Have been using MGA synchronization on both cows and heifers for over 15 years, was written about in Beef magazine back in the 90s. Over the next week I am breeding 400 heifers in four herds all using MGA. My worst conception rate over the past years has been 60%, I have hit 100% in a herd of cows last year, but they were hand selected. My average over the past 15 years has been 76% on both cows and heifers.
The protocol we are using is 14 days of .5 MGA, then 19 days later a shot of prostaglandin, then breed on heat. An alternative I have had success with is 14 days of MGA, 19 days later the Prostaglandin, breed on heat, then at 70 hours breed everything that has not shown heat and give them a GnRH shot. Last year on two herds of 100+ cows each, using this program I hit 85%, and had both done in 3 days of actual breeding.
Have been using CIDRs since before they were legal in this country, started using them when breeding elk. There sure were a lot of pump diaphragms that came into the country for three years from north of the border, and from south of the border for that matter, but most of those were in boot boxes. If you can put up with the extra labor, they work well, but that is an indivdual call. I have found that a key to making them work is washing and disinfecting the applicator and disinfecting the CIDRs just before insertion. That has sure cut down on infections and a couple of vaginal prolapses that occured early in the learning process of using them. Last year bred 600 cows and heifers using them, had a 75% conception rate on the whole group, and that included one herd of 160 that we time bred and thanks to a shipping mixup did not have the GnRH. In talking to the rancher this afternoon, he said we hit 54%, so that pulled the average down a bit.
One problem in overfeeding the MGA is that the product is fat soluble and is stored in the body fat of the animal. When this happens, especially in long term feeding as in feedlot heifers, it continues to be released over a longer period of time, in some cases as much as 20-30 days after the feeding has stopped. If you are expecting to breed them 19-23 days after stopping feeding, you will be breeding on the sub fertile heat off the MGA. Had one customer who also thought more is better and fed them 1mg for 14 days. They were in good (fat) shape and did not start cycling for 35 days after the program was supposed to end. That was an easy one to win when she threatened to sue me for ruining her heifers.