The fate of carbon from long-chain fatty acids and glucose in dairy cows which were fed with protected fat was studied using stable isotope technique. The experiment was carried out on two groups of dairy cows (n=16 in each group) during the first 15 weeks of the lactation period. The cows were fed isoenergetic and isoproteinogenous diets based on corn silage. About 1.8 kg of tapioca starch in the diet of the starch group was substituted by about 0.7 kg of rumen protected fat (Ca salts of palm oil and soybean oil) in the diet of the fat group. The carbon atoms of dietary fat were naturally depleted in 13C as compared to carbon atoms of starch. Daily milk performance and lactose output were significantly (P < 0.05) higher among the cows fed with fat diet. In comparison to the starch group, the enrichment of milk fat with 13C was significantly lower, while that of breath CO2 was significantly higher in the fat group (P < 0.05). This means the fatty acids were incorporated into milk fat in preference to metabolic oxidation. Further studies showed that blood glucose is oxidized to a lower extent and is used for the synthesis of lactose to a higher proportion if the cows were fed with the fat diet. The glucose entry rate into the body glucose pool was not different between the diets. In conclusion, the dietary fatty acids perform a glucose sparing effect and improve the glucose supply for the mammary gland.

Genetic improvement of dairy cows has led to a dramatic increase in milk production associated with an overall decrease in reproductive performance.In this study, the effect of a linoleic acid enriched fat diet on reproductive parameter in high yielding dairy cows will be considered with respect to metabolic parameters.Altogether 32 Holstein Friesian cows were allocated into 2 groups.The experiment was started 40 days before parturition and finished 100 days after calving.Feeding prior to parturition enclosed 4 components and was equal for control and experimental group.After parturition diet contained 13 components.In contrast to controls, in the experimental group the tapioca pellets were replaced by Ca-protected fat (80 % palm fat and 20 % soya).Blood was drawn 2 times per week by venous puncture.Furthermore 5 animals per group were used for frequent blood sampling via catheter about 8 hours on days 25, 30, 35 and 40 after parturition to investigate characteristics of LH secretion.Ultrasonographic examinations of follicular development were carried out 2 to 3 times per week.Milk performance in 305 days was 9514 ± 1167 kg in the control group and 10142 ± 1444 kg in the experimental group.Body mass and backfat thicknes decreased significantly (p<0.05) in experimental and control groups.In both groups glucose and insuline concentrations showed the same pattern.However, concentrations were significantly increased for severals weeks in control animals.Concentrations of ß-hydroxybutyrat were higher (p<0.05) in animals of experimental group from week 4 to 14 after parturition.Although plasma and follicular cholesterol concentrations of dominant follicles 7 days after ovulation were increased (p<0.05) by the fat diet, there was no positive effect on the total number of follicles >5 mm in diameter, and on the interval from calving to first ovulation.In the experimental group the frequency of LH pulses was also higher than in controls (2.8 to 4.0 vs. 3.2 to 4.8 pulses in 8 hours).However, these data did not find a reflection in a better reproductive fitness.The interval from calving to first ovulation was longer in experimental group compared to controls (66.4 ± 48.4 vs. 49.2 ± 37.2 days).In summary, data suggest that replacement of carbohydrates by protected fatty acids in the chosen manner did not improve reproductive functions.Obtained results ask the question, if high yielding dairy cows would utilize additional energy for improvement of reproductive fitness or for acceleration of milk production.