Effects of feeding crystalline triglycerides (TGA), free fatty acids (FFA), and a starch-rich ration (STA) on metabolite and hormone concentrations in blood plasma were studied in high-yielding dairy cows over a 24-h period in week 9 and 19 of lactating. Energy-corrected milk production in the three groups was similar, but was lower in week 19 than in week 9. Energy and protein intakes were greater in week 9 than in week 19, but energy and protein balances in the three groups and in weeks 9 and 19 were similar. Plasma glucose and triglyceride concentrations were lower in week 9 than in week 19. In cows fed FFA, glucose concentrations were highest in week 9. Plasma triglyceride, phospholipid and cholesterol concentrations were highest, whereas beta-hydroxybutyrate concentrations were lowest in FFA-fed cows in weeks 9 and 19. Concentrations of insulin-like growth factor-I in week 19 were lower in cows fed TGA and FFA than in those fed the starch-rich ration. Post-prandial responses were usually greater following morning than afternoon meals. Fructosamine, albumin, urea, growth hormone, thyroxine, and 3,5,3'-triiodothyronine concentrations were similar in weeks 9 and 19 and were not influenced by dietary treatment or feeding times. In conclusion, there were distinct metabolic and endocrine effects of feeding TGA and FFA compared with STA and the concentrations as well as the 24-h changes of various metabolic and endocrine traits in weeks 9 and 19 of lactation were also different.

The absorption of recombinant human insulin-like growth factor I (rhIGF-I), [¹²⁵I]rhIGF-I, xylose and [³H]lysine, administered into a clamped jejunal segment in anesthetized neonatal calves, was studied by measuring their appearance in the mesenteric vein draining the gut segment. Only trace amounts of IGF-I and of [¹²⁵I]rhIGF-I and/or ¹²⁵I were absorbed following dissolution in saline, buffer or colostrum. The absorption rate of both [³H]lysine and/or 3H and of xylose was much greater than the absorption of rhIGF-I, [¹²⁵I]rhIGF-I and/or ¹²⁵I but was also transient. Biological effects of ingested IGF-I in neonatal calves should barely occur as a consequence of intestinal absorption even in 1-day-old calves, known to absorb various peptides and proteins.

Summary Concentration of (total) globulin was relatively stable in blood plasma of mares, but rapidly decreased in colostrum to very low levels within 2 days after parturition. In foals, after intake of the first colostrum, globulin increased within 1 day in blood plasma, but remained at lower concentrations than those measured in mare plasma. Concentrations of immunoreactive insulin (iI) were high during the first 2 months of lactation in blood plasma of mares and then decreased, were high in first colostrum and then decreased drastically, and remained at low concentrations up to weaning in blood of foals. In mares, concentration of immunoreactive insulin‐like growth factor I (iIGF‐I) in plasma increased during late pregnancy, peaked 2 days after parturition, and then gradually declined until weaning. iIGF‐I was highest in first colostrum and then dramatically decreased within the first 2 days of lactation. In foals, iIGF‐I gradually increased over the first 2 months of life. IGF‐I in the horse appears to be bound to proteins of similar molecular weight as in cattle. The study demonstrates different patterns of changes in plasma iIGF‐I and iI concentrations in mares and their foals, whereas iI, iIGF‐I and globulin changes in colostrum and milk occurred in parallel. Furthermore, plasma iI and iIGF‐I behaved differently, while colostrum iI and iIGF‐I behaved similarly, in mares compared with dairy cows.

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