1Almquist J O.Effects of sexual preparation on sperm output se-men characteristics and sexual activity of beef bulls with a com-parison to dairy bulls[J].J Anim Sci,1976,36:331-336.
2Saeed A,Chaudhry R A,Khan I H,et al.Studies on morphologyof buffalo bull semen of different age groups[J].Buffalo J,1989,1:99-102.
3Brückmann A,Yang X,Schallenberge E.The effects of age on fer-tility,ejaculate parameters and testosterone,estradiol-17b andluteinizing hormone concentration in breeding bulls[A].14th In-ternational Congress on Animal Reproduction,2000,Abstracts 3:20.
4Schawb W,Kupferschmied H,Bachmann P.Factors affecting se-men production in bulls[J].Zuchthygiene,1987,22:241-246.
5Lorton S P,Winter J L,Pace M M,et al.Evaluation of two semi-nal collection regimens for mature Holstein bulls[J].J Anim Sci,1984,58:l-5.
6Druet T,Fritz S,Sellem E,et al.Estimation of genetic parame-ters and genome scan for 15 semen characteristics traits of Hol-stein bulls[J].J Anim Breed Genet,2009,126(4):269-277.
7Mathevon M,Buhr M M,Dekkers J C.Environmental,manage-ment,and genetic factors affecting semen production in Holsteinbulls[J].J Dairy Sci,1998,81(12):3321-3330.
8Wells M E,Awa O A,Fancy S S.Effect of season on acrosomestatus in the bull[J].J Dairy Sci,1971,55:1174-1178.
9Everett R W,Bean B.Environmental influences on semen output[J].J Dairy Sci,1982,65:1303-1310.
10Sarder Md J U.Environment related variations in the semen char-acteristics of bulls used for artificial insemination(AI)pro-gramme in Bangladesh[J].J Zool Rajshahi Univ,2007,26:81-88.
