Repeatability and relationship with field mating performance of a serving capacity pen test in rams

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.

The relationship between ram breeding capacity and flock fertility

The effect of breeding capacity of rams on flock fertility was studied by exposing each of 15 rams to 1 of 15 flocks of 200 naturally-cycling ewes for 17 days. Five of the rams were arbitrarily designated as being of high breeding capacity (mean+/-SEM = 14.7+/-0.5 services in 2 3-hour pen breeding tests); five rams were designated as being of medium capacity (7.3 +/- 0.2); and the remaining five were designated as being of low breeding capacity (1.7 +/- 0.5). Breeding capacity was shown to be positively correlated with the number of services during flock mating, to the number of ewes mated and to insemination success. Breeding capacity as measured in a pen test of shorter duration (1 hour) was shown to be similarly related to flock fertility. Further, the number of services during flock mating was also positively correlated with the number of ewes mated and impregnated, as well as to the number of fetuses conceived and to insemination success. Breeding frequency of the ram is, therefore, closely related to flock fertility, but breeding capacity, as measured in the present study, is only a moderately accurate indicator of breeding frequency.