Where is trigger toboost ewe AI rates?
Where is trigger toboost ewe AI rates?
Improving forage use, suckler cow efficiency, pig welfare, lighting to reduce cow lameness,
sheepmeat eating quality, rearing dairy heifers, and how videos of a ewes cervix could
help boost AI rates. These were just some of a huge range of topics discussed at the
British Society of Animal Sciences annual meeting last week at Scarborough, Yorks.
Sue Rider and Simon Wragg report over the next six pages
CONCEPTION rates to cervical AI of ewes with frozen or thawed semen should improve now researchers better understand what activates the cervix.
Margaret King and John Robinson of SAC Aberdeen have been observing how the cervix reacts to a change in the physiological state of the ewe.
"We want to examine what activates the cervix to make it optimise its function," explained Dr Robinson. The cervix is responsive to certain hormones and the ram – AI takes out these natural stimuli and as a result it is more difficult to get frozen semen into the womb, he said.
Unlike cattle, sheep have a convoluted cervix which is difficult to manipulate by hand. Conception rates following AI with frozen or thawed semen have been as low as 15-20% as a result; 46-52% has been achieved since then but only by inserting four small doses of semen into the cervix.
"Laproscopic AI is achieving conception rates of 80%, so we must try to approach 70% with the cervical method," said Dr Robinson. Cervical observations have helped to explain the variable conception rates with cervical AI.
"The observations give us chance to identify which natural stimuli are missing with AI so we can try to create the conditions to emulate that sort of natural response."
In the SAC trial Mule ewes were synchronised using sponges and PMS; 48 hours later they were restrained by a neck yolk which allowed the rams access to the head and posterior of the ewe.
Miss King then used a hysteroscope device – inserted via the vagina – to view the cervix.
"While the cervix relaxed and contracted in response to a number of external stimuli, there was considerable between ewe variation in the occurrence and strength of the response," said Miss King. Ewes treated with oxytocin, for example, had a more dilated cervix, as did those stimulated by the ram. "But the variation between ewes was very large – some responded very well to the stimuli – others not so well," Miss King said.
The aim is to find an agent which will dilate the cervix sufficiently to allow deeper insemination and better conception.
By observing how the cervix reacts to a change in the physiological state of the ewe, researchers hope to improve conception rates to AI.