نوع مقاله : مقاله پژوهشی
نویسندگان
1 کارشناس ارشد، گروه علوم دامی، دانشکدۀ کشاورزی، دانشگاه بیرجند، بیرجندـایران
2 استاد گروه علوم دامی، دانشکدۀ کشاورزی، دانشگاه بیرجند، بیرجندـایران
3 دانشیار گروه علوم دامی، دانشکدۀ کشاورزی، دانشگاه بیرجند، بیرجندـایران
4 کارشناس ارشد مرکز اصلاح نژاد دام و بهبودی تولیدات دامی کشور، بیرجندـایران
کلیدواژهها
عنوان مقاله English
نویسندگان English
The objective of the present research was to apply logistic analysis for investigating some factors
affecting incidence probability of milk fat depression (MFD) in early lactation of Iranian Holstein cows.
The data set was comprised 80381 test day records (milk, fat and protein traits) belonging to 80254 first
parity cows in 427 herds with calving year between 1995 and 2009. Based on fat to protein percentages
for the first month of the lactation and also with respect to threshold point of -0.12, dependent variable
was defined as a dichotomous (zero code for lack of MFD and unit code for MFD) variable. A logistic
mixed generalized linear model was fitted on the data using GLIMMIX procedure of SAS software. In
the model, fixed effects of sperm type (local or exotic), production season, first calving age, cow type
(grade or pure Holstein) and random effect of animal’s sire were included. Cow type had no significant
affect on MFD. Estimation of odds ratio for comparing different ages was found to be 1.112 indicating
that cows calving at lower age of 25 months are expected to show MFD by 11.2 percent smore than the
cows calving at the greater ages. The estimate of odds ratio for comparing of spring with summer, autumn
and winter seasons were 0.73, 0.722 and 1.182, respectively. The corresponding figures for summer as
compared to autumn and winter seasons were 0.987 and 1.615, respectively, and autumn as compared to
winter was found to be 1.636. Daughters of the local bulls are expected to show MFD by 10.8 percent
more than that of the daughters of the foreign bulls.
کلیدواژهها English
| تعداد مشاهده مقاله | 2,571 |
| تعداد دریافت فایل اصل مقاله | 1,465 |
