The objective of this study was to evaluate the effect of the European and Zebu age of the bull and semen collection periods on the physical and morphological characteristics of the semen produced by animals in an artificial insemination station, from 1993 to 1999. The semen production data were grouped in five age classes: 12 to 36 months, 37 to 60 months, 61 to 84 months, 85 to 108 months and 109 to 142 months; and in four collection periods: 1 - December to February; 2 - March to May, 3 - June to August and 4 - September to November. Significant effects of age and collection periods on semen characteristics were observed. Volume, sperm turbulence, primary, secondary, tertiary and total abnormalities, acrosome integrity and the average amount of doses per ejaculate showed statistical differences among age classes, with higher values for Zebu in period 4 (September to October). For both subspecies, the highest percentage of total abnormalities was observed in the younger (12 to 36 month-old) and older (109 to 142 month-old) groups of animals. The older Zebu group produced more concentrated semen and showed high average amount of doses per ejaculate. The effect of age on semen characteristics could be observed during the productive and reproductive life of the cattle studied, except for sperm motility and sperm vigor of fresh semen. Less concentrated semen and high percentage of abnormal spermatozoa were observed in the European bulls during season 1 (December to February), as a consequence, a small quantity of semen doses per ejaculate was produced by this subspecies. It could be an effect of the heat stress suffered by these animal immediately before semen collection.
cattle semen; seasonality; semen quality
