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Context: Most Brazilian beef breeding programs perform selection for young bodyweight, which will inevitably increase mature weight due to the genetic correlation among weights at different ages. Aims: The objective of the present study was to estimate genetic parameters for bodyweight from birth to maturity in Gir, Guzerat, Nelore and Caracu cows born between 1981 and 2014 at Centro APTA Bovinos de Corte, Instituto de Zootecnia, Sertãozinho, São Paulo, Brazil. Methods: The model included the fixed effects of contemporary group (herd and year of birth), month of birth and previous reproductive status (calved = 1, or not calved = 0), the linear and quadratic effects of animal and cow age as covariates, and direct additive genetic, maternal genetic and maternal permanent environmental effects as random effects. The genetic parameters were estimated by univariate analysis of weights adjusted at birth, and at 120, 210, 378, 450 and 550 days of age, and annually from 2 to 10 years. In addition, multivariate analysis was performed considering weights at birth, and at 210 and 550 days, and at 5 years of age for all breeds. Key results: For the different breeds, the heritability estimates ranged from 0.28 to 0.49 for birthweight, from 0.11 to 0.31 for weaning weight, from 0.25 to 0.43 for yearling weight, and from 0.25 to 0.69 for weights from 2 to 10 years of age. The genetic correlations were high and positive, indicating that selection at any age will affect weights at the other ages. Conclusions: The results suggest the possibility of genetic progress for weights at different ages and the use of the young weights to monitor the mature weight of the animals. Implications: As the trait most strongly correlated with mature weight was yearling weight, already used as the selection criteria for females in the breeding program of the Instituto de Zootecnia, selection indexes should be derived to keep the mature cow weight constant, since heavier cows could be undesirable for pasture-based Brazilian production systems. Selecting cattle for bodyweight at young ages alters mature weight, which may not be desirable due to the rearing of cows in extensive pasture systems and the increased nutritional requirements of larger animals. High and positive genetic correlations indicated a strong association among measurements at different ages, and selection for the desired mature weight should be performed through selection indices to simultaneously select the desired weight at young age and at maturity. [ABSTRACT FROM AUTHOR]

Context: The energy availability for cow–calf systems is related to climate disturbances, and energy use is influenced by the age of the cows. Both factors determine the productivity and resilience of herds after climate disruption. Aims: Identify the time needed for the herds composed of cows of a varying age to achieve resilience after energy restriction in the pre- and postpartum. Methods: The resilience of systems was compared by deterministic dynamic simulation and herds were considered initially stable but different in (1) energy availability for all herd in the first year of production, namely at 50% (low, L), 75% (medium, M) of 100% (high, H) of the requirements according to the NRC (2000 , 2016) , with these energy levels being restricted to 60 days before and 60 days after the birth, and (2) the maximum age of the cull cow (lifetime, LT), namely 4 (LT4L, LT4M, LT4H), 6 (LT6L, LT6M, LT6H) of 11 (LT11L, LT11M, LT11H) years. From the second year, availability returned to meet the energy requirements of all animals. The availability of energy for the herd was simulated in natural and cultivated pasture. The productivity was determined as the relation between the kilograms of animals sold and the area used for production over a productive cycle. The system model was considered resilient when 95% of the standard productivity was reached (prior to energy restriction). Key results: The time required to return to stability was 2 years in the LT6 and LT11, whereas LT4 required 3 years. Furthermore, LT6 had a higher productivity than did the other herds. The older the culled cow was, the greater was the change in the composition of the product commercialised. Conclusions: Cows with an intermediate culling age allowed a sustainable intensification of the system, because they showed better productivity than did older cull cows. Furthermore, after climate disturbance, they presented more resilience than did younger cull cows. The level of energy restriction did not directly influence the time to resilience within each evaluated discard-age group. Implications: Herds that culled females before reaching adult age are less resilient after disturbances, such as changes in climate or changes of any nature that interfere with reproductive rates. The sufficient length of the cow's lifetime in the beef cattle herd allows to mitigate problems in the cow–calf systems generated by the reduction in food availability. The intermediate age (6 years) of culling the cows allowed better resilience of the herd, after restriction (50% or 75%) of energy during 60 days pre- and 60 days postpartum for the cows. The intermediate lifespan of cows allowed for better resilience and productivity in cow–calf systems. [ABSTRACT FROM AUTHOR]

Context: Length of productive life is defined as the number of days from first calving to the last day of milking records, when the cow is no longer sufficiently productive. Although it has economic implications, length of productive life has not yet been included in Brazilian dairy cattle breeding programs because it depends on other traits such as age at first calving, milk production level and disease occurrence. In addition, its evaluation occurs later in life, and heritability coefficients are low. Aims: The aim of this study was to identify the effects of both age at first calving and accumulated 305-day milk yield in the first lactation on length of productive life in Holstein cows. Methods: Official dairy control data of 31 562 Holstein cows, calved from 2010 to 2014, in 321 herds from Paraná state, Brazil, were analysed by using the Kaplan–Meier estimator and Cox regression model. Key results: First calving at <21 months was associated with shortest productive life (1197.01 ± 232.40 days), whereas first calving at 24 months was associated with the lowest hazard ratio (0.572), suggesting that this is the most suitable age of first calving for a longer productive life. Low-yielding cows (first lactation yield <6392 kg) had the second lowest survival probability (47.20%), the shortest productive life (1150.60 ± 234.51 days) and the highest voluntary hazard ratio (1.30) and were prematurely culled from the herds. High-yielding cows (first lactation yield >12 024 kg) had lower culling risk at the first lactation. Conclusions: Cows that started their reproductive life ∼16 months of age (first calving at 24 months) had the longest productive life and an average first lactation milk yield ∼9000 kg. Implications: Reproductive management practices could affect length of productive life through effects on age at first calving and first lactation milk yield. Most of the Holstein semen used in Brazil comes from countries where longevity has already been included in selection indexes; thus, early identification of cow longevity could be used for culling decisions. Having long-lived, more profitable and more functional cows in the herd is one of the biggest challenges in dairy farming in Brazil. We assessed the effects of age at first calving and accumulated 305-day milk yield in the first lactation on length of productive life in Holstein cows. Cows that started reproductive life at ∼16 months of age had the longest productive life and an average first lactation milk yield ∼9000 kg. [ABSTRACT FROM AUTHOR]

Context: The beef market faces an increasing demand for an environmentally friendly production system with high-quality final products. The use of strategies that improve system efficiency without detriment on quality are desired for both producers and consumer. Aims: This study aimed to evaluate the effects of residual feed intake (RFI) and dietary inclusion of crude glycerin on carcass and meat quality traits of feedlot-finished Nellore cattle. Methods: Nellore bulls selected for growth and classified as high (n = 14) and low (n = 14) RFI, with average liveweight of 328 kg and age of 552 days were used. Bulls received a high-concentrate diet for 96 days before slaughter and were randomly allocated to two experimental diets in a 2 × 2 factorial arrangement: RFI class (low or high) and dietary inclusion (CG) or not (WCG) of crude glycerin (20% on dry-matter basis). Data were analysed with the SAS MIXED procedure considering RFI class and diet as fixed effects and selection line as a random effect. Key results: There were no significant differences between RFI classes for dry-matter intake during finishing or production traits. Dry-matter intake tended to be reduced by 16% in CG bulls, without alterations in production. Dietary glycerin inclusion tended to increase the protein content in the Longissimus muscle and significantly reduced the fat content. In low-RFI bulls, shear force was higher in unaged beef, and shear force and myofibrillar fragmentation index tended to be higher in meat aged for 14 days. RFI class did not affect Longissimus muscle fatty acid profile, which was highly influenced by dietary glycerin inclusion. Bulls allocated to the CG treatment had a reduction in saturated fatty acids, an increase in odd-chain fatty acids, and a trend towards increased omega-3 fatty acids, which significantly increased the omega-3:omega-6 ratio. Conclusions: The use of Nellore bulls classified as low-RFI and crude glycerin inclusion in finishing diets of Nellore cattle do not compromise production, carcass traits or beef properties. Implications: This approach increases the efficiency and sustainability of the production process and improves the nutritional characteristics of beef for human consumption. The study provides a strategy to improve beef production, through the optimisation of processes involving feed efficiency, beef quality and their interface. Our findings indicated that using efficient Nellore bulls and providing them high-energy feeds during the finishing phase increases efficiency of production and improves beef nutritional traits. [ABSTRACT FROM AUTHOR]

Context: The estimation of genetic parameters for traits related to the production of milk, beef or both may assist in defining the selection criteria and objectives of the breeding program, as well as in the identification and selection of genetically superior animals. Aims: The objectives of this study were to estimate genetic parameters for body weight and 305-day milk yield of Guzera cattle and to perform cluster analysis on the basis of estimated breeding values for these traits, to identify groups of animals that could be selected for the production of beef, milk or dual purpose. Methods: Body weights (N = 253 012) of males and females were ecorded at 120 days of age (BW120), at weaning (WW), at 365 days (BW365), at yearling stage (YW) and at 24 months (BW24), and 6237 complete lactations (MY305) of 4723 cows were used to estimate the genetic parameters. The bi-trait animal models included direct additive genetic, maternal permanent environmental and temporary random effects for body weights and additive genetic, permanent environmental and temporary environmental random effects for MY305. The fixed effects for all the traits were contemporary group and age of cow at calving. Key results: The estimates of heritability ranged from 0.14 ± 0.01 for WW to 0.23 ± 0.01 for MY305. The genetic correlations between body weights at different ages and milk yield were positive and ranged from 0.27 ± 0.11 to 0.38 ± 0.19. Two principal components explained 86.74% of the total genetic variance among the traits. Conclusions: Cluster analysis identified four different clusters and showed that the Guzera breed had bulls with different genetic patterns that permits genetic selection for beef, milk or dual purpose. Implications: The genetic correlations of the present study suggest that selection to increase milk yield will lead to a slight genetic gain in the same direction for body weight at different ages, in contrast to reports from some other studies. The Guzera breed is in second position among Zebu breeds for milk production and is also used as a dual-purpose breed in some Brazilian production systems. The genetic correlations suggest that selection to increase milk yield will lead to selection in the same direction for body weight at different ages. The Guzera breed has the genetic potential to meet different selection objectives, either beef or milk production, or to produce dual-purpose animals as indicated by principal component analysis and cluster analysis. [ABSTRACT FROM AUTHOR]

Context: Lactation persistency (LP) is an economically important characteristic to include in the selection objectives of the Gyr breed. Two persistency measures were tested to establish their contribution to the genetic evaluation of milk production in this genotype. The second measure of persistency studied would be the more appropriate measure to use in the genetic evaluation of lactation persistency. Aim: The aim of this work was to study LP in Gyr cows by using a random regression model (RRM) in two-trait analysis. Methods: Test-day milk yields (TDMY) of the first two lactations of Gyr cows were analysed. RRM was performed by Bayesian inference using the GIBBS3F90 program. Fourth-order Legendre polynomials were used to describe the random additive genetic and permanent environmental effects of the animal. The fixed effects included in the model were contemporary group and, as covariates, age of cow at calving and the regression function according to the TDMY class of lactation as the average trajectories of lactation curve, distinguished by calving order. Two persistency measures (PS i , i.e. PS1 and PS2) were used in the analyses. Rank correlations were calculated between the predicted breeding values for PS i , 305-day lactation milk yield (MY305), and the regression coefficients a 0 and a 1, to determine the percentage of matching animals between rankings when different selection intensities are applied on the basis of the ranking for MY305. Key results: The heritability estimates for PS1, PS2 and for MY305 were 0.19, 0.12 and 0.41 respectively, in the first lactation, and 0.43, 0.27 and 0.38 in the second lactation. The genetic correlation between MY305 and PS1 was negative and of low magnitude. The rank correlation between breeding values for PS i , obtained for bulls with at least five daughters with production records, was higher than 0.80 in the two lactation periods. Conclusions: The results indicated that PS2 is the more suitable of the two persistency measures used in this work, for inclusion in genetic evaluations of lactation persistency in Brazilian Gyr cows. Implications: PS2 must be included as a selection criteria in a breeding program for the Gyr breed. The Gyr breed has been selected in Brazil for 40 years, mainly for total milk yield. The lactation persistency is closely related to the profitability of a milk production system. More persistent cows need less inputs, they get less sick, have more stayability and behave better reproductively. The results indicated that it is possible to make a selection for lactation persistency and that the second measure considered is better suited to the behavior of milk yield in Gyr breed. [ABSTRACT FROM AUTHOR]

Context: Studies assessing the relationship between cattle reactivity and growth performance, as well as suitability to the feedlot, in Zebu cattle are limited. Based on previous studies using Bos Taurus cattle, it is expected that reactivity measured at weaning could be used as a predictor of feedlot performance, and that cattle with greater flight speed (FS) would have reduced average daily gain (ADG). Aims: The aims of this study were to (1) determine if FS (m/s) measured before entry into the feedlot could be used as a predictor of cattle performance, (2) evaluate the consistency of FS over time, and (3) determine when FS should be measured to best predict animal suitability to the feedlot. Methods: A total of 54 Nellore and 40 Guzerat calves were assessed by using FS, which was collected at the time of (FS0) and 1 week after weaning (FS1), as well as on Day 28 (FS28), 56 (FS56) and 168 (FS168) after entry into the feedlot, and a FS average was calculated using FS28, FS56 and FS168 (FS28–168). Performance using ADG (kg/calf.day) was calculated for each animal over three periods: ADG1–28, ADG28–168 and ADG1–168. Bunk attendance (min/calf.day) was recorded over a 173-day feeding period. Key results: The ADG28–168 was reduced by 0.14 kg/calf.day for each unit increase in FS0 (P < 0.05). Both ADG28–168 and ADG1–168 were reduced by 0.02 kg/calf.day for each unit increase in FS1 (P ≤ 0.01), but neither FS0 nor FS1 was associated with ADG1–28 (P > 0.10). A significant increase was observed between FS1 and FS28 (P < 0.01), followed by a reduction in FS56 (P < 0.01) and FS168 (P < 0.01). Conclusion: FS measured at or within 1 week of weaning has the potential to be used as an indicator of feedlot growth performance in Nellore and Guzerat cattle. Implications: Although our results do not indicate the efficacy of FS as a predictor of early suitability of cattle to the feedlot, it does have the potential to support its recommendation as an indicator of overall feedlot growth performance in Nellore and Guzerat breeds. There is evidence that cattle vary in their ability to adapt to potential stressors within a feedlot environment, ultimately affecting animal welfare and production efficiency. Our findings suggest that temperament assessed before entry into the feedlot can potentially be used as an indicator of growth performance. This finding may aid producers in the early identification of individual cattle that would perform poorly in a feedlot environment, so that they could be managed using an alternative production strategy. [ABSTRACT FROM AUTHOR]

The objective of the present study was to assess the relationship between residual feed intake (RFI) evaluated in a feedlot-performance test and on pasture, and to determine the effect of feedlot RFI classification on enteric methane (CH4) production in the feedlot and on pasture. Seventy-three animals (25 with a low RFI, 24 with a medium RFI and 24 with a high RFI) classified in a feedlot performance test were subjected to performance testing on Brachiaria brizantha cv. Marandu pasture. Enteric CH4 was measured in a sample of these animals (n = 47, with high and low RFI) by the sulfur hexafluoride tracer-gas technique after the feedlot-performance test and during the performance test on pasture. In the feedlot-performance test, dry-matter intake (DMI) of low-RFI animals was 9.4% and 19.7% lower (P < 0.05) than that of medium- and high-RFI animals respectively. However, there was no difference in DMI and, consequently, in RFI on pasture among animals classified as low, mediumand high RFI. Accordingly, there is evidence of re-ranking of animals for RFI performance tested in the feedlot after weaning and, subsequently, on pasture. During the period of enteric CH4 measurement in the feedlot and on pasture, the DMI, neutral detergent-fibre intake and gross-energy intake of low-RFI animals were lower than those of high- RFI animals, and low-RFI animals exhibited greaterDMand neutral detergent fibre digestibility only in the feedlot. Enteric CH4 production did not differ between low- and high-RFI animals either in the feedlot (101 and 107 gCH4/day) or on pasture (101 and 95.9 g CH4/day). A significant difference in CH4 yield (CH4/kg DMI) was observed on pasture between animals with low and high RFI (17.6 and 13.7 gCH4/kgDMIrespectively). The results did not support the hypothesis that an increase in feed efficiency, evaluated in growing animals in feedlot-performance tests, decreases enteric CH4 production (g/day) proportionally to the lower DMI. [ABSTRACT FROM AUTHOR]