Santana Santana M.L.,Federal University of Mato Grosso |
Bignardi A.B.,Federal University of Mato Grosso |
Pereira R.J.,Federal University of Mato Grosso |
Stefani G.,CRV Lagoa |
El Faro L.,Institute Zootecnia
Animal | Year: 2016
Tropical and sub-tropical climates are characterized by high temperature and humidity, during at least part of the year. Consequently, heat stress is common in Holstein cattle and productive and reproductive losses are frequent. Our objectives were as follows: (1) to quantify losses in production and quality of milk due to heat stress; (2) to estimate genetic correlations within and between milk yield (MY) and milk quality traits; and (3) to evaluate the trends of genetic components of tolerance to heat stress in multiple lactations of Brazilian Holstein cows. Thus, nine analyses using two-trait random regression animal models were carried out to estimate variance components and genetic parameters over temperature–humidity index (THI) values for MY and milk quality traits (three lactations: MY×fat percentage (F%), MY×protein percentage (P%) and MY×somatic cell score (SCS)) of Brazilian Holstein cattle. It was demonstrated that the effects of heat stress can be harmful for traits related to milk production and milk quality of Holstein cattle even though most herds were maintained in a modified environment, for example, with fans and sprinklers. For MY, the effect of heat stress was more detrimental in advanced lactations (−0.22 to −0.52 kg/day per increase of 1 THI unit). In general, the mean heritability estimates were higher for lower THI values and longer days in milk for all traits. In contrast, the heritability estimates for SCS increased with increasing THI values in the second and third lactation. For each trait studied, lower genetic correlations (different from unity) were observed between opposite extremes of THI (THI 47 v. THI 80) and in advanced lactations. The genetic correlations between MY and milk quality trait varied across the THI scale and lactations. The genotype×environment interaction due to heat stress was more important for MY and SCS, particularly in advanced lactations, and can affect the genetic relationship between MY and milk quality traits. Selection for higher MY, F% or P% may result in a poor response of the animals to heat stress, as a genetic antagonism was observed between the general production level and specific ability to respond to heat stress for these traits. Genetic trends confirm the adverse responses in the genetic components of heat stress over the years for milk production and quality. Consequently, the selection of Holstein cattle raised in modified environments in both tropical and sub-tropical regions should take into consideration the genetic variation in heat stress. © The Animal Consortium 2016
Cardoso V.L.,Polo Regional Centro Leste |
Lima M.L.P.,Polo Regional Centro Leste |
Nogueira J.R.,Polo Regional Centro Leste |
de Carneiro R.L.R.,CRV Lagoa |
And 3 more authors.
Revista Brasileira de Zootecnia | Year: 2014
The objective of this study was to calculate economic values for milk (MY), protein (PY) and fat productions (FY) and somatic cell count (SCC) which could be used to compose an economic index to rank animals involved in an international genetic evaluation program of Holstein cattle used in the commercial dairy population in Brazil. The main milk production systems (MPS) prevailing in the South and Southeast were defined based on the feeding management and production level of herds. To calculate feeding costs, energy requirements for the production of one kg of milk with the respective average protein and fat contents of each MPS were calculated. Feeding costs were obtained based on the regional prices of the diets' components. To calculate revenues, milk prices were obtained from the payment tables practiced by seven milk industries. Economic values were calculated from the marginal differences between revenues and costs, for the interest of maximizing the profit, assuming a fixed number of animals in the herd. The average economic values (R$) for MY, PY and FY were 0.51, 6.41 and 1.94, respectively. The economic impact of increasing the original SCC values in the individual records of cows in the population by 1% was -R$ 1.40 per cow, per year. Due to changes observed in the last years in the milk market in Brazil, selection for milk components became economically advantageous. As a result, the calculation of economic values and the proposition of an economic index based on these traits became feasible. Somatic cell count does have an economic impact on the final price of milk and consequently on the annual profit of herds. It has also been used in breeding programs as an indicator of mastitis resistance and should not be neglected in breeding programs of dairy cattle. © 2014 Sociedade Brasileira de Zootecnia.
Savegnago R.P.,São Paulo State University |
Rosa G.J.M.,University of Wisconsin - Madison |
Valente B.D.,University of Wisconsin - Madison |
Herrera L.G.G.,Technological University of Pereira |
And 4 more authors.
Journal of Dairy Science | Year: 2013
The objectives of the present study were to estimate genetic parameters of monthly test-day milk yield (TDMY) of the first lactation of Brazilian Holstein cows using random regression (RR), and to compare the genetic gains for milk production and persistency, derived from RR models, using eigenvector indices and selection indices that did not consider eigenvectors. The data set contained monthly TDMY of 3,543 first lactations of Brazilian Holstein cows calving between 1994 and 2011. The RR model included the fixed effect of the contemporary group (herd-month-year of test days), the covariate calving age (linear and quadratic effects), and a fourth-order regression on Legendre orthogonal polynomials of days in milk (DIM) to model the population-based mean curve. Additive genetic and nongenetic animal effects were fit as RR with 4 classes of residual variance random effect. Eigenvector indices based on the additive genetic RR covariance matrix were used to evaluate the genetic gains of milk yield and persistency compared with the traditional selection index (selection index based on breeding values of milk yield until 305 DIM). The heritability estimates for monthly TDMY ranged from 0.12. ±. 0.04 to 0.31. ±. 0.04. The estimates of additive genetic and nongenetic animal effects correlation were close to 1 at adjacent monthly TDMY, with a tendency to diminish as the time between DIM classes increased. The first eigenvector was related to the increase of the genetic response of the milk yield and the second eigenvector was related to the increase of the genetic gains of the persistency but it contributed to decrease the genetic gains for total milk yield. Therefore, using this eigenvector to improve persistency will not contribute to change the shape of genetic curve pattern. If the breeding goal is to improve milk production and persistency, complete sequential eigenvector indices (selection indices composite with all eigenvectors) could be used with higher economic values for persistency. However, if the breeding goal is to improve only milk yield, the traditional selection index is indicated. © 2013 American Dairy Science Association.
Savegnago R.P.,São Paulo State University |
Nascimento G.B.D.,São Paulo State University |
Rosa G.J.D.M.,University of Wisconsin - Madison |
Carneiro R.L.R.D.,CRV Lagoa |
And 3 more authors.
Livestock Science | Year: 2016
Animal selection in dairy cattle can vary depending on the objectives of the breeding programs. The objective of this study was to explore the genetic curve pattern of EBVs for test day milk yields (TDMY) in Holstein cows using cluster analyses to identify the most suitable animals for selection based on their genetic curve for milk yield. A data set with 29,477 monthly TDMY records from 3543 first lactations of Brazilian Holstein cows were used to predict the breeding values for TDMY with random regression model. Hierarchical and non-hierarchical cluster analyses were performed based on the EBVs for 30, 60, 90, 120, 150, 180, 210, 240, 270, and 305 days in milk (DIM) to explore the genetic curve patterns of milk production of animals within the population. At first moment, the population was divided into three groups based on animals' genetic curve pattern for milk yield using hierarchical cluster analysis. According to non-hierarchical cluster analysis, one of those groups had EBVs along the lactation curve above the population average. Further cluster analysis done only with those animals with genetic curve pattern above the population mean showed specific subgroups of animals with different genetic curves for milk yield despite of all of those animals had EBVs above the population average, along the lactation curve. It indicated that specific subgroup of animals with a specific genetic curve pattern for milk yield can be chosen depending on the objectives of the breeding program. It was concluded that the cluster analyzes could be used to select animals based on the shapes of the genetic curve for milk production together with the EBV for milk yield at 305 days in milk. Thus, it can be possible to select at the same time more productive animals with genetic curves that met the goals of breeding programs that take into account the milk production in other parts along the milk production curve. © 2015 Elsevier B.V.