Braz . ./ . vet. Res. anim. .Sc/ .. São Paulo, v.34. h .3. p. 167-172. 1997. Seasonal variations in stallion sperm features and their relationship with fertility of the breeding stock Variações sazonais nas características do sêmen de garanhões e sua relação com a fertilidade do plantei Celso AUGUSTO1; Francisco GACEK:; Rinaldo ARTES-’ C O R R ES P O N D EN C E TO: Francisco Gacek Departamento de Fisiologia e Biofísica Instituto de Ciências Biomédicas da USP Av. Prol. Lineu Prestes. 1374 - C idade U niversitária Arm ando Salles de Oliveira 05508-900 - São Paulo - SP - Brasil e -m a il: g a cek@ bm b.icbl. usp .br 1 - Estação Experimental de Eqüinos de Colina Instituto de Zootecnia, Colina, SP 2 - Departamento de Fisiologia e Biofísica Instituto de Ciências Biomédicas da USP ■ SP 3 ■ Departamento de Estatística Instituto de Matemática e Estatística da USP - SP SUMMARY Seasonal influence upon spermatozoal concentration, progressive motility and percentage of morphologic abnormalities in the semen of horses was studied, and the fertility of the breeding stock during the corresponding breeding season was assessed. The semen of 7 stallions was collected monthly during 12 months for microscopic examination, and the matings were made by natural service. The highest spermatozoal concentration was recorded during autumn and the lowest, during spring. Along the months, the highest records were those in July and the lowest, in June, but no significant statistical differences were found for the seasonal and monthly variations. The highest rate of progressive motility was observed during summer and the lowest, during spring. Among the months, July presented the highest rate and April the lowest. Differences were significative between months (p < 0,05) and between seasons (p < 0,10). The highest rate of sperm morphologic abnormalities was recorded in summer (p < 0,05). January presented the highest rates of abnormal cells and March the lowest, but the differences among months were not statistically significant. During the breeding season, the fertility of the stock measured by pregnancy rate per cycle increased in a linear manner from 29% in October to 95% in February, not showing any apparent relationship with the seminal characteristics studied. UNITERMS: Semen; Seasonality; Fertility; Equidae fertility of the stock during the breeding season. MATERIAL AND METHODS Collection ami analysis o f semen: seven stallions were studied in this experiment and were maintained at the Equine Experiment Station of Colina, in the State of São Paulo. Brazil (20”43'05’’S and 48"32’38” W). Three of the stallions belonged to Brasilcira- dc- Hipismo breed and 4 to Breton Postier, and were aged between 4 and 8 years except for one. which was 20 years old. Flic animals were kept in 24 h-turns in a stable and pasture, and had free access to hay and ration of concentrates. During the breeding season stallions mated regularly, according to the farm schedule. Single ejaculates of semen were collected from each stallion at the end of each month for microscopic examination, from March 1990 to February 1991, using an artificial vagina. Spermatozoal progressive motility was evaluated immedi- ately after semen collection, by placing one drop of semen between a microscope slide and a glass cover previously warmed at 37”C and observed at lOOx to 400x magnification with a light microscope. Spermatozoal concentration was determined using a haemoeytometric counting chamber and spermatozoal morpho- 167 INTRODUCTION M any physiological and ambiental factors affect some features of stallion semen, among which the photope- riod is one. In equine species, reproductive seasonality is not as conspicuous in males as in females, hut an endogenous circannual rhythm in male is recognized, upon which photoperiod acts as a synchronizer*1 ' through melatonin1-43. Indeed, many authors have reported modifications in the reproductive activity of stallions connected with the period of the y Car- - ?.4.,2,|‘>.2| .’ 5.26.2K,2M..io,í.? j4.í6..i7.íx, |-,ut rcsu]ts are conflicting. Microscopic examination of semen is a method commonly employed for evaluating the fertility of stallions6,710-1-•’O -21 '-35-40--4-. The relationship between sperm features and fertility of stallions has deserved much attention1 '-7-10-11-16-1 but little is referred to the relationship between sperms characteristics of stallions and their influence on fertility of the breeding stock as a whole. In the present study we have examined seasonal influence upon the most common features used for evaluation of semen quality: spermatozoal concentration, progressive motility rate and percent of sperm morphologic abnormalities. We have also at- tempted to verify if a variation in these parameters affect the