Effects of conjugated linoleic acid on the belly firmness and fatty acid composition of genetically lean pigs

A study of the effects of conjugated linoleic acid (CLA) on the belly firmness and fatty acid composition of genetically lean pigs was conducted. From 75 to 120 kg live weight, 30 gilts were allowed ad libitum access to a corn-soybean meal diet supplemented with either 1% CLA oil (CLA-60) or 1% sunflower oil (SFO) or were fed the sunflower oil-supplemented diet restricted to the amount consumed by pigs fed the CLA-60 diet (RSFO). Conjugated linoleic acid oil consists of 60% positional and geometric isomers of CLA. Pigs fed SFO exhibited higher average daily gains (0.98 vs 0.80 kg/d, P < 0.01) than RSFO-fed pigs, but there were no effects of dietary treatment on feed intake or feed efficiency. Dietary treatment did not affect (P > 0.05) backfat thickness or longissimus muscle area. Bellies of gilts fed CLA-60 were subjectively evaluated to be firmer (2.91 vs 2.43 or 2.07 +/- 0.13, P < 0.01) than those of SFO- or RSFO-fed gilts, respectively. The longissimus muscle of gilts fed CLA-60 contained more saturated fatty acids (39.77 vs. 36.04 or 36.73 +/- 0.74%, P < 0.001) and less unsaturated fatty acids (60.23 vs 63.96 or 63.27 +/- 0.74%, P < 0.001) than that of gilts fed SFO or RSFO, respectively. The belly fat of gilts fed CLA-60 contained more saturated fatty acids (44.45 vs. 37.50 or 36.60 +/- 0.46%, P < 0.001) and less unsaturated fatty acids (54.78 vs. 61.75 or 62.47 +/- 0.46%, P < 0.001), resulting in lower iodine values (57.69 vs 66.37 or 65.62 +/- 0.91, P < 0.001) than that of gilts fed SFO or RSFO, respectively. Gilts fed CLA-60 accumulated more CLA in the longissimus muscle (0.55 vs 0.09 or 0.09 +/- 0.03%, P < 0.01) and belly fat (1.56 vs. 0.13 or 0.13 +/- 0.15%, P < 0.001) than did gilts fed SFO or RSFO, respectively. Dietary treatment did not affect (P > 0.05) 24-h pH, drip loss or subjective quality evaluations of the longissimus muscle. The effect of supplemental CLA to improve belly firmness is of practical significance and may provide a nutritional solution to carcass fat and belly firmness problems, thereby enhancing the overall value of extremely lean carcasses.

Evaluation of conjugated linoleic acid and dietary antibiotics as growth promotants in weanling pigs

An experiment was conducted to determine the efficacy of dietary conjugated linoleic acid (CLA) as a growth promotant in weanling swine. Weanling pigs (n = 192; 7.6 kg and 29 d of age) were randomly assigned to four treatments that were arranged as a 2 x 2 factorial. Concentrations of dietary CLA (0 or 0.6%) and antibiotics (+/-) constituted the main effect variables. Dietary CLA treatments consisted of a 1% addition of an oil containing 60% CLA isomers or 1% soybean oil, and dietary antibiotic treatments were antibiotics or no antibiotics. The experimental diets were fed for 9 wk in four phases (1, wk 1; 2, wk 2 and 3; 3, wk 4 through 6; and 4, wk 7 through 9), after which all pigs were fed identical medicated diets for the duration of the finishing phase. Live weights were recorded at wk 17 postweaning and at marketing to determine any residual effects of dietary treatments on finisher ADG and days to market. Medicated diets fed during phases 1 and 2 contained 55 mg carbadox/kg; during phase 3 contained 299 mg tilmicosin/kg; and during phase 4 contained 110 mg tylosin and 110 mg sulfamethazine/kg. Pigs fed medicated diets had higher overall ADG than pigs fed unmedicated diets for wk 0 through 9 (P < 0.03). Gain:feed (G:F) was greater for pigs fed medicated diets than for pigs fed unmedicated diets during phase 1 (P < 0.03) and for the duration of the nursery phase (P < 0.03). There were no effects of CLA on ADG, ADFI, or G:F. There were no residual effects of nursery CLA or antibiotics on finisher ADG and days to market. Blood samples collected from a subset of pigs (n = 72) at the completion of phases 2, 3, and 4 were assayed for serum IGF-I and antibody concentrations to porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae. There was a tendency for pigs fed medicated diets to have greater IGF-I concentrations than pigs fed unmedicated diets at the completion of phase 4 (P < 0.06). Pigs fed CLA had greater antibody titers (P < 0.02) to Mycoplasma hyopneumoniae at d 63 than pigs fed diets without CLA. These results indicate that feeding 0.6% dietary CLA did not enhance growth performance in weanling swine and that the use of dietary antibiotics can increase production efficiency in nursery pigs. Furthermore, there were no interactions between CLA and dietary antibiotics on the variables addressed in this study.

Evaluation of alternative measures of pork carcass composition

Carcass and live measurements of 203 pigs representing seven genetic populations and four target live weights (100, 114, 128, and 152 kg) were used to evaluate alternative measures of carcass composition. Measures of carcass lean (fat tissue-free lean, FFLM; lipid-free soft tissue, LFSTIS; and dissected lean in the four lean cuts, DL), fat (total carcass fat tissue, TOFAT), and lipid mass (soft tissue lipid, STLIP) were evaluated. Overall, LFSTIS was 22.8% greater than FFLM (47.8 vs 38.9 kg) and TOFAT was 30% greater than STLIP (38.5 vs 29.6 kg). The allometric growth coefficients relative to carcass weight were different for the measures: b = 0.776, 0.828, 0.794, 1.37, and 1.49 for FFLM, LFSTIS, DL, TOFAT, and STLIP, respectively. At 90 kg carcass weight, the predicted growth of FFLM, LFSTIS, TOFAT, and STLIP was 0.314, 0.420, 0.553, and 0.446 kg/kg increase in carcass weight. The difference between FFLM and LFSTIS, representing nonlipid components of the carcass fat tissue, was greater for barrows than for gilts (9.2 vs 8.6 kg). Lipid-free soft tissue mass was predicted more accurately from carcass or live animal measurements than FFLM with smaller relative RSD (4.6 vs 6.5% of their mean values). The alternative measures of carcass composition were evaluated as predictors of empty body protein (MTPRO) and lipid (MTLIP) mass. Empty body protein was predicted with similar accuracy (R2 = 0.74 to 0.81) from either DL, FFLM, LFSTIS, or ribbed carcass measurements. Empty body lipid was predicted more accurately from TOFAT (R2 = 0.92) or STLIP (R2 = 0.93) than ribbed carcass measurements (R2 = 0.88). Although the alternative measures of lean mass (LFSTIS vs FFLM) and lipid mass (TOFAT vs STLIP) were highly related to each other (r = 0.93 to 0.98), they had different relative growth rates (allometric coefficients) and thus cannot be predicted as linear functions of the similar alternative variable without significant weight group biases. From the 100- to 152-kg target weight groups, gilts gained 12.9% greater FFLM and 12.1% greater MTPRO but only 4.4% greater LFSTIS than barrows. Fat-free lean mass is more precise as a measure of muscle growth and as a predictor of lysine requirements. Lipid-free soft tissue can be obtained more quickly and predicted more accurately from carcass or live animal measurements.

Expression of porcine transcription factors and genes related to fatty acid metabolism in different tissues and genetic populations

Several transcription factors are involved in regulating lipid metabolism in various tissues of animals. Adipocyte determination and differentiation-dependent factor 1 (ADD1), peroxisome proliferator activated receptor alpha (PPAR alpha), and peroxisome proliferator activated receptor gamma (PPAR gamma) regulate both lipogenesis and fatty acid oxidation. We determined the tissue distribution and genetic difference in mRNA concentrations of these transcription factors in two genetic populations of pigs (Newsham XL-sired Newsham Landrace x Large White Duroc and Duroc-sired US Yorkshire x Duroc-Landrace). We also determined the tissue distribution and genetic difference in the mRNA concentration of fatty acid synthase (FAS) and acyl-CoA oxidase (ACO). Our data showed that ADD1 was highly expressed in adipose tissue and liver and that mRNA concentrations of ADD1 were similar between the two genotypes. The PPAR alpha mRNA concentration was high in adipose tissue and was similar between the two genotypes. In both populations, PPAR gamma mRNA was detected only in adipose tissue. There was no difference between the two genotypes in PPAR gamma mRNA concentration. The ACO mRNA was expressed in adipose tissue, skeletal muscle, and liver with no difference between genotypes. The FAS mRNA concentration in adipose tissue was seven times higher than that in the liver. There was no detectable FAS mRNA in skeletal muscle. These data support the concept that pig adipose tissue has considerable capability for fatty acid oxidation and synthesis. The uniqueness of expression patterns for FAS and ADD1 mRNA further indicates that adipose tissue is significantly involved in fatty acid and triacylglycerol synthesis in pigs.

Physiological response to acute endotoxemia in swine: effect of genotype on energy metabolites and leptin

Certain high lean gain swine genotypes have greater sensitivity to pathogen and nonpathogen stressors evident by reduced productivity and increased mortality during disease stress or in suboptimal production environments. Saline (control) and an immunologic challenge (LPS; 25 microg lipopolysaccharide/kg BW) were administered to three genetic populations (each pig used as its own control): high lean (H), moderate lean terminal cross (MT), and moderate lean maternal cross (MM). LPS induced anorexia, and significantly increased body temperature and circulating TNF-alpha, cortisol, and NEFA in all genotypes (P < 0.0004). LPS reduced circulating glucose, insulin, and IGF-1 in all genotypes (P < 0.05). The LPS-induced hypoglycemia was significantly greater in MM versus MT and H pigs (P < 0.03). The hypoinsulinemia was significantly greater in MM versus H pigs (P < 0.02). MM pigs recovered from hypoinsulinemia slower than MT pigs (P < 0.03). Control insulin was higher in H versus MT pigs (P < 0.08), but relative to basal, the insulin response to LPS was similar. Plasma haptoglobin response to LPS was lower for MM versus MT and H pigs (P < 0.02), and tended to be lower in MT versus H pigs (P < 0.09). LPS treatment caused similar decreases in plasma IGF-1 concentrations among genotypes. Ten hours after LPS treatment, leptin mRNA abundance in adipose tissue was significantly reduced (relative to control) in MM and H pigs (P < 0.02) but not in MT pigs (P > 0.05). Physiological differences in leptin, a potent regulator of food intake and energy metabolism, may be important factors in the genetic variation in sensitivity to environmental stress.

Analysis of body composition changes of swine during growth and development

This study was conducted to model the growth of carcass, viscera, and empty body components and component composition of pigs. Quantitative tissue and chemical composition of 319 swine, representative of barrows and gilts from five commercial genetic populations, was determined at eight stages of growth between 25 and 152 kg. After whole body grinding and carcass dissection, proximate analyses were performed to calculate concentrations of protein, lipid, moisture, and ash of carcass, viscera, empty body, carcass lean, and carcass fat. Linear and nonlinear equations were developed to investigate the growth patterns of each component. Nonlinear growth functions accounted for the greatest amount of variation in empty body protein, lipid, moisture, and ash mass. Differences (P < .05) existed between barrows and gilts for nearly all components investigated. Carcass lean and fat tissues significantly increased in lipid percentage and decreased in moisture percentage as live weight increased. There were significant changes in the ratio and composition of the tissues of barrows and gilts during growth. Nonlinear models fitted the data better than allometric equations for nearly all of the components investigated.

Biases associated with genotype and sex in prediction of fat-free lean mass and carcass value in hogs

Carcass and live measurements of 165 market hogs that represented seven genotypes were used to investigate genotype and sex biases associated with the prediction of fat-free lean mass (FFLM) and carcass value. Carcass value was determined as the sum of the product of weight of individual cuts and their average unit prices adjusted for slaughter and processing costs. Independent variables used in the prediction equations included carcass measurements, such as optical probe, midline ruler, ribbed carcass measurements, and electromagnetic scanning (EMSCAN), and live animal ultrasonic scanning. The effect of including subpopulation mean values of independent variables in the prediction equations for FFLM and carcass value was also investigated. Genotype and sex biases were found in equations in which midline backfat, ribbed carcass, EMSCAN, and live ultrasonic scanning were used as single technology sets of measurements. The prediction equations generally undervalued genotypes with above-average carcass value. Biases were reduced when measurements of combined technologies and mean adjusted variables were used. The FFLM and carcass value of gilts were underestimated, and they were overestimated of barrows. Equations that combined OP and EMSCAN technologies were the most accurate and least biased for both FFLM and carcass value. Equations that included carcass weight and midline last-rib backfat thickness measurements were the least accurate and most biased. Genotype and sex biases must be considered when predicting FFLM and carcass value.

Characterization of growth parameters needed as inputs for pig growth models

Swine growth models have the potential to evaluate alternative management decisions and optimize production systems. However, the lack of economical, yet accurate methods to obtain the growth parameters required to characterize pig genotypes, and which are required by growth models, limits their widespread implementation. The four primary parameters required are 1) daily whole-body protein accretion potential, 2) partitioning of energy, intake over maintenance between protein and lipid accretion, 3) maintenance requirements for energy, and 4) daily feed intake. Estimation of daily protein accretion rates requires that serial estimates of composition and growth be fitted to flexible nonlinear functions. Serial dissection and chemical analysis are too expensive to be routinely conducted on an adequate number of pigs for precise daily protein accretion rates at different live weights. Three alternate methods include 1) serial slaughter and double sampling; 2) use of serial live measurements to estimate composition, i.e., serial ultrasonic measurements; and 3) use of generalized functions that estimate daily protein accretion as a function of mean daily fat-free lean gain over a specified weight interval. The energy partitioning between lipid and protein accretion can be expressed as two interchangeable measurements, either as the slope of protein accretion or the change in the lipid: protein gain ratio as a function of energy intake at each live weight. Both methods require serial estimates of composition and scale feeding of pigs to specified energy intake levels. Maintenance requirements for energy are better expressed as a function of protein mass than body weight. However, differences in body protein mass do not fully explain difference in maintenance requirements between various pig genotypes. Daily feed intakes at each live weight can be estimated by accurately collecting feed intake data at least three live weight ranges and fitting the data to nonlinear functions. An alternative method to estimate daily feed intake is to develop daily lipid and protein accretion curves. On the basis of their energetic costs of lipid and protein deposition and assumed maintenance requirements, daily energy intakes can be estimated. Genetic selection changes the underlying growth parameters. The selection criteria and testing environment direct the relative genetic change for each growth parameter. The different sexes may also be affected differently by selection. For this reason, each closed uniformly selected population must be evaluated for each parameter for each sex.

Prediction of daily protein accretion rates of pigs from estimates of fat-free lean gain between 20 and 120 kilograms live weight

The objective of this study was to evaluate a method for predicting daily protein accretion rates of various genotypes of pigs reared in different environmental conditions using easily obtained mean daily fat-free growth rates. Data were obtained for seven genotype-environment groups of gilts and nine groups of barrows. Daily empty body protein accretion rates were estimated at 1.0-kg intervals between 20 and 120 kg live weight. The estimates were fitted to a generalized exponential function, PA = A e(B x WT + C/WT + D x WT2), where WT is kilograms of live weight and A, B, C, and D are estimated parameters for each sex. Nonlinear least squares methods were used to estimate the intercept and regression coefficients expressing each parameter estimate (A, B, C, and D) as a linear function of the mean fat-free lean gain for each sex-genotype-environment group. The mean percentage absolute errors were 3.5% for gilts and 6.1% for barrows. The largest errors occurred between 110 and 120 kg live weight. From 20 to 110 kg, mean percentage errors averaged 2.7% for gilts vs 4.8% for barrows. These results offer encouraging evidence that a generalized equation can be used to predict daily protein accretion rates from mean fat-free lean growth data. Further research, with additional genotype-environment populations, is needed to increase accuracy of the generalized growth functions.

Alternative pork carcass evaluation techniques: I. Differences in predictions of value

Dissected and predicted wholesale and lean boneless values for 154 pork carcasses representing seven genotypes with substantial variation in carcass composition and percentage of lean were determined. Dissected carcass value was determined using a component pricing model, and four alternative models were specified to predict that value. The models included measurements from a ruler (RULER) and two carcass evaluation technologies, Hennessy probe (PROBE) and electromagnetic scanner (EMS1). A combination of the PROBE and EMS1 models (EMS2) was also used. For wholesale value, R2 were .40, .70, .59, and .74, and the RSD were 8.18, 5.77, 6.76, and 5.38 ($/100 kg of carcass value) for RULER, PROBE, EMS1, and EMS2, respectively. For lean boneless value, the R2 were .41, .73, .59, and .74, and the RSD were 8.34, 5.67, 6.99, and 5.51 ($/100 kg of carcass value) for RULER, PROBE, EMS1, and EMS2, respectively. The results indicate that a combination of probe and electromagnetic scanner measurements provided the best fit to dissected value.

Alternative pork carcass evaluation techniques: II. Statistical analysis of error attributable to sex, genotype, and weight

Carcasses of 154 hogs representing seven genotypes with substantial variation in carcass composition and percentage of lean were completely dissected and analyzed. Measurements from a ruler, Hennessy probe, and electromagnetic scanner were each used to predict wholesale and lean boneless carcass value. Error, defined as dissected value minus predicted value, due to the omission of sex, genotype, weight, and their interactions was estimated for each model. The errors were significantly different from zero for the models using ruler and electromagnetic scanning measurements separately (P < .01). Errors due to sex, genotype, weight, and their interactions were greatest for the less lean barrows. A combination of probe and electromagnetic scanner measurements resulted in the least error. The value of barrows with low percentage of lean was consistently overpredicted, whereas the value of leaner gilts was underpredicted for the models using ruler and electromagnetic scanning separately (P < .001).

The impact of ractopamine, energy intake, and dietary fat on finisher pig growth performance and carcass merit

An experiment was conducted to determine the effect of ractopamine, energy intake, dietary fat level, and sex on performance and carcass composition in finishing pigs. Three hundred six barrows and gilts were used in a factorial arrangement of treatments replicated over three seasons. Treatments consisted of two ractopamine levels (0 vs 44.7 mg/d), two sexes (barrows and gilts), two levels of fat addition (0 vs 5% added fat), and four energy intake levels (8.3, 8.9, 9.5, and 10.1 Mcal of ME/d for barrows and 7.7, 8.3, 8.9, and 9.5 Mcal of ME/d for gilts). Diets were formulated to maintain an equal lysine (28.5 g/d) intake at each feeding level through cornstarch dilution of the basal (7.7 Mcal of ME/d) diets. Pigs were fed daily based on a standard feed intake curve and prior weekly body weights. At slaughter (104 kg), carcass measurements and TOBEC HA-1 scanner measurements were recorded. Dietary fat addition improved live weight and lean efficiency (grams of carcass lean gain/kilogram of feed, P < .05). Dietary fat addition did not affect growth rate or carcass composition. Increasing energy intake resulted in a linear increase in average daily gain for both barrows and gilts (P < .01). Dietary ractopamine influenced the response of lean tissue accretion, lean tissue accretion efficiency, and fat tissue accretion to energy intake. Pigs with no added ractopamine demonstrated increased lean tissue accretion and improved efficiency and decreased fat tissue accretion with increasing energy intake (up to 9.5 Mcal of ME intake for barrows and 8.9 Mcal of ME intake for gilts). In contrast, pigs with added ractopamine did not respond to increasing energy intake and demonstrated increased fat tissue accretion with increasing energy intake. The response to ractopamine for growth was greatest from d 6 to 22 on test or during the test gain period of 7 to 18 kg. After d 22, the response of ractopamine declined linearly. These results indicate that ractopamine increases growth rapidly at the onset of feeding until a plateau is reached, after which there is a linear decline in growth response.

Genotype and treatment biases in estimation of carcass lean of swine

Carcasses of 181 barrows, representing five genotypes, 1) H x HD, 2) SYN, 3) HD x L[YD], 4) L x YD, and 5) Y x L (H = Hampshire, D = Duroc, SYN = synthetic terminal sire line, L = Landrace, and Y = Yorkshire), and two levels of ractopamine (RAC) treatment (0 and 20 ppm) were completely dissected and the data were used to examine genotype and treatment (RAC) biases in estimation of fat-standardized lean weight and to evaluate accuracies and precisions realized by use of equations based on variables derived from different technologies. Independent variables used to establish regression equations represented technologies of direct carcass measurements, optical probe data, TOBEC (total body electrical conductivity) readings, and dissected (DHMLN) and fat-standardized (FSHMLN) ham lean. Genotype bias existed when any equation from a single technology was used and was minimized by combining FSHMLN with one TOBEC reading, carcass length, and the probe measurement of 10th rib fat depth. Large RAC biases appeared when equations from direct carcass measurements or optical probe data were used and were minimized by an equation using either DHMLN or FSHMLN. A practical equation with relatively high R2 value and small genotype and RAC biases were developed by combining TOBEC readings with direct carcass measurements of 10th rib fat depth and warm carcass weight.

Growth, development, and carcass composition in five genotypes of swine

An experiment with 127 barrows representing five genotypes, 1) H x HD, 2) SYN, 3) HD x L[YD], 4) L x YD, and 5) Y x L (H = Hampshire, D = Duroc, SYN = synthetic terminal sire line, L = Landrace, and Y = Yorkshire), was conducted to evaluate growth and development of swine from 59 to 127 kg live weight. Animals were allowed ad libitum access to a pelleted finishing diet containing 18.5% CP, .95% lysine, and 10.5% fat, with an energy density of 3,594 kcal of ME/kg. Pigs were serially slaughtered at either 59, 100, 114, or 127 kg live BW. After slaughter, carcasses were chilled and backfat was measured at four locations. The right side of each carcass was fabricated into primal cuts of ham, loin, Boston Butt, picnic, and belly. Composition of each primal cut was determined by physical dissection into lean, fat, bone, and skin. Estimated allometric growth coefficients for carcass length, carcass weight, and longissimus muscle area relative to BW; carcass lean, fat, bone, and skin relative to both BW and carcass weight; and lean in each of the primal cuts relative to total carcass lean did not differ (P greater than .05) among genotypes. Relative to BW, the pooled growth coefficient(s) for carcass weight was (were) greater (P less than .001) than unity, whereas those for carcass length, longissimus muscle area, and backfat at first rib were smaller (P less than .001) than unity. Those for other backfat measurements were close to 1.00. Relative to either BW or carcass weight, the pooled coefficient(s) for fat was (were) greater (P less than .001) than unity, whereas those for lean, bone, and skin were smaller (P less than .001) than unity. Growth of lean, backfat, bone, and skin in the carcass were nearly linearly associated with increases in BW. The increase in fat weight was curvilinear as the pig grew and was accelerated in later growth stages, indicating that carcass fat percentage increased with increased BW.

Evaluation of alternative techniques to determine pork carcass value

Three techniques for estimating the value of pork carcasses were evaluated: an optical probe, a real-time ultrasound scanner, and an electromagnetic scanner (EMSCAN). The ability of these techniques to predict carcass value was compared to the predictive ability of actual measures of backfat depth and longissimus muscle area taken with a ruler and a dot grid. Results indicated the EMSCAN model was the best predictor of carcass value. However, the optical probe, ultrasound, and the ruler/dot grid all provided information not contained in the EMSCAN model. The choice among ultrasound, the optical probe, and the ruler/dot grid depends on how the carcass will be used. There is no significant difference between ultrasound and the ruler/dot grid or the optical probe and the ruler/dot grid if the carcass is to be marketed in wholesale primal form, but the ruler/dot grid is superior if the ham and loin are to be sold as lean, boneless products. A model combining the EMSCAN and optical probe readings provided more accurate value predictions than either technique alone. A carcass value matrix for use in pricing pork carcasses was developed using readings from the optical probe. Carcass use has a substantial impact on value differences between fat and lean pigs.

Genetic improvement programs in livestock: swine testing and genetic evaluation system (stages)

Genetic evaluations for the U.S. swine industry are conducted by the eight purebred associations of the National Association of Swine Records. Within-herd evaluations of the growth traits (days to 105 kg [market] and backfat depth) were first reported in 1986. Analyses of the maternal traits (litter size at birth and weaning, and litter 21-d weight) were inaugurated in 1987. Expected progeny differences (EPD) are reported for all traits and for general, paternal, and maternal bioeconomic indexes. A sow productivity index combining only maternal traits is available. All records are adjusted according to National Swine Improvement Federation (NSIF) guidelines for effects such as number of pigs transferred at crossfostering and age at recorded observation prior to the BLUP evaluation. Within-herd analyses of individual contemporary groups are conducted immediately on receipt of performance records at each breed association office. All parents in the herd and the young pigs in the current group are evaluated. A report is returned to the breeder for use in herd selection and the EPD are placed in the pedigree file. The genetic base of each herd is defined as the first n tested pigs or litters, where n is the number of pigs registered annually within the herd. Change in mean EPD between groups is indicative of genetic trend. Periodic across-herd analyses are used to update interim within-herd analyses and a national sire summary is published.

Effects of ractopamine, genotype, and growth phase on finishing performance and carcass value in swine: I. Growth performance and carcass merit

A replicated factorial experiment using 183 individually fed crossbred barrows was conducted. Pigs were fed an 18.5% CP (.95% lysine) diet with 3,594 kcal of ME/kg. The effects of five genotypes (GT): 1) Hampshire (H) x (H x Duroc [D]), 2) synthetic terminal sire line, 3) (H x D) x (Landrace [L] x [Yorkshire (Y) x D]), 4) L x (Y x D), and 5) Y x L; two levels of ractopamine (RAC) treatment: 0 and 20 ppm; and three treatment weight periods (WT): 1) 59 to 100, 2) 73 to 114, and 3) 86 to 127 kg live weight on growth performance and carcass traits were evaluated. Ractopamine increased (P less than .0001) amount (FSL) and percentage (PFSL) of carcass lean standardized to 10% fat content, loin eye area (LEA), and dressing percentage (PDRES) and reduced (P less than .01) amount (DF) and percentage (PDF) of dissected fat. Magnitudes of RAC effects were smaller than those reported by other researchers. Effects of GT and WT on all growth and carcass traits were highly significant (P less than .001) except for those of WT on ADG (P less than .05) and GT on average feed intake (AFI) and backfat thickness at the last rib (BFLR; P less than .05). Genotype 3 performed better for most economically important traits than did GT 1 and 4, suggesting that heterosis existed in GT 3, which essentially was obtained by crossing GT 1 and 4. Among the three treatment periods, WT 2 had the highest ADG. As BW increased from WT 1 to 3, AFI and AFI/ADG ratio (FCR) increased and lean percentage decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ractopamine, genotype, and growth phase on finishing performance and carcass value in swine: II. Estimation of lean growth rate and lean feed efficiency

A replicated factorial experiment using 183 individually fed crossbred barrows was conducted. The pigs were fed an 18.5% CP (.95% lysine) diet with 3.594 kcal of ME/kg. The effects of five genotypes (GT): 1) Hampshire (H) X (H X Duroc [D]), 2) synthetic terminal sire line, 3) (H X D) X (Landrace [L] X [Yorkshire (Y) X D]), 4) L X (Y X D), and 5) Y X L; two levels of ractopamine (RAC) treatment: 0 and 20 ppm; and three treatment weight periods (WT): 1) 59 to 100, 2) 73 to 114, and 3) 86 to 127 kg live weight on ADG of dissected lean (ADLG) and fat standardized lean adjusted to 10% fat content (ADSLG) and feed efficiency of ADLG (LFE) and ADSLG (SLFE) were evaluated. Initial carcass lean quantity of each individual animal was determined by a regression equation (R2 = .95) generated from 30 additional barrows (six per GT) slaughtered at 59 kg and 30 (six per GT) untreated pigs slaughtered at 100 kg average live weight. Logarithmic and reciprocal transformations of dependent variables were used to stabilize heterogeneous variances and to improve normality of the residuals. Ractopamine increased (P less than .0001) ADLG, ADSLG, LFE, and SLFE, respectively, by 19.5, 25.0, 19.6, and 25.5%. Differences (P less than .001) were observed among genotypes for all traits, showing that considerable variation existed in the data and indicating that genetic improvement can be realized through the identification and selection of superior genotypes.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of somatotropin and genotype on the requirement for energy in two lines of finishing pigs

Eighty barrows were used in a 2 x 2 x 4 factorial experiment to examine the effects of genetic line (Hampshire x Yorkshire, H x Y, and Yorkshire x Landrace, Y x L), somatotropin (dose, 0 and 5 mg/d) and energy intake (ad libitum, 93%, 86% and 80%) on growth performance and energy requirements for lean gain over the finishing phase of growth. Four diets were formulated to maintain equal intakes of protein, vitamins and minerals at different energy intakes. Somatotropin increased growth rate 30 to 35% across diets despite an 8 to 12% reduction in ad libitum feed intake. Lean growth rate (kg/d) was increased preferentially by ST in the faster-growing H x Y barrows, which showed a 2.8-fold greater maximum rate increase than the slower-growing Y x L barrows. In control barrows, 10% reductions in energy intake had no effect on lean gain and improved feed/lean gain about 10%. In somatotropin-treated barrows, lean gain was reduced with each energy restriction in H x Y; energy intake had no effect on lean gain in Y x L barrows. Feed/lean gain was improved 22% in Y x L barrows at the lowest energy intake. Data indicate that somatotropin accentuates breed differences in lean gain and energy requirements. Pigs with low lean-growth potential will benefit from restricted feeding, whereas strategies to increase energy intake in pigs with high lean-growth potential may be desirable.

Practical means for estimating pork carcass composition

Three hundred sixty-one market-weight barrow and gilt carcasses were physically dissected into bone, skin, fat and muscle. A three-variable multiple linear regression equation containing the same independent variables (warm carcass weight, 10th rib loin muscle area and 10th rib fat depth) used (U.S.) to determine pork carcass lean weight was found to be the most practical means for predicting weight of muscle standardized to 10% fat. Multiple linear regression equations containing more than three independent variables produced only slight improvements in R2 values; however, the standard deviation about the regression line was not greatly improved by the addition of more independent variables to this three-independent-variable regression model. A single multiple linear regression equation using the three independent variables above may not be adequate to describe variation over the entire live-weight range for all hogs marketed in the U.S. For most accurate muscle weight prediction, different equations should be used for weight subclasses with one equation for carcasses under 100 kg and another for those heavier than 100 kg. A single prediction equation for muscle weight was adequate for carcasses of both barrows and gilts.

Effects of ractopamine on adipose tissue metabolism and insulin binding in finishing hogs. Interaction with genotype and slaughter weight

Twenty-four barrows were divided among eight treatments in a 2 x 2 x 2 design to quantify the influence of ractopamine (0 or 20 mg/kg diet) over the final 40 kg of gain on metabolic activity in adipose tissue. Interactions with genotype (Hampshire cross or Landrace cross) and slaughter weight (100 or 127 kg) were investigated also. Backfat was removed at slaughter and rates of lipolysis and fatty acid synthesis (FS), activities of malic enzyme (ME) and fatty acid synthetase (FAS), and insulin binding to adipocytes were assessed. Adipocytes from ractopamine-fed pigs were less sensitive (EC50 increased 90%) and had a lower maximum lipolytic response (40%) to ractopamine stimulation. Rates of basal and insulin-stimulated FS were decreased 40% in ractopamine-fed pigs and were reflected in lower activities of ME (50%) and FAS (15%). Breed and slaughter weight had no consistent influence on the ractopamine response. Landrace-cross pigs had greater insulin binding capacity (30-60%) whether data were expressed on a cell or surface area basis. Ractopamine feeding did not consistently affect insulin binding capacity. Results suggest that ractopamine interacts in vivo with the beta-adrenergic receptor of swine adipocytes, decreasing lipogenic capacity and diminishing responsiveness to beta-adrenergic stimulation.

Adapting best linear unbiased prediction (BLUP) for timely genetic evaluation: I. Progeny traits in a single contemporary group for each sex

The first step of a procedure to partially circumvent the voluminous calculations with extremely large matrices for the usual algorithms for a BLUP (best linear unbiased prediction) approach is presented. This procedure, specific for a hierarchical portion of a model relevant to many animal breeding populations, is pertinent especially for polytocous species such as swine and poultry. For these, the occurrence of full-sib families makes the inclusion of dam effects in the model more necessary than in dairy or beef cattle models, where dam effects often are omitted. The formulas are derived for the hierarchical model for sires, dams within sires, individuals within full-sib family, and records within individuals, showing a relatively simple structure for such predictors. These formulas provide the basis for an alternative computing algorithm for obtaining evaluations having the statistical properties of best linear unbiased prediction. Formulas also are developed to approximate the prediction error variances for such models. Following this, the methodology for combining separate BLUP predictors, both error-independent and correlated, is developed.

Adapting best linear unbiased prediction (BLUP) for timely genetic evaluation: II. Progeny traits in multiple contemporary groups within a herd

The second step of a procedure to partially circumvent the voluminous calculations for some BLUP (Best Linear Unbiased Prediction) computing algorithms for genetic evaluation is presented. In addition, the procedure allows timely evaluations of each contemporary group. This procedure is pertinent especially for polytocous species such as swine and poultry, for which the occurrence of full-sib families makes the inclusion of dam effects in the model necessary and tests are completed throughout the year. Formulas are developed for a model including sires, dams, individuals within full-sib families and records within individuals. This model has a fundamentally hierarchical structure but includes some cross-classification. The formulas for predictors combine information across contemporary groups within a herd and incorporate relationships between sires and(or) dams in that herd. Formulas to approximate prediction error variances also are developed.

Use of farrowing rate as a measure of fertility of boars

The first 100 single-boar services of 140 boars were analyzed to determine whether the farrowing rate resulting from initial services predicted the farrowing rate of subsequent services. The data were analyzed for the influence of parity, number of matings per estrus, season of service, and interaction of these variables on farrowing rate. Sow parity influenced farrowing rate. Sows with parity greater than 8 and gilts had the lowest farrowing rates (P less than 0.01). Sows with parity 2 through 5 had the highest farrowing rates (P less than 0.01). One and 2 matings/estrus resulted in reduced farrowing rates (P less than 0.01), compared with farrowing rates of greater than 2 matings/estrus. Farrowing rate for services during the summer was lower than that for other seasons of the year (P less than 0.01). Evidence of interaction among these variables was not found. Therefore, the results of each service recorded was adjusted to the mean farrowing rate of sows with parity 2 through 5, sows mated greater than or equal to 3 times/service, and sows serviced in the spring. After these adjustments, the farrowing rates for the first 10, 20, 30, 40, and 50 services were analyzed to determine associations with farrowing rates for subsequent services through 100 farrowings. These data also were analyzed to determine whether the associations were strengthened by removal of the first 10 services from the data. The best farrowing rate association indicated that for each 1% increase in farrowing rate subsequent to the first 50 services, the farrowing rate for the second 50 services increased 0.33% (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships among measures of testicular development and endocrine function in boars

Nine blood samples were taken at 30-min intervals from 36 Landrace X Large White boars at each of eight ages (42, 56, 70, 84, 98, 112, 126 and 140 d). Serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T) and estradiol-17 beta (E2) were quantified by radioimmunoassay procedures. The maximum concentration of LH and the age at maximum concentration were predicted for each boar. Variability of LH samples was described for each boar by the pooled within age variance among LH samples and by the number of LH peaks. Measurements of testicular development taken at 140 d of age included: in situ testis width and length, excised testis weights and histological traits of excised testes (seminiferous tubule diameter, percentage of tubules with a lumen and percentage of tubules with active spermatogenesis). Pooled within line correlations were calculated with data from boars selected for either high or low testis weight. Correlations among the testicular traits ranged from .45 to .88. Luteinizing hormone concentration (mean over all ages) was related to measures of testicular development (r = .24 to .49). Concentrations of LH from 42 to 84 d of age were more highly correlated with testicular traits than were the concentrations from 98 to 140 d.(ABSTRACT TRUNCATED AT 250 WORDS)

Testicular development and endocrine characteristics of boars selected for either high or low testis size

Thirty-six Landrace x Large White cross boars were selected from litters with either high or low estimated breeding values for 150-d paired testis weight. Blood samples were taken via jugular venipuncture at eight ages (42, 56, 70, 84, 98, 112, 126 and 140 d). At each sampling age, nine blood samples were taken at 30-min intervals. Luteinizing hormone (LH) was determined on the individual serum samples. Serum samples from each boar at each age were pooled and concentrations of follicle-stimulating hormone (FSH), estradiol-17 beta (E2) and testosterone (T) were determined. Paired testis width, testis length and body weight were measured at 98, 112, 126 and 140 d of age. Backfat probe, weights of excised testes and histological data on testes were obtained at 140 d of age. Boars with high testis weight (HTW) were heavier (P less than .05), had higher adjusted backfat probes (P less than .01) and had consistently larger in situ testis measurements (P less than .01) than did low testis weight (LTW) boars. Boars with HTW had heavier (P less than .01) testes and epididymides at 140 d of age. They also had a higher percentage of seminiferous tubules in which spermatogenesis was present (P less than .05), a larger percentage of tubules with a lumen (P less than .05) and tubules had a larger mean diameter (P less than .01) than did those of boar with LTW. Adjustment of in situ testis measurements and excised testis weights for body weight reduced line differences by less than 20%. A rise in LH concentrations occurred at approximately 100 d of age. Boars with HTW had higher (P less than .05) and more variable (P less than .01) LH concentrations than did boars with LTW. Boars with HTW also had higher maximum concentrations of LH during the pubertal rise (P less than .01) and these concentrations tended to reach maximum levels at younger ages. Concentrations of T increased in a fashion that was nearly linear with age (P less than .01) and tended to be higher for the boars with HTW (P less than .10). Concentrations of E2 changed little from 42 to 84 d of age but increased steadily thereafter. Boars with HTW had a more rapid increase in E2 concentrations than did boars with LTW (P less than .05).(ABSTRACT TRUNCATED AT 400 WORDS)