Interrelationship between measures of collagen, compression, shear force and tenderness.

This study examined the relationship between collagen content as determined by hydroxyproline assay with other measures of connective tissue, shear force and tenderness in lamb muscle. Samples were taken from both m. longissimus lumborum (LL, loin) and the m. semimembranosus (SM, topside) of 99 lambs. Sensory tenderness and compression of the LL were not correlated to any measure of collagen or connective tissue, with one exception where compression was correlated (r=-0.28; P<0.05) to the percentage of connective tissue determined by imaging. Intramuscular fat (IMF) was linearly correlated (P<0.05) to sensory tenderness and compression, such that a 1% increase in IMF increased the tenderness score by 2.3±0.83 units and reduced compression by 0.73±0.21 N. There was no correlation between SM shear force and collagen concentration. The data suggest that measurement of collagen concentration did not explain the variation in shear force and sensory tenderness observed in the meat from lambs.

The effect of combination treatment with trenbolone acetate and estradiol-17ß on skeletal muscle expression and plasma concentrations of oxytocin in sheep.

Implantation of trenbolone acetate (TBA) in conjunction with estradiol-17ß (E(2)) increases growth, feed conversion efficiency, and carcass leanness in cattle. Our previous study in Brahman steers suggested that the neuropeptide hormone oxytocin (OXT) may be involved in increasing muscle growth after TBA-E(2) treatment. The present study aimed to determine whether OXT mRNA expression in the longissimus muscle (LM) is also up-regulated in TBA-E(2-)implanted wethers as has been found in steers. Real-time quantitative PCR was used to measure the expression of the gene encoding the OXT precursor, three genes with increased expression in the LM muscle of TBA-E(2)-treated steers, MYOD1 (muscle transcription factor), GREB1 (growth regulation by estrogen in breast cancer 1), and WISP2 (Wnt-1 inducible signaling pathway protein 2), and two genes encoding IGF pathway proteins, IGF1, IGFR, in the LM of both untreated and TBA-E(2)-treated wethers. The expression of OXT mRNA in wethers that received the TBA-E(2) treatment was increased ~4.4-fold (P = 0.01). TBA-E(2) treatment also induced a 2.3-fold increase in circulating OXT (P = 0.001). These data, together with the observation that untreated wethers had much higher baseline concentrations of circulating OXT than previously observed in steers, suggest that wethers and steers have quite different OXT hormone systems. TBA-E(2) treatment had no effect on the expression of IGF1, IGFR, and the muscle regulatory gene MYOD1 mRNA levels in wethers (P ≥ 0.15), but there was an increase in the expression of the two growth-related genes, GREB1 (P = 0.001) and WISP2 (P = 0.04). Both genes are common gene targets for both the estrogen and androgen signaling pathways. Consequently, their actions may contribute to the positive interaction between TBA and E(2) on additive improvements on muscle growth.

Bovine myofiber characteristics are influenced by postweaning nutrition.

This study determined the extent to which bovine longissimus lumborum muscle (LLM) myofibers are influenced by nutrition for 120 d from weaning and the time-course of recovery after severe postweaning nutritional restriction. After weaning, 3 groups of Belmont Red cattle, a tropically adapted breed, were fed to achieve rapid growth (RG, > or =0.6 kg of BW gain/d; n = 16), slow growth (SG, 0.2 kg of BW gain/d; n = 17), or BW loss (WL, 10% loss of weaning weight; n = 17) over 120 d. They were then grazed as 1 group at pasture with forage supplementation for 600 d until slaughter at approximately 500 kg of BW. Samples of LLM were taken from 8 to 12 animals per treatment 6 d before (baseline) and 115, 204, 324, and 476 d after commencement of the study and from all cattle at slaughter (d 721). Myofiber characteristics were determined by immunocytochemical staining of myosin heavy chains. Cross-sectional areas (CSA) of the major myofiber types 1, 2A, and 2X in WL were reduced at d 115 compared with baseline and with the growth groups (all P < 0.001); however, there was little difference in the percentage of the different myofiber types (all P > 0.10). Differences in CSA of the major myofiber types between WL and the growth groups at 115 d were smallest for type 1 (slow oxidative) and greatest for type 2X (fast glycolytic). Consequently, the relative area (percentage of total myofiber area) of type 1 myofibers in WL was significantly greater at 115 d than in the growth groups (P < 0.001). During recovery from postweaning nutritional restriction, significant differences in major myofiber type percentages were not evident (all P > 0.10), and by 721 d CSA of myofiber types differed little between the treatment groups, although SG had greater CSA of type 1 (P < 0.05) and type 2A (P < 0.01) myofibers than WL and RG. At 721 d, the relative area of type 2A myofibers was less in WL compared with SG (P < 0.01) and RG (P < 0.05) and of type 2X myofibers greater (P < 0.05) in WL compared with SG. It is concluded that in the LLM of cattle undergoing severe nutritional restriction immediately postweaning, the size of the more glycolytic fiber types is more adversely affected than the more oxidative types, resulting in an increased relative area of type 1, slow oxidative myofibers. However, given adequate time and nutriment at pasture, LLM myofiber characteristics of cattle recovered to near normal after severe, chronic nutritional restriction immediately postweaning, consistent with earlier findings for beef quality.

Changes in connective tissue of M. semitendinosus as a response to different growth paths in steers.

The effect of growth path, as opposed to advancing age, on the biophysical and biochemical properties of muscle connective tissue was investigated. Nine-month old Brahman-cross steers were grown across either an uninterrupted path, or paths that incorporated weight-loss and then weight gain on two different diets: one group was realimented on pasture, whilst the other was realimented on a grain-based diet. Biophysical attributes of connective tissue toughness (Compression and Adhesion) in the semitendinosus muscle, were significantly reduced by treatment (P<0.05): weight loss with grain realimentation being the least tough in regard to the connective tissue component. Variance within the biophysical attributes was modelled statistically. Statistically significant models included terms for the post-slaughter connective tissue content as well as tissue contents of the enzymes lactate dehydrogenase and isocitrate dehydrogenase. The data suggest that biochemical measurements made up to 100 days prior to slaughter, may have value as indicators of final connective tissue toughness.

Effect of growth path on the tenderness of the semitendinosus muscle of Brahman-cross steers.

The growth paths of 36, nine-month-old Brahman-cross steers were modified to determine the effect of their growth history on tenderness of the semitendinosus (ST) muscle. Steers were assigned to one of three treatment groups. One group of steers (uninterrupted group) was grazed on improved tropical pasture for 257 days and had an average weight gain of 0.6 kg day(-1). The other two groups were fed a restricted diet of low-quality grass hay and lost on average ~ 13% of their initial live weight over 100 days. These groups were then regrown for 157 days on either pasture (pasture finished) with the uninterrupted group, or on a grain-based feedlot diet (grain finished). Growth rates of the previously restricted groups during the regrowth phase were indicative of compensatory growth and were significantly different (p < 0.05) at 0.76 (sem 0.03) kg day(-1) and 1.22 (0.05) kg day(-1), pasture and grain finished groups, respectively. Growth rates for both restricted groups were significantly different (p < 0.05) from the uninterrupted group [0.55 (0.02) kg day(-1)]. At slaughter, the grain finished group had heavier carcases, higher dressing percentages and more fat coverage, than either the uninterrupted or pasture finished groups, the latter being significantly lighter than the uninterrupted group. Tenderness was assessed by shear, compression (C) and adhesion (ADH) measurements. Shear peak force (PF) values of cooked ST samples did not differ significantly between groups. However, PF values of pressure-heat treated ST samples from the grain finished group were significantly less (p < 0.05) than comparable values from the uninterrupted group suggesting a reduced contribution of connective tissue to toughness. The pasture finished group mean PF value was not significantly different from either the uninterrupted group or grain finished group means. C and ADH values were significantly less (p < 0.05) in the grain finished group compared to the pasture finished groups values, again indicating a reduced connective tissue contribution to toughness. We conclude that the physical properties of the connective tissue component of the ST muscle may be altered by rapid compensatory growth after a weight loss phase and reduce the connective tissue contribution to toughness which may enhance meat tenderness.

Digestion of host immunoglobulin and activity of midgut proteases in the buffalo fly Haematobia irritans exigua.

The digestion of blood by the buffalo fly (Haematobia irritans exigua) was monitored for 6h at 33 degrees C after a single meal. Following the meal, the concentration of soluble protein within the midgut increased to a peak at 2 hours then decreased steadily over the next 4h. The magnitude of the increase in soluble protein at 2h indicated a release of protein from another source; most likely from lysed red blood cells. The immunoglobulin (IgG) fraction of the blood meal was digested rapidly (50% within one hour of feeding) and fully digested within 4h. This is indicative of its accessibility to digestive enzymes within the midgut. In contrast, when flies had continuous access to blood, the concentration of IgG in the midgut remained at a more constant level. The loss of antigen-binding activity of a specific antibody was more rapid than complete degradation of the IgG, with 70% of binding activity lost within one hour of feeding. The level of trypsin activity in the midgut increased from pre-feeding levels to reach a peak at 2h before returning to basal levels after 6h. The pattern of trypsin activity follows closely that of the concentration of soluble protein in the midgut (r=0.88). The activity of leucine aminopeptidase in the midgut also increased immediately after feeding and remained elevated for 4 h before declining to a basal level after 6h. The rapid digestion of IgG and subsequent loss of antibody activity suggests that for a specific anti-buffalo fly antibody to be effective it would need to be able to either evade the digestive system or induce a rapid response.

Composition of the peritrophic matrix of the tsetse fly, Glossina morsitans morsitans.

The three-layered peritrophic matrix of Glossina morsitans morsitans is shown, by histochemistry, to be formed of a mixture of glycosaminoglycans, glycoproteins and chitin. In all three layers the glycosaminoglycans contain GlcNAc-hexuronic and Gal-GlcNAc moieties, together with chitin. Glycosaminoglycans in layer 3 are sulphated and sulphated sites have a mean interspace distance of 53 nm - similar to the spacing of fixed charge sites in glomerular basement membrane suggesting a rôle for these sites in the filtration properties of the peritrophic matrix. O-linked oligo- saccharides are present in all three layers. Layer 1 contains the widest variety of glycoprotein oligosaccharide constructs GlcNac and alphalinked GalNAc possibly as GalNAcalpha1,3GalNAc, the latter apparently distal to Galbeta1-4GlcNAc. Lectin binding suggests that layer 2 contains GalNAcalpha1,3Galbeta1,3GlcNAc and that layer 3 contains GalNAc and Galbeta1,4GlcNAc. The evidence for N-linked oligosaccharides is more equivocal. Two dimensional electrophoresis showed that the peritrophic matrix contains a range of proteins, most of which require relatively harsh treatment for their solubilization.

Isolation and characterization of a trypsin-like enzyme from the buffalo fly, Haematobia irritans exigua.

The incorporation of soybean trypsin inhibitor (SBTI) into the diet of the buffalo fly, Haematobia irritans exigua (De Meijere), results in increased mortality and reduced fecundity. A trypsin-like enzyme which binds to SBTI was isolated by affinity chromatography on a Sepharose-SBTI column followed by ion-exchange chromatography. The enzyme was inhibited by benzamidine, phenylmethylsulfonyl fluoride, ovomucoid, leupeptin and alpha-2 macroglobulin. The enzyme was not inhibited by EDTA or p-chloromecuribenzoic acid and had a broad pH optimum of pH 7-9. Vaccination of sheep produced antibodies specific for the trypsin-like enzyme which inhibited enzyme activity in vitro but did not affect the survival of flies maintained in in vitro culture.

Acquired immune response of cattle exposed to buffalo fly (Haematobia irritans exigua).

Naturally acquired immunity to buffalo fly (Haematobia irritans exigua) infestation was examined in cattle. Animals exposed to flies had serum antibodies to buffalo fly antigens at levels that correlated with the intensity of exposure. Two weeks of intense exposure to buffalo fly induced an increase in peripheral blood eosinophil numbers and a concomitant rise in serum antibody levels in exposed animals. Antigens specific for antibody induced by natural exposure were identified using antisera from exposed cattle to probe Western blots of whole fly homogenate separated using SDS-PAGE. Similar immunoreactive bands were found with buffalo fly saliva. Immunoreactive proteins were partially purified from whole fly homogenates by anion-exchange chromatography. Fractions eluted from columns were screened using Western blots probed with serum from exposed animals. Exposed animals showed immediate hypersensitivity to partially purified antigens and to buffalo fly saliva. Flies which fed on exposed animals with high serum levels of antibody to fly antigens did not show greater mortality than flies fed on unexposed animals.

Effect of temperature on late immature stages of Culicoides brevitarsis (Diptera: Ceratopogonidae).

Fourth-instar larvae of the biting midge, Culicoides brevitarsis Kieffer, were reared to adult in agar medium at temperatures of 20, 26, 30.5, 33, 35.5, 38 and 40 degrees C. Optimum (greater than 80%) survival to adult occurred from 26 to 33 degrees C. Temperatures outside this range disrupted development. Above 35.5 degrees C, all immatures died before completing development. Duration of development from fourth instar to adult was shortest at 30.5 degrees C (4.3 d). The estimated duration of development from egg to adult at 26-33 degrees C was 11-13 d. The increased mortality of immature stages at temperatures greater than 33 degrees C may be significant in the reduction of adult populations during summer in inland areas of the northern Australian tropics, where mean monthly maxima exceed 35 degrees C from October until February.