Assessment of dioxins in foods from animal origins.

Dioxin is the common name for 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) but is also used for the structurally and chemically related polychlorinated dibenzo-para-dioxins (PCDD), dibenzofurans (PCDF), and the coplanar polychlorinated biphenyls (PCB). There are 75 PCDD congeners, 135 PCDF, and 209 PCB. Seven PCDD and 10 PCDF with substitutions at the 2,3,7, and 8 positions are considered toxic, and 11 PCB have dioxin-like toxicity. The majority of toxic dioxin is and(or) has been derived from industrial chlorination processes, incineration of municipal waste, and production of certain herbicides. The potential for health risks due to the cancer-promoting, immunomodulating, and teratogenic activities of dioxins in rodents has raised concerns over their presence in the human food chain. The lipophilic nature of dioxins results in higher concentrations in the fat of animal and fish products, and their excretion via milk secretion in dairy cattle may result in relatively high concentrations of dioxin contamination in high-fat dairy products. Surface contamination of plant foods and soil due to deposition of atmospheric emissions may also be a significant direct source of dioxin ingestion for livestock and thereby an indirect source of dioxin for humans. Despite numerous epidemiological studies, dioxin has not been conclusively determined to be problematic for humans. Certain management practices such as trimming fat from meat, consuming low-fat dairy products, and simply cooking food can substantially decrease exposure to dioxin compounds.

Dose-response effects of recombinant bovine somatotropin (Posilac) on growth performance and body composition of two-year-old rainbow trout (Oncorhynchus mykiss).

Two hundred rainbow trout (Oncorhynchus mykiss, mean weight 301.5 g) were allotted to four treatments with five replicates in a randomized block design to determine the dose-response effects of recombinant bovine somatotropin (rbST; Posilac) on growth performance and carcass composition. Treatments were sham-injected controls (S), 10 micrograms/g BW of rbST (L), 20 micrograms/g BW of rbST (M), and 30 micrograms/g BW of rbST (H). The tanks held 135 L; water flow = 15.1 L/min; temperature = 15 degrees C. The fish were maintained in a 12-h light:dark cycle and hand-fed twice daily. The fish received a single intraperitoneal (i.p.) injection on d 0 and were weighed on d 0, 14, 28, and 56. On d 56 the fish were killed. The whole body (WBW), eviscerated carcass (EC), viscera (VIS), and reproductive organ weights and the increase in average daily body length (ADL) were determined. Recombinant bST reduced (linear, P < .004) feed intake 17.6% from d 0 to 14 and improved ADG 44.8% from d 0 to 14 (linear, P < .001) and 8.1% from d 0 to 56 (linear, P < .022). Treated groups had improved (linear, P < .001) feed efficiencies for d 0 to 28. Treatment with rbST increased final weight (linear, P < .018) and length (linear, P < .001), decreased carcass dry matter (linear, P < .001) and fat (linear, P < .001), content, increased carcass ash (linear, P < .001) and tended to increase carcass protein (linear, P < .054) content. Recombinant bST increased WBW (linear, P < .018) and EC (linear, P < .003) but decreased (linear, P < .015) testes weight. Ovary weights, VIS and overall gonadosomatic index were unaffected (P > .05) by rbST. Recombinant bST was undetectable in serum samples taken on d 56 as determined by radioimmunoassay. Overall, the improved ADG, feed efficiency, body mass, and composition indicate that administration of rbST to rainbow trout may be an efficacious method of modulating growth in fish.

Regulation of muscle cell proliferation by extracts from crushed muscle.

Cell culture studies were conducted to determine whether myotrophic factors were released from mature murine or bovine muscle following a crush injury. Murine crushed muscle extract (mCME) was added to C2 muscle (satellite) cell cultures at concentrations of 0, 50, 100, 200, and 400 micrograms of total protein/mL. Bovine crushed muscle extract (bCME) was added at concentrations of 0, 100, 200, 400, and 500 micrograms/mL. Murine CME and bCME at each concentration caused an increase (P < .01) in [3H]TdR incorporation into muscle cells compared to control cultures. The saturating concentrations (P < .01) of CME in the presence of 2% FBS were approximately 200 and 400 micrograms/mL for murine and bovine extracts, respectively. Murine CME or bCME acted in an additive fashion with independent, saturating concentrations of the insulin-like growth factors (IGF-I and IGF-II), basic fibroblast growth factor (bFGF), and transforming growth factor-beta (TGF-beta) to increase (P < .01) C2 muscle cell proliferation. Subsequently, in separate experiments, mCME or bCME acted additively with a combination of all growth factors to increase (P < .01) cell proliferation. Combining mCME and bCME at saturating levels in one treatment was not (P > .05) additive to that elicited by either CME alone. These results suggest that myotrophic factors are released following injury in mature skeletal muscle, and they are not species-specific.

Bioavailability and interaction of vitamin A and vitamin E in ruminants.

Recent interest in antioxidant vitamins and animal nutrition has resulted in the investigation of feeding levels of vitamin E which are considerably higher than NRC requirements. Relatively high levels of vitamin E are required to improve animal product quality such as extending beef color stability and minimizing off-flavors in milk due to lipid oxidation. Concerns regarding a negative effect of vitamin A on vitamin E utilization and the suitability of currently used standard activity values for vitamin E supplements for ruminants have been raised. High dietary levels of vitamin A have depressed vitamin E utilization in most animals studied. In the dairy cow, 675,000 IU of vitamin A acetate per head per day is required to significantly depress vitamin E utilization. This is approximately 10-fold greater than the highest levels currently fed to dairy or beef cattle and therefore should not cause a practical problem. Synthetic and naturally derived alpha-tocopherol, and their ester forms, are commonly used as vitamin E supplements. These various forms give rise to isomer differences, ester differences and formulation differences that can affect their absorption and subsequent utilization. The current research indicates that the commonly used standard activity values based on a value of 1.00 IU per mg of all-rac-alpha-tocopheryl acetate are probably too low for the ruminant. The roles of isomeric forms and gastrointestinal tract absorption have not been completely resolved regarding their effects on the bioavailability of vitamin E supplements.

Effects of recombinant bovine somatotropin implants on serum concentrations of somatotropin, insulin-like growth factor-I and blood urea nitrogen in steers.

Four cross-bred beef steers averaging 346 kg were used in a 4 x 4 Latin square design to determine the effect of prolonged-release recombinant bovine somatotropin (rbGH) implants on serum concentrations of somatotropin (GH), insulin-like growth factor-I (IGF-I) and blood urea nitrogen (BUN). Recombinant bGH implants of 0, 40, 80 or 160 mg were administered subcutaneously in the tailhead during the 4 trial periods. Each steer received each treatment starting at 06:00 on day 0 with 21 days between treatments. Jugular vein blood samples were collected on days 0, 1, 2 and 3 (4 day time course for GH, IGF-I and BUN) and every 15 min (GH profile) for 6 h on day 3. Serum baseline GH values were higher (P < 0.10) for the 80 and 160 mg treatments than for the control, and peak amplitude was decreased (P < 0.05) by the 40 and 160 mg treatments. There was a trend (P < 0.11) for fewer GH peaks during the 160 mg treatment. Somatotropin concentrations decreased from day 1 to day 3 (P < 0.05) in a linear manner. Serum IGF-I concentrations increased (P < 0.05) in a linear dose-dependent manner from the 0 mg to the 160 mg treatment. BUN concentrations were not significantly altered by rbGH treatment. Results from this experiment indicate that rbGH implants significantly increase serum IGF-I and GH baseline concentrations while suppressing GH peak amplitude in finishing steers.

Efficacy of vaginal spaying and anabolic implants on growth and carcass characteristics in beef heifers.

Ninety crossbred beef heifers averaging 260 kg were blocked by weight and allotted randomly to 15 pens of six heifers each, with three replicates per treatment. The treatments were spayed heifers (S); intact heifers (I); S + Synovex-H7 (SH); I + Synovex-H (IH); and S + Synovex-S7 (SS). The heifers were spayed vaginally with a Willis instrument; intact heifers were rectally palpated for reproductive soundness. Heifers were fed a growing diet (55 d), re-implanted and subsequently fed a finishing ration (73 or 101 d). All heifers were observed for estrus daily at approximately 0600 and 2000 until d 69. A jugular vein blood sample was obtained from each heifer on d 48, 55, 62 and 69 for blood progesterone analysis. Results of blood progesterone analysis and reproductive tract examination indicated that two spayed heifers were incompletely spayed, a 96% success rate. The SH and SS heifers continued to exhibit estrous behavior despite being successfully spayed. Heifers implanted with Synovex-H had greater (P less than .01) ADG and were more efficient (P less than .03) than nonimplanted heifers. The SS heifers had greater ADG (P less than .05) during the finishing phase than SH heifers, but no advantage of SS over SH was apparent during the growing phase. The overall ADG response to implantation was fourfold greater (P less than .07) in the spayed heifers than in the intact heifers (32 vs 8%). Heifers implanted with Synovex-H had greater adjusted hot carcass weight (P less than .02) and ribeye area (P less than .002) than nonimplanted heifers. For adjusted live weight and ribeye area, the response to implantation was approximately threefold greater in the spayed heifer than the intact heifer. These results demonstrate that spaying and implanting heifers can increase rates and efficiency of gain even though behavioral estrus is not eliminated.

Efficiency of Glasshouse Pot Experiments Rotating versus Stationary Benches.

Pot cultures of rice (Oryza sativa L., var. Colusa) in flooded soil were used to measure comparative uniformity of growth where mutual shading was the primary source of variation. Data were analyzed according to various divisions of each layout into blocks, sections, and replicate pots to compare statistical efficiencies.Experiments on stationary benches were subject to large border effects that were not suitably compensated for by any of the systems of replication tested. On the turntable, which carried 24 pots in single file, all plans of analysis tested were acceptable and resulted in coefficients of variability ranging from 2.5 to 4.5%.Consideration of these results, along with the cost of increased replication and the fact that use of a turntable minimizes the effects of environmental variability inherent in greenhouses, leads to the conclusion that the turntable provides more efficient use of greenhouse space for precision experiments than do stationary benches.