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Evaluation and validation of the growth and estimation models for growth to dairy replacement heifers in commercial farms at tropical conditions

Grant number: 19/02307-2
Support type:Scholarships in Brazil - Doctorate
Effective date (Start): June 01, 2019
Effective date (End): March 31, 2021
Field of knowledge:Agronomical Sciences - Animal Husbandry - Animal Nutrition and Feeding
Principal Investigator:Dante Pazzanese Duarte Lanna
Grantee:Marcos Busanello
Home Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil

Abstract

Both, growth and models for estimation of energy and protein utilization, have been extensively studied over the years in several countries. However, the studies about the growth and the validation of these models for different regions and breeds need to be verified. In tropical regions, especially in Brazil, growth parameters and models for Growing Calves and Heifers (GCH) follow the recommendations for animals of different breeds and reared under different conditions originally used in the development of those models. Thus, the true and estimated growth may present differences and those models for energy and protein utilization may not be the most adequate in tropical conditions and, therefore, our objective is to study the growth and validate the models for energy and protein utilization and growth parameters of the NRC, 2001 for GCH in tropical conditions for Holstein, crossbreed and zebu animals. Data from GCH (body weight, age, height of withers and hip, among others) will be collected in dairy farms to study the curves of growth. These analyses will be done using correlations, linear and/or non-linear regressions. Dairy farms will be selected using an approach based on a non-probabilistic sampling of "quotas" followed by "convenience sampling" to collect data on approximately 150 heifers from each of the 3 type of heifers (Holstein, crossbred and zebu). In addition, a database with several information will be obtained from studies conducted in Brazil and tropical regions. To evaluate the models of energy and protein utilization of the NRC (2001) published articles in national and international scientific journals will be used. The main variables collected will be the breed of the animals, body weight, weight gain, age, diet composition, among others. Descriptive and graphical analyzes will be used to verify the biological validity and coherence of the data for subsequent statistical analyses. Evaluations of outliers, observed values and predicted values of the models will be done using regression methods. The accuracy and precision of the model estimates will be verified using mean bias error analysis, mean squared prediction error, concordance correlation coefficient and its components. The coefficient of determination (R2) and other measures to compare the model will also be calculated. (AU)