Serological discrimination between infected and vaccinated animals (DIVA):

• Standard ELISA measures overall antibody titer against mixed antigens without resolving individual viral structural vs non-structural protein molecular weights.
• Radioimmunoassay quantifies hormone or antigen concentrations using radiolabels.
• Western Blot immunoassay (immunoblotting) electrophoretically separates viral/bacterial antigens by molecular weight and probes them with host serum, permitting definitive visual discrimination between antibody patterns elicited by marker/subunit vaccines (lacking specific non-structural proteins, NSPs) versus natural wild-type infections (which generate broad antibodies against all structural and non-structural viral bands).
• Flow cytometry characterizes physical and antigenic properties of intact single cells in suspension.

One-carbon folate metabolism in thymidylate biosynthesis:

• Purine deoxynucleotides (dATP) require one-carbon formyl-THF donors, but are not the singular product of thymidylate synthase.
• dCTP is synthesized by ribonucleotide reductase directly from cytidine diphosphate without folate requirement.
• The synthesis of deoxythymidine triphosphate (dTTP) requires thymidylate synthase, which uses $N^5,N^{10}$-methylene-tetrahydrofolate as the essential methyl donor to convert dUMP into dTMP (which is subsequently phosphorylated to dTTP). In folate deficiency, thymidylate synthase activity is severely compromised, specifically depleting cellular dTTP pools and impairing DNA replication (resulting in uracil misincorporation and megaloblastic arrest).
• dGTP synthesis does not depend on thymidylate synthase.

Biochemical role of cobalt in animal nutrition:

• Vitamin B1 (thiamine) does not contain cobalt and is synthesized independently.
• Vitamin B6 (pyridoxine) is an unrelated pyridine derivative.
• Cobalt is an essential structural trace element that forms the central metallic coordination ion within the corrin ring of Vitamin B12 (cobalamin). In ruminants, rumen microorganisms utilize dietary cobalt exclusively to synthesize Vitamin B12; thus, primary dietary cobalt deficiency directly results in secondary Vitamin B12 deficiency (manifested as wasting disease, "pine", anorexia, and failure of methylmalonyl-CoA mutase and methionine synthase).
• Vitamin C is synthesized endogenously by domestic livestock from glucose.

Etiology of lysosomal storage diseases:

• Pompe disease (glycogen storage disease type II) is caused by deficiency of lysosomal Acid alpha-glucosidase (acid maltase, matching IV), causing glycogen accumulation in cardiac and skeletal muscle.
• Gaucher disease (sphingolipidosis) is caused by deficiency of lysosomal Acid beta-glucosidase (glucocerebrosidase, matching III), causing glucocerebroside accumulation in reticuloendothelial macrophages.
• Tay-Sachs disease (GM2 gangliosidosis) is caused by deficiency of Beta-hexosaminidase A (matching II), leading to neurodegenerative GM2 ganglioside storage.
• Hunter syndrome (mucopolysaccharidosis type II) is an X-linked disorder caused by deficiency of Iduronate sulfatase (matching I), causing heparan and dermatan sulfate accumulation.