Somatomedin C and other hormones, as well as blood metabolites, were measured during the dry period and during lactation in dairy cows, given different amounts of energy and protein, to study metabolic and endocrine adaptations. Somatomedin C, specifically measured by radioimmunoassay after separation from its binding protein, did not exhibit typical diurnal variations, in contrast to somatotropin and insulin, which increased particularly after concentrate intake. Somatomedin C markedly decreased at parturition and reached lowest values around the peak of lactation, while levels of somatotropin, nonesterified fatty acids and ketone bodies were high and those of glucose, insulin, thyroxine and triiodothyronine were low. Thereafter somatomedin C values slowly increased up to the 12th week of lactation and remained elevated. Low energy and protein balances were characterized by particularly low somatomedin C concentrations. An additional protein deficit at peak lactation, when cows were already provided with low amounts of energy, did not further decrease somatomedin C levels. However, when high amounts of energy were given in the form of starch or crystalline fat, somatomedin C increased. Overall, there was a positive correlation of somatomedin C primarily with energy, but also with protein balances and a negative correlation with milk yield. Conversely, somatotropin increased markedly after parturition and was positively correlated with milk production and negatively with protein and energy balances. Thus, somatomedin C levels were paradoxically low in the presence of high circulating somatotropin. Insulin most closely paralleled somatomedin C levels. Therefore the anabolic state of metabolism at the end of pregnancy was characterized by high somatomedin C and insulin and relatively low somatotropin, whereas the catabolic state of early lactation was characterized by high somatotropin, low somatomedin C, insulin and thyroid hormones.

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.

An experiment was performed using 18 dairy cows with 2 2 lactations from parturition until week 20 of lactation to investigate the effects of feeding rumen-protected crystalline fat (group A) or free fatty acids (group B) compared with a control group not fed supplementd fat or fatty acids (group C). The feeding effects studied were those on milk yield and composition, body weight (By, body conditions scores (BCS), skinfold values (a measure of subcutaneous fat tissue thickness), backfat thickness and longissimus dorsi muscle diameter (measured by ultrasound), as well as on blood plasma metabolic and endocrine traits. Fat and fatty-acid feeding reduced roughage intake. Net energy and protein balances during the first week of lactation were negative. Milk yield was sirmlar in all groups, but concentrations of milk fat were reduced in group B and of milk protein i n groups A and B. BW, BCS, skinfold value, backfat thickness and longissimus dorsi musde diameter similarly decreased in all groups until weeks 8-12.Concentrations of glucose and fructosamine decreased transiently during early lactation, whereas levels of /3-hydroxybutyrate, urea, total protein and albumin increased reversibly and similarly in all groups. Concentrations of creatinine decreased similarly in all groups until week 4 and those of nonesterified fatty acids until week 12. Triglyceride concentrations increased continuously unul week 18, whereas concentrations of phospholipid and cholesterol increased until week 10 and then remained elevated. Triglyceride, phospholipid and cholesterol concentrations were higher in group B than in groups A and C throughout the experiment. Concentrations of insulin, insulin-like growth factor-1, thyroxine and 3,5,3'triiodothyronine started to increase after the first 6-8 weeks of lactation, while those of growth hormone were transiently low in week 16. None of the hormones exhibited group differences. In this study rumenprotected fat or fatty-acid supplementation failed to improve the energy and protein balances during early lactation and did not affect milk yield, likely due to decreased roughage intake. BCS, skinfold values and backfat ultrasound measurements of subcutaneous adipose tissue mass and of longissimus dorsi muscle diameter indicated mobilization of fat tissue and protein mobilization in early lactation and were mirrored by typical changes of metabolic and endocrine traits.

An experiment was performed to compare the bioavailability of D,L-methionine (Met) of two rumen (polymer and fat)-protected Met forms (Smartamine; Rhône-Poulenc, Animal Nutrition, Antony, France and Mepron; Degussa AG, Hanau, Germany, respectively) fed once daily (at 0730 h) in amounts of 50 g per cow for 5 d. Six dairy cows were used in the crossover design. Blood samples were obtained from jugular veins 3 d before and 5 d after the start of Met supplementation at 1000, 1400, and 1800 h, and the three blood samples were pooled for analyses. Smartamine M feeding caused elevations of sulfur-containing amino acids (Met, Cys, and taurine) and reductions of Val and Ile and the total of branched-chain amino acids (Val + Leu + Ile). Mepron M85 feeding caused only a rise of Met concentrations. Concentrations of Met, taurine, and Gln were higher when Smartamine M than when Mepron M85 was fed. Concentrations of nonesterified fatty acids were reduced, and those of insulin were increased only by Mepron M85 feeding. Milk urea concentrations were lower in cows fed Mepron M85 than in controls, but milk yields; concentrations of fat, protein, and lactose; and somatic cell counts did not significantly change during the experiment and were not different between groups. Food intake, body weight, and body condition scores were not affected. In conclusion, only Mepron M85 supplementation influenced nonesterified fatty acids and insulin concentrations. However, the bioavailability of Met from Smartamine M was greater than of Mepron M85 and effects on other plasma-free amino acids were more marked. Whether less Met in the form of Smartamine M as Mepron M is needed to have the same effects on milk yield and composition needs to be investigated with doses used in practice.