23 August 2002

POORNUTRITIONATTUPPING

TIMEBLIGHTSLAMBCROPS…

Ensuring ewes and rams

receive the correct level of

nutrition during late summer

will boost lamb crops next

spring. Richard Allison

seeks the latest advice

POOR ewe nutrition around tupping not only reduces lamb crops in the short-term, but future crops from the following years ewe lambs can also be up to 0.3 lambs a ewe lower.

Ewe nutrition in the period leading up to tupping affects the number of eggs released at ovulation, says SAC animal reproduction professor John Robinson. "A fixed number of follicles are already committed six months before ovulation and nutrition over this period affects how many will survive and ovulate."

Follicles require the correct level of certain hormones at the right time to mature into eggs. Key nutrients are also essential at certain times to maintain follicle development.

While little can be done to prevent follicle losses when ewes are under harsh conditions in summer, flushing ewes before tupping will compensate. This is because improving nutrition before tupping minimises losses of remaining follicles before ovulation, says Prof Robinson.

The aim is to achieve a body condition score of 3 at mating for crossbred ewes, says sheep adviser Pat McCambridge of Greenmount College, Co Antrim. "With hill ewes this may be more difficult to achieve and a target of 2.5-3 is more appropriate.

Six weeks

It takes about six weeks on good grazing to improve ewe body condition by one unit. Normally, three weeks flushing is required in most flocks, but this may need to be extended when grazing conditions are poor. Mr McCambridge advises body scoring ewes at least eight weeks before tupping.

"Ewes in poor condition with a score 1.5-2.5 should be offered preferential grazing on swards 6-7cm high with grass covers of more than 2000kg DM/ha in front of fitter ewes."

But flushing can be overdone, warns Prof Robinson. While ovulation rates will increase further as body condition exceeds the recommended target, embryo mortality rates also increase." This leads to fewer lambs born, which are generally poor, and is why fat ewes often produce a small single lamb."

This may explain why some flocks saw their highest lambing percent this spring, says Devon-based Signet consultant Rob Shields. "Many ewes were trapped in overstocked fields by foot-and-mouth restrictions and lost body condition before tupping. Ewes were then offered supplements when with rams, helping to maximise embryo survival."

This year, excess body condition is likely to be a greater problem than in previous years with lots of grass available on many farms.

Slimmed down

Fat ewes can be slimmed down by increasing stocking rates to 25-30/ha (10-12/acre) or placing in a building and offering straw. But young ewes need plenty of feed, as they are still growing. Mr Shields advises separating shearlings and offering extra feed according to body condition.

Overfeeding ewes during the first month of pregnancy also increase embryo mortality, says Prof Robinson.

High feeding levels increases liver size leading to more progesterone being removed from blood.

"Low blood progesterone levels at days 10-11 post-mating were found to increase embryo mortality. Fortunately, grazing alone is ideal for maximising embryo survival after conception."

He believes ewe nutrition during the first month of pregnancy also affects reproductive performance of the foetus in later life. "Key nutrients are essential during certain stages of embryo development for switching genes on or off, affecting performance in adult life."

Latest data suggests poor ewe nutrition can permanently reduce lamb crops by 0.2-0.3 lambs a ewe. But the effects have been observed up to the third crop with work to examine subsequent years still progressing.

"The reason for this reduced prolificacy is unknown. It could be either a reduction in egg numbers at ovulation or increased embryo loss after tupping."

Ensuring tups are at the correct body condition score is also crucial. Mr Shields believes tups are also likely to be over fat this autumn having nothing to do since last autumn and having plenty of grass, says Mr Shields. "Semen quality tends to be poorer with fatter tups. Aim for a body condition of 2.5-3 at tupping."

Body condition

But Mr McCambridge believes tup body condition should be higher, building them up gradually over a seven-week period to a body score of four at the point of mating. Rams lose about 15% of their body weight during the mating period.

Also aim to complete vet treatments of tups well in advance of mating, he advises. "A settled period of 4-5 weeks duration is important before mating."

The pre-tupping health check should look for problems with teeth, feet, testicles and penis. Worming is also recommended, as tups will be joining ewes on infected pastures.

To ensure good crops next year, Mr Shields advises using teasers to maximise conception rates. Ideally one teaser should be used/100 ewes, and one tup for every 35 ewes. &#42

&#8226 Excess body condition.

&#8226 Long-term effects.

&#8226 Check tup health.

Poor ewe nutrition during early pregnancy can reduce reproductive performance of the next generation, says John Robinson.