Contribution of some productive and reproductive traits in affecting the daily rate of milk production in Holstein-Friesian cows.

• A.A. Zaied

  Animal Production Department. Faculty of Agriculture, Omar Al-Mukhtar University, Libya

  Author

• A.D.S. Kharoofa

  Animal Health Branch. College of Veterinary Medicine. University of Al Mosul. Iraq.

  Author

• M-K. A. Ahmed

  Faculty of Animal Production, University of Khartoum, Sudan

  Author

• S.A. Salhab.

  Animal Production Department. Faculty of Agriculture, University of Damascus, Syria.

  Author

The method of path analysis was used to calculate an assumed amodel bout the causal relationships between variables affecting average daily production of milk during the first two lactations. These include age at first conception, gestation period, dry period, lactation length and total production. Data comprising 1315 lactation records of Holstein cows completed on a dairy farm in eastren Libya were analysed. Path analysis was used to compute direct and indirect effects on average daily production of milk. Coefficients of determination and the percentage of effects not included in the model were also calculated. The results showed that the total and direct effect of dry period, lactation length and total production on daily average were - 0.0803, -0.5787 and 0.3897; 0.0199, - 1.0162 and 0.9197 consecutively. These effects were statistically significant. However these factors did not have a significant effect on average daily production in the second lactation except for the overall effect of total production (0.1828). The percentage contribution of the variables to the variation in average daily production in the first lactation was 94.48%. It was close to zero in the second lactation (0.01%).

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