Pregnancy tests a valuable tool

01-05-2010 | Dave Robertson

At Oamaru and East Otago Veterinary Services we are well through the beef cow pregnancy testing.

Conditions for the beef cow in Otago and South Canterbury are tough at present, with the prospect of a long winter ahead with depleted feed reserves in traditional cow blocks. Many beef cows are already in light condition.

Pregnancy testing results have been in the usual range of 0-40% empty, with most achieving less than 10% empty after three cycles of mating.

Hard hill-country cows have come out the worst, with 15-30 % empty not uncommon. Those that have mated earlier (November-December) have got cows in calf, but since January cows have been under pressure in the dry conditions, with many farmers taking the option to wean calves early to reduce the amount of condition being sucked off the cow's back.

This season, pregnancy testing has been a valuable tool for making stocking decisions. Empty cows can be culled immediately, third cycle or late calvers are identified, and preferential feed can be made available for early calvers.

Twin-bearing cows can also be identified.

Many farmers have traditionally just tested for wet-dry, but the extra information from the tests is useful if cow numbers need to be cut further. For aging foetuses cows need to be between 35-110 days pregnant at the time of scanning , and as many clients have tested earlier this year it has made foetal aging possible.

The dynamic between cow condition and resumption of cycling is a key factor. Unlike sheep, beef cows cannot be "flushed" for cycling. The resumption of breeding cycles depends very much on what condition they have left on their back from calving. A sobering fact is that a cow beef cow should be at her fattest (BSC 5.5+) at weaning in order to rear a decent calf next year.

Other important factors are calving spread, heifer performance and the age structure of the herd. Disease such as BVD can have a disastrous effect on reproduction, and mineral deficiencies (particularly selenium) are also known to affect cow fertility.

On the bull side, injury and lameness, lack of libido and low fertility are the three main categories of poor performance. The effect of a broken down bull(s) on the mating result depends on the mating management factors such as bull ratios, rotation, and bull socialisation.

Jump testing bulls is well worth doing to look for any problems in the bull team, especially before the bull sales, which are coming up over the next month or two.

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