By Scout Nelson
A change in shearing time could offer sheep producers a relatively simple way to improve lamb birth weights and potentially support lamb survival, according to research from South Dakota State University.
The research found that shearing pregnant ewes around day 50 of gestation resulted in larger and heavier lambs, particularly among ewes carrying twins and triplets.
The work explores an interesting question about pregnancy and temperature: While the negative effects of heat stress on developing animals are well recognized, could limited exposure to colder temperatures produce a beneficial physiological response?
SDSU researcher Alex Vasquez-Hidalgo believes it may.
“It appears that some cold stress, not extreme of course, but some cold stress is beneficial for the physiology of the pregnant ewe,” Vasquez-Hidalgo said.
In the United States, ewes expected to lamb in the spring are commonly shorn at approximately 120 days of pregnancy, in part to improve cleanliness at lambing.
Research conducted outside the U.S., however, had suggested that shearing earlier in pregnancy could improve lamb birth weights.
Vasquez-Hidalgo and his team set out to determine whether similar results could be achieved under U.S. conditions.
Why Day 50 Matters
The researchers didn't choose day 50 simply as an earlier shearing date.
It coincides with an important period of placental development. SDSU Extension notes that most placental growth takes place during early to mid-gestation and is largely completed by around day 90.
Because the placenta supplies oxygen and nutrients to the developing fetus, changes occurring during this stage could influence fetal development.
Vasquez-Hidalgo and SDSU graduate student Mara Johnson compared ewes shorn at day 50 with ewes that were not shorn.
From days 50 through 110 of pregnancy, ultrasound was used to monitor umbilical blood flow along with fetal and placental development.
When the lambs were born at approximately day 147, researchers recorded lamb and placental weights and collected placental tissue for additional analysis.
Multiple-Birth Lambs Showed Differences
Some of the most notable results involved ewes carrying multiple lambs.
Johnson's SDSU thesis reports that lambs from twin- and triplet-bearing ewes shorn during pregnancy tended to be heavier at birth than their counterparts from the control group, averaging 5.02 kilograms, or about 11.1 pounds, compared with 4.56 kilograms, or about 10.1 pounds.
Researchers also observed greater umbilical blood flow among the shorn ewes later in gestation.
Among ewes carrying multiples, umbilical blood flow at day 110 averaged about 317.6 milliliters per minute in the shorn group compared with 227.9 milliliters per minute in the control group.
Measurements also pointed to differences in fetal size during pregnancy.
The benefits may have extended beyond lambing.
At 60 days of age, lambs from shorn ewes tended to be heavier, averaging approximately 34.7 kilograms, or 76.6 pounds, compared with 30.8 kilograms, or 67.9 pounds for lambs in the control group.
Researchers caution, however, that not every measurement differed significantly between the groups. When singleton, twin and triplet pregnancies were analyzed together, there was no significant difference in lamb birth weight.
That distinction makes multiple-bearing ewes particularly important when considering the research's potential application on farms.
Why Birth Weight Matters
For sheep producers, increasing birth weight within a healthy range can be important because birth weight is associated with lamb survival.
“Our research showed that twin and triplet lambs born to ewes shorn at day 50 had higher birth weights,” Vasquez-Hidalgo said. “This is good for producers because there is a positive correlation between birth weight and survivability.”
Researchers believe one possible explanation is that removing the ewe's wool temporarily increases the energy required to maintain body temperature.
That physiological response may alter nutrient partitioning, placental function or blood flow in ways that benefit fetal development.
SDSU Extension says shearing during pregnancy can affect metabolic activity and may increase nutrient delivery to the placenta and influence hormones associated with growth and metabolism.
But the research should not be interpreted as a reason to deliberately expose pregnant sheep to dangerously cold conditions.
The theory involves limited cold stress, not extreme exposure. Appropriate shelter, nutrition and animal-welfare management remain important, particularly during South Dakota winters.
A Management Tool Without a Major New Input
The potential advantage for farmers is that shearing is already a normal part of sheep management.
Changing when it occurs may therefore offer producers an opportunity to influence lamb development without purchasing an additional feed additive, animal health product or piece of equipment.
“We can tell a producer it is likely if you shear ewes on day 50 of pregnancy, specifically if they’re carrying twins or triplets, you’re probably going to improve lamb birth weights and survivability,” Vasquez-Hidalgo said. “This is a managerial tool that producers don’t have to spend more on.”
Timing would still require planning.
Producers would need to know approximate breeding dates to identify the appropriate stage of pregnancy. Identifying which ewes are carrying twins or triplets could make pregnancy ultrasound particularly useful if producers were considering a targeted early-shearing strategy.
More Research Underway
The researchers aren't finished investigating the phenomenon.
Vasquez-Hidalgo is now studying whether offspring from early-shorn ewes perceive temperature differently and whether that could provide a longer-term advantage in growth or survival.
Another important question is whether limited cold exposure is responsible for the response or whether something associated with the actual shearing process produces part of the effect.
Answering those questions could help determine how broadly the practice should be applied.
For South Dakota sheep producers, the initial results provide an intriguing possibility: something as straightforward as adjusting the timing of an existing management practice could potentially improve the performance of lambs, particularly twins and triplets.
Photo Credit: Pexels - Ulrick Trappschuh
Categories: South Dakota, Livestock, Goats & Sheep