Genetic parameters of growth curve parameters in male and female chickens.

1. Individual growth curves of 7143 chickens selected for the form of the growth curve were fitted using the Laird form of the Gompertz function, BW4=BW0xe(L/K)(1-e-Kt) where BWt is the body weight at age t, BW0 the estimated hatching weight, L the initial specific growth rate and K the maturation rate. 2. Line and sex effects were significant for each parameter of the growth curve. In males, L, BW0, age and body weight at inflection (T(I)and BWI) were higher whereas K was lower than in females. Lines selected for high adult body weight had higher BW0 and BW(I) whereas lines selected for high juvenile body weight had larger estimates of L and lower estimates of T(I). 3. Data from 38,474 animals were included in order to estimate the genetic parameters of growth curve parameters in males and females, considering them as sex-limited traits. Genetic parameters were estimated with REML (REstricted Maximum Likelihood) and an animal model. Maternal genetic effects were also included. 4. Heritabilities of the growth curve parameters were moderate to high and ranged between 0.31 and 0.54, L, BW0 in both sexes and BW(I) in males exhibited significant maternal heritability. Heritabilities differed between males and females for BWI and T(I). Genetic correlations between sexes differed significantly from one for all parameters. L, K and T(I) were highly correlated but correlations involving BW0 and BW(I) were low to moderate. 5. Sexual dimorphism of body weight at 8 and 36 weeks and of L, K and T(I) was moderately heritable. Selection on growth curve parameters could modify the difference between sexes in precocity and thus in body weight at a given age.     

Divergent selection for shape of growth curve in Japanese quail. 1. Responses in growth parameters and food conversion.

1. HG and LG quail lines selected for high and low relative weight gain between 11 and 28 d of age (RG11-28), respectively, and an unselected C line were compared. Mature body weight of both selected lines was held at that of the C line. Progeny of generation 6 were used for analysis. 2. Divergent selection for RG11-28 brought about opposite changes in the growth rates shortly after hatching. 3. Parameters of the Richards function were used to describe the growth curve. The largest differences between HG and LG lines occurred in age (t+) and body weight (y+) at the inflection point of the growth curve (on average for both sexes 28% and 20%, respectively). For HG quail, the parameter t+ was 5 d later than that for LG quail (18.6 vs 14.1 d for males and 20.6 vs 15.6 d for females, respectively), and consequently the parameter y+ was greater (90.3 vs 84.0 g for males and 104.5 vs 96.1 g for females, respectively). The shape of the growth curve expressed by the y+/A ratio was substantialy different for HG and LG quail (44.8% vs 39.6% for males and 43.5% vs 36.8% for females, respectively). 4. The food/gain ratios for the fattening period (3 to 35 d of age) were 3.21, 3.47 and 3.34 for the HG, LG and C lines, respectively. The HG quail started to utilise food more efficiently than the LG quail as early as 10 to 14 d, that is, at the age when their relative growth rate first became greater. 5. The relative deviations of the HG and LG lines from the C line are discussed.     

Modifying growth curve parameters by multitrait genomic selection

The use of genomic selection for changing the growth curve shape of animals, acting simultaneously on the 3 parameters of a Gompertz growth curve, was studied using computer simulation. Results showed that genomic selection modified the growth curve. Responses to all selection criteria were accompanied with a correlated response in mature weight due to the high genetic correlations between mature weight and the 2 rate parameters. Responses to selection were affected by the loss of accuracy over generations of genomic selection due to the loss of gametic disequilibrium between SNP and genes determining the parameters. In conclusion, genomic selection can be used for changing growth curve parameters. However, changing the whole curve (birth weight, adult BW, and curve shape) is not easy due to the correlation between all BW along the growth of the animal. Applying genomic selection will require a constant reevaluation of the associations between SNP and genes determining the curve parameters.     

Genetic parameters in two populations of chickens under reciprocal recurrent selection

Genetic information on two traits, age at sexual maturity and survivors’ per cent production, was obtained from two strains of the White Leghorn breed under a reciprocal recurrent selection scheme where the reciprocal crosses were raised at three locations representing diversified environments.

Genotype by environment interactions were detected by a number of methods; (1) from analyses of variance of sire means within years and over locations where sires, locations, and sire by location interactions were important sources of variation; (2) from genetic correlations of the same trait at different locations; (3) from comparisons of the components that constitute the genetic correlations between the two traits at the same versus different locations.

The sire by location interaction variance components when taken as a percentage of the total variation, although not large, 10 per cent for sexual maturity and 8 per cent for egg production, were found to be significant sources of variation.

The genetic correlations between the age at sexual maturity and per cent production had a negative relationship when studied at the same or at different locations. Positive relationships, with one exception, of small magnitude were observed from genetic correlations of the sire's purebred and crossbred progeny.     

Divergent selection for shape of growth curve in Japanese quail. 2. Embryonic development and growth

1. Embryonic growth and development were analysed using meat type lines of Japanese quail, HG and LG, divergently selected for shape of the growth curve. A total of 1020 embryos of generations 9, 10 or 13 were used for analysis. 2. Considerable inter-line differences were observed in the rate of embryonic development. When compared to HG, LG embryos appeared to be developmentally accelerated during the first 42 h of incubation (larger blastoderm diameter, more somites and higher frequency of more advanced Hamburger-Hamilton stages) as well as at the end of the prenatal period (more embryos with the yolk sac inside the body cavity, shorter incubation period). This corresponded with the trend in postnatal development. 3. Embryonic growth of both lines exhibited an exponential trend. However, considerable inter-line differences were noted in the rate of embryonic growth. Initial growth retardation compensated subsequently by a higher growth rate of HG vs LG quail, characterised the lines after hatching. The same growth pattern repeated three times during the prenatal period (between d 0 and 3, 3 and 8, and 8 and 16). 4. The repeated occurrence of transient decreases in growth rate of the developmentally delayed HG line could be associated with a delayed onset of genetically determined physiological functions mediating utilisation of nutrient supply. 5. Hence, different shapes of growth curves in two genotypes with similar growth potential reveal inter-line differences in physiological age persisting during the whole ontogenesis.     

Divergent selection for shape of the growth curve in Japanese quail. 8. Effect of long-term selection on embryonic development and growth

1. Changes in embryonic development and growth were analysed in relation to direct changes in postnatal growth and correlated responses in egg parameters using Japanese quail lines selected for more than 30 generations for high (HG) and low (LG) relative gain of body weight (BW) between 11 and 28 d of age, and constant BW at 49 d of age.

2. During the first 42 h as well as at the end of incubation, LG embryos were developmentally accelerated in comparison with their HG counterparts. An expected increase of line divergence across generations was observed only in traits analysed at the end of incubation.

3. In contrast to early generations, LG embryos continuously exhibited a higher BW than HG embryos and this difference temporarily disappeared only around incubation d 8. Analogous to early generations, the HG compared with LG embryos showed two periods of transient growth retardation compensated subsequently by a higher growth rate (incubation d 3–8 and 8–16).

4. More pronounced growth retardation of HG versus LG embryos in late versus early generations corresponded to more distinct decrease of HG versus LG growth rate during the first post-hatch days. Likewise, a disappearance of line BW differences on incubation d 8 characterising the late generations corresponded to the elimination of line differences in adult BW.

5. Alterations of growth pattern were associated with changes of egg size. While HG quail maintained a relatively constant adult BW and egg size across generations, the gradually increasing incidence of large eggs in the LG line allowed selection of birds with higher growth potential, which in turn amplified the line differences in the embryonic BW and eliminated the line differences in adult BW. Line differences in egg composition (larger albumen with lower density in LG compared with HG eggs) apparently contributed to the strengthening of line developmental divergence during incubation.

6. Transient lack of nutrient supply to HG embryos due to their developmental delay is probably responsible for a higher HG versus LG embryo mortality.     

Genetic and environmental aspects of the growth curve parameters in beef cows

Brody's growth curve, a three-parameter function, and Richards' function, a four-parameter function, were fit to data from 233 inbred and linecross cows to study the genetic and environmental aspects of the growth curve parameters and to compare the two functions. Fitting Brody's curve was faster and less costly to compute than Richards' function, but Richards' function had smaller sums of squares and a better fit to actual data points. Year of birth had an effect on the A (P less than .05), b (P less than .01) and k (P less than .01) parameters of Brody's curve. Parameter estimates from data of the youngest cows were at the extremes. The b parameter was the largest when estimated from data with no recorded birth weights. Year of birth was also an important effect for the b (P less than .01), k (P less than .05) and m (P less than .01) parameters of Richards' function, but year effects were less interpretable. Mating system affected (P less than .01) the A parameter of both functions; inbreds were lighter than linecrosses at maturity. Line of sire was an important source of variation (P less than .01) for the A parameter of both functions. The heritability estimate of the A parameter from both functions was .44 +/- .27; apparently the same trait in both curves. The estimate for the b parameter from Brody's curve was .39 +/- .27, comparable with literature estimates of birth weight. The heritability estimate for k from Brody's curve was .20 +/- .26. The heritability estimates for b, k and m parameters from Richards' function were .24 +/- .26, .32 +/- .27 and .21 +/- .26, respectively. The genetic correlations between the A and k parameters in both curves indicated that cows with lighter mature weights reached that weight at younger ages.     

Genetic relationships between feed conversion ratio, growth curve and body composition in slow-growing chickens

1. Relationships between feed conversion ratio, growth curve parameters and carcase composition were investigated on 1061 chickens from a slow-growing line of label-type chickens. The growth curve was modelled with the Gompertz function. Individual feed conversion ratio (FCR) was recorded between 8 and 10 weeks of age and residual feed consumption (RES) was calculated over the same interval. Abdominal fat yield (AFY), breast yield (BRY) and leg yield (LY) were also measured on the birds following slaughter at 75 d of age. 2. The means for FCR and RES were 3.15 and 0.62 g, respectively. Growth curve parameters were 0.141/d for initial specific growth rate (L), 0.031/d for maturation rate (K) and 48.9 d for age at inflexion (TI). Mean values for BRY, LY and AFY were 166, 306 and 40 g/kg, respectively. 3. Heritability of FCR and RES were moderate to high (0.33 and 0.38 to 0.45). Growth curve parameters and LY were moderately heritable (0.22 to 0.34) and BRY and AFY were highly heritable (0.50 and 0.66). Genetic correlations between growth curve parameters and either FCR or RES were low to moderate (-0.31 to 0.51). LY and AFY were highly correlated with FCR (-0.70 and 0.44) and RES (-0.32 and 0.44) but BRY was not (0.00 and -0.35). These results show that indirect selection for feed conversion ratio is possible by using growth curve parameters and abdominal fatness, which do not require rearing the chickens in cages.     

Divergent selection for shape of growth curve in Japanese quail. 4. Carcase composition and thyroid hormones

1. Changes in the relative weights of carcase, abdominal fat, breast and leg muscles, and plasma thyroid hormone concentrations occurring during the first 6 weeks of postnatal growth were analysed in males of HG and LG lines divergently selected for high and low relative body weight (BW) gain between 11 and 28 d of age, respectively, and constant adult BW. 2. The second week of postnatal life was a critical age at which the HG males exhibited a relatively faster growth in comparison to their LG counterparts and permanently exceeded LG males in the percentage by weight of carcase, breast and leg muscle. A higher production of muscle tissues was associated with lower accumulation of abdominal fat before sexual maturity. 3. In general, the plasma T(3) level of HG quail exceeded that of LG quail. Nevertheless, significant differences were found only at 14, 21 and 28 d of age, that is, in the period during which the highest inter-line differences in relative growth rate were noted. Also the T(3)/T(4) ratio followed a similar trend while plasma T(4) level showed no clear and consistent inter-line differences. 4. The results suggest that the selection for the shape of the growth curve, like the selection for body fat, modifies the carcase quality owing to shortening/prolongation of the acceleration growth phase. Individuals with a short acceleration phase of the growth curve are characterised by low carcase quality during the fattening period.     

Genetic correlation between growth and female and male contributions to fertility in rabbit

A Bayesian bivariate Linear-Threshold Animal Model was implemented to determine the genetic correlation between fertility (F), defined as success or failure to conceive, and average daily gain (ADG) in a rabbit line selected for ADG. A total of 27 234 records of F from 7895 females and 1293 males, and 114 135 records of ADG were used for the analysis. The pedigree included 114 485 animals. The model used for ADG included the systematic effects of year-season, parity order and number of kids born alive, the animal additive effect, the maternal and paternal permanent environmental effects, the common litter permanent environmental effect and the residual. The model for the liability of F included the systematic effects of year-season and physiological status of the female, the female and male additive genetic effects, the female and male permanent environmental effects and the residual, which was divided into a permanent environmental effect related to the common litter effect for ADG, and an independent term. The estimated heritabilities were 0.15 for ADG and 0.07 and 0.04 for the female and male contributions to F, respectively. Male and female contributions to F had a positive genetic correlation (0.34). The genetic correlation between ADG and the female component of F was low to moderate and negative (-0.31), whereas it was null for the male contribution to F. Thus, it is expected that only the female contribution to reproductive performance may be impaired by selection for ADG in rabbit lines.     

固始鸡新品系生长发育曲线拟合分析

为了解固始鸡的生长发育规律，通过运用Logistic、Gompertz和Bertallanffy3种非线性模型分别对固始公、母鸡0-12周龄体重生长数据进行了曲线拟合和分析。结果表明，3种模型均能很好地模拟固始鸡生长曲线．拟合度均达到了0．997以上。经比较．3种生长曲线中以Bertallanffy模型拟合度最高为1．000．但其A值与实际观测值相差较大，不符合实际；Logistic模型A值与实际值比较接近，但拟合度相对较小；Gompertz模型拟合效果较佳，A值也比较接近实际值。进一步分析Gompertz模型拟合参数．发现固始公鸡成年体重（2273．859g）显著高于固始母鸡（1984．083g）。且固始公鸡拐点时间为7．541周，较固始母鸡的拐点时间7．686周早。     

Genetic and environmental parameters for traits derived from the Brody growth curve and their relationships with weaning weight in Angus cattle

Direct and maternal genetic and environmental variances and covariances were estimated for weaning weight and growth and maturing traits derived from the Brody growth curve. Data consisted of field records of weight measurements of 3,044 Angus cows and 29,943 weaning weight records of both sexes. Growth traits included weights and growth rates at 365 and 550 d, respectively. Maturing traits included the age of animals when they reached 65% of mature weight, relative growth rates, and degrees of maturity at 365 and 550 d. Variance and covariance components were estimated by REML from a set of two-trait animal models including weaning weight paired with a growth or maturing trait. Weaning and cow contemporary groups were defined as fixed effects. Random effects for weaning weight included direct genetic, maternal genetic, and permanent environmental effects. For growth and maturing traits, a random direct genetic effect was included in the model. Direct heritability estimates for growth traits ranged from .46 to .52 and for maturing traits from .31 to .34. Direct genetic correlations between weaning weight and weights and growth rates at 365 and 550 d ranged from .56 to .70. Correlations of maternal weaning genetic effects with direct genetic effects on weights at 365 and 550 d were positive, but those with growth rates were negative. Between weaning weight and degrees of maturity at both 365 and 550 d, direct genetic correlation estimates were .55 and maternal genetic correlations estimates were -.05, respectively. Direct genetic correlations of weaning weight with relative growth rates and age at 65% of mature weight ranged from .04 to .06, and maternal-direct genetic correlation estimates ranged from -.50 to -.56, respectively. These estimates indicate that higher genetic capacity for milk production was related to higher body mass and degrees of maturity between 365 and 550 d of age but was negatively related to absolute and relative growth rates in that life stage.     

Genetic investigations on male and female fertility in cattle

More than one million inseminations from Red Danish (RDM), Black and White Danish (SDM) and Danish Jersey (DJ) bulls were analyzed to obtain heritability estimates on non-return rate (NR%). The results ranged from 0.010 ± 0.003 to 0.036 ± 0.009. Three NR% and three methods of calculation are used in the analyses.Investigations on 32,100 first calving intervals (CI) within the same breeds yielded heritability estimates of 0.096±0.014, 0.030±0.011 and 0.031±0.018 for RDM, SDM and DJ, respectively.The phenotypic correlations between the bulls' own (NR%) fertility and that of their daughters' (CI) were ?0.17, ?0.16 and 0.10 for RDM, SDM and DJ, the corresponding genetic correlations being ?0.30, ?0.35 and 0.20.It is suggested that in a possible breeding scheme for fertility, attention should concentrate on the female's side (progeny testing).     

Sensorial quality and bone strength of female and male broiler chickens are influenced by weight and growth rate

1. An experiment was conducted with 98 male and 98 female broiler chickens (Ross 308) to study the effect of growth rate, induced by different dietary means, sex and live weight (1500?g and 2000?g) at slaughter on production parameters, bone strength and sensorial characteristics of the breast meat.

2. The birds were divided into four groups and individually fed a standard commercial diet, a high energy diet or low energy diet from d?11 to slaughter at between d 28 and 39. Three groups were fed ad libitum and a further group was fed a restricted amount of the high energy feed. Half of the birds in each group were slaughtered at approximately 1500?g and the other half at 2000?g live weight.

3. The diets resulted in different growth rates. The chickens fed the high energy and the commercial diet had the highest growth rate at both live weights at slaughter. The restricted fed chickens had lower bone strength than the chickens fed the low energy diet.

4. Breast meat from male broilers was juicer, more tender and less hard than breast meat from females. Chickens slaughtered at 2000?g live weight were juicer than those slaughtered at 1500?g. Chickens given the high energy feed ad libitum and restricted had different growth rates, but the sensory parameter related to texture showed no difference.

5. It was concluded that an increased slaughter weight might improve meat quality due to improved juiciness.     

Divergent selection for shape of growth curve in Japanese quail. 6. Hatching time,hatchability and embryo mortality

1. Hatching time, hatchability of fertile eggs and embryo mortality under standard egg storage (1 or 5 days at 12?±?1°C and 55% relative humidity) and incubation conditions (37·5?±?0·2°C and 50% relative humidity) were analysed in lines long-term selected for high (HG) and low (LG) relative weight gain between 11 and 28?d of age, respectively, and constant body weight at 49?d of age.

2. Egg storage duration did not have an effect on average hatching time. LG quail, characterised by a fast postnatal growth rate immediately after hatching, hatched earlier than HG quail with a low early growth rate (about 391 vs. 406?h after egg setting, respectively).

3. In contrast to hatching time, the hatchability of fertile eggs was influenced by line as well as egg storage duration. Extended storage decreased hatching success in both lines. However, LG eggs exhibited a higher hatchability than HG eggs (1?d storage: 96·0 vs. 82·5%; 5?d storage: 88·7 vs. 72·7%, respectively).

4. Lower hatchability resulted mostly from a higher frequency of embryo death during early (up to d 7) and late (d 14 and later) phases of incubation.

5. An inadequate nutrient supply to embryos in consequence of developmental delay seems to be a key factor decreasing viability of embryos during incubation.     

Alterations with age in composition and lipolytic activity of adipose tissue from male and female chickens

The composition and lipolytic activity of adipose tissue from male and female chickens between 4 weeks of age and maturity was studied. The triglyceride to DNA ratio doubled in male adipose tissue during this time but increased seven‐fold in females, suggesting that the latter had larger adipocytes. The protein to DNA ratios were constant throughout.

The lipolytic sensitivity of adipocytes to glucagon did not alter with age but the concentration of glucagon producing a maximal response decreased. Noradrena‐line sensitivity, never very great, was lost after 16 weeks but re‐appeared in the adult male. The total lipolytic response of the tissue decreased, in terms of the dry weight (representing triglyceride content), but was constant in terms of the DNA content of the tissue, suggesting that the cell protoplasm was equally active at all ages from 12 weeks to maturity.     

Genetic parameters for a heavy female turkey line: impact of simultaneous selection for body weight and total egg number

1. The objective of this study was to investigate the strength of the genetic association between growth and reproduction traits in turkeys selected for body weight, conformation and egg production. 2. Two distinct populations but derived from the same heavy turkey female line and situated in different locations (UK and USA), were used to estimate genetic parameters using multivariate REML for the following traits: body weight at 14 (BW14), 19 (BW19) and 24 (BW24) weeks of age and total egg number (EGG). 3. A Box-Cox transformation was applied to egg production data to reduce the impact of non-normality. 4. The heritability estimates for each trait for the UK and USA populations, respectively, were: BW14 0.37 and 0.48; BW19 0.34 and 0.43; BW24 0.28 and 0.43; EGG 0.22 and 0.34. 5. The genetic correlation between the body weight at all ages and the total egg production was strongly negative, reaching a value of -0.75 for the UK and -0.55 for the USA population. 6. The comparison of our results with published estimates in turkeys suggests that the genetic correlation may get stronger in magnitude following selection for increased body weight. 7. This could arise from fixation during selection of genes favouring larger weights but with minimal effect on egg production, leaving the segregating genetic variation dominated by pleiotropic loci with antagonistic effects on the traits. 8. Thus, in order to avoid continued selection for body weight reducing egg production to a point where natural selection offsets selection gains, alternative selection strategies should be considered.     

Effects of somatostatin immunoneutralization on growth and endocrine parameters in chickens

The effects of somatostatin immunoneutralization on growth rate, growth hormone (GH) secretion and circulating insulin-like growth factor I (IGF-I) concentrations were investigated in chickens through the use of passive and active immunization techniques. Intravenous bolus injection of goat-antisomatostatin stimulated a significant (P less than .05) increase in plasma GH levels for one hour post-injection in four and six week old male broiler chickens. The GH response to an intravenous bolus injection of hGRF44NH2 was similar in the antisomatostatin treated chicks and normal goat serum treated controls. Despite the presence of circulating somatostatin antisera after 28 hours, plasma GH levels were not different between control and antisomatostatin-treated chicks at that time. Continuous administration of somatostatin antisera by Alzet pump over a two-week period resulted in significant (P less than .05) elevations in plasma GH levels at one week post-implantation and in circulating IGF-I concentrations after two weeks of administration. Chicks which developed antibodies against somatostatin following active immunization exhibited a 7.1% increase in growth rate which was associated with a significant decrease in abdominal fat. However, neither GH nor IGF-I concentrations were elevated in the chicks which developed somatostatin antibodies. Thus, the benefits gained from somatostatin immunoneutralization may be exerted through mechanisms other than GH.     

Effects of growth curve parameters on cow efficiency.

Weight-age data from 50 Retinta beef cows from 8 to 97 mo of age located in southwestern Spain were fitted to von Bertalanffy, Brody, and Richards functions to determine the relationship between growth curve parameters and cow efficiency. Only cows having at least 31 weights were included in the analysis. Von Bertalanffy, Brody, and Richards functions were fitted to weights of each cow. Relevant parameters of the three functions are A and K, associated with the asymptotic mature weight and rate of maturing, respectively. Criteria for comparisons among the three functions were computing difficulty, goodness of fit, and lack of bias of A. Productivity indicators were number of calves weaned during the first five calving seasons (NC), average birth weight (BWT), average weaning weight (WW), and average weaning weight per cow per year (WWY). The von Bertalanffy function was selected as the most appropriate. Least squares means for A and K were 650 +/- 8.17 kg and .038 +/- .001 mo-1, respectively. The values of NC, BWT, WW, and WWY were 4.0 +/- .11 calves, 38.2 +/- .4 kg, 218 +/- 5 kg, and 172 +/- 5 kg, respectively. Regression analysis for A indicated a decrease in NC when mature weight increased (P less than .05). There was a nonsignificant trend for heavier cows (higher A) to have calves with heavier BWT or WW. The value of WWY increased (P less than .05) with increased maturing rate (K) of cows. No significant associations were found between K and BWT or WW.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic parameter estimates for reproductive traits of male and female littermate swine

Reproductive traits of purebred and crossbred pigs produced in a four-breed diallel mating system using the Duroc, Landrace, Spotted and Yorkshire breeds were collected for five consecutive farrowing seasons (two farrowing seasons/year) beginning in fall 1976. Paternal half-sib heritabilities and genetic correlations for testicular traits (120 boars from 36 sires), serum testosterone (TE) and luteinizing hormone (LH) concentrations before and after treatment with gonadotropin releasing hormone (GnRH; 131 boars from 37 sires) and breeding performance traits (151 boars from 38 sires) were estimated. Heritability estimates were generally small to moderate except for sperm/gram testis (SGT), LH concentrations before (LHO) and at 3 h (LH3) after treatment with GnRH (.73 +/- .48, .61 +/- .46 and 1.19 +/- .45, respectively). A large positive genetic correlation was found for LHO with LH3 (.94 +/- .39), while a negative relationship existed for LH3 with TE concentrations at 3 h after GnRH injection. The genetic correlation between a boar's average first service conception rate and average conception rate also was significant (.82 +/- .54). Genetic correlations among littermate traits would suggest that selection for decreased age at puberty in gilts could cause an increase in LH concentrations in boar offspring, before and after GnRH injection, and may also have adverse effects on their ability to settle females. Selection for increased weight at puberty of gilts could cause TE concentrations of boar offspring to increase while having little effect on their breeding performance.