Improving lambing, Out-of-season breeding increases herd productivit
“Reproductive efficiency has a really large impact on the productivity and profitability of sheep operations,” said Marlon Knights of West Virginia University’s Davis College of Agriculture, Natural Resources and Design. “Perhaps it is the single most important factor when talking about productivity and profitability.”
While there are a number of factors impacting profits on a sheep operation, Knights noted lambing rates provides a global view of flock performance, and increasing that number improves flock potential.
Knights said lambing rate is described as the number of lambs born per ewe, but he also emphasized that the value should be calculated on the basis of ewes exposed, not the number of ewes that lamb.
“This helps us to determine lambing proportion,” he said. “Prolificacy is the number of lambs delivered by each ewe that is actually giving birth.”
“If we combine these two factors, we get our lambing rate,” Knights said.
For instance, if 100 ewes were exposed to rams, the lambing proportion is 90 percent. If 180 lambs are born, the prolificacy is 200 percent.
Lambing rate is determined by multiplying proportion by prolificacy. In this scenario, Knights noted the lambing rate is 180 percent.
In the U.S., lambing rate has maintained between 100 and 110 percent for many years, and Knights said, “This is not a level that we would think of as being extremely good.”
“Smaller flocks in the East have lambing rates at 140 or 150 percent, and in some cases, large extensive production systems see lambing rates that are smaller than the national average,” he explained.
In addition to lambing rates, the seasonality of reproduction has an impact on the profitability and potential of operations.
“In temperate regions, such as North America, sheep are reproductively active during a very defined season,” Knights commented. “The percentage of ewes in stages of reproductive activity increases in July, August and September, then begins to decline in December, January and February.”
He continued, “By March, very few ewes actually exhibit any signs of estrus or reproductive activity.”
The timing of natural reproductive activity is driven by exposure to daylight.
“The ewe measures daylight, and the time of sexual receptivity correspond to the period of shorter days in the fall,” Knights said. “The animals will be at peak reproductive activity in October, November and December, and as days begin to get longer, reproductive activity ceases. Then, ewes enter a period of anestrus.”
Because of the seasonal nature of reproduction, Knights commented that several impacts are felt by operations.
“Seasonality of reproduction confines the breeding season to one time for the year, and as a result, we have lower annual lifetime productivity of ewes,” he said, continuing that when breeding and lambing occurs within defined windows, the result is lambs reach market weight over a defined period, as well, which has depreciative effect on prices.
“Most of our lambs hit the market at the same time, in the fall period, when prices are relatively low,” Knights explained. “We see that feeder lamb prices tend to be high in June and July before going low for the fall season. Low prices coincide with high lamb supply.”
He added, “Out-of-season breeding would allow us to target higher prices and get lambs to market when prices are high. If we look at an out-of-season breeding model, it suggests if we can breed animals so they lamb in the fall, perhaps our lambs will be ready for market when prices are relatively high.”
Knights posed the question, however, of how can ranchers influence ewes to breed out of season.
“Their reproductive system is, in a sense, deactivated out of season, so we need to get the reproductive system of the ewe going again,” he said.
Luteinizing hormone (LH) is commonly used as a measure of reproductive activity in the ewe. When LH is high, ewes are reproductively active.
“If we want to get ewes back into reproductive activity, we need to do something to increase the secretion of LH,” Knights comments.
A handful of measures can be utilized to influence ewes to produce LH.
First, Knights said light manipulation can be effective but only for small numbers of ewes.
“If we can perhaps make the ewe think it’s fall, with short days, she might begin cycling again,” he said. “The problem is, this strategy is not very practical. We can’t take a large group of ewes and exclude them from light in the summer very easily.”
An alternative would be to treat the ewe with melatonin, known as the “hormone of darkness.”
“Melatonin is only secreted during the night,” Knights explained. “Synthetic melatonin is available to treat the animal and make her believe she experiencing the shortened days of the breeding season, but it is not currently approved for use in ewes.”
The most popular method of inducing estrus is the “ram effect.”
“It was discovered some time ago that if we introduce rams to a group of ewes in anestrus that have been separated from rams for a period of time, the abrupt introduction would stimulate the secretion of LH, eventually resulting in ovulation,” Knights explained.
Research has shown that, if rams are introduced to a flock of ewes, two peaks in estrus activity are observed at 17 and 24 days after introduction.
“Within two to three days after introduction of rams, some ewes start to ovulate, but at least in some proportion of ewes, that ovulation is silent, resulting in no estrus,” he said. “We see estrus and ovulation occurring after 17 days, at which point ewes are sexually receptive and pregnancy can be established.”
Knights presented during a webinar sponsored by the American Sheep Industry Association’s Let’s Grow program. Learn more about out-of-season breeding from Knight’s presentation in upcoming articles in the Wyoming Livestock Roundup.
Saige Albert is managing editor of the Wyoming Livestock Roundup. Send comments on this article to firstname.lastname@example.org.