Abortions and open cows rob potential income from cow-calf producers every year. Dr. Colin Palmer, associate professor of theriogenology at the Western College of Veterinary Medicine, is often consulted when damages mount up. Though reproductive scene investigations aren’t the stuff of high-rated television shows, they certainly capture the undivided attention of his audiences.
By following a trail of clues and questions, you may be able to sleuth out the most likely culprit on your own. If not, your input will be instrumental in helping the experts solve the mystery.
CASE ONE: OPEN HEIFERS… the bull didn’t do it
You can chalk it up to Mother Nature’s culling process if about five per cent or fewer of your cows come up open. When numbers start to rise higher than the norm, the first instinct is to blame it on the bull. As is generally the case in television crime shows, the obvious suspect usually isn’t the guilty one.
In this case, the herd consisted of 500 cross-bred heifers managed in two groups. In group one, there were 237 home-raised heifers split into two subgroups. At preg checking, 57 per cent were found open. It was determined that 18 per cent had caught to AI sires, and 24 per cent were bred by the cleanup bulls. Group two included 263 heifers purchased from three producers in the area. This group was split into six subgroups. All told, 39 per cent of the heifers in group two came up open, 31 per cent were in calf to the AI sires and 30 per cent were bred to bulls on pasture. The producer had spent about $100 per heifer in the AI program alone.
1. Breeding Program:
A progesterone implant-based (CIDR-controlled internal drug release) fixed-time AI protocol was used. This suspect was ruled out following a line of questioning about the products and procedures.
Group one was exposed to four bulls for about two months beginning 10 days after AI. Group two was turned out to pasture with four cleanup bulls for 10 months. The breeding soundness exams and semen tests showed that all of these two-year-old bulls were fit for work. The only concern was the bull-to-female ratio at 1:60 was somewhat on the high side considering that 1:25 or 30 is the standard recommendation. Ratios in the 1:50 range have been known to produce good results when mature, fertile bulls are used, so the verdict was that the breeding program and bulls were not likely to blame.
2. Vaccination Program:
The heifers had been vaccinated with a modified live virus product for IBR, BVD, Pl3 and BRSV. Two treatments were given three weeks apart and the program had been completed two months prior to breeding. Even though the vaccination protocol was top notch, infectious diseases, suchas trichomoniasis, neospora or a wild strain of BVD, were still suspects. Normal investigative procedure calls for pulling blood samples from the heifers and bulls to detect titres to diseases, however, by the time Palmer and his associates were consulted, the bulls had been culled and the heifers had been shipped to a feedlot. 3. Feed and Nutrition:
Each group had been fed a balanced ration consisting of 30 per cent barley grain during the AI period. The summer pasture was native grass and salt was provided. Nothing that would cause this degree of reproductive failure turned up during this leg of the investigation.
After ruling out other probable causes, exposure to a wild strain of BVD prior to breeding was deemed to be the most likely cause. The acute form of BVD in mature animals may cause inflammation of the ovaries lasting up to two months. It may have been introduced by a persistently infected animal or via fence-line contact with neighbouring cattle. BVD is