عنوان
پدید آورنده
موضوع
رده
کتابخانه
محل استقرار
TLpq303817155
انگلیسی
The genetic analysis of production and reproduction traits in Nili-Ravi buffalo in Pakistan
[Thesis]
D. Salah ud
W. R. Harvey
The Ohio State University
1989
215
Ph.D.
The Ohio State University
1989
The magnitude of environmental and genetic sources of variation was studied for various economic traits in Nili-Ravi buffalo herds maintained by Military Farms Headquarters, Okara (Pakistan) during the period 1967-1988 involving 3,907 lactation records. Adjustment factors for lactation length (beyond 300 days) and age at calving were developed and milk records were adjusted with these factors prior to analyses to estimate genetic parameters. Phenotypic and genetic parameters such as heritability, repeatability and phenotypic, genetic and environmental correlations were estimated for weight, age at first conception, age at calving, milk production and reproduction traits. Heritability estimates for weight at birth, first conception and first calving were 0.30, 0.19 and 0.13, respectively. Birth weight was not influenced by year and season, but weight at first conception and calving were significantly affected. High positive genetic correlations were estimated among weight traits (0.49 to 0.76) indicating that correlated response would result due to selection for any one of these traits. Heritability for age at first conception and calving was estimated to be 0.31 and 0.30 with a genetic correlation of 0.99. Herd, year and season of calving significantly influenced milk production. High temperatures during the summer seem to have a direct effect on an animal and it's environment causing a substantial reduction in production. Despite a negative yearly environmental trend, a genetic gain in milk yield of 5.5 kg per annum occurred, on the average, across birth year groups (1967-83). Heritability estimates for milk production based on first lactation and all lactation records were 0.06 and 0.01, respectively, which were low compared to other studies. The repeatability estimate for milk yield was 0.41 when adjustment was made for lactation length. Negative heritability estimates were obtained for calving interval (0.07) and dry period (0.06), which suggests that all variation in these reproductive traits is environmental.
Biological sciences
Buffalo
Genetics
Livestock
D. Salah ud
W. R. Harvey
مطالعه متن کتاب p
[Thesis]
276903
a
Y
