Breeding season will be soon underway for the mid April and May calving cow herds. However, we all have some late calving cows that are less than 40 to 60 days postpartum. The question is how can we “jump start” some of those late calving cows to start cycling and move them up in the calving season?
A tool that is effective and can be used with natural service or artificial insemination is the CIDR, an intervaginal progesterone insert. The CIDR is recognized as a synchronization hormone, however, can also effectively induce cyclicity in anestrous cows.
Prior to the start of an estrous cycle post calving, an increase in progesterone is necessary to “prime” the system for the other reproductive hormones to begin functioning. Research conducted at the University of Minnesota (2006), demonstrated that 55% of anestrous cows approximately 40 days post calving reinitiated cycling after a CIDR and prostaglandin injection. The exogenous form of progesterone from the CIDR “primed” the system and reduced the occurrence of short estrous cycles.
An insertion of the CIDR for 7 days is a protocol that is effective and easy for the use with natural service. This will jump start cows but not cause them to be too tightly synchronized for bulls to cover. The question of bull to cow ratio is concern to many. Studies confirm that a 1:25 ratio is acceptable. However, caution needs to be taken in regards to bull’s age, breeding soundness and libido. It has been shown that an experienced bulls are better suited for breeding cows that have been synchronized.
The combination of a CIDR with gonadotropin releasing hormone (GnRH) and/or prostaglandin (PGF) can be used with artificial insemination. Refer to the 2014 Beef Cow Protocols developed by the Beef Reproductive Task Force for CIDR based synchronization protocols.
Progestin based hormones are an effective method of inducing estrous cycles, however, not the magic bullet. All cows will experience uterine involution, the time when the uterus regresses back to normal shape and size before she will start cycling. This takes at least 20 to 40 days post calving. It is important not to insert a CIDR within 21 days of calving because it can hinder uterine contractions which is an important process of uterine involution. Nutritional status and body condition score prior to calving plays a critical role in the length of the postpartum interval. Lastly, the suckling effect has an influence on the time from calving to breeding.
Another progestin based protocol that was not covered in this article is melengesterol acetate (MGA). MGA can also induce estrous cycles. Contact Robin Salverson, SDSU Extension Cow-Calf Field Specialist, for additional information at 605.374.4177.