Genetic study of reproductive and productive perfomance in Pitangueiras cattle (5/8 Red Poll x 3/8 Zebu)

Abstract

Our data consisted of 500 Pitangueiras females with a total of 1723 lactations distributed over 13 years from 1962 to 1974. The following economic traits were analysed: age at first calving, calving interval, milk and fat production and lenght of lactation period. The variance analysis were made according to the least square method and the heritability estimated through correlations between paternal half-sisters. The mean for age at first calving was 42,87 ± 0,28 months (C.V.=14,31%),for 483 observations. The earliest parturition occurred at age of 23,3 months and the latest at about 76,6 months, showing a great amplitude of variation (53,3 months). The effects of generation and year of parturition had a significant influence on this trait. On relation to calving interval the mean value of the trait was 432.41 ± 2.97 days with a coefficient of variation as 23,73%. The greatest calving interval occurred between 1^st and 2^nd parturitions and the shortest between the 3^rd and 4^th parturitions. The repeatibility estimate was 0,01 ±0,07. The mean for milk production at first lactation was 2556,2 ± 33,1 kg (C.V.=27,6%). The maximum production occurred at 5^th lactation with an increase of 22,6% from first lactation to productive maturity. Generation, age and year of parturition contributed significantly to the variability of milk production was 0,32 ±0,07. The mean for butterfat production was 117,37 ± 0,84kg (C.V.= 29,33%). The values for butterfat percentage, were 4,15 ± 0,02% with a coefficient of variation as 6,49%. These are completely satisfactory for animals bred in tropics. The repeatability of buttierfat production was 0,31 ± 0,07 . For the studied females about 10,79% of lactations finished before 218 days and 66,59% did not exceeded the 305 days of milking (data for 1^st lactation). The mean value of this trait was 281,32 ± 1,39 days (C.V. =20,51%) for 1723 observations. The repeatibility of lactation lenght was 0,15 ± 0,06.