Thursday, March 28, 2024

Nothing is simple

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As the ewe pregnancy scanning results came in over the past two months it confirmed that getting high scannings and/or low dries is the result of a complex combination of events. Just having the best genetics has certainly proved to not be the key factor. Similarly just keeping the ewe condition up has not necessarily been protective, although, unless condition score is closely monitored, being half a condition score behind would not be noticed yet have a big effect.
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A flushing effect has in many cases not appeared to have helped. The real feature of the scannings I have come across is how variable they have been.

While overall the results are back about 10% or less, there have been some real anomalies. To me this illustrates that getting all the ducks in a row is necessary to get a good result.

Of course being able to clearly identify the duck out of line when presented with data 90 days after the event is nigh impossible. No amount of testing of empty or single ewes will show up the cause. Reflecting on ewe condition and feeding levels in the autumn is too often guesswork. It is disconcerting, though, when that data is available, and it was not indicative of a problem, to still have a poor result.

Clearly other feed factors are operating that we do not understand, let alone measure. It has been surprising how well many of the flocks, heavily supplemented in the face of a drought, have performed. Has this diet taken out some of the “hidden” factors that exist in pasture? Often these supplemented flocks are underfed because the cost of feed so easily puts up a psychological barrier to the amount fed. Despite that, so many have performed well.

The role of endophyte toxins in depressing ewe breeding performance is often suspected, rarely proven, and certainly difficult to measure. These are probably one of those hidden feed factors.

The absence or presence of toxic signs, in young stock in particular, is usually the only way of having any idea if these toxins are about. Ryegrass staggers is the most obvious sign. These symptoms were rarely seen this summer and autumn.

I have always suspected that the level of toxins in pastures in the autumn has a major affect on the number of dry ewes. The scanning results this winter have been surprising in the low dry rates in many flocks despite being light at mating. Does weight and/or condition at mating (within reason) determine just the multiple ovulation rate, not the dry rate? If so, then other factors must have the most impact on the dry rate.

Of course this is not the case for two-tooth ewes. The dry rate in these is closely linked to their weight at mating and is still an obstacle to good scannings in many two-tooths.

Once again, the incidence of wasting ewe hogget pregnancies is high enough for us to know that we are missing something. We can conclusively say that it is not due to the infections that we know about in many of the cases. Its recurrence on properties is not always a feature, but is the case for some. The big proportion of hoggets in some mobs that have this wasting is huge: up to 50% is now not surprising us.

Other unusual findings are this being in one mob on the farm and not in another.

Given the extra profitability that lambing hoggets can bring to many if not most sheep breeding systems, finding solutions to this problem has to be a priority. Considerable effort is going into this, but progress in useful outcomes is slow. A big frustration with the ewe hogget problem is that nearly $3/hogget has been spent on pregnancy saving disease vaccines. Seldom are these diseases being found in the problem flocks.

Vaccine costs now are significant contributors to the total animal health costs. The reproductive vaccines for both sheep and cattle are effective and considerable risk is being taken by excluding them from the breeding programme.

Nevertheless doing cost-benefit analyses on the use of these vaccines is difficult, unlike the twinning vaccines, or more aptly, the vaccines against singles. For flocks that are scanning below 150%, it is relatively easy to work out the cost/benefit equation for investing in these vaccines. For two-tooth ewes getting $2.80 of sensitisers and boosters, a modest gain of 10% more lambs weaned gives well over twice the return on the vaccine cost. Furthermore, if that vaccination status is boosted the next year, the return on the vaccine costs is at least three times.

Of course the package that supports good lamb survival has to be concurrently applied to get such benefits. The test of the effectiveness of that package is now on our doorstep for all flocks. 

Trevor Cook, veterinarian, Manawatu.

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