No abstract

The present experiment was undertaken to determine the effects of dietary supplements of folic acid and vitamin B12 given from 3 wk before to 8 wk after calving on lactational performance and metabolism of 24 multiparous Holstein cows assigned to 6 blocks of 4 cows each according to their previous milk production. Supplementary folic acid at 0 or 2.6 g/d and vitamin B12 at 0 or 0.5 g/d were used in a 2 x 2 factorial arrangement. Supplementary folic acid increased milk production from 38.0 +/- 0.9 to 41.4 +/- 1.0 kg/d and milk crude protein yield from 1.17 +/- 0.02 to 1.25 +/- 0.03 kg/d. It also increased plasma Gly, Ser, Thr, and total sulfur AA, decreased Asp, and tended to increase plasma Met. Supplementary B12 decreased milk urea N, plasma Ile, and Leu and tended to decrease Val but increased homocysteine, Cys, and total sulfur AA. Liver concentration of phospholipids was higher in cows fed supplementary B12. Plasma and liver concentrations of folates and B12 were increased by their respective supplements, but the increase in plasma folates and plasma and liver B12 was smaller for cows fed the 2 vitamins together. In cows fed folic acid supplements, supplementary B12 increased plasma glucose and alanine, tended to decrease plasma biotin, and decreased Km of the methylmalonyl-coenzyme A mutase in hepatic tissues following addition of deoxyadenosylcobalamin, whereas it had no effect when cows were not fed folic acid supplements. There was no treatment effect on plasma nonesterified fatty acids as well as specific activity and gene expression of Met synthase and methylmalonyl-coenzyme A mutase in the liver. Ingestion of folic acid supplements by cows fed no supplementary B12 increased total lipid and triacylglycerols in liver, whereas these supplements had no effect in cows supplemented with B12. The increases in milk and milk protein yields due to folic acid supplements did not seem to be dependent on the vitamin B12 supply. However, when vitamin B12 was given in combination with folic acid, utilization of the 2 vitamins seems to be increased, probably more so in extrahepatic tissues. Metabolic efficiency seems also to be improved as suggested by similar lactational performance and dry matter intake for cows fed supplementary folic acid but increased plasma glucose and decreased hepatic lipids in cows fed folic acid and vitamin B12 together.

This experiment was conducted to determine the variations in carotenoid, vitamins A and E concentrations, and color in the plasma and milk of dairy cows following a shift from a hay diet to diets containing increasing levels of carotenoids and vitamin E. This study was performed on 32 multiparous Montbéliarde dairy cows in midlactation. After a 6-wk preexperimental period on a diet based on hay and concentrates, the cows were allocated to 4 homogeneous groups, and thereafter fed for 6 wk on isoenergetic experimental diets where the hay was replaced by an experimental feed rich in carotenoids and vitamin E, consisting in 75% grass silage and 25% alfalfa protein concentrate (PX Agro Super Desialis, Châlons en Champagne, France). The hay-to-experimental feed ratios were 100/0 in group 1, 67/33 in group 2, 33/67 in group 3, and 0/100 in group 4, providing 1.6, 3.6, 5.4, and 7.4 g/d of total carotenoids, respectively. Variations in carotenoid, vitamins A and E concentrations as well as variations in color index (CI) were monitored from d -7 through to d 42 on the experimental diets. Zeaxanthin, lutein, 13-cis-beta-carotene, and all-trans-beta-carotene accounted for an average 3, 10, 9, and 78%, respectively, of total carotenoids in plasma and 0, 17, 12, and 71%, respectively, of total carotenoids in milk. The switch from preexperimental to experimental diets only slightly affected zeaxanthin, lutein, and vitamin A concentrations in plasma and milk. A rapid increase in vitamin E and beta-carotene (BC) was observed during the first week in both plasma and milk. For vitamin E, the time to reach a plateau was from 8 d (group 2) to 28 d (group 4) in plasma, and 5 d (groups 2-4) in milk. Plasma concentrations of BC had stabilized after 28 d in group 2 but were not stabilized after 42 d in groups 3 and 4, whereas milk concentrations of BC plateaued from d 21 in group 2 and d 28 in groups 3 and 4. At the end of the experimental period, BC and vitamin E concentrations in plasma and vitamin E concentrations in milk fat were linearly related to the proportion of experimental feed in the diet. In contrast, BC concentrations in milk fat did not differ between groups 2, 3, and 4, reflecting saturation at high levels of carotenoid intake (i.e., when plasma BC exceeded 5 mug/mL). These results suggested that under high-carotenoid diets, milk secretion of BC is not limited by the amount of plasma BC arriving to the mammary gland but by mechanisms involved in the BC transfer from plasma to milk. These mechanisms will need to be investigated. The BC concentrations were responsible for more than 80% of CI variations in plasma and 56% of CI variations in milk, where there was wide variability among individuals. Plasma CI appeared to be a more promising tool than milk CI as an indicator of the carotene content of the diets ingested by dairy cows.

Simultaneous quantification of various liposoluble micronutrients is not a new area of interest since these compounds participate in the nutritional quality of feeds that is largely explored in human, and also in animal diet. However, the development of related methods is still under concern, especially when the carotenoid composition is complex such as in forages given to ruminants or in lipid-rich matrices like milk. In this paper, an original method for simultaneous extraction and quantification of all carotenoids, vitamins E, and A in milk was proposed. Moreover, a new UPLC method allowing simultaneous determination of carotenoids and vitamins A and E in forage, plasma and milk, and separation of 23 peaks of carotenoids in forages was described. This UPLC method using a HSS T3 column and a gradient solvent system was compared to a previously published reverse-phase HPLC using two C18 columns in series and an isocratic solvent system. The UPLC method gave similar concentrations of carotenoids and vitamins A and E than the HPLC method. Moreover, UPLC allowed a better resolution for xanthophylls, especially lutein and zeaxanthin, for the three isomers of beta-carotene (all-E-, 9Z- and 13Z-) and for vitamins A, an equal or better sensitivity according to gradient, and a better reproducibility of peak areas and retention times, but did not reduce the time required for analysis.

Summary ― The production of very low density lipoproteins (VLDL) by the liver results from very complex processes that involve coordinated mechanisms of both protein and lipid synthesis and packaging. Alterations in these metabolic functions can cause negative effects on the health of human subjects or animals. The objectives of this paper were to review the latest developments in the biological mechanisms of these processes and the role of nutritional and hormonal factors. The present study addresses the following issues: i) the main steps in the hepatic metabolism of lipids (long-chain fatty acids, triacylglycerols, phospholipids) and proteins (apolipoprotein B, microsomal transfer protein) primarily involved in the synthesis and secretion of VLDL particles; ii) the metabolic deviations of hepatic VLDL (hypo-and overproduction) in man, rodents and farm animals (poultry, dairy cows).

No abstract

Recent knowledge is presented on the composition of ruminant milk fat fractions and the nutritional strategies known to alter their amount. The development of lipidomic and proteomic analyses has allowed for the characterization of minor components, such as proteins, liposoluble vitamins, and phospholipids of the milk fat globule (MFG), in addition to the triacylglycerols (TAG), which are the major constituents of the MFG core. Few differences in these components among ruminant species exist, and they have been outlined mainly on the fatty acids (FA) profile of the TAG, whereas comparative data are still lacking on vitamins and proteins. The effects of dietary treatments enriched in n‐3 polyunsaturated FA (PUFA) on the composition of the milk fat fraction are explored. In particular, pasture and plant oilseeds increase milk n‐3 PUFA and cis‐9,trans‐11 CLA and decrease saturated FA, whereas data with new feed resources, such as algae, are still rare. The peculiarities of the response of the milk fat to diets that induce a milk fat depression in cows but in lesser extent in small ruminants are described. The potential effects of polar lipids, proteins, and liposoluble vitamins of the MFG on human health are reviewed, highlighting the nutraceutical properties of milk. Practical Applications: This review provides an overview of the different components of the milk fat fraction in ruminant species and on nutritional strategies to alter their amounts to improve the nutritional quality of milk. Furthermore, this review presents recent data on species peculiarities of the milk fat fraction composition and of its response to nutritional factors, which offers a promising model to identify news levers of regulation of this fraction and foster the identification of new feeding strategies to better control milk fat composition and feed efficiency. This review synthesizes data on the composition of the milk fat fraction in ruminant species, reports advances in nutritional strategies to alter their amounts and species‐specific responses to nutrition, as well as the potential effects on human health of the major and minor components of this fraction.

The main aim of this work was to assess the effect of lactation period on the secretion of carotenoids in cow's milk. Our objective was to determine the variations in carotenoids in the plasma and milk of dairy cows from drying off to wk 12 of lactation, and to specify whether these variations depend on body stores of these micronutrients at calving. We also investigated the relationship between beta-carotene (BC) and color in plasma and milk to evaluate the methods based on direct or indirect characterization of these micronutrients for traceability of feeding management. The experiment was carried out on 18 dairy cows, which were dried off 8 wk before their expected date of parturition. They were then divided into 2 homogeneous groups and fed diets contrasting in carotenoid content, high (grass silage) vs. low (corn silage), from wk -7 until parturition. From parturition through wk 12 of lactation, both groups received a grass silage-based diet. Variations in concentrations of carotenoids and the color index (CI) in plasma and milk were monitored from drying off to wk 12 of lactation. Other components of nutritional interest (i.e., vitamins A and E) were also measured. Lutein, all-trans BC and cis-13 BC were the carotenoids found in plasma and milk. Plasma concentrations of carotenoids, vitamin A, and vitamin E decreased throughout the dry period and in the first week of lactation, then increased through the first 3 mo of lactation, parallel to grass silage intake. For both groups, carotenoid and vitamin concentrations in milk drastically decreased during the first week of lactation, then did not vary significantly throughout the remainder to the experiment (wk 12). Plasma concentrations of carotenoids and vitamins were higher in the high-carotenoid group than in the low-carotenoid group during the dry period. Those differences were also observed in colostrum and disappeared in both plasma and milk during the first 10 d of the lactation period. This work allowed us to conclude that, unlike in plasma, variations in carotenoids, vitamin A, and vitamin E in milk were only slight in early lactation. In both plasma and milk, the concentrations were only transitorily affected by the nature of forage fed during the dry period, showing that they depended mainly on the dietary supply, even during the lipid mobilization period. The relationship between concentrations of BC and the CI was linear in plasma (R2 = 0.51) and milk (R2 = 0.37) and reached a plateau in the milk + colostrum data set (R2 = 0.77). The changes in CI during the first 3 mo of lactation were not negligible compared with variations related to the nature of forage reported in previous studies. This implies that methods being developed for the traceability of feeding management of dairy cows based on direct or indirect characterization of these micronutrients in milk, plasma, or both will need to account for changes in relation to lactation stage, which requires further investigation.