RESUMO
Two studies were conducted to analyse the repeatability of a serving capacity (SC) pen test and to evaluate the correlation of the results of such a test with field performance. The Laborde SC test, which measures SC by exposing an individual ram for 40min to two restrained non-oestrous ewes in a pen was used. In the first study, SC was measured on four and six occasions during the autumn of 1994 and 1995, respectively. The results indicated that this test is reliable in measuring SC of rams, since SC was repeatable within, and between, breeding season of consecutive years (p<0.05). In the second study conducted on two commercial farms, two groups of ewes synchronised with intravaginal sponges containing medroxyprogesterone acetate, were served by rams of high or low SC. On both the farms, the group of ewes served by rams of high SC had higher pregnancy rates than those served by low SC rams (p<0.05). The Laborde test proved to be a reliable test for the evaluation of SC in rams and that high SC rams had better field performance.
RESUMO
The objective of the present study was to describe seasonal changes in scrotal circumference (SC), live weight (LW), sperm morphology and plasma levels of testosterone (T) and thyroxine (T4) in young Corriedale rams reared under extensive conditions typical for the southern Latin American region. A total of 31 Corriedale rams, 11 months of age and with a LW of 36 +/- 1.1 kg and (SC) of 23.0 +/- 0.5 cm at the beginning of the experiment (September) were kept on natural pastures. At monthly intervals LW was recorded, animals were clinically examined, and SC was measured. None of the animals were used for breeding. Fifteen animals were randomly selected and bled once a month from January to December and plasma concentrations of T and T4 were determined. In addition, one semen sample was collected by electroejaculation and morphological studies were performed. The mean individual LW increase was 18 kg (50% of the initial LW) during the experiment (p < 0.01). LW decreased in autumn, with the nadir in late autumn. SC reached mean maximum levels in late summer (31.1 +/- 0.4 cm, p < 0.01), then decreased until the beginning of winter (26.3 +/- 0.4 cm, p < 0.01) and remained low until early spring (27.5 +/- 0.5 cm, p > 0.05) to increase again between mid-spring and the end of the experimental period the following summer (30.7 +/- 0.5 cm, p < 0.01). The mean SC in winter was 16% lower than that in late summer. Semen could be collected from the rams throughout the experiment. Frequencies of sperm head, mid-piece and total abnormalities showed monthly variation (p < 0.05), but tail abnormalities were not affected by month. Low abnormalities were found in autumn (9.4% +/- 2.2%). T was high during autumn (p < 0.01). Minimal T4 concentrations were observed during late summer and early autumn (p < 0.01) when T levels were high. Maximum T4 concentrations were registered in late autumn (p < 0.01); when SC was decreasing; in mid-spring (p < 0.01) one month after shearing and in early summer (p < 0.01). The results suggest that Corriedale rams under Uruguayan extensive management systems show a reproductive seasonality that, in general terms, coincides with photoperiodic variations.