The objective of this study was to establish the developmental pattern and tissue specificity of porcine myostatin expression and to evaluate expression in skeletal muscle during circumstances in which muscle growth was altered. Northern blot analysis revealed two transcripts (1.5 and 0.8 kb). Myostatin mRNA was detected in whole fetuses at 21 and 35 days and was markedly increased ( P < 0.05) by 49 days. At birth, mRNA abundance in longissimus muscle had declined significantly ( P < 0.05) from that at day 105 of gestation and continued to decrease ( P < 0.05) to its lowest level 2 wk postnatally (4 kg body wt). Myostatin expression was higher ( P < 0.05) at 55, 107, and 162 kg body wt than at 4 kg body wt. Postnatally, myostatin mRNA was detected in skeletal muscle and mammary gland. Expression at birth was 65% higher ( P < 0.04) in longissimus muscle of low-birth-weight piglets (0.57 ± 0.052 kg body wt) vs. normal (1.37 ± 0.077 kg body wt) littermates, irrespective of gender. However, suppression of longissimus muscle growth by food deprivation (3 days) did not alter ( P > 0.15) myostatin expression in either 4- or 7-wk-old piglets. Additionally, myostatin mRNA abundance was not changed by porcine growth hormone administration in growing animals. These data indicate that myostatin expression in skeletal muscle peaks prenatally and that greater expression is associated with low birth weight. Expression in mammary gland indicates a possible role for myostatin in mammary gland development and/or lactation.

The product of the leptin (i.e., obese) gene may be an important regulator of energy metabolism, adiposity, and reproduction, and is perhaps linked to meat quality determinants such as marbling. Molecular probes were developed using polymerase chain reaction (PCR) technology to evaluate leptin expression in adipose depots and to evaluate the tissue-dependent nature of expression reported in other species. A 438 bp fragment representing the coding region of the bovine leptin gene excluding the N-terminal secretory signal was amplified, cloned into a plasmid vector (pASK75), and expressed in E. coli. Sequence analysis of the cDNA and the corresponding polypeptide indicate that, overall, both share approximately 87% homology with the mouse and human leptin genes and polypeptides. Amino terminal sequencing (30 amino acid residues) of the recombinant bovine leptin (rBL) protein revealed 100% homology with mouse and human leptin. The bovine leptin gene is expressed as a 3,090 nt mRNA which is detected in adipose tissue, but is not found in brain (despite the appreciable fat content and lipid metabolism) or other tissues. Leptin gene expression in several adipose depots (subcutaneous, renal, and omental) was similar (P = .73) in finished cattle.

The product of the obese gene, leptin, may be an important regulator of adiposity via its regulation of feed intake and energy metabolism. Probes were developed using the polymerase chain reaction to analyze gene expression and determine the structure of the porcine ob gene. Porcine ob was expressed in adipose tissue as a 3,100 bp mRNA. Finished pigs (136 kg) had higher (P<.01) levels of ob mRNA (per unit of 6-actin mRNA) in subcutaneous adipose tissue than did growing pigs (60 kg). Obese gene expression was not detected in tissues other than adipose depots. A genomic DNA fragment containing the ob gene was isolated from a cosmid DNA library. Sequence analysis indicates that the ob gene has three exons. A short untranslated sequence was identified as exon 1 and the amino acid coding sequence was located in the second and third exons. The gene structure, intron/exon boundaries, and the amino acid sequence was highly conserved in mammalian species. The porcine leptin amino acid sequence was 95%, 92% and 89% similar to cattle, human and mouse leptin sequences, respectively.

Forty-eight growing pigs (23 kg BW) were assigned to four treatments (n = 12) arranged as a 2 x 2 factorial. Dietary energy source (conventional [CON] vs high-oil corn [HOC]), with or without an immunological challenge (IC) regimen constituted main effects. The IC regimen consisted of injection of endotoxin (E. coli lipopolysaccharide [LPS]) and vaccination for porcine respiratory and reproductive syndrome (PRRS). Growth performance data were collected over a 5-wk period and are presented as prechallenge (d 1 to 14; d 1 was the 1st d of the study), challenge (d 15 to 21), and postchallenge (d 22 to 36) periods, and overall. Overall, the pigs fed HOC consumed less feed (P < .11) and gained more efficiently (P < .03). During the immunological challenge period, ADG was depressed 21% and feed intake 15% (P < .01). The IC resulted in lower (P < .01) serum alpha-1-acid glycoprotein (AGP) concentrations on d 22, and the magnitude of the reduction was greater in the pigs fed the CON diet (energy source x immune challenge, P < .10). Serum AGP concentrations remained lower (P < .08) in challenged pigs on d 36. Immunoreactive prostaglandin concentrations were higher (55%, P < .08) in the pigs fed HOC immediately following the IC period (d 22). The data reported herein indicate that the performance of pigs fed HOC is satisfactory, and that feeding HOC does not compromise growth performance during or after an immunological challenge.

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