Skinny ewes less productive

01-08-2010 | Jackie Harrigan

The skinny look might be popular on the catwalk, but when it comes to ewes in a sheep flock, skinny holds back profitability.

Trevor Cook, of Totally Vets, told farmers at last month's Tararua Monitor Farmer day that the single most important driver of profitability in a high lamb price environment was the weight of lambs weaned a hectare.

Weight of lambs weaned a hectare is driven by stocking rate, number of lambs weaned a ewe, and lamb growth rate, Cook says, and the single most important factor determining weight of lambs weaned a hectare is the percentage of tail-end ewes in the flock - those with a body condition score (BCS) below three at mating and lambing.

"There are direct benefits to having fewer lighter ewes at lambing - with a significant jump in gross margins from reducing the number of light condition ewes in your flock," he says.

The two pressure points are premating and at lambing (particularly for multiple-bearing ewes).

Cook showed a potential 15% increase in scanning rate by reducing the number of tail-end ewes at mating (those with BCS of 2.5 or less) from 15% of the flock to 5%. Changing the ratio would lead to higher conception and scanning rates, adding $35 to the gross margin a hectare, he says. The increased lamb survival and weaning weights achieved from putting condition on the tail end ewes has the potential to add $73 to the gross margin per ha.

Some would think it unusual to have 15% of the flock at BCS 2.5, but Cook says it is quite common, and if ewes have more than four weeks' wool growth it is impossible to condition score them by sight.

The effect of higher condition scores prelambing is even more marked, as lamb survival falls 5% for each 0.5 of a condition score lost in the four weeks before lambing, and it falls 5% for every 0.5 condition score below three at lambing.

Winter feeding of multiple-bearing ewes is crucial, he says, because "multiple-bearing ewes are very high-risk animals".

"Allowing multiple-bearing ewes to lose condition coming into lambing is disastrous to production," Cook says.

Lamb weaning weights can fall by 6% if more than 0.5 BCS is lost over the winter, with 4% decrease in weaning weight for every 0.5 BCS lost in the last four weeks before lambing. For every 0.5 BCS below three at lambing in the ewe, the lamb weaning weights are reduced by 6%.

In the six weeks before lambing, twin-lambing ewes need 25% more feed than singles and triplet-bearing ewes require 44% more.

Even yarding triplet-bearing ewes is problematic - aim for a minimum time off grass close to lambing, Cook says. After 21⁄2 to three hours in the yards the level of beta hydroxybutyrate doubles in the ewes. The ketone, produced by the body to provide energy for the brain when blood glucose is low, depresses the lambs, making them less vigorous feeders.

The percentage of the flock below BCS 3 at mating and at lambing sets the performance level of the flock, Cook says.

"Aim for as few ewes as possible below BCS 3."

Cook encouraged farmers to focus on the light-end multi-bearing ewes at scanning time; this was where the biggest gains would be made to profitability - by capturing gains in lamb survival and increased lamb weaning weights.

Skinny ewes at lambing cannot wean heavy lambs nor guarantee their survival, Cook says, because they can't equip lambs with the energy needed to stand and look for food - particularly in bad weather where energy is used to maintain body heat.

Scanning time is the time to make a difference to the lighter ewes, he says.

"Put your total focus on multiple ewes, take off any with BCS < 2.5 and drench and preferentially feed them.

"They must not lose condition in the five weeks before lambing - put the date in your diary to remind you when the five weeks starts."

At lambing the single most important factor in lamb survival is how quickly the lamb stands up. By reducing the time it takes for a lamb to first stand from 45 to 15 minutes, the lamb has a 94% greater chance of being alive at weaning, and the time taken to stand is determined largely by the fat and energy stores a lamb has at birth from its mother.

A ewe produces 40-50% of her total milk supply in the first four weeks of lactation and has a longer and strong milk supply if she has lambed at BCS>2.5 and is fed so that she loses less than one BCS over lambing.

"Feed quality is the key during this period as the ewe can eat up to 5% of her liveweight at this time - at no other time can she eat as much."

By docking the lambs are ruminants getting a milk top-up, he says, and 80% of the diet from docking to weaning is from grass because most of the milk supply is gone by eight weeks.

The speed of rumen growth is due to energy intake from the milk and quality grass; the faster the lamb grows its rumen the faster it grows.

"Lamb growth is not very fast until the rumen is fully functional."

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