Effects of Plasma Insulin, Glucose and NEFA Concentrations of Feeding Frequency During LongTerm in Lambs

Feeding management is a primary tool for influencing growth performance and metabolic health in sheep. In particular, the pattern of feed deliverywhether animals receive a single large meal, multiple small meals, or a continuous supplyaffects the dynamics of plasma insulin, glucose, and nonesterified fatty acids (NEFA). These metabolites act as signals that regulate tissue metabolism, appetite, and body composition. The following review summarises current knowledge on how feeding frequency influences these plasma constituents over the long term in lambs, the physiological mechanisms involved, and practical implications for producers.

1. Background: Why Feeding Frequency Matters

Lambs, especially during the preweaning and early postweaning phases, are in rapid growth and tissue development. Their endocrine system is highly responsive to nutrient cues. When feed is presented infrequently, the postprandial rise in blood glucose is sharp, prompting a pronounced insulin surge. Conversely, frequent or continuous feeding produces a flatter glucose profile and a more stable insulin response. These patterns affect the mobilization or storage of NEFA, the primary circulating form of fatty acids released from adipose tissue.

2. Plasma Insulin Responses

2.1 Acute vs. Chronic Patterns

Acute studies show that a single bolus of concentrate can raise plasma insulin 3 to 5fold within 30minutes, returning to baseline after 23hours. When the same amount of feed is divided into 34 meals per day, the peak insulin concentration is reduced (50% of the singledose peak), but the hormone stays elevated for a longer period. Over weeks to months, lambs on a highfrequency feeding regime tend to develop a lower basal insulin concentration and a blunted postprandial peak, indicating improved insulin sensitivity.

2.2 Mechanisms

• Betacell responsiveness: Repeated moderate glucose excursions reduce the workload on pancreatic cells, preventing hypersecretion.
• Insulin receptor signalling: Stable insulin exposure enhances receptor density and downstream signalling, fostering better glucose uptake.
• Hormonal crosstalk: Lower insulin peaks reduce antagonistic effects on glucagon, preserving hepatic gluconeogenesis during fasting intervals.

3. Plasma Glucose Dynamics

3.1 Postprandial Peaks and Troughs

In lambs fed twice daily, plasma glucose peaks at ~6mmolL within 45minutes after feeding and drops to ~3.5mmolL before the next meal. In contrast, fourtimesdaily feeding smoothes the curve, maintaining glucose between 4.55.5mmolL throughout the day. Continuous access to a lowenergy diet often results in a steady glucose concentration around 4.8mmolL.

3.2 LongTerm Adaptations

Extended periods (8weeks) of highfrequency feeding lead to a modest (510%) reduction in fasting glucose compared with lowfrequency regimes. This reflects improved peripheral glucose utilization and a shift toward greater reliance on oxidative metabolism rather than glycolysis alone.

4. NonEsterified Fatty Acids (NEFA) Patterns

4.1 Relationship With Feeding Frequency

During long fasting intervals, NEFA concentrations rise sharply, often exceeding 0.8mmolL, indicating active lipolysis. Frequent meals blunt this rise, keeping NEFA generally below 0.4mmolL. Continuous feeding maintains NEFA at the lowest levels (0.20.3mmolL), suggesting a persistent anabolic state.

4.2 Metabolic Consequences

• Energy balance: Lower NEFA values are associated with better energy balance and reduced risk of ketosis, especially in rapidly growing lambs.
• Body composition: High NEFA peaks are linked to increased intramuscular fat deposition, while stable low NEFA supports lean tissue accretion.
• Immune function: Chronic NEFA elevation can impair neutrophil function; thus, moderate feeding frequencies may aid disease resistance.

5. Interaction With Diet Composition

The magnitude of metabolic responses to feeding frequency is modulated by the carbohydratetoprotein ratio of the diet. Highstarch concentrates amplify insulin spikes, whereas highfiber diets produce more gradual glucose increases. In practice, combining a moderatefrequency feeding schedule with a balanced concentrateforage mix yields the most favorable insulinglucoseNEFA profile.

6. Practical Recommendations for Lamb Producers

1. Determine growth targets: For maximum average daily gain (ADG), a 3timesdaily feeding schedule with a moderateenergy concentrate (12% CP, 20% starch) is effective.
2. Monitor metabolic indicators: Periodic blood sampling (e.g., biweekly) for insulin, glucose, and NEFA can identify animals at risk of metabolic imbalance.
3. Adjust frequency with age: Preweaning lambs benefit from more frequent meals (45times/day) due to limited rumen capacity; postweaning, 23times daily is sufficient.
4. Consider continuous lowenergy access: Providing ad libitum hay or silage alongside timed concentrate meals can keep NEFA low while preserving rumen health.
5. Integrate with health programs: Stable insulin and NEFA concentrations support vaccine response and reduce the incidence of digestive upsets.

7. Gaps in Knowledge & Future Research

Most longterm studies have been limited to 1216weeks and focus on a single breed. Future work should explore:

• Genotypic differences in metabolic adaptation to feeding frequency.
• Interactions between feeding frequency and environmental stressors (e.g., heat stress).
• Use of precision feeding technologies (automated feeders) to finetune meal timing.

Understanding these aspects will enable producers to tailor feeding programs that optimise growth, health, and feed efficiency.

8. Conclusions

Feeding frequency exerts a profound influence on the plasma concentrations of insulin, glucose, and NEFA in lambs. Frequent, moderate meals tend to stabilise glucose, reduce insulin spikes, and keep NEFA low, fostering an environment conducive to lean growth and metabolic health. Conversely, infrequent large meals provoke high insulin peaks and NEFA fluctuations, which may compromise longterm efficiency. By aligning feeding frequency with diet composition, age, and production goals, lamb producers can exploit these metabolic pathways to achieve better performance and animal welfare.

References: Recent studies in Small Ruminant Research, Journal of Animal Science, and reviews on ruminant metabolism (20202024).