Phenotypic and genetic variation in body weight,food intake and energy utilisation in Hereford cattle II. Effects of age and length of performance test

The effects of length of test, age when evaluations are made, and correction of data for body weightat the start of test on genetic and phenotypic parameters describing performance test results in beef cattle were studied. The data consisted of body weight, food intake and carcass composition measurements on 542 Hereford bull calves, from 200 to 400 days of age. The traits studied included weights at various ages, weight gain, lean growth rate, food intake, food conversion ratio, lean food conversion ratio, food intake in relation to metabolic body weight, energy required for protein and fat deposition, and predicted maintenance expenditure. Traits were derived for the whole test as well as for part test periods of 200–300 days and 300–400 days.Heritabilities for all traits, except those describing weight at a given age, were lower for the 300–400-day period than for either the 200–300-day period or the whole test. Correlations, however, were higher between whole test and 300–400-day traits than between whole test and 200–300-day traits. Phenotypic correlations between the same trait measured in the two-part test period were very low and much lower than the genetic correlations. Corrections for body weight at the start of test had only a trivial effect on the heritabilities of all traits, the relationships between traits and potential genetic progress in traits measured during the test.     

Estimates of genetic parameters and predicted selection responses for growth, fat and lean traits in mice

Heritabilities (?2) and genetic correlations (rG) were estimated by regression of offspring on sire in two replicate, unselected lines of mice. Traits were associated with growth, feed efficiency, fat deposition and lean tissue. The ?2 for growth traits ranged from .34 to .42, except for 3-wk body weight, which was only .05. The ?2 for feed efficiency was .28. Ranges in ?2 were .45 to .50 for fat deposition traits and .36 to .42 for lean tissue traits. The rG involving 3-wk to 6-wk feed efficiency with hind carcass and fat measurements at 12 wk were small. Antagonisms were found between the sign of rG and the direction of usual breeding goals for pairs of traits (e.g., rG greater than 0 between fat deposition and hind carcass weight and rG less than 0 between hind carcass as a percentage of body weight and body weight). Selection indexes were developed to counteract these antagonisms. Modified selection indexes were compared where responses in individual traits rather than the aggregate breeding value were of major importance. The aggregate breeding values and selection indexes included: 1) epididymal fat pad weight and body weight, 2) hind carcass weight and body weight, or 3) all three traits. Economic weights in retrospect were calculated for the modified selection indexes. In some cases, expected correlated responses in component traits were not influenced greatly over a wide range of ratios of economic weights, but in other cases the component traits changed sharply over a narrow range of ratios.     

Interrelationships between energy intake and endogenous porcine growth hormone administration on the performance, body composition and protein and energy metabolism of growing pigs weighing 25 to 55 kilograms live weight

Thirty-six barrows were used in a 2 X 3 factorial experiment to investigate the effects of porcine growth hormone (pGH) administration (USDA-pGH-B1; 0 and 100 micrograms.kg body weight-1.d-1) and three levels of feeding of a single diet (EI; ad libitum, 1.64 and 1.38 kg/d) on the performance, body composition and rates of protein and fat deposition of pigs growing over the live weight phase 25 to 55 kg. Raising EI resulted in linear increases in growth rate and in protein and fat accretion but had no effect on the feed to gain ratio (F/G). Carcass fat content and carcass fat measurements also increased with EI, whereas carcass protein and water decreased (P less than .01). Growth hormone administration resulted in improvements in growth rate (16 to 26%), F/G (23%), protein deposition (34 to 50%) and increases in carcass protein and water at each level of feeding, but reduced ad libitum feed intake (P less than .01), carcass fat content (P less than .01) and carcass fat measurements (P less than .01). Estimated maintenance energy expenditure was increased by pGH administration (2.02 vs 1.72 Mcal digestible energy/d). Results indicate that the effects of pGH on growth performance and energy and protein metabolism were largely independent of, and additive to, the effects of energy intake.     

A deterministic computer simulation model of life-cycle lamb and wool production.

A deterministic mathematical computer model was developed to simulate effects on life-cycle efficiency of lamb and wool production from genetic improvement of performance traits under alternative management systems. Genetic input parameters can be varied for age at puberty, length of anestrus, fertility, precocity of fertility, number born, milk yield, mortality, growth rate, body fat, and wool growth. Management options include mating systems, lambing intervals, feeding levels, creep feeding, weaning age, marketing age or weight, and culling policy. Simulated growth of animals is linear from birth to inflection point, then slows asymptotically to specified mature empty BW and fat content when nutrition is not limiting. The ME intake requirement to maintain normal condition is calculated daily or weekly for maintenance, protein and fat deposition, wool growth, gestation, and lactation. Simulated feed intake is the minimum of availability, DM physical limit, or ME physiological limit. Tissue catabolism occurs when intake is below the requirement for essential functions. Mortality increases when BW is depressed. Equations developed for calculations of biological functions were validated with published and unpublished experimental data. Lifetime totals are accumulated for TDN, DM, and protein intake and for market lamb equivalent output values of empty body or carcass lean and wool from both lambs and ewes. These measures of efficiency for combinations of genetic, management, and marketing variables can provide the relative economic weighting of traits needed to derive optimal criteria for genetic selection among and within breeds under defined industry production systems.     

Influence of a high-protein diet on energy balance in obese cats allowed ad libitum access to food

The influence of a high-protein [HP, 47% of metabolizable energy (ME)] diet on energy balance was evaluated in obese cats allowed ad libitum access to food. Energy intake, body weight, body composition, energy expenditure, and concentrations of hormones and metabolites associated with carbohydrate and lipid metabolism (glucose, insulin, free fatty acids, triglycerides and leptin) were measured in cats after consuming either a moderate protein (MP, 27% of ME) or HP diet for 4 months. Indirect respiration calorimetry showed that resting and total energy expenditure (kJ/day) adjusted for either body weight or lean body mass was increased in cats consuming the HP in relation to MP diets. However, voluntary energy intake also was increased in the HP treatment and, thus, there was no difference in body weight between animals consuming the two diets. Body composition measurements using deuterium oxide dilution showed that dietary protein content did not alter amounts of either lean body mass or fat mass. No significant differences (p > 0.05) were observed between the two treatment groups for blood glucose, free fatty acid or leptin concentrations, although there was a trend (p = 0.054) towards an increase of serum insulin concentrations in the cats eating the HP diet. This study showed that short-term ad libitum feeding of an HP diet did not reduce food intake or promote weight loss in obese cats. However, energy expenditure was increased in the HP diet group and it is possible that this effect of HP might help promote weight loss when energy intake is restricted.     

Effect of dietary betaine on nutrient utilization and partitioning in the young growing feed-restricted pig

The purpose of this study was to examine the effects of dietary betaine over a range of concentrations (between 0 and 0.5%) on growth and body composition in young feed-restricted pigs. Betaine is associated with decreased lipid deposition and altered protein utilization in finishing pigs, and it has been suggested that the positive effects of betaine on growth and carcass composition may be greater in energy-restricted pigs. Thirty-two barrows (36 kg, n = 8 pigs per group) were restrictively fed one of four corn-soybean meal-skim milk based diets (18.6% crude protein, 3.23 Mcal ME/kg) and supplemented with 0, 0.125, 0.25, or 0.5% betaine. Feed allotment was adjusted weekly according to BW, such that average feed intake was approximately 1.7 kg for all groups. At 64 kg, pigs were slaughtered and visceral tissue was removed and weighed. Carcasses were chilled for 24 h to obtain carcass measurements. Subsequently, one-half of each carcass and whole visceral tissue were ground for chemical analysis. Linear regression analysis indicated that, as betaine content of the diet was elevated from 0 to 0.5%, carcass fat concentration (P = 0.06), P3 fat depth (P = 0.14) and viscera weight (P = 0.129) were decreased, whereas total carcass protein (P = 0.124), protein deposition rate (P = 0.98), and lean gain efficiency (P = 0.115) were increased. The greatest differences over control pigs were observed in pigs consuming 0.5% betaine, where carcass fat concentration and P3 fat depth were decreased by 10 and 26%, respectively. Other fat depth measurements were not different (P > 0.15) from those of control pigs. In addition, pigs consuming the highest betaine level had a 19% increase in the carcass protein:fat ratio, 23% higher carcass protein deposition rate, and a 24% increase in lean gain efficiency compared with controls. Dietary betaine had no effects (P > 0.15) on growth performance, visceral tissue chemical composition, carcass fat deposition rate, visceral fat and protein deposition rates, or serum urea and ammonia concentrations. These data suggest that betaine alters nutrient partitioning such that carcass protein deposition is enhanced at the expense of carcass fat and in part, visceral tissue.     

Energy utilization in mature ewes from seven breeds with diverse production potentials

Effects of genetic changes in reproduction, growth, body composition or lactation on the efficiency of market lamb production depend partly on the associated changes in feed intake requirements for maintenance and for protein and fat deposition. To evaluate these relationships, feed intake and body weight changes were monitored for six pairs of open, dry, mature ewes from each of seven diverse breeds fed pelleted alfalfa (53% TDN) ad libitum (AL) or restricted (MN) to 64% of ad libitum levels, for an average of 41 d. After a 56-h fast, heat production (FHP) was measured calorimetrically for 16 h before slaughter and analysis of empty body composition. The estimated daily metabolizable energy intake/kg(.75) of body weight for no change in body energy (MEm) was 167 kcal for the AL vs 147 kcal for MN ewes, and ranged from 139 to 169 among breeds (P less than .05). Estimated above-maintenance ME requirements, kcal/g tissue deposited, were 30 to 50 for protein and 10 to 14 for fat deposition. Mean FHP/d, adjusted by regression to zero activity, was 72 kcal/kg(.75) weight and was nonsignificantly higher (3.3) for the leaner MN than for AL ewes. Thus, the lower total MEm for MN than for AL ewes was necessarily derived from reduced metabolic and physical activity and(or) higher digestibility. Genetic increases in lean vs fat deposition would reduce above-maintenance feed by one-third to one-fourth because of the high water content of lean, but more lean mass may increase maintenance costs.     

Genetic parameters for dry matter, energy and protein intake, and their relationships with performance and carcass traits in Japanese Black cattle

Genetic parameters for feed intake and performance traits of 514 bulls and carcass traits of 22 099 of their progeny, and the relationships of measures of feed intake with performance and carcass traits were estimated. Feed intake traits were dry matter intake (DMI), concentrate intake (CONI), roughage intake, ratio of roughage intake to DMI, metabolizable energy intake (MEI) and digestible crude protein intake (DCPI). Performance traits included daily gain, metabolic weight, live weight at the end of test, dry matter conversion ratio and residual feed intake. Progeny carcass traits were carcass weight, percentage of meat yield, rib eye area (REA), subcutaneous fat, marbling score, meat colour (MCS), fat colour (FCS) and meat quality grade. All the feed intake and performance traits were moderately heritable. The heritabilities for REA and MCS were moderate, and that for FCS was low, while those for the other carcass traits were high. Selection against DMI, CONI and DCPI would reduce excessive intake of feed, but would have undesirable effects on growth and most of the carcass traits. Selection against MEI would lead to improvements in feed efficiency and growth traits. Selection against DCPI would also improve feed efficiency; however, responses in growth traits would decrease. Results indicate that selection against MEI might be better than any other measures of feed intake to improve feed efficiency with simultaneous improvement in growth and most of the carcass traits.     

Genetic Differences in Energy Partitioning in Growing Pigs

Energy partitioning was studied in pigs differing in potential for carcass lean growth and fatty tissue content from 25 to 105 kg body weight, by the means of repeated measures of detailed body composition and individual feed intake. In total, 141 pigs were included from the three genetic groups Norwegian Landrace (lean and efficient), Duroc and Landrace 2 LP (a fat and slow-growing selection line) (LLP). Individual feed consumption was registered, and detailed body composition measured repeatedly by computed tomography. Energy consumption [MJ metabolizable energy (ME) day -1 ] did not differ between the genetic groups. In general, about 40-50% of consumed energy was partitioned to growth. The genetic groups partitioned equal proportions of daily energy consumption to growth (ME GROWTH ) and maintenance (MEm) early and late in the growth period. From 50 to 85 kg body weight Landrace partitioned more to growth and less to maintenance compared with Duroc ( P <0.05). When considering partitioning of ME above maintenance, the genetically fat LLP had the highest net energy retention relative to the heat increment of feeding and was therefore the most efficient, Duroc was in an intermediate position while the lean Landrace had the lowest proportion. The partitioning of ME GROWTH to fatty tissue and carcass lean growth differed between the genetic groups ( P <0.001) according to genetic potential for carcass lean and fatty tissue gain. Increasing proportions were partitioned to fatty tissue growth with increasing body weight. The genetic groups partitioned equal proportions of ME GROWTH to non- fat visceral components (NFVC) growth. MEm varied between 0.65 and 0.68 MJ kg -0.75 day -1 . MEm increased with increasing weight of carcass lean and viscera ( P <0.01), more so in the modern breeds than in the LLP.     

不同屠宰体重商品猪胴体性能、肉品质及相关关系研究

测定了体重70～140 kg阶段120头商品猪的胴体品质和肉质特性,分析了商品猪胴体性能、肉质性状随体重的变化规律及相关程度,为确定适宜上市屠宰体重提供依据。结果表明:70～100 kg体重阶段,随体重增大,平均背膘厚、眼肌面积、皮脂率、肉色和大理石纹显著升高,后腿比例、瘦肉率、骨骼率、L和b值显著降低。胴体和肉质性状间相关程度有强有弱,相关系数有正有负。相同性状间有较强的正相关,相反性状间有较强的负相关。在70～140 kg阶段,胴体重、胴体直长、胴体斜长、眼肌面积、平均背膘厚、瘦肉率、皮脂率、骨骼率、肉色和L值与体重之间呈显著的回归关系,其他指标与体重间的线性相关不显著。     

Synergistic effects of betaine and conjugated linoleic acid on the growth and carcass composition of growing Iberian pigs

An experiment was conducted to determine the efficacy of dietary betaine, CLA, or both as growth promotants and carcass modifiers in growing Iberian pigs. Twenty gilts (20 kg of BW) were individually penned and fed barley- and soybean meal-based diets (12% CP, 0.81% Lys, and 14.8 MJ of ME/kg of DM) containing either no added betaine or CLA (control), 0.5% betaine, 1% CLA, or 0.5% betaine + 1% CLA, at 95% of ad libitum energy intake. An additional group of 5 pigs was slaughtered at the beginning of the experiment to obtain the initial body composition. At 30 kg of BW, a balance experiment was conducted. At 50 kg of BW, pigs were slaughtered and viscera was removed and weighed. Betaine or CLA alone did not affect growth performance. However, betaine + CLA increased ADG (601 vs. 558 g, P = 0.03) and gain relative to ME intake (25.4 vs. 22.2 g/MJ, P = 0.03) compared with control pigs. Digestibility of nutrients and metabolizability of energy did not differ among diets (P = 0.46 to 0.75). Carcass protein, water, and lean deposition (g/d) increased (19.8, 24.2, and 23.4%, respectively, P < 0.01) in pigs fed betaine + CLA compared with control pigs. Similarly, protein deposition relative to ME intake increased by 28% in betaine + CLA-supplemented pigs (P < 0.05). Fat and mineral deposition did not differ among treatments. Carcass protein, water, and lean content (g/kg of carcass) of pigs fed betaine + CLA-supplemented diets tended to increase (P = 0.07 to 0.09) and carcass fat content tended to decrease (P = 0.09). Similarly, estimated composition of carcass gain was affected, such that water and lean content tended to increase (P = 0.06 to 0.08), whereas fat tended to decrease (P = 0.08) in pigs fed betaine + CLA-supplemented diets. Longissimus muscle area was not altered by treatments (P = 0.49). The liver of pigs fed betaine + CLA diets had increased weight (19%, P < 0.05) compared with control pigs. Overall, dietary supplementation of betaine + CLA increased ADG, protein, water, and lean deposition in growing Iberian gilts. There appears to be a synergistic action when betaine and CLA are used together.     

Economic values for lean meat and fat efficiency in Norwegian Landrace nucleus pig population

A profit function was developed to estimate economic values for new efficiency traits for fattening pigs in Norwegian Landrace. These traits were lean meat efficiency (LME) and fat efficiency (FE). LME and FE described how much feed the animal used to produce 1?kg lean meat and fat as a deviation from the mean. Both traits were derived from analysing total feed consumption in a random regression model which included lean meat and fat content of the carcass (FC) as random covariates. In addition, economic values and breeding values were calculated for days from 40 to 100/120?kg live weight (DAYS), lean meat percentage (LMP) and FC. To compare LME and FE with total feed intake (FI), two indexes were constructed. One index included LME, FE, DAYS, LMP and FC and was referred to as breeding goal A and one index included FI, LMP and DAYS and was referred to as breeding goal B. The standardized economic values for LME and FE were 8.9 and 2.9 EUR/σ_a, respectively. There was a larger variation in the index for breeding goal A (SD?=?5.65) than B (SD?=?3.97). The results suggested that the two efficiency traits had an economic importance in pork production and that there was a potential for increased genetic gain in profit by using breeding goal A compared to breeding goal B.     

Effect of dietary protein source and lysine:DE ratio on growth performance, meat quality, and body composition of growing-finishing pigs.

The effects of four protein sources (soybean meal, sunflower meal, pea, and fish meal as the main protein source) and three apparent ileally digestible Lys:DE ratios (0.50, 0.43, 0.36 and 0.42, 0.36, 0.30 g Lys/MJ DE for 30 to 60 kg BW and 60 to 105 kg BW, respectively) in pig diets on growing-finishing performance, and carcass and meat quality traits were investigated. Eight individually housed animals per treatment received the diets from 30 to 105 kg BW at a level of 3.0 times maintenance requirements of energy. The ileal digestibility of protein sources was determined in a previous digestibility experiment. Protein sources showed no differences in growth performance from 30 to 105 kg BW. From 30 to 60 kg BW soybean treatment had lowest performance. The protein sources had no effect on lean meat percentage, liver weight, or meat quality (intramuscular fat content, pH at 45 min and 24 h after slaughter, drip loss, and meat color measured 24 h and 4 d after slaughter). The experimental diets formulated on the basis of similar apparent ileal digestible lysine content resulted in similar body composition regardless of the protein source used (P > 0.05). Reducing the Lys:DE ratio from 0.50/0.43 to 0.36/0.30 (by about 28%) reduced BW gain by 119 g/d from 30 to 60 kg and by 151 g/d from 60 to 105 kg BW. The gain:feed ratio increased by 82 g/kg in the first phase and by 47 g/kg in the second phase for the highest Lys:DE treatment compared with the lowest. Reducing Lys:DE ratio did not modify meat quality traits. A high Lys:DE ratio was associated with a high lean meat percentage. Differences between the medium- and low-Lys:DE groups were not significant. Lowering the Lys:DE ratio increased (P < 0.05) crude fat and fatty tissue content and decreased (P < 0.05) protein and muscle content in the body. Ash content and bone volume were not affected by Lys:DE ratio (P > 0.05). The chemical composition of the carcass can be predicted with moderate accuracy (R2 = 0.39 to 0.58) using volumetric composition data of previously frozen carcasses. In conclusion, similar growth performance, carcass and meat quality, and body composition can be expected if diet formulation is based on the apparent ileally digestible amino acid contents of feedstuffs, independent of dietary protein sources. Diminishing Lys:DE ratios reduce growth performance but do not modify meat quality traits. The chemical composition of the carcass can be predicted with moderate accuracy using the volumetric composition of thawed carcasses.     

A within-breed comparison of RYR1 pig genotypes for performance, feeding behaviour, and carcass, meat and fat quality traits

Data on 187 DNA‐tested purebred Landrace pigs were used to compare heterozygous RYR1 genotypes (Nn) and normal homozygotes (NN) in performance (growth, fat deposition rate and feeding behaviour patterns), and carcass, meat and fat quality traits. From 75 to 165 days of age, live body weight (BW), ultrasonic midback (UMB) and loin (ULB) backfat measurements were recorded periodically on the same animal. Individual voluntary feed intake (DFI), number of visits (NVD) and feeding time (FTD) were measured on a daily basis using an automatic feeding system. Polynomial models with random regression coefficients were used to describe BW, UMB, ULB, DFI, NVD and FTD as a function of age. Carcass, meat and fat quality traits were analysed using a mixed model with the RYR1 genotype as a fixed effect. No significant (p < 0.05) differences were observed between NN and Nn genotypes for growth, feed intake and feed efficiency at any age, but the NN pigs showed higher values for UMB and ULB (0.68 ± 0.30 mm and 0.88 ± 0.40 mm, respectively, at 165 days). The Nn pigs had higher predicted carcass lean content (+11.1 ± 3.7 g/kg) and higher proportion of ham in the carcass (+2.9 ± 1.4 g/kg). However, they showed lower values of pH measurements at 45 min post‐mortem (–0.26 ± 0.05 in M. longissimus dorsi, LD), and higher electrical conductivity at 45 min (+1.03 ± 0.17 μs in LD) and 24 h post‐mortem (+1.63 ± 0.29 μs in LD). No significant differences were found between genotypes for intramuscular fat in the M. semimembranosus (SM) and for fatty acid profiles in the subcutaneous backfat and in the intramuscular fat of the SM. The results of this study suggest that Nn pigs would attain their maximum growth rate at later stages than the NN without any relevant change in the feeding behaviour pattern. Also they confirm that Nn pigs are leaner, have greater proportion of high‐priced cuts in the carcass and are more prone to develop pale, soft and exudative meats. However, no effect on fat quality traits was found.     

Associations between genetic markers and growth and carcass traits in a paternal half-sib family of Angus cattle

Segregation of polymorphic marker genes in a paternal half-sib family of Angus cattle was used to detect associations between genetic markers and quantitative traits. The half-sib family selected (n = 146) had a sire that was heterozygous at six polymorphic marker loci; BoLA-A (class I major histocompatibility complex), B, C and F blood group systems, serum transferrin and vitamin D binding protein. Segregation of alleles fit the expected ratios for all marker loci. Performance data analyzed for all half-sibs included birth, 205-d and 365-d adjusted weights and pre- and post-weaning average daily gains. Carcass data for steers (n = 61) included carcass weight, rib-eye area, 12th rib fat thickness, percent kidney, heart and pelvic fat and yield grade. Least squares means were compared for differences in performance and carcass traits between groups of half-sibs that inherited alternative paternal alleles. Significant effects were found for two of the six marker systems. Half-sibs that inherited the chromosomal segment (CS) marked by the RBC-B system BGKOxY2A'O' phenogroup had heavier 205-d (9.1 kg) and 365-d (17.3 kg) adjusted weights, faster preweaning average daily gains (.04 kg) and less fat thickness (-2.6 mm) than sibs that inherited the CS marked by I2Y2E'1Y'. Also, sibs that inherited the CS marked by the BoLA-w2 allele had larger rib-eye areas (4.1 cm2) than sibs that inherited BoLA-w28. These data indicate the probable presence of genes linked to the RBC-B and BoLA systems that affect preweaning growth and lean muscle content.     

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.     

Use of carbohydrate and fat as energy source by obese and lean swine

Genetically obese and lean pigs were fed isonitrogenous-isoenergetic (digestible energy) amounts of a high or low fat diet from 25 kg body weight. Obese pigs gained less and required more feed per unit gain than lean pigs. Lean pigs were more muscular with less fat than obese pigs. Obese pigs utilized more dietary amino acids for energy (greater plasma urea N) than did lean pigs. Weight gain was similar at all intermediate periods in obese pigs fed the two diets. However, gain tended (P less than or equal to .10) to be greater and the ratio of dietary energy intake to gain tended (P less than or equal to .10) to be less in obese pigs fed high compared with low fat diets. Similar results were observed in lean pigs fed the two diets. The high fat diet produced more carcass adipose tissue deposition in both strains after 20 wk of feeding (detectable by ultrasound at 14, but not at 7 wk). Adipose tissue lipogenic rate (glucose incorporation) was similarly depressed by fat feeding in both obese and lean pigs. Obese and lean pigs both utilized dietary carbohydrate and fat differentially but there was no indication of genetic divergence regarding this utilization. In both strains of pigs, energy from the fat-enriched diet was preferentially partitioned into carcass adipose tissue.     

Effects of ractopamine on genetically obese and lean pigs

Twenty-eight genetically obese and 24 lean barrows (65.0 and 68.7 kg average BW, respectively) were allotted within genotype to a 16% CP corn-soybean meal basal diet or this basal diet + 20 ppm ractopamine (a phenethanolamine beta-adrenergic agonist) and allowed ad libitum access to feed for 48 d. Compared to lean pigs, obese pigs had lower ADG, gain to feed ratio, longissimus muscle area, predicted amount of muscle, and weights of trimmed loin and ham, ham lean, heart, spleen, kidney and gastrointestinal tract (P less than .05). Obese pigs also had shorter carcass but higher dressing percentage, backfat thickness, fat depth, fat area, untrimmed loin weight and fasting plasma urea N concentration (P less than .05). Dietary supplementation with 20 ppm ractopamine reduced daily feed intake and improved gain to feed ratio in both lean and obese pigs (P less than .05). Pigs fed ractopamine had shorter carcasses, less fat depth and fat area, smaller weights of stomach and colon plus rectum, but higher dressing percentages, longissimus muscle areas, weights of trimmed Boston butts, picnics and loins, ham lean and predicted amounts of muscle than pigs not fed ractopamine (P less than .05). Supplemental ractopamine had no effect on fasting plasma concentrations of urea N, nonesterified fatty acids, triglyceride or glucose (P greater than .05). No genotype x ractopamine interactions for the criteria described above were detected (P greater than .05). These results suggest that ractopamine will improve the efficiency of feed utilization and carcass leanness in swine with different propensities for body fat deposition.     

Ractopamine treatment biases in the prediction of pork carcass composition

Carcass and live measurements of 45 barrows were used to evaluate the magnitude of ractopamine (RAC) treatment prediction biases for measures of carcass composition. Barrows (body weight = 69.6 kg) were allotted by weight to three dietary treatments and fed to an average body weight of 114 kg. Treatments were: 1) 16% crude protein, 0.82% lysine control diet (CON); 2) control diet + 20 ppm RAC (RAC16); 3) a phase feeding sequence with 20 ppm RAC (RAC-P) consisting of 18% crude protein (1.08% lysine) during wk 1 and 4, 20% crude protein (1.22% lysine) during wk 2 and 3, 16% crude protein (0.94% lysine) during wk 6, and 16% crude protein (0.82% lysine) during wk 6. The four lean cuts from the right side of the carcasses (n = 15/treatment) were dissected into lean and fat tissue. The other cut soft tissue was collected from the jowl, ribs, and belly. Proximate analyses were completed on these three tissue pools and a sample of fat tissue from the other cut soft tissue. Prediction equations were developed for each of five measures of carcass composition: fat-free lean, lipid-free soft tissue, dissected lean in the four lean cuts, total carcass fat tissue, and soft-tissue lipid mass. Ractopamine treatment biases were found for equations in which midline backfat, ribbed carcass, and live ultrasonic measures were used as single technology sets of measurements. Prediction equations from live or carcass measurements underpredicted the lean mass of the RAC-P pigs and underpredicted the lean mass of the CON pigs. Only 20 to 50% of the true difference in fat-free lean mass or lipid-free soft-tissue mass between the control pigs and pigs fed RAC was predicted from equations including standard carcass measurements. The soft-tissue lipid and total carcass fat mass of RAC-P pigs was overpredicted from the carcass and live ultrasound measurements. Prediction equations including standard carcass measurements with dissected ham lean alone or with dissected loin lean reduced the residual standard deviation and magnitude of biases for the three measures of carcass leanmass. Prediction equations including the percentage of lipid of the other cut soft tissue improved residual standard deviation and reduced the magnitude of biases for total carcass fat mass and soft-tissue lipid. Prediction equations for easily obtained carcass or live ultrasound measures will only partially predict the true effect of RAC to increase carcass leanness. Accurate prediction of the carcass composition of RAC-fed pigs requires some partial dissection, chemical analysis, or alternative technologies.     

Comparison of feed energy costs of maintenance, lean deposition, and fat deposition in three lines of mice selected for heat loss

Three replications of mouse selection populations for high heat loss (MH), low heat loss (ML), and a nonselected control (MC) were used to estimate the feed energy costs of maintenance and gain and to test whether selection had changed these costs. At 21 and 49 d of age, mice were weighed and subjected to dual x-ray densitometry measurement for prediction of body composition. At 21 d, mice were randomly assigned to an ad libitum, an 80% of ad libitum, or a 60% of ad libitum feeding group for 28-d collection of individual feed intake. Data were analyzed using 3 approaches. The first approach was an attempt to partition energy intake between costs for maintenance, fat deposition, and lean deposition for each replicate, sex, and line by multiple regression of feed intake on the sum of daily metabolic weight (kg(0.75)), fat gain, and lean gain. Approach II was a less restrictive attempt to partition energy intake between costs for maintenance and total gain for each replicate, sex, and line by multiple regression of feed intake on the sum of daily metabolic weight and total gain. Approach III used multiple regression on the entire data set with pooled regressions on fat and lean gains, and subclass regressions for maintenance. Contrasts were conducted to test the effect of selection (MH - ML) and asymmetry of selection [(MH + ML)/2 - MC] for the various energy costs. In approach I, there were no differences between lines for costs of maintenance, fat deposition, or protein deposition, but we question our ability to estimate these accurately. In approach II, selection changed both cost of maintenance (P = 0.03) and gain (P = 0.05); MH mice had greater per unit costs than ML mice for both. Asymmetry of the selection response was found in approach II for the cost of maintenance (P = 0.06). In approach III, the effect of selection (P < 0.01) contributed to differences in the maintenance cost, but asymmetry of selection (P > 0.17) was not evident. Sex effects were found for the cost of fat deposition (P = 0.02) in approach I and the cost of gain (P = 0.001) in approach II; females had a greater cost per unit than males. When costs per unit of fat and per unit of lean gain were assumed to be the same for both sexes (approach III), females had a somewhat greater estimate for maintenance cost (P = 0.10). We conclude that selection for heat loss has changed the costs for maintenance per unit size but probably not the costs for gain.