人乳替代脂鲳鱼油和巴沙鱼油的脂肪酸、甘油三酯 组成及含量分析

为寻找与中国人乳脂脂质组成高相似的天然人乳替代脂,分析比较了3种鱼油(金鲳鱼油、银鲳鱼油和巴沙鱼油)的总脂肪酸、sn-2位脂肪酸、甘油三酯组成和含量。结果表明：金鲳鱼油中棕榈酸、油酸和亚油酸含量分别为24.93%、25.61%和26.52%,其中sn-2位棕榈酸的含量为39.71%,占总棕榈酸比例为53.10%;在3种鱼油中,金鲳鱼油总脂肪酸组成最接近中国人乳脂;甘油三酯组成分析结果证实,金鲳鱼油中富含1-油酸-2-棕榈酸-3-亚油酸甘油三酯(OPL,24.36%),其含量显著高于其他两种鱼油,且其1,3-二油酸-2-棕榈酸甘油三酯(OPO)的含量(16.79%)接近报道的中国人乳脂的平均含量(15.84%)。因此,金鲳鱼油是理想的中国婴儿配方奶粉专用油脂基料油,在人乳替代脂中具有良好的发展前景。     

Dietary fat and nitrogen composition of milk from lactating cows

Effects of dietary fat on milk composition, particularly milk N, were evaluated in lactating dairy cows at two stages of lactation. Complete mixed diets containing 0, 3.5, or 7% of the diet DM as animal fat were fed to 12 cows in a 3 X 3 Latin square. Cows were divided into two status categories based on stage of lactation resulting in two squares of early and two of late lactation cows. Percentages of fat, solids, lactose, and protein were decreased and ash increased in the milk of cows fed the 7% fat diet. Percent of casein N was elevated while nonprotein N was depressed by fat fed in diet. Percentage of solids and protein was higher and lactose lower for cows in late lactation than for those in early lactation. Dietary fat reduced the proportion of short-chain fatty acids in milk fat and increased C18:0 and C18:1 fatty acids. Digestibility of DM, energy, and fiber was not significantly affected by dietary fat, but estimates decreased with increased dietary fat. Cows in late lactation had a higher digestibility of dietary fractions than early lactation cows even though intakes of DM were similar.     

Temporal changes in milk fatty acid composition during diet-induced milk fat depression in lactating cows

Diet-induced milk fat depression (MFD) in lactating cows has been attributed to alterations in ruminal lipid metabolism leading to the formation of specific fatty acid (FA) biohydrogenation intermediates that directly inhibit milk fat synthesis. However, the mechanisms responsible for decreased lipid synthesis in the mammary gland over time are not well defined. The aim of this study was to evaluate the effect of diet on milk FA composition and milk fat production over time, especially during MFD, and explore the associations between MFD and FA biohydrogenation intermediates in omasal digesta and milk. Four lactating Finnish Ayrshire cows used in a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments and 35-d experimental periods were fed diets formulated to cause differences in ruminal and mammary lipid metabolism. Treatments consisted of an iso-nitrogenous total mixed ration based on grass silage with a forage to concentrate ratio of 65:35 or 35:65 without added oil, or with sunflower oil at 50 g/kg of diet dry matter. The high-concentrate diet with sunflower oil (HSO) induced a 2-stage drop in milk fat synthesis that was accompanied by specific temporal changes in the milk FA composition. The MFD on HSO was associated especially with trans-10 18:1 and also with trans-9,cis-11 conjugated linoleic acid (CLA) in milk and omasal digesta across all diets and was accompanied by the appearance of trans-10,cis-15 18:2. Trans-10,cis-12 CLA was increased in HSO, but milk fat secretion was not associated with omasal or milk trans-10,cis-12 CLA. The temporal changes in milk fat content and yield and milk FA composition reflect the shift from the predominant ruminal biohydrogenation pathway to an alternative pathway. The ambiguous role of trans-10,cis-12 CLA suggests that trans-10 18:1, trans-9,cis-11 CLA and trans-10,cis-15 18:2 or additional mechanisms contributed to the diet-induced MFD in lactating cows.     

Reproductive performance of lactating Holstein cows fed supplemental beta-carotene

Fifty-six Holstein cows were used in a replicated study to determine whether supplemental beta-carotene improved reproductive performance. Each of two replicates was of completely randomized design with 2 X 2 factorial arrangement of two diets with or without beta-carotene supplementation. On a dry matter basis, diet 1 was 5% hay, 20% haylage, 25% corn silage, and 50% concentrate. Diet 2 was 7.5% hay, 42.5% corn silage, and 50% concentrate. The diets contained adequate amount of vitamins A, D, and E. From 10 d postpartum until pregnancy was confirmed by rectal palpation, half the cows on each diet received a supplement of 400 mg beta-carotene per head daily. The remaining cows on each diet received a supplement of 160,000 IU vitamin A per head daily. Supplemental beta-carotene increased plasma beta-carotene throughout the trials. Median days to first ovulation, first service, days open, and mean services per conception were: 22, 77, 97, and 1.6 for cows receiving beta-carotene supplement compared with 19.5, 73, 82, and 1.9 in controls. Supplementation did not affect first service conception rate, uterine involution, or milk yield. Incidence of follicular cysts, luteal cysts, pyometra, and endometritis in cows fed beta-carotene were 11, 7, 0, and 7% compared with 8, 21, 4, and 13% in control cows. Supplemental beta-carotene did not improve the fertility of Holstein cows.     

Responses of milk fat composition to dietary fat or nonstructural carbohydrates in Holstein and Jersey cows

Milk fat from Jersey cows contains less oleic acid (cis-C18:1) and more short- and medium-chain fatty acids than does milk fat from Holstein cows. The objective of this experiment was to determine responses in milk fat composition when Jersey and Holstein cows were fed diets either high (37% of dry matter) or low (27% of dry matter) in content of nonstructural carbohydrates (NSC) and supplemented with either 0 or 2.5% (of dry matter) of a mostly saturated fat source. Four Holstein cows and four Jersey cows were used in a Latin square design with 28-d periods; diets were in a 2 x 2 factorial arrangement. Fat supplementation decreased contents of fatty acids synthesized de novo within the mammary gland and increased contents of C18:0 and cis-C18:1. Low-NSC diets tended to increase C16:0 and to decrease C18:0, cis-C18:1, and C18:3. Despite the differences in fatty acid composition between breeds, both breeds generally responded similarly to dietary treatments. An interaction of breed and fat indicated that the content of cis-C18:1 in milk fat was increased more by supplemental fat in Holsteins than in Jerseys. Interactions of breed x fat and breed x carbohydrate type showed that the ratio of cis-C18:1 to C18:0 decreased when Jerseys were supplemented with fat but increased for Holsteins, and decreased when Jerseys were fed the low-NSC diet but increased when Holsteins were fed low NSC. The data are consistent with the hypothesis (Beaulieu and Palmquist, 1995, J. Dairy Sci. 78:1336-1344) that mammary activity of stearoyl-coenzyme A desaturase is lower in Jerseys than in Holsteins.     

Effects of feeding or abomasal infusion of canola oil in Holstein cows. 1. Nutrient digestion and milk composition

We determined the effects of feeding canola oil or infusing it into the abomasum on rumen fermentation, nutrient digestibility, duodenal flows of fatty acids, and milk composition in Holstein cows. Five ruminally and duodenally cannulated Holstein cows in late lactation were used in a 3 x 5 incomplete Latin square design. Treatments were 1) Control: basal diet (CON), 2) Control+supplementation of canola oil at 1 kg/d in the feed (FED), and 3) Control+abomasal infusion of canola oil at 1 kg/d (INF). Compared with CON, feed intake, ruminal fermentation characteristics, ruminal and total tract digestibilities of nutrients were not significantly affected by FED treatment but duodenal flows and milk concentrations of fatty acids (FA) such as trans-11 18:1 and cis-9 trans-11 18:2 (conjugated linoleic acid, CLA) were increased. In contrast to the effects of FED, INF reduced feed intake, total VFA production, intestinal flows of nutrients, FA digestibility and yields of milk and milk fat. Both FED and INF significantly reduced the proportions of saturated and medium-chain FA, and increased cis 18:1 in milk. Concentrations of 18:2n-6 and 18:3n-3 in milk were increased nearly 2-fold with INF relative to CON. Dietary or postruminal supplementation of canola oil to late-lactation cows reduced saturated FA and increased unsaturated C18 in milk but nutrient digestion was adversely affected with abomasal infusion of canola oil.     

Effects of monensin and dietary soybean oil on milk fat percentage and milk fatty acid profile in lactating dairy cows

The objective of this study was to investigate the effect of monensin (MN) and dietary soybean oil (SBO) on milk fat percentage and milk fatty acid (FA) profile. The study was conducted as a randomized complete block design with a 2 × 3 factorial treatment arrangement using 72 lactating multiparous Holstein dairy cows (138 ± 24 d in milk). Treatments were [dry matter (DM) basis] as follows: 1) control total mixed ration (TMR, no MN) with no supplemental SBO; 2) MN-treated TMR (22 g of MN/kg of DM) with no supplemental SBO; 3) control TMR including 1.7% SBO; 4) MN-treated TMR including 1.7% SBO; 5) control TMR including 3.4% SBO; and 6) MN-treated TMR including 3.4% SBO. The TMR (% of DM; corn silage, 31.6%; haylage, 21.2%; hay, 4.2%; high-moisture corn, 18.8%; soy hulls, 3.3%; and protein supplement, 20.9%) was offered ad libitum. The experiment consisted of a 2-wk baseline, a 3-wk adaptation, and a 2-wk collection period. Monensin, SBO, and their interaction linearly reduced milk fat percentage. Cows receiving SBO with no added MN (treatments 3 and 5) had 4.5 and 14.2% decreases in milk fat percentage, respectively. Cows receiving SBO with added MN (treatments 4 and 6) had 16.5 and 35.1% decreases in milk fat percentage, respectively. However, the interaction effect of MN and SBO on fat yield was not significant. Monensin reduced milk fat yield by 6.6%. Soybean oil linearly reduced milk fat yield and protein percentage and linearly increased milk yield and milk protein yield. Monensin and SBO reduced 4% fat-corrected milk and had no effect on DM intake. Monensin interacted with SBO to linearly increase milk fat concentration (g/100 g of FA) of total trans-18:1 in milk fat including trans-6 to 8, trans-9, trans-10, trans-11, trans-12 18:1 and the concentration of total conjugated linoleic acid isomers including cis-9, trans-11 18:2; trans-9, cis-11 18:2; and trans-10, cis-12 18:2. Also, the interaction increased milk concentration of polyunsaturated fatty acids. Monensin and SBO linearly reduced, with no significant interaction, milk concentration (g/100 g of FA) of short- and medium-chain fatty acids (<C16). Soybean oil reduced total saturated FA and increased total monounsaturated FA. These results suggest that monensin reduces milk fat percentage and this effect is accentuated when SBO is added to the ration.     

Influence of dietary fish oil on conjugated linoleic acid and other fatty acids in milk fat from lactating dairy cows

Lactating cows were fed menhaden fish oil to elevate concentrations of conjugated linoleic acid, transvaccenic acid, and n-3 fatty acids in milk. Twelve multiparous Holstein cows at 48+/-11 DIM were assigned randomly to a replicated 4 x 4 Latin square. Each treatment period was 35 d in length, with data collected d 15 to 35 of each period. On a dry matter (DM) basis, diets contained 25% corn silage, 25% alfalfa hay, and 50% of the respective concentrate mix. Fish oil was supplemented at 0, 1, 2, and 3% of ration DM. Linear decreases were observed for DM intake (28.8, 28.5, 23.4, and 20.4 kg/d) and milk fat (2.99, 2.79, 2.37, and 2.30%) for 0 to 3% dietary fish oil, respectively. Milk yield (31.7, 34.2, 32.3, and 27.4 kg/d) increased as dietary fish oil increased from 0 to 1% but decreased linearly from 1 to 3% dietary fish oil. Milk protein percentages (3.17, 3.19, 3.21, and 3.17) were similar for all treatments. When the 2% fish oil diet was fed, concentrations of conjugated linoleic acid and transvaccenic acid in milk fat increased to 356% (to 2.2 g/ 100 g of total fatty acids) and 502% (to 6.1 g/100 g), respectively, of amounts when 0% fish oil was fed. There were no additional increases in these fatty acids when cows were fed 3% fish oil. The n-3 fatty acids increased from a trace to over 1 g/100 g of milk fatty acids, when the 3% fish oil diet was fed. Fish oil supplementation to diets of dairy cows increased the conjugated linoleic acid, transvaccenic acid, and n-3 fatty acids in milk.     

Effects of a supplemental yeast culture on heat-stressed lactating Holstein cows

Multiparous, lactating Holstein cows (n = 23; 120 ± 30 d in milk, 690 ± 67 kg of body weight) housed in climatic chambers were randomly assigned to 1 of 2 dietary treatments: a diet containing a novel yeast culture formulation (YC) for heat stress (n = 12, 10 g/d) or a control diet (n = 11). The trial length was 28 d and consisted of a 7-d thermal neutral period (TN; 18°C, 20% humidity) followed by 21 d of heat stress (HS; cyclical daily temperatures ranging from 29.4 to 37.8°C and 20% humidity). Cows were individually fed a total mixed ration consisting primarily of alfalfa hay and steam-flaked corn. During TN, the YC feeding had no effect on production variables or most body temperature indices. During HS, all body temperature indices increased and YC had no effect on rump surface temperature, respiration rate, or sweating rates. Cows fed YC had lower rectal temperatures at 1200 and 1800 h (40.29 vs. 40.02°C and 40.35 vs. 40.12 ± 0.07°C, respectively) compared with control-fed cows. Cows fed both diets lost body weight (42 kg) during HS, but there were no differences between diets. Control-fed cows had increased dry matter intake (DMI) and milk yield (19.1 vs. 17.9 ± 0.5 kg/d and 32.15 vs. 29.15 ± 0.02 kg/d, respectively) compared with YC-fed cows, but intake and milk production were similar between diets when evaluated on a body weight basis. Heat stress progressively decreased DMI (29%) and milk yield, with milk production reaching a nadir (33%) in the third week. Heat stress decreased milk protein (7%) and lactose (5%) levels, but did not alter milk fat content. Heat-stressed cows were in calculated negative energy balance (−1.91 ± 0.70 Mcal/d) and this was unaffected by diet. Independent of diet, HS decreased plasma glucose (11%), but neither diet nor HS altered basal nonesterified fatty acid levels. Heat stress increased plasma urea N concentrations (11.5 vs. 14.8 ± 0.4 mg/dL). Despite YC-fed cows having slightly reduced body temperatures indices, feeding YC did not prevent the negative effects of HS.     

DHA单细胞油脂的脂肪酸分布及甘油三酯组成分析

测定了DHA单细胞油脂的总脂肪酸组成,采用脂肪酶Lipozyme 435醇解DHA单细胞油脂获得2-单甘酯(2-MAG),结合薄层色谱法和气相色谱法,分析其脂肪酸分布,并选择超高效液相色谱(UPLC)串联四级杆飞行时间质谱(Q-TOF-MS/MS)在电喷雾离子化(ESI)模式下对DHA单细胞油脂的甘油三酯进行了分离鉴定。结果表明:DHA单细胞油脂中含量较高的脂肪酸是DHA(51.37%)、棕榈酸(31.13%)和DPA(10.78%);sn-2位DHA和DPA含量分别为72.65%和18.21%,sn-1,3位棕榈酸含量为43.61%;DHA和DPA平均分布在甘油三酯的sn-1,3位和sn-2位,棕榈酸主要分布在sn-1,3位。DHA单细胞油脂中含量较高的甘油三酯是22∶6-22∶5-16∶0(12.76%),22∶5-16∶0-16∶0(8.93%),22∶6-22∶6-22∶6(8.78%),22∶6-22∶6-22∶5(6.62%),16∶0-16∶0-16∶0(6.61%),占总甘油酯的43.7%。     

Replacing stearic acid with oleic acid in supplemental fat blends improves fatty acid digestibility of lactating dairy cows

The objective of our study was to determine the effects of altering the ratio of stearic (C18:0; SA) and oleic (cis-9 C18:1; OA) acids in supplemental fatty acid (FA) blends on FA digestibility and milk yield of dairy cows. Eight multiparous Holstein cows (mean ± SD; 157 ± 11.8 d in milk) were randomly assigned to treatment sequence in a replicated 4 × 4 Latin square design with 14-d periods. Digestibility and production data were collected during the last 4 d of each period. The treatments were an unsupplemented control diet (CON), and 3 diets incorporating FA supplement blends at 1.4% of diet dry matter (DM) containing (as a % of total FA) 50% SA and 10% OA, 40% SA and 20% OA, or 30% SA and 30% OA. The FA blends were balanced to contain 33% palmitic, 5% linoleic, and <0.5% linolenic acids. The FA supplements replaced soyhulls in the CON diet. Preplanned contrasts were as follows: (1) overall effect of FA treatments [CON vs. the average of the FA-supplemented diets; (50:10 + 40:20 + 30:30)/3], (2) the linear effect of OA inclusion in the supplemental FA blend, and (3) the quadratic effect of OA inclusion in the supplemental FA blend. There was no effect of treatment on DM intake, but the replacement of soyhulls in the FA treatments decreased neutral detergent fiber intake. Overall, compared with CON, FA treatments increased DM and neutral detergent fiber digestibility, and increasing OA within FA treatments quadratically increased digestibility of DM and neutral detergent fiber. Overall, FA treatments increased the intake of total, 16-carbon, and 18-carbon FA, decreased the digestibility of total and 18-carbon FA, but increased absorption of total, 16-carbon, and 18-carbon FA. Within FA treatments, increasing OA linearly increased the digestibility of total, 16-carbon, and 18-carbon FA, as well as the absorption of total, 16-carbon, and 18-carbon FA. Overall, FA treatments increased the yields of milk, energy-corrected milk, and milk fat, and tended to increase milk protein yield. Compared with CON, FA treatments had no effect on the yield of de novo milk FA and increased the yields of mixed and preformed milk FA. Within FA treatments, increasing OA did not affect the yields of milk or milk components, linearly decreased the yield of de novo FA, and quadratically affected the yield of mixed and preformed milk FA. Overall, FA treatments increased plasma nonesterified fatty acids but did not affect β-hydroxybutyrate or insulin. Within FA treatments, increasing OA quadratically affected plasma nonesterified fatty acids, and tended to linearly increase β-hydroxybutyrate and quadratically affect insulin. In conclusion, supplemental FA blends containing different ratios of SA and OA did not affect DM intake but increased the yields of milk and milk components. Supplemental FA blends also increased digestibility of DM and neutral detergent fiber and decreased digestibility of total and 18-carbon FA compared with CON. Although increasing OA within FA supplements did not alter milk production, increasing OA within FA supplements increased total, 16-carbon, and 18-carbon FA digestibility and FA absorption. Further research is required to determine longer term effects of SA and OA on nutrient digestion and partitioning and opportunities for maintaining or improving FA digestibility with increasing SA intake and availability in the small intestine.     

Effect of replacing solvent-extracted canola meal with high-oil traditional canola, high-oleic acid canola, or high-erucic acid rapeseed meals on rumen fermentation, digestibility, milk production, and milk fatty acid composition in lactating dairy cows

The objective of this experiment was to investigate the effects of replacing conventional, solvent-extracted canola meal (control; CTRL) with high oil content; conventional, mechanically extracted canola meal (CMEC); high-oleic, low polyunsaturated fatty acid (FA) canola meal (HOLL); and high-erucic acid, low-glucosinolate rapeseed meal (RPS) on rumen function, digestibility, milk production, and milk FA composition in lactating dairy cows. The experimental design was a replicated 4 × 4 Latin square with 8 lactating dairy cows. Four of the cows were ruminally cannulated. All oilseed meals were included at approximately 12 to 13% of dietary dry matter (DM). Crude protein and fat concentrations (% of DM) of the meals were 43 and 3.1%, 32.8 and 16.1%, 45.2 and 13.7%, and 34.3 and 17.9% for CTRL, CMEC, HOLL, and RPS, respectively. All diets were formulated to supply net energy of lactation in excess of requirements. The CMEC and RPS diets were predicted to be about 1% deficient in metabolizable protein. Relative to the CTRL, inclusion of high-oil seed meals in the diet lowered ruminal acetate concentration and the molar acetate:propionate ratio and decreased DM intake. Milk yield generally followed DM intake and was lower for CMEC and RPS than the CTRL. Treatments had no effect on milk composition, other than an increase in milk urea nitrogen concentration for HOLL. Fat-corrected milk (3.5%) feed efficiency was increased by HOLL and RPS compared with CTRL. Urinary urea nitrogen losses were increased by HOLL, which, as a consequence, increased the ammonia-emitting potential of manure. The ratio of milk N-to-N intake was greater for CMEC and RPS. Replacing solvent-extracted canola meal with the high-oil meal decreased milk fat 12:0, 14:0, 16:0, and total saturated FA content and enhanced cis-9 18:1 and total monounsaturated FA concentrations. Relative to the CTRL, canola increased total trans FA in milk, whereas inclusion of HOLL in the diet increased trans-11 18:1 and cis-9, trans-11 CLA content. The RPS increased milk fat cis-13 22:1 content from 0.07 to 2.33 g/100 g of FA. In conclusion, HOLL or RPS, which are likely to come from small-scale biodiesel plants where oil is cold pressed without hexane extraction, fed at levels at or above 12 to 13% of dietary DM may decrease feed intake and milk production, but can be used to alter milk FA composition in lactating dairy cows.     

Fatty acid composition of milk from multiparous Holstein cows treated with bovine somatotropin and fed n-3 fatty acids in early lactation

Multiparous cows (n = 59) were blocked by expected calving date and previous milk yield and assigned randomly to treatments to determine effects of bovine somatotropin (bST; Posilac, Monsanto Animal Agricultural Group, St. Louis, MO) and source of dietary fat on milk fatty acid composition during the first 140 d in milk. Diets were provided from calving and included whole, high-oil sunflower seeds (SS; 10% of dietary dry matter; n-6/n-3 ratio of 4.6) as a source of linoleic acid or a mixture of Alifet-High Energy and Alifet-Repro (AF; Alifet USA, Cincinnati, OH; 3.5 and 1.5% of dietary dry matter, respectively; n-6/n-3 ratio of 2.6) as a source of protected n-3 fatty acids (15.7% 18:3, 1.3% 20:5, and 1.3% 22:6). Treatments were derived from a 2 × 2 combination of supplemental fat source (SS, AF) and with 0 (SSN, AFN) or 500 (SSY, AFY) mg of bST administered every 10 d from 12 to 70 d in milk and at 14-d intervals thereafter. Milk fatty acid composition was determined in samples collected from 32 cows (8 complete blocks) during wk 2, 8, and 20 of lactation. Data were analyzed as repeated measures using mixed model procedures to determine the effects of diet, bST, week of lactation, and their interactions. Proportions of 18:3 (4.02 vs. 3.59 ± 0.16%), 20:5 (0.52 vs. 0.41 ± 0.02%), and 22:6 (0.11 vs. 0.02 ± 0.02%) were greater and the n-6/n-3 fatty acid ratio (7.40 vs. 8.80 ± 0.30) was reduced in milk from cows fed AF compared with SS. Proportions of de novo-synthesized fatty acids increased and preformed fatty acids decreased as lactation progressed, but bST administration delayed this shift in origin of milk fatty acids. Transfer efficiency of 18:3, 20:5, and 22:6 from AF to milk fat averaged 36.2, 4.9, and 5.2%, respectively. These efficiencies increased as lactation progressed, but were delayed by bST. Apparent mammary Δ⁹-desaturase activity and milk conjugated linoleic acid (cis-9, trans-11 conjugated linoleic acid) content increased through the first 8 wk of lactation. Based on the product-to-substrate ratio of 14:1/14:0 fatty acids in milk, there was an interaction of diet and bST because bST decreased apparent Δ⁹-desaturase activity in SSY cows but increased it in AFY cows (0.10, 0.09, 0.08, and 0.09 ± 0.01 for SSN, SSY, AFN, and AFY, respectively). Feeding Alifet-Repro increased n-3 fatty acids in milk and bST prolonged the partitioning of dietary fatty acids into milk fat.     

The effect of dietary forage to concentrate ratio and forage type on milk fatty acid composition and milk fat globule size of lactating cows

We examined the effects of 2 grass silage-based diets differing in forage:concentrate (FC) ratio and those of a red clover silage-based diet on intake, milk production, ruminal fatty acid (FA) biohydrogenation, milk FA composition, and milk fat globule (MFG) size distribution. Ten multiparous Nordic Red cows received the following treatments: grass silage-based diets containing high (70:30, HG) or low (30:70, LG) FC ratio or a red clover silage-based diet with an FC ratio of 50:50 (RC) on a dry matter basis. Determinations of MFG were performed from fresh milk samples without addition of EDTA so the results of fat globules >1 µm in diameter are emphasized instead of the entire globule population. Lower FC ratio in grass silage-based diets increased milk production with no effect on daily fat yield, leading to 13% lower milk fat concentration. The effect of FC ratio on MFG size was moderate. It did not affect the volume-weighted diameter in grass silage-based diets, although LG lowered the volume-surface diameter of MFG in the size class >1 µm compared with HG. Compared with HG, feeding LG moderately decreased the biohydrogenation of 18:2n-6, leading to a higher level of polyunsaturated fatty acids in milk fat. Feeding RC lowered milk fat concentration and daily milk fat yield compared with grass silage-based diets. The volume-weighted diameter of MFG in the size class >1 µm was smaller in RC milk compared with grass silage-based diets. Feeding RC increased the flow of 18:3n-3 at the omasum by 2.4-fold and decreased the apparent ruminal 18:3n-3 biohydrogenation compared with grass silage-based diets despite similar intake of 18:3n-3. It also resulted in the lowest amount of saturated FA and the highest amounts of cis-9 18:1, 18:3n-3, and polyunsaturated FA in milk. In conclusion, LG decreased milk fat content and induced minor changes in MFG size distribution compared with HG, whereas RC lowered milk fat production, altered milk FA composition to nutritionally more beneficial direction, and led to smaller MFG compared with grass silage-based diets.     

Within-milking variation in milk composition and fatty acid profile of Holstein dairy cows

Changes in milk composition during a milking are well characterized, but variation in milk fatty acid (FA) profile is not well described and may affect the accuracy of in-line milk composition analyzers and could potentially be used for selective segregation of milk. Within-milking samples were collected from 8 multiparous high-producing Holstein cows (54.86 ± 6.8 kg of milk/d; mean ± standard deviation). A milk-sampling device was designed to allow collection of multiple samples during a milking without loss of vacuum or interruption of milk subsampling. Milk was collected during consecutive morning and afternoon milkings (12-h intervals) and was replicated 1 wk later. Each sample represented approximately 20% of the milking and was analyzed for fat, true protein, and lactose concentration and FA profile. Milk fat concentration markedly increased over the course of milk let down (4.4 and 4.2 percentage units at the a.m. and p.m. milking, respectively), whereas milk fat globule size did not change. Milk protein and lactose concentration decreased slightly during milking. Modest changes in milk FA profile were also observed, as milk de novo and 16-C FA concentrations increased approximately 10 and 8%, respectively, whereas the concentration of preformed FA decreased about 7% during the milking. In agreement, mean milk FA chain length and unsaturation modestly decreased during milking (0.59 and 0.014 U, respectively). The observed changes in milk fat concentration during a milking are consistent with previous reports and reflect the dynamic nature of milk fat secretion from the mammary gland. Changes in milk FA profile are not expected to practically affect the accuracy of spectroscopy methods for determination of milk fat concentration. Furthermore, the small variation in FA profile during a milking limits the use of within-milking milk segregation to tailor milk FA profile.     

Lactation performance and fatty acid composition of milk from Holstein cows fed 0 to 5% oleamide.

Diets containing 0 to 5% oleamide were fed to Holstein cows to determine linear or nonlinear responses to the fat supplement on lactation performance and milk fatty acid composition. Six rations containing concentrate, corn silage, and 0, 1, 2, 3, 4, or 5% (dry matter basis) added oleamide were fed to six multiparous cows in a 6 x 6 Latin square for 2-wk periods. As the oleamide concentration in the ration increased from 0 to 5%, dry matter intake declined, fiber and dry matter digestibilities remained constant, and digestibilities of protein and fatty acids increased. Milk yield declined as dietary oleamide increased, although yield was not depressed numerically until oleamide exceeded 2% of the diet dry matter. The C18:1 concentration doubled in milk as oleamide in the diet increased from 0 to 5%. Ratios of C18:1 to C16:0 in milk fat were 0.56, 0.83, 1.34, 1.53, and 1.73 for the diets supplemented with 0, 1, 2, 3, 4, and 5% oleamide, respectively. No amide was detected in milk samples taken from cows fed the 5% oleamide diet. Results show that intake of diets containing 2 to 3% oleamide substantially increased the milk C18:1:C16:0 ratio without greatly affecting milk yield or causing detectable amounts of amide in milk.     

Interaction of unsaturated fat or coconut oil with monensin in lactating dairy cows fed 12 times daily. II. Fatty acid flow to the omasum and milk fatty acid profile

Feeding animal-vegetable (AV) fat or medium-chain fatty acids (FA) to dairy cows can decrease ruminal protozoal counts. However, combining moderate to large amounts of AV fat with monensin (tradename: Rumensin, R) could increase the risk for milk fat depression (MFD), whereas it is not known if diets supplemented with coconut oil (CNO; rich in medium-chain FA) with R would cause MFD. In a 6 × 6 Latin square design with a 2 × 3 factorial arrangement of treatments, 6 rumen-cannulated cows were fed diets without or with R (12 g/909 kg) and either control (no fat), 5% AV fat, or 5% CNO. Diets were balanced to have 21.5% forage neutral detergent fiber, 16.8% crude protein, and 42% nonfiber carbohydrates. Omasal flows of FA were characterized by an increased percentage of trans 18:1 for AV fat and CNO diets compared with the control, a higher percentage of 12:0 and 14:0 for CNO, and higher cis 18:1 for AV fat. Milk FA composition reflected the changes observed for omasal FA digesta flow. The de novo FA synthesis in the mammary gland was decreased by the main effects of R compared without R (averaged over fat treatments) and for added fat (AV fat and CNO) versus control (averaged over R). The percentages of 6:0, 8:0, and 10:0 in milk fat were lower for R and for AV fat and CNO compared with the control. The percentage of trans 18:1 FA in milk fat also higher for AV fat and CNO compared with the control. Against our hypotheses, the feeding of CNO did not prevent MFD, and few interactions between R and fat source were detected. The feeding of CNO did compromise ruminal biohydrogenation, with accumulation of trans 18:1 in the rumen and in milk fat.     

Fatty acid metabolism in liver of dairy cows fed supplemental fat and nicotinic acid during an entire lactation

Liver biopsies from 38 multiparous Holstein cows were used to determine rates of peroxisomal beta-oxidation and total beta-oxidation of palmitate in liver homogenates and contents of total lipid, triglyceride, and glycogen during the lactation cycle. Cows were assigned to one of four diets from wk 4 through wk 42 of lactation: control, control plus nicotinic acid (12 g/d), supplemental fat, or supplemental fat plus nicotinic acid. Liver biopsies were obtained at wk 3 (covariate), 6, 12, 24, and 42 of lactation. Neither supplemental fat nor nicotinic acid affected palmitate oxidation in liver homogenates or liver composition. Peroxisomal beta-oxidation capacity and the ratio of peroxisomal to total beta-oxidation decreased from wk 3 to 12 and then increased at wk 42. Contents of total lipid and triglyceride decreased, and content of glycogen increased, from wk 3 to 12. Total oxidation capacity in liver homogenates was correlated negatively with total lipid and triglyceride in liver, yields of milk and solids-corrected milk (SCM), and plasma nonesterified fatty acids (NEFA), and was correlated positively with liver glycogen, dry matter intake (DMI), energy balance, and plasma glucose. Peroxisomal beta-oxidation was correlated negatively with yields of milk and SCM. The ratio of peroxisomal to total beta-oxidation was correlated positively with liver total lipid, liver TG, and plasma NEFA and negatively with DMI and energy balance. When only data from wk 3 postpartum were considered, both total and peroxisomal beta-oxidation were correlated negatively with hepatic concentrations of total lipid and TG. Peroxisomal beta-oxidation in liver of dairy cows is not affected by feeding supplemental fat or nicotinic acid during wk 4 to 42 of lactation but may be a part of the hepatic adaptations to negative energy balance.