Multiple mating and siring success during natural oestrus in the ewe

Abstract

Summary. Ewes were each mated on four separate occasions, at 3, 9, 15 and 21 h after the start of oestrus and at each time by a different ram. The progeny were assigned to sires by blood typing, supplemented by resemblance between lambs and rams. The paternity of 64 lambs, born to 41 ewes, was established: 2 were conceived at a 3-h mating, 27 at 9 h, 23 at 15 h and 12 at 21 h. The optimum time for a ram to inseminate, when in competition with others, is therefore 9\p=n-\15h after onset of oestrus, and this finding accords with behavioural observations. Ewes tended to lamb during the same half of the day as that when they had come into oestrus.

Soay rams target reproductive activity towards promiscuous females’ optimal insemination period

“…It is possible that females may have accepted copulations before the onset of focal watching in some cases; however, we do not believe that this would lead to any systematic bias in our analyses. We estimated the OIP to be 12 h after the onset of behavioural oestrus, as this is the midpoint of the 9-15 h OIP that has been demonstrated in a study of domestic sheep ( Jewell et al 1986), which is also consistent with the conclusions of earlier investigations (Slee 1964;Dziuk 1970). The minimum and maximum times from the OIP for each mate-guarding period were used as explanatory terms when testing for an association between male competitive ability and the proximity to the OIP.…”

Factors that affect fertility in a feral population of sheep

“…After that, however, the ram stops tending the ewe and she is again harassed by other rams . This behaviour of the ram accords with our evidence that the most likely period for fertile matings is between 9 and 15 hours after the start of oestrus ( 'Jewell, Hall & Rosenberg, 1986). Even so, the ram may still need to ensure his success as a sire by depositing a large quantity of semen and spermatozoa at the female's cervix during this period to compete with sperm ejaculated there by other rams.…”

“…In a recent paper we showed that when four different rams mate a ewe at 3, 9, 15 and 2 1 hours after the start of oestrus the successful sire is likely to be the one that inseminates the ewe at 9 or 15 hours Uewell, Hall & Rosenberg, 1986); of64 lambs born 27 had been conceived at 9 h and 23 at 15 h. The majority of ewes involved in this experiment were crossbreds but 22 lambs were born to ewes of primitive breeds and 13 of these had been conceived at the earlier insemination time of 9 h. Almost no conceptions resulted from the 3 h matings and few from those at 2 1 h. Evidently when rams are in competition the timing of insemination is important.…”

La conducta sexual del carnero. Revisión

“…Jewell et al (111) found that rams which copulate between 9 and 15 h after estrus started, have higher probabilities to gestate females, since this is the most fertile moment, and it is during this time that dominant males remain rounding these females, avoiding the copulations of subordinates (112) . However, when late copulations occur, the submissive male extract up to 50 % of the semen previously existing in the vagina of females recently covered (113) , in an attempt to increase the chances of their sperm to fertilize.…”

“…Jewell et al (111) encontraron que los carneros que copulan entre las 9 y 15 h de iniciado el celo, tienen mayores probabilidaders de gestar hembras, ya que éste es el momento más fértil, por lo que es durante este tiempo que los machos dominantes permanecen en derredor de estas hembras, evitando las cópulas de los subordinados (112) . Sin embargo, al realizar cópulas tardías, el macho sumiso extrae hasta el 50 % del semen previamente existente en la vagina de hembras recientemente cubiertas (113) , en un intento de incrementar las posibilidades de sus espermatozoides para fecundar.…”