A. Arieli

Effects of dietary fats differing in n-6:n-3 ratio fed to high-yielding dairy cows on fatty acid composition of ovarian compartments, follicular status, and oocyte quality

The objectives were to determine the incorporation of dietary encapsulated fats differing in n-6:n-3 ratio into milk fat, plasma, and various ovarian compartments and to examine the effects on ovarian follicular status, preovulatory follicle characteristics, and oocyte quality. Twenty-four multiparous Israeli Holstein cows, averaging 114 d in milk, were assigned to 1 of 3 treatment groups: 1) control (n=7), in which cows were fed a lactating cow diet; 2) E-FLAX (n=8), in which cows were fed a lactating cow diet that consisted of 1kg/d of encapsulated fat (3.8% of dry matter) containing 40.8% flaxseed oil, providing 242.2g of C18:3n-3 (low n-6:n-3 ratio); or 3) E-SUN (n=9), in which cows were fed a lactating cow diet that consisted of 1kg/d of encapsulated fat (3.8% of dry matter) containing 40.8% sunflower oil, providing 260.0g of C18:2n-6 (high n-6:n-3 ratio). Ovaries were monitored by ultrasonography for follicular status, and after synchronization, follicles >7mm were aspirated and evaluated. Ovum pickup was performed (19 sessions for the control and E-FLAX groups and 11 for the E-SUN group), and in vitro maturation and oocyte fertilization were conducted. The E-FLAX treatment increased the proportions of C18:3n-3 (5.8 fold), C20:5n-3, and C22:5n-3 (approximately 4-fold) in milk fat as compared with the other 2 treatments. The proportion of C18:3n-3 fatty acid in plasma increased dramatically with the E-FLAX treatment, from 1.43 and 1.49% in the control and E-SUN groups, respectively, to 7.98% in the E-FLAX group. Consequently, the n-6:n-3 ratio in plasma was reduced from approximately 42 in the control and E-SUN groups to 6.74 in the E-FLAX group. Proportions of C18:3n-3 in follicular fluid and granulosa cells were approximately 5-fold higher in the E-FLAX group than in the other 2 groups. The percentage of C18:2n-6 in cumulus-oocyte complexes of cows in the E-SUN group was 54% higher than that in the E-FLAX group and was 2.4-fold higher than that in the control group; the proportion of C18:3n-3 in the E-FLAX group was 4.73% and was not detected in the other groups. The average numbers of 2- to 5-mm follicles on d 5 and 9 of the cycle were higher in the E-FLAX group than in the E-SUN group, whereas the average numbers of follicles > or =10mm on d 5, 9, and 13 were higher in the E-SUN group than in the other 2 groups. The estrous cycles of the cows were synchronized and PGF(2alpha) was injected on d 16 to 17 of the cycle. The interval from PGF(2alpha) injection to behavioral estrus was longer in the E-FLAX group than in the E-SUN group, and the beginning of the luteal phase of the subsequent cycle was delayed. Concentrations of estradiol in follicular fluid of the preovulatory follicles were higher in the E-SUN group than in the E-FLAX group. The number of follicles aspirated by ovum pickup was higher in the E-FLAX group than in the control group, and the cleavage rate in the E-FLAX group was higher than in the control group, but not the E-SUN group. In conclusion, dietary n-3 fatty acids influenced the follicular status and increased the cleavage rate of oocytes as compared with those of control cows. These findings could be related to modifications of the fatty acid composition in plasma and ovarian compartments in response to dietary supplementation.

Effects of increased supplementation of n-3 fatty acids to transition dairy cows on performance and fatty acid profile in plasma, adipose tissue, and milk fat.

The objective of this study was to determine the effects of feeding an increased amount of extruded flaxseed with high proportions of n-3 fatty acids (FA) to transition dairy cows on performance, energy balance, and FA composition in plasma, adipose tissue, and milk fat. Multiparous Israeli-Holstein dry cows (n = 44) at 256 d of pregnancy were assigned to 2 treatments: (1) control cows were fed prepartum a dry-cow diet and postpartum a lactating-cow diet that consisted of 5.8% ether extracts; and (2) extruded flaxseed (EF) cows were supplemented prepartum with 1 kg of extruded flaxseed (7.9% dry matter)/cow per d, and postpartum were fed a diet containing 9.2% of the same supplement. The EF supplement was fed until 100 d in milk. On average, each pre- and postpartum EF cow consumed 160.9 and 376.2g of C18:3n-3/d, respectively. Postpartum dry matter intake was 3.8% higher in the EF cows. Milk production was 6.4% higher and fat content was 0.4% U lower in the EF group than in the controls, with no differences in fat and protein yields. Energy balance in the EF cows was more positive than in the controls; however, no differences were observed in concentrations of nonesterified fatty acids and glucose in plasma. Compared with controls, EF cows had greater proportions of C18:3n-3 in plasma and adipose tissue. The proportion of n-3 FA in milk fat was 3.7-fold higher in the EF cows, and the n-6:n-3 ratio was decreased from 8.3 in controls to 2.3 in the EF cows. Within-group tests revealed that the C18:3n-3 content in milk fat in the EF cows was negatively correlated with milk fat percentage (r = -0.91) and yield (r = -0.89). However, no decrease in de novo synthesis of less than 16-carbon FA was found in the EF group, whereas C16:0 yields were markedly decreased. It appears that the enrichment of C18:3n-3 in milk fat was limited to approximately 2%, and the potential for increasing this n-3 FA in milk is higher for cows with lower milk fat contents. In conclusion, feeding increased amounts of C18:3n-3 during the transition period enhanced dry matter intake postpartum, increased milk production, decreased milk fat content, and improved energy balance. Increased amounts of EF considerably influenced the FA profile of plasma, adipose tissue, and milk fat. However, the extent of C18:3n-3 enrichment in milk fat was limited and was negatively correlated with milk fat content and yield.

Effects of faecal n-alkane recovery in estimates of diet composition

The outer surfaces of plant leaves and stems are covered with a waxy layer, a considerable fraction of which comprises n-alkanes which are not digested and, therefore, can be used as markers in animal nutrition studies. Most plant species have a characteristic pattern of n-alkane concentrations in their cuticular wax and this enables the diet composition to be estimated by comparison with the pattern of the n-alkanes in faeces. N-alkane recovery in faeces was determined in a digestibility trial involving three different diets given to four goats, six cows and five calves. The validity of using n-alkane markers to determine diet composition was examined in in vivo feeding trials with goats and cows. The recovery of the odd chain length n-alkanes increased linearly with n-alkane chain length, with no significant differences between treatments. Estimates of diet composition were affected by the faecal n-alkane recovery rate. N-alkanes in plant cuticular wax can be used as natural markers for estimating diet composition, but a recovery factor should be used to correct for incomplete recovery in faeces. More research is needed to extend the findings to wider ranges of diets, animals, environmental conditions and physiological and reproductive states.

Dietary unsaturated fatty acids influence preovulatory follicle characteristics in dairy cows

Dietary unsaturated fatty acids (UFAs) have been implicated in several reproductive processes in dairy cows through a variety of mechanisms. This study examined the effects of periparturient supplementation of rumen bypass fats low or high in proportion of UFAs (oleic and linoleic) on preovulatory follicle characteristics. Forty-two 256-day pregnant dairy cows were divided into three groups and were fed a control diet (n=14) or supplemented with fats either low (LUFA; n=14) or high (HUFA; n=14) in UFAs. At 14-15 days following behavior estrus, the cows received a prostaglandin F(2)(alpha) injection and 48 h later >7 mm follicles were aspirated. Progesterone (P(4)), androstenedione (A(4)), and estradiol (E(2)) were determined in the follicular fluid. Out of 75 follicles, 37 follicles that were aspirated between 55 and 70 days post partum were regarded as E(2)-active follicles (E(2)/P(4) ratio >1) and subjected for further analysis. The diameter of preovulatory follicles was greater in cows fed HUFA than in those fed control or LUFA. The concentrations and content of A(4) and E(2) in follicles and E(2)/P(4) ratio were higher in the HUFA group than in the other two groups. The P450 aromatase mRNA expression in granulosa cells that were collected from the aspirated preovulatory follicles was also higher in the HUFA cows than in the other groups. A significant correlation was observed between E(2) concentrations in preovulatory follicles and E(2) concentrations in plasma at aspiration. In conclusion, dietary UFA increased the size of and elevated steroid hormones in preovulatory follicles, which may be beneficial to consequent ovarian function.

Performance of high-yielding dairy cows supplemented with fat or concentrate under hot and humid climates

Multiparous Israeli-Holstein cows (n=42) averaging 158 d in milk and 621 kg of body weight were used to investigate the effects of energy source (fat or concentrate) on production, rumination time, energy balance, metabolic heat production, and efficiency under hot and humid conditions. Cows were assigned to 3 diet treatment groups: a lactating-cow ration (1.75 Mcal of net energy for lactation/kg of dry matter (DM; control); supplemented with 0.825 kg/d per cow of ground corn grain (2.7% of diet; HG); or supplemented with 0.300 kg/d per cow of calcium salts of fatty acids (1.5% of diet; HF). Milk production, body weight, and rumination time were recorded daily. Rectal temperature and respiratory rate (RR) were measured weekly. Mean daily maximum ambient temperature, relative humidity, and temperature-humidity index were 31.5 degrees C, 86.6%, and 76.8, respectively. Dry matter intake was lower in HF and HG cows than in controls. Average daily rumination time was lowest in the HG group: 393.0, 377.7, and 390.8 min/d for control, HG, and HF cows, respectively. Milk production was higher in the control group than in the HG group; milk fat content was 0.38 units higher and fat yield was 11% greater in HF cows than in HG cows. Fat-corrected milk yield was higher in HF cows than in HG cows, but not higher than in controls. Energy balance in HF cows was lower than in both other groups, and nonesterified fatty acid concentrations in plasma were increased by fat supplementation. Rectal temperature was highest in HF cows, and RR was higher in the HF cows than in the controls. Metabolic heat production was similar in HG and HF cows and lower than in controls. Body weight gain of the HG cows tended to be higher than that of the others. Efficiency of conversion of DM or energy intake to milk and fat-corrected milk was higher in HF cows than in both other groups; however, when taking the energy retention in body mass into account, no differences in energy utilization were observed between HF and HG groups. A principal component analysis revealed that rumination time played a pivotal role in the deleterious effect of heat stress in dairy cows. In conclusion, increasing the energy density in diets of heat-stressed mid-lactation cows over 1.75 Mcal/kg of DM was not effective in enhancing production. Both dietary treatments were effective in reducing metabolic heat production, but the changes were not reflected in rectal temperature and RR. Fat supplementation increased metabolic efficiency; however, whereas HF cows prioritized milk production, HG cows channeled energy for body mass deposition.

Lipopolysaccharide challenge of the mammary gland in bovine induced a transient glandular shift to anaerobic metabolism

Support of milk production in modern dairy cows demands a large proportion of its own metabolic resources, such as glucose, which might be required under stressful situations. The aim of the experiment was to test the hypothesis that acute immune stress shifts oxidative metabolism to glycolysis. Two mammary quarters in 6 Holstein cows were infused with lipopolysaccharide (LPS), whereas the 2 counter quarters served as controls to the treatment. An additional 6 cows were infused with saline and served as running controls. The LPS challenge induced dramatic transient increases in milk lactate (75-fold) and malate (11-fold) concentrations (both markers of glycolysis) at 24h posttreatment. No significant changes in lactate and malate concentrations were recorded in control quarters and control animals, indicating that the effect of LPS was restricted to the treated gland. The LPS challenge induced a dramatic transient decrease in milk yield, and lactose and citrate (a marker of mitochondrial metabolism) secretion at 24h posttreatment. The kinetics were inversely proportional to those of lactate and malate concentrations. Thus, our data suggest that LPS challenge induces acute conversion of epithelial cell metabolism from principally mitochondrial-oxidative to principally cytosolic (glycolytic), which allows the diversion of metabolic resources normally used to synthesize milk to support the immune system. An in vitro bacterial growth test showed that concentrations of lactate, malate, and lactose equivalent to those found in the in vivo experiment delayed and reduced the growth of a pathogenic Escherichia coli strain, suggesting that they play a role in diminution of bacterial multiplication in the mammary gland.

Lipopolysaccharide challenge of the mammary gland in cows induces nitrosative stress that impairs milk oxidative stability.

The aim of this work was to study the effects of mastitis induced by intramammary lipopolysaccharide (LPS) challenge on milk oxidative stability, as well as to understand the underlying biochemical processes that cause such changes. LPS challenge was associated with nitric oxide burst from the surrounding mammary epithelial cells and consequently induced nitrosative stress that was induced by the formation of NO2• from nitrite by lactoperoxidase. This response was associated with an ∼3-fold increased formation of hazardous compounds: nitrotyrosines, carbonyls and lipid peroxides. We sustained the involvement of xanthine oxidase as a major source of hydrogen peroxide. In consistent with previous findings, catalase has been shown to play a major role in modulating the nitrosative stress by oxidizing nitrite to nitrate. The current hygienic quality criteria cannot detect mixing of low-quality milk, such as milk with high somatic cells, and nitrite with high-quality milk. Thus, development of an improved quality control methodology may be important for the production of high-quality milk.

Incorporation of dietary n-3 fatty acids into ovarian compartments in dairy cows, and the effects on hormonal and behavioral patterns around estrus

The objective of this study was to examine the incorporation of dietary n-3 fatty acids (FAs) into ovarian compartments and the effects on hormonal and behavioral patterns around estrus. Multiparous 256-day pregnant cows were fed either a standard diet both prepartum and postpartum (PP) (control; n=22) or supplemented with extruded flaxseed (E-FLAX) providing C18:3n-3 at 172.2 and 402.5  g/day per cow prepartum and PP respectively (n=22). The estrous cycle was synchronized, and at day 7 of the cycle, the cows were injected with prostaglandin F(2)(α) (PGF(2)(α)) and then subjected to 5 days of intensive examination. Compared with those in the control, in the E-FLAX group, the interval from PGF(2)(α) injection to behavioral estrus peak tended to be longer (3.6  h; P<0.1), that to estradiol (E(2)) peak was 6.5  h longer (P<0.03), and that to LH peak tended to be longer (5.3  h; P<0.07). The durations of behavioral estrus and E(2) surge were longer, and the area under the E(2) curve was greater in the E-FLAX cows. Afterward, 7-8 days following behavioral estrus, follicular fluids (FFs) from >7  mm follicles were aspirated. The proportions of n-3 FA increased in plasma, FF, and granulosa cells in the E-FLAX group. The concentrations of PGE(2) in the E(2)-active follicles tended to be lower in the E-FLAX cows (P<0.06). In conclusion, several modifications in hormonal and behavioral estrus patterns were demonstrated in cows fed n-3 FA, which might be attributed to alterations in membrane FA composition and partly mediated by lower PGE(2) synthesis.

Dietary α-linolenic acid from flaxseed oil improved folliculogenesis and IVF performance in dairy cows, similar to eicosapentaenoic and docosahexaenoic acids from fish oil

The objectives of this study were to determine the differential incorporation of various omega-3 (n-3) fatty acids (FAs) supplemented to dairy cows into ovarian compartments and assess the effects on IVF. Forty-two 256-day pregnant cows were supplemented with encapsulated fats, in treatments designated as i) SFA - saturated fat at 240 and 560 g/day per cow, prepartum and post partum (PP) respectively; ii) FLX - flaxseed oil at 300 and 700 g/day per cow prepartum and PP respectively; and iii) FO - fish oil at 300 and 700 g/day per cow prepartum and PP respectively. Commencing at 60 days in lactation, ovum pickup (OPU) was performed twice weekly (20 sessions; five cows per group) and in vitro maturation and IVF were conducted. The proportion of α-linolenic acid (ALA) was greater in follicular fluid (FF), granulosa cells, and cumulus-oocyte complexes (COCs) of FLX cows than in other groups (P<0.001). The proportion of docosahexaenoic acid (DHA) was 6.7 times as great in FF of FO as in other groups (P<0.001); docosapentaenoic acid n-3 and DHA were detected in COCs of FO but not in others. The follicle number during OPU was higher in FLX and FO than in SFA (P<0.05), and the oocyte cleavage rate was higher in FLX and FO than in SFA (P<0.01). Also, the percentage of oocytes that developed to blastocysts tended to be higher in both n-3 groups than in SFA (P<0.1). In conclusion, both dietary n-3 FAs similarly improved folliculogenesis and IVF performance; therefore, ALA-rich botanical n-3 seems to be a satisfactory approach to improve oocyte quality.

Assessment of energy expenditure by daily heart rate measurement—validation with energy accretion in sheep

Abstract An experiment was conducted in sheep to test the validity of the heart rate method as a tool for determining energy expenditure. A comparison was made between assessments of energy expenditure by this method and the comparative slaughter technique. Animals were kept individually in metabolic cages and were fed ad libitum. One group was fed a high-energy diet, comprised of 75% concentrates and 25% alfalfa hay cubes (C diet) for 84 d. A second group was fed 25% concentrates and 75% of alfalfa hay cubes (R diet) for a 42 d, and then switched to the C diet for 42 d. The third group received the R diet cubes for 84 d. Body composition was determined in four animals at the start of the experiment, and in 12 animals at its termination. The entire experimental period was divided into four sub-periods. For each diet, metabolizability and average heart rate were determined for 3 consecutive days. Individual oxygen consumption was determined by the mask technique and the ratio of oxygen consumption to heart rate, the O2 pulse (O2P), was established for each sub-period. The average ratio of energy expenditure values computed from the product of daily heart rate times O2P to those obtained from the difference between metabolizable energy intake and energy accretion derived from the comparative slaughter technique, was 1.067. We concluded that the monitoring of heart rate combined with a repeatable calibration of individual O2P is a reliable and useful method for determining energy expenditure in ruminants.