Breeding ewe lambs at eight months may increase crop, genetic improvementWritten by Emilee Gibb
Breeding ewe lambs at eight months of age may potentially increase the ewe lamb’s lifetime production, operation production, reduce generation interval and be useful for selecting for fertility, said Paul Kenyon, head of the Institute of Veterinary, Animal and Biomedical Sciences at Massey University in New Zealand.
Kenyon gave a presentation for the American Sheep Institute’s Let’s Grow initiative on improving reproductive performance of ewe lambs bred at eight months.
He noted that, while breeding ewe lambs can prove to be beneficial for producers, it should be a decision made on a yearly and individual basis.
“Ewe lamb breeding should be a year-by-year decision. It needs to be a flexible policy and should be dependent on ewe lamb live weight and predicted feeding levels,” said Kenyon.
Different breeds and breed crosses have differing fertility, with different lines within breeds expressing greater fertility compared to breed averages, said Kenyon.
“Within breeds, there are lines that are very suitable for ewe lamb breeding,” he explained.
When selecting which ewe lambs to breed, it is important that they are at least 60 percent of the mature weight for their breed.
“When we look at mature weight, we want to be around 60 percent of the mature weight to get 80 percent pregnancy rate,” continued Kenyon.
He noted that many farmers do not breed all of their ewe lambs but selectively breed the lambs that have reached the target weight.
Producers can also evaluate body condition score to evaluate whether a ewe lamb is ready to be bred, with performance dropping off dramatically below a score of 2.5.
“When we think about the physiology behind puberty, in all mammals, puberty is triggered when the brain believes that the animal is physiologically mature enough to cope with pregnancy and lactation,” said Kenyon. “One of the triggers that the brain uses is the amount of adipose tissue, or fat.”
As body condition score is a subjective measure of body fat, it can be an accurate tool to determine if ewe lambs have reached their target weight.
“I would argue that that’s a better indicator than live weight,” explained Kenyon.
According to Kenyon, the most important thing to do is to monitor the weight of ewe lambs from weaning to breeding to determine whether they are on track to meet live weight goals.
“The earlier we know we have a problem by monitoring, the more likely we are to successfully fix that problem,” stressed Kenyon. “It’s no good being a month out and figuring that ewes are four or five kilos behind where they should be because it’s going to be too difficult to get them there.”
“Many farmers are excited because they can get their ewe lambs to 40 or 40-plus kilos at breeding. They think they’ve won the game when really, the match has just started,” said Kenyon. “All we’ve done is allow that ewe lamb to get to the start line.”
To be successful, Keynon advised that producers feed pregnant ewe lambs throughout their pregnancy. Traditionally, mature ewes are held at a maintenance diet for the first two thirds of pregnancy.
“We can do this because they’ve reached their mature weight. We can’t do that with a young female because she needs to grow in those first 110 days,” continued Kenyon.
The fetus will use the majority of the nutrients that the ewe lamb ingests in the last third of gestation regardless of whether her nutritional needs for growth are met.
“If we haven’t grown her in that earlier two-thirds, what we’re doing there is setting her up for a large fetus – because it’s going to happen anyway – but she hasn’t grown, and she’s going to have those birthing difficulties,” said Kenyon.
The lighter the ewe lamb is three weeks prior to lambing, the greater chance she will not successfully rear her lamb.
“If we’re going to go to the effort of getting her pregnant and feeding her extra so she gets to that target weight for breeding, we want a lamb to be successfully there at weaning,” he stressed.
Many producers wean lambs off of ewe lambs slightly earlier to give her more time to recover before being rebred.
“Lactation itself is an energy drawer, and it’s harder for the ewe to gain weight during that time. We can also go into feeding her lambs that are lighter using a high quality feed,” said Kenyon.
He summarized the goals of a nutritional program by stating, “It’s about making sure we’ve determined what that target live weight is at breeding for our various breeds, monitoring her so she achieves that and then ensuring that she continues to grow throughout pregnancy.”