Intracerebroventricular and intravenous administration of growth hormone secretagogue L-692,585, somatostatin, neuropeptide Y and galanin in pig: dose-dependent effects on growth hormone secretion

Central regulation of growth hormone (GH) secretion by the GH secretagogue, L-692,585 (585), was determined in Yorkshire barrows (40-45kg BW) with intracerebroventricular (icv) stainless steel cannulas placed by stereotaxic coordinates and indwelling external jugular vein (iv) cannulas for injecting 585 or saline during 3h serial blood sampling. Dose-dependent effects of 585 were determined by icv injections of saline vehicle, 3, 10, and 30microg/kg BW by once daily increment. A switchback study of iv and icv 585 treatment determined central and peripheral regulation of GH secretion by the secretagogue at 30microg/kg BW. When administered icv, 585 increased GH concentration in a dose-dependent manner, with a return to baseline by 60min. GH secretion was attenuated by increased numbers of icv 585 injections (p<0.05); however, it was not affected by increased numbers of iv 585 injections. Icv administration of somatostatin (SRIF) decreased (p<0.05) GH secretion compared with saline-treated controls, and decreased (p<0.05) peak GH response when given in combination with 585 as compared with 585 alone. Porcine galanin (pGAL) modestly increased (p<0.05) GH levels compared with saline controls, but when given icv in combination with 585 peak GH response was lower (p<0.05) compared with 585 alone. Porcine neuropeptide Y (pNPY) administered icv was without effect on GH levels compared with saline controls and decreased (p<0.05) peak GH response when given in combination with 585 as compared with 585 alone. The pharmacological actions by icv administration indicate that the GH secretagogue and neuropeptides act at the level of both porcine pituitary and hypothalamus.

Identification of genetic markers associated with residual feed intake and meat quality traits in the pig

Residual feed intake (RFI) has become increasingly important and is being considered as a more reasonable approach to evaluate feed efficiency in livestock. However, the cost and technical difficulties in measuring this trait restrict the extensive adoption of RFI selection, and this makes marker assisted selection (MAS) a feasible tool. In addition, the effects on meat quality caused by low RFI selection have yet to be clarified. In this study, 11 SNPs from eight candidate genes were evaluated in a Yorkshire pig experimental population (n=169) consisting of a low RFI selection line and a randomly selected control line. Associations of these SNPs with RFI, growth rate, carcass composition, and meat quality measures including water holding capacity, pH at 2d postmortem, meat color and sensory traits were analyzed. The SNPs FTO p.Ala198Ala and TCF7L2 c.646+514A>G showed significant (P<0.05) and suggestively significant (P<0.1) associations with RFI, respectively. The MC4R SNP p.Asp298Asn was associated with backfat but it was not with ADG and meat quality attributes. Both SNPs within HNF1A were associated with intramuscular lipid content and sensory juiciness. The SNPs ACC1 c(*)384C>T and TCF7L2 c.646+514A>G were significantly (P<0.05) associated with ADG. The SNPs CTSZ p.Arg64Lys and TCF7L2 c.646+514A>G were associated with both visual scoring of meat color and the objective L-value measure of meat color. This study has identified potential genetic markers suitable for MAS in improving RFI, ADG, and meat color traits, but these associations need to be validated in other larger populations.