الفهرس 
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Abstract
The current study was conducted at the Animal Production Experimental Station, Sakha, Kafrelsheikh Governiment (located in the north of the Nile Delta) from May to September 2020. Cooperation with Animal Production Department faculty of Faculty of Agriculture, Kafrelsheikh University, his study was conducted after an agreement from the Animal Care and Ethics Committee of Kafrelsheikh University, Egypt .
A total of 40 Friesian cows, 20 cows were unable to conceive after 1 service only (high-fertility) or 20 cows were failed to conceive after 3 services (low-fertility) were used. Cows had 46 to 86 months old and body weight of 460-580 kg. Animals were fed on concentrate feed mixture, maize silage, rice straw, and berseem (Trifolium alexandrinum) hay according to the systems adopted by Animal Production Research Institute (APRI). Cows were housed unrestrained in semi-open barns, fresh water was always available.
Animals were divided into four groups, cows in G1 and G3 were high-fertility, however, cows in G2 and G4 were low-fertility.