Primiparous and multiparous lactating crossbred dairy cows with a mature corpus luteum and a follicle with >10 mm in diameter were treated with cloprostenol. Those cows that showed oestrus within 5 days after treatment were inseminated (Group P). The other cows (Group PG) were treated with GnRH 2 days after cloprostenol treatment and timed artificial insemination (AI) was performed on the consecutive day, or were inseminated (Group G) after detected oestrus and treated with GnRH immediately after AI. The control cows (Group C) after detected oestrus were only inseminated. All of the AIs using frozen semen were done between 6 and 7 a.m. while the ultrasonographic examinations after AI were performed between 4 to 6 p.m. The ovaries of each cow were scanned by means of transrectal ultrasonography from the day of AI until ovulation. Daily blood samples were collected for progesterone measurements. The ovulation and preg- nancy rates among the groups changed between 84.6% and 95.5%, as well as 44.4% and 60%, respectively, however the differences were not statistically significant.

All the cows were evaluated according to date of ovulation after AI and the pregnancy rate was 55.4% (Group 1: ovulation occurred between AI and 9-11 h after AI), 54.5% (Group 2: ovulation occurred between 9-11 h and 33-35 h after AI) and 35.5% (Group 3: ovulation occurred between 33-35 h and 57-59 h after AI), respectively. There was a trend (P=0.087) for 2.2 greater odds of staying open among cows inseminated between 33 to 35 h and 57 to 59 h before ovulation compared to cows inseminated within 9 to 11 h before ovulation. If ovulation occurred before AI, the pregnancy rate was only 22.2%, therefore determination of optimal time for AI is of great importance.

In literature, it is known that a Light Emitting Diode (LED) could be used as a light sensor. It is also known that its emitted light spectrum and sensitivity spectrum can be partially overlapped. This work presents how commercial LEDs can be used as light emitters and simultaneously as sensors of the reflected portion of the light emitted by themselves. The realized devices present a unique characteristic: the transmitter and the receiver coincide spatially as they are the same device. This ensures the perfect overlapping between transmission and reception radiation lobes that could provide many benefits in several applications like as distance measurements or image sensors. Some simple electronic configurations that use LEDs as detectors of their own emitted light are presented. It has been also demonstrated how these LEDs_Tx-Rx can work as image sensors by acquiring an image of a simple test object, and how they can realize distance sensors with respect to other known techniques. Further advantages can be obtained by realizing LED_Tx-Rx array in single integrated devices. With the realization of such devices, it will be also possible to experiment new constructive solutions for commonly used applications, without the need of using separate emitter and receiver.