Endogenous and dietary lipids influencing feed intake and energy metabolism of periparturient dairy cows

The effect of heat stress on performance, fertility, and adipokines involved in regulating systemic immune response during lipolysis of early lactating dairy cows

The aim of this study was to assess the potential effect of heat stress on dairy cow productivity, fertility, and biochemical blood indices during the early lactation stage in a temperate climate. Additionally, the study aimed to determine the role of leptin and adiponectin in regulating the immune response accompanying lipolysis after calving in dairy cows. The study included 100 clinically healthy Polish Holstein-Friesian dairy cows selected based on parity and 305 d of milk yield from 5 commercial farms with similar herd management and housing systems. Prospective cohort data were recorded from calving day until 150 d in milk, and microclimate loggers installed inside the barns were used to record temperature and relative humidity data to calculate daily temperature-humidity index (THI) on the calving day, through +7, +14, and +21 d during early lactation. Additionally, monthly productive performance parameters such as milk yield, chemical composition, fatty acids composition, and fertility indices were analyzed. Results showed that the THI from calving day through +7, +14, and +21 d during early lactation was negatively associated with fertility parameters such as delayed first estrus postpartum and an elongated calving interval, respectively, by 29, 27, 25, and 16 d. Furthermore, an increase in THI value during early lactation was associated with an elongated artificially inseminated service period, days open, and intercalving period. Increasing THI from calving day (0 d) through +7, +14, and up to +21 d during early lactation was also linked to decreased milk yield by 3.20, 4.10, 5.60, and 5.60 kg, respectively. The study also found that heat stress during early lactation was associated with a lower body condition score in dairy cows and higher concentrations of leptin, nonesterified fatty acids, and β-hydroxybutyrate, accompanied by a drastic reduction in adipose tissue-secreted adiponectin levels after calving. Additionally, heat stress-induced lipolysis in adipose tissue caused an inflammatory response that increased biochemical blood indices associated with immune responses such as cytokines, acute phase proteins, and heat shock protein. These findings suggest that exposing dairy cows to heat stress during early lactation can negatively affect their productive performance, fertility, and biochemical blood indices in subsequent lactations. Thus, farm management changes should be implemented during early lactation to mitigate the negative consequences of heat stress occurrence.

Gene expression of free fatty acids-sensing G protein-coupled receptors in beef cattle

Many physiological functions are regulated by free fatty acids (FFA). Recently, the discovery of FFA-specific G protein-coupled receptors (FFARs) has added to the complexity of their actions at the cellular level. The study of FFAR in cattle is still in its earliest stages focusing mainly on dairy cows. In this study, we set out to map the expression of genes encoding FFARs in 6 tissues of beef cattle. We also investigated the potential effect of dietary forage nature on FFAR gene expression. To this end, 16 purebred Charolais bulls were fed a grass silage ration or a maize silage ration (n = 8/group) with a forage/concentrate ratio close to 60:40 for 196 d. The animals were then slaughtered at 485 ± 42 d and liver, spleen, ileum, rectum, perirenal adipose tissue (PRAT), and Longissimus Thoracis muscle were collected. FFAR gene expression was determined by real-time quantitative PCR. Our results showed that of the five FFARs investigated, FFAR1, FFAR2, FFAR3, and GPR84 are expressed (Ct < 30) in all six tissues, whereas FFAR4 was only expressed (Ct < 30) in PRAT, ileum, and rectum. In addition, our results showed that the nature of the forage, i.e., grass silage or maize silage, had no effect on the relative abundance of FFAR in any of the tissues studied (P value > 0.05). Taken together, these results open new perspectives for studying the physiological role of these receptors in beef cattle, particularly in nutrient partitioning during growth.

Feeding spent hemp biomass to lactating dairy cows: Effects on performance, milk components and quality, blood parameters, and nitrogen metabolism

The legalization of industrial hemp by the 2018 Farm Bill in the United States has driven a sharp increase in its cultivation, including for cannabinoid extraction. Spent hemp biomass (SHB), produced from the extraction of cannabinoids, can potentially be used as feed for dairy cows; however, it is still illegal to do so in the United States, according to the US Food and Drug Administration Center for Veterinary Medicine, due to the presence of cannabinoids and the lack of data on the effect on animals. To assess the safety of this byproduct as feed for dairy cows, late-lactation Jersey cows (245 ± 37 d in milk; 483 ± 38 kg body weight; 10 multiparous and 8 primiparous) received a basal total mixed ration (TMR) diet plus 13% alfalfa pellet (CON) or 13% pelleted SHB for 4 wk (intervention period [IP]) followed by 4 wk of withdrawal period (WP), where all cows received only the basal TMR during WP. The dry matter intake (DMI), body weight, body condition score, milk yield, milk components, and fatty acid profile, blood parameters, N metabolism, methane emission, and activity were measured. Results indicated that feeding SHB decreased DMI mainly due to the low palatability of the SHB pellet, as the cows consumed only 7.4% of the total TMR with 13.0% SHB pellet offered in the ration. However, milk yield was not affected during the IP and was higher than CON during the WP, leading to higher milk yield/DMI. Milk components were not affected, except for a tendency in decreased fat percentage. Milk fat produced by cows fed SHB had a higher proportion of oleate and bacteria-derived fatty acids than CON. The activity of the cows was not affected, except for a shorter overall lying time in SHB versus CON cows during the IP. Blood parameters related to immune function were not affected. Compared with CON, cows fed SHB had a lower cholesterol concentration during the whole experiment and higher β-hydroxybutyric acid during the WP, while a likely low-grade inflammation during the IP was indicated by higher ceruloplasmin and reactive oxidative metabolites. Other parameters related to liver health and inflammatory response were unaffected, except for a tendency for higher activity of alkaline phosphatase during IP and a lower activity of gamma-glutamyl transferase during WP in the SHB group versus CON. The bilirubin concentration was increased in cows fed SHB, suggesting a possible decrease in the clearance ability of the liver. Digestibility of the dry matter and protein and methane emission were not affected by feeding SHB. The urea, purine derivatives, and creatinine concentration in urine was unaffected, but cows fed SHB had higher N use efficiency and lower urine volume. Altogether, our data revealed a relatively low palatability of SHB affecting DMI with minimal biological effects, except for a likely low-grade inflammation, a higher N use efficiency, and a possible decrease in liver clearance. Overall, the data support the use of SHB as a safe feed ingredient for lactating dairy cows.

Unraveling the immune and metabolic changes associated with metritis in dairy cows

The objective was to unravel the peripartum immune and metabolic changes associated with metritis in Holstein cows. Holstein cows (n = 128) had blood collected at -14, 0, 3, and 7 d relative to parturition (DRP). Flow cytometry was used to evaluate blood leukocyte counts, proportions, and activation. Total cells, live cells, single cells, monocytes (CD172α+/CD14+), polymorphonuclears (CD172α+/CD14-/SSChigh), B-cells (CD21+/MHCII+), CD4+ T-cells (CD4+), CD8+ T-cells (CD8+), and γδ T-cells (γδTCR+) were evaluated. Both CD62L and CD11b were used as markers of cell activation. Major histocompatibility complex class II was used as a marker of antigen presentation in monocytes. A Milliplex Bovine Cytokine/Chemokine 08-plex kit was used to evaluate plasma concentrations of IFN-γ, IL-1α, IL-1β, IL-4, IL-6, IL-8, IL-10, and tumor necrosis factor-α. The body weight (BW) change prepartum was calculated as the difference between calving BW and prepartum BW divided by the number of days between measurements. Plasma fatty acids (FA) were measured at -14 and 0 DRP using untargeted gas chromatography with time-of-flight mass spectrometry. Data were analyzed by ANOVA for repeated measures. Cows that developed metritis (n = 57) had greater prepartum BW, prepartum BW loss, and greater FA concentrations at calving. Plasma FA at calving was positively correlated with IL-1β. Cows that developed metritis had persistent systemic inflammation, which was demonstrated by greater B-cell activation, greater pro-inflammatory cytokine concentrations, and greater cell damage pre- and postpartum. Postpartum, we observed greater polymorphonuclear cell activation and extravasation but lesser monocytes and CD4+ T-cells activation and extravasation, which suggests postpartum immune tolerance. Greater prepartum adiposity in cows that developed metritis may lead to systemic inflammation pre- and postpartum and immune tolerance postpartum, which may lead to failure to prevent bacterial infection, and development of puerperal metritis.

N-3 Polyunsaturated Fatty Acids as a Nutritional Support of the Reproductive and Immune System of Cattle-A Review

This paper focuses on the role of n-3 fatty acids as a nutrient crucial to the proper functioning of reproductive and immune systems in cattle. Emphasis was placed on the connection between maternal and offspring immunity. The summarized results confirm the importance and beneficial effect of n-3 family fatty acids on ruminant organisms. Meanwhile, dietary n-3 fatty acids supplementation, especially during the critical first week for dairy cows experiencing their peripartum period, in general, is expected to enhance reproductive performance, and the impact of its supplementation appears to be dependent on body condition scores of cows during the drying period, the severity of the negative energy balance, and the amount of fat in the basic feed ration. An unbalanced, insufficient, or excessive fatty acid supplementation of cows' diets in the early stages of pregnancy (during fetus development) may affect both the metabolic and nutritional programming of the offspring. The presence of the polyunsaturated fatty acids of the n-3 family in the calves' ration affects not only the performance of calves but also the immune response, antioxidant status, and overall metabolism of the future adult cow.

Invited Review: Increasing Milk Yield and Negative Energy Balance: A Gordian Knot for Dairy Cows?

The continued increase in milk production during the last century has not been accompanied by an adequate dry matter intake (DMI) by cows, which therefore experience a negative energy balance (NEB). NEB is low and of minor importance at low milk yield (MY), such as for the nutrition of one calf, and under these circumstances is considered "natural". MY and low DMI around parturition are correlated and are the reason for the genetic correlation between increasing MY and increasing NEB up to 2000 MJ or more for 2-3 months postpartum in high-genetic-merit dairy cows. The extension and duration of NEB in high-producing cows cannot be judged as "natural" and are compensated by the mobilization of nutrients, particularly of fat. The released non-esterified fatty acids (NEFAs) overwhelm the metabolic capacity of the cow and lead to the ectopic deposition of NEFAs as triglycerides (TGs) in the liver. The subsequent lipidosis and the concomitant hampered liver functions cause subclinical and clinical ketosis, both of which are associated with "production diseases", including oxidative and endoplasmatic stress, inflammation and immunosuppression. These metabolic alterations are regulated by homeorhesis, with the priority of the physiological function of milk production. The prioritization of one function, namely, milk yield, possibly results in restrictions in other physiological (health) functions under conditions of limited resources (NEB). The hormonal framework for this metabolic environment is the high concentration of growth hormone (GH), the low concentration of insulin in connection with GH-dependent insulin resistance and the low concentration of IGF-1, the so-called GH-IGF-1 axis. The fine tuning of the GH-IGF-1 axis is uncoupled because the expression of the growth hormone receptor (GHR-1A) in the liver is reduced with increasing MY. The uncoupled GH-IGF-1 axis is a serious impairment for the GH-dependent stimulation of gluconeogenesis in the liver with continued increased lipolysis in fat tissue. It facilitates the pathogenesis of lipidosis with ketosis and, secondarily, "production diseases". Unfortunately, MY is still increasing at inadequate DMI with increasing NEB and elevated NEFA and beta-hydroxybutyric acid concentrations under conditions of low glucose, thereby adding health risks. The high incidences of diseases and of early culling and mortality in dairy cows are well documented and cause severe economic problems with a waste of resources and a challenge to the environment. Moreover, the growing public concerns about such production conditions in agriculture can no longer be ignored.

Milk and plasma proteomes from cows facing diet-induced milk fat depression are related to immunity, lipid metabolism and inflammation

Milk proteins are a source of bioactive molecules for calves and humans that may also reflect the physiology and metabolism of dairy cows. Dietary lipid supplements are classically used to modulate the lipid content and composition of bovine milk, with potential impacts on the nutrient's homeostasis and the systemic inflammation of cows that remains to be more explored. This study aimed at identifying discriminant proteins and their associated pathways in twelve Holstein cows (87 ± 7 days in milk), multiparous and non-pregnant, fed for 28 d a diet either, supplemented with 5% DM intake of corn oil and with 50% additional starch from wheat in the concentrate (COS, n = 6) chosen to induce a milk fat depression, or with 3% DM intake of hydrogenated palm oil (HPO, n = 6) known to increase milk fat content. Intake, milk yield and milk composition were measured. On d 27 of the experimental periods, milk and blood samples were collected and label-free quantitative proteomics was performed on proteins extracted from plasma, milk fat globule membrane (MFGM) and skimmed milk (SM). The proteomes from COS and HPO samples were composed of 98, 158 and 70 unique proteins, respectively, in plasma, MFGM and SM. Of these, the combination of a univariate and a multivariate partial least square discriminant analyses reveals that 15 proteins in plasma, 24 in MFGM and 14 in SM signed the differences between COS and HPO diets. The 15 plasma proteins were related to the immune system, acute-phase response, regulation of lipid transport and insulin sensitivity. The 24 MFGM proteins were related to the lipid biosynthetic process and secretion. The 14 SM proteins were linked mainly to immune response, inflammation and lipid transport. This study proposes discriminant milk and plasma proteomes, depending on diet-induced divergence in milk fat secretion, that are related to nutrient homeostasis, inflammation, immunity and lipid metabolism. The present results also suggest a higher state of inflammation with the COS diet.

Hepatic Lipidosis in Ruminants

Hepatic lipidosis (ie, fatty liver) occurs primarily during the first weeks of lactation in dairy cows because of excessive lipolysis overwhelming the concomitant capacity for beta-oxidation and hepatic export of triglycerides. Besides economic losses due to reduced lactational and reproductive performance, close associations with concomitantly occurring infectious and metabolic health disorders, in particular ketosis, exist. Hepatic lipidosis is not only a consequence from the postpartal negative energy balance but also acts as a disease component for further health disorders.

Role of functional fatty acids in modulation of reproductive potential in livestock

Fatty acids are not only widely known as energy sources, but also play important roles in many metabolic pathways. The significance of fatty acids in modulating the reproductive potential of livestock has received greater recognition in recent years. Functional fatty acids and their metabolites improve follicular development, oocyte maturation and embryo development, as well as endometrial receptivity and placental vascular development, through enhancing energy supply and precursors for the synthesis of their productive hormones, such as steroid hormones and prostaglandins. However, many studies are focused on the impacts of individual functional fatty acids in the reproductive cycle, lacking studies involved in deeper mechanisms and optimal fatty acid requirements for specific physiological stages. Therefore, an overall consideration of the combination and synergy of functional fatty acids and the establishment of optimal fatty acid requirement for specific stages is needed to improve reproductive potential in livestock.

Cow's microbiome from antepartum to postpartum: A long-term study covering two physiological challenges

Little is known about the interplay between the ruminant microbiome and the host during challenging events. This long-term study investigated the ruminal and duodenal microbiome and metabolites during calving as an individual challenge and a lipopolysaccharide-induced systemic inflammation as a standardized challenge. Strong inter- and intra-individual microbiome changes were noted during the entire trial period of 168 days and between the 12 sampling time points. Bifidobacterium increased significantly at 3 days after calving. Both challenges increased the intestinal abundance of fiber-associated taxa, e.g., Butyrivibrio and unclassified Ruminococcaceae. NMR analyses of rumen and duodenum samples identified up to 60 metabolites out of which fatty and amino acids, amines, and urea varied in concentrations triggered by the two challenges. Correlation analyses between these parameters indicated a close connection and dependency of the microbiome with its host. It turns out that the combination of phylogenetic with metabolite information supports the understanding of the true scenario in the forestomach system. The individual stages of the production cycle in dairy cows reveal specific criteria for the interaction pattern between microbial functions and host responses.

Rutin Supplementation Reduces Oxidative Stress, Inflammation and Apoptosis of Mammary Gland in Sheep During the Transition Period

Rutin, a common dietary flavonoid, exhibits remarkable pharmacological activities such as antioxidant and anti-inflammatory functions. Metabolic stress in mammals during the transition period affects mammary gland health. The aim of this experiment was to evaluate the protective effect of rutin supplementing against metabolic stress in the mammary glands of sheep during the transition period, particularly after parturition. Transition Hu sheep (2-3 years old with 62.90 ± 2.80 kg) were randomly divided into three groups, the control group was fed a diet without rutin, while rutin (50 and 100 mg/kg body weight/day) was administered to the two treatment groups (-28 day to +28 day relative to parturition). Serum and blood samples were collected from jugular vein on days -14, -7, +1, +2, +7, +14, +21, +28 relative to parturition. Mammary tissue biopsy samples of four sheep from the treatment group were harvested on day +28 postpartum. Compared to that in the control group, rutin supplementation resulted in lower β-hydroxybutyrate (BHBA) while increasing the concentrations of non-esterified fatty acids (NEFA) and globulin after lactation. Furthermore, rutin treatment led to lower hydrogen peroxide (H2O2) and malonaldehyde (MDA) levels, resulting in increased catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and total antioxidant potential (T-AOC). Compared to that in the control group, rutin inhibits the mRNA expression of inflammatory markers such as tumor necrosis factor-α (TNF-α). In addition, rutin markedly downregulated the ratio of phosphorylated NF-κB p65 (p-p65) to total NF-κB p65 (p65). Meanwhile, rutin supplementation resulted in high mRNA abundance of the nuclear factor erythroid 2-like 2 (NFE2L2, formerly NRF2) and its target gene, heme oxygenase-1 (HO-1), which plays critical roles in maintaining the redox balance of the mammary gland. Furthermore, rutin treatment lowered the levels of various downstream apoptotic markers, including Bax, caspase3 and caspase9, while upregulating anti-apoptotic Bcl-2 protein. These data indicate the positive effect of rutin against inflammation, oxidative stress status, and anti-apoptotic activity in the mammary gland. The mechanism underlying these responses merits further study.

The Occurrence of a Negative Energy Balance in Holstein-Friesian and Simmental Cows and Its Association with the Time of Resumption of Reproductive Activity

Intensive lactation (lactogenesis) in cows is conducive to a negative energy balance (NEB), so the search for traits associated with the physiological capacity to cope with its consequences is a current area of research. This is especially important because NEB overlaps with the resumption of the reproductive cycle, which determines the profitability of herds. This study analysed the relationship between NEB and the time of resumption of reproductive activity in cows with varying genetic potential (Simmental and Holstein-Friesian), fed a similar diet (TMR). The aim of the study was to analyse the dependencies between NEB markers and changes in progesterone levels between 25 and 31 days postpartum. A strong positive correlation was shown between daily milk production (DMP) and loss of body condition (LBCS; 0.772; p ≤ 0.05). These parameters were associated with the levels of NEB biomarkers. Higher values of NEB indicators (LBCS, C16:0, C18:1, NEFA, and BHBA) were usually noted during periods with higher DMP (II and III). The trends observed were confirmed by positive correlation coefficients (r), which ranged from 0.324 to 0.810 (p ≤ 0.05). The reverse trend was noted for glucose and leptin, which decreased as productivity increased, as confirmed by r values from -0.368 to -0.530 (p ≤ 0.05). In both breeds, the glucose and leptin levels decreased as DMP increased. Higher values for NEB indicators were shown to be negatively correlated with progesterone levels (r from -0.300 to -0.712; p ≤ 0.05), and a lower progesterone level was associated with a longer calving-to-first-service interval and calving-to-conception interval. The rate of postpartum triglyceride release depends on daily milk production, and therefore the adaptability of the liver should be considered an important element of mitigation of the consequences of NEB. This may have practical applications by extending productive life, which is often shortened due to deteriorating reproductive performance.

The Bovine Hepatic Cell Line BFH12 as a Possible Model for Hepatosteatosis in Dairy Cows

Hepatosteatosis is a common metabolic disorder of dairy cows, especially during early lactation. Currently, there are a few models of bovine hepatic steatosis available, including primary hepatocytes, liver slices, and animal models. Studies that elucidate the influence of single fatty acids on lipid classes, fatty acid pattern, gene expression, and phenotypic changes are still limited. Hence, we investigated the suitability of the fetal bovine hepatocyte-derived cell line BFH12 as a model for hepatosteatosis. To create a steatotic environment, we treated BFH12 with stearic acid, palmitic acid, or oleic acid in non-toxic doses. Thin-layer chromatography and gas chromatography were used to analyze lipid classes and fatty acid pattern, and qPCR was used to quantify gene expression of relevant target genes. Lipid droplets were visualized with confocal laser scanning microscopy and evaluated for number and size. Treatment with oleic acid increased triglycerides, as well as lipid droplet count per cell and upregulated carnitine palmitoyl transferase 1, which correlates with findings of in vivo models. Oleic acid was largely incorporated into triglycerides, phospholipids, and non-esterified fatty acids. Stearic acid was found mainly in non-esterified fatty acids and triglycerides, whereas palmitic acid was mainly desaturated to palmitoleic acid. All three fatty acids downregulated stearyl-CoA-desaturase 1. In conclusion, BFH12 can acquire a steatotic phenotype by incorporating and accumulating fatty acids. Oleic acid is particularly suitable to produce hepatosteatosis. Therefore, BFH12 may be a useful in vitro model to study bovine hepatosteatosis and its underlying molecular mechanisms.

Differentiation of Subclinical Ketosis and Liver Function Test Indices in Adipose Tissues Associated With Hyperketonemia in Postpartum Dairy Cattle

Past studies suggested that during early lactation and the transition period, higher plasma growth hormone (GH) levels in subclinical ketosis (SCK) might involve the initiation of body adipose tissues mobilization, resulting in metabolic disorders in ruminants particularly hyperketonemia. The upregulated GH mRNA expression in adipose tissue may take part in the adipolysis process in SCK-affected cows that paves a way for study further. This study aimed to characterize the plasma levels of GH, β-hydroxybutyrate acid (BHBA) and non-esterified fatty acid (NEFA) and glucose (GLu) in ketotic cows and healthy control (CON) cows; to measure the liver function test (LFT) indices in ketotic and healthy CON cows, and finally the quantitative real-time PCR (qRT-PCR) assay of candidate genes expressed in adipose tissues of ketotic and healthy CON cows during 0 to 7 week postpartum. Three experiments were conducted. Experiment-1 involved 21 Holstein cows weighing 500–600 kg with 2–5 parities. Results showed that GH, BHBA, and NEFA levels in ketotic cows were significantly higher and the GLu level significantly lower. Pearson's correlation analysis revealed a significant positive correlation of GH with BHBA, NEFA, and GLu in ketotic and healthy CON cows. In experiment-2, dynamic monitoring of LFT indices namely, alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyl transpeptidase (GGT), total bilirubin (TBIL), direct bilirubin (DBIL), total protein (TP), albumin (ALB), globulin (GLOB) and albumin/globulin (A/G) were examined. The TBIL, DBIL, and GGT indices were significantly higher in ketotic cows and TP was significantly lower. In experiment-3, mRNA expression levels of GHR and peroxisome-proliferator-activated receptor alpha (PPARα) genes in adipose tissue were significantly upregulated in ketotic cows. However, the mRNA expression of insulin-like growth factor-I (IGF-1), insulin-like growth factor-I receptor (IGF-1R), and sterol regulatory element-binding protein-1c (SREBP-1c) genes in adipose tissue were downregulated in ketotic cows. Our study concluded that during postpartum, higher plasma GH levels in SCK cows might involve the initiation of body adipose tissue mobilization, resulting in hyperketonemia.

Peripartal Rumen-Protected L-Carnitine Manipulates the Productive and Blood Metabolic Responses in High-Producing Holstein Dairy Cows

This study aimed to monitor the effect of including rumen-protected L-carnitine (Carneon 20 Rumin-Pro, Kaesler Nutrition GmbH, Cuxhaven, Germany) in the transition diet on the productive and metabolic responses of multiparous high-producing Holstein dairy cows. Thirty-two multiparous cows were allocated in a completely randomized design to receive the same diet plus 60 g fat prill containing 85% palmitic acid (control, n = 16) or 100 g rumen-protected L-carnitine (RLC, n = 16); at 28 days before expected calving until 28 days in milk (DIM). Fat prill was included in the control diet to balance the palmitic acid content of both experimental diets. Milk production over the 28 DIM for the control and RLC groups was 46.5 and 47.7 kg, respectively. Milk fat content tended to increase upon rumen-protected L-carnitine inclusion (p = 0.1). Cows fed rumen-protected L-carnitine had higher fat- and energy-corrected milk compared with the control group. Pre- and post-partum administration of L-carnitine decreased both high- and low-density lipoprotein concentrations in peripheral blood of post-partum cows. The results of this study indicated that the concentration of triglycerides and beta-hydroxybutyrate was not significantly different between the groups, whereas the blood non-esterified fatty acid concentration was markedly decreased in cows supplemented with L-carnitine. Animals in the RLC group had a significant (p < 0.05) lower blood haptoglobin concentration at 7 and 14 DIM than the control. Animals in the RLC group had a lower concentration of blood enzymes than those of the control group. The mRNA abundance of Toll-like receptors 4, cluster of differentiation 14, and myeloid differential protein 2 did not significantly change upon the supplementation of L-carnitine in the transition diet. In summary, the dietary inclusion of RLC improved dairy cow's performance during the early lactation period. Greater production, at least in part, is driven by improved energy utilization efficiency and enhanced metabolic status in animals during the periparturient period.

Prevention of mastitis in multiparous dairy cows with a previous history of mastitis by oral feeding with probiotic Bacillus subtilis

Mastitis is a very common inflammatory disease of the mammary gland of dairy cows, resulting in a reduction of milk production and quality. Probiotics may serve as an alternative to antibiotics to prevent mastitis, and the use of probiotics in this way may lessen the risk of antibiotic resistant bacteria developing. We investigated the effect of oral feeding of probiotic Bacillus subtilis (BS) C‐3102 strain on the onset of mastitis in dairy cows with a previous history of mastitis. BS feeding significantly decreased the incidence of mastitis, the average number of medication days and the average number of days when milk was discarded, and maintained the mean SCC in milk at a level substantially lower than the control group. BS feeding was associated with lower levels of cortisol and TBARS and increased the proportion of CD4⁺ T cells and CD11c⁺ CD172a^high dendritic cells in the blood by flow cytometry analysis. Parturition increased the migrating frequency of granulocytes toward a milk chemoattractant cyclophilin A in the control cows, however, this was reduced by BS feeding, possibly indicating a decreased sensitivity of peripheral granulocytes to cyclophilin A. These results reveal that B. subtilis C‐3102 has potential as a probiotic and has preventative capacity against mastitis in dairy cows.

Genomic Selection and Genome-wide Association Study for Feed-Efficiency Traits in a Farmed Nile Tilapia (Oreochromis niloticus) Population

Nile tilapia is a key aquaculture species with one of the highest production volumes globally. Genetic improvement of feed efficiency via selective breeding is an important goal, and genomic selection may expedite this process. The aims of this study were to 1) dissect the genetic architecture of feed-efficiency traits in a Nile tilapia breeding population, 2) map the genomic regions associated with these traits and identify candidate genes, 3) evaluate the accuracy of breeding value prediction using genomic data, and 4) assess the impact of the genetic marker density on genomic prediction accuracies. Using an experimental video recording trial, feed conversion ratio (FCR), body weight gain (BWG), residual feed intake (RFI) and feed intake (FI) traits were recorded in 40 full-sibling families from the GIFT (Genetically Improved Farmed Tilapia) Nile tilapia breeding population. Fish were genotyped with a ThermoFisher Axiom 65 K Nile tilapia SNP array. Significant heritabilities, ranging from 0.12 to 0.22, were estimated for all the assessed traits using the genomic relationship matrix. A negative but favourable genetic correlation was found between BWG and the feed-efficiency related traits; -0.60 and -0.63 for FCR and RFI, respectively. While the genome-wide association analyses suggested a polygenic genetic architecture for all the measured traits, there were significant QTL identified for BWG and FI on chromosomes seven and five respectively. Candidate genes previously found to be associated with feed-efficiency traits were located in these QTL regions, including ntrk3a, ghrh and eif4e3. The accuracy of breeding value prediction using the genomic data was up to 34% higher than using pedigree records. A SNP density of approximately 5,000 SNPs was sufficient to achieve similar prediction accuracy as the full genotype data set. Our results highlight the potential of genomic selection to improve feed efficiency traits in Nile tilapia breeding programmes.

The Capacity of Holstein-Friesian and Simmental Cows to Correct a Negative Energy Balance in Relation to Their Performance Parameters, Course of Lactation, and Selected Milk Components

A significant factor in improving the performance of dairy cows is their physiological ability to correct a negative energy balance (NEB). This study, using Simmental (SIM) and Holstein-Friesian (HF) cows, aimed to assess changes in NEB (non-esterified fatty acid; body condition score; and C16:0, C18:0, and C18:1) and its effect on the metabolic efficiency of the liver (β-hydroxybutyrate and urea). The effects of NEB on daily yield, production at peak lactation and its duration, and changes in selected milk components were assessed during complete lactation. Up to peak lactation, the loss of the body condition score was similar in both breeds. Subsequently, SIM cows more efficiently restored their BCS. HF cows reached peak lactation faster and with a higher milk yield, but they were less able to correct NEB. During lactation, their non-esterified fatty acid, β-hydroxybutyrate, C16:0, C18:0, C18:1, and urea levels were persistently higher, which may indicate less efficient liver function during NEB. The dynamics of NEB were linked to levels of leptin, which has anorectic effects. Its content was usually higher in HF cows and during intensive lactogenesis. An effective response to NEB may be exploited to improve the production and nutritional properties of milk. In the long term, it may extend dairy cows' productive life and increase lifetime yield.

Invited review: The influence of immune activation on transition cow health and performance-A critical evaluation of traditional dogmas

The progression from gestation into lactation represents the transition period, and it is accompanied by marked physiological, metabolic, and inflammatory adjustments. The entire lactation and a cow's opportunity to have an additional lactation are heavily dependent on how successfully she adapts during the periparturient period. Additionally, a disproportionate amount of health care and culling occurs early following parturition. Thus, lactation maladaptation has been a heavily researched area of dairy science for more than 50 yr. It was traditionally thought that excessive adipose tissue mobilization in large part dictated transition period success. Further, the magnitude of hypocalcemia has also been assumed to partly control whether a cow effectively navigates the first few months of lactation. The canon became that adipose tissue released nonesterified fatty acids (NEFA) and the resulting hepatic-derived ketones coupled with hypocalcemia lead to immune suppression, which is responsible for transition disorders (e.g., mastitis, metritis, retained placenta, poor fertility). In other words, the dogma evolved that these metabolites and hypocalcemia were causal to transition cow problems and that large efforts should be enlisted to prevent increased NEFA, hyperketonemia, and subclinical hypocalcemia. However, despite intensive academic and industry focus, the periparturient period remains a large hurdle to animal welfare, farm profitability, and dairy sustainability. Thus, it stands to reason that there are alternative explanations to periparturient failures. Recently, it has become firmly established that immune activation and the ipso facto inflammatory response are a normal component of transition cow biology. The origin of immune activation likely stems from the mammary gland, tissue trauma during parturition, and the gastrointestinal tract. If inflammation becomes pathological, it reduces feed intake and causes hypocalcemia. Our tenet is that immune system utilization of glucose and its induction of hypophagia are responsible for the extensive increase in NEFA and ketones, and this explains why they (and the severity of hypocalcemia) are correlated with poor health, production, and reproduction outcomes. In this review, we argue that changes in circulating NEFA, ketones, and calcium are simply reflective of either (1) normal homeorhetic adjustments that healthy, high-producing cows use to prioritize milk synthesis or (2) the consequence of immune activation and its sequelae.

Altering the ratio of dietary palmitic and oleic acids affects production responses during the immediate postpartum and carryover periods in dairy cows

The objectives of our study were to determine the effects of altering the dietary ratio of palmitic (C16:0) and oleic (cis-9 C18:1) acids on production and metabolic responses of early-lactation dairy cows during the immediate postpartum period and to evaluate carryover effects of the treatment diets early in lactation. Fifty-six multiparous cows were used in a randomized complete block design and randomly assigned to 1 of 4 treatments (14 cows per treatment) fed from 1 to 24 d in milk (DIM). The treatments were: (1) control (CON) diet not supplemented with fatty acids (FA); (2) diet supplemented with a FA blend containing 80% C16:0 and 10% cis-9 C18:1 (80:10); (3) diet supplemented with a FA blend containing 70% C16:0 and 20% cis-9 C18:1 (70:20); and (4) diet supplemented with a FA blend containing 60% C16:0 and 30% cis-9 C18:1 (60:30). The FA supplement blends were added at 1.5% of diet DM by replacing soyhulls in the CON diet. All cows were offered a common diet from d 25 to 63 postpartum (carryover period) to evaluate carryover effects. Three preplanned contrasts were used to compare treatment differences: CON versus FA-supplemented diets (80:10 + 70:20 + 60:30)/3; the linear effect of cis-9 C18:1 inclusion in diets; and the quadratic effect of cis-9 C18:1 inclusion in diets. During the treatment period, FA-supplemented diets increased milk yield, 3.5% fat-corrected milk (FCM), and energy-corrected milk (ECM) compared with CON. Compared with CON, FA-supplemented diets increased milk fat content, milk fat yield, yield of mixed FA, and tended to increase protein yield and lactose yield. Also, compared with CON, FA-supplemented diets tended to increase body condition score (BCS) change. A treatment by time interaction was observed for body weight (BW), due to 80:10 inducing a greater BW loss over time compared with other treatments. Increasing cis-9 C18:1 in FA treatments tended to linearly increase dry matter intake (DMI) but did not affect milk yield, 3.5% FCM, ECM, and the yields of milk fat, protein and lactose. Increasing cis-9 C18:1 in FA treatments linearly decreased milk fat content and milk lactose content. Also, increasing cis-9 C18:1 in FA treatments linearly decreased BW and BCS losses. During the carryover period, compared with CON, FA-supplemented diets tended to increase milk yield. Also, FA-supplemented diets increased 3.5% FCM, ECM, and milk fat yield, and tended to increase milk protein yield compared with CON. A treatment by time interaction was observed for BW due to 80:10 increasing BW over time compared with CON. Our results indicate that feeding FA supplements containing C16:0 and cis-9 C18:1 during the immediate postpartum period increased milk yield and ECM compared with a nonfat supplemented control diet. Increasing cis-9 C18:1 in the FA supplement increased DMI and reduced BW and BCS losses. Additionally, the fat-supplemented diets fed during the immediate postpartum period had a positive carryover effect during early lactation, when cows were fed a common diet.

Review: Pro-inflammatory cytokines and hypothalamic inflammation: implications for insufficient feed intake of transition dairy cows

Improvements in feed intake of dairy cows entering the early lactation period potentially decrease the risk of metabolic disorders, but before developing approaches targeting the intake level, mechanisms controlling and dysregulating energy balance and feed intake need to be understood. This review focuses on different inflammatory pathways interfering with the neuroendocrine system regulating feed intake of periparturient dairy cows. Subacute inflammation in various peripheral organs often occurs shortly before or after calving and is associated with increased pro-inflammatory cytokine levels. These cytokines are released into the circulation and sensed by neurons located in the hypothalamus, the key brain region regulating energy balance, to signal reduction in feed intake. Besides these peripheral humoral signals, glia cells in the brain may produce pro-inflammatory cytokines independent of peripheral inflammation. Preliminary results show intensive microglia activation in early lactation, suggesting their involvement in hypothalamic inflammation and the control of feed intake of dairy cows. On the other hand, pro-inflammatory cytokine-induced activation of the vagus nerve transmits signalling to the brain, but this pathway seems not exclusively necessary to signal feed intake reduction. Yet, less studied in dairy cows so far, the endocannabinoid system links inflammation and the hypothalamic control of feed intake. Distinct endocannabinoids exert anti-inflammatory action but also stimulate the posttranslational cleavage of neuronal proopiomelanocortin towards β-endorphin, an orexigen promoting feed intake. Plasma endocannabinoid concentrations and hypothalamic β-endorphin levels increase from late pregnancy to early lactation, but less is known about the regulation of the hypothalamic endocannabinoid system during the periparturient period of dairy cows. Dietary fatty acids may modulate the formation of endocannabinoids, which opens new avenues to improve metabolic health and immune status of dairy cows.

Review: Control of feed intake by hepatic oxidation in ruminant animals: integration of homeostasis and homeorhesis

Feed intake is controlled through a combination of long- and short-term mechanisms. Homeorhetic mechanisms allow adaptation to changes in physiological states in the long term, whereas homeostatic mechanisms are important to maintain physiological equilibrium in the short term. Feed intake is a function of meal size and meal frequency that are controlled by short-term mechanisms over the timeframe of minutes that are modulated by homeorhetic signals to adapt to changes in the physiological state. Control of feed intake by hepatic oxidation likely integrates these mechanisms. Signals from the liver are transmitted to brain feeding centers via vagal afferents and are affected by the hepatic oxidation of fuels. Because fuels oxidized in the liver are derived from both the diet and tissues, the liver is able to integrate long- and short-term controls. Whereas multiple signals are integrated in brain feeding centers to ultimately determine feeding behavior, the liver is likely a primary sensor of energy status.

Negative Energy Balance Influences Nutritional Quality of Milk from Czech Fleckvieh Cows due Changes in Proportion of Fatty Acids

The objective of this study was to evaluate the influence of negative energy balance on fatty acids proportion in the milk of Czech Fleckvieh cows after calving. Milk quality was determined based on fatty acid group proportion. Milk quality was evaluated in relation to selected negative energy balance (NEB) traits: body condition change (DEC) and milk citric acid content (CAC) after calving. Milk samples (n = 992) were collected once per week from 248 Czech Fleckvieh cows during the first month of lactation. Fatty acid content (%) in milk samples was determined and results were grouped as saturated (SFA) (hypercholesterolemic or volatile fatty acids) or unsaturated (UFA) (monounsaturated or polyunsaturated). Our results showed that cows with a deep NEB produce milk that is healthier for human consumption. Cows with a more significant DEC or the highest level of CAC in milk had the lowest proportion of SFA and the highest proportion of UFA (p < 0.01). These cows experienced higher physiological stress after calving; however, they produced milk of higher nutritional quality. Nowadays, we can see preventive efforts to mitigate NEB periods as a result of modern breeding trends regarding vitality, robustness, or longevity.

Impact of the severity of negative energy balance on gene expression in the subcutaneous adipose tissue of periparturient primiparous Holstein dairy cows: Identification of potential novel metabolic signals for the reproductive system

The severity of negative energy balance (NEB) in high-producing dairy cows has a high incidence among health diseases. The cow’s energy status during early lactation critically affects metabolic and reproductive parameters. The first objective of this study was to investigate by RNA-seq analysis and RT-qPCR the gene expression profile in white adipose tissue and by gene ontology and upstream regulation tools the relationships with energy metabolism and reproduction in two groups of primiparous dairy cows with extreme NEB statuses (NEB < -9 Mcal/day vs. NEB > -9 Mcal/day) around parturition. The second objective was to determine the potential involvement of a new adipokine identified as a candidate for the regulation of ovarian function in our RNA-seq analysis by using bovine primary granulosa culture, thymidine incorporation to determine cell proliferation and ELISA assays to measure progesterone secretion. The RNA-seq analysis revealed that 514 genes were over-expressed and 695 were under-expressed in the adipose tissue of cows with severe NEB (SNEB) and cows with moderate NEB (MNEB) during the -4 and 16 wkpp period. In addition, 491 genes were over-expressed and 705 genes were under-expressed in the adipose tissue of SNEB cows compared to MNEB cows. Among these differently expressed genes (DEGs), 298 were related to metabolic functions and 264 to reproductive traits. A set of 19 DEGs were validated by RT-qPCR, including CCL21 (C-C motif chemokine ligand 21). Moreover, CCL21, a gene known to be secreted by adipose tissue, was chosen for further analysis in plasma and ovaries. The use of next-generation sequencing technologies allowed us to characterise the transcriptome of white adipose tissue from primiparous cows with different levels of NEB during lactation. This study highlighted the alteration of the expression of genes related to lipid metabolism, including CCL21, which is released in the bloodstream and associated with the in vitro regulation of ovarian functions.

Effects of close-up dietary energy level and supplementing rumen-protected lysine on energy metabolites and milk production in transition cows

The objective of this study was to investigate the effects of dietary energy levels and rumen-protected lysine supplementation on serum free fatty acid levels, β-hydroxybutyrate levels, dry matter (DM) intake, and milk production and composition. Treatments were arranged in a 2 × 2 factorial design with 2 dietary energy levels [high net energy for lactation (NE_L) = 1.53 Mcal/kg of DM vs. low NE_L = 1.37 Mcal/kg of DM; HE vs. LE) fed either with rumen-protected lysine (bypass lysine; 40 g/cow per day) or without rumen-protected lysine (control). Sixty-eight third-lactation Holstein dairy cows entering their fourth lactation were randomly allocated to 4 treatments groups: HE with bypass lysine, HE without bypass lysine, LE with bypass lysine, and LE without bypass lysine. Groups were balanced based upon their expected calving date, previous milk yields, and body condition score. All cows were fed the same diet (NE_L = 1.34 Mcal/kg of DM) during the dry period prior to the trial. Rumen-protected lysine was top-dressed on a total mixed ration to deliver 9.68 g/d of metabolizable lysine to pre- and postpartum cows. After calving, all cows received the same TMR (1.69 Mcal/kg of DM). Blood samples were collected at -21, -14, -7, 0, 3, 7, 14, and 21 d relative to calving, and free fatty acids and β-hydroxybutyrate concentrations were measured. Amount of feed offered and orts were collected and measured for individual cows 4 d/wk. Milk samples were collected once per week following calving, and milk composition was analyzed. Feeding high NE_L to close-up cows decreased the concentrations of free fatty acid and β-hydroxybutyrate in prepartum cows but not in postpartum cows. Addition of rumen-protected lysine increased postpartum DM intake, and decreased serum free fatty acid and β-hydroxybutyrate concentrations. Neither energy nor rumen-protected lysine supplementation nor their interaction affected milk yield or fat or lactose yields. However, cows in the group receiving HE with bypass lysine tended to produce more milk compared with other groups and had a lower blood β-hydroxybutyrate concentration postpartum. These results indicate that feeding a high-energy diet together with rumen-protected lysine improved DM intake and lowered serum free fatty acid and β-hydroxybutyrate concentrations in transition cows.

Characterizing the metabotype and its persistency in lactating Holstein cows: An approach toward metabolic efficiency measures

The variation in feed efficiency among dairy cows is due to differences in fermentation and digestion characteristics, but recent studies have suggested that various aspects of postabsorptive metabolic processes including heat production or the metabolizable energy for maintenance are more crucial. Thus, metabolic efficiency largely determines feed efficiency, but whether divergent feed efficient cows differ in O₂ consumption and metabolic CO₂ production, directly determining the metabolic rate has not been investigated. Therefore, the objective of the present study was to determine whether variation in ME intake (MEI), O₂ consumption, and metabolic CO₂ production account for the variation in metabolic efficiency of dairy cows and whether this effect persists across the lactation cycle. Eighteen cows with different German breeding value functional herd life were kept in freestalls with ad libitum access to a total mixed ration that was kept constant in composition throughout the first lactation. Cows were blood sampled and weighed at wk 5, 13, and 42 postpartum (pp) and transferred into respiration chambers. Animals were retrospectively clustered according to MEI, O₂ consumption, and metabolic CO₂ production, each normalized to metabolic body weight (mBW). Cluster analysis revealed 9 high metabolically efficient (high-Meff) and 9 low metabolically efficient cows. The high-Meff cows had greater MEI and feed conversion efficiency, produced less metabolic CO₂ and methane, had a stronger negative energy balance, and tended to have a lower metabolic respiratory quotient. Further, high-Meff cows had lower residual MEI, less heat energy loss, and lower plasma glucose concentrations, but used a greater portion of body reserves instead of feed energy for milk synthesis, particularly at wk 5 and 13 pp. However, these group differences did not persist by wk 42 pp. Cow groups were not different in O₂ consumption, milk yield, metabolizable energy for maintenance, or the efficiency of tissue utilization for milk synthesis, but high-Meff cows tended to have the lower German relative breeding value functional herd life, indicating a link between metabolic performance and productive lifespan. In conclusion, the use of a clustering approach involving MEI/mBW, O₂/mBW, and CO₂/mBW seems to be a promising method to differentiate cows with divergent metabolic efficiency but does not allow identifying an individual metabotype that persists across the whole lactation cycle.

Dietary supplementation with glucogenic precusors and fatty acids improves performance and health of periparturient dairy cows

This experiment aimed to make a comparison between the effect of a mix of two energy preparations (a glucogenic preparation (G) and a free fatty acid preparation (F)), administered in the diet during the transition period over different periods of time (5 or 8 weeks), on the animal condition, feed intake, yield and composition of milk, and blood and urine parameters. The experimental additive was a mixture (1:1) of two energy preparations, namely, a loose mixture of propylene glycol and sodium propionate and a free fatty acid preparation in the form of rumen-undegradable pellets. The study included 50 Polish Black-and-White Holstein–Friesian dairy cows, allocated into five treatment groups, including one control (C) and four experimental ones (G1F1, G2F2, G2F1 and G1F2). The preparations were mixed at a 1:1 weight ratio (500 g per head, comprising 250G and 250F) and they were administered to all experimental groups of cows daily as a component of the experimental concentrate for 5 weeks (from the 2nd week before the expected calving and until the 3rd week of lactation). From the 4th until the 6th week of lactation, the supplementation in the experimental groups changed and animals received either no additive (G1F1), or were continuously supplemented with the G–F mix (G2F2), or received only G (G2F1) or only F (G1F2). The preparations used in the study had a long-term influence on the increase in the milk yield of cows, on the improvement of their health condition, and on the reduction of weight loss. The study results confirmed that prolongation of the supplementation until the 6th week of lactation may cause favourable changes in animal performance and milk quality. Due to different modes of action, the simultaneous supplementation of G and F reduced the negative energy balance in the cow and improved milk production and composition. The best results were obtained after administration of the mixture (1:1) of the G and F at the dose of 500 g/cow.day over the 8-week periparturient period.

Effects of timing of palmitic acid supplementation on production responses of early-lactation dairy cows

The objective of our study was to evaluate the effects of timing of palmitic acid (C16:0) supplementation on production responses of early-lactation dairy cows. Fifty-two multiparous cows were used in a randomized complete block design experiment. During the fresh period (FR; 1-24 d in milk) cows were assigned to either a control diet containing no supplemental fat (CON) or a diet supplemented with C16:0 (palmitic acid, PA; 1.5% of diet dry matter). During the peak (PK) period (25-67 d in milk) cows were assigned to either a CON diet or a PA (1.5% of diet dry matter) diet in a 2 × 2 factorial arrangement of treatments considering the diet that they received during the FR period. During the FR period, we did not observe treatment differences for dry matter intake or milk yield. Compared with CON, PA increased the yield of 3.5% fat-corrected milk by 5.30 kg/d, yield of energy-corrected milk (ECM) by 4.70 kg/d, milk fat content by 0.41% units, milk fat yield by 280 g/d, and protein yield by 100 g/d. The increase in milk fat associated with the PA treatment during the FR period occurred due to an increase in yield of 16-carbon milk fatty acids (FA) by 147 g/d (derived from both de novo synthesis and extraction from plasma) and preformed milk FA by 96 g/d. Compared with CON, PA decreased body weight (BW) by 21 kg and body condition score (BCS) by 0.09 units and tended to increase BW loss by 0.76 kg/d. Although PA consistently increased milk fat yield and ECM over time, a treatment × time interaction was observed for BW and BCS due to PA inducing a greater decrease in BW and BCS after the second week of treatments. Feeding PA during the PK period increased milk yield by 3.45 kg/d, yield of 3.5% fat-corrected milk by 4.50 kg/d, yield of ECM by 4.60 kg/d, milk fat content by 0.22% units, milk fat yield by 210 g/d, protein yield by 140 g/d, and lactose yield by 100 g/d but tended to reduce BW by 10 kg compared with CON. Also, during the PK period we observed an interaction between diet fed in the FR and PK periods for milk fat yield due to feeding PA during the PK period increasing milk fat yield to a greater extent in cows that received the CON diet (+240 g/d) rather than the PA diet (+180 g/d) during the FR period. This difference was associated with the yield of preformed FA because feeding PA during the PK period increased the yield of preformed milk FA only in cows that received the CON diet during the FR period. In conclusion, feeding a C16:0 supplement to early-lactation cows consistently increased the yield of ECM in both the FR and PK periods compared with a control diet. For some variables, the effect of feeding C16:0 was affected by timing of supplementation because milk yield increased only during the PK period and BW decreased to a greater extent in the FR period. Regardless of diet fed in the FR period, feeding a C16:0 supplement during the PK period increased yields of milk and milk components.

Lactational challenges in transition dairy cows

Lactation evolved to be the core functional system of providing maternal care in mammalian species. The mammary gland provides an ideally composed nutrient source for the newborn. In addition, colostrum provides passive immunisation after birth, and each suckling process supports the establishment and maintenance of a close mother–offspring bonding. The importance of lactation for the survival of the offspring is represented by a high metabolic priority of the mammary gland within the organism of the lactating animal. Therefore, animal breeding for high milk production has been quite successful, and modern breeding methods have allowed an enormous increase in the performance within only few generations of cows. Mainly in early lactation, most of the available nutrients are directed to the mammary gland, both those from feed, and those mobilised from body tissue. Therefore, milk production can be maintained at a high level despite a negative energy balance. However, the high metabolic load and mobilisation of body tissue requires adequate endocrine and metabolic regulation, which can be successful or less successful in individual animals, i.e. the dairy cow population consists of both metabolically robust and metabolically vulnerable dairy cows. While robust animals adapt adequately, vulnerable cows show often high plasma concentrations of non-esterified fatty acids and β-hydroxybutyrate, and are prone to various production-related diseases. In pasture- or forage-based feeding systems, an additional challenge is a limited availability of nutrients for milk production. Forage feeding without complementary concentrate leads to enormous metabolic disorders in high-yielding cows, but is tolerated in dairy cows with a moderate genetic-performance level.