Genome-wide population structure and admixture analysis reveals weak differentiation among Ugandan goat breeds.

Uganda has a large population of goats, predominantly from indigenous breeds reared in diverse production systems, whose existence is threatened by crossbreeding with exotic Boer goats. Knowledge about the genetic characteristics and relationships among these Ugandan goat breeds and the potential admixture with Boer goats is still limited. Using a medium-density single nucleotide polymorphism (SNP) panel, we assessed the genetic diversity, population structure and admixture in six goat breeds in Uganda: Boer, Karamojong, Kigezi, Mubende, Small East African and Sebei. All the animals had genotypes for about 46 105 SNPs after quality control. We found high proportions of polymorphic SNPs ranging from 0.885 (Kigezi) to 0.928 (Sebei). The overall mean observed (HO ) and expected (HE ) heterozygosity across breeds was 0.355 ± 0.147 and 0.384 ± 0.143 respectively. Principal components, genetic distances and admixture analyses revealed weak population sub-structuring among the breeds. Principal components separated Kigezi and weakly Small East African from other indigenous goats. Sebei and Karamojong were tightly entangled together, whereas Mubende occupied a more central position with high admixture from all other local breeds. The Boer breed showed a unique cluster from the Ugandan indigenous goat breeds. The results reflect common ancestry but also some level of geographical differentiation. admixture and f4 statistics revealed gene flow from Boer and varying levels of genetic admixture among the breeds. Generally, moderate to high levels of genetic variability were observed. Our findings provide useful insights into maintaining genetic diversity and designing appropriate breeding programs to exploit within-breed diversity and heterozygote advantage in crossbreeding schemes.

Between-breed variations in resistance/resilience to gastrointestinal nematodes among indigenous goat breeds in Uganda.

Gastrointestinal nematodes (GINs), Haemonchus contortus, are a major health problem in goat production. Resistance to H. contortus, the most prevalent GIN in Uganda, was studied among three indigenous goat breeds to assess their differences. Twelve male goats of each breed approximately 7 months old of small East African (SEA), Mubende, and Kigezi goats from smallholder farmers in Arua, Mubende, and Kabale were assembled for the study. At the station, they were dewormed with a combination therapy of the broad-spectrum dewormers closantel and albendazole to free the goats of gastrointestinal parasites. During experimentation, the goats were kept indoors and ad libitum fed on clean banana peels and napier grass. On attainment of zero-worm-egg status, the goats were artificially infected with 18,000 third-stage (L3) larvae of H. contortus prepared according to Baermann's procedure. Data were collected on fecal egg count (FEC), packed cell volume (PCV), and body weight (BW) on a 2-week basis until 12 weeks post infection and carcass weight and total worm count (WC) in the abomasum at termination of the experiment. The data on FEC, PCV, and BW were subjected to repeated-measure analysis of variance and the others by one-way analysis of variance. FEC between breeds was only significantly different at 12 weeks post infection (p = 0.04). Generally, higher FEC was recorded in Kigezi compared to SEA and Mubende goats. Carcass weight was significantly different among breeds (p < 0.05), with Mubende having the highest carcass weight, followed by Kigezi and SEA. PCV and daily weight gains were significantly different between breeds (p < 0.05). WC was not significantly different between the breeds. FEC and PCV were weakly significant at later stages of the experiment with higher parasite burden suggesting potential variation in resistance to H. contortus. These differences could be exploited in designing breeding programs with disease resistance in indigenous goat breeds.

Genetic correlations between lactation performance and growing-finishing traits in pigs.

Genetic selection for increased litter size of sows increases the risk of a large negative energy balance during lactation. Furthermore, the feed intake capacity of the lactating sows might be reduced due to the simultaneous selection for greater feed efficiency during the growth phase when sows were actually reared as finishers but later on selected for breeding. There is a need to improve lactation performance of sows and continue selection for feed efficiency of grower-finishers in commercial breeding. Therefore, this study was conducted to estimate genetic correlations between growing-finishing traits and lactation performance traits. An additional objective was to study the impact of including additive social effects in the animal model on genetic correlation estimates. Analyses were performed on a population of 1,149 commercial crossbred sows with repeated observations on lactation performance traits and their 7,723 grower-finisher offspring. The genetic correlation between daily BW gain of grower-finishers and starting BW of lactating sows was positive (rg = 0.24; P < 0.05). The correlation between off-test backfat of grower-finishers and fat mass of lactating sows was also positive (rg = 0.53; P < 0.05). The genetic regulation of feed intake from the beginning of lactation seems to differ from the genetic regulation of feed intake during the growing-finishing period, as the correlation between these 2 traits was low (rg = +0.23; P < 0.05). Feed efficiency during growing-finishing and lactation phases showed similar tendencies as the genetic correlation between residual feed intake of the grower-finisher and lactation efficiency of sows was -0.51 (P < 0.05). Taking heritable social effects into account for daily BW gain and feed intake did not affect the genetic correlation estimates, either within growing-finishing traits or between growing-finishing traits and lactation performance traits. It was concluded that in the absence of antagonistic genetic correlations, selection for growing-finishing traits in dam lines could be combined with selection for lactation performance traits.

Nitrogen excretion at different stages of growth and its association with production traits in growing pigs.

The objectives of this study were to determine nitrogen loss at different stages of growth and during the entire growing period and to investigate the associations between nitrogen excretion and production traits in growing pigs. Data from 315 pigs of an F(2) population which originated from crossing Pietrain sires with a commercial dam line were used. Nitrogen retention was derived from protein retention as measured using the deuterium dilution technique during different stages of growth (60 to 90 kg, 90 to 120 kg, and 120 to 140 kg). Pigs were fed ad libitum with 2 pelleted diets containing 17% (60 to 90 kg) and 16.5% (90 to 120 and 120 to 140 kg) CP. Average daily nitrogen excretion (ADNE) within each stage of growth was calculated on the basis of the accumulated difference between average daily nitrogen intake (ADNI) and average daily nitrogen retention (ADNR). Least ADNE, nitrogen excretion per BW gain (NEWG) and total nitrogen excretion (TNE) were observed during growth from 60 to 90 kg. In contrast, the greatest ADNE, NEWG, and TNE were found during growth from 120 to 140 kg. Statistical analyses indicated that gender, housing type, the ryanodine receptor 1 (RYR1) gene, and batch influenced nitrogen excretion (P < 0.05), but the degree and direction of influences differed between growth stages. Gender differences showed that gilts excreted less nitrogen than barrows (P < 0.05), which was associated with decreased feed conversion ratio (FCR; feed:gain) and lipid:protein gain ratio. Single-housed pigs showed reduced nitrogen excretion compared with group-housed pigs (P < 0.05). In comparison to other genotypes, pigs carrying genotype NN (homozygous normal) at the RYR1 locus had the least nitrogen excretion (P < 0.05) at all stages of growth except from 60 to 90 kg. The residual correlations indicated that NEWG and TNE have large positive correlations with FCR (r = 0.99 and 0.91, respectively) and moderate negative correlations with ADG (r = -0.53 and -0.48, respectively), for the entire growing period. Improvement in FCR, increase in ADG and reduction in lipid:protein gain ratio by 1 phenotypic SD reduced TNE per pig by 709 g, 307 g, and 211 g, respectively, over the entire growing period. The results indicate that nitrogen excretion changes substantially during growth, and it can be reduced most effectively by improvement of feed efficiency and to a lesser extent through the improvement of BW gain or body composition or both.

The contribution of social effects to heritable variation in finishing traits of domestic pigs (Sus scrofa).

Social interactions among individuals are ubiquitous both in animals and in plants, and in natural as well as domestic populations. These interactions affect both the direction and the magnitude of responses to selection and are a key factor in evolutionary success of species and in the design of breeding schemes in agriculture. At present, however, very little is known of the contribution of social effects to heritable variance in trait values. Here we present estimates of the direct and social genetic variance in growth rate, feed intake, back fat thickness, and muscle depth in a population of 14,032 domestic pigs with known pedigree. Results show that social effects contribute the vast majority of heritable variance in growth rate and feed intake in this population. Total heritable variance expressed relative to phenotypic variance was 71% for growth rate and 70% for feed intake. These values clearly exceed the usual range of heritability for those traits. Back fat thickness and muscle depth showed no heritable variance due to social effects. Our results suggest that genetic improvement in agriculture can be substantially advanced by redirecting breeding schemes, so as to capture heritable variance due to social effects.

Genetic parameters and predicted selection results for maternal traits related to lactation efficiency in sows.

The increased productivity of sows increases the risk of a more pronounced negative energy balance during lactation. One possibility to prevent this is to increase the lactation efficiency (LE) genetically and thereby increase milk output for a given feed intake and mobilization of body tissue. The benefits of selection for LE depend on its heritability and the relationships with other traits of interest. The objectives of this study were to estimate genetic parameters for LE, its underlying traits, and to predict the consequences of current selection strategies in dam lines. Data from 4 farms were available to estimate genetic parameters. Heritabilities were estimated by using a univariate repeatability model, and genetic correlations were estimated bivariately. Selection index theory was used to predict the genetic progress by 3 alternative breeding programs: 1) a breeding program that aimed at balanced progress in the total number of piglets born, piglet mortality, and percent prolonged interval from weaning to estrus; 2) extension of this breeding goal with LE; and 3) a breeding goal that included only one selection criterion, litter weight gain, to demonstrate the effect of indirect selection for milk production. The heritability for LE was low (0.12). Body fat mass (0.52) and BW (0.45) of sows at the beginning of lactation showed the greatest heritabilities. Protein mass at the beginning of lactation, protein loss, weight loss, and ad libitum feed intake during lactation showed moderate heritabilities (0.39, 0.21, 0.20, and 0.30, respectively). Low to moderate heritabilities were found for litter weight at birth, within-litter SD in the birth weight of piglets, litter weight gain, fat loss, and restricted feed intake during lactation (0.19, 0.09, 0.18, 0.05, and 0.14, respectively). Within-litter SD in the weaning weight of piglets showed no genetic variability. It was predicted that a breeding goal for dam lines with an emphasis on the total number of piglets born, piglet mortality, and percent prolonged interval from weaning to estrus would not dramatically change BW or body composition at the beginning of lactation, or mobilization of body tissue and feed intake during lactation. Inclusion of LE in the breeding goal will improve stayability, as defined by the first-litter survival of sows and LE itself, without negative consequences for other economically important traits. Nevertheless, it might be worthwhile to design a breeding goal in which LE increases and feed intake remains unchanged.

Breeding for societally important traits in pigs.

Pig breeding programs traditionally focus on the genetic improvement of production and reproduction traits that have a clear economic value. Because citizens and consumers increasingly attach value to traits that have little or no direct relationship to production costs or to the price of a product, pig breeding organizations want to pay more attention to societally important traits, such as the welfare and health of pigs, the ecological effects of pork production, and the healthiness and sensory quality of pork. Most societally important traits have an economic and a noneconomic value and are sufficiently heritable for effective genetic selection, although many genetic and phenotypic (co)-variances still have to be estimated. However, it often is not clear to a pig breeding organization how it may deal with the noneconomic value of breeding-goal traits. In this study, a retrospective selection-index method is proposed to obtain the proper weights for societally important traits in the breeding goal. First, the genetic-progress space for each breeding-goal trait is explored by increasing the weights, in a stepwise manner, to each societally important trait in the breeding goal, starting from zero. Subsequently, a pig breeding organization can adopt the resulting genetic-progress scenario that it considers most sustainable or most acceptable. The weights underlying the adopted scenario are considered to be the proper breeding-goal weights. The noneconomic value of each societally important breeding-goal trait is found by deducting its economic value from its obtained weight and is thereby expressed in monetary units. In addition to obtaining weights for societally important breeding-goal traits, the proposed method offers the possibility to estimate the societal costs of selecting for economic traits only, as well as the societal benefits and the economic costs of selecting for traits with a noneconomic value. The method is therefore a useful tool for the development of sustainable breeding goals. An example has been worked out for a sow-line breeding program.

Economic weights for feed intake in the growing pig derived from a growth model and an economic model.

Economic weights are obtained for feed intake using a growth model and an economic model. The underlying concept of the growth model is the linear plateau model. Parameters of this model are the marginal ratio (MR) of extra fat and extra protein deposition with increasing feed intake (FI) and the maximum protein deposition (Pd(max)). The optimum feed intake (FI0) is defined as the minimum feed intake that meets energy requirements for Pd(max). The effect of varying FI and MR on performance traits was determined. An increase in FI results in a larger increase in growth rate with lower MR. For a given MR, feed conversion ratio is lowest when FI equals FI0. Lean meat percentage (LMP) is largest for a low MR in combination with a low FI. The decrease in LMP with higher FI islargest when FI exceeds FI0. Economic weights for FI, MR and Pd(max) depend on FI in relation to FI0. Economic weights for FI are positive when FI is less than FI0 and negative when FI is larger than FI0. The MR has only then a negative economic weight, when FI is below FI0. Economic weights of FI and MR have a larger magnitude with lower MR and lower Fl. In contrast, economic weights for growth rate and FI derived from the economic model only change in magnitude and not in sign with different levels of these traits. The economic model always puts a negative economic weight on FI since it expresses profit due to a decrease in FI with constant growth rate and LMP. This holds the risk of continuous decrease in FI in pig breeding programs. In contrast, the use of growth models for genetic improvement allows direct selection for an optimum feed intake which maximizes feed efficiency in combination with maximum lean meat growth. It is concluded that recording procedures have to be adapted to collect the data necessary to implement growth models in practical pig breeding applications.

The importance of a high feed intake during lactation of primiparous sows nursing large litters.

The objective of this study was to investigate whether nursing a large number of piglets has negative effects on lactation and postweaning performance of primiparous sows and whether a greater lactation feed intake can prevent possible negative effects. Data were recorded on 268 ad libitum-fed sows of three genotypes (G1, G2, and G3) in an experiment where litter size was standardized to 8, 11, or 14 piglets during a 4-wk lactation. Compared to G1 and G2, G3 sows were heavier (P < 0.05) and leaner (P < 0.05) at weaning of their litters, lost similar amounts of BW and backfat, and their piglets grew faster (P < 0.05). Compared to G1, feed intake during lactation was higher for G3 sows (P < 0.05), and their risk of a prolonged weaning-to-estrus interval was lower (P < 0.01). Daily feed intake by sows was not affected by litter size in G1 and G3, but it was quadratically affected in G2 (P < 0.05), with a maximum at 10.8 piglets. Backfat loss of the sows increased linearly with litter size (P < 0.05) in G1 and G3. In G2, backfat loss increased only at litter sizes > 9.8 piglets (P < 0.01). Body weight loss of the sow and litter weight gain increased linearly with litter size (P < 0.001). Per extra piglet nursed, sows had a 23% (P < 0.01) higher probability of a prolonged weaning-to-estrus interval. A higher daily feed intake during lactation reduced tissue loss of the sow, increased litter weight gain (P < 0.01), and reduced the probability of a prolonged weaning-to-estrus interval (by 42% per extra kilogram; P < 0.01). Sows with a lower daily body weight loss during first lactation had a larger second litter (1.28 piglets/kg; P < 0.01), and their probability of a prolonged weaning-to-estrus interval was reduced by 61% per kilogram (P < 0.001). With increasing litter size, it is therefore recommended to reduce body weight loss during lactation by stimulating daily feed intake and by genetic selection.

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.

Effect of missing data on the estimate of average daily feed intake of growing pigs.

The effect of missing records for feed intake per day (FID) on the estimate of average daily feed intake (DFI) during the test period of individual pigs was studied. Data from 192 growing pigs tested with single-space computerized feeding stations during an average of 93 d were used. True DFI was computed by averaging FID records per pig, individually. A first- and third-degree polynomial and a nonlinear function were fit to FID records per pig to estimate DFI by averaging estimated FID records per pig, individually. The three functions showed small differences for goodness of fit. Missing FID records were simulated by random as well as period-wise deletions of FID records. The effect of missing FID records was judged on the Pearson correlation between true and estimated DFI. Deleting randomly up to 70% of FID records per pig before fitting each function reduced this correlation only from 1.00 to .96 for each function. Deleting 25 successive FID records (approximately 27% of records) before fitting reduced the correlation to values ranging from .92 to .96 and from .59 to .96 for the first- and third-order degree polynomial function, respectively, and from .80 to .97 for the nonlinear function. Using iteratively reweighted least squares regression methods to exclude undesirable effects of outlier values gave similar results for the effect of missing FID records on estimated DFI. Results imply that considering incorrect FID records as missing is a good alternative for adjusting incorrect data in combination with using functions to estimate DFI of growing pigs. Use of a first-degree polynomial function is recommended. Moreover, use of functions enables a more efficient use of feeding stations by recording feed intake data during only parts of the test period.

Repeatability of taste panel tenderness scores and their relationships to objective pig meat quality traits.

Repeatabilities of 12 meat quality measurements were calculated as a value for the accuracy of those measurements. Sixty-four Duroc and Dutch Yorkshire boars and gilts were slaughtered during 8 wk. The repeatabilities between carcass halves within animals were .53 for repeated taste panel tenderness scores based on 12.4 observations of different panelists per mean, .08 for two repeated tenderness scores of different panelists within one animal, .50 for two repeated tenderness scores of one panelist within one animal, and 41 for repeated measurements of maximum shear force. Repeatabilities of other meat quality traits ranged from .29 for cooking loss to .76 for the Minolta L* color coordinate. The phenotypic correlation between tenderness assessed by a panel and maximum shear force was -.50. The phenotypic correlation between those traits corrected for measurement errors was -.74. A correlation of zero was found between the total amount of collagen and meat tenderness, between amount of intramuscular fat and tenderness, and between ultimate pH and tenderness. The other correlations with meat tenderness ranged from -.00 for Minolta b* color coordinate to -.44 for drip loss. It was concluded that the measurement of maximum shear force can be used as an effective indicator of pig meat tenderness.

Economic values of optimum traits: the example of meat quality in pigs.

In this paper a method is outlined to derive marginal-income functions and to calculate economic values for traits with an intermediate optimum such as meat-quality traits. A normal distribution of the quality trait was assumed, but the method can be used for other distributions as well. The parameters necessary to use this method are distribution of the quality trait, population mean and the standard deviation of the quality trait, optimum range, and price differences between products within and outside the optimum range. Especially, the optimum range for the quality trait and the price differences to be used have to be derived from consumer and processing research. Some alternative methods that can be used for selection on quality traits, such as restricted selection index, desired-gains index, and indices based on a quadratic aggregate genotype, are discussed.

Effects of recombinant porcine somatotropin on metabolic rate in growing pigs.

Effects of recombinant porcine somatotropin (rpST) on metabolic rate were studied in two trials with 24 crossbred barrows (Yorkshire x Landrace) in each. The barrows weighed about 80 kg (SE within trials 2.2 kg) at the start of the measurements and in each trial 12 pigs received 4 mg of rpST and 12 received a placebo. The diet contained 2.57 Mcal NE/kg and 20% CP (about 1% lysine). Animals were fed approximately 2.8 times maintenance (280 kcal ME.kg-.75.d-1). Heat production (gaseous exchange of CO2 and O2) and activity were measured continuously. Heat production associated with activity was calculated from the regression of heat production on activity. Animals treated with rpST exceeded controls in rate of gain by 252 g/d (P less than .001) and in metabolic rate by 14.5 kcal.kg-.75.d-1 (P less than .01). The rpST treatment increased rectal (+ .2 degrees C) and surface (+ .8 degrees C) temperatures. Activity-related heat production in treated pigs was increased, but this was only partly related to the increase in metabolic rate with rpST. The daily patterns of total and activity-related heat production were similar between pigs in both experimental treatments.

Effect of recombinant porcine somatotropin on body composition and meat quality in growing pigs; Interactions with genotype, sex and slaughter weight.

Body composition in 96 pigs and meat quality in 36 pigs treated with porcine somatotropin (rpST) were investigated. Animals included both barrows and gilts from Pietrain, F(1) (Dutch Yorkshire × Dutch Landrace) and Duroc and were slaughtered at either 100 or 140 kg live weight. Treatment consisted of either 14 mg rpST or placebo twice weekly and started at 60 kg. Treatment with rpST enhanced the proportion of lean parts (on average +2·8% at 100 kg and + 5·5% at 140 kg) and reduced the proportion of fatty parts (-10·1% and -12·9% respectively). The latter tended to be more apparent in fatter animals (Duroc -14·5% and -13·3%, barrows -12·0% and -13·7%). Most organs increased in weight, especially kidneys (+14·8% at 100 kg and +17·6% at 140 kg). Meat quality parameters appeared to be not significantly affected, though intramuscular fat percentage was slightly decreased. Administration of rpST led to less fat and more uniformity in carcasses and meat quality among genotypes and sexes. No serious adverse effects were detected.

Effect of recombinant porcine somatotropin on growth and carcass quality in growing pigs: interactions with genotype, gender and slaughter weight.

Effects of recombinant porcine somatotropin (rpST) on growth, lean tissue growth, feed intake, feed conversion, lean tissue feed conversion, backfat thickness and lean percentage were examined in 96 growing pigs. The experiment used barrows and gilts from the genotypes Duroc, F1 (Dutch Yorkshire x Dutch Landrace) and Pietrain. Half the pigs received 14 mg rpST i.m. twice each week starting at 60 kg; others received a placebo. Pigs had ad libitum access to a diet containing 2,162 kcal net energy and 182 g crude protein per kilogram and were slaughtered at either 100 or 140 kg live weight. From 60 to 100 and from 100 to 140 kg, live weight responses to rpST averaged as follows: daily gain, +4.5 and +19.9%; feed intake, -4.4 and +3.5%; feed conversion, -8.4 and -13.9%; backfat thickness, -13.8 and -22.8%; lean percentage, +4.4 and +8.7%; lean tissue growth rate, +8.6 and +35.8%; and lean tissue feed conversion, -13.1 and -24.9%. No gender x rpST interaction was detected. However, a genotype x treatment interaction was significant for backfat thickness at both slaughter weights, showing a higher response to rpST in Duroc than in Pietrain and F1. Growth performance was improved more by rpST in F1 and Pietrain than in Duroc, especially at higher weights, but carcass traits were improved more by rpST in Duroc. The response to rpST in lean tissue growth rate from 60 to 100 kg was highest in fatter animals (Duroc, barrows), whereas from 100 to 140 kg, response in lean tissue growth rate to rpST was highest in leaner animals (Pietrain, F1, gilts).

Effect of exogenous porcine somatotropin administration on nitrogen and energy metabolism in three genotypes of pigs.

Effects of exogenous administration of porcine recombinant somatotropin (rpST) on protein gain and metabolic rate were measured in three genotypes (castrated males) of pigs (Pietrain, Duroc and a crossbreed between Dutch Yorkshire and Dutch Landrace). Six pigs of each genotype were assigned at approximately 60 kg to receive pST doses of either 0 (C) or 14 mg (T) administered i.m. twice weekly over 10 wk. Pigs were housed in individual metabolism cages at a room temperature of 20 to 22 degrees C and received feed at 2.6 times maintenance. Protein gain (N x 6.25) was measured over the final 6 wk of the 10-wk test period. For 2 wk in the test period (wk 2 and wk 5), six pigs of each treatment x genotype group were placed in a large respiration chamber and energy balances (in protein and fat) and metabolic rate were measured. Rate of weight gain measured over the final 6 wk of the experimental period increased by 105 g/d (13%) with rpST administration (P less than .01). Daily protein gain over 6 wk was increased by 48 g/animal with application of rpST (P less than .001). There was a genotype x treatment interaction (P less than .01) for protein gain. Daily protein gain in Durocs with pST treatment was increased (39%) more than in crossbreds (31%). Daily fat gain was decreased by 42 g/animal (P less than .001) by T. Daily heat production with rpST was increased by 12 kcal/kg.75, which is comparable to a 12% increase in the maintenance energy requirement.