Leptin as an indicator for carcass composition in farm animals

Associations of feed efficiency with circulating IGF-1 and leptin, carcass traits and meat quality of lambs

The aim of this study was to investigate the effects of feed efficiency classifications on live animal measurements, circulating IGF-1 and leptin concentrations, and carcass, non-carcass and meat quality traits of lambs. One-hundred and two lambs approximately 70 days-old with initial live weight of 24.6 ± 3.71 kg (mean ± SD) were individually fed for 56 days to determine residual feed intake (RFI) and residual feed intake and gain (RIG). Lambs were then classified as phenotypically Low-, Medium- or High-RFI and Low-, Medium- or High-RIG phenotypes. Circulating leptin and IGF-1 concentrations were higher in more efficient lambs (Low-RFI or High-RIG). Variation in RFI and RIG did not affect meat redness or tenderness, but High-RIG lambs had darker meat. These findings show that the phenotypically more efficient Low-RFI and High-RIG lambs produced carcasses with similar characteristics and meat quality as the less efficient High-RFI and Low-RIG lambs but have a strategic advantage of lower feed intake to achieve similar production outcomes.

Genetic and management factors affecting beef quality in grazing Hereford steers

Attributes contributing to differences in beef quality of 206 Hereford steers finished on pasture were assessed. Beef quality traits evaluated were: Warner-Bratzler meat tenderness and muscle and fat color at one and seven days after slaughter and trained sensory panel traits (tenderness, juiciness, flavor, and marbling) at seven days. Molecular markers were CAPN1 316 and an SNP in exon 2 on the leptin gene (E2FB). Average daily live weight gain, ultrasound monthly backfat thickness gain and rib-eye area gain were estimated. Molecular markers effects on meat quality traits were analyzed by mixed models. Association of meat quality with post weaning growth traits was analyzed by canonical correlations. Muscle color and marbling were affected by CAPN1 316 and E2FB and Warner-Bratzler meat tenderness by the former. The results confirm that marker assisted selection for tenderness is advisable only when beef aging is a common practice. The most important sources of variation in tenderness and color of meat remained unaccounted for.

Leptin in farm animals: where are we and where can we go?

Fat affects meat quality, value and production efficiency as well as providing energy reserves for pregnancy and lactation in farm livestock. Leptin, the adipocyte product of the obese (ob) gene, was quickly seen as a predictor of body fat content in animals approaching slaughter and an aid to assessing reproductive readiness in females. Its participation in inflammation and immune responses that help animals survive infection and trauma has clear additional relevance to meat and milk production. Furthermore, almost a decade of discoveries of nucleotide polymorphisms in the leptin and leptin receptor genes has suggested useful applications relating to feed intake regulation, the efficiency of feed use, the composition of growth, the timing of puberty, mammogenesis and mammary gland function and fertility in cattle, pigs and poultry. The current review attempts to summarise where research has taken us in each of these aspects and speculates on where future research might lead.

Leptin and leptin receptor genes in Atlantic salmon: Cloning, phylogeny, tissue distribution and expression correlated to long-term feeding status

The present study reports the complete coding sequences for two paralogues for leptin (sLepA1 and sLepA2) and leptin receptor (sLepR) in Atlantic salmon. The deduced 171-amino acid (aa) sequence of sLepA1 and 175 aa sequence for sLepA2 shows 71.6% identity to each other and clusters phylogenetically with teleost Lep type A, with 22.4% and 24.1% identity to human Lep. Both sLep proteins are predicted to consist of four helixes showing strong conservation of tertiary structure with other vertebrates. The highest mRNA levels for sLepA1 in fed fish (satiation ration=100%) were observed in the brain, white muscle, liver, and ovaries. In most tissues sLepA2 generally had a lower expression than sLepA1 except for the gastrointestinal tract (stomach and mid-gut) and kidney. Only one leptin receptor ortholog was identified and it shares 24.2% aa sequence similarity with human LepR, with stretches of highest sequence similarity corresponding to domains considered important for LepR signaling. The sLepR was abundantly expressed in the ovary, and was also high in the brain, pituitary, eye, gill, skin, visceral adipose tissue, belly flap, red muscle, kidney, and testis. Fish reared on a rationed feeding regime (60% of satiation) for 10 months grew less than control (100%) and tended to have a lower sLepA1 mRNA expression in the fat-depositing tissues visceral adipose tissue (p<0.05) and white muscle (n.s.). sLepA2 mRNA levels was very low in these tissues and feeding regime tended to affect its expression in an opposite manner. Expression in liver differed from that of the other tissues with a higher sLepA2 mRNA in the feed-rationed group (p<0.01). Plasma levels of sLep did not differ between fish fed restricted and full feeding regimes. No difference in brain sLepR mRNA levels was observed between fish fed reduced and full feeding regimes. This study in part supports that sLepA1 is involved in signaling the energy status in fat-depositing tissues in line with the mammalian model, whereas sLepA2 may possibly play important roles in the digestive tract and liver. At present, data on Lep in teleosts are too scarce to allow generalization about how the Lep system is influenced by tissue-specific energy status and, in turn, may regulate functions related to feed intake, growth, and adiposity in fish. In tetraploid species like Atlantic salmon, different Lep paralogues seems to serve different physiological roles.

Genetic correlations among carcass cross-sectional fat area ratios, production traits, intramuscular fat, and serum leptin concentration in Duroc pigs

Animals accumulate fat in tissues as subcutaneous, intermuscular, intramuscular, and abdominal fat. Genetic interrelationships of respective fat depositions, however, have not been examined in depth. This study estimated genetic parameters for subcutaneous, intermuscular, and abdominal fat areas of 545 Duroc purebred pigs slaughtered at 105 kg of BW. Measurements were obtained using an image analysis system for positions between the 5th and the 6th thoracic vertebra (56TV), at half body length (HBL), and at the last thoracic vertebra (LTV) of the carcass. Moreover, serum leptin, which is a hormone product that is synthesized and predominantly expressed by adipocytes, was measured to determine if serum concentrations of leptin are useful as physiological predictors of fat accumulation in pigs. The heritability estimate of all fat area percentage at the HBL (0.70 +/- 0.03) was significantly greater than at the 56TV (0.53 +/- 0.03) or the LTV (0.55 +/- 0.04). Furthermore, the heritability estimate of subcutaneous fat areas at the HBL (0.71 +/- 0.04) was greater than at the 56TV (0.56 +/- 0.04) or LTV (0.60 +/- 0.03). Moreover, high heritabilities were estimated for ultrasound backfat thickness (BF; 0.72 +/- 0.03) on the left side at the position of HBL, intramuscular fat content of the loin (0.51 +/- 0.03), the seam fat score (SFS; 0.49 +/- 0.04), and the serum leptin concentration (0.62 +/- 0.05). Increased genetic correlations of BF with the fat area percentage of subcutaneous fat and all fat at 56TV (0.90 +/- 0.03 and 0.91 +/- 0.03), at HBL (0.88 +/- 0.03 and 0.94 +/- 0.01), and at LTV (0.88 +/- 0.03 and 0.90 +/- 0.02) were estimated. The genetic correlations of serum leptin concentration with the percentage of subcutaneous fat area and all fat areas at each position were also high (0.72 to 0.82 and 0.83 to 0.84, respectively). These results suggest that BF and leptin are good indicators of selection for decreasing fat deposition. Increased genetic correlation of the SFS with intermuscular fat area at 56TV (0.74) suggests that SFS is an effective indicator for decreasing intermuscular fat. The genetic correlation between the leptin concentration and feed conversion ratio was high (0.75 +/- 0.04). Results of this study indicate that the combination of BF and serum leptin concentration is a valuable indicator that can be incorporated into selection programs to improve carcass quality and feed efficiency in pigs.