Interaction of dietary carbohydrate and fat on glucose metabolism in growing pigs.

Increased consumption of fructose has been suggested to be a contributing cause of the increased rates of obesity in humans. Rodent studies have shown an increase in de novo lipogenesis and decreased insulin sensitivity in response to feeding high levels of fructose, but it is unclear if these effects occur in the same progression in humans. We aimed to develop a swine model for studying changes in glucose metabolism and insulin resistance resulting from dietary carbohydrate alone or in combination with high dietary fat. Two experiments were conducted to determine if the source of dietary carbohydrate, with or without added fat, had an effect on body weight gain, glucose metabolism, or insulin response in growing pigs. In the first experiment, pigs (24 barrows, initial body weight 28 kg) were fed one of 4 diets in which the source of carbohydrate was varied: 1) 20% starch; 2) 10% glucose + 10% starch; 3) 10% fructose + 10% starch; and 4) 20% fructose for 9 weeks. There were no differences in growth rate or glucose clearance observed. Experiment 2 was conducted as a 3 × 2 factorial with the main effects of carbohydrate source (20% starch, glucose, or fructose) and added fat level (0 vs 10%). Pigs (24 barrows, initial body weight 71 kg) were fed one of 6 experimental diets for 9 weeks. Compared to the other dietary treatments, pigs fed fructose with high fat had an elevated glucose area under the curve during the GTT (Carbohydrate x Fat interaction, P < 0.01). This same group had a lower insulin response (Carbohydrate x Fat, P < 0.05). This work demonstrates that pigs can be a viable model to assess the long-term effects of dietary carbohydrates on metabolism and body composition. Studies of longer duration are needed to determine if these changes are indicative of insulin resistance.

A cooperative study on the standardized total-tract digestible phosphorus requirement of twenty-kilogram pigs.

A cooperative study comprising growth performance, bone mineralization, and nutrient balance experiments was conducted at 11 stations to determine the standardized total-tract digestible (STTD) P requirement of 20-kg pigs using broken-line regression analysis. Monocalcium phosphate and limestone were added to a corn-soybean meal-based diet at the expense of cornstarch to establish 6 concentrations of STTD P from 1.54 to 5.15 g/kg in increments of 0.62 g/kg at a constant Ca:total P of 1.52:1.0. Diets were fed to 936 pigs (average initial BW of 19 kg) in 240 pens for 20 replicate pens of barrows and 20 replicate pens of gilts per diet. As STTD P increased from 1.54 to 5.15 g/kg of the diet for d 0 to 14, 14 to 28, and 0 to 28, the ADG, ADFI, and G:F increased ( < 0.01). Barrows gained and ate more ( < 0.05) than gilts during d 14 to 28 and 0 to 28. There was no interaction between sex and STTD P concentration for any of the growth performance response criteria. There were both linear and quadratic increases ( < 0.05) in mineral density and content of ash, Ca, and P in the femur expressed as a percentage of dry, fat-free metacarpal as dietary STTD P increased. Furthermore, the maximum load of the femur and mineral density and content and maximum load as well as the Ca and P expressed as a percentage of metacarpal ash linearly increased ( < 0.01) with increasing dietary concentrations of STTD P. There were both linear and quadratic increases ( < 0.01) in apparent digestibility and retention of P with increasing concentrations of STTD P in the diets. Digestibility and retention of Ca linearly ( < 0.01) increased with increasing dietary concentrations of STTD P. Breakpoints determined from nonlinear broken-line regression analyses revealed estimates of 4.20 ± 0.102, 3.20 ± 0.036, or 3.87 ± 0.090 g/kg for ADG during d 0 to 14, 14 to 28, or 0 to 28, respectively. Corresponding estimates using G:F as the response criterion were 4.34 ± 0.146, 3.38 ± 0.139, or 4.08 ± 0.195 g/kg. When mineralization of the femur was used as criteria of response, estimates of STTD P requirement were 4.28, 4.28, or 4.34, g/kg for mineral density, mineral content, or maximum load, respectively. Using mineralization of the metacarpal as criteria of response, estimates of STTD P requirement ranged from 3.5 to 5.0 g/kg depending on the metacarpal response criteria. The study provided empirical estimates of STTD P requirements of 20- to 40-kg pigs.

Supplementation of organic and inorganic selenium to diets using grains grown in various regions of the United States with differing natural Se concentrations and fed to grower-finisher swine.

Grains grown in various regions of the United States vary in their innate or natural Se contents. A regional study evaluated the effects of adding inorganic Se (sodium selenite) or organic Se (Se yeast) to diets with differing innate Se contents. A 2 × 2 + 1 factorial experiment evaluating 2 Se sources (organic or inorganic) at 2 Se levels (0.15 or 0.30 mg/kg) in 18 total replicates (n = 360 total pigs). A basal diet was fed without supplemental Se and served as the negative (basal) control. The study was conducted as a randomized complete block design in 9 states (Georgia, Illinois, Kentucky, Nebraska, North Carolina, Ohio, South Dakota, Texas, and Wisconsin) with each station conducting 2 replicates. Pigs were fed from 25 to approximately 115 kg BW. Similar dietary formulations were used at each station, incorporating a common source of trace mineral and Se premixes. Three pigs per treatment in 16 replicates (n = 240) were bled at 55, 85, and 115 kg BW and serum Se and glutathione peroxidase (GSH-Px) activities were determined. Three pigs (n = 260) from each treatment pen were killed at 115 kg BW and issues (liver, loin, and hair) were analyzed for Se. The corn Se content from the various states ranged from 0.026 to 0.283 mg Se/kg while the soybean meal Se content ranged from 0.086 to 0.798 mg Se/kg. Tissue and serum Se concentrations were greater (P < 0.01) when supplemental organic Se was fed, whereas serum GSH-Px was greater (P < 0.01) as Se level increased. There were linear increases (P < 0.01) in loin and quadratic increases (P < 0.01) in liver and hair Se concentrations as dietary Se level increased within each state. There was a source × level interaction (P < 0.01) for each tissue resulting in a greater increase when organic Se was fed. Serum Se and GSH-Px activity increased (P < 0.01) when both Se sources were fed and plateaued at each state at 0.15 mg Se/kg. There was a high and significant correlation between each tissue Se, serum Se, and GSH-Px activity to dietary Se level indicating that those states having greater grain natural Se contents also had greater tissue Se concentrations. These results indicate that a large difference in corn and soybean meal Se concentrations exists between states, that the addition of organic or inorganic Se to these grains increased tissue and serum Se in each state, and that organic Se was incorporated at greater concentrations in the loin, liver, and hair tissues of grower-finisher pigs than inorganic Se.

Nutritional value of ensiled grocery food waste for cattle.

Assessment of nutrient variability, feed value, ensiling capability, intake, and digestibility of grocery food waste recycled from large retail stores was conducted in 3 experiments. In Exp. 1, 115 proximate nutrient analyses of grocery byproduct feed (GBP) from stores in the southern United States from April 8, 2011, to November 18, 2012, were evaluated for variation in nutrient concentration. Grocery byproduct feed was characterized as being a readily fermentable, high-moisture energy feed with an average DM content of 17.5 ± 3.7% and TDN of 89.8 ± 7.1%. In Exp. 2 and 3, grocery food waste consisting of fruit, vegetables, and bakery items from large retail stores in the Atlanta, GA, area was used for ensiling and feeding studies. The GBP material for Exp. 2 was processed on farm into homogenous slurry and treated to reduce its moisture content and preserved in experimental silos. Drying treatments included 3 levels of citrus pulp substitution (8, 16, and 24% as-fed basis), or passively removing liquid as seepage after stacking for 24 h, or oven drying (24 h at 80°C). All GBP mixtures effectively ensiled after 28 d, as determined by changes in pH, soluble carbohydrates, and fermentation acids. Ensiled GBP was moderately stable during 72-h aerobic exposure. In Exp. 3, a feeding/digestibility trial, 8 yearling Holstein steers were used in a replicated 4 × 4 Latin Square and fed 4 incremental levels of ensiled GBP in total mixed rations (TMR). Steers were fed 0, 18, 36, and 54% ensiled GBP as part of a TMR containing 68% wheat silage and 32% concentrate on a DM basis. The rations averaged 35.9, 30.7, 26.8, and 23.8% DM with incremental levels of GBP. Steers increased DM intake and digestibility when fed increasing GBP (P < 0.5). Digestible energy and TDN were linearly related to the level of GBP fed (P < 0.01). The TDN content of GBP was 82.7% (DM basis) and similar to predicted TDN values from commercial feed analyses of GBP. The feeding and nutritive value of ensiled GBP indicates it can be priced to be used effectively as an energy supplement in TMR for cattle.

Effects of nesfatin-1 on food intake and LH secretion in prepubertal gilts and genomic association of the porcine NUCB2 gene with growth traits.

Nesfatin-1, a product of the nucleobindin 2 (NUCB2) gene, purportedly plays important roles in whole-body energy homeostasis. Experiments were conducted to determine how NUCB2 expression in fat depots may be controlled in the pig and to test the hypothesis that nesfatin-1 regulates appetite and LH secretion in the gilt. Prepubertal gilts were used to study expression of NUCB2 in fat and the effects of intracerebroventricular (i.c.v.) injection of nesfatin-1 on food intake and pituitary hormone secretion. Growing pigs (gilts and barrows at 22 wk of age, n = 1,145) or sexually mature gilts (n = 439) were used to test association of SNP in the NUCB2 gene with growth traits. The expression of NUCB2 was similar for subcutaneous fat compared with perirenal fat. An i.c.v. injection of the melanocortin-4 receptor agonist [Nle4, d-Phe7]-α-melanocyte-stimulating hormone did not alter expression of NUCB2 mRNA in the hypothalamus but reduced (P = 0.056) NUCB2 mRNA expression in subcutaneous fat. Short-term (7 d) submaintenance feeding reduced (P < 0.05) BW and did not alter expression of mRNA for NUCB2, visfatin, or leptin but increased (P < 0.05) expression of adiponectin mRNA in fat. Central injection of nesfatin-1 suppressed (P < 0.001) feed intake. Secretion of LH was greater (P < 0.01) after i.c.v. injection of nesfatin-1 than after saline. Single nucleotide polymorphisms in the porcine NUCB2 gene were not associated with adiposity of growing pigs or age at puberty in gilts but were associated (P < 0.05) with BW at puberty. These data indicate that NUCB2 is expressed in fat depots of the pig and that the level of expression is sensitive to stimulation of appetite-regulating pathways in the hypothalamus. It is confirmed herein that nesfatin-1 can regulate appetite in the pig and affect the gonadotropic axis of the prepubertal pig. Association of SNP in the porcine NUCB2 gene with BW at puberty suggests that regulation of appetite by nesfatin-1 in the pig affects growth, which may have important consequences for adult phenotypes.

Dietary lipid sources and levels for weanling pigs.

Collaborative studies comprising growth performance and metabolism experiments were conducted to reevaluate growth performance and nutrient and energy utilization responses of nursery pigs to dietary lipid sources and levels. Two lipid sources (soybean oil or tallow) were included at the rate of 1%, 3%, or 5% at the expense of cornstarch in a 2 × 3 factorial arrangement for 6 diets, and Lys was added to maintain a constant calorie:Lys ratio. A growth performance experiment (d 0 to 7, d 7 to 21, and d 21 to 35 postweaning) involving a total of 822 crossbred pigs was conducted at 9 research stations. Each station contributed 2 to 7 replicate pens with 4 to 6 pigs per pen, resulting in a total of 28 replicate pens per diet. The initial BW ranged from 5.9 to 7.3 kg, and the final BW ranged from 20.9 to 28.9 kg. Diets fed during d 7 to 21 and d 21 to 35 were evaluated with 120 barrows in 2 metabolism experiments with 10 individually fed barrows per diet to determine digestibility and retention of nutrients and energy. Lipid source and the interaction between lipid level and source did not affect growth performance. Lipid did not affect growth performance from d 0 to 7. There was a quadratic decrease (P < 0.05) in ADG with increasing level of added lipid only during d 7 to 21 postweaning. The ADFI was decreased (P < 0.01) both during d 7 to 21 and d 21 to 35 postweaning with increasing level of lipid supplementation. A linear improvement (P < 0.001) in G:F with increasing level of lipid supplementation occurred during both d 21 to 35 and d 0 to 35 postweaning. There was a linear increase in DE, ME, and nitrogen-corrected ME (MEn) of diets fed during d 7 to 21 postweaning with increasing lipid level regardless of lipid source. For diets fed during d 21 to 35 postweaning, there were interactions (P < 0.05) between lipid source and level for digestibility of DM, N, lipid, and energy and for DE, ME, and MEn of diets. The improved feed efficiency was, perhaps, partly attributable to the increase in ME content of the diets with added lipids. There were interactions (P < 0.05) between lipid source and level for efficiency of energy use for BW gain for diets fed during d 21 to 35. The efficiencies of use of DE, ME, and NE for BW gain were not affected in pigs fed diets containing increasing levels of soybean oil; however, there were linear increases in these response criteria for pigs fed diets containing increasing levels of tallow. These results indicate that the energy values of soybean oil from the 2012 NRC study used in formulating these diets were fairly accurate.

Effect of dietary acids on growth performance of nursery pigs: a cooperative study.

An experiment involving 854 crossbred pigs (20 replicate pens of 4 to 8 pigs per pen) was conducted at 8 experiment stations to determine the effects of acids in nursery pig diets and their inclusion amounts on growth performance using diets and weaning ages typical of those used in the United States commercial pork industry. Diets were formulated to have constant a ME and contain 1.45, 1.45, and 1.30% standardized ileal digestible Lys for phases 1, 2, and 3, respectively. The basal diets were supplemented with various types and concentrations of acid at the expense of corn (Zea mays). Treatment diets included 0% acid (control), 0.1 or 0.2% phosphoric acid, 1 or 2% organic acids, and 0.1% phosphoric acid plus 1% organic acids with or without an antibiotic. The organic acids consisted of 50% citric acid and 50% fumaric acid by weight. All but the final diet contained the antibiotic carbadox. All diets contained 3,000 mg of Zn/kg diet from zinc oxide during phases 1 and 2 and had limited acid buffering capacity, ranging from 142, 127, and 122 mEq/kg of feed for phases 1, 2, and 3, respectively. At each participating station, pigs were randomly allotted to dietary treatments on the basis of their initial BW. Sex and ancestry were equally distributed across the treatments. Results indicated that treatment effects on pig performance were observed in phases 1 and 2 but not in phase 3. In phase 1, ADG of pigs fed 0.2% phosphoric acid was greater than that of pigs fed the combination of acids with no antibiotic (P = 0.041). In phase 2, pigs fed treatments containing an antibiotic had a greater ADG than those fed the combination of acids without antibiotic (P < 0.05). Addition of acids to diets did not affect growth performance during any phase or the overall period. Over the 4-wk study, growth rate was slowest on the treatment without antibiotic, with specific differences that were often statistically significant (P < 0.05). In summary, under the conditions of this experiment, the acid treatments had no effect but the antibiotic improved growth performance.

Effects of corn distillers dried grains with solubles on quality traits of pork.

The high cost of feed grains has led swine producers to seek alternative feedstuffs, such as distillers dried grains with solubles (DDGS). However, little is known about the effects of high levels of DDGS in swine diets on pork quality. The objective of this study was to evaluate belly processing and bacon, sausage, and loin quality of pigs fed high levels of DDGS. Sixty pigs averaging 34 kg BW were fed fortifi ed corn-soybean meal diets containing 0%, 15%, 30%, or 45% DDGS. At 120 kg BW, the pigs were humanely harvested and bellies, loins, and shoulders were removed from the left side of each carcass. Flex tests of bellies indicated that they became softer (linear, P < 0.03) as DDGS levels increased. The PUFA in backfat and belly fat increased linearly (P < 0.005), as did iodine values with increasing 0DDGS in the diet. Bellies were pumped to target 12% brine retention, cooked, and sliced at a commercial facility. Slicing yield was not affected by DDGS level fed. Fresh bacon slices were scored 1 to 6 with 1 representing no visible cracks in the fat and 6 representing a spider weblike shattering of the fat. Shatter scores decreased (linear, P < 0.001) with increasing dietary DDGS. Bratwurststyle sausage was produced by combining ground Boston butts and picnics to target 30% fat, blended with commercial seasonings, and stuffed into natural casings. Loose sausage was placed on trays, overwrapped with polyvinyl chloride wrap, and stored under constant, cool white fl orescent lighting (1,300 lx) at 4°C. Objective color values (L*, a*, and b*) were taken on loosepackaged sausage mix at 6 locations at the same time daily for 7 d. Sausage was also sampled for thiobarbituric acid reactive substances (TBARS) at the same time daily on d 0, 3, 5, and 7. Color scores of sausage were not consistently affected by DDGS level in the diet and the changes were slight. The TBARS in sausage from pigs fed the 30% and 45% DDGS diets increased to a greater extent from d 0 to 7 than in those fed the control or 15% DDGS diets. An 8-member, trained panel evaluated the sensory attributes of bacon slices, sausage, and loin chops. The DDGS resulted in a softer texture (P < 0.004) and increased juiciness (P < 0.04) in sausages, but no differences in sensory scores were found in bacon slices or loin chops. The results indicate that the softer bellies, greater concentrations of PUFA in carcass fat, and greater iodine values associated with feeding increased DDGS did not negatively affect slicing yield of cured bellies, quality of fresh bacon slices, or eating quality of bacon, sausage, or loin chops.

Effect of dietary conjugated linoleic acid on marbling and intramuscular adipocytes in pork.

Dietary CLA has been reported to decrease backfat and increase marbling in pigs. Our objective was to determine whether the increase in marbling involved changes in intramuscular adipocyte number or size or both. Twenty barrows (53 kg) were penned in pairs and pens were randomly assigned to receive diets containing either 1% soybean oil (SBO) or CLA (60% CLA isomers) for 6 wk. Body weight and feed intake were determined weekly. At slaughter, loin samples were obtained and flash frozen for RNA extraction and real-time reverse-transcription PCR analysis of gene expression. After a 24-h chill, loin eye area and backfat depth were measured and subjective marbling and color scores were assigned. Loin, backfat, and belly fat samples were obtained for fatty acid analysis by gas chromatography. Loin samples were also frozen in ice-cold isopentane for histological analysis of intramuscular adipocytes. Dietary CLA did not affect BW or feed intake at any point (P > 0.10), nor did treatment groups differ in HCW (P = 0.417) or loin color (P = 0.500). The CLA-fed pigs did have less (P = 0.018) backfat and smaller (P = 0.047) loin eye area than SBO-fed pigs and had a trend for an increase (P = 0.069) in marbling score. Relative gene expression for markers of preadipocytes (preadipocyte factor 1; Pref-1), differentiating adipocytes (PPARγ), and mature adipocytes [fatty acid binding protein 4 (FABP4) and perilipin (PLIN)] were determined and normalized to the expression of acidic ribosomal phosphoprotein. No significant differences were detected, but the expression of PPARγ (P = 0.265), PLIN (P = 0.265), and FABP4 (P = 0.148) was numerically greater in CLA-fed pigs than in SBO-fed pigs. Loin samples were stained with Oil Red O to identify intramuscular adipocytes. The average cell area was increased (P = 0.030) in CLA-fed pigs. The cis-9,trans-11 and trans-10,cis-12 CLA isomers were incorporated (P = 0.006) into backfat and belly fat, but only trans-10,cis-12 CLA was increased in the loin (P = 0.004) of CLA-fed pigs. The proportion of SFA was increased (P = 0.006) by CLA in all tissues. These results indicate that the increase in marbling in pigs fed CLA may be related to increased intramuscular adipocyte size, and the combination of increased marbling and degree of saturation could improve the eating quality of CLA-fed pork.

Corn distillers dried grains with solubles in diets for growing-finishing pigs: a cooperative study.

An experiment involving 560 crossbred pigs (28 replications of 4 to 6 pigs per pen) was conducted at 9 research stations to assess the effects of dietary concentrations of corn distillers dried grains with solubles (DDGS) on pig performance and belly firmness. Fortified corn-soybean meal diets containing 0, 15, 30, or 45% DDGS were fed in 3 phases from 33 to 121 kg of BW. A common source of DDGS containing 90.1% DM, 26.3% CP, 0.96% Lys, 0.18% Trp, 9.4% crude fat, 34.6% NDF, 0.03% Ca, and 0.86% P was used at each station. Diets were formulated to contain 0.83, 0.70, and 0.58% standardized ileal digestible (SID) Lys during the 3 phases with diets changed at 60 and 91 kg of BW, respectively. The DDGS replaced corn and soybean meal, and up to 0.172% Lys and 0.041% Trp were added to maintain constant SID concentrations of Lys and Trp in each phase. At each station, 2 pigs from each pen in 2 replications were killed and a midline backfat core was obtained for fatty acid analysis and iodine value. In most instances, there were differences among stations (P < 0.01), but the station × treatment interactions were few. Body weight gain was linearly reduced in pigs fed the greater amounts of DDGS (0 to 45%) during phase I (950, 964, 921, and 920 g/d; P < 0.01) and over the entire experimental period (944, 953, 924, and 915 g/d; P = 0.03), but ADFI (2.73, 2.76, 2.68, and 2.70 kg) and G:F (347, 347, 345, and 341 g/kg) were not affected (P = 0.15 and P = 0.33, respectively) during the entire test. Backfat depth was reduced (linear, P < 0.02) by increasing amounts of DDGS (22.5, 22.7, 21.4, and 21.6 mm), but LM area (47.4, 47.4, 46.1, and 45.4 cm(2)) was not affected (P = 0.16) by treatments. Estimated carcass fat-free lean was 51.9, 52.2, 52.4, and 52.1% for 0 to 45% DDGS, respectively (linear, P = 0.06). Flex measures obtained at 6 stations indicated less firm bellies as dietary DDGS increased (lateral flex: 11.9, 8.6, 8.4, and 6.6 cm; linear, P < 0.001; vertical flex: 26.1, 27.4, 28.2, and 28.7 cm; linear, P < 0.003). Saturated and monounsaturated fatty acid concentrations in subcutaneous fat decreased linearly (P < 0.001) and PUFA concentrations increased linearly (P < 0.001) with increasing DDGS in the diet. Iodine values in inner (61.1, 68.2, 74.7, and 82.2) and outer (67.9, 73.6, 79.6, and 85.8) backfat increased linearly (P < 0.001) as DDGS in the diet increased. In this study, feeding diets with 30 or 45% DDGS did not have major effects on growth performance, but resulted in softer bellies. Regression analysis indicated that iodine values increased 4.3 units for every 10 percentage unit inclusion of DDGS in the diet.

Effect of body composition on diet selection in finishing pigs.

The objective of this work was to determine if pigs of similar BW, but differing in 10th-rib backfat thickness, would differ in their selection of dietary protein. The first experiment was conducted with gilts and was designed in a 2 x 2 factorial arrangement with the main effects of body fat (lean vs. fat) and feeding program (single vs. choice). Crossbred gilts (n = 32) with an initial BW of 79 kg were sorted into high (2.24 cm, fat) and low backfat (1.51 cm, lean; P < 0.001) groups based on real-time ultrasound scans at the 10th rib. Diets were 1) a low-protein corn-based diet supplemented with crystalline AA (8.5% CP, 0.58% Lys) and 2) a high-protein corn- and soybean meal-based diet (22.7% CP, 1.275% Lys). During wk 1, all pigs were fed a 50:50 mix of the low-protein and high-protein diets. From d 7 to 28, one-half the pigs in the lean and fat groups were given a choice of low- and high-protein diets in separate feeders, whereas the others remained on the 50:50 mix. Initial differences in 10th-rib backfat thickness were maintained through d 28 (fat, 3.02 cm; lean, 2.42 cm; P < 0.001). Circulating leptin concentrations were greater in the fat pigs than in the lean pigs (3.84 vs. 3.35 ng/mL; P < 0.05). Average daily gain (1.06 kg/d) and ADFI (2.64 kg/d) were not different between treatment groups. However, the pattern of selection was different in the choice groups such that lean pigs consumed more (64.4%) of the high-protein diet than did fat pigs (35.6%, P < 0.01), resulting in a difference in the percentage of protein consumed (lean = 16.9% CP; fat = 12.8% CP; P < 0.01). A second experiment of similar design, but with barrows (n = 32; initial BW 69 kg), was conducted. Barrows classified as fat had 2.33 cm of 10th-rib backfat as compared with 1.75 cm in the lean group (P < 0.01). The percentage of protein in the diet selected by the fat barrows was not different from that selected by the lean barrows (15.9 vs. 17.4%). The lack of difference in selection pattern in barrows may be accounted for by the relatively smaller difference in body composition between the fat and lean classifications in the barrows in the choice feeding program as compared with body composition of the gilts. These results demonstrate that gilts of similar BW, but differing in composition, likely have different nutrient requirements and diet selection patterns. Although allowing pigs to self-select did not alter growth rate, the results indicated that diet selection can be used to allow pigs to meet their individual nutrient requirements more closely.

Board-invited review: the biology and regulation of preadipocytes and adipocytes in meat animals.

The quality and value of the carcass in domestic meat animals are reflected in its protein and fat content. Preadipocytes and adipocytes are important in establishing the overall fatness of a carcass, as well as being the main contributors to the marbling component needed for consumer preference of meat products. Although some fat accumulation is essential, any excess fat that is deposited into adipose depots other than the marbling fraction is energetically unfavorable and reduces efficiency of production. Hence, this review is focused on current knowledge about the biology and regulation of the important cells of adipose tissue: preadipocytes and adipocytes.

Genetic components of heat stress in finishing pigs: Parameter estimation.

The objective of this study was to describe genetic variability of pig carcass weight as a function of heat stress. Data included carcass weights of 23,556 crossbred pigs [Duroc x (Landrace x Large White)] raised on 2 farms in North Carolina and harvested from May 2005 through December 2006. Weather data were obtained from a weather station located about 20 km from the furthest farm. Weekly heat load was calculated as degrees of average temperature-humidity index (THI) in excess of 18 degrees C. The total heat load (H) was the sum of heat loads for 10 wk before harvest. Variance components were estimated with 3 models: univariate (UNI)-not accounting for heat stress, 2-trait (MT2), and random regression (RR). In all of the models, effects included contemporary group, sex, age at harvest, sire, and litter. In MT2, observations in months in which heat stress was observed ("hot") and not observed ("cold") were treated as separate traits. Heat stress was observed in the months of August to November 2005, as well as July to October 2006. No heat stress was observed in the months of May to July 2005, January to June 2006, and November to December 2006. The RR model added a random regression on heat load for the sire effect. Heat load was adjusted to a scale ranging from 0 (no heat stress) to 5 (greatest heat stress). The heritability estimate +/- SE of carcass weight in UNI was 0.17 +/- 0.01. In MT2, the estimates were 0.14 +/- 0.01 for "cold" and 0.28 +/- 0.01 for "hot"; the genetic correlation between carcass weight in "hot" and "cold" months was 0.42 +/- 0.13. The heritability estimates obtained with RR were 0.20 +/- 0.11, 0.19 +/- 0.15, and 0.51 +/- 0.17 for H = 0, 2.5, and 5, respectively. The genetic correlation between the performance in "cold" months (H = 0), and performance under maximum heat load (H = 5) was 0.02, between H = 0 and intermediate heat load (H = 2.5) was 0.52, and between H = 2.5 and H = 5 was 0.86. Rank correlations between EPD derived from the different models ranged from 0.82 to 0.94 between carcass weights under similar H, 0.18 to 0.54 between carcass weights under high and low H, and 0.66 to 0.91 between carcass weights of intermediate and high/low H. Heritability for growth was greater under heat stress. Selection for crossbred performance would be optimal when data for periods both in the absence and presence of heat stress were considered.

Genetic components of heat stress in finishing pigs: development of a heat load function.

The objective of this study was to quantify the effect of heat stress during the life of a pig on its final weight, as a first step toward a genetic evaluation for heat tolerance. Data included carcass weights of 23,556 crossbred pigs [Duroc x (Landrace x Large White)] raised on 2 farms in North Carolina and slaughtered from May 2005 through December 2006. Weather data were available from a nearby weather station. Lifetime of a pig was assumed to be partitioned into 2 periods. During an initial period, the effect of heat stress was assumed to be negligible or compensated for later. During the second period ending in slaughtering, the ADG was assumed to be affected linearly by heat load. Weekly heat load was calculated as degrees of average temperature-humidity index in excess of a threshold (18 degrees C). The total heat load (H) was the sum of weekly heat loads during the second period. During the months of January to May H was 0; H reached a peak in September. The final BW during the peak of heat stress decreased about 6 kg compared with BW during months of non-heat stress. Weekly and monthly averages of carcass weight generally moved similarly to H. However, there were large fluctuations unrelated to H; the fluctuations were different on the 2 farms. The model included the effects of farm-year of slaughter, sex, age at slaughter, and H, where age at slaughter and H were linear regressions. In analyses, the threshold was varied from 16 to 20 degrees C, and the second period was varied from 8 to 16 wk. The greatest R(2) (10.4%) was at the threshold of temperature-humidity index = 18 degrees C for a period of 10 wk. Varying the threshold and the length of time reduced R(2) less than 1%. Least squares means of year-month and year-week of carcass weight were calculated using a model with the fixed effects farm-year-month or farm-year-week of slaughter, sex, and age at slaughter (linear covariate), and the random effect of birth litter. Changes in BW of finisher pigs due to heat stress can be quantified by H during the last 10 wk of the life of the pig.

The influence of thiazolidinediones on adipogenesis in vitro and in vivo: potential modifiers of intramuscular adipose tissue deposition in meat animals.

Thiazolidinediones (TZD) are insulin sensitizing agents currently used for the treatment of type 2 diabetes and are widely used as adipogenic agents because they are ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), a key adipogenic transcription factor. In vivo and in vitro studies of TZD as potential modifiers of intramuscular or marbling adipogenesis are reviewed. Thiazolidinedione-induced adipogenesis has been reported in numerous cell culture systems, including rodent, human, bovine, and porcine adipose tissue stromal-vascular (S-V) cell cultures. Studies of porcine S-V cell cultures derived from semitendinosus muscle show that TZD can potentially modify intramuscular or marbling adipogenesis. Preadipocyte recruitment was TZD-dependent in muscle S-V cultures but TZD-independent in adipose S-V cultures. There appear to be differences between adipocytes in muscle and subcutaneous adipose tissue, reminiscent of differences observed in adipocytes from different adipose tissue depots. Troglitazone, a TZD, induces marbling adipogenesis without inhibiting myogenesis when cells are grown on laminin precoated culture dishes. Additionally, troglitazone treatment does not increase lipid content in porcine adipose tissue or muscle S-V cell cultures. Thiazolidinedione treatment increases lipid content of muscle in rodents and humans; however, rosiglitazone treatment for 49 d in pigs did not influence muscle lipid content and meat quality, but several significant changes in muscle fatty acid composition were observed. Although timing of treatment with TZD needs to be optimized, evidence suggests these compounds may enhance marbling deposition in swine.

The effect of anabolic implants on intramuscular lipid deposition in finished beef cattle.

Two experiments were conducted to determine the effects of anabolic implants on performance, changes in ultrasound measurements, carcass quality, cellularity of i.m. and s.c. adipose depots, and mRNA expression of acetyl CoA carboxylase (ACC), stearoyl CoA desaturase (SCD), and lipoprotein lipase (LPL) in i.m. adipose tissue of finished beef cattle. Angus heifers (experiment 1: n = 10; 411 kg of BW) and steers (experiment 2: n = 18; 279 kg of BW) were randomly allotted as control (C) or implanted with Synovex-Plus (SP) at d 0 and midway through the finishing period. The cattle were fed a high-concentrate diet and were weighed at approximately 28-d intervals. Heifers and steers were finished for 108 and 133 d, respectively. At slaughter, a section of the LM (sixth to ninth rib) was removed, and i.m. adipose tissue was dissected for mRNA analysis. Subcutaneous and i.m. adipose tissues also were collected for determination of cellularity. At 48 h postmortem, carcass data were collected, and a steak (12th rib) was removed for analysis of lipid and fatty acid composition. Body weight did not differ (P > 0.10) between treatments until after reimplanting of the heifers (d 55) or steers (d 73). Average daily gain was 36 and 16% faster (P < or = 0.01) for implanted heifers and steers, respectively, compared with their control counterparts. Implanting resulted in larger (P < or = 0.10) HCW and LM area for heifers and steers. However, implanting did not affect (P > 0.10) dressing percent, fat thickness, percentage of KPH, yield grade, or marbling score. Intramuscular lipid content and concentrations of major fatty acids did not differ (P > 0.10) between treatments. Percentage of SC adipocytes was greater at larger diameters ( > 150 microm), whereas the majority of i.m. adipocytes were at small to middle diameters (50 to 150 microm). The number of i.m. adipocytes per gram of tissue was greater (P < 0.05) for SP than C and also were greater (P < 0.05) than the number of s.c. adipocytes in SP heifers. In experiment 2, adipocytes per gram of tissue tended to be greater (P = 0.07) for SP than C and were greater (P < 0.01) for i.m. than s.c. In experiment 1, average cell diameter and volume did not differ (P > 0.10) between treatments and tissues, but in experiment 2 both cellularity traits were greater (P < 0.01) for s.c. than for i.m.. Implanting did not alter mRNA expression of ACC, SCD, or LPL in i.m. adipose tissue. This study shows that anabolic implants do not appear to have direct effects on i.m. lipid deposition.

Evaluation of pet food by-product as an alternative feedstuff in weanling pig diets.

Three experiments were conducted to evaluate pet food by-product (PFB) as a component of nursery starter diets and its effects on pig performance. The PFB used in these studies was a pelleted dog food that contained (as-fed basis) 21% CP, 1.25% total lysine, and 8.3% ether extract. In Exp. 1, 288 early-weaned pigs (5.2 kg at 14 d) were used to determine the effects of replacing animal protein and energy sources with PFB at 0, 10, 30, and 50% (as-fed basis) inclusion levels in phase I (d 0 to 7 after weaning) and phase II (d 7 to 21 after weaning) diets. Phase I diets contained 27.5% whey, 18.75% soybean meal, 1.50% lysine, 0.90% Ca, and 0.80% P, with PFB substituted for corn, fat, plasma protein, fish meal, limestone, and dicalcium phosphate. Phase II diets had a constant 10% whey, 1.35% lysine, and PFB was substituted for blood cells, a portion of the soybean meal, and other ingredients as in phase I diets. In phase I, growth performance by pigs fed PFB-containing diets was similar to that of the control diet. In phase II, ADG (linear; P < 0.05 and quadratic, P < 0.005), ADFI (linear and quadratic, P < 0.01), and G:F (quadratic, P < 0.01) were increased with increasing PFB inclusion. In Exp. 2, 80 weaned pigs (6.7 kg at 21 d) were fed a common phase I diet for 1 wk and used to further evaluate the effect of PFB in phase II diets (same as Exp 1; initial BW = 8.1 kg) on growth performance and apparent total tract nutrient digestibility. There were no differences in ADG, ADFI, or G:F across treatments. Dry matter and energy digestibility did not differ among diets; however, digestibilities of CP (P < 0.05) and the essential AA, arginine (P < 0.02), histidine (P < 0.01), lysine (P < 0.001), threonine (P < 0.01), and valine (P < 0.01), were greater as PFB was increased in the diet. In Exp. 3, the performance by pigs (n = 1 70; 5.5 kg; 21 d of age) fed diets with 0 or 30% PFB in both phases I and II was examined. Growth performance was similar in both diets. These studies demonstrate that pet food by-product can effectively be used as a partial replacement for animal protein sources and grain energy sources in the diets of young nursery pigs.

Effects of ractopamine on performance and composition of pigs phenotypically sorted into fat and lean groups.

Crossbred barrows (n = 144; 80 kg) from four farrowing groups were phenotypically selected into fat (FAT) and lean (LEAN) pens using ultrasound. The difference in 10th-rib fat depth between the LEAN and FAT groups was > or =0.5 cm. Within a farrowing group, pigs were assigned to pens (five pigs per pen and eight pens per phenotype) to equalize pen weight and fat depth. Pigs were fed a corn-soybean meal diet containing 19% CP, 1.0% added animal/vegetable fat, and 1.1% lysine (as-fed basis). Half the pens received 10 ppm (as-fed basis) of ractopamine (RAC) during the 28-d finishing phase. At 7-d intervals, live weight and feed disappearance were recorded to calculate ADG, ADFI, and G:F, and 10th-rib fat depth and LM area were ultrasonically measured to calculate fat-free lean and fat and muscle accretion rates. During the first 7 d on feed, LEAN pigs fed RAC gained less (P < 0.05) than FAT pigs fed RAC or LEAN and FAT pigs fed the control diet (RAC x phenotype; P = 0.02); however, RAC did not (P > 0.25) affect ADG after the second, third, and fourth weeks, or over the entire 28-d feeding period. Although wk-2 and -3 ADG were higher (P < or = 0.03) in LEAN than in FAT pigs, phenotype did not (P = 0.08) affect overall ADG. Dietary RAC decreased (P < or = 0.05) ADFI over the 28-d feeding trial, as well as in wk 2, 3, and 4, but intake was not (P > 0.20) affected by phenotype. Neither RAC nor phenotype affected (P > 0.10) G:F after 7 d on trial; however, RAC improved (P < or = 0.04) wk-3, wk-4, and overall G:F. Lean pigs were more efficient (P < or = 0.05) in wk 2 and 3 and over the duration of the trial than FAT pigs. Ultrasound LM accretion (ULA) was not (P > or = 0.10) affected by RAC; however, LEAN pigs had greater (P < or = 0.02) ULA in wk 2 and 4 than FAT pigs. Although fat depth was lower (P < 0.01) in RAC-fed pigs than pigs fed the control diet, ultrasound fat accretion rate indicated that RAC-pigs deposited less (P = 0.04) fat only during wk 4. In addition, calculated fat-free lean (using ultrasound body fat, ULA, and BW) was increased (P < 0.05) in RAC pigs after 3 and 4 wk of supplementation. In conclusion, RAC enhanced the performance of finishing swine through decreased ADFI and increased G:F, whereas carcass lean was enhanced through decreases in carcass fat and increases in carcass muscling.

Use of pet food-grade poultry by-product meal as an alternate protein source in weanling pig diets.

Three experiments were conducted to evaluate pet food-grade poultry by-product meal (PBM) as a replacement protein source for fish meal (FM), blood meal (BM), and spray-dried plasma protein (SDPP) in weanling pig diets. In the first study, 200 crossbred pigs (initial BW = 6.5 kg) were weaned (21 d) and randomly allotted to one of four dietary treatments, which included a control and three test diets where PBM was substituted for FM, blood products, or both. Experimental diets were fed during Phase I (d 0 to 5 postweaning) and Phase II (d 5 to 19), and a common Phase III diet was fed from d 19 to 26. Overall (d 0 to 26), there was no difference in performance of pigs fed PBM in place of the other ingredients. However, during Phase I, BW (P < 0.05), ADG (P < 0.02), and intake (P < 0.001) in pigs fed diets containing SDPP were greater than those fed diets with PBM. In Exp. 2, the performance of pigs (n = 100, initial BW = 6.5 kg) fed diets containing 20% PBM (as-fed basis, replacing SDPP, BM, FM, and a portion of the soybean meal) in all phases of the nursery diet was compared with a group fed conventional diets without PBM. There were no differences in overall performance (d 0 to 26); however, ADG (P < 0.10) and feed intake were higher (P < 0.01) for pigs fed the conventional diet than for pigs fed the 20% PBM diet during Phase I (d 0 to 5). Experiment 3 was a slope-ratio assay to determine the ability of PBM to replace SDPP. A total of 320 pigs (initial BW = 7.32 kg) was weaned (21 d) and allotted to five treatment groups in three trials in a blocked design with product (SDPP or PBM) as the first factor, and lysine level (1.08, 1.28, 1.49%; as-fed basis) as the second factor. Growth rate increased with increasing lysine (P < 0.05), regardless of the source. These results indicate that PBM can be used in nursery diets in place of blood meal and fish meal without affecting performance. Furthermore, although feeding PBM in Phase I diets was not equivalent to SDPP during the first week, there was no overall difference in performance at the end of the nursery phase.