oil refinery lipid (3.6 Mcal DE/kg). The C diet, MoorMan's[R] GROSTRONG[R] 13% Pelleted Feed, contained 3% fat (2.6 Mcal DE/kg). Intake of concentrate was measured at each feeding. Weekly plasma samples were collected 30 min post feeding for analysis of leptin and insulin. Body weights and BCSs were assessed weekly and increased over time in all mares (P > 0.4), but did not differ with respect to diet. There were no differences in feed intake (HF = 1.38 [+ or -] 0.02 vs. C = 1.46 [+ or -] 0.02 kg) or plasma insulin levels (HF = 48.55 [+ or -] 6.8 vs. C = 47.98 [+ or -] 6.8 IU). Conversely, plasma leptin levels were greater among mares fed HF vs. C diets (1.54 [+ or -] 0.12 vs. 0.88 [+ or -] 0.12 ng/ml, respectively; P=0.03). We conclude that there is no evidence that growth is adversely affected when growing yearling mares are fed an added fat diet vs. a low fat diet. Furthermore, these data provide evidence that the type of diet may affect the animal's perception of its body composition as reflected by the differences in plasma leptin levels in horses fed high fat vs. low fat rations. Key Words: Leptin, Horse, Fat-supplementation

Leptin is an adipocyte-derived hormone that suppresses feed intake and increases energy expenditure. Leptin is also involved in regulating body temperature, and thus the presence of leptin in milk, which can be absorbed through the gut of the neonate, may aid in survival of neonates born in cold weather. Our objectives were to determine the relationship between concentrations of leptin in postpartum ewe blood serum (EBS) and ewe milk serum (EMS), and to determine if EBS and EMS leptin levels were correlated with levels of leptin in the blood serum of their lambs (LBS). Approximately 1 wk before the expected date of lambing, blood samples, weights, and body condition scores (BCS; 1 to 5 scale) were collected from 27 mixed-parity ewes. Following parturition, blood and milk samples were collected within 2 h of parturition (d 0), between 12 and 24 h after parturition (d 1), on d 5 and weekly thereafter for 6 wk. Lambs were bled and weighed within 2 h of parturition (d 0), bled daily until d 5, and bled and weighed weekly thereafter for 6 wk. The postpartum interval was classified as early (d 0 to d 26; i.e., preceding peak lactation) or late (d 27 to d 47; i.e., following peak lactation). Pre-lambing EBS leptin was positively correlated with congruent BCSs ([r.sup.2]=0.10, P=0.06) but not weight (P=0.14). During early lactation, EBS leptin was correlated with ewe weight and BCSs ([r.sup.2]=0.16, P=0.0001; [r.sup.2]=0.16, P=0.0001; respectively). During late lactation EBS leptin was correlated with ewe weight ([r.sup.2]=0.17, P=0.0003) but not BCS (P=0.9). EMS leptin was not correlated with ewe BCS, weight, or EBS leptin (P>0.1); however, both EBS and EMS leptin varied with day of lactation (P=0.0001). EBS and EMS leptin levels were greatest within 24 h of birth and declined to nadir levels by d 5. LBS leptin was correlated with EMS leptin, ([r.sup.2]=0.04; P=0.0004), but not EBS leptin (P>0.1). LBS leptin increased from birth to d 5 and declined thereafter to nadir levels by d 19. High levels of leptin in milk during the early stages of lactation may provide a mechanism for thermoregulation, satiation, and homeostatic endocrine control in the neonate. Key Words: Leptin, Ewe, Lamb

Four studies were designed to determine whether 1) tumor necrosis factor-α (TNF) and the Lipopolysaccharide (LPS) binding ligand, CD14, are produced by sheep adipose tissue; 2) nutritional reserves and/or short-term fasting affect circulating concentrations of TNF; 3) there is a relationship between TNF and metabolic factors in sheep; and 4) inflammation alters circulating concentrations of leptin. In Exp. 1 and 2, ewes were assigned, based on ultrasonic assessments of last-rib subcutaneous fat measurements to fat (fat thickness >1 cm; mean = 1.52 ± 0.03 cm) or thin (fat thickness <1 cm; mean = 0.25 ± 0.03 cm) groups. Fat and thin ewes were assigned to fed or fasted groups for a total of four groups (fed-fat; fasted-fat; fed-thin; fasted-thin). Fed-ewes had ad libitum access to feed, and fasted-ewes were prohibited feed 48 h before initiation of sample collection. In Exp. 1, subcutaneous fat samples were collected from just above the last rib for detection of TNF and CD14 mRNA, and immunoreactivity. Tumor necrosis factor-α-like immunoreactivity in adipocytes was sparse, more pronounced in cells in fed-ewes than fasted-ewes, and localized to membranes between adjacent cells in nucleated regions. Immunoreactivity for CD14 was minimally observed but present in adipocytes and widely expressed in infiltrating monocytes and epithelial vascular cells. Leptin was detected in adipocytes. In Exp. 2, plasma samples collected every 6 h for 24 h were analyzed for plasma concentrations of TNF. Fat ewes had greater plasma concentrations of TNF than thin ewes (P = 0.039). In Exp. 3, wethers were injected i.v. with interleukin-1β or TNF. Blood samples were collected every 15 min for 8 h following injection. Plasma concentration of leptin was not affected by treatment (P > 0.39). In Exp. 4, wethers were injected with LPS. Blood samples were collected every 15 min for 8 h following injection. Plasma concentration of leptin was not altered by LPS (P > 0.20). These results provide evidence: 1) of TNF-like immunoreactivity within fat tissue; 2) that elements within fatty tissues have CD14 that may allow adipocyte function to be directly affected by LPS; 3) that plasma concentrations of leptin are not altered by LPS treatment; and 4) that circulating concentrations of TNF are elevated with obesity in sheep. [ABSTRACT FROM AUTHOR]