Knowing when cows have taken the bull is a vital bit of information. It helps to explain what the beef herd is doing and the data can be used to winter later cows differently, or third cycle cows can be the first to go if numbers need to be reduced.
The data is really useful for checking bull performance. Poor performing bulls can be identified and culled before the next round of bull sales.
If you have more dry cows than normal but have not age pregnancy tested, you have missed a big opportunity to get to the cause of the problem. Outlined here are several interesting pregnancy testing cases I have been involved with this year that highlight the usefulness of gathering more than the standard wet-dry data.
A target for beef heifer mating is to join for a maximum of two cycles (42 days). If 65% conception rate is achieved each cycle, then 88% of heifers should be in-calf at the end. For mixed-age cows mated for an additional third cycle the target would be 95% in-calf.
Data is useful for identifying poor performing bulls.
Case 2
Too many good empty cows: 120 mixed-age beef cows mated three cycles (63 days, November 25-January 27), 23 dries (19%). Four bulls were used. One was noted to have broken down during mating.
For the first cycle, 67 pregnancies were recorded (56%), 17 pregnancies second cycle (32%), and 13 pregnancies (36%) third cycle. What has gone on here? What are the bull issues and what are the cow factors?
There appears to be a reasonable number of first cycle pregnancies, slightly below the 65% conception rate sought for a top result. It is the second and third cycle conception rate that drops right off.
Yes, bull break-down could contribute to this, and the sires will be service tested in due course, but after the first cycle there were only 53 cows left to get in calf; even if two bulls broke down, there should be plenty of bull power to maintain conception rates.
“They’re probably riddled with BVD”
A sample of 15 cows last year for BVD antibodies showed an S:P ratio of 0.91 (less than 0.75 suggests no recent exposure). The status can be repeated and if there was a persistently infected (PI) animal among them two months ago causing embryonic loss in naive animals the anibody S:P ratio will be much higher than last year. This test is pending, but I will be surprised if BVD is still on the suspect list.
“They are lacking something…”
Selenium and copper were supplemented recently and no obvious ill thrift or mineral issues (other than selenium, which has been addressed) have been diagnosed. Selenium is an important trace element for all sorts of reasons and we have diagnosed deficiency being associated with poor conception rates in other herds. This herd has had long-acting injection of selenium which reliably sorts this out.
“It’s just the dry season”
In Otago the spring was cold and dry and the summer hot-dry (driest in 53 years). Calf growth rates were back on last year and cows were not able to graze the usual blocks because they were skinned out. All this points to cows not getting enough to eat at a critical point in their production cycle, most likely pointing to a non-cycling issue.
- Cows in November-December need 18kg of drymatter to hit peak milk production for the calf and be on a rising plane to trigger cycling activity and ensure good conception rates. That is actually a truckload of grass. We usually don’t notice this in a good year because this is when most farms are in feed surplus. This year I think many beef cows were under nutritional stress during peak lactation when the bull is out – so something has to give.
Accuse the cows
Okay, so let’s just blame the dry conditions, end of story? Not quite. I suspect there are cow calving spread factors that are part of the empty rate.
- Analysis of calving dates of the dry cows shows that 12 of the empty cows were late calvers from last year. These cows would have had calves around mid to late October. In ideal conditions it takes about 40 days for a cow to start cycling again after calving and the first cycle is never as fertile as subsequent heats. A late-calving beef cow not being fully fed in a dry summer, if lucky, might have her first (less fertile ) heat in the second or third cycle of the bull being out, or when under feed stress has prolonged anoestrus and ends up not being mated at all. Once a late calver, always late, if it arrives at all.
The summary of facts suggests calving spread from last year, the lack of quality feed to produce good cycling activity, and some bull sub-fertility were all complicit in a higher than normal empty rate in this herd. Being able to identify late calvers at scanning, and calculating conception rates based on age pregnancy testing data is useful information to diagnosing beef reproduction performance and vital to implementing change that ensures better results for the next season.
- Dave Robertson BSVc BSc, Oamaru Veterinary Centre.
