Alva D. Mitchell

Growth and Tissue Accretion Rates of Swine Expressing an Insulin-like Growth Factor I Transgene

Abstract The goal of this research was to determine whether directing expression of an insulin-like growth factor I (IGF-I) transgene specifically to striated muscle would alter the growth characteristics in swine. Transgenic pigs were produced with a fusion gene composed of avian skeletal α-actin regulatory sequences and a cDNA encoding human IGF-I. Six founder transgenic pigs were mated to nontransgenic pigs to produce 11 litters of G1 transgenic and sibling control progeny. Birth weight, weaning weight, and proportion of pig survival did not differ between transgenic and control pigs. The ADG of pigs as they grew incrementally from 20 to 60 kg, 60 to 90 kg, and 90 to 120 kg, respectively, did not significantly differ between transgenic and control pigs. Efficiency of feed utilization (gain:feed) was also similar for transgenic and control pigs. Plasma IGF-I and porcine growth hormone (pGH) concentrations were determined at 60, 90, and 120 kg body weight. Plasma IGF-I concentrations were 19% higher in transgenic gilts than control gilts and 11.1% higher in transgenic boars than control boars (P = 0.0005). Plasma IGF-I concentrations for boars were also higher than for gilts (P = 0.0001). At 60, 90, and 120 kg body weight each pig was scanned by dual energy X-ray absorptiometry (DXA) to derive comparative estimates of carcass fat, lean, bone content of the live animal. Control pigs had more fat and less lean tissue than transgenic pigs at each of the scanning periods and the difference became more pronounced as the pigs grew heavier (P < 0.005 at each weight). Transgenic pigs also had a slightly lower percentage of bone than control pigs (P < 0.05 at each weight). While daily rates of lean tissue accretion did not differ for transgenic and control pigs, daily rates of fat accretion were lower in transgenic pigs than in control pigs (P < 0.05). Based on these results we conclude that expression of IGF-I in the skeletal muscles gradually altered body composition as pigs became older but did not have a major affect on growth performance. #Mention of trade names or companies does not constitute an implied warranty or endorsement by the USDA or the authors.

Prediction of pork carcass composition based on cross-sectional region analysis of dual energy X-ray absorptiometry (DXA) scans

Dual energy X-ray absorptiometry (DXA) was used to measure pork carcass composition by performing a total scan of the right half of 262 pork carcasses (42.7±5.2 kg). The DXA scans were analyzed for percentage fat in the entire half-carcass as well as the shoulder, ham, loin, and side regions. In addition, a total of 14 cross-sections (57.6 mm wide) were analyzed: six in the shoulder/thoracic region, three in the loin region, and five in the ham region. Relative to the DXA measurement of total fat content, the coefficient of determination (R(2)) for a single cross-sectional slice ranged from 0.908 to 0.976. Relative to chemical analysis, a single slice from the ham region predicted the percentage of fat or lean in the half-carcass with an R(2) of 0.81 and a standard error of the estimate of 2.04. Prediction equations were used to analyze a separate group of 65 half-carcasses. These results indicate that carcass fat and lean percentages can be measured by performing a single-pass cross-sectional scan that would be compatible with on-line processing.

Transgenic overexpression of bone morphogenetic protein 11 propeptide in skeleton enhances bone formation.

Bone morphogenetic protein 11 (BMP11) is a key regulatory protein in skeletal development. BMP11 propeptide has been shown to antagonize GDF11 activity in vitro. To explore the role of BMP11 propeptide in skeletal formation in vivo, we generated transgenic mice with skeleton-specific overexpression of BMP11 propeptide cDNA. The mice showed a transformation of the seventh cervical vertebra into a thoracic vertebra in our previous report. Presently, further characterizations of the transgenic mice indicated that ossification in calvatia was dramatically enhanced in transgenic fetuses at 16.5 dpc in comparison with their wild-type littermates. At 10 weeks of age, bone mineral content and bone mineral density were significantly (P<0.05) higher in transgenic mice than that in their wild-type littermates based on dual energy X-ray absorptiometry analysis. The relative trabecular bone volume measured by histological analysis was dramatically increased in transgenic mice compared with their wild-type littermates. The enhanced bone formations in the transgenic mice appear to result from increase osteoblast activities as the expressions of four osteoblast markers - α1 type 1 collagen, osteocalcin, alkaline phosphatase and phex were significantly higher in transgenic fetuses than that in their wild-type littermates. These results suggest that over-expression of BMP11 propeptide stimulates bone formation by increasing osteoblast cell functions.

Body Composition Analysis of the Pig by Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) has been evaluated in a number of studies as a direct in vivo method for assessing the status of body fat. MRI has been used successfully to measure total body and subcutaneous fat in humans1,2 and regional fat content of pigs3. In those and other studies, the image slices were taken at selected locations on the body. For evaluating the compositional growth of the pig it is of value to have information on both fat and muscle content. MRI has been used to measure the size of the pectoralis muscle in chickens4. In the study reported here, we have utilized images taken throughout the body and measured both fat and muscle volumes and compared them with dissected tissue weights as well as total carcass protein and lipid.

Vibrational spectroscopy of LDLL-mixtures of amino acids

Abstract In equimolar mixtures of l - and dl -proline, the vibrational spectra of the ldll -mixture is not an average between that of the l - and the dl -isomers. Instead the dl -mixture is clearly intermediate between the l - and the ldll -spectra. Adding l -isomer to the dl -isomer, the solid state spectra becomes less similar to that of the l -isomer. Replacing respectively the ll -half and the dl -half with a second amino acid, each set can significantly alter the conformation of proline and/or the second amino acid, even though both sets ( ldll - and lldl -mixtures) have identical structural composition. Large changes in spectral properties between ldll - and lldl -amino acids are consistent with diastereoismeric interactions between isomers. Infrared frequencies for chiral structures in an achiral localized environment are not predictive of the frequencies for the same chemical structures in a chiral environment.

13C CP/MAS of ldll mixtures of amino acids

A unit cell in which three isomers are in an L configuration and one is in a D configuration is inherently asymmetrical. For LDLL mixtures of amino acids with identical chemical structures (apart from chirality), the inter- and intramolecular interactions observed from the 13C CP/MAS NMR spectra are even larger than those which have been observed with mixtures of diastereoisomers in the solid state. This occurs even though the chemical composition of these molecular clusters consists only of nearest neighbor enantiomers. Because D and L isomers have identical chemical shifts, changes in chemical shift and peak intensities of these asymmetrical solid mixtures cannot be unambiguously assigned to either the D or one of the L isomers. In LLDL mixtures of amino acids in which half is L isomers and the other half is DL isomers, the NMR spectra clearly depend upon which amino acid contains the D isomer. Any further structural interpretation of these molecular clusters is equivocal without assigning chemical shifts to the D isomer (or alternatively designated the R, [-] or [+] isomer). Both more rigorous mathematical analysis and new NMR experiments are required which link interactions at chiral centers with NMR spectra of LLDL mixtures in the solid state.

Lipid Composition in Miscible and Immiscible Phases

Lipids play a vital role in the architecture of cell membranes. About one third of the known cellular proteins are located in the membrane lipid and these are largely the transporters, signalers, receptors and defense systems. The fatty acid component in membranes across species and in different cell types is species, organ and sub cellular specific. In human cell types, the inner cell membrane is dominated by arachidonic acid whilst that of the photo receptor and neural synapse is strikingly rich in docosahexaenoic acid. The biophysical basis for this molecular specificity in not understood.