Monday, April 22, 2024

Pregnancy information is vital

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At the Veterinary Centre in North Otago we are well into beef cow pregnancy testing. Conditions for beef cows in Otago and South Canterbury have been very good for the last couple of years but with dry conditions it is important to look after beef cow condition heading into winter. With reasonable rain in December and January our area is certainly not as badly off as many other parts of the country. The first east Otago calf sale saw prices very positive, $2.50/kg LW for steer calves and over $2/kg LW for heifers demonstrates there is still feed out there and optimism for the beef market. 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. However, some farmers are taking the option to wean calves early to reduce the amount of condition being sucked off the cows’ backs.
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This season pregnancy testing has been a valuable tool for making stocking decisions. Empty cows can be culled immediately, third cycle/late calvers are identified and preferential feed made available for early calvers.

Many farmers have traditionally just tested for wet-dry but the extra information from the tests is useful if cow numbers need to be reduced further. For aging foetuses the cows need to be 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 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 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 on the mating result depends on the mating management factors such as bull ratios, rotation and bull socialisation.

A veterinary capacity test of bulls is well worth doing to look for any problems in the bull team, especially before the bull sales. It is a good opportunity to review mating procedures for next year.

Making tough decisions for a tough winter

The four basics of beef cow performance that must always be in mind when reviewing the place of a beef herd in your system are:

Rearing  a good even line of weaners by calf sale day (eg 450kg Angus cow rearing a 230kg weaner in 200 days)

Have a tight calving spread (95% of m/a cows in-calf after three cycles/63 days).

Eat summer-autumn roughage and convert to back fat and milk for the calf. This improves pasture for sheep and fat stores can be burnt off over winter without affecting production.

Heifers well grown and mated over a short period (two cycles).

If the beef herd is not achieving these basics the system needs to change. You cannot hope for better results next year without action.

A light, late calving cow now is at best the same next year or more likely an empty cow. In a year like this opening the gates to skinned-out blocks and leaving light cows to it for the winter is a sleep walk to a financial and welfare crisis.

The critical issue for pregnant beef cows right now in the dry conditions is that many pregnant beef cows have not been able to put on condition over the summer to “work” over the winter. If the reserve tank is empty right now with a 120 day winter ahead, spring is looking grim for calf and milk production.

In dry conditions you have to make a plan and take action early. Prioritising is important.

Remove empty cows ASAP.

Identify and draft out light condition cows (<4.5BCS) pre-winter, often 2ndcalvers. These pregnant cows cannot afford to lose further condition over the winter and will benefit from supplementary feeding. Cows that calve in light condition (<BSC 4) and on low covers (<1500kg DM/ha) are at a much greater risk of getting milk fever (calcium deficiency), grass staggers (magnesium deficiency) and ketosis (energy deficiency). Other effects from this are poor milk production and calf growth and greater time taken to resume cycling activity –ie, more likely to end up a late calver or empty.

Remove skinny cows <BSC 3. They will not make it in a tough winter without a lot of TLC. Limited feed resources may be better directed to preventing more animals falling into this category.

Identify late calving cows and graze separately or they can be the next lot of cows to go if conditions demand it. This forced action can have benefits for subsequent beef herd productivity by lifting the system out of the late calving rut and allow for more consistent weaner calf production.

Fat, well fleshed cows (>5.5BSC) can afford to work over the winter. This is the beauty of the beef cow. Losing 1 BCS, ie 50kg, from these cows over winter will not affect subsequent milk and calf production provided the feed can be put in front of them during peak milk production between two and four months after calving. Calving in forward store condition (4.5-5 BCS) is optimal.

BCS 4. Borderline condition. Outline of spine slightly visible.  Outline of three to five ribs visible. Some fat over ribs and hips. 

Do a feed budget

A written feed budget of some sort will help to clarify what measures need to be taken.

The feed demand of a pregnant cow increases significantly in the last trimester of pregnancy. This is at the end of winter when feed supply is at its lowest. Provisions for this period need to be made early. In basic terms you need to know: 

1 How fat/skinny the cows are now. Look hard at how many light cows there are and make a realistic feed plan for them or quit them.

What they have got to eat over the winter. The simplest way to visualise supplementary feed requirements is by using small hay bale equivalents. For example, maintenance for a beef cow is about 7kg DM/day (a third of a small bale). For a cow in late pregnancy this increases to half a bale of hay a day. If you’ve made the decision to retain capital stock start sourcing supplement feed now. It is unlikely to get any cheaper.

Feed budgets are more useful if they are simple, practical and constantly reviewed. They can quickly lose relevance when conditions change. Good, objective advice will help.

Growing stock, replacement heifers and hoggets cannot be compromised nutritionally for long periods. Decisions such as grazing away, starting on supplements, not breeding, selling store etc need to be made as early in the pinch as possible for the long term future of the breeding unit.

There is no right or wrong decision in these adverse times, the real wrong thing is not making a decision. In extreme situations more extreme management decisions need to be made. 

Other animal health considerations

When stock are stressed nutritionally, the effects of other diseases become more apparent.

Parasitism effects are greatest in light stock and when grazing close to the ground. A pre-winter and or pre-calving drench to lighter cows will help.

Deficiencies of magnesium and calcium leading up to calving can be minimised by dusting magnesium oxide through silage or hay or on pasture three to four weeks pre-calving. 100-day magnesium bullets are convenient and effective, especially with lighter cows on low covers.

The demand for copper is greatest in the beef cow in late pregnancy. This coincides with copper being at its lowest plant levels in late winter and molybdonem levels (that prevent copper uptake) being the highest. A copper bullet pre-winter is the gold standard but injectable copper will boost levels for up to three months.  Selenium for beef cows is often overlooked. When extensively run, they are not getting it through fertiliser prils and are not vaccinated or drenched with selenised products. An injection of long acting selenium pre-winter is convenient and will reliably boost levels right through to calving and mating. 

– David Robertson BSc BVSc is from Oamaru Vet Services.

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