Feeding rumen-protected fat (RPF) is an alternative to increase energy density of the diet and therefore energy intake in dairy cows. To investigate metabolic and endocrine changes in dairy cows fed either a diet containing RPF (FD) or a control diet with an increased amount of cornstarch (SD), 3 Holstein cows (83 +/- 1 d in milk) were fitted with catheters in the portal vein, a mesenteric artery, and 2 mesenteric veins. Cows were fed consecutively SD and FD for 3 wk, respectively. In FD, cornstarch [92 g/kg of dry matter (DM)] was replaced by 50 g of RPF/kg of DM (mainly C16:0 and C18:1). Tracer infusions of NaH(13)CO3 and D-[U-(13)C6]glucose were performed into a jugular vein to measure rate of appearance and oxidation of glucose. Arterial and portal blood samples were collected to measure concentrations of glucose, lactate, volatile fatty acids, nonesterified fatty acids, beta-hydroxybutyrate, triglycerides, AA, insulin, and glucagon. Concomitantly, para-aminohippurate was infused into a mesenteric vein for measurement of portal plasma flow. Although DM intake was slightly lower in FD, protein and energy intakes were unaffected by diets. Milk and lactose yields were higher in FD than SD. Arterial plasma glucose concentration was lower with FD than SD, whereas nonesterified fatty acid and triglyceride concentrations were higher in FD. Glucagon concentration and glucagon-to-insulin ratio were both augmented by FD feeding. When feeding FD, greater milk and lactose yields, but not energy-corrected milk, were associated with elevated lipid status and higher glucagon concentrations but occurred despite lower plasma glucose concentration and were not linked with changes in whole body glucose rate of appearance. This study suggests a glucose-sparing effect allowing an enhanced lactose synthesis when feeding RPF.

Unbalanced metabolic status in the weeks after calving predisposes dairy cows to metabolic and infectious diseases. Blood glucose, IGF-I, non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHB) are used as indicators of the metabolic status of cows. This work aims to (1) evaluate the potential of milk mid-IR spectra to predict these blood components individually and (2) to evaluate the possibility of predicting the metabolic status of cows based on the clustering of these blood components. Blood samples were collected from 241 Holstein cows on six experimental farms, at days 14 and 35 after calving. Blood samples were analyzed by reference analysis and metabolic status was defined by k-means clustering (k=3) based on the four blood components. Milk mid-IR analyses were undertaken on different instruments and the spectra were harmonized into a common standardized format. Quantitative models predicting blood components were developed using partial least squares regression and discriminant models aiming to differentiate the metabolic status were developed with partial least squares discriminant analysis. Cross-validations were performed for both quantitative and discriminant models using four subsets randomly constituted. Blood glucose, IGF-I, NEFA and BHB were predicted with respective R 2 of calibration of 0.55, 0.69, 0.49 and 0.77, and R 2 of cross-validation of 0.44, 0.61, 0.39 and 0.70. Although these models were not able to provide precise quantitative values, they allow for screening of individual milk samples for high or low values. The clustering methodology led to the sharing out of the data set into three groups of cows representing healthy, moderately impacted and imbalanced metabolic status. The discriminant models allow to fairly classify the three groups, with a global percentage of correct classification up to 74%. When discriminating the cows with imbalanced metabolic status from cows with healthy and moderately impacted metabolic status, the models were able to distinguish imbalanced group with a global percentage of correct classification up to 92%. The performances were satisfactory considering the variables are not present in milk, and consequently predicted indirectly. This work showed the potential of milk mid-IR analysis to provide new metabolic status indicators based on individual blood components or a combination of these variables into a global status. Models have been developed within a standardized spectral format, and although robustness should preferably be improved with additional data integrating different geographic regions, diets and breeds, they constitute rapid, cost-effective and large-scale tools for management and breeding of dairy cows.

Improving feed utilization efficiency in dairy cattle could have positive economic and environmental effects that would support the sustainability of the dairy industry. Identifying key differences in metabolism between high and low feed-efficient animals is vital to enhancing feed conversion efficiency. Therefore, our objectives were (1) to determine whether cows grouped by either high or low feed efficiency have measurable differences in net fat and carbohydrate metabolism that account for differences in heat production (HP), and if so, whether these differences also exists under conditions of feed withdrawal when the effect of feeding on HP is minimized, and (2) to determine whether the abundance of mitochondria in the liver can be related to the high or low feed-efficient groups. Ten dairy cows from a herd of 15 (parity = 2) were retrospectively grouped into either a high (H) or a low (L) feed-efficient group (n = 5 per group) based on weekly energy-corrected milk (ECM) divided by dry mater intake (DMI) from wk 4 through 30 of lactation. Livers were biopsied at wk −4, 2, and 12, and blood was sampled weekly from wk −3 to 12 relative to parturition. Blood was subset to be analyzed for the transition period (wk −3 to 3) and from wk 4 to 12. In wk 5.70 ± 0.82 (mean ± SD) postpartum (PP), cows spent 2 d in respiration chambers (RC), in which CO 2 , O 2 , and CH 4 gases were measured every 6 min for 24 h. Fatty acid oxidation (FOX), carbohydrate oxidation (COX), metabolic respiratory quotient (RQ), and HP were calculated from gas measurements for 23 h. Cows were fed ad libitum (AD-LIB) on d 1 and had feed withdrawn (RES, restricted diet) on d 2. Additional blood samples were taken at the end of the AD-LIB and RES feeding periods in the RC. During wk 4 to 30 PP, H had greater DMI/kg of metabolic body weight (BW 0.75 ), ECM per kilogram of BW 0.75 yield, and ECM/DMI ratio, compared with L, but a lower body condition score between wk 4 and 12 PP. In the RC period, we detected no differences in BW, DMI, or milk yield between groups. We also detected no significant group or group by feeding period interactions for plasma metabolites except for Revised Quantitative Insulin Sensitivity Check Index, which tended to have a group by feeding period interaction. The H group had lower HP and HP per kilogram of BW 0.75 compared with L. Additionally, H had lower FOX and FOX per kilogram of BW 0.75 compared with L during the AD-LIB period. Methane, CH 4 per kilogram of BW 0.75 , and CH 4 per kilogram of milk yield were lower in H compared with L, but, when adjusted for DMI, CH 4 / DMI did not differ between groups, nor did HP/DMI. Relative mitochondrial DNA copy numbers in the liver were lower in the L than in the H group. These results suggest that lower feed efficiency in dairy cows may result from fewer mitochondria per liver cell as well as a greater whole-body HP, which likely partially results from higher net fat oxidation.

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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.