Abstract
Records of Gyr cows selected for milk production were obtained from the National Gyr Dairy Cattle Breeding Program (Embrapa/CNPGL) and analyzed, in order to estimate genetic parameters for the first three lactations and to verify the effects of some environmental factors on milk production from 1979 to 1994. Genetic parameters were estimated by REML with an animal model and a group of fixed effects that included classes of herd, year, season and age at calving. Milk production means and standard deviations were 2,183 kg, 707 kg; 2,682 kg, 762 kg and 2,638 kg, 851 kg, for first, second, and third lactations, respectively. Heritability estimates were 0.20, 0.12, and 0.19 for first, second, and third lactations, respectively, and repeatability was 0.44. Genetic correlation estimates were: 0.68 between first and second lactations, 0.84 between first and third lactations and 1.0 between second and third lactations. Results confirm other research for specialized dairy breeds and firmly suggest that even in breeds of Indian origin the best time to make selection decisions is during the first lactation.
Highlights
The low productivity of Brazilian dairy herds and scarcity of specialized breeds or animal groups with good genetic potential for milk yield and adaptability to the environmental conditions of the country have been cited as reasons contributing to reduced economic efficiency of the dairy industry
Mean overall milk yield and mean lactation length per herd ranged from 1172 to 3205 kg and 232 to 333 days in the first lactation, 2165 to 3791 kg and 267 to 330 days in the second lactation, and 2166 to 3991 kg and 263 to 334 days in the third lactation. These values indicate that most herds considered in the present study had mean milk yields and lactation lengths close to those reported in the literature for the same breed
It was observed that increased milk yield in some herds was not associated with prolonged lactation length, suggesting an effect of selection within and between herds performed over the years in an attempt to obtain more productive animals
Summary
The low productivity of Brazilian dairy herds and scarcity of specialized breeds or animal groups with good genetic potential for milk yield and adaptability to the environmental conditions of the country have been cited as reasons contributing to reduced economic efficiency of the dairy industry. The trait milk yield is considerably affected by environmental factors, which, in addition to genetic differences, are responsible for the marked variation between breeds and animals within the same breed, and between herds. It is fundamentally important to quantify sources of variation that affect dairy cow productivity so that breeding programs may be conducted properly in order to obtain a better equilibrium between genetics and environment and, con-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
