Study of stayability in Nellore cows using a threshold model1

In order to achieve improvements in production efficiency in livestock, herds of high sexual precocity and good fertility are needed. These traits increase the availability of animals in herd, either for sale or selection, allowing both greater selective intensity and greater genetic progress. This study aimed at estimating genetic parameters for reproductive traits measured directly in females in order to verify whether they could be used as selection criteria for genetic improvement in Nellore cows, as well as estimating the genetic relationship among these traits and scrotal circumference (SC), the traditional selection criterion for sexual precocity in cattle. In addition to SC, stayability (STAY), number of calvings at 53 months (NC53) and heifers rebreeding (HR) were studied. The (co)variances and genetic parameters were estimated using Bayesian inference. STAY, NC53 and HR were analyzed assuming a threshold model, whereas SC was analyzed with a linear model. Heritability estimated for NC53 was 0.22, and this trait was strongly and positively correlated with STAY, meaning selection for NC53 would improve productive longevity of Nellore cows. Correlations estimated between HR and STAY (≈0.97) and between HR and NC53 (≈0.99) allow an improvement on HR rates if selection was applied to traits related to longevity. Genetic correlations among SC and female reproductive traits were positive but weak, suggesting the need to use reproductive traits directly measured in females in order to obtain greater improvements in sexual precocity and longevity.

Section: Resultssupporting

confidence: 81%

Genetic relationship among reproductive traits in Nellore cattle

Guarini¹,

Neves²,

Schenkel

et al. 2015

“…On some farms, according to 'Associaçã o Nacional de Criadores e Pesquisadores' (data not published), this was already occurring or came as a response correlating this trait with another that was undergoing selection within the herd (indirect selection). Van Melis et al (2007) reported that the mean genetic value for stayability in the herd increased with time.…”

Section: Discussionmentioning

confidence: 99%

“…Cows' longevity, expressed as their continuing presence in the herd, is an economically important trait that is directly related to the yield of the meat production system through its relationship with production efficiency (Van Melis et al, 2007). Inclusion of this trait in genetic -E-mail: danisio@unesp.fcav.br evaluation programs may make it possible to select bulls that have female offspring with a greater likelihood of remaining productive in the herd for a longer period of time or for a time established by the producer.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the variable cow's age at last calving as a measurement of longevity by using the Kaplan–Meier estimator and the Cox model

Caetano

Rosa

Savegnago

et al. 2013

In most studies on beef cattle longevity, only the cows reaching a given number of calvings by a specific age are considered in the analyses. With the aim of evaluating all cows with productive life in herds, taking into consideration the different forms of management on each farm, it was proposed to measure cow longevity from age at last calving (ALC), that is, the most recent calving registered in the files. The objective was to characterize this trait in order to study the longevity of Nellore cattle, using the Kaplan-Meier estimators and the Cox model. The covariables and class effects considered in the models were age at first calving (AFC), year and season of birth of the cow and farm. The variable studied (ALC) was classified as presenting complete information (uncensored 5 1) or incomplete information (censored 5 0), using the criterion of the difference between the date of each cow's last calving and the date of the latest calving at each farm. If this difference was .36 months, the cow was considered to have failed. If not, this cow was censored, thus indicating that future calving remained possible for this cow. The records of 11 791 animals from 22 farms within the Nellore Breed Genetic Improvement Program ('Nellore Brazil') were used. In the estimation process using the Kaplan-Meier model, the variable of AFC was classified into three age groups. In individual analyses, the logrank test and the Wilcoxon test in the Kaplan-Meier model showed that all covariables and class effects had significant effects (P , 0.05) on ALC. In the analysis considering all covariables and class effects, using the Wald test in the Cox model, only the season of birth of the cow was not significant for ALC (P . 0.05). This analysis indicated that each month added to AFC diminished the risk of the cow's failure in the herd by 2%. Nonetheless, this does not imply that animals with younger AFC had less profitability. Cows with greater numbers of calvings were more precocious than those with fewer calvings.

“…HP at 14 months is the probability that a cow conceives after the end of the breeding season when exposed to a bull or inseminated (Doyle et al, 1996;Evans et al, 1999;Eler et al, 2002). In contrast, STAY is the probability of a cow to remain in the herd until a specific age, given the opportunity to reach this age (Hudson and Van Vleck, 1981;Silva et al, 2006;Van Melis et al, 2007). Both the traits are binary, and a value of 1 is attributed for success and a value of 0 for failure.…”

Section: Introductionmentioning

confidence: 99%

Genetic relationship between growth and reproductive traits in Nellore cattle

Júnior

Eler

Ferraz

et al. 2012

The objective of this study was to evaluate the genetic relationship between postweaning weight gain (PWG), heifer pregnancy (HP), scrotal circumference (SC) at 18 months of age, stayability at 6 years of age (STAY) and finishing visual score at 18 months of age (PREC), and to determine the potential of these traits as selection criteria for the genetic improvement of growth and reproduction in Nellore cattle. The HP was defined as the observation that a heifer conceived and remained pregnant, which was assessed by rectal palpation at 60 days. The STAY was defined as whether or not a cow calved every year up to the age of 6 years, given that she was provided the opportunity to breed. The Bayesian linear-threshold analysis via the Gibbs sampler was used to estimate the variance and covariance components applying a multitrait model. Posterior mean estimates of direct heritability were 0.15 6 0.00, 0.42 6 0.02, 0.49 6 0.01, 0.11 6 0.01 and 0.19 6 0.00 for PWG, HP, SC, STAY and PREC, respectively. The genetic correlations between traits ranged from 0.17 to 0.62. The traits studied generally have potential for use as selection criteria in genetic breeding programs. The genetic correlations between all traits show that selection for one of these traits does not imply the loss of the others.