Question 5 Flashcards
Explain what type of hormone manipulation of the estrous cycle the CIDR is, describe the physiological process of each intervention (e.g. device insertion and injections), and provide a diagram of the CIDR protocol
Controlled internal drug release (CIDR) is a method of extending the luteal phase by administering progestins (progesterone). High progesterone levels will keep the cow in diestrus, and luteolysis will not occur. This P4 will have negative feedback on the hypothalamus, reducing basal GnRH amplitude and frequency. This prevents development of preovulatory follicles, production of estrogen, LH surge and mating behaviour. Without an LH surge, ovulation will not occur (P4 block).
Typical protocol leaves CIDR in for 7-8 days. One day prior to removal of CIDR, the cow is given a Prostaglandin F2a (PGF2a) injection which causes regression of the corpus luteum (CL) if present. The animal must be at least six days into their luteal phase for the injection to work. PGF2a allows for the transition into the follicular phase (proestrus then estrus). During the proestrus stage, GnRH release leads to FSH and LH secretion. Ovarian follicular development starts, and a follicle will reach the preovulatory stage. During estrus, this preovulatory follicle will ovulate following an LH surge. This all occurs within a couple of days of the PGF2a injection, so the cow should be monitored for signs of estrus and then inseminated in a timely manner. This technology can be used to synchronize estrus in groups of cows, control when an animal enters estrus, or help bring anestrous or heifer cows into heat.
Look at diagram
What other alternative to address DRTC challenges would you recommend to the manager? Explain the physiological mechanisms of your proposed method.
A CIDR protocol requires estrus detection, which is difficult in a tie-stall system like the DRTC. My main recommendation would be implementing a protocol like OvSynch, which does not require estrus detection. Instead of synchronizing estrus, we would be synchronizing ovulation. In OvSynch, a GnRH injection is given at day zero, which causes LH and FSH release and therefore ovulation and new follicle growth. At day seven, a PGF2a injection is given, which causes the CL to regress followed by maturation of the dominant follicle. At day nine, a second GnRH infection is given which induced ovulation, and then 16-20 hours later the cow should be artificially inseminated. Ovsynch works well in herds with poor estrus detection rates, and has high pregnancy rates. In order to improve conception rate, we could even combine the Ovsynch protocol with a CIDR device. CIDR would be put in at day zero, at the same time as the first GnRH injection, and left in until the PGF2a injection on day seven.
Ovsynch can be more costly to producers, even more so if doing the “CIDR-synch” protocol, so I also wanted to talk about ways to improve estrus detection rate without complicated protocols. The best for a tie-stall system would likely be temperature loggers. These can be placed in the vagina, and detect changes in temperature related to various stages of the estrous cycle. There should be an increase in temperature for a couple hours during estrus, associated with LH surge and ovulation.
Look at ovsynch diagram
