Post-weaning Weight Research Articles

Growth curves of carcass traits obtained by ultrasonography in three lines of Nellore cattle selected for body weight.

The effect of selection for postweaning weight was evaluated within the growth curve parameters for both growth and carcass traits. Records of 2404 Nellore animals from three selection lines were analyzed: two selection lines for high postweaning weight, selection (NeS) and traditional (NeT); and a control line (NeC) in which animals were selected for postweaning weight close to the average. Body weight (BW), hip height (HH), rib eye area (REA), back fat thickness (BFT), and rump fat thickness (RFT) were measured and records collected from animals 8 to 20 (males) and 11 to 26 (females) months of age. The parameters A (asymptotic value) and k (growth rate) were estimated using the nonlinear model procedure of the Statistical Analysis System program, which included fixed effect of line (NeS, NeT, and NeC) in the model, with the objective to evaluate differences in the estimated parameters between lines. Selected animals (NeS and NeT) showed higher growth rates than control line animals (NeC) for all traits. Line effect on curves parameters was significant (P < 0.001) for BW, HH, and REA in males, and for BFT and RFT in females. Selection for postweaning weight was effective in altering growth curves, resulting in animals with higher growth potential.

Intramuscular fat in lamb muscle and the impact of selection for improved carcass lean meat yield

Intramuscular fat percentage (IMF%) has been shown to have a positive influence on the eating quality of red meat. Selection of Australian lambs for increased lean tissue and reduced carcass fatness using Australian Sheep Breeding Values has been shown to decrease IMF% of the Muscularis longissimus lumborum. The impact this selection has on the IMF% of other muscle depots is unknown. This study examined IMF% in five different muscles from 400 lambs (M. longissimus lumborum, Muscularis semimembranosus, Muscularis semitendinosus, Muscularis supraspinatus, Muscularis infraspinatus). The sires of these lambs had a broad range in carcass breeding values for post-weaning weight, eye muscle depth and fat depth over the 12th rib (c-site fat depth). Results showed IMF% to be highest in the M. supraspinatus (4.87±0.1, P<0.01) and lowest in the M. semimembranosus (3.58±0.1, P<0.01). Hot carcass weight was positively associated with IMF% of all muscles. Selection for decreasing c-site fat depth reduced IMF% in the M. longissimus lumborum, M. semimembranosus and M. semitendinosus. Higher breeding values for post-weaning weight and eye muscle depth increased and decreased IMF%, respectively, but only in the lambs born as multiples and raised as singles. For each per cent increase in lean meat yield percentage (LMY%), there was a reduction in IMF% of 0.16 in all five muscles examined. Given the drive within the lamb industry to improve LMY%, our results indicate the importance of continued monitoring of IMF% throughout the different carcass regions, given its importance for eating quality.

Estimates of (co)variance components and genetic parameters of growth traits in Marwari sheep

The present investigation was undertaken to estimate the (co)variance components and genetic parameters for different growth traits in Marwari flock comprising records of 1649 animals distributed over a period of 12 years (1999–2010), maintained at Arid Region Campus of Central Sheep and Wool Research Institute, Bikaner, Rajasthan, India. The estimation was done by restricted maximum likelihood procedures, fitting six animal models with various combinations of direct and maternal effects. As per likelihood ratio test, direct heritability estimates from the best model for body weight at birth, weaning, 6, 9 and 12 months of age, and average daily gain during birth to weaning, weaning to 6 and 6–12 months of age were 0.28 ± 0.058, 0.27 ± 0.050, 0.28 ± 0.049, 0.30 ± 0.080, 0.29, 0.26 ± 0.050, 0.16 ± 0.040 and 0.31, respectively. Maternal genetic effect declined from 4% at 6 months weight to 1% at 9 months and was zero at 12 months of age. Maternal genetic effect on the post-weaning traits was a carryover effect of the maternal influences during pre-weaning age. Maternal permanent environmental effects contributed 19% of the total phenotypic variation in birth weight and 8% for weaning weight. The evidence for maternal genetic effect for average daily gain was observed only during 6–12 months of age where the additive maternal heritability was estimated as 8%. The genetic correlation between direct and maternal genetic effects was found significantly large and negative for all the traits, indicating antagonistic pleiotropy, which must be considered while formulating breeding plans. A modest rate of genetic progress seems possible in the flock through selection. Genetic correlations between body weight traits were positive and ranged from 0.23 between birth weight and weight at 6 months to 0.88 between weaning weight and weight at 9 months of age. The positive and high genetic correlation of weaning weight with weight at subsequent ages suggests that genetic gain in post-weaning weight will be maintained even if selection age is reduced to 3 months.

Multi-trait linear reaction norm model to describe the pattern of phenotypic expression of some economic traits in beef cattle across a range of environments.

The multi-trait reaction norm (MTRN) model was extended to beef cattle reared under tropical conditions with the following objectives: to compare multi-trait (MT) and MTRN models regarding the genetic parameters obtained; and to characterize G × E, the pattern of phenotypic expression, and the environmental sensitivity of animals for postweaning weight gain (PWG), scrotal circumference (SC), and annual average productivity of the cow (PRODAM). There was divergence in the estimates between the MT and MTRN models when the posterior probability intervals of additive genetic variances and heritability coefficients of PWG and PRODAM were analyzed. The MTRN model indicated an increase in heritability for PWG and PRODAM with improvement of the environmental conditions. For SC, heritability was practically the same, irrespective of the environmental conditions. The genetic correlations between the traits studied were low but varied over environments by the MTRN model. Considering genetic correlations obtained by the MTRN model for the same trait, lower estimates were obtained between extreme favorable and unfavorable environments. This finding suggest re-ranking of breeding values in different environments mainly for PWG and PRODAM. Thus, G × E is more important for PWG and PRODAM than for SC and should be included in the genetic evaluation of these traits. The traits PWG and PRODAM can be considered plastic traits, whereas SC is poorly plastic. The genetic trends in individual animal slopes indicate that the population is moving towards greater plasticity. This could be a matter of concern for breeders since greater plasticity seems to limit heritability and, consequently, the responses to selection.

Carcase weight and dressing percentage are increased using Australian Sheep Breeding Values for increased weight and muscling and reduced fat depth

Pre-slaughter live weight, dressing percentage, and hot standard carcase weight (HCWT) from the 2007, 2008, 2009 and 2010 birth-years of the Information Nucleus Flock Lambs (n=7325) were analysed using linear mixed effects models. Increasing the sire breeding value for post-weaning weight (PWWT), and c-site eye muscle depth (PEMD), and reducing the sire breeding value for fat depth (PFAT) all had positive impacts on HCWT. The magnitude of the PWWT effect was greater in pure bred Merinos compared to Maternal and Terminal sired progeny. The improved HCWT resulting from increased PEMD was entirely due to its impact on improving dressing percentage, given that it had no impact on pre-slaughter live weight. There were marked differences between sire types and dam breeds, with pure-bred Merinos having lower pre-slaughter weight, reduced dressing percentage, and lower HCWT than progeny from Terminal and Maternal sired lambs or progeny from Maternal (1st cross) dams.

Increasing vitamin A in post-weaning diets reduces food intake and body weight and modifies gene expression in brains of male rats born to dams fed a high multivitamin diet

High multivitamin gestational diets (HV, 10-fold AIN-93G levels) increase body weight (BW) and food intake (FI) in rat offspring weaned to a recommended multivitamin (RV), but not to a HV diet. We hypothesized that high vitamin A (HA) alone, similar to HV, in post-weaning diets would prevent these effects of the HV maternal diet consistent with gene expression in FI and reward pathways. Male offspring from dams fed HV diets were weaned to a high vitamin A (HA, 10-fold AIN-93G levels), HV or RV diet for 29 weeks. BW, FI, expression of genes involved in regulation of FI and reward and global and gene-specific DNA methylation of pro-opiomelanocortin (POMC) in the hypothalamus were measured. Both HV and HA diets slowed post-weaning weight gain and modified gene expression in offspring compared to offspring fed an RV post-weaning diet. Hypothalamic POMC expression in HA offspring was not different from either HV or RV, and dopamine receptor 1 was 30% (P<.05) higher in HA vs. HV, but not different from RV group. Hippocampal expression of serotonin receptor 1A (40%, P<.01), dopamine receptor 2 (40%, P<.05) and dopamine receptor 5 (70%, P<.0001) was greater in HA vs. RV fed pups and is 40% (P<.01), 50% (P<.05) and 40% (P<.0001) in HA vs. HV pups, respectively. POMC DNA methylation was lower in HA vs. RV offspring (P<.05). We conclude that high vitamin A in post-weaning diets reduces post-weaning weight gain and FI and modifies gene expression in FI and reward pathways.

High multivitamin intake during pregnancy leads to dopamine dysregulation in the nucleus accumbens of Wistar rat dams post‐weaning (47.6)

Diet‐induced obesity is known to alter dopamine neurochemistry within central reward circuitry essential for coding the rewarding properties of palatable foods. Our objective was to investigate whether high multivitamin (10‐fold, HV) intake during pregnancy alone, which increases post‐weaning (PW) weight gain in Wistar rat dams, affects their dopamine (DA) metabolism and related gene expression in the nucleus accumbens (NAc) when exposed to an obesogenic environment. Pregnant Wistar rats were fed an AIN‐93G diet with either the recommended vitamin (1‐fold, RV) or HV mix (n=15/group). During lactation, dams were fed a RV diet until weaning and then a high fat (RV with 60% fat) diet for 16 weeks. Dams fed the HV diet gained 30% (p&lt;0.05) more weight after weaning than RV dams. Although differences in food intake were not detected, HV dams had a 10% (p&lt;0.05) reduced preference for sucrose when exposed to a two‐bottle preference test (4% sucrose vs. water) at 12 weeks PW suggesting a state of reward hypofunction. Total DA, DA receptor 1a/2, catechol‐O‐methyl transferase and monoamine‐oxidase A mRNA expression in the NAc was unaffected by diets. However, turnover rate of homovanillic acid, but not di‐hydroxypheneylactic acid, was significantly lower in HV dams (p&lt;0.05). In conclusion, HV diet during pregnancy in Wistar rat dams induces DA dysregulation in the NAc later in life and is consistent with PW weight gain.Grant Funding Source: Supported by Canadian Institutes of Health Research, Institue of Nutrition, Metabolism and Diabetes

Body chemical composition, tissue deposition rates and gain composition of young Nellore cattle selected for postweaning weight

Empty body and carcass chemical composition were determined in 67 Nellore bulls from Selection Nellore (NeS) and Control Nellore (NeC) herds of an animal breeding program for growth, slaughtered at 570 days of average age, after 100 days of feedlot. Selection Nellore animals had, respectively, 360 and 430 kg of initial and slaughter body weight, and NeC animals had 318 and 373 kg for the same traits. Animals were slaughtered and empty body composition was determined by chemical analysis of the components blood, hide, head and feet, viscera and carcass. Tissue deposition rates and gain chemical composition were also determined based on gains estimated by comparative slaughter technique. Significant differences were detected between NeS and NeC animals for slaughter body weight, empty body weight, empty body gain rate, and contents of water, protein, ash and retained energy in empty body, showing that selected animals had greater body sizes and growth rates. There were no significant differences in fat contents in empty body and carcass, suggesting that selected animals had higher growth rates as compared with the control, and were slaughtered with good body and carcass fat contents in the same feedlot time. Control Nellore animals showed a 10% higher gain in fat percentage than NeS in the period. This shows that the growth of bone and muscle ceased earlier and NeC group accumulated more fat. Animals selected for growth have heavier carcasses and greater tissue deposition rates with proportional composition similar to unselected animals.

Thesis Abstract Study of different structures of additive genetic groups to increase the efficiency of genetic selection in beef cattle

The structure of genetic groups is a technique that allows animals with unknown paternity to be included in genetic evaluation programs. The ways these groups are formed are still arbitrary, making it important to study different formation strategies for genetic groups, aiming for a suitable framework for the genetic evaluation of seedstock in animal breeding programs. Therefore, the aim of this study was to define the structure of genetic groups suited for genetic evaluations, comparing them in regard to changes in the effective efficiency of the processing of animals with unknown parentage. Data from 116,368 Nellore cattle were analyzed focusing on the traits weaning weight, post-weaning weight, post-weaning weight gain, scrotal circumference at 18 months of age, and visual muscularity score at 18 months of age. Three scenarios were simulated from a database consisting only of complete pedigree animals (control group). The first scenario cut 30% of sires, the second cut 50%, and the third 70%. The training strategies for additive genetic groups were: the birth farm of the animal with unknown parentage; birth year (CROP) and the concatenation of year of birth and birth farm (CROPFARM). The variance components were calculated for the data bank control program by VCE, and breeding values were predicted using the PEST software, with two structures of models that differ by the inclusion or not of the fixed effect of additive genetic groups. The definition of the structure of genetic group suitable for genetic evaluation of animals was based on the efficiency of selection and comparison of estimated breeding values to the “control” breeding values and the rank of animals, where it was assumed that control animalswould have the maximum response to selection and any other group of animals would result in a reduction thereof. The results demonstrated that the additive genetic groups provide an improvement in the genetic prediction of animals with unknown paternity. Strategies that provided values closer to those of the control group were CROP and CROPFARM, and although showing similar values, the CROP strategy was superior in selecting the best animals.

Genotype by environment interaction for post-weaning weight gain, scrotal circumference, and muscling score of composite beef cattle in different regions of Brazil.

The objectives of this study were to characterize and define homogenous production environments of composite beef cattle in Brazil in terms of climatic and geographic variables by using multivariate exploratory techniques; to evaluate the presence of genotype by environment interaction (GxE) for post-weaning weight gain (PWG), yearling scrotal circumference (SC), and yearling muscling (MUS). Hierarchical and nonhierarchical cluster analysis was used to group farms located in regions with similar environmental variables into clusters. Six clusters of farms were formed. The effect of sire-cluster interaction was tested by single-trait analysis. Genetic parameters were estimated by multi-trait analysis considering the same trait to be different in each cluster. The effect of sire-cluster interaction was significant (P <0.01) for PWG and MUS. Estimates of genetic correlations among clusters ranged from 0.31 to 0.93 for PWG, 0.64 to 0.89 for SC, and 0.18 to 0.80 for MUS. These results indicate the need for a genetic analysis on a regional basis or inclusion of the GxE effect in the statistical model to permit appropriate evaluation of the animals.

Genetic Parameter Estimates for Growth and Reproductive Trait of Sheep for Genetic Improvement and Designing Breeding Program in Ethiopia: A Review

Small ruminants in general and sheep in particular are important investments in the highlands of Ethiopia. Genetic and environmental improvements offer an opportunity to increase production from existing animal resources. Development of effective genetic evaluation and improvement programs requires knowledge of the genetic parameters (genetic variance of each trait and covariance among traits) for economically important production traits. Direct heritability estimates for birth weight of Afar sheep (0.13 to 0.38) and BHS (0.20 to 0.58) using univariate analysis; for Horro sheep (0.18 - 0.32) and Menz sheep (0.46) by fitting a multi-trait individual animal model. The weaning weight direct heritability estimates for sheep in Ethiopia, Afar sheep (0.11 - 0.37) and BHS (0.00 - 0.29), Horro sheep (0.10 - 0.26) and Menz sheep (0.48). Fertility, litter size and lamb survival are the components of the overall ewe reproduction traits. It appears that heritability estimates of these traits are rather low and reflect the generally small genetic variance for most reproductive traits. Moreover, litter size has a higher heritability (0.16 - 0.19) than the other components traits like fertility (0.10) and survival rate (0.07 - 0.09) for Awassi sheep breed. Genetic correlations among most pairs of traits were higher than the corresponding phenotypic correlations. Live weights measured at successive ages were highly correlated, ranging from 0.61 to 0.98 for Menz sheep. Genetic correlations were also high between pre-weaning daily gain and weaning weight for Afar and BHS sheep. Except for Blackhead Somali sheep breed which has high genetic correlation between birth weight and weaning weight, Horro, Menz and Afar sheep have high genetic correlation between post-weaning weight traits. This indicates that selection for one trait improves the other trait in those sheep breeds. In order to develop alternative improvement program for sheep breeds in Ethiopia, estimates of genetic parameters for economical growth and reproduction traits should be done by designing experiments since the information on most sheep breed is nonexistence.

Early reproductive losses are a major factor contributing to the poor reproductive performance of Merino ewe lambs mated at 8–10 months of age

The reproductive performance of Merino ewe lambs is lower than that achieved by mature ewes and is highly variable. It is likely that embryo loss represents a major source of reproductive wastage in Merino ewe lambs, but to our knowledge no studies have attempted to determine when the major reproductive losses occur or identify predisposing factors that are likely to lead to high rates of pregnancy failures in ewe lambs. After characterising where reproductive losses occurred in Merino ewe lambs mated at 8–10 months of age, we tested the hypothesis that pregnancy failure in ewe lambs is influenced by nutrition and liveweight change around conception and the genetic potential for growth of the ewe lamb. Two-hundred and twenty-four Merino ewe lambs born from 10 sires with Australian Sheep Breeding Values were teased for 14 days using vasectomised rams, and then fed two different diets for 68 days during mating. All ewe lambs were weighed and the appearance of crayon marks on their rump was recorded most days. Blood samples for progesterone assay were collected on Days 5, 12 and 17 after the first record of a crayon mark. Ultrasonography using a trans-rectal probe was used to measure the number of corpora lutea present, as a proxy for ovulation rate, 9 days after the first record of a crayon mark during the mating period. A further trans-rectal ultrasonography was undertaken 30 days after marking from the entire ram to determine pregnancy status and count the number of embryos. Over the entire mating period 54% of ewe lambs were pregnant with 66 fetuses per 100 ewes mated. The average ovulation rate was 150% however up to 84% of this potential was lost by weaning and the major contributor to this apparent deficit was the loss that occurred during the first 17 days after mating. Pregnancy failure was not significantly related to nutrition or liveweight change during mating however, there were significant differences in pregnancy failure between different sire groups. Pregnancy failure was significantly less for ewe lambs from sires with higher breeding values for weight and fat at post-weaning age (8–10 months). Only 60% of ewe lambs had achieved puberty when rams were introduced and only 83% by 35 days after mating. In addition, almost half of the ewe lambs that were mated for the first time during the first 35 days after rams were introduced, but failed to get pregnant, then seemed to skip a cycle or did not cycle again before the end of the 68-day mating period. Liveweight at introduction of entire rams was positively related to fertility, ovulation rate and reproductive rate. This study confirms that selection of sires with higher breeding values for post-weaning weight and fat will increase the fertility and reproductive rate of Merino ewe lambs mated at 8–10 months. This response is due in part to enhancing the onset of puberty and increasing the proportion of ewe lambs cycling at the start of mating and reducing pregnancy failure.

Genetic parameters for live weight traits in South African terminal sire sheep breeds

Genetic parameter estimates for live weight traits were derived using Residual Maximum Likelihood (REML) procedures for the South African Dormer, Ile de France and Merino Landsheep terminal sire sheep breeds. Birth weight and weaning weight records were available for all breeds. However, pre-weaning weights were available for only the Ile de France and Merino Landsheep breeds, while post-weaning weights were available only for the Dormer breed. Direct heritability estimates (h2) derived using single-trait analyses were 0.25, 0.28 and 0.37 for birth weight, weaning weight and post-weaning weight respectively for the Dormer breed. Corresponding h2 estimates for the Ile de France and Merino Landsheep breeds were respectively 0.13, 0.53 and 0.14 and 0.23, 0.36 and 0.17 for birth weight, pre-weaning weight and weaning weight. The haphazard data structure of the respective populations resulted in complications in the partitioning of maternal effects into maternal genetic (m2) and maternal permanent environmental (c2) components. Low to moderate maternal heritability (m2) and dam permanent environmental (c2) estimates were derived for the Dormer and Ile de France breeds. Genetic, phenotypic and environmental correlations were estimated using three-trait analysis and were found to be moderate to high for live weight traits in the Dormer and Ile de France breeds. The moderate genetic parameter estimates obtained in this study led to the conclusion that direct selection for live weight traits in the terminal sire breeds will result in improved growth in the terminal sire sheep breeds.

Breed effect and non-genetic factors affecting growth performance of sheep in a semi-arid region of Nigeria

Objective: This study was conducted to investigate the effects of breed and some non-genetic factors on growth performance of Balami and Uda sheep in a semi-arid region of Nigeria. Methodology and results : Data on birth weight (BWT), 90-day weaning weight (90-DWWT), 6-month weight (6-MWT), 9-month weight (9-MWT) and yearling weight (Y-WT) of 595 lambs (306 Balami and 209 Uda) born in the Sheep Meat Project of the Federal Livestock Department (FLD), Katsina, between 1996 and 1998 inclusive were collected and used for this study. Pre and post weaning weight gains were also estimated on each lamb. Data was subjected to analysis of variance using the generalized linear model (GLM) procedure of SAS to determine the effects of breed, parity, sex, type of birth, season of birth and year of birth on the growth of lambs. Breed and sex significantly (P<0.05) affected body weights at all ages. Pre and post-weaning growth rates were significantly (P<0.05) affected by all the factors examined except parity of dam and year of birth. Significantly low to moderate phenotypic correlations were observed between the growth traits studied. Conclusion and application of findings: Most of the non-genetic factors have been shown to be important sources of variation in the growth performance of sheep. Therefore, effects of environmental factors need to be corrected for if mixed model approaches such as the Best Linear Unbiased Prediction (BLUP) values are to be used for breeding value evaluation in Balami and Uda lambs. Key words: Sheep, Balami, Uda, Pre and Post weaning growth, Sex, Parity.

Intramuscular fat in the longissimus muscle is reduced in lambs from sires selected for leanness

Selection for lean growth through Australian Sheep Breeding Values (ASBVs) for post weaning weight (PWWT), eye muscle depth (PEMD) and c-site fat depth (PFAT) raises concerns regarding declining intramuscular fat (IMF) levels. Reducing PFAT decreased IMF by 0.84% for Terminal sired lambs. PEMD decreased IMF by 0.18% across all sire types. Female lambs had higher IMF levels and this was unexplained by total carcass fatness. The negative phenotypic association between measures of muscling (shortloin muscle weight, eye muscle area) and IMF, and positive association between fatness and IMF, was consistent with other literature. Hot carcass weight increased IMF by 2.08% between 12 and 40kg, reflective of development of IMF as lambs approach maturity. Selection objectives with low PFAT sires will reduce IMF, however the lower impact of PEMD and absence of a PWWT effect, will enable continued selection for lean growth without influencing IMF. Alternatively, the negative impact of PFAT could be off-set by inclusion of an IMF ASBV.

Genetic and non-genetic effects on calf vigor at birth and preweaning mortality in Nellore calves

The objective of the present study was to evaluate the genetic and non-genetic effects that influence vigor at birth and preweaning mortality in Nellore calves. A total of 11,727 records of births that occurred between 1978 and 2006, offspring of 363 sires, were analyzed. Poor calf vigor at birth (VB) and preweaning mortality divided into stillbirth (SB), early mortality (EM) and total mortality (TM) were analyzed as binary variables. Generalized linear models were used for the evaluation of non-genetic effects and generalized linear mixed models for genetic effects (sire and animal models). The incidences were 4.75% for VB, 2.66% for SB, 5.28% for EM, and 7.99% for TM. Birth weight was the effect that most influenced the traits studied. Calves weighing less than 22 kg (females) and less than 24 kg (males) were at a higher risk of low vigor and preweaning mortality. Preweaning mortality was higher among calves born from cows aged <3 and >11 years at calving compared with cows aged 7 to 10 years. Male calves presented less vigor and higher preweaning mortality than female calves. Selection for postweaning weight did not influence preweaning mortality. The heritability estimates ranged between 0.01 and 0.09 for VB, 0.00 and 0.27 for SB, 0.03 and 0.17 for EM and 0.02 and 0.10 for TM. Stillbirth should be included as a selection criterion in breeding programs of Nellore cattle, alone or as part of a selection index, aiming to reduce preweaning mortality.

Definição de grupos genéticos aditivos visando melhor predição de valores genéticos em bovinos de corte

O objetivo do estudo foi avaliar a estrutura de grupos genéticos aditivos como uma alternativa para melhor ajuste de animais com paternidade desconhecida nas avaliações genéticas. As características estudadas foram: peso a desmama; peso ao sobreano; ganho de peso pós-desmama em 345 dias; perímetro escrotal ao sobreano e o escore visual de musculosidade ao sobreano. Um banco em que todos os animais tinham paternidade conhecida foi utilizado como grupo controle. A partir deste, três cenários foram criados em que 30; 50 ou 70% dos indivíduos foram aleatoriamente assumidos como animais com paternidade desconhecida. As estratégias consideradas de grupos genéticos aditivos foram: ano de nascimento do animal com paternidade desconhecida; fazenda de nascimento do animal com paternidade desconhecida; ano de nascimento e fazenda de nascimento do animal e um grupo controle negativo que manteve os animais com pais desconhecidos. A estratégia adequada de grupo genético aditivo foi escolhida como sendo aquela que resultou em um maior coeficiente de regressão e com valor genético aditivo mais próximos ao predito para os animais do grupo controle. Os resultados que incluíram a estratégia de grupo genético aditivo nos modelos de predição dos valores genéticos mostraram maior coerência com o grupo controle, frente a não inclusão destes nas análises. Dentre as estratégias propostas, ano de nascimento e fazenda de nascimento do animal e apenas ano de nascimento do animal com paternidade desconhecida obtiveram os melhores resultados.

Reproductive tract development and puberty in two lines of Nellore heifers selected for postweaning weight

The objective was to evaluate reproductive tract development (ovary and uterus) and onset of puberty in two lines of Nellore heifers (Bos indicus) selected for postweaning weight. A total of 123 heifers, including 46 from the control Nellore line (NeC) and 77 from the selection Nellore line (NeS) were used. Every 18 to 21 days from 12 to 24 months of age, average ovarian area (OVA), endometrial thickness (ETh), and diameter of the largest follicle in each ovary were evaluated (using transrectal ultrasonography), and body weight, hip height, and body condition score were measured. There were no differences between NeS and NeC heifers for ETh or OVA (P < 0.05). Genetic selection for higher postweaning weight had no negative influence on the onset of puberty, with 52% and 48% of NeC and NeS heifers, respectively, pubertal at 24 months of age (P = 0.49). Heifers that reached puberty at the end of the study were heavier (NeC, 296.9 vs. 276.7 kg; NeS, 343.5 vs. 327.9 kg; P < 0.01) and younger (NeC, 23.4 vs. 24.2 mo; NeS, 22.7 vs. 24.0 months; P < 0.01) than those that did not. Furthermore, heifers that were heavier at weaning reached puberty earlier. Pubertal heifers had a greater OVA (4.15 vs. 3.14 cm2; P < 0.01) and ETh (12.15 vs. 9.93 mm; P < 0.01) than nonpubertal heifers. Taken together, OVA and ETh had positive effects (P < 0.01) on the onset of puberty and were suitable indicator traits of heifer sexual precocity in pasture management systems. However, selection for weight did not alter ovarian or endometrial development, or manifestation of puberty at 24 months of age. Among the growth traits studied, weaning weight and weight at puberty had significant positive effects on manifestation of first estrus.

TENDÊNCIAS GENÉTICAS PARA CARACTERÍSTICAS DE CRESCIMENTO EM REBANHOS NELORE CRIADOS NA REGIÃO DO TRÓPICO ÚMIDO DO BRASIL

(Co)variances, heritability and genetics change were estimated for weight at 120 (W120), 210 (W210), 365 (W365), 450 (W450) and 550 (W550 ) days of age in Nellore cattle from the Humid Tropical region of Brazil. A total of 65,876 records of animals born between 1993 to 2010 and raised on pasture were used. The (co)variance components were estimated by restricted maximum likelihood, and breeding values ??were predicted using an individual animal model. The genetic trends were plotted by linear regression of breeding values ??in the animals’ birth year. The heritability coefficients due to direct genetic effect were 0.37±0.019; 0.39±0.019; 0.41±0.013; 0.41±0.015 and 0.41±0.021 The maternal heritability estimates for W120 and W210 were 0.05±0.011 and 0.06±0.011, respectively. The genetic gains were 1.326, 2.014, 2.670, 3.056 and 3.128 kg/year for W120, W210, W365, W450 and W550, respectively. The estimates of genetic parameters and trends indicate the existence of genetic progress in pre- and post-weight traits from herds of Brazil Tropic Humid region. KEYWORDS: animal breeding program; (co)variances; genetic gain; heritability; post-weaning weight; pre-weaning weight.

Multivariate approach for young bull selection from a performance test using multiple traits of economic importance

This study used multivariate statistics to identify clusters of animals with similar expected progeny difference (EPD) and also identify leading traits that discriminate between bulls. Various linear selection indices based on specific selection criteria were proposed. Records were collected from 880 young Nelore bulls submitted to performance testing in central Brazil between 2001 and 2012. Pre-weaning average daily gain and weights at 210 days with direct and maternal effects were used in the analysis, in addition to post-weaning weight, scrotal circumference at 365 and 450 days, carcass finish and rib eye area. EPDs were classified into three groups, and the EPD means of two of these groups stood out and were considered important based on principal component analysis that associated higher values of direct EPD of weights, average daily weight gain and scrotal circumference. The EPDs for weight at 210, 365 and 450 days, pre- and post-weaning daily gain and scrotal circumference at 365 and 450 days were major causes of variation. Each linear selection index proposed (SI₁, SI₂, SI₃, SI₄ and SI₅) defined a specific approach meaning that a different selection index should be used depending on breeding goals and selection criteria.