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 ofthe equine leptin and leptin receptor genes so as to enable the design of primers for RT-PCR determination of leptin and leptin receptor gene presence and distribution in tissues, 2) develop a radioimmunoassay 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 radioimmunoassay 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.

Our objective was to determine if serum concentrations of leptin could be used to predict carcass composition and merit in feedlot finished cattle. Two different groups of crossbred Bos taurus steers and heifers were managed under feedlot conditions near Miles City, MT. The first group consisted of 88 1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise composite gene combination steers (CGC) harvested at the ConAgra processing facility in Greeley, CO. The second group (Lean Beef Project; LB) consisted of 91 F2 steers and heifers born to Limousin, Hereford, or Piedmontese by CGC F1 cows crossed to F1 bulls of similar breed composition and harvested at a local processing facility in Miles City, MT. Blood samples were collected approximately 24 h before harvest (CGC) or approximately 3 d before and at harvest (LB). No differences in serum concentrations of leptin were detected (P > 0.10) between Hereford, Limousin, or Piedmontese F2 calves nor between LB steers and heifers. Positive correlations (P < 0.01) existed between serum leptin and marbling score (r = 0.35 and 0.50), fat depth measured between the 12th and 13th rib (r = 0.34 and 0.46), kidney, pelvic, and heart fat (KPH) (r = 0.42 and 0.46), and quality grade (r = 0.36 and 0.49) in CGC and LB cattle, respectively. Serum leptin was also positively correlated with calculated yield grade for CGC steers (r = 0. 19; P = 0. 10) and LB cattle (r = 0.52; P < 0.01). Longissimus area was not correlated with serum leptin in CGC steers (r = 0.12; P > 0.10). However, a negative correlation existed between longissimus area and serum leptin in the LB cattle (r = -0.45; P < 0.01). Serum concentrations of leptin were significantly associated with carcass composition (marbling, back fat depth, and KPH fat) and quality grade in both groups of cattle studied and may provide an additional indicator of fat content in feedlot cattle.

Leptin is 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 off-spring. 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 (r2 = 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 (r2 = 0.14, P < 0.0001, r2 = 0.12, P < 0.0001, and r2 = 0.028, P = 0.04). Leptin in milk serum was correlated with ewe weight (r2=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, (r2 = -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.

The objective of this study was to evaluate the relationship between serum concentrations of the hormone leptin with growth and carcass traits insix distinct breeds of pigs entered into the 2000 National Barrow Show Sire Progeny Test. Breeds evaluated were Berkshire (n = 131), Chester White (n = 33), Duroc (n = 40), Landrace (n = 23), Poland China (n = 26), and Yorkshire (n = 41). Serum samples were collected and assayed for concentrations of leptin at entry into test (On-Test Leptin) at 34 +/- 6.7 kg of live weight and again 24 h prior to harvest (Off-Test Leptin) at 111 +/- 3.1 kg of live weight. Carcass measurements taken included hot carcass weight, carcass length, backfat, longissimus muscle area (LMA), longissimus pH, Hunter L-value, chemically determined intramuscular fat (IMF), and subjective color, marbling, and firmness scores. Average daily gain, IMF percentages, and water-holding capacity (WHC) were also determined. On-Test Leptin concentrations were not different (P > 0.10) between swine breeds; however, Off-Test Leptin concentrations did differ (P < 0.001) across genotype. Berkshire had the greatest Off-Test Leptin concentrations (6.58 +/- 0.43 ng/mL), and Duroc and Yorkshire had the lowest (3.49 and 3.96 +/- 0.68 ng/mL; respectively). In addition, Off-Test Leptin concentrations were correlated with average daily gain (r = 0.29; P < 0.001), last-rib fat thickness (r = 0.48; P < 0.001), 10th rib backfat (r = 0.52; P < 0.001), LMA (r = -0.33; P < 0.001), percent fat-free carcass lean (r = -0.51; P < 0.001), and WHC (r = 0.15; P < 0.05). Off-Test Leptin concentrations also differed by gender, with barrows having greater (P < 0.001) serum concentrations of leptin than gilts (6.55 +/- 0.48 vs 3.35 +/- 0.44). Differences exist between breeds of pigs in a manner consistent with breed-specific traits for growth, leanness, and quality; thus, leptin may serve as a useful marker for selection or identification of specific growth and carcass traits.

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