Substrate utilization by fetal pig skeletal muscle

The ability of fetal pig skeletal muscle (biceps femoris) to metabolize glucose, fructose, lactate, acetate and palmitate in vitro was examined at 70, 90 and 110 d of gestation. Even though succinate dehydrogenase activity increased as fetal age increased (P less than .01), the rate of oxidation of glucose, fructose, acetate and palmitate to CO2 was not influenced by fetal age (P greater than .05), but each rate was dose-dependent (P less than .01). At higher concentration, lactate oxidation to CO2 proceeded at a faster rate in the muscle of 70-d fetuses when compared with 90- or 110-d fetuses. Muscle glycogen content increased (P less than .01) from 70 to 110 d of gestation. The rate of glucose incorporation into glycogen increased over this same time frame (P less than .06). Glucose-6-phosphate dehydrogenase activity did not change with age when activity was expressed per unit wet weight of muscle (P greater than .05). The ratio [1-14C]glucose/[6-14C]glucose oxidized to CO2 was independent of age and substrate concentration, and indicated significant pentose cycle activity in fetal muscle. Incorporation of lactate and palmitate into phospholipid was greatest at 70 d of gestation, a time period that coincides with establishment of mature muscle fiber number and fiber hypertrophy. The rate of palmitate incorporation into triacylglycerol was dependent on concentration of substrate (P less than .01) but not on age (P greater than .05). The rate of fructose oxidation to CO2 was lower than the rate for glucose, lactate and acetate when compared at similar concentrations. Acetate carbons were not incorporated into free fatty acids or lipid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of dietary forage and energy intake on metabolism and acyl-CoA synthetase activity in bovine ruminal epithelial tissue.

Twenty calves (7 mo old) were blocked by breed, sex, and weight into five groups of four calves and randomly assigned to either a 90% forage (alfalfa) or a 90% grain (50% sorghum and 50% wheat) diet fed at one (1M) or two (2M) times NEm for 140 d. Samples of ruminal epithelial tissue were collected from the anterior ventral sac, and papillae were cut free by hand and used for in vitro incubations and acyl-CoA synthetase assays. Substrates were acetate (90 mM), propionate (60 mM), butyrate (30 mM), and glucose (20 mM). Net productions of beta-hydroxybutyrate and acetoacetate from acetate were greater (P less than .01) with the 2M feeding; however, 14CO2 production from acetate was greater (P less than .05) with the grain diet. Net production of lactate (P = .09) and pyruvate (P less than .01) from propionate increased with the 2M feeding, whereas net lactate production from glucose decreased (P less than .01). Uptakes of VFA were similar with 1M and 2M feeding and were about 10-fold greater than uptakes of glucose. Production of 14CO2 from propionate was two- to fivefold greater than from acetate, butyrate, or glucose. Oxygen consumption was greater (P less than .01) with 2M feeding and unaffected by substrate. Activities of butyryl-CoA synthetase (nmol.mg of tissue-1.h-1) were greater (P less than .05) for animals consuming the forage diets. Addition of butyrate inhibited acetyl- and propionyl-CoA synthetase activity by 63 and 92%, respectively for all dietary treatments. Overall, metabolism of ruminal epithelial tissue tended to increase with the 2M feeding. Influence of dietary forage content on metabolism and activity of acyl-CoA synthetases was minimal, but the high-forage diet caused slight increases.     

Influence of environmental temperature on growth, muscle and adipose tissue metabolism, and meat quality in swine.

An experiment involving 32 individually housed, castrated male pigs was conducted to determine the effects of environmental temperature (12 degrees C = T12 or 28 degrees C = T28) on the performance, carcass characteristics, muscle and adipose tissue metabolism, and meat quality of pigs fed to achieve equal rates of weight gain between 8 and 92 kg live weight. The T12 pigs had less muscle (P less than .01) and more subcutaneous fat (P less than .01) in the ham than did T28 animals. Thyroids and adrenals were heavier (P less than .01) in T12 than in T28 pigs. Percentage of type I muscle fibers was higher (P less than .01) and fiber cross-sectional areas smaller (P less than .01) in semispinalis muscle (SS) of T12 pigs, whereas no effect of temperature was noticed in longissimus muscle (LD). Cold exposure induced a larger increase in oxidative metabolism in SS (+30 to 32%, P less than .001) than in LD (+14 to 17%, P less than .10) and an enhanced glycolytic metabolism in LD (P less than .05). Lipid concentration was higher in SS of T12 than in that of T28 pigs. Lipogenic enzyme activities and unsaturation of backfat were higher in T12 than in T28 pigs, whereas no effect of temperature was noticed in leaf fat. Cold treatment resulted in a faster postmortem pH decline (P less than .01), higher glycolytic potential (P less than .01), and lower ultimate pH (P less than .01) in LD. The results indicate that 12 degrees C vs 28 degrees C induced detrimental effects on growth, ham composition, and muscle and adipose tissue quality.     

Changes in ruminal and fecal particle weight distribution of steers fed coastal bermudagrass hay at four levels

Samples of digesta from the ruminal upper strata (RUS) and feces (F) were taken from four ruminally cannulated steers fed Coastal bermudagrass hay (78% NDF) in the long form to evaluate the effects of feeding level and time postfeeding on particle breakdown. The experimental design was a 4 x 4 Latin square with 18-d periods. Treatments based on previous intakes were set at 50, 70, 90 and 110% (3.1, 4.4, 5.5 and 6.7 kg/d, respectively) of feed consumed per animal and fed at 12-h intervals. Samples were taken at 2, 6 and 12h postfeeding and wet-sieved. Dry matter weight distribution of total recovered particles was used to partition RUS and F digesta among percentages of large (greater than 4.0 mm), medium (greater than 4.0 and less than or equal to 1.0 mm), small (less than 1.0 and greater than or eual to .125 mm) and fine (less than .125 and greater than or equal to .0027 mm) particles. With increasing feeding level, the percentage of medium RUS particles increased linearly (P less than .02), whereas the percentage of fine RUS particles decreased linearly (P less than .01). Increased time postfeeding resulted in a linear decrease in the percentage of large RUS particles (P less than .01), a linear increase in the percentage of small RUS particles (P less than .01) and in a quadratic increase in the percentage of fine RUS particles (P less than .01). Percentage of medium RUS particles remained unchanged. Increasing feeding level resulted in linear increases in mean RUS (P less than .01) and F (P less than .02) particle sizes. Percentages of RUS and F material passing through a 1.0-mm sieve averaged 52.8 and 88.8%, respectively. Animal-to-animal variation in proportions of RUS and mixed reticuloruminal particles was not entirely removed by rumination and was still reflected in the percentages of F particles. Factors such as particle entrapment in the fiber mat, reticular sedimentation, changes in specific gravity, swelling and hydration capacity, reticuloruminal motility and amount of digesta exiting per contraction appear to be more important than particle size reduction in the regulation of the passage of digesta from the reticulorumen.     

Effects of mimosine on fiber shedding, follicle activity, and fiber regrowth in Spanish goats

Ten 2-yr-old Spanish wethers (58.2 +/- 7.21 kg BW) were used to determine effects of 2-d intravenous infusion of mimosine (beginning on January 8) on fiber shedding, follicle activity, and fiber regrowth. Primary and secondary follicle activity on d 0 were 43 +/- 6.2% and 96 +/- 1.7%, respectively. Five wethers were infused with mimosine at 120 mg/(kg BW x d) and the other five received saline. At 7 to 10 d after the start of infusion, all five goats infused with mimosine exhibited shedding, whereas shedding by controls was not observed. Cashmere fiber shedding score (5-point scale: 1 = no shedding, 5 = excessive shedding) on d 4 was greater for mimosine goats than for controls (1.2 vs 2.0; P < .001), and shedding score for wethers receiving mimosine was greater (P < .05) on d 12, 16, and 20 than on d 0 and 4 (4.1 to 4.6 vs 1.4 and 2.0). Guard hair shedding score for goats receiving mimosine was greatest (P < .01) among the days after infusion for d 12 and greater (P < .01) on d 16 than on d 0 and 4. Nonetheless, cashmere fiber yield from combed fleece of mimosine goats (average of 73%) was much greater than for a clipping of the uncombed side (average of 28%) when the cashmere fiber shedding score exceeded 4.0. Secondary follicle activity on d 12 was lower (P < .01) for mimosine than for control wethers (6.8 vs 67.7%), and secondary follicle activity for mimosine-infused goats on d 12 was lower (P < .01) than on d 0 (98.9%), 4 (98.3%), and 20 (99.5%). Mimosine infusion resulted in no detectable fiber regrowth in wk 4 to 7 after the start of infusion, but regrowth rate in the following two 4-wk periods was similar for mimosine and control wethers. In conclusion, 2-d intravenous infusion of mimosine at 120 mg/(kg BW x d) in the winter induced cashmere shedding but had less effect on guard hairs, suggesting future potential use of chemicals such as mimosine to remove cashmere fiber.     

Net energy value of ammoniated wheat straw

Eight steers (327 kg average) were fed diets containing either nontreated or anhydrous NH3-treated wheat straw in a two-period crossover design. Intake and digestibilities of dry matter, gross energy, neutral detergent fiber, acid detergent fiber and crude protein were measured by total collection. Energy losses in urine and methane were determined. Heat production was determined by indirect respiration calorimetry on steers fed both diets and after they were fasted. Ammoniation of the straw raised its N content from .49 to 1.59% (P less than .001). Dry matter (DM) intake was increased (P less than .01) by the process from 1.0 to 1.3% of body weight. Digestibility coefficients of dry matter and energy, as well as those for fiber, were increased (P less than .001) by four percentage units or more. Crude protein digestibility, however, was depressed (P less than .001) from 67.8% to 53.5% by ammoniation. Urinary energy as a percentage of gross energy intake (GEI) was reduced (P less than .05) by NH3 treatment from 4.10 to 3.74%. Methane energy was not different (P greater than .10). Metabolizable energy was improved (P less than .001) by ammoniation, increasing from 45.2 to 50.0% of GEI. Daily heat production was higher (P less than .01) for steers consuming the ammoniated straw diet, increasing from 113.7 to 125.3 kcal/wt.75), and was due to higher metabolizable energy intake (MEI) since partial efficiency of MEI used for maintenance did not differ (P greater than .10) between diets. The higher net energy value of the ammoniated wheat straw diet (1.45 vs 1.26 kcal/g DM) was due mainly to decreased fecal loss and a slight decline in urinary loss.     

Dietary protein level and ruminal degradability for mohair production in Angora goats.

Twenty-eight Angora goat doelings (average BW 22.1 kg) were used in a 150-d study to examine the effects of dietary CP level and degradability on mohair fiber production. A 2 x 2 factorial arrangement was instituted using conventional, solvent-extracted soybean meal (high degradability) or expelled, heat-treated soybean meal (low degradability) incorporated into low- (12%) or high- (19%) CP diets. Grease and clean mohair weights were greater (P less than .05) in goats fed the diets containing 19% CP. Mohair fiber diameter was not affected (P greater than .10) by dietary CP level. Clean mohair weight tended (P less than .08) to be higher in the goats fed diets containing expelled, heat-treated soybean meal. Body weight gains were not affected (P greater than .10) by CP level or degradability, whereas DMI increased (P less than .01) with increasing CP level. Ruminal fluid pH and total VFA concentrations were not affected (P greater than .10) by diet. Ruminal ammonia N concentration increased (P less than .05) as CP level in the diet increased, and postprandial changes in concentrations were less noticeable in the group fed expelled, heat-treated soybean meal. Plasma urea N (P less than .001) and total protein (P less than .01) concentration increased as dietary CP level increased. Plasma glucose was elevated (P less than .001) 2 h after feeding in the goats fed conventional, solvent-extracted soybean meal, whereas glucagon concentrations were greater at 0 and 4 h in the group fed expelled, heat-treated soybean meal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histopathological observation of stress myopathy in M. longissimus in the pig and relationships with meat quality, fattening and slaughter traits

The characteristic myopathic features revealed by histological observations included strong proliferation of connective and fatty tissue, perivascular infiltrations and necrosis of muscle fibers with phagocytosis to the lesser extent. In the myopathic muscle, as well as in giant fibers, histochemical techniques showed a reduction in succinate dehydrogenase and lactate dehydrogenase activity in type beta R (slow-twitch, oxidative) and alpha R (fast-twitch, oxidative and glycolytic). Magnesium-activated adenosine triphosphatase reaction ranged from diffuse to negative in beta R, alpha R and alpha W (fast-twitch, glycolytic) fiber types. Diffuse reaction for acid phosphatase and total loss of glycogen content were observed. The micrographs of the myopathic muscle indicated enlarged mitochondria with atrophy or complete destruction of cristae. Many myofibrils were hypercontracted. Giant fibers possessed mitochondria enlarged to an even greater extent and many of the myofibrils had loss of continuity, were narrow, depleted and were also hypercontracted. Significant differences between myopathic and normal groups were found in number of beta R fibers (lower in the myopathic group), number of alpha R fibers and percent of alpha R and alpha W fibers (higher in the myopathic group). Differences (P less than .01) existed between meat pH1 value in the myopathic group (mean value of 5.95) and the normal group (mean value of 6.29). Meat from the myopathic group of pigs also had a lower (P less than .01) pH24 value and reduced water-holding capacity (P less than .01) relative to the meat of the normal pigs. The lack of difference of fattening and slaughter traits between the groups suggested that the White Zlotnicka pigs is of particular value because it is possible to improve the production traits without increasing the incidence of these syndromes within the breed. Negative correlations (P less than .05) between number of giant fibers and percent of alpha W fibers, and between percent of giant fibers and percent of alpha W fibers indicate that alpha W fibers can undergo degeneration and be transformed into giant fibers. Therefore, it it suggested that giant fibers should be treated as muscular, pathological results of past stresses and not as an additional type of normal muscle cells.     

Effects of dietary alfalfa:orchardgrass hay and lasalocid on nutrient utilization by gravid sows

Twenty-four third- and fourth-parity crossbred gravid sows were housed in metabolism stalls and randomly allotted to four dietary treatments: corn-alfalfa:orchardgrass hay (46%; CH), CH plus lasalocid (CHL), corn-soybean meal (CS) or CS plus lasalocid (CSL). Daily feed intake was 2.36 kg for CH- and CHL-fed sows and 1.66 kg for CS- and CSL-fed sows. Lasalocid intake was 110 mg X sow-1 X d-1. Total feces and urine were collected during two 5-d collection periods, 40 and 80 d postcoitum. Digestible energy (DE), metabolizable energy (ME), nitrogen (N) retention, dry matter (DM), neutral detergent fiber (NDF) and acid detergent fiber (ADF) digestibilities, and retention of calcium (Ca), total phosphorus (P), magnesium (Mg), sodium (Na) and potassium (K) were determined. Percentage DE and ME were greater (P less than .0001) for CS- and CSL-fed sows (88.3 and 83.4%) than for CH- and CHL-fed sows (65.2 and 61.3%). Lasalocid did not influence (P greater than .05) DE and ME values but decreased (P less than .01) the ME:DE ratio. Percentage N digestibility was greater (P less than .0001) for CS- and CSL-fed sows (85.7%) than for CH- and CHL-fed sows (60.8%), but there was no significant difference in N retention, expressed as a percentage of N intake. Lasalocid increased (P less than .03) percentage N digestibility; however, the diet X additive interaction decreased (P less than .005) grams N retained X sow-1 X d-1 for CSL-fed sows. The CH- and CHL-fed sows digested more grams of DM, NDF and ADF but had lower percentage digestibilities of DM and fiber fractions than did CS- and CSL-fed sows. The diet X additive interaction decreased (P less than .05) percentages of Ca, P and K digested and decreased (P less than .05) grams mineral retained (Ca, P, Mg and K) and mineral retained expressed as a percentage of intake for CSL-fed sows. Results indicate that alfalfa:orchardgrass hay and lasalocid influenced energy, fiber, nitrogen and mineral utilization by gravid sows.     

Dietary protein-induced changes in porcine muscle respiration, protein synthesis and adipose tissue metabolism

Growth rate, physically separable tissues of the ham and loin, heat production, skeletal muscle respiration and protein synthesis, and lipogenesis and lipolysis in s.c. adipose tissue were measured in a single experiment in which pigs were offered a 13 (n = 8), or 21% (n = 6) protein diet from 20 to 100 kg live weight. Pigs that were fed the 13% protein diet gained body weight slower, ate less, converted feed less efficiently and took 31 d longer to reach 100 kg live weight. Fat depth (cm) was greater (P less than .05) and loin eye area (cm2) was less (P less than .01) in pigs fed the 13% protein diet (2.6 vs 2.3 and 29.8 vs 35.3). Pigs that were fed the 13% protein diet had lower (P less than .05) ham and loin separable muscle and greater (P less than .05) ham and loin separable fat. The mean heat production was less (P less than .05) in pigs offered the 13% (22.49) vs 21% (24.63 MJ/d) protein diets. In the intercostal muscle preparation, total and Na+,K+-ATPase-dependent respiration (microliter O2.mg-1.h-1) were lower (P less than .05) in pigs offered the 13% (2.39 and .41) vs the 21% (3.89 and .68) protein diets. The energy used for the support of Na+ transport across membrane accounted for approximately 17% of muscle respiration. Absolute rates of protein synthesis in the muscle preparations were lower (P less than .01) at 13 than at 21% dietary protein. Lipogenesis in s.c. adipose tissue was not affected by dietary protein level. There was no difference in basal and norepinephrine-stimulated lipolysis between the two dietary protein levels.     

Utilization of nitrogen and energy by Holstein steers fed formaldehyde- and formic acid-treated alfalfa or orchardgrass silage at two intakes

Our objective was to measure the utilization of energy (E) and N by Holstein steers when fed alfalfa and orchardgrass silages offered at 65 and 90 g DM/kg live weight (LW).75 daily. Twelve steers adapted to the Beltsville respiration chambers were assigned to three Latin squares with 42-d periods. Steers in one square had permanent catheters in the portal and two mesenteric veins. Energy and N balance were measured during a 7-d collection of feces and urine that included a 3-d measurement of respiratory exchange. Energy and N variables were not different between catheterized and uncatheterized steers. Apparent digestibilities of DM, OM, CP, neutral detergent solubles and permanganate lignin were higher (P less than .01) and digestibilities of NDF and ADF, hemicellulose and cellulose were lower (P less than .01) for steers consuming alfalfa compared to orchardgrass silage. When fed alfalfa, steers' daily gross energy intake, DE, urine energy, ME, heat production and tissue energy retention were greater (P less than .01) and fecal energy losses were less (P less than .01) than when they were fed orchardgrass. Partial efficiency of ME use for tissue energy (TE) was greater (P less than .01) for steers when fed alfalfa (46.1%) than when fed orchardgrass (35.6%). Apparent ME (kcal/LW.75) required for maintenance of TE was similar for steers when fed alfalfa (133.9) and orchardgrass (131.2) silages. Nitrogen retention (g/d) was 48% greater (P less than .01) for steers when fed alfalfa (30.6) than when fed orchardgrass (20.7). This study demonstrates that steers used ME from alfalfa more efficiently for TE deposition than ME from orchardgrass.     

Effect of intraperitoneal administration of lysine and methionine on mohair yield and quality in Angora goats.

Eight mature Angora wethers (average BW 47.2 kg) were used in a 4 x 4 replicated Latin square design to evaluate responses to intraperitoneal (IP) administration of amino acids. The IP treatments consisted of saline (Control), methionine 1 g/d (Met), lysine 2 g/d (Lys), and methionine + lysine (Met + Lys). The amino acids dissolved in Control were infused continuously for the first 14 d of each 28-d period using peristaltic infusion pumps. Average d-28 grease and clean mohair yields (grams/100 square centimeters), and fiber diameter (micrometers) and length (centimeters) measurements during Control administration were 8.8, 7.6, 40, and 2.3, respectively. Mean clean mohair yield and fiber diameter increased by 5.3% (P less than .039) and 2.5% (P less than .067), respectively, with Met administration but were decreased by 9.2% (P less than .033) and 3.8% (P less than .001), respectively, by Lys administration; however, mean fiber length was increased (P less than .014) 21.7% by Lys infusion. The goats did not exhibit increased grease (P greater than .939) and clean (P greater than .477) mohair yields and fiber diameter (P greater than .619) when treated with Met+Lys. A N balance trial was conducted during d 10 through 14 of each period. Total retained N (grams per day) during Control administration was 18.4 and 24% greater than Met (P greater than .281) and Lys (P less than .061), respectively. When expressed as a proportion of N intake, retained N was lowest (P less than .127) in the Lys infusion group. Jugular blood ammonia N and plasma glucose and total protein concentrations were not affected (P greater than .10) by treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of genetic capacity for lean tissue growth on rate and efficiency of tissue accretion in pigs fed ractopamine.

The influence of genetic capacity for lean tissue (LT) growth on responses of pigs to ractopamine, in terms of rate and efficiency of body growth and the distribution and accretion rate of body tissues, was determined in this study. Two sources of pigs representing low and high LT genotypes were used. Within each source, two littermate barrows from each of eight litters were individually penned and given ad libitum access to a lysine-supplemented, corn-soybean meal diet (17.7% CP, 1.08% lysine) containing 0 or 20 ppm of ractopamine hydrochloride from 63 to 104 kg. Carcasses were physically dissected into muscle, fatty tissue, skin, and bone. Within each source, four additional pigs were killed for determination of initial body composition. Pigs of high LT genotype gained BW and muscle faster (P < .01), required less (P < .01) feed per unit of gain, and produced carcasses that contained more (P < .01) muscle and bone and less (P < .01) fatty tissue. Ractopamine increased (P < .01) weight gain and improved (P < .01) feed:gain ratio in both genotypes. Ractopamine enhanced the accretion rate and the amount of carcass muscle in both genotypes, but the degree of improvement was greater in pigs of the high than in those of the low LT genotype (genotype x ractopamine, P < .02). Ractopamine also reduced the accretion rate and amount of dissectible fat by a greater magnitude in the high LT genotype (genotype x ractopamine, P < .04). Based on these data, ractopamine increases muscle accretion to a greater degree in pigs with a high genetic capacity for LT growth than in those with a low capacity.     

Effects of whole blood clots, time, and implant size on vascularization and collagen deposition along Teflon-ensheathed carbon fibers implanted in ewes

Seventy-two subcutaneous implants were examined to evaluate connective tissue response to Teflon-ensheathed carbon fibers and whole blood clots. Carbon fibers significantly (P less than or equal to 0.001) increased vascularization and collagen formation within the Teflon sheath. Carbon fibers provide a potentially strong scaffold that would physically support cell migration during wound healing. However, obvious foreign body reactions occurred, which indicate that further studies on the biologic features of carbon fiber are needed before carbon fibers become entirely acceptable for long-term implantation. Compared with no-clot controls, Teflon tubes containing only whole blood clots stimulated a significant (P less than or equal to 0.001) wound-healing response, including organized collagen fiber formation. Other variables tested in this study such as length and diameter of the Teflon tubes did not significantly influence connective tissue responses.     

Influence of limestone level in high concentrate and high roughage diets on site and extent of digestion in lambs

Two digestion and slaughter trials were conducted to evaluate the influence of limestone level on site and extent of digestion and rumen fermentation in lambs. In trial 1, 11 wether lambs (avg wt 40.7 kg) were fed 75% concentrate diets supplemented with .6, 1.5 or 3.0% limestone (.6,1.2,1.7% dietary Ca, respectively) in a completely randomized design. Dry matter intake increased linearly (P less than .10) with limestone level; therefore, other data were analyzed with dry matter intake as a covariate. Total tract organic matter digestion decreased linearly (P less than .05) with increasing limestone but dry matter and fiber digestion were not affected by limestone. Ruminal digestion of dry matter and organic matter declined linearly (P less than .05) with increasing limestone. Ruminal neutral detergent fiber (NDF) digestion was higher with the 1.5 than the .6 and 3.0% limestone diets (quadratic effect, P less than .05) but ruminal digestion of other fiber components was not affected by limestone. Ruminal volatile fatty acids were not affected by limestone level; however, rumen ammonia concentrations decreased linearly (P less than .05) with increasing limestone level. In trial 2, 12 wether lambs (avg wt 43.3 kg) were fed a 35% concentrate diet with .1, 1.5 or 3.0% limestone (.5, 1.2 and 1.6% dietary Ca, respectively) in a completely randomized design. Dry matter intake was not affected by limestone level, but digestibility of dry matter, organic matter and starch (P less than .10), energy, crude protein, acid detergent fiber (ADF) and cellulose (P less than .05) responded quadratically to limestone level, with increases at the 1.5% limestone level. Ruminal dry and organic matter (P less than .05), NDF (P less than .10), ADF (P less than .01), cellulose (P less than .05) and starch (P less than .05) digestion responded quadratically to limestone level with higher values at the 1.5% limestone level. Proportions of ruminal propionate increased linearly (P less than .01) with increasing limestone level and acetate: propionate ratio declined linearly (P less than .01) with limestone level.     

Nitrogen metabolism by lactating ewes and their lambs

Twenty multiparous ewes and their newborn lambs were assigned to a 2 x 2 factorial experiment in which ewes were fed ad libitum either a moderate (MP, 15%) or a low (LP, 10%) CP diet and nursed either twin (T) or single (S) lambs. Nitrogen (N) balance trials were conducted on both the ewes and lambs during wk 2, 4 and 8 of lactation. Nitrogen balance, N digested and the portion of digested N retained were greater (P less than .01) with the MP diet. Nitrogen retention and serum urea-N values were lower for the ewes nursing T lambs. Plasma beta-hydroxybutyrate and serum glucose values were lower (P less than .01) for ewes fed the LP diet, and certain plasma amino acids and the ketogenic amino acids were lower with the LP diet. Insulin increased (P less than .01) with time throughout lactation. Triiodothyronine (T3) concentrations were higher (P less than .01) in ewes nursing T lambs. Thyroxine (T4) was greater (P less than .04) with the LP diet and greater (P less than .01) for ewes nursing T lambs. The T4:T3 ratio was lower (P less than .02) in the ewes consuming LP. The portion of the ewe's retained N used for milk synthesis was lower (P less than .01) with the MP diet. Ewes fed LP and nursing T lambs utilized all of their retained N plus a portion of their body protein reserves for milk production by the 2nd wk of lactation. Body weights of creep-fed lambs were not changed by protein content of the ewe's diet.     

Growth and carcass characteristics of pigs selected for fast or slow gain in relation to feed intake and efficiency.

Selection in pigs for either fast (line F) or slow (line S) postweaning gain was replicated in spring (SREP) and fall (FREP) farrowing groups. Littermate barrows were sampled from F and S during Generations 2, 3, and 4 of the SREP and Generation 3 of the FREP. Beginning at approximately 35 kg (OTWT), barrows were either allowed ad libitum access to feed (AL) or limited to a standard total feed intake (LIM). Blocks of the line x intake level factorial were removed from test and carcass data collected when the average weight of barrows in the block was approximately 110 kg. Carcass data were also collected on an additional barrow from each litter at OTWT to allow estimation of lean tissue gain per unit of feed consumed (LTFC) of tested barrows. In Generations 3 and 4 of the SREP, F-AL was greater (P less than .01) than S-AL for average daily intake and ADG; carcass backfat was greater (P less than .01) but LTFC tended to be less (P less than .10) for F-AL than for S-AL. When LIM was imposed in the SREP, F barrows gained faster (P less than .05) than S barrows in Generation 4, but across generation the lines did not differ for carcass backfat and LTFC was greater (P less than .01) for F than for S. In the FREP, F-AL was greater (P less than .05) than S-AL for average daily intake and ADG and was less (P less than .05) for LTFC, but F and S did not differ for these traits when LIM was imposed; carcass backfat of F was greater (P less than .01) than that of S by .46 cm under AL and .38 cm under LIM. Most of the response in ADG could be attributed to changes in intake, but results in Generation 4 of the SREP indicated that changes in efficiency had also contributed. Most of the additional intake in F vs S resulted in deposition of fat, probably due in part to the heavier weight of F-AL vs S-AL barrows.     

Effects of dry corn gluten feed on feedlot cattle performance and fiber digestibility

Effects of dry corn gluten feed (DCGF) on feedlot cattle performance and fiber digestibility were investigated. In Trial 1, 120 growing steers were fed corn silage-based diets containing 0, 40, 60 or 80% DCGF. Increasing levels of DCGF resulted in a curvilinear response in gain (P less than .05) and a linear increase in feed/gain (P less than .01). When the same steers subsequently were fed the same levels of DCGF in corn-based diets (Trial 2), increasing the percentage of dietary DCGF resulted in a linear decrease in gain (P less than .01) and a linear increase in feed/gain (P less than .01). In Trial 3, 46 crossbred steers were fed individually in a 2 x 2 factorial design to determine effects of 60 or 80% dietary high-moisture corn (HMC) or DCGF on feedlot cattle performance. Steers fed HMC had faster (P less than .08) and more efficient (P less than .05) gains than those fed DCGF, which had greater feed intakes (P less than .05). In Trial 4, 120 Angus crossbred steers were used to compare effects of 20 or 40% dietary HMC or DCGF on feedlot performance. Steers fed diets containing 40% HMC or DCGF had greater gains (P less than .01) and feed intakes (P less than .01) than those fed 20% diets. Steers fed HMC gained more efficiently than those fed DCGF (P less than .01). In an in situ trial, 0, 40, 60 or 80% dietary DCGF did not affect in situ DCGF DM or NDF disappearance. When DCGF was fermented in vitro in combination with corn silage, increasing the level of DCGF from 0 to 100% resulted in a linear increase (P less than .01) in 24 and 48 h NDF disappearance. These results suggest that at high dietary levels DCGF will support feedlot cattle gains that are nearly equal to those of cattle fed corn silage but somewhat less than those fed corn.     

Influence of level and source of dietary fat on its comparative feeding value in finishing diets for feedlot steers: metabolism

Six crossbred steers (315 kg) with cannulas in the rumen, proximal duodenum and distal ileum were used to study the influence of level and source of dietary fat on characteristics of digestion. Dietary treatments consisted of a steam-rolled barley-based finishing diet containing 1) no supplemental fat; 2) 4% yellow grease (YG); 3) 4% blended animal-vegetable fat (BVF); 4)8% YG; 5) 8% BVF or 6) 6% BVF and 2% crude lecithin. Increasing level of fat supplementation resulted in linear decreases (P less than .01) in ruminal and total tract digestion of OM and ADF and intestinal digestion of fat (P less than .05). At the 4 and 8% levels of supplementation, intestinal true digestibility of fat averaged 80.1 and 69.3%, respectively. Ruminal molar proportions of acetate decreased, and propionate molar proportion, as well as DE and ME values of the diet, increased linearly (P less than .01) with level of fat supplementation. The DE and ME values for fat were 8.17 and 9.76 at the 4% level and 7.35 and 8.72 Mcal/kg at the 8% level of supplementation, respectively. Yellow grease supplementation resulted in greater (P less than .05) ruminal fiber digestion and greater ruminal molar proportions of propionate than BVF. Intestinal fat digestion was similar (P greater than .10) for YG and BVF. Adding 25% lecithin to BVF resulted in greater ruminal fiber digestion and greater ruminal molar proportions of acetate; however, lecithin tended (P less than .10) to have a lower ME value than BVF.     

Effect of supplementation with concentrates and lasalocid during late pregnancy and lactation on productivity of Rambouillet ewes and development of wool follicles in their lambs

A total of 64 Rambouillet ewes was utilized in this study. Ewes were fed a 50:50 mixture of alfalfa and prairie hay ad libitum and either no concentrates (C), .4 kg concentrates . head-1 X d-1 (S) or .4 kg concentrates containing 73 ppm lasalocid . head-1 X d-1 (SL) during the last 50 d of pregnancy and through 60 d of lactation. A total of 163 skin samples was obtained from the mid-side region of the lambs at birth, 1 and 2 mo of age, and follicle traits were estimated by histological techniques. Wool growth per unit area (100 cm2) was estimated by clipping wool from both right and left mid-sides of all ewes 60 d postpartum. Birth weight of single lambs did not differ (P greater than .20) among treatments. Twin lambs of supplemented ewes were heavier (P less than .01) at birth than those of control ewes and the difference between S and SL groups was not significant. Compared with the control, concentrate supplementation with or without lasalocid increased (P less than .01) postnatal lamb survival and ewe productivity, expressed as kilograms of lamb weaned per ewe lambed. The C, S and SL groups weaned 12.50, 18.52 and 20.72 kg/ewe lambed (P less than .01), respectively. Maternal concentrate supplementation did not influence secondary to primary wool follicle ratio (Sf/Pf) of single lambs (P greater than .20). Twin lambs of the S ewes tended to have higher Sf/Pf than controls. The SL twins had intermediate Sf/Pf values (P greater than .20).(ABSTRACT TRUNCATED AT 250 WORDS)