Evaluation of mature cow weight: genetic correlations with traits used in selection indices, correlated responses, and genetic trends in Nelore cattle

Genetic analysis of growth, visual scores, height, and carcass traits in Nelore cattle

Covariance components were estimated for growth traits (BW, birth weight; WW, weaning weight; YW, yearling weight), visual scores (BQ, breed quality; CS, conformation; MS, muscling; NS, navel; PS, finishing precocity), hip height (HH), and carcass traits (BF, backfat thickness; LMA, longissimus muscle area) measured at yearling. Genetic gains were obtained and validation models on direct and maternal effects for BW and WW were fitted. Genetic correlations of growth traits with CS, PS, MS, and HH ranged from 0.20 ± 0.01 to 0.94 ± 0.01 and were positive and low with NS (0.11 ± 0.01 to 0.20 ± 0.01) and favorable with BQ (0.14 ± 0.02 to 0.37 ± 0.02). Null to moderate genetic correlations were obtained between growth and carcass traits. Genetic gains were positive and significant, except for BW. An increase of 0.76 and 0.72 kg is expected for BW and WW, respectively, per unit increase in estimated breeding value (EBV) for direct effect and an additional 0.74 and 1.43, respectively, kg per unit increase in EBV for the maternal effect. Monitoring genetic gains for HH and NS is relevant to maintain an adequate body size and a navel morphological correction, if necessary. Simultaneous selection for growth, morphological, and carcass traits in line with improve maternal performance is a feasible strategy to increase herd productivity.

Carcass and efficiency metrics of beef cattle differ by whether the calf was born in a dairy or a beef herd

Beef originates from the progeny of either dairy or beef dams. The objective of the present study was to identify contributing factors to the differences in the carcass merit of progeny from both dam types. This goal was achieved using slaughter records from 16,414 bucket-reared dairy animals (DXD), 5,407 bucket-reared dairy-beef animals (BXD), 42,102 suckle-reared animals from a beef × dairy F1 cross dam (BXF1), and 93,737 suckle-reared animals from a beef × beef cow (BXB). Linear mixed models were used to quantify the least squares means for carcass characteristics in the various progeny genotypes. Nuisance fixed effects adjusted for in the models were: animal heterosis and recombination loss, dam parity, age at slaughter, and contemporary group; age at slaughter was replaced as an independent variable with both carcass weight and carcass fat score where the dependent variable was age at slaughter. In a follow-up analysis, models were re-analyzed where the genetic merit of the sire was adjusted for; a further analysis set the genetic merit of the dam for the dependent variable to be identical for both the dairy and beef dams. The final analysis adjusted to a common sire and dam genetic merit facilitating the estimation of just differences in early-life rearing strategies. Irrespective of the genetic merit of the sire and dam, animals originating from beef herds had heavier and more conformed carcasses. BXB animals had a 67 kg heavier carcass, with a conformation score (scale 1 [poor] to 15 [excellent]) of 5 units greater compared with DXD animals. When the genetic merit of all dams was set to be equal, BXB animals were heavier and better conformed than BXD animals. When the genetic merit for both the sire and dam were set to be equal, carcasses of the BXB animals were 15 kg heavier, with a 0.69 unit superior conformation score compared with the DXD animals; this difference is due to early life experiences. In conclusion, the majority of the inferiority in carcass metrics of calves from dairy herds compared with beef herds is due to differences in the genetic merit of the parents. Nevertheless, even after adjusting the parents to the same genetic merit, progeny from dairy herds were still inferior to their contemporaries born in beef herds, due most likely to the persistence of early life experiences.

Genetic associations between mature size and condition score of Nelore cows, and weight, subjective scores and carcass traits as yearlings

The size and body condition of female livestock is critical for improving production efficiency. However, we know little about how height and body condition score in mature beef cattle are genetically related to traits observed when the animals are younger. In the present study, we used data from 321650 Nelore cattle, first, to compare genetic parameters and breeding values on the basis of different models employing weight (MW), height (MH) and body condition score (BCS) of mature cows (3–17 years old). Next, we estimated the genetic correlations between the three traits and assorted yearling traits (YW, weight; YC; conformation score; YP, precocity score; YM, muscling score; YN, navel score; LMA, longissimus muscle area; BF, back fat thickness). Finally, we obtained the expected direct responses to selection for MW, MH and BCS of cows and correlated responses for these traits when the selection was applied to yearling traits. For MW and MH, single-trait Bayesian analyses were used to evaluate the effects of including BCS when defining contemporary groups (BCS included, CG1; BCS not included, CG2). For BCS trait, linear and threshold animal models were compared. After, bi-trait analyses that included MW, MH or BCS with yearling traits were performed. The CG1 scenario resulted in a higher heritability for MW (0.45 ± 0.02) than did CG2 (0.39 ± 0.02). Both scenarios yielded the same heritability estimates for MH (0.35 ± 0.02). Sires’ rank correlations between predicted breeding values under CG1 and CG2 were 0.60–0.92 for MW and 0.90–0.98 for MH, considering different selection intensities. Thus, only for MW genetic evaluations, the incorporation of BCS in the definition of the contemporary groups is indicated. For BCS trait, the same sires were selected regardless of the model (linear or threshold). Genetic correlations between MW and five yearling traits (YW, YC, YP, YM and YN) ranged from 0.18 ± 0.03 to 0.84 ± 0.01. The MH had a higher and positive genetic association with YW (0.64 ± 0.02) and YC (0.54 ± 0.03), than with YN (0.18 ± 0.03). However, MH was negatively and lowly genetically correlated with YP (–0.08 ± 0.03) and YM (–0.14 ± 0.03). The BCS had positive genetic associations with all yearling traits, particularly with YP (0.61 ± 0.06) and YM (0.60 ± 0.07). Mature size and carcass traits exhibited a low to moderate negative genetic correlations. However, BCS had positive genetic associations with LMA (0.38 ± 0.12) and BF (0.32 ± 0.14). Despite a shorter generation interval, selection at the yearling stage will result in a slower genetic progress per generation than does direct selection for cow MW, MH or BCS. Moreover, using YW and YC as selection criteria will increase cattle size at maturity without altering BCS. Last, LMA or BF-based selection will reduce mature size, while improving BCS, as a correlated response.

Threshold and linear models for genetic evaluation of visual scores in Hereford and Braford cattle

Data from 127539 Hereford and Braford cattle were used to compare estimates of genetic parameters for navel, conformation, precocity, muscling and size visual scores at yearling, using linear and threshold animal models. In a second step, these models were cross-validated using a multinomial logistic regression in order to quantify the association between phenotype and genetic merit for each trait. For navel score, higher heritability was obtained with the threshold model (0.42 ± 0.02) in relation to the linear model (0.22 ± 0.02). However, similar heritability was estimated in both models for conformation, precocity, muscling and size, with values of 0.18 ± 0.01, 0.19 ± 0.01, 0.19 ± 0.01 and 0.26 ± 0.01, respectively, using linear model, and of 0.19 ± 0.01, 0.19 ± 0.01, 0.20 ± 0.01, and 0.29 ± 0.01, respectively, using threshold model. For navel score, Spearman correlations between sires’ breeding values predicted using linear and threshold models ranged from 0.60 (1% of the best sires are selected) to 0.96 (all sires are selected). For conformation, precocity, muscling and size scores, low changes in sires’ rank are expected using these models (Spearman correlations >0.86), regardless of the proportion of sires selected. Except for navel with the linear model, the direction of the associations between phenotype and genetic merit were in accordance with its expectation, as there were increases in the phenotype per unit of change in the breeding value. Thus, the threshold model would be recommended to perform genetic evaluation of navel score in this population. However, linear and threshold models showed similar predictive ability for conformation, precocity, muscling and size scores.

Genetic relations and indirect response to selection based on indices for scrotal circumference, visual scores and weight gain in beef cattle

Genetic improvement in beef cattle involves evaluation for fertility, growth, carcass and visual scores traits. In general, genetic and economic parameters of these traits are considered for selection index construction. The present study was conducted to establish the magnitude of genetic and phenotypic correlations between visual scores of conformation, precocity and muscling at weaning and at yearling, birth to weaning weight gain, weaning to yearling weight gain and yearling scrotal circumference, and between these traits with selection indices applied in this population. In addition, the expected gains were obtained in such traits by taking under consideration the adopted selection criteria based on indices. Positive and high genetic correlations were estimated between weaning traits (visual scores and weight gain), ranging from 0.70 ± 0.02 to 0.97 ± 0.01. In genetic terms, the same visual scores, but evaluated in two ages (weaning and yearling) showed positive and high associations, with values of 0.90 ± 0.01 (conformation), 0.88 ± 0.01 (precocity) and 0.84 ± 0.02 (muscling). Genetic associations between yearling visual scores with scrotal circumference and weaning to yearling weight gain ranging from 0.36 ± 0.02 to 0.53 ± 0.01. Using the weaning index, are expected genetic gains ranging from 0.26% to 0.70%/year of the phenotypic mean of each weaning trait. Using the yearling index, annual genetic gains estimated for weaning traits (ranging from 0.25% to 0.63% of the phenotypic mean of the trait) were lower than that obtained at yearling (ranging from 0.27% to 0.98% of the phenotypic mean of the trait). Selection for one of traits obtained at weaning should result, by correlated response, in gain for the others. Also, the choice of animals with higher breeding values for weaning visual scores, beyond anticipate the selection process, should lead to favourable changes in these traits at yearling. Selection for better body composition at yearling (higher scores) should provide increase in scrotal circumference and weight gain. The use of higher values of the indices should result in positively correlated response, but in different magnitudes for each trait used in these indices. However, in both weaning and yearling, higher genetic gains to visual scores are expected in the same period, when the selection is based on the values of these indices.

Genetic study of visual scores and hip height at different ages in Nelore cattle

The objective of the present study was to evaluate the genetic variability of visual scores used as selection criteria in Nelore cattle, as well as their associations with yearling hip height (YH) and mature hip height (MH), to determine whether the selection considered would change the hip height of animals. (Co)variance components were obtained by two-trait animal model using Gibbs sampling, including YH or MH in each analysis. Breeding values for YH and MH were used to obtain the response to selection. The posterior mean of the heritability estimates for conformation, finishing precocity (or body condition) and muscling at weaning (WC: 0.21 ± 0.02; WP: 0.21 ± 0.02; and WM: 0.18 ± 0.02 respectively) were lower than those obtained for the same traits at yearling (YC: 0.34 ± 0.02; YP: 0.37 ± 0.02; and YM: 0.38 ± 0.02 respectively). Heritability estimates for YH and MH were 0.28 ± 0.01 and 0.33 ± 0.03 respectively. The results suggested that these traits should respond to selection process, but in different magnitudes. Positive and high genetic correlations were estimated between WC and YH and YC and YH (0.80 ± 0.03 and 0.76 ± 0.03 respectively), and lower values between these scores and MH (0.48 ± 0.09 and 0.36 ± 0.07 respectively). Weak genetic associations were obtained between finishing precocity score and YH and muscling score and YH (ranging from 0.05 ± 0.05 to 0.18 ± 0.06). Moreover, negative and favourable genetic associations between each of WP, WM, YP and YM, and MH (ranging from –0.21 ± 0.07 to –0.12 ± 0.09) were estimated. Correlated responses are expected to be unfavourable for hip height, measured at yearling and at maturity, when animals better genetically evaluated for conformation in relation to finishing precocity and muscling scores are selected. Genetic changes obtained for YH and MH were null (–0.02 cm/year and 0.03 cm/year respectively). It can be explained, in part, by smaller weights in the selection index for conformation rather than finishing precocity and muscling, as applied in the studied herds. However, in herds of beef cattle not evaluated and selected for finishing precocity and muscling scores or that have cows with larger size than acceptable, the adoption of mature hip height as one of the selection criteria can be one alternative for obtaining females with a desirable size.