📄 agriculture

Late-gestation feed restriction reduces colostrum quality and lamb birth weight in Awassi ewes under semi-arid conditions

Late-gestation feed restriction in Awassi ewes under semi-arid conditions induces negative energy balance, reduces lamb birth weight, and significantly impairs colostrum quality—particularly in twin-bearing ewes—highlighting the critical need for targeted nutritional supplementation to support productivity in low-input systems.

Original authors: Ali Salah Wadday, János Posta, Renáta Knop

Published 2026-07-01

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CC BY 4.0

Original authors: Ali Salah Wadday, János Posta, Renáta Knop

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a sheep farm in the hot, dry deserts of Iraq, where the local sheep (called Awassi) are the main breed. These sheep are like hardy, local heroes, but they face a tough challenge: food often runs short just when they need it most.

This study is like a controlled experiment to see what happens when these pregnant sheep don't get enough food right before their babies are born. The researchers wanted to know: Does starving a mom sheep for the last two weeks of pregnancy hurt her, her milk, and her babies?

Here is the story of what they found, broken down into simple parts:

1. The Setup: The "Half-Full" vs. "Full" Tank

The researchers took 80 pregnant sheep and split them into two groups:

The "Full Tank" Group: These sheep got 100% of the food they needed. Think of this as a car getting a full tank of gas before a long trip.
The "Half-Full" Group: These sheep got only 60% of the food they needed. This is like trying to drive that same long trip with the gas gauge hovering near "E."

They watched these sheep closely for the last two weeks of pregnancy, through the birth, and for a week after.

2. The Metabolic Crisis: The Body Eating Itself

When the "Half-Full" sheep didn't get enough food, their bodies went into emergency mode. Because the babies inside were growing fast and demanding a lot of energy, the moms' bodies had to start burning their own fat reserves to keep going.

The "Fat Leak": Imagine the sheep's body as a warehouse. When food stops coming in, the warehouse starts breaking down its own stored boxes (fat) to sell for cash (energy). This released a lot of "fat particles" (called NEFA) into the sheep's blood.
The "Toxic Smoke": As the liver tried to burn this extra fat for energy, it produced a byproduct called ketones (measured as BHBA). In the restricted sheep, these levels got so high that they crossed the line into "subclinical ketosis." Think of this as the engine running so hot it's starting to smoke, even though the car is still moving.

The sheep that were fully fed didn't have this problem; their engines ran cool and clean.

3. The Surprise: Twins vs. Singletons

The researchers also noticed something interesting about the size of the family.

Singletons: Sheep carrying one baby.
Twins: Sheep carrying two babies.

When food was scarce, the sheep carrying twins suffered the most. Their bodies were like a small car trying to pull two heavy trailers with a half-tank of gas. They produced the worst quality milk. However, when the twins were fully fed, their milk quality was just as good as the single-baby sheep. The extra food completely fixed the disadvantage of carrying twins.

4. The Consequences: Milk and Babies

The lack of food had two main results:

The Milk (Colostrum): The first milk a sheep produces is like a "super-drink" full of antibodies (immunity) for the newborn. The restricted sheep produced milk that was thinner and weaker (lower "Brix" score). It was like serving watered-down juice instead of the rich, nutritious punch the babies needed to fight off germs.
The Babies: The lambs born to the hungry moms were lighter. Whether they were single or twins, they weighed less than the babies born to the well-fed moms. It's like a baby born to a mother who didn't eat enough during pregnancy being smaller at birth.

5. The Big Takeaway

The study concludes that in these dry, low-budget farming systems, the last two weeks of pregnancy are critical.

If you don't feed a pregnant sheep enough during this time, her body starts eating itself, her milk becomes weak, and her babies are born smaller. The damage is especially bad for moms carrying twins.

The Simple Lesson: If you want healthy lambs and strong immunity for the newborns, you must make sure the moms get plenty of food right before they give birth. It's the difference between a car running on fumes and a car running on a full tank. For the moms carrying twins, this extra food isn't just a luxury; it's the only thing that levels the playing field.

Technical Summary: Late-Gestation Feed Restriction in Awassi Ewes

Problem Statement
Awassi sheep constitute the dominant indigenous breed in Iraq, typically raised in low-input, semi-arid systems characterized by seasonal feed scarcity. During the final 40–50 days of gestation, fetal growth accelerates, drastically increasing maternal requirements for net energy and glucose. When feed intake fails to meet these demands, ewes enter a state of negative energy balance (NEB), leading to adipose mobilization, elevated non-esterified fatty acids (NEFA), and the production of ketone bodies (specifically $\beta$ -hydroxybutyric acid, BHBA). This metabolic state predisposes ewes to subclinical ketosis and pregnancy toxemia, conditions with high mortality rates, particularly in twin-bearing animals. Furthermore, periparturient undernutrition is linked to reduced colostrum quality and lower lamb birth weights, representing significant economic losses in systems with limited veterinary intervention. Despite the recognized importance of this issue, there is a scarcity of controlled, field-based studies quantifying the metabolic and productive consequences of feed restriction specifically in Awassi ewes under semi-arid conditions.

Methodology
The study was conducted on a sheep farm in the Bahr Al-Najaf depression, Iraq, between December 2024 and May 2025. Eighty clinically healthy, multiparous Awassi ewes were enrolled and stratified by litter type (singleton vs. twin-bearing) and parity. Using a randomized allocation procedure, ewes were assigned to one of two feeding groups during the final two weeks of gestation:

Restricted Group (R60, n=40): Fed 60% of estimated metabolizable energy and crude protein requirements.
Control Group (C100, n=40): Fed 100% of estimated requirements.

The experimental ration consisted of barley grain, maize, wheat bran, soybean meal, salt, and a limestone–digestive premix. Feed intake was individually recorded daily.

Measurements and Analysis:

Metabolic Profiling: Blood samples were collected at four timepoints: 14 days pre-lambing (Day -14), 7 days pre-lambing (Day -7), within 4 hours of parturition (Day 0), and 7 days post-lambing (Day +7). Serum was analyzed for BHBA, NEFA, glucose, total protein, albumin, blood urea nitrogen (BUN), minerals (calcium, phosphorus), liver enzymes (AST, ALT, GGT), and lipids (triglycerides, cholesterol).
Production Traits: Body weight and body condition score (BCS) were recorded at each timepoint. Colostrum was collected within 2 hours of the first nursing event, and quality was assessed via Brix refractometry as a proxy for immunoglobulin G (IgG) concentration. Lamb birth weight was recorded within 1 hour of parturition, and survival was monitored to Day +14.
Statistical Approach: Data were analyzed using linear mixed models (for repeated measures), two-way ANOVA (for colostrum quality), and non-parametric tests (Mann–Whitney U, Fisher's exact test) where appropriate.

Key Results

Metabolic Status: Feed restriction induced a pronounced negative energy balance. R60 ewes exhibited significantly higher overall levels of BHBA (0.89 vs. 0.81 mmol/L; P < 0.001) and NEFA (0.83 vs. 0.65 mmol/L; P < 0.001) compared to controls.
- Subclinical Ketosis Risk: By Day -7, 85% of R60 ewes exceeded the subclinical ketosis threshold (BHBA $\ge$ 0.8 mmol/L) compared to 50% of controls. This disparity persisted through Day +7 (80.0% vs. 40.0%).
- Lipid Mobilization: NEFA levels in restricted ewes continued to rise through lambing and remained elevated post-partum, indicating that the metabolic debt of late gestation was not resolved at parturition.
Litter Type Effects: Twin-bearing ewes, regardless of feeding group, had higher BHBA and NEFA concentrations than singleton-bearing ewes, confirming their greater metabolic susceptibility.
Colostrum Quality: Restriction significantly reduced colostrum Brix values (19.77% in R60 vs. 22.27% in C100; P < 0.001).
- Interaction Effect: A significant interaction was observed between feeding group and litter type. In the restricted group, twin-bearing ewes produced the lowest quality colostrum (18.45% Brix), whereas under full feeding (C100), colostrum quality did not differ significantly between single and twin-bearing ewes.
Lamb Birth Weight: Lambs from restricted ewes were significantly lighter than those from controls across both litter types (e.g., singletons: 3.80 kg vs. 4.20 kg; twins: 3.40 kg vs. 3.68 kg).
Correlations: At lambing, colostrum Brix was negatively correlated with NEFA levels ( $\rho$ = -0.305) and positively correlated with glucose levels ( $\rho$ = 0.246).

Significance and Claims
The paper claims that adequate nutrition during the final two weeks of gestation is critical for preserving the metabolic health of Awassi ewes in semi-arid environments. Specifically, the study demonstrates that:

Feed restriction to 60% of requirements precipitates a state of negative energy balance, elevating the risk of subclinical ketosis and pregnancy toxemia.
The negative impact of restriction on colostrum quality is not uniform; it is disproportionately severe in twin-bearing ewes. Adequate feeding appears to offset the inherent colostrum disadvantage associated with carrying twins.
Restriction leads to lighter lambs, which is a direct risk factor for neonatal survival and growth in low-input systems.

The authors conclude that targeted supplementation of late-gestation Awassi ewes, with a specific priority on twin-bearing animals, is a practical and necessary management intervention for low-input, semi-arid production systems to mitigate metabolic disease and improve neonatal outcomes. The study acknowledges limitations regarding its single-site design and the proportional nature of the feed restriction (affecting energy, protein, and minerals simultaneously), but asserts that energy deficit was the dominant factor driving the observed metabolic and productive changes.