Recovery After Surgery: Cellular Immunonutrition and Tissue Regeneration

Why does the body work differently after surgery?

The metabolic response to surgical trauma has been described for close to a century. The classical two-phase model, accepted since Cuthbertson's early work, describes an initial ebb phase focused on preserving circulation, followed by a flow phase lasting days. The second phase is hypermetabolic: cortisol, catecholamines and glucagon rise, peripheral insulin sensitivity falls, and the body begins drawing on its own tissue as a source of amino acids.

In practice this means that in the first days after an operation the patient's nutritional requirement does not fall — it rises, while appetite moves in the opposite direction. Pain, post-anaesthetic nausea, stress and an unfamiliar environment suppress intake just as metabolic demand climbs. The real fragility of convalescence lies in that gap.

What is negative nitrogen balance, and why does it matter?

Nitrogen balance is the difference between protein nitrogen taken in and nitrogen excreted. In the catabolic phase excretion exceeds intake and the balance turns negative. When the body cannot obtain enough amino acids from the diet for the work of repair, it breaks down its own skeletal muscle to feed the free amino acid pool. Clinically this appears as rapid loss of muscle mass, weakness and a prolonged recovery.

In cats the picture moves faster. In an obligate carnivore the protein requirement is high by species and tolerance of protein restriction is low; even a few days of inadequate intake can leave a measurable deficit in lean body mass. This is precisely why the WSAVA nutritional assessment guidelines recommend recording nutritional status as the fifth vital assessment at every examination.

MECHANISM: The nutritional groundwork of tissue regeneration

The amino acid pool and protein synthesis

New tissue is built from the existing amino acid pool. When that pool contracts, the rate of protein synthesis falls — this is not a question of therapy but of substrate. Post-Op Liquid's 50,000 mg of L-lysine per kilogram provides concentrated nutritional support to one essential component of that pool. Lysine cannot be synthesised by mammals; all of it must come from the diet.

The collagen matrix and cross-linking

The triple helix of collagen, the structural scaffold of connective tissue, is composed largely of glycine, proline and hydroxyproline residues. Two points here intersect directly with nutrition:

• Hydroxylation: The prolyl and lysyl hydroxylase enzymes that convert proline to hydroxyproline and lysine to hydroxylysine use vitamin C as a cofactor. Where ascorbate is insufficient, helical stability is impaired — the best-characterised nutritional dependency in collagen biochemistry.

• Cross-linking: The covalent cross-links formed through hydroxylysine residues determine the tensile strength of the matrix. The enzyme driving this reaction, lysyl oxidase, is copper-dependent — which is where the copper in Elixir of Postop's enriched mineral profile becomes meaningful.

Alongside lysine, the DL-methionine in Post-Op Liquid contributes to the cysteine pathway as a sulphur donor; cysteine is a precursor both of structural proteins and of glutathione, the cell's principal antioxidant. L-arginine feeds proline synthesis via ornithine and behaves as semi-essential during periods of increased demand — one of the most studied amino acids in repair physiology since Barbul's classical reviews.

Oxidative load and cellular balance

Metabolic activity concentrated at a site of repair inevitably generates reactive oxygen species. In the lipid phase of cell membranes vitamin E (alpha-tocopherol, 5,000 mg/kg) interrupts the lipid peroxidation chain, while vitamin C acts in the aqueous phase and in the re-reduction of oxidised tocopherol. This cooperation, set out mechanistically by Traber and Stevens, contributes to maintaining oxidative balance.

The turmeric extract (1,500 mg/kg) and milk thistle extract (200 mg/kg) in the formulation are botanical companions within this picture. The literature on curcumin and silymarin is extensive; here, however, these components appear not as therapeutic agents but as part of the whole nutritional support of convalescence.

Energy metabolism

Increased synthetic work demands energy. Vitamin B1 (thiamine, 200 mg/kg), in its thiamine pyrophosphate form, is the cofactor of central enzymes such as pyruvate dehydrogenase and transketolase, and contributes to sustaining normal energy metabolism. Intake of this water-soluble vitamin gains importance in periods of high metabolic flux.

Components that accompany the natural defences

Beta 1,3/1,6 glucan (7,500 mg/kg) is a polysaccharide investigated for its action through pattern-recognition receptors on immune cells; the review by Stier and colleagues gathers the immune-modulation literature on dietary beta-glucan. Propolis (1,500 mg/kg) and echinacea (500 mg/kg) complete the formulation as botanical components that accompany the body's natural defence balance. These components do not prevent infection, do not replace antibiotics and are not an alternative to surgical asepsis.

What "immunonutrition" means — and what it does not

The term immunonutrition describes treating specific nutrients not merely as calories and building blocks but as substrates that influence immune and repair physiology. It developed as a sub-topic of critical care nutrition in human surgery and entered the veterinary intensive care literature through work such as Chan's.

What the term does not mean should be stated plainly: immunonutrition is not a treatment protocol. Nutritional support does not replace a correctly established diagnosis or a treatment plan set by a veterinary surgeon. Diagnosis, treatment and medication decisions rest with the veterinary surgeon alone; this text is a framework on the nutritional physiology of convalescence, not clinical decision support.

Where do Post-Op Liquid and Elixir of Postop sit in this picture?

Both products are complementary feeds — not veterinary medicinal products or drugs.

Post-Op Liquid (liquid, 120 ml, cats and dogs) is a liquid form designed to deliver a dense nutritional contribution in a small volume during periods when appetite is suppressed. That it can be mixed into food or given directly by mouth is a practical advantage on days when voluntary intake falls. With an amino-acid-weighted backbone, vitamin support and botanical components, it focuses on the increased nutritional needs of convalescence.

Elixir of Postop (wet food plus sachet, 90 g, cats) addresses the same period from the feeding side. Its high mackerel-based protein content gives nutritional support to maintaining muscle mass, while a high energy density helps meet daily energy needs in small portions. Probiotic cultures, a zinc–iron–copper–manganese mineral profile, B group vitamins, vitamin E and taurine — essential for cats — complete the formulation, with echinacea, dandelion and nettle forming the botanical contribution.

The two are not alternatives to one another but answers to two different questions: Post-Op Liquid is a concentrated nutritional contribution, Elixir of Postop a feeding form that carries the meal through the period. Which to use, in what order and in what amount depends on the patient's species, weight, appetite and clinical picture, and should follow the dose determined by your veterinary surgeon.

A practical framework for the clinician

• Record nutrition as a parameter. Body weight, body condition score and muscle condition score belong in postoperative monitoring — serial measurement, not a single glance, is what informs.

• Quantify voluntary intake. The answer to "did it eat?" should be a number, not an impression; where intake is low, how many days the deficit has run is critical data.

• Account for volume tolerance. Where nausea and early satiety are present, dense small-volume forms help preserve voluntary intake.

• Set the owner's expectations accurately. Nutritional support feeds a process; it carries no promise of shortening a timeline.

References

• Cuthbertson DP. Observations on the disturbance of metabolism produced by injury to the limbs. Quarterly Journal of Medicine, 1932.

• Freeman L, Becvarova I, Cave N, et al. WSAVA Nutritional Assessment Guidelines. Journal of Small Animal Practice, 2011;52(7):385–396.

• Chan DL. Nutritional support of the critically ill small animal patient. Veterinary Clinics of North America: Small Animal Practice — critical care nutrition reviews.

• National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, 2006.

• Barbul A. Arginine: biochemistry, physiology, and therapeutic implications. Journal of Parenteral and Enteral Nutrition, 1986.

• Stechmiller JK. Understanding the role of nutrition and wound healing. Nutrition in Clinical Practice, 2010;25(1):61–68.

• Molnar JA, Underdown MJ, Clark WA. Nutrition and chronic wounds. Advances in Wound Care, 2014;3(11):663–681.

• Traber MG, Stevens JF. Vitamins C and E: beneficial effects from a mechanistic perspective. Free Radical Biology and Medicine, 2011;51(5):1000–1013.

• Stier H, Ebbeskotte V, Gruenwald J. Immune-modulatory effects of dietary yeast beta-1,3/1,6-D-glucan. Nutrition Journal, 2014;13:38.

• Hewlings SJ, Kalman DS. Curcumin: a review of its effects on human health. Foods, 2017;6(10):92.

• Regulation (EC) No 767/2009 of the European Parliament and of the Council — placing on the market and use of feed; definition of complementary feed.

Author: Vet. Hek. Metehan Çalıkuşu — Scientific Content, VetUX London

This content is for information only and does not replace veterinary examination, diagnosis or treatment. Post-Op Liquid and Elixir of Postop are complementary feeds; they are not veterinary medicinal products.