Hepatic lipid metabolism in transition dairy cows fed flaxseed

Thirty-three Holstein cows averaging 687 kg of body weight were allotted 6 wk before the expected date of parturition to 11 groups of 3 cows blocked within parity for similar calving dates to determine the effects of feeding different sources of fatty acids on blood parameters related to fatty liver and profile of fatty acids in plasma and liver. Cows were fed lipid supplements from 6 wk before the expected date of parturition until d 28 of lactation. Cows within each block were assigned to 1 of 3 isonitrogenous and isoenergetic dietary supplements: control with no added lipids (CO); unsaturated lipids supplied as whole flaxseed (FL; 3.3 and 11.0% of the dry matter in prepartum and postpartum diets, respectively); and saturated lipids supplied as Energy Booster (EB; 1.7 and 3.5% of the DM in prepartum and postpartum diets, respectively). Diets EB and FL had similar ether extract concentrations. Multiparous cows fed EB had lower dry matter intake and milk production, higher concentrations of nonesterified fatty acids and β-hydroxybutyrate in plasma and triglycerides (TG) and total lipids in liver, and lower concentrations of plasma glucose and liver glycogen than those fed FL and CO. Production of 4% fat-corrected milk was similar among treatments. Multiparous cows fed FL had the highest liver concentrations of glycogen on wk 2 and 4 after calving and lowest concentrations of TG on wk 4 after calving. Liver C16:0 relative percentages in multiparous cows increased after calving whereas those of C18:0 decreased. Relative percentages of liver C16:0 were higher in wk 2 and 4 postpartum for multiparous cows fed EB compared with those fed CO and FL; those of C18:0 were lower in wk 4 postpartum for cows fed EB compared with those fed CO and FL. Liver C18:1 relative percentages of multiparous cows increased after calving and were higher in wk 4 for cows fed EB compared with those fed CO and FL. The inverse was observed for liver C18:2 relative percentages. In general, diets had more significant effects on plasma concentrations of nonesterified fatty acids, β-hydroxybutyrate, and glucose and liver profiles of fatty acids, TG, total lipids, and glycogen of multiparous than primiparous cows. These data suggest that feeding a source of saturated fatty acids increased the risk of fatty liver in the transition cow compared with feeding no lipids or whole flaxseed. Feeding flaxseed compared with no lipids or a source of saturated fatty acids from 6 wk before calving could be a useful strategy to increase liver concentrations of glycogen and decrease liver concentrations of TG after calving, which may prevent the development of fatty liver in the transition dairy cow.     

Digestion,milk production,milk composition,and blood composition of dairy cows fed whole flaxseed

A total of 90 lactating Holstein cows averaging 628 kg (SE = 8) of body weight (BW) were allotted at calving to 30 groups of three cows blocked for similar calving dates to determine the effects of feeding whole untreated flaxseed on milk production and composition, fatty acid composition of blood and milk, and digestibility, and to determine whether flaxseed could substitute for other sources of fat such as Megalac and micronized soybeans. Cows were fed a total mixed diet based on grass and corn silage and fat supplements for ad libitum intake. The experiment was carried out from calving up to wk 16 of lactation. Cows within each block were assigned to one of the three isonitrogenous, isoenergetic, and isolipidic supplements based on either whole flaxseed (FLA), Megalac (MEG), or micronized soybeans (SOY). Intake of dry matter and change in BW were similar among diets. Cows fed FLA had greater milk yield than those fed MEG (35.7 vs. 33.5 kg/d) and there was no difference between cows fed FLA and those fed SOY (34.4 kg/d). Fat percentage was higher in the milk of cows fed MEG (4.14%) than in the milk of those fed FLA (3.81%) or SOY (3.70%), but milk protein percentage was higher for cows fed FLA (2.98%) than for those fed MEG (2.86%) and SOY (2.87%). Digestibilities of acid detergent fiber, neutral detergent fiber, and ether extract were lower for cows fed FLA than for those fed SOY and MEG. Retention of N was similar among diets. Feeding FLA resulted in the lowest omega-6-to-omega-3-fatty-acids ratio, which would improve the nutritive value of milk from a human health point of view. The data suggest that micronized soybeans and Megalac can be completely substituted by whole untreated flaxseed as the fat source in the diet of early lactating cows without any adverse effect on production and that flaxseed increased milk protein percentage and its omega-6-to-omega-3-fatty-acids ratio.     

Digestion,milk production,milk composition,and blood composition of dairy cows fed formaldehyde treated flaxseed or sunflower seed

Forty midlactation Holstein cows averaging 635 kg of body weight (SE = 8) were allotted at wk 25 of lactation to ten groups of four cows blocked for similar calving dates to determine the effects of formaldehyde treatment of flaxseed and sunflower seed on fatty acid composition of blood and milk, milk yield, feed intake, and apparent digestibility. Cows were fed a total mixed diet based on grass silage and supplements for ad libitum intake over a 10-wk period. Cows within each block were assigned to one of the four isonitrogenous supplements based on either untreated whole flaxseed, formaldehyde-treated whole flaxseed, untreated whole sunflower seed, or formaldehyde-treated whole sunflower seed. Cows fed whole flaxseed compared with sunflower seed maintained greater dry matter (DM) intake (20.3 vs. 18.9 kg/d). Intake of DM, expressed as a percentage of body weight, was increased by adding formaldehyde to oilseeds (3.24 vs. 2.98%). Milk production was similar for cows fed flaxseed and those fed sunflower. Formaldehyde treatment of flaxseed and sunflower seed increased milk production by an average of 2.65 kg/d. Efficiency of fat-corrected milk yield per kilogram of DM intake was increased by formaldehyde treatment (1.31 vs. 1.21), and it was greater with sunflower seed than with flaxseed (1.33 vs.1.21). Protein concentration in milk was greater for cows fed flaxseed (3.38%) compared with those fed sunflower seed (3.21%) and formaldehyde had no effect. Apparent digestibility of DM was not affected by type of seed but it was greater for cows fed formaldehyde-treated seeds. Cows fed formaldehyde-treated flaxseed had the greatest apparent digestibilities of acid detergent and neutral detergent fiber compared with those fed the other diets. Apparent digestibilities of fatty acids were greater for sunflower seed than for flaxseed-based diets. In general, formaldehyde treatment had limited effect on milk fatty acid composition, suggesting that formaldehyde was not very effective in protecting polyunsaturated fatty acids against ruminal biohydrogenation. Feeding flaxseed resulted in the lowest omega 6 to omega 3 fatty acid ratio. The data suggest that both flaxseed and sunflower seed are acceptable fat sources for midlactating cows and that flaxseed increases milk protein percentage compared to sunflower seed.     

Milk composition, milk fatty acid profile, digestion, and ruminal fermentation in dairy cows fed whole flaxseed and calcium salts of flaxseed oil

Four ruminally lactating Holstein cows averaging 602 ± 25 kg of body weight and 64 ± 6 d in milk at the beginning of the experiment were randomly assigned to a 4 × 4 Latin square design to determine the effects of feeding whole flaxseed and calcium salts of flaxseed oil on dry matter intake, digestibility, ruminal fermentation, milk production and composition, and milk fatty acid profile. The treatments were a control with no flaxseed products (CON) or a diet (on a dry matter basis) of 4.2% whole flaxseed (FLA), 1.9% calcium salts of flaxseed oil (SAL), or 2.3% whole flaxseed and 0.8% calcium salts of flaxseed oil (MIX). The 4 isonitrogenous and isoenergetic diets were fed for ad libitum intake. Experimental periods consisted of 21 d of diet adaptation and 7 d of data collection and sampling. Dry matter intake, digestibility, milk production, and milk concentrations of protein, lactose, urea N, and total solids did not differ among treatments. Ruminal pH was reduced for cows fed the CON diet compared with those fed the SAL diet. Propionate proportion was higher in ruminal fluid of cows fed CON than in that of those fed SAL, and cows fed the SAL and CON diets had ruminal propionate concentrations similar to those of cows fed the FLA and MIX diets. Butyrate concentration was numerically higher for cows fed the SAL diet compared with those fed the FLA diet. Milk fat concentration was lower for cows fed SAL than for those fed CON, and there was no difference between cows fed CON and those fed FLA and MIX. Milk yields of protein, fat, lactose, and total solids were similar among treatments. Concentrations of cis-9 18:1 and of intermediates of ruminal biohydrogenation of fatty acids such as trans-9 18:1 were higher in milk fat of cows fed SAL and MIX than for those fed the CON diet. Concentration of rumenic acid (cis-9, trans-11 18:2) in milk fat was increased by 63% when feeding SAL compared with FLA. Concentration of α-linolenic acid was higher in milk fat of cows fed SAL and MIX than in milk of cows fed CON (75 and 61%, respectively), whereas there was no difference between FLA and CON. Flaxseed products (FLA, SAL, and MIX diets) decreased the n-6 to n-3 fatty acid ratio in milk fat. Results confirm that flax products supplying 0.7 to 1.4% supplemental fat in the diet can slightly improve the nutritive value of milk fat for better human health.     

热应激时奶牛血液中游离氨基酸流向与乳蛋白下降的关系研究

目的:探讨热应激时奶牛血液中氨基酸与乳蛋白的相互关系。方法:选取6头相同泌乳期奶牛,正常饲喂和饮水,实验期35 d(6月29日—8月5日)。每日10:00和18:00记录气温,统计产奶量,每周取全天奶样,Foss乳成分分析仪检测乳蛋白含量。于实验开始第1周和最后1周采集颈静脉血液,反相高效液相色谱法检测血液中游离氨基酸含量。结果:随着气温的升高(由26℃升高至最高38℃),实验奶牛日均产奶量由15.2 kg/d下降至10 kg/d,乳蛋白产量由0.47 kg/d下降至0.31 kg/d。血液中Glu、Asp、Gly和Val等主要的生糖氨基酸(参与糖异生作用)以及Leu、Ile等生酮氨基酸均升高或显著升高(0.01P0.05);总支链氨基酸(Val、Ile、Leu,主要参加免疫反应)含量显著增加(P0.05),在必需氨基酸中所占的比例由54.75%增至67.89%。结论:在夏季高温高湿条件下,奶牛可发生热应激,产奶量和乳蛋白含量均降低,但血液中游离氨基酸,特别是支链氨基酸含量显著升高。提示热应激时奶牛血液中高水平的游离氨基酸并未完全用于乳蛋白的合成,还发挥了除此之外的其他作用,而后者的作用优先于参与乳蛋白的合成,即可能优先作为功能性氨基酸参与了机体的其他活动。     

Effect of feeding extruded flaxseed with different grains on the performance of dairy cows and milk fatty acid profile

Sixteen Holsteins cows were used in a Latin square design experiment to determine the effects of extruded flaxseed (EF) supplementation and grain source (i.e., corn vs. barley) on performance of dairy cows. Extruded flaxseed diets contained 10% [dry matter (DM) basis] of an EF product that consisted of 75% flaxseed and 25% ground alfalfa meal. Four lactating Holsteins cows fitted with rumen fistulas were used to determine the effects of dietary treatments on ruminal fermentation. Intakes of DM (23.2 vs. 22.2 kg/d), crude protein (4.2 vs. 4.0 kg/d), and neutral detergent fiber (8.3 vs. 7.9 kg/d) were greater for cows fed EF diets than for cows fed diets without EF. Milk yield and composition were not affected by dietary treatments. However, 4% fat-corrected milk (30.5% vs. 29.6 kg/d) and solids-corrected milk (30.7 vs. 29.9 kg/d) were increased by EF supplementation. Ruminal pH and total volatile fatty acid concentration were not influenced by EF supplementation. However, feeding barley relative to corn increased molar proportions of acetate and butyrate and decreased that of propionate. Ruminal NH₃-N was lower for cows fed barley than for cows fed corn. Milk fatty acid composition was altered by both grain source and EF supplementation. Cows fed EF produced milk with higher polyunsaturated and lower saturated fatty acid concentrations than cows fed diets without EF. Feeding EF or corn increased the milk concentration of C18:0, whereas that of C16:0 was decreased by EF supplementation only. Extruded flaxseed supplementation increased milk fat α-linolenic acid content by 60% and conjugated linoleic acid content by 29%. Feeding corn relative to barley increased milk conjugated linoleic acid by 29% but had no effect on milk α-linolenic concentration. Differences in animal performance and milk fatty acid composition were mainly due to EF supplementation, whereas differences in ruminal fermentation were mostly due to grain source.     

Immune response of postpartum dairy cows fed flaxseed

Thirty Holstein cows were allotted at calving to 10 groups of three cows blocked for similar calving dates to determine the effects of dietary fatty acids on functional properties of immunocompetent cells in early lactation and at breeding. Cows were assigned at calving to one of three isonitrogenous, isoenergetic, and isolipidic supplements based on either calcium salts of palm oil, Megalac, micronized soybeans, or whole flaxseed. On the day of AI and 20 d later, cows were injected with ovalbumin to measure the antibody response. Blood samples were taken at different times after calving (d 5, 21, 42, and 105) and after AI (d 0, 10, 20, and 40) for quantification of serum progesterone, fatty acids, and prostaglandin E2 concentrations. Isolated peripheral blood mononuclear cells were cultured to evaluate the proliferative response to concanavalin A and in vitro productions of interferon-gamma and prostaglandin E2. In general, feeding flaxseed increased serum omega-3 fatty acids concentration compared with feeding Megalac or soybeans, which decreased the omega-6 to omega-3 fatty acids ratio. There was a significant diet x day interaction for the proliferative response of mononuclear cells after calving and AI, indicating that cell responses from cows fed flaxseed were transiently reduced compared with those fed Megalac and soybeans. Moreover, during the breeding period, serum progesterone concentration was significantly greater in cows fed flaxseed compared with those fed Megalac, whereas serum concentration of prostaglandin E2 was significantly lower in cows fed flaxseed than in those fed Megalac or soybeans. Dietary treatments had no effect on the antibody response to ovalbumin and on in vitro productions of interferon-gamma and prostaglandin E2. However, interferon-gamma and prostaglandin E2 were impaired in the first 3 wk after parturition regardless of dietary treatment. These results suggest that changes in fatty acids, progesterone, and prostaglandins E2 concentrations in serum due to dietary treatment and physiological status influenced systemic immunity as shown by reduced proliferative response. However, other mechanisms must be considered and are discussed to explain dietary effect on lymphocyte proliferative response to mitogenic stimulation and other immune functions.     

Apparent recovery of duodenal odd- and branched-chain fatty acids in milk of dairy cows

This study compared flows of odd- and branched-chain fatty acids (OBCFA) at the duodenum with corresponding yields in milk. Four mid-lactation Holstein-Friesian dairy cows were offered 4 dietary treatments, based on different ratios of ryegrass silage and concentrates (80:20, 65:35, 50:50, and 35:65 on a dry matter basis), in a 4 × 4 Latin square design experiment with 4-wk periods. Samples of milk and duodenal digesta were collected during the final week of each period and analyzed for fatty acids. Biohydrogenation of linoleic and α-linolenic acids (C18:2 and C18:3) was extensive for all treatments, with a tendency to be lower for C18:3 with increased concentrate feeding. The proportion of duodenal flows of these fatty acids that appeared in milk declined with increasing concentrate feeding. There was little change in the yield of OBCFA in milk in response to increasing level of concentrate inclusion and no significant relationship with the yield of microbial protein at the duodenum. The efficiency of transfer of iso C15:0 and anteiso C15:0 from the duodenum to milk was similar to that for C18:3, with a reduced proportion transferred into milk at higher flows. Yields of C15:0, C17:0, and iso C17:0 in milk were higher than duodenal flows, confirming synthesis in animal tissues.     

Free fatty acids promote degranulation of azurophil granules in neutrophils by inducing production of NADPH oxidase–derived reactive oxygen species in cows with subclinical ketosis

Subclinical ketosis (SCK) in dairy cows, a common metabolic disorder during the peripartal period, is accompanied by systemic inflammation. Excessive release of azurophil granule (AG) contents during degranulation of polymorphonuclear neutrophils (PMN) could contribute to systemic inflammation in SCK cows. Although the increase in blood free fatty acids (FFA) in SCK cows may promote AG degranulation from PMN, the underlying mechanisms are unclear. Thirty multiparous cows (within 3 wk postpartum) with similar lactation numbers (median = 3, range = 2–4) and days in milk (median = 6, range = 3–15) were classified based on serum β-hydroxybutyrate (BHB) level as control (n = 15, BHB < 0.6 mM) or SCK (n = 15, 1.2 mM < BHB < 3.0 mM). Cows with SCK had greater levels of serum haptoglobin, serum amyloid A, IL-1β, IL-6, IL-8 and tumor necrosis factor-α. These proinflammatory factors had strong positive correlations with myeloperoxidase (MPO), a marker protein of PMN AG, whose content was greater in the serum of SCK cows. Both the number of AG and the protein abundance of MPO were lower in PMN isolated from SCK cows. Additionally, we found a greater ratio of blood CH138A⁺/CD63^high cells and greater mean fluorescence intensity of CD63 on the PMN membrane, further confirming the greater degree of AG degranulation in cows with SCK. In vitro FFA dose response (0, 0.3, 0.6, 1.2, and 2.4 mM for 4 h) and time course (0, 0.5, 1, 2, and 4 h with 0.6 mM) experiments were performed on PMN isolated from control cows. The increase in MPO content in extracellular supernatant resulting from those experiments led to the selection of 0.6 mM FFA for 1 h duration as conditions for subsequent studies. After FFA treatment, release of intracellular MPO was increased along with increased levels of CD63 mean fluorescence intensity on the PMN membrane, confirming that FFA promoted degranulation of AG. In addition, FFA treatment increased reactive oxygen species (ROS) production by PMN, an effect that was attenuated by incubation with diphenyleneiodonium chloride (DPI), a NADPH oxidase-derived ROS inhibitor. The mitochondrial-derived ROS inhibitor carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP) did not affect ROS in response to FFA treatment. Treatment with FFA increased p47 phosphorylation and mRNA abundance of NCF1, NCF2, and CYBB in PMN. Furthermore, DPI, but not FCCP, dampened the degranulation of PMN AG induced by FFA in vitro. These data suggested that the degranulation of AG in PMN induced by FFA was mediated by NADPH oxidase-derived ROS. As verified ex vivo, PMN from SCK cows had greater levels of ROS, phosphorylation of p47, and mRNA abundance of NCF1, NCF2, and CYBB. Overall, the present study revealed that high blood concentrations of FFA in SCK cows induce the production of NADPH oxidase-derived ROS, thereby promoting degranulation of AG in PMN. The stimulatory effect of FFA on the release of AG content during degranulation, especially MPO, provides a new insight into the systemic inflammation experienced by peripartal cows with SCK.     

Short communication: Effects of dietary addition of N-carbamoylglutamate on milk composition in mid-lactating dairy cows

The present study was conducted to investigate the effect of N-carbamoylglutamate (NCG) on milk production and composition in mid-lactating Holstein dairy cows. Sixty multiparous cows with a mean body weight of 669 kg (standard deviation = 71) and 176 days in milk (standard deviation = 55) were blocked based on parity and milk production and randomly assigned into 4 treatments, a basal diet supplemented with 0, 10, 20, or 40 g of NCG/d per cow. Milk yield and composition were recorded weekly, whereas dry matter intake and plasma variables were determined every 2 wk. The results showed that the addition of NCG had no effect on the dry matter intake and milk yield of the cows. Milk fat content and yield increased linearly with NCG addition. The contents of milk protein and total solid also increased linearly in the cows fed NCG, whereas the yield of protein was not affected by the treatments. Conversely, dietary addition of NCG increased the plasma nitric oxide content in a quadratic manner. Moreover, addition of NCG linearly increased the plasma Arg content. Overall, the results indicate that dietary NCG addition increased the milk protein and fat contents, which improved the milk quality of lactating dairy cows.     

饱和脂肪酸对泌乳中期热应激奶牛呼吸、体温和能量平衡的影响

为研究饱和脂肪酸对高温环境条件下泌乳中期奶牛呼吸、体温和能量平衡的影响.选择产后150 ～210 d的中国荷斯坦奶牛48头,根据产奶量、分娩时间和胎次分为对照组(SFA0)、1.5％ (SFA1.5)和3％( SFA3)饱和脂肪酸试验组.试验期间牛舍最小湿热指数(THI)在72以上.结果表明饱和脂肪酸可以显著提高奶牛产奶量、乳脂和干物质含量(P＜0.05),降低14:00牛的直肠温度(P＜0.05),但试验组之间差异不显著,添加量对14:00奶牛的直肠温度的效应呈显著的二次关系(P＜0.05),呼吸频率试验牛之间差异不显著.SFA0、SFA1.5和SFA3.0组的能量平衡分别为1.49 Mcal/d、0.27 Mcal/d和1.22 Mcal/d,差异不显著.日粮添加饱和脂肪酸降低了泌乳中期热应激奶牛日高温时间的体温,对呼吸频率和能量平衡无影响.     

Short communication: Effects of a monensin premix on milk fatty acid content during subacute ruminal acidosis in dairy cows

The effects of a monensin premix on milk fatty acid content during grain-induced subacute ruminal acidosis (SARA) in Holstein cows receiving a total mixed ration was investigated. Six multiparous, rumen-fistulated Holstein cows were used in a two-treatment, two-period crossover design with 6-wk periods. Experimental treatments were either a monensin premix or a placebo premix. At the beginning of wk 4, SARA was induced in experimental cows for a 10-d period using a grain challenge model. The administration of a monensin premix elevated milk fat proportion of total short-chain saturated fatty acids (sum of C4 to C15). Milk fat proportions of conjugated linoleic acid isomers were unaffected. Linolenic acid (C18:3n3) proportion in milk fat of monensin-treated cows were lower when compared with placebo-treated cows during the SARA period. Results from this study indicate that dietary supplementation with monensin during SARA had little effect on milk fatty acid content.     

Effect of dose of calcium salts of conjugated linoleic acid (CLA) on percentage and fatty acid content of milk fat in midlactation holstein cows

Increasing conjugated linoleic acid (CLA) content of milk fat from lactating dairy cattle has become a research interest due to the possible health benefits afforded humans consuming CLA. Dietary supplementation of CLA to lactating dairy cows is one potential method by which CLA content of milk and dairy products may be enhanced. Feeding CLA in calcium salt form could potentially deliver CLA to the lower digestive tract through prevention of biohydrogenation by rumen microbes. Milk fat depression (MFD) occurs when cows receive CLA-60, a commercially available CLA source containing numerous CLA isomers, abomasally. Our objectives were to determine the quantity of CLA as calcium salts required to elicit maximal MFD and to evaluate the effects of CLA supplementation on fatty acid composition of milk fat. Five Holstein cows at approximately 93 DIM were utilized in a 5 x 5 balanced Latin square crossover design. Periods were 14-d in length with a 5-d treatment phase and 9-d rest phase. Treatments were 5-d supplementation of 0, 12.5, 25, 50, and 100 g of CLA-60 in calcium salt form. Milk samples were collected on d 5 of CLA supplementation and analyzed for composition and fatty acid profile. Regression analysis of milk fat data suggested that MFD was not maximized over the dose levels investigated, despite delivery of 34.5 g of trans-10, cis-12 CLA in the 100-g dose of CLA. Supplementation with 50 and 100 g of CLA per day resulted in a reduction of milk fat percent of 29 and 34%, respectively. Trend analysis indicated a linear decrease in the milk fat content of caprylic, capric, and lauric acids as the dose of CLA increased. Milk fat content of cis-9, trans-11, and trans-10, cis-12 CLA increased at an increasing rate as dose increased.     

Performance of lactating dairy cows fed varying amounts of soyhulls as a replacement for corn grain

Fifteen multiparous Holstein cows averaging 112 d in milk were used in a replicated 5 x 5 Latin square to evaluate the incremental substitution of soyhulls for corn in the diet. Diets contained 23% alfalfa silage, 23% corn silage, and 54% concentrate on a dry matter basis. Pelleted soyhulls replaced corn in the concentrate to supply 0, 10, 20, 30, or 40% of the dietary dry matter. Dry matter intake decreased linearly as soyhulls replaced corn in the diet, but the major decrease in dry matter intake occurred when soyhulls provided 30 and 40% of the dietary dry matter. Intakes of both acid and neutral detergent fiber increased linearly as soyhulls increased from 0 to 40% of dietary dry matter. Production of milk tended to decrease when soyhulls supplied 40% of the dietary dry matter. Production of 3.5% fat-corrected milk, milk crude protein percentage and yield, milk urea N, and total solids yield were not affected by treatments. Production of true protein, but not percentage, tended to decrease by about 5% when soyhulls supplied 40% of the dietary dry matter. Increasing the percentage of soyhulls in the dietary dry matter increased linearly milk fat content and yield, and total solids content in milk. These data suggest that soyhulls can successfully supply up to about 30% of the dry matter intake of midlactation cows without depressing animal performance. Furthermore, replacing part of the corn with soyhulls in high grain diets may be viable when milk fat has a high monetary value or when soyhulls can be purchased at a more competitive price than grains on a nutrient content basis.     

Effects of flaxseed on protein requirements and N excretion of dairy cows fed diets with two protein concentrations

Thirty-eight midlactating Holstein cows averaging 597 kg of body weight (SD = 59) were used to determine the effects of dietary flaxseed on protein requirement and N excretion in urine and feces. Milk yield and composition, intake, and digestibility were also determined. Cows were allotted from wk 20 to 30 of lactation to 1 of 4 TMR containing 1) no flaxseed (control) and 16% protein (MPC), 2) whole flaxseed and 16% protein (MPF), 3) no flaxseed (control) and 18% protein (HPC), and 4) whole flaxseed and 18% protein (HPF). Cows fed high protein diets had greater feed intake than those fed medium protein diets (20.2 vs. 18.4 kg/d), and cows fed no flaxseed had greater dry matter intake than those fed flaxseed (20.1 vs. 18.5 kg/d). Milk yield was lower for cows fed MPF (20.3 kg/d) than for those fed HPC (24.4 kg/d), HPF (24.9 kg/d), or MPC (24.0 kg/d). Milk protein and lactose concentrations were similar for cows fed MPC and HPC, but flaxseed decreased milk protein concentration in cows fed MPF or HPF compared with cows fed the control diets. Milk fat concentration was similar in cows fed diets with or without flaxseed, but it was decreased by higher protein concentration. Digestibility was generally reduced when diets contained flaxseed and lower protein concentration. Dietary protein had no effect while dietary flaxseed increased fecal N excretion. Retention of N was lower in cows fed flaxseed compared with cows fed the control diets. Feeding flaxseed decreased milk concentrations of short- and medium-chain fatty acids and increased those of long-chain fatty acids. Flaxseed had no effect on the dietary requirement of N by midlactating dairy cows.     

Production performance and milk composition of dairy cows fed whole or ground flaxseed with or without monensin

Eight multiparous Holstein cows averaging 570 ± 43 kg of body weight and 60 ± 20 d in milk were used in a double Latin square design with four 21-d experimental periods to determine the effects of feeding ground or whole flaxseed with or without monensin supplementation (0.02% on a dry matter basis) on milk production and composition, feed intake, digestion, blood composition, and fatty acid profile of milk. Intake of dry matter was similar among treatments. Cows fed whole flaxseed had higher digestibility of acid detergent fiber but lower digestibilities of crude protein and ether extract than those fed ground flaxseed; monensin had no effect on digestibility. Milk production tended to be greater for cows fed ground flaxseed (22.8 kg/d) compared with those fed whole flaxseed (21.4 kg/d). Processing of flaxseed had no effect on 4% fat-corrected milk yield and milk protein and lactose concentrations. Monensin supplementation had no effect on milk production but decreased 4% fat-corrected milk yield as a result of a decrease in milk fat concentration. Feeding ground compared with whole flaxseed decreased concentrations of 16:0, 17:0, and cis6-20:4 and increased those of cis6-18:2, cis9, trans11-18:2, and cis3-18:3 in milk fat. As a result, there was a decrease in concentrations of medium-chain and saturated fatty acids and a trend for higher concentrations of long-chain fatty acids in milk fat when feeding ground compared with whole flaxseed. Monensin supplementation increased concentrations of cis9 and trans11-18:2 and decreased concentrations of saturated fatty acids in milk fat. There was an interaction between flaxseed processing and monensin supplementation, with higher milk fat concentration of trans11-18:1 for cows fed ground flaxseed with monensin than for those fed the other diets. Flaxseed processing and monensin supplementation successfully modified the fatty acid composition of milk fat that might favor nutritional value for consumers.     

Effect of feeding oilseed supplements to dairy cows on ruminal and milk fatty acid composition

The objective of this study was to compare the effects of oilseed‐based supplements, rapeseed and linseed, against a barley‐based control, on the fatty acid composition, and subsequent solid fat ratio, of the milk fat from dairy cows. In addition, as a means of understanding the digestive processes which influence the milk fat composition, ruminal extracts were collected from the cows and analysed for fatty acid composition. Four lactating dairy cows each fitted with a rumen fistula were provided with silage and one of four concentrate diets. The main constituent of the concentrate supplements was either rapeseed (ground or unground), linseed (unground) or a barley control. The diets were offered in accordance with a 4 × 4 Latin square arrangement. The oilseed‐supplemented concentrates provided the cows with 620–640 g fatty acids day^?1. Experimental treatments were provided to the cows for 2 weeks, after which ruminal extracts were collected over a 24 h period and a milk sample was taken. All extracts were analysed for fatty acid composition. The diets fed influenced the long‐chain fatty acid composition of the ruminal extracts and milk fat. The proportion of C18:1n‐9 in the ruminal extracts increased from 202–224 to 282–321 g kg^?1 of the total fatty acids when the cows were provided with the rapeseed‐based diets. The linseed‐based diet increased the C18:1n‐9 proportion of the ruminal extracts from 164 to 218 g kg^?1 of the total fatty acids. Both rapeseed‐based diets also resulted in a higher proportion of C18:0 in the ruminal extract, possibly owing to biohydrogenation of the dietary fatty acids. This proportion of C18:0 in the ruminal extract was lowest immediately after feeding, increasing to a maximum 4–6 h later. Both rapeseed‐based concentrates increased the proportion of C18:1n‐9 in the milk fat to approximately 300 g kg^?1 of the total fatty acids as compared with 214 g kg^?1 for the control. The proportion of C18:1n‐9 in the milk fat from the cows offered the linseed‐based concentrate was 246 g kg^?1 of the total fatty acids. There were also significant decreases in the proportions of C16:0 in the milk fat from the cows offered all oilseed‐based concentrates. There was no difference between the fatty acid compositions of the milk fats from the cows fed the ground or unground rapeseed‐based supplements. The oilseed‐based supplements also resulted in significant decreases in the solid fat content of the milk fat at temperatures ranging from 0 to 35 °C, which would be indicative of a softer, more spreadable butter. © 2002 Society of Chemical Industry