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.

Dose-response effects of recombinant bovine somatotropin implants on feedlot performance in steers.

One hundred twenty crossbred beef steers averaging 377 kg were used in a 2 x 4 factorial experiment to determine the dose-response effects of recombinant bovine somatotropin (rbST) implants on growth performance and carcass characteristics. The implant dosages were 0 (sham), 40, 80, or 160 mg/wk administered s.c. in the tailhead region on a weekly basis throughout the experiment. The steers were fed a high-concentrate diet, which contained either a degradable (DP; soybean meal) or an escape (EP; corn gluten and blood meal) protein source. No dietary protein effect or dietary protein x rbST level interactions were detected. Recombinant bST decreased both DMI (P less than .10) and feed/gain (P less than .05) in a linear dose-dependent manner. Dosage of rbST did not significantly affect (P greater than .10) ADG or final weight of the steers. Recombinant bST decreased backfat depth (P less than .10), marbling score (P less than .05), and quality grade (P less than .10) and increased yield grade (P less than .10) in a linear dose-dependent manner. Soft tissue composition of the 9-10-11th rib section was altered (P less than .01) by rbST administration in a linear dose-dependent manner. The percentage of protein in the rib section was increased by 9.4% and fat was decreased by 11.8% at the 160 mg/wk rbST level compared with the sham-implanted steers. Recombinant bST did not affect (P greater than .10) dressing percentage, hot carcass weight, kidney, pelvic, and heart fat, or longissimus muscle area.(ABSTRACT TRUNCATED AT 250 WORDS)

Periodic changes in body composition and in priorities for tissue storage and retrieval in mature beef cows.

Sixty mature (4 to 6 yr), nonpregnant, nonlactating beef cows of two breed types, Angus (n = 30) and Simmental (n = 30), were used in a four-period, split-plot study (371 d) to determine the seasonal differences in body composition. Periods were chosen to represent each of the four seasons in one year that ran consecutively from June 14, 1986 to June 20, 1987. Initially, all cows were assigned randomly within breed type to one of four feeding levels based on the cows' estimated maintenance requirement (75, 87.5, 112.5, and 125% of weight maintenance) and were rotated such that all animals were fed at all four feeding levels during the course of the study. Body composition was estimated via isotope dilution initially and at the end of Periods 1 through 3 and via derived regression relationships after Period 4. Body composition differed by breed; Simmental cows had greater (P less than .05) amounts of empty body protein (79.4 vs 55.8 kg, respectively) and less (P less than .05) empty body fat (85.3 vs 93.9 kg, respectively) than the Angus cows. These differences also were apparent when expressed as a percentage of live weight. Season altered components of the empty body. On the average, both breeds mobilized (P less than .05) empty body protein (-3.6 and -5.4 kg for Angus and Simmental cows, respectively) in the summer while simultaneously gaining (P less than .05) empty body fat (15.3 and 30.1 kg for Angus and Simmental cows, respectively). Both breeds subsequently tended to gain empty body protein in the winter and spring.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of season on the maintenance requirements of mature beef cows.

Sixty mature, nonpregnant, nonlactating beef cows of two breed types, Angus and Simmental, were used in a four-period, split-plot study to determine the effects of season on maintenance requirements. Periods were chosen to represent each of the four seasons and ran consecutively from June 14, 1986 through June 20, 1987. All cows were fed at one of four feeding levels (75, 87.5, 112.5, and 125% of estimated ME required for maintenance) a cottonseed hull-based diet in each of the four seasons and were rotated such that all cows received all feeding levels during the study. Retained energy for all cows within periods was determined through changes in body composition determined initially and at the end of each period. Mean DM digestibility (DMD) was similar for both breeds (54.4%), and in both breeds DMD was similar in the summer, fall, and spring and lower (P less than .05) in the winter. Mean DE was 61.4% and also was similar between breeds. Season affected DE, which was greatest (P less than .05) for both breeds in the fall (62.5%). Simmental cows had a 16.1% greater (P less than .05) overall daily ME requirement for weight maintenance than Angus cows (123.5 vs 103.6 kcal/kg.75), and both breeds had greater (P less than .05) requirements during the summer and lower (P less than .05) requirements during the winter (122.6 vs 91.4 and 145.9 vs 109.3 kcal/kg.75 for Angus and Simmental cows, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of anabolic status and phase and rate of growth to priorities for protein and fat deposition in steers.

The effects of anabolic implants, growth phase (growing vs finishing) and rate of growth on the priorities for protein and fat deposition were determined in yearling cattle. Santa Gertrudis crossbred yearling steers weighing 290 kg were individually fed diets varying in forage and grain content and either not implanted (n = 16) or implanted (90-d intervals) with Ralgro (n = 13) or Synovex-S (n = 12) implants. The cattle were fed toward a similar expected final empty BW (455 kg). Initial and interim empty body composition was measured via deuterium oxide dilution; final composition was determined by carcass specific gravity. During a 100-d growing phase, rates of protein gain were increased (P less than .12) to 118 and 131 g/d from 98 g/d for Ralgro and Synovex vs nonimplanted cattle, respectively. Concurrently, the fraction of protein in empty body growth was increased (P less than .09) from 17.5% for controls to 23.8 and 19.7% for Ralgro- and Synovex-implanted steers, respectively. This change in protein growth occurred concomitant with mobilization of fat and a reduction (P less than .04) in fat gain with Ralgro and Synovex implants. During the 136-d finishing phase, protein accretion was 115 and 132 vs 93 g/d for Ralgro- and Synovex-implanted cattle vs nonimplanted cattle; this represented a 24 and 42% increase (P less than .03) with Ralgro and Synovex, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nutritional level and biological type on gonadotropin-releasing hormone-induced luteinizing hormone release and plasma progesterone, estrone and estradiol concentrations in pre- and post-partum beef heifers.

Forty-six beef heifers (16 to 23 mo) of two biological types (small = Red Poll-sired, large = Charolais-sired) were individually fed from d 90 of gestation through parturition to evaluate the effects of nutritional restriction on plasma LH and steroid hormone concentrations. Heifers were allotted to one of two nutritional treatments to achieve a BW reduction (loss, fed at 1% of BW/d) or to maintain initial BW (maintenance, fed 1.5% of BW/d) to parturition. Gonadotropin-releasing hormone (100 micrograms) was injected i.m. three times during gestation (d 130; d 200; d 270) and twice after parturition (d 1 to 14; d 23 to 36). Blood samples were collected at 20-min intervals after GnRH for 4 h. Maternal BW change from d 90 to parturition differed (P less than .01) between loss and maintenance heifers. Mean plasma progesterone concentrations were greater (P less than .05) at d 130 and 270 of gestation in small than in large heifers and were greater (P less than .01) at d 23 to 36 postpartum in maintenance than in loss heifers. Mean concentrations of estrone and estradiol were greater (P less than .05) in large than in small heifers at d 200 of gestation. Mean plasma LH concentrations following GnRH injection were greater (P less than .01) in loss than in maintenance heifers at 200 and 270 d of gestation. Metabolizable and retained energy were related inversely to LH release during mid and late gestation.(ABSTRACT TRUNCATED AT 250 WORDS)

Anabolic implant and frame size effects on growth regulation, nutrient repartitioning and energetic efficiency of feedlot steers.

Rates of growth and partitioning of nutrients among tissues were measured in large (Simmental x [Hereford x Brahman]; n = 34) and very large (Chianina x Angus and Maine Anjou x Angus; n = 37) steers implanted with different anabolic growth regulators. All cattle were fed individually a whole shelled corn (13% crude protein) diet. Implant strategies were: none (n = 13), Ralgro 36 mg (n = 15), Ralgro 72 mg (n = 14), Synovex-S (n = 15) and Ralgro 36-Synovex-S (n = 14) administered at d 0 and 90. Empty body composition of all cattle was measured initially and at 90 d by D2O dilution procedures and at slaughter (average, 182 +/- 4.1 d) by carcass specific gravity. Empty body weight for large and very large cattle averaged 274 and 324 kg (P less than .05) initially and 497 and 603 kg (P less than .05) at slaughter. Empty body protein differed (P less than .05) for large and very large steers and averaged 51 and 61, 67 and 79, and 87 and 103 kg initially, at midpoint and at slaughter, respectively. Percentage empty body fat was lower for very large steers (13.5 vs 15.6%) initially (P less than .05) but was similar for very large and large steers at the midpoint (18.7 vs 18.1%) and at slaughter (23.2 vs 21.9%). Daily rates of empty body gain (DEBG) were greater (P less than .05) for very large vs large steers for both growing and finishing periods and averaged 1.53 vs 1.26 kg/d overall. Daily rates of protein gain (DPG) were similar for very large and large steers for the growing phase (204 vs 202 g/d) but greater (P less than .05) in very large steers for the finishing phase and overall (253 vs 204, and 229 vs 202 g/d). All implant strategies, except R36, increased DEBG and DPG and tended to decrease the percentage of fat in daily gain. In both large and very large cattle, implant growth regulators increased growth rate and partitioned nutrient use away from fat toward protein accretion, with the magnitude of partitioning toward protein increasing with greater rates of growth. These data indicate that anabolic growth regulators are viable strategies to enhance lean beef production in steers, regardless of animal size.

Ionophores alter hepatic concentrations of intermediary carbohydrate metabolites in steers.

The effects of ionophores on liver weight and function were determined in finishing steers (n = 24; avg weight 440 kg). Steers were group-fed one of three treatments (control, lasalocid or monensin at 33 mg/kg feed) for 46 d prior to slaughter. Three days prior to slaughter, blood was collected for the determination of serum Ca and Mg. At slaughter, the liver was removed, weighed, sampled, frozen in liquid nitrogen and subsequently analyzed for concentrations of carbohydrate metabolites and minerals. Liver weight (5.9 kg) was unaffected by treatment. Serum and hepatic Ca and Mg were not affected by ionophore treatment. Hepatic glycogen levels in steers fed ionophores were unaffected by treatment. Fructose 1,6-bisphosphate was 21% lower (P less than .10) in hepatic tissue of steers fed ionophores, whereas dihydroxyacetone phosphate was 15 to 37% greater in hepatic tissue of steers fed monensin (P less than .20) or lasalocid (P less than .10). Glyceraldehyde 3-phosphate was elevated more extensively by lasalocid than by monensin with increases of 72 (P less than .05) and 132% (P less than .001), respectively, over controls. Glycerol 3-phosphate levels were 37% (P less than .05) and 12% (NS) greater with these ionophores. Hepatic levels of pyruvate were elevated 12 (NS) to 36% (P less than .17) for monensin and lasalocid. Fructose 2,6-bisphosphate levels were 25% lower (P less than .25) in hepatic tissue of steers fed ionophores than in hepatic tissue from control steers. Other metabolites of carbohydrate metabolism in hepatic tissue were not altered appreciably. Changes in levels of intermediary metabolites of carbohydrate metabolism suggest alterations in hepatic carbohydrate metabolism favoring gluconeogenesis in steers fed ionophores.

Gonadotropin-releasing hormone-induced luteinizing hormone release in heifers: effect of nutrition during gestation.

The effects of nutrition during the last two trimesters of gestation on GnRH-induced LH release were assessed in crossbred heifers. Heifers (n = 58) were allotted at 90 d gestation to one of three levels of an experimental diet fed at 1, 1.5 or 2% of BW to attain maternal BW loss, BW maintenance or BW gain, respectively, at parturition. Twenty-two heifers were injected (i.m.) once with 100 micrograms GnRH between d 14 and 1 before parturition, and 32 heifers were injected (i.m.) once with 100 micrograms GnRH between d 8 and 21 after parturition. Jugular blood samples were collected before and at 30-min intervals after GnRH for 4 h. Least squares means for BW change differed (P less than .01) among BW loss (-17.6%), BW maintenance (-6.0%) and BW gain (7.0%) heifers. Basal plasma LH concentration was not influenced by nutritional treatment and was similar before and after parturition for all groups. However, in response to GnRH, peak plasma LH concentration was greater (P less than .10) for prepartum than for postpartum heifers. Mean LH peak amplitude in prepartum heifers was approximately twofold greater (P less than .10) in the BW loss and maintenance groups compared with the BW gain group. Prepartum LH release was related inversely (r = -.64) to change in heifer BW and increased (P less than .01) as BW loss increased during gestation. After parturition, mean LH peak amplitude and area under the response curve averaged 50% less (P less than .10) in the BW loss and maintenance groups than in the BW gain group.(ABSTRACT TRUNCATED AT 250 WORDS)

Site and extent of apparent magnesium and calcium absorption in steers fed monensin.

Eight crossbred steers (avg wt, 350 kg) with duodenal and ileal cannulas were used in two experimental periods in a single-reversal design to determine the effects of monensin on site and extent of apparent absorption of Mg and Ca. Steers were fed a cottonseed hull:concentrate diet (30:70) with or without 25 mg monensin/kg. The diet contained .20% Mg and .38% Ca. Each diet contained .25% Cr2O3 as a digesta marker. During each period, steers were fed the control diet for 10 d before allotment to treatments. Each period consisted of 17 d for diet adjustment and 6 d for collection. During the collection phase, fecal samples were obtained beginning on d 1 and continuing through d 6 at 12-h intervals progressing 2 h each day. Apparent Mg availability (grams apparently absorbed expressed as a percentage of grams of intake) increased (P less than .05) from 18.4 to 32.5% when monensin was fed. Feeding monensin increased (P less than .05) the apparent Mg availability and amount of Mg absorbed in the preintestinal region (47.7 vs 29.8% and 8.5 vs 5.1 g/d, respectively). Larger quantities (P less than .05) of Mg were secreted into the small intestine when monensin was fed. Monensin did not alter (P less than .05) apparent Ca availability or absorption in any segment of the digestive tract. These data indicate that monensin increased Mg and did not change Ca availability in the preintestinal region.

Performance and carcass quality of steers supplemented with zinc oxide or zinc methionine.

Forty-five Angus steers (avg initial wt 330 kg) were individually fed for 112 d to assess the value of supplemental Zn and source on performance and carcass quality. Steers had ad libitum access to a control diet (81 ppm Zn) of 33% whole corn, 33% ground milo, 15% cottonseed hulls and 13% cottonseed meal, or this control diet with 360 mg Zn/d added from either zinc methionine or zinc oxide. Steers were slaughtered on d 114, and carcass composition was determined by specific gravity. Average daily gain and feed efficiency were not affected by dietary treatments. Steers fed zinc methionine had a higher (P less than .05) USDA quality grade than those fed the control and zinc oxide diets. Marbling score was higher (P less than .05) for steers fed zinc methionine than for those fed control and zinc oxide treatments (4.4 vs 4.0 and 4.0, respectively, where 3 = slight, 4 = small, 5 = modest). Steers fed zinc methionine tended to have more (P less than .10) external fat (13 mm) than steers fed the control diet (10 mm); steers supplemented with zinc oxide had intermediate amounts of external fat (11 mm). Steers fed zinc methionine had 10.5 and 12.8% more (P less than .05) kidney, pelvic and heart (KPH) fat than steers fed control or zinc oxide diets, respectively. The effects of zinc methionine on carcass quality grade and marbling score may be due to Zn and (or) methionine. Regardless of the mechanism, the difference represents a potential economic benefit to producers.

Anabolic effects on rate, composition and energetic efficiency of growth in cattle fed forage and grain diets.

The effects of anabolic implants on rate, composition and energetic efficiency of growth were determined in steers fed diets varying in forage and grain content. Santa Gertrudis-cross steers averaging 337 kg were group-fed (n = 72) or individually fed (n = 45) ad libitum one of three diets and either not implanted or implanted (90-d intervals) with Ralgro or Synovex-S implants. Steers were fed to a similar empty body weight (463 kg). Initial empty body composition of individually fed steers was determined via D2O dilution, and final composition of all steers was determined by carcass specific gravity. Rate of empty body gain increased (P less than .05) from 695 g/d for nonimplanted steers to 798 and 844 g/d for Ralgro- and Synovex-implanted steers. Anabolic implants increased (P less than .01) daily empty body protein gain from 91 to 119 and 133 g for Ralgro and Synovex, an increase of 31 and 46%, respectively. The fraction of protein in empty body gain increased (P less than .01) from 13.8% to 15.6 and 15.9%, and the percentage of fat in empty body gain decreased (P less than .01) from 41.7% to 32.9 and 31.3% with Ralgro and Synovex, respectively. Daily rates of protein deposition increased at a decreasing rate, and rates of fat deposition increased at an increasing rate with increasing rate of empty body gain. Implanted steers deposited more protein and less fat at any rate of growth; the magnitude of this shift in nutrient partitioning from fat to protein growth increased with rate of growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Visual and chemical tissue markers for bovine carcass components.

A two-component, nontoxic, quantifiable animal/carcass tracing system was developed using riboflavin as an on-premises, initial carcass identifier visible under longwave ultraviolet (UV) light and deuterium oxide (D2O) as a tracer analytically quantified via fixed wavelength infrared spectrophotometry. Twenty-four cull cows and heifers were allocated into eight antemortem treatment groups (1, 12, 24, 48, 72, 96, 120, 144 h) for evaluation of the efficacy of riboflavin and D2O as tissue tracers in postmortem meat tissues. All cattle were slaughtered using conventional procedures and inspection. To study postmortem riboflavin marker changes due to constant light exposure over time, fluorescence and emission intensity scores were obtained by a trained panel 24, 48, and 168 h postslaughter. The riboflavin marker intensity rating means for UV fluorescence were classified as identifiable on all carcasses when evaluated under UV light, but were classified as not identifiable when evaluated under ambient light. Deuterium oxide levels in all tissue water samples, regardless of antemortem infusion group, contained D2O concentrations at least 2.5 times greater than those found in background water. Deuterium oxide was shown to disperse rapidly throughout living tissues. Correlations within animals for D2O levels from blood and muscle were all highly significant (r = .99).

Gestation nutrition, tissue exchange and maintenance requirements of heifers.

Forty-six pregnant, crossbred, 2-yr-old heifers of large or small mature size were individually fed a 70% cottonseed hull diet during gestation. Heifers were fed at either 1.0% (nutritionally restricted) or 1.5% (nonrestricted) of body weight from 90 d gestation through parturition. Live weight, from 90 d gestation to parturition, was reduced by 20.5% and 1.0% for restricted and nonrestricted heifers, respectively. Whereas nonrestricted heifers gained maternal protein (3.2 kg) from d 90 through parturition, restricted heifers lost (P less than .05) protein (-5.4 kg) and mobilized twice (P less than .05) as much fat (49 vs 25 kg). Percentage of empty body protein increased 13.1 and 9.3% in restricted and nonrestricted heifers, respectively, whereas fat decreased (P less than .05) 31.7% (restricted) and 23.5% (nonrestricted) from 90 d to parturition. Daily metabolizable energy for maintenance (MEm) was greater for large than for small mature size heifers (169 vs 158 kcal/kg.75). Efficiency of ME use for gain was greater for small than for large mature size heifers (36.5 vs 31.2%). Efficiency in early gestation (45.4%) was greater than in late gestation (29.4%) and averaged 33.8% for 90 d gestation to parturition. Maintenance ME requirements increased 25% and efficiency of ME use decreased 35% with advancing stage of gestation. Nutritional restriction of heifers reduced (P less than .05) calf birth weight (27.3 vs 30.2 kg) and decreased gestation lengths (275 vs 282 d) compared with nonrestricted heifers. This research indicates that nutritional restriction of beef heifers alters birth weight, repartitions maternal tissues and changes rate of tissue mobilization.

Maintenance requirements and energetic efficiency of cows of different breed types.

Dry, nonpregnant, mature cows (greater than 10 yr) of five breeds (Angus, A; Brahman, B; Hereford, He; Holstein, Ho; and Jersey, J) and their crosses (n = 60) were used in a 428-d experiment to determine maintenance energy requirements and efficiency of energy exchange. Cows were fed individually (via Calan electronic gates) a 70% cottonseed hull diet for four consecutive periods (127, 105, 97 and 99 d) at each of four levels (50, 83, 117 and 150% of each animal's estimated maintenance requirement). Each of four cows/breed group was assigned to one of the four feeding levels each period, with one cow fed each level each period. Body composition was measured initially and following each period in all cows via D2O dilution with a two-pool kinetics model procedure. Average ending live weight and empty body weight, protein and fat were similar to beginning values, indicating that cows began and ended in similar body composition. Dry matter digestibility (DMD) following the last period averaged 54.7%. Average DMD was 53.5, 57.8, 52.0, 55.0 and 51.7% (standard error of mean [SE] = 2.1) for A, B, He, Ho and J; values for He and J were lower (P less than .05) than for B. Diet digestible energy (DE) was similar for all breed types and averaged 62.4% of gross energy (GE). A small decrease in DE with increasing GE intake was noted for all breed types. The daily metabolizable energy requirement for weight equilibrium for A, B, He, Ho and J differed (P less than .01) and was 100, 98, 108, 119 and 152 kcal/kg.75 (SE 4.8), respectively, with an overall mean of 107. The ME for maintenance (MEm) was 91.6, 93.8, 95.3, 115.7 and 140.4 kcal/kg.75 for A, B, He, Ho and J (SE 6.0), respectively, with an overall mean of 101.9. Efficiency of weight change for A, B, He, Ho and J differed (P less than .01) and was 116, 135, 80, 116 and 58 g/Mcal ME intake, respectively, with an overall mean of 96. The respective efficiency of ME use for tissue energy gain or loss was 80.6, 66.8, 66.0, 36.5 and 36.2% for A, B, He, Ho and J, with an average energetic efficiency of 60.1%. In general, maintenance requirements for weight and energy equilibrium were lower in beef breeds and their crosses than in dairy breeds and their crosses. Efficiency of ME use also favored the beef breeds over the dairy breeds.(ABSTRACT TRUNCATED AT 400 WORDS)

Digestion of hay protein in different segments of the equine digestive tract.

Mature ponies fitted with permanent ileal cannulas were used in a 3 X 3 Latin square experiment to quantify prececal, postileal and total tract digestion of hay protein. Coastal Bermuda grass (CB), containing 11.7% crude protein, and two qualities of alfalfa, containing 15.0% (low-protein alfalfa; LA) and 18.1% (high-protein alfalfa; HA) crude protein, were fed in coarsely chopped form at 2% of body weight daily. Total tract apparent digestibility of the N in HA (73.8%) was higher than that in CB (57.0%; P less than .05) and was slightly higher than that in LA (66.1%; P less than .10). Nitrogen in LA was apparently more digestible than that in CB (P less than .05). Apparent prececal digestibilities of N in LA and CB were 1.3% and 9.6%, respectively, and were lower (P less than .05), or tended to be lower (P less than .10), than the 21.0% observed for HA. In relative terms, an average of 9.4% of the total N digestion occurred in the upper tract when CB and LA were fed, whereas 28.5% of total N digestion occurred in the foregut when HA was fed. There was a slightly higher concentration of total plasma free amino acids (P less than .10) at 1 h postfeeding when horses were fed alfalfa. Also, N retention was higher when ponies were fed HA (P less than .05) than when LA or CB were fed. Apparent postileal N digestibility was 52.5% for CB, 65.7% for LA and 66.9% for HA. Differences were not significant, and the large intestine appeared to compensate for the inefficiency of N digestion in the upper tract.(ABSTRACT TRUNCATED AT 250 WORDS)