Testicular morphology in Corriedale rams : influence of feeding management under extensive rearing conditions in the Río de la Plata grasslands

Seasonality is a basic trait o f sheep reproduction. Nutrition and photoperiod interact to modulate the seasonality of ram testis form and function. The influences o f these cues vary according to breed, location, and management strategies applied. Since nutrition affects testis development, feeding conditions during early life might influence testis activity later. The overall aim o f this thesis was to study the influence o f seasonality and feeding regimes on testis morphometry in Corriedale rams reared on extensive systems in Uruguay. Experimental studies looked for influences o f differential feeding management on testis morphology and function, particularly on seasonal changes and on testis development, from foetal to post-pubertal life.Testis morphology was studied in 24 rams grazing either improved or native pastures over a one-year period. Clinical recordings, testosterone measurements, and quantitative histology o f testes, epididymides, and seminal vesicles were performed in autumn (March), winter (July), spring (September), and summer (December). Both groups had highest values in autumn, lowest in winter, and recovered thereafter. Rams grazing improved pastures showed a somewhat smaller testicular winter regression and recovered earlier in spring.The influence o f improved feeding on the seasonal (autumn-winter) changes in testicular form and function was studied in rams fed improved pastures plus grain supplement (controls were grazing native pasture). Castration/histology studies were performed in autumn (March: autumn control group, n = 6, native pasture) and in winter (August: winter control group, n = 7, native pasture; treated group, n = 7, improved pasture plus grain supplement). Clinical recordings and testosterone measurements were performed monthly. The seasonal testis regression was described morphometrically. The treatment applied alleviated slightly this regression, but did not reverse the declining trend in testicular size and activity.The influence o f long-lasting differential grazing regimes from 1 to 30 months o f age on testicular growth and morphology by adult age was studied in 41 ram lambs. Animals grazed either native or improved pastures (groups H and L, respectively; 1-8 months of age, Period 1). By moving half the animals to the opposite treatment, groups HH, HL, LH, and LL were created (8-18 months of age, Period 2). Finally, all remaining rams shared the same grazing regime (18-30 months o f age, Period 3). Clinical results were recorded every other month. Half the animals from each group were castrated for histology at 18 and 30 months o f age. Scrotal circumference (SC) was higher in group H during Period 1. During Period 2, the SC of group LH rams equalized values o f group HH, and SC in groups HL and LH reached similar values. Testis weight, volume, and stereological parameters did not differ between groups by the end o f Periods 2 or 3. No differences in SC were seen between groups during most o f Period 3.The impact o f improved feeding of the ewe-lamb unit during foetal and early postnatal life on the testicular development of the ram lamb was studied in 14 ewe-lamb units fed improved pasture plus grain supplement from mid-pregnancy to pre-pubertal life, as compared with 12 ewe-lamb units grazing native pasture (half o f lambs castrated for histology at 99 days of age). Clinical and endocrinological studies were performed from birth to castration. Puberty was hastened in grain-supplemented lambs and their Sertoli cell numbers tended to be higher.In conclusion, this thesis describes the morphometry o f the seasonal testis regression o f Corriedale rams and shows that this regression is not easily reverted by the hereby tested level o f improved feeding. The enhancement in testis development when pre- and post-pubertal Corriedale rams grazed improved pasture was short-lived. The tendency to higher Sertoli cell numbers elicited by treating animals with improved pasture plus grain supplementation from foetal to pre-pubertal life might result in longer-lived consequences in spermatogenetic capacity