Producers often correlate lambing ease directly with ram genetics, and while selecting the right sire is always important, there are a other key factors at play.
And ease of lambing doesn’t have to mean smaller lambs - in fact a strong larger lamb from the right ewe will increase both survival and growth rates.
That’s according to Lincoln University's Professor in Animal Breeding and Genetics Jon Hickford.
“If a lamb comes out under 2.5kg (single or multiple) that is a good rule of thumb to suggest it will die. As it gets up to 3.5kg its chances of survival goes up dramatically, and survival goes up further as weight does,” Professor Hickford said.
“For those people who have lamb survival issues, if they weigh dead lambs and they are under 2.5kg, those lambs aren’t big enough at birth and they need to improve pregnancy nutrition. A small lamb is on the back-foot growth wise and does not grow rapidly...you are left with a situation where you started out bad and it just gets worse. Growthy lambs are big to start with, if lambs are small at birth you are playing catch up through to weaning and beyond.”
And the size of the lamb is primarily feed related, according to Professor Hickford.
The good autumn and early winter seasonal conditions in much of the sheep growing area of Australia has led to better late pregnancy growth in lambs this year and Professor Hickford said that should lead to two things - slightly bigger lambs and lambs metabolically better off.
“This means a lamb typically has better reserves of brown fat - stored energy on its carcass - and that brown fat is incredibly important for that lamb when it comes out, because it is associated with having increased vigour,” he said.
That vigour equates to lambs that are up on their feet and mobile soon after birth, getting them off the cold ground and allowing them a better chance to escape predators.
“Also, if the lamb doesn't get up the ewe can lose interest in it, that is a mothering ability issue, so it may not get a drink, it misses out on colostrum and misses out on that first good stomach full of milk that gets it going,” Professor Hickford added. “You will often find dead lambs still have clean feet and if you split them open their stomachs will be empty, they never actually drank.”
Professor Hickford said producers using Poll Dorset ram should focus first on nutrition, and also consider ewe size.
“Starving ewes in late pregnancy is not a smart thing to do whether you are using a terminal Poll Dorset ram to produce lambs for the meat trade, or you are using a Merino ram to produce replacement ewes for wool production, lambs that are starved in utero and late pregnancy ewes that are underfed is really bad thing...the key time for feeding sheep is coming up to birth,” he said.
“You’ll hear from Merino producers that ‘the lamb was too big because it was a Poll Dorset and it got caught on the way out - dystocia’. That is a real problem, and it is associated with bigger lambs, but it is also associated with smaller ewes. Especially smaller ewes that have never been selected on ease of birthing.
“The argument then is that overly large lambs cause problems at lambing -but that is probably not true, it is more a reflection of the ewe - it is easy to blame the lamb, but it is actually the ewe.
“The policy here in NZ is if the lamb doesn’t come out the ewe dies and the lamb dies. And that isn’t a problem, as it takes out a poor mother. Sit on ewes that don’t perform at lambing - studs do this the most effectively culling out poor mothering lines but we also need to do that on commercial properties.”
Professor Hickford said we don’t want ewes too big, because the maintenance cost of feeding, but too small and they will produce smaller lambs, as well as less wool if it is a Merino flock.
“Larger ewes have better survival rates - the size of the uterus is bigger, and a bigger lamb has a small surface area to volume ratio and it is through the surface you lose heat. Small animals have a small surface to volume ratio, so they lose a lot of heat. Larger lambs produce more heat and have a large surface to volume ratio.”
Mothering ability is a key selection tool for the more successful producers across the ditch, Professor Hickford said, as it is a heritable trait.
“Based on observation we are culling out the poor mothers, and their lambs too...we are not using those as breeding stock as you are perpetuating a problem. A bad ewe is a bad ewe is a bad ewe.”
“The national average weaning rate in NZ is 126-7 per cent, but plenty are achieving up to 180 percent. Lifting lambing from 120 to 150 per cent, in terms of farm finances, that is a huge lift. Often you can do it with no investment at all, just better feed and management.”
Bad weather is another element to lamb survival which is overstated, Professor Hickford said, referring to it as a “bit of a copout”.
“For a lamb that is light and frail and has no energy, bad weather may be the killer blow to them - but for a lamb that has come out with good body reserves and is on its feet they are remarkably resilient, they can tolerate immense cold and heavy frosting. As long as they are on their feet and aren’t lying as they can freeze to the ground, they can tolerate temps -10 and below.”
“A focus on ewe nutrition will improve lamb survival. Any ewe that is a bad mother is a cost to your operation - regardless of the size of the lamb. There are other genes that impact the ability of the lamb to mobilise fat and keep warm and we have been selecting for that in NZ for a number of years - a simple gene test we run, and find those rams that are better at breeding lambs that mobilise brown fat reserves and keep warm.
“But it is the icing on the cake - but basic feeding systems and mothering ability are right, and we can then deliver genetics that improve your survival.”