Alterations in ruminal bacterial populations at induction and recovery from diet-induced milk fat depression in dairy cows

Ten ruminally cannulated Holstein cows were used in a crossover design that investigated changes in ruminal bacterial populations in response to induction and recovery from diet-induced milk fat depression (MFD). Further, the effect on the ruminal microbiota of the cows with diet-induced milk fat depression inoculated with rumen contents from non-milk fat-depressed donor cows was evaluated. Milk fat depression was induced during the first 10 d of each period by feeding a low-fiber, high-starch, and high-polyunsaturated fatty acid diet (26.1% neutral detergent fiber, 28.1% starch, 5.8% total fatty acids, and 1.9% C18:2), resulting in a 30% decrease in milk fat yield. Induction was followed by a recovery phase, where all cows were switched to a high-fiber, low-starch, and low-polyunsaturated fatty acid diet (31.8% neutral detergent fiber, 23% starch, 4.2% total fatty acids, and 1.2% C18:2) and were allocated to (1) control (no inoculation) or (2) ruminal inoculation with donor cow digesta (8 kg/d for 6 d). Ruminal samples were collected at the end of induction (d 10) and during recovery (d 13, 16, and 28), separated to solid and liquid fractions, extracted for DNA, PCR- amplified for the V1-V2 region of the 16S rRNA gene, and analyzed for bacterial diversity. Results indicated that bacterial communities were different between fractions. In each fraction, differences were significant between the induction (d 10) and recovery (d 13, 16, and 28) periods; however, differences were less apparent with time during the recovery period. The MFD (d 10) was typified by a reduction in the relative sequence abundance of Bacteroidetes and an increase in the relative sequence abundance of Firmicutes and Actinobacteria across both fractions. At the genus level, relative sequence abundance of unclassified Lachnospiraceae, Butyrivibrio, Bulleidia, and Coriobacteriaceae were higher on d 10 and were positively correlated with trans-10,cis-12 CLA and the trans-10 isomer, suggesting their potential role in altered biohydrogenation reactions. A switch to the recovery diet resulted in a sharp increase in the Bacteroidetes lineages and a decrease in Firmicutes members on d 13; however, this shift appears to stabilize by d 28, indicating the restoration process for ruminal bacteria from an altered state is gradual and complex. Inoculation of 10% of rumen contents from non-MFD donor cows to MFD cows revealed this procedure had transient effects on only a few bacterial populations, and such effects disappeared after d 16 following cessation of inoculation. It can be concluded that alterations in milk FA profiles at induction are preceded by microbial alterations in the rumen driven by dietary changes.     

Dietary molasses increases ruminal pH and enhances ruminal biohydrogenation during milk fat depression

Feeding high-concentrate diets has the potential to cause milk fat depression, but several studies have suggested that dietary sugar can increase milk fat yield. Two experiments were conducted to evaluate the ability of dietary molasses to prevent milk fat depression in the presence of a 65% concentrate diet. In trial 1, molasses replaced corn grain at 0, 2.5, or 5% of diet dry matter in diets fed to 12 second-lactation Holstein cows (134 ± 37 d in milk) in a 3 × 3 Latin square design. Trial 1 demonstrated that replacing up to 5% of dietary dry matter from corn with molasses had positive effects on de novo fatty acid synthesis, increasing the yield of short- and medium-chain fatty acids during diet-induced milk fat depression. Increasing inclusion rate of molasses increased milk fat concentration, but decreased milk yield and milk protein yield. Trial 2 used 7 ruminally cannulated, multiparous, late-lactation Holstein cows (220 ± 18 d in milk) to evaluate effects of dietary molasses on ruminal parameters and milk composition, and also to assess whether increased metabolizable protein supply would alter these responses. Cows were randomly assigned to a dietary treatment sequence in a crossover split plot design with 0 and 5% molasses diets. Dietary treatments were fed for 28 d, with 16 d for diet adaptation, and the final 12 d for 2 abomasal infusion periods in a crossover arrangement. Abomasal infusions of water or AA (5 g of l-Met/d + 15 g of l-Lys-HCl/d + 5 g of l-His-HCl-H₂O/d) were administered 3 times daily for 5 d, with 2 d between infusion periods. Administration of AA had no effect on concentration or yield of any milk components. Addition of molasses increased milk fat concentration (2.71 vs. 2.94 ± 0.21%), but had no effect on yields of milk fat or protein. Dietary molasses decreased total volatile fatty acid concentration (141 vs. 133 ± 4.6 mM), decreased the molar proportion of propionate, and increased the molar proportion of butyrate in ruminal fluid. Molasses also increased ruminal pH (5.73 vs. 5.87 ± 0.06), decreased the yield of trans-10 C18:1, and increased the yield of trans-11 C18:1 in milk fat. These data provide evidence that molasses may promote mammary de novo fatty acid synthesis in cows fed high-energy rations by moderating ruminal pH and altering ruminal fatty acid biohydrogenation pathways.     

Induction of and recovery from milk fat depression occurs progressively in dairy cows switched between diets that differ in fiber and oil concentration

Milk fat depression (MFD) caused by intermediates of ruminal biohydrogenation commonly occurs in dairy cattle. The time course of recovery from MFD is important to mechanistic investigation and management of the condition. Nine cows were used in a repeated design, allowing analysis of recovery from diet-induced MFD. A high-fiber, low-oil diet was fed during the control and recovery periods, and a low-fiber, high-oil (LFHO) diet was fed during the induction period. Milk yield was not affected by treatment. Milk fat percentage and yield decreased progressively during induction and were lower by d 3 and 5, respectively. Milk fat concentration and yield increased progressively when cows were fed the recovery diet and were not different from control on d 19 and 15, respectively. Yield of de novo synthesized fatty acids (FA) decreased progressively during the induction period and was lower than that of controls by d 5. A biphasic response was seen for milk fat trans isomers, where trans-11 C18:1 and cis-9,trans-11 conjugated linoleic acid (CLA) were elevated initially and trans-10 C18:1 and trans-10,cis-12 CLA increased progressively during the induction period. A similar biphasic response was seen during recovery from MFD, with trans-10 C18:1 and trans-10,cis-12 rapidly decreasing initially and trans-11 C18:1 and cis-9,trans-11 CLA increasing slightly above control levels during the second phase. Recovery from diet-induced MFD occurs gradually with a short lag when dietary fiber and oil concentrations are corrected. This time course provides a framework to identify factors causing MFD and set expectations during recovery from MFD.     

Short communication: Effect of antioxidant supplementation on milk production,milk fat synthesis,and milk fatty acids in dairy cows when fed a diet designed to cause milk fat depression

This study evaluated the effect of a blend of synthetic antioxidants on the yield of milk and milk components and milk fatty acid composition in dairy cows fed a diet designed to cause milk fat depression (MFD). We hypothesized that supplementing a synthetic antioxidant to diets with a high rumen unsaturated fatty acid load (RUFAL) would decrease the severity of MFD. Sixteen lactating Holstein cows (163 ± 47 d in milk), in a crossover design with two 21-d periods, were fed a corn silage and grass silage-based diet containing 15% distillers grains. The diet contained 34% neutral detergent fiber, 18% crude protein, 26% starch, and 4.3% total fatty acids (dry matter basis). Cows were fed the diet without supplementation (control; CON) or supplemented with 0.02% (dry matter basis) of a synthetic antioxidant (AOX; Agrado Plus, Novus International Inc., St. Charles, MO). Dry matter intake and milk yields were recorded daily. Milk samples were collected at the start of the study for baseline values and the end of each period (d 20–21) and analyzed for milk components and fatty acid composition. Dry matter intake and milk yield were unaffected by treatment and averaged 25.9 and 50.2 kg/d, respectively. Similarly, we observed no effect of treatment on yields of fat, protein, lactose, 3.5% fat-corrected milk, energy-corrected milk, feed efficiency, body weight, or body condition score. Milk fat concentration and yield were both reduced by the high RUFAL diets. We observed a tendency for AOX to increase the concentration of milk fat and decrease the concentration of milk protein. Yields of de novo and preformed fatty acids were not affected by treatment, although we detected a trend for a slight increase in the yield of 16-carbon fatty acid for AOX compared with CON. Treatment had only minor effects on individual milk fatty acids, except for the concentration and yield of linoleic acid, which were over 90% higher for AOX compared with CON. In conclusion, milk fat concentration and yield were reduced by a high RUFAL diet containing 15% distillers grains; however, supplementation with AOX did not overcome the MFD induced by this diet.     

Effect of dietary vitamin E on rumen biohydrogenation pathways and milk fat depression in dairy cows fed high-fat diets

Six lactating Holstein cows were assigned to a replicated Latin square design to test the effect of dietary vitamin E on milk fat depression and on the increased production of milk trans-10 C18:1 classically observed when feeding high doses of unsaturated fatty acids with low-fiber diets. Two diets (linseed diet and linseed diet + 12,000 IU of vitamin E/d) were compared during 2 periods of 21 d. The linseed diet presented a forage-to-concentrate ratio of 50:50 and contained extruded linseed (1.86 kg/d) and linseed oil (190 g/d). It was conceived to favor the “trans-11 to trans-10 shift” (low structural value and high level of unsaturated fatty acids). Milk yield and protein content were not affected by the diets. Milk of cows fed the linseed diet presented the typical symptoms of milk fat depression associated with a shift in biohydrogenation pathways: low fat content and high level of trans-10 C18:1. However, the high dose of dietary vitamin E provided significantly increased milk fat content (by 17.93%) and yield (by 15.56%) and decreased trans-10 C18:1 content (by 47.06%). In addition, it managed to significantly increase the daily yields of vaccenic (by 102.56%) and rumenic acids (by 56.67%). However, the sequence of administration of vitamin E influenced its effect, as vitamin E seemed to be more active in limiting the “trans-11 to trans-10 shift” when it was incorporated in the diet simultaneously with the fat. Once the shift had occurred, the subsequent addition of vitamin E was no longer able to completely counteract this process.     

Effect of unsaturated fatty acids and triglycerides from soybeans on milk fat synthesis and biohydrogenation intermediates in dairy cattle

Increased rumen unsaturated fatty acid (FA) load is a risk factor for milk fat depression. This study evaluated if increasing the amount of unsaturated FA in the diet as triglycerides or free FA affected feed intake, yield of milk and milk components, and feed efficiency. Eighteen Holstein cows (132 ± 75 d in milk) were used in a replicated 3 × 3 Latin square design. Treatments were a control (CON) diet, or 1 of 2 unsaturated FA (UFA) treatments supplemented with either soybean oil (FA present as triglycerides; TAG treatment) or soybean FA distillate (FA present as free FA; FFA treatment). The soybean oil contained a higher concentration of cis-9 C18:1 (26.0 vs. 11.8 g/100 g of FA) and lower concentrations of C16:0 (9.6 vs. 15.0 g/100 g of FA) and cis-9,cis-12 C18:2 (50.5 vs. 59.1 g/100 g of FA) than the soybean FA distillate. The soybean oil and soybean FA distillate were included in the diet at 2% dry matter (DM) to replace soyhulls in the CON diet. Treatment periods were 21 d, with the final 4 d used for sample and data collection. The corn silage- and alfalfa silage-based diets contained 23% forage neutral detergent fiber and 17% crude protein. Total dietary FA were 2.6, 4.2, and 4.3% of diet DM for CON, FFA, and TAG treatments, respectively. Total FA intake was increased 57% for UFA treatments and was similar between FFA and TAG. The intakes of individual FA were similar, with the exception of a 24 g/d lower intake of C16:0 and a 64 g/d greater intake of cis-9 C18:1 for the TAG compared with the FFA treatment. Compared with CON, the UFA treatments decreased DM intake (1.0 kg/d) but increased milk yield (2.2 kg/d) and milk lactose concentration and yield. The UFA treatments reduced milk fat concentration, averaging 3.30, 3.18, and 3.11% for CON, FFA, and TAG treatments, respectively. Yield of milk fat, milk protein, and 3.5% fat-corrected milk remained unchanged when comparing CON with the UFA treatments. No differences existed in the yield of milk or milk components between the FFA and TAG treatments. The UFA treatments increased feed efficiency (energy-corrected milk/DM intake), averaging 1.42, 1.53, and 1.48 for CON, FFA, and TAG treatments, respectively. Although milk fat yield was not affected, the UFA treatments decreased the yield of de novo (<16-carbon) synthesized FA (40 g/d) and increased the yield of preformed (>16-carbon) FA (134 g/d). Yield of FA from both sources (16-carbon FA) was reduced by the UFA treatments but to a different extent for FFA versus TAG (72 vs. 100 g/d). An increase was detected in the concentration of trans-10 C18:1 and a trend for an increase in trans-10,cis-12 C18:2 and trans-9,cis-11 C18:2 for the UFA treatments compared with CON. Under the dietary conditions tested, UFA treatments supplemented at 2% diet DM as either soybean FA distillate or soybean oil increased milk yield but did not effectively cause a reduction in milk fat yield, with preformed FA replacing de novo synthesized FA in milk fat. Further research is required to determine if the response to changes in dietary free and esterified FA concentrations is different in diets that differ in their risk for milk fat depression.     

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.     

The effect of rumen digesta inoculation on the time course of recovery from classical diet-induced milk fat depression in dairy cows

Ten ruminally cannulated cows were used in a crossover design that investigated the effect of rumen digesta inoculation from non-milk fat-depressed cows on recovery from classical diet-induced milk fat depression (MFD) characterized by reduced fat yield, reduced de novo milk fat synthesis, and increased alternate trans isomers. Two additional cows fed a high-fiber and low-polyunsaturated fatty acid (FA) diet (31.8% neutral detergent fiber, 4.2% FA, and 1.2% C18:2) were used as rumen digesta donors. Milk fat depression was induced during the first 10 d of each period by feeding a low-fiber and high-polyunsaturated FA diet (induction; 26.1% neutral detergent fiber, 5.8% FA, and 1.9% C18:2), resulting in a 30% decrease in milk fat yield. A recovery phase followed where all cows were switched to the high-forage, low-polyunsaturated FA diet and were allocated to (1) control (no inoculation) or (2) ruminal inoculation with donor cow digesta (8 kg/d for 6 d). Milk yield and composition were measured every 3 d. Milk yield progressively decreased during recovery. Milk fat concentration increased progressively during the recovery phase and no effect of treatment existed at any time point. Also, no treatment effect of milk fat yield was detected. The concentration of milk de novo FA increased progressively during recovery for both treatments and was higher for inoculated compared with control cows on d 6. In agreement, milk fat concentration of trans-10,cis-12 conjugated linoleic acid decreased progressively in both treatments and was lower in inoculated cows on d 3 and 6. Ruminal inoculation from non-milk fat-depressed cows did not change milk fat yield, but slightly accelerated the rate of recovery of de novo FA synthesis and normal ruminal FA biohydrogenation, demonstrating a possible opportunity for other interventions that improve the ruminal environment to accelerate recovery from this condition.     

Detection of non-milk fat in milk fat by gas chromatography and linear discriminant analysis

Gas chromatography was utilized to determine triacylglycerol profiles in milk and non-milk fat. The values of triacylglycerol were subjected to linear discriminant analysis to detect and quantify non-milk fat in milk fat. Two groups of milk fat were analyzed: A) raw milk fat from the central region of Mexico (n = 216) and B) ultrapasteurized milk fat from 3 industries (n = 36), as well as pork lard (n = 2), bovine tallow (n = 2), fish oil (n = 2), peanut (n = 2), corn (n = 2), olive (n = 2), and soy (n = 2). The samples of raw milk fat were adulterated with non-milk fats in proportions of 0, 5, 10, 15, and 20% to form 5 groups. The first function obtained from the linear discriminant analysis allowed the correct classification of 94.4% of the samples with levels <10% of adulteration. The triacylglycerol values of the ultrapasteurized milk fats were evaluated with the discriminant function, demonstrating that one industry added non-milk fat to its product in 80% of the samples analyzed.     

Relationships between rumen lipopolysaccharide and mediators of inflammatory response with milk fat production and efficiency in dairy cows

The main objective of this study was to evaluate correlative relationships between rumen lipopolysaccharide (LPS) and mediators of acute phase response with milk fat yield and efficiency in dairy cows challenged with graded amounts of barley grain in the diet. An additional aim of the study was to quantify the intercow variation in relation to milk fat production and acute phase response in cows fed graded amounts of grain. Eight primiparous, lactating Holstein cows (60 d in milk) were assigned to 1 of the 4 total mixed rations containing barley grain at 0, 15, 30, and 45% (dry matter basis) in a replicated 4 × 4 Latin square design. Free rumen LPS, plasma acute phase proteins, and milk fat content were quantified in multiple samples collected on d 5 and 7 of the measurement periods shortly before the morning feeding. Results showed markedly greater concentrations of rumen LPS with increasing dietary grain level. The correlative analysis revealed strong negative relationships between rumen LPS and milk fat content and yield. The predictor variable of rumen LPS explained 69% of the variation during the milk fat reduction of the cows. The stronger depression in milk fat percentage was obtained when rumen LPS exceeded a threshold of 5,564 ng/mL, corresponding to a milk fat content of 3.39%. The increase in concentration of rumen LPS was also associated with declines in milk fat yield and 3.5% fat-corrected milk (R² = 0.50), as well as milk energy efficiency (R² = 0.43). The correlative analysis also indicated that the increase of plasma C-reactive protein (CRP) in response to higher grain feeding was associated with a linear decrease of milk fat content and yield (R² = 0.28 to 0.46). Furthermore, the statistical analysis revealed high percentages of intercow variation related to milk fat variables, as well as the responses of rumen LPS and plasma CRP. Taken together, the current results implicate rumen LPS and the host CRP response in the lowering of milk fat content and milk energy efficiency in dairy cows fed high-grain diets. Further research is warranted to understand the mechanism(s) by which rumen LPS and inflammatory responses to LPS lower milk fat synthesis and milk energy efficiency and to develop novel strategies for their prevention.     

Effect of dietary supplementation or cessation of magnesium-based alkalizers on milk fat output in dairy cows under milk fat depression conditions

We aimed to evaluate the effects of dietary supplementation with magnesium oxide and calcium-magnesium dolomite on milk fat synthesis and milk fatty acid profile or persistency in milk fat synthesis after their cessation in dairy cows under milk fat depression conditions. Twenty-four multiparous dairy cows in early lactation (mean ± standard deviation; 112 ± 14 d in milk) were used in a randomized complete block design. Milk fat depression was induced in all cows for 10 d by feeding a diet containing 35.2% starch, 28.7% neutral detergent fiber, and 4.8% total fatty acid (dry matter). The experiment was conducted in 2 periods. During the Mg-supplementation period (d 1–20), cows were randomly assigned to (1) the milk fat depression diet used during the induction phase (control; n = 8), (2) the control diet plus 0.4% magnesium oxide (MG; n = 8), or (3) the control diet plus 0.8% calcium-magnesium dolomite (CMC; n = 8). Compared with the control group, feeding the magnesium-supplemented diets increased milk fat concentration and yield by 12% within 4 d. During the 20-d Mg-supplementation period, both the MG and CMC diets increased milk fat concentration and yield, as well as 3.5% fat-corrected milk and energy-corrected milk yield, without affecting dry matter intake, milk yield, and milk protein and lactose concentrations. In the Mg-cessation period (d 21–30), all cows received the control diet, which resulted in a greater milk fat concentration and yield in the cows that had already received the MG and CMC diets in the Mg-supplementation period. Whereas, milk fat concentration and yield remained high after discontinuation of the magnesium-containing alkalizer until d 27. The difference in milk fat synthesis was associated with lower trans-10 C18:1 (?22%) and higher trans-11 C18:1 (+12.5%) concentrations in milk during the Mg-supplementation period. Furthermore, it was evident that within 2 d of supplementation, the trans-10:trans-11 ratio was lower in MG and CMC cows compared with cows receiving the control. This suggested that the effect of magnesium-based alkalizers on milk fat synthesis was mediated via a shift in ruminal biohydrogenation of cis-9,cis-12 C18:2 in the rumen. In conclusion, abrupt addition of magnesium oxide and calcium-magnesium dolomite increased milk fat synthesis, which persisted for 7 d after cessation of magnesium-based alkalizers. A similar ability to recover milk fat synthesis and normal fatty acid biohydrogenation pathways was observed for magnesium oxide and calcium-magnesium dolomite.     

A randomized herd-level field study of dietary interactions with monensin on milk fat percentage in dairy cows

This field trial evaluated the effects of dietary supplementation with 16 mg/kg (based on total dry matter intake) of monensin sodium on bulk tank milk fat percentage (MFP) of commercial dairy herds. Interactions between monensin and nutritional factors on MFP were studied. The trial was conducted in 47 Holstein dairy herds in Québec, Canada, between November 2005 and May 2006. The herd was the unit of interest. Enrolled herds were followed for a 7-mo period. Monensin treatment was randomly allocated in a crossover design where monensin was supplemented to the lactating dairy cow diet for a consecutive 12-wk period. Twenty-four herds were allocated to monensin treatment for the first period of trial, and 23 herds were allocated for the second period. Diet composition and ration physically effective particle level were collected every 8 wk. Milk fat percentage data were retrieved from weekly bulk tank measures. Data were analyzed in linear mixed models using repeated measures within herd where MFP was considered the outcome variable. In addition to the main effect of monensin treatment, the following covariates were forced a priori into all statistical models: treatment period, weekly herd mean parity, and weekly herd mean days in milk. The majority of herds were fed a total mixed ration (n = 29) and were housed in tie-stalls (n = 42). Monensin significantly decreased bulk tank MFP by 0.12 percentage points. The reduction of MFP associated with monensin was larger for herds having a diet high (>39.7%) in nonfiber carbohydrates, having a low level of physically effective particles in ration (>45.0%; ≥8 mm), and not feeding dry hay as first meal in the morning. Significant interactions between monensin and nutritional factors on bulk tank MFP were related to nonfiber carbohydrate and fiber concentrations in the diet.     

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 376.2 g 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.     

Trans-9, cis-11 conjugated linoleic acid reduces milk fat synthesis in lactating dairy cows

Under certain dietary situations, rumen biohydrogenation results in the production of unique fatty acids that inhibit milk fat synthesis. The first of these to be identified was trans-10, cis-12 conjugated linoleic acid (CLA), but others are postulated to contribute to diet-induced milk fat depression (MFD). Our objective was to examine the potential role of trans-9, cis-11 CLA in the regulation of milk fat. In a preliminary study, we used gas-liquid and high-performance liquid chromatography techniques to examine milk fat samples from a diet-induced MFD study and found that an increase in trans-9, cis-11 CLA corresponded to the decrease in milk fat yield. We investigated this further using a CLA enrichment of 9, 11 isomers to examine the biological effect of trans-9, cis-11 CLA on milk fat synthesis. Four rumen-fistulated Holstein cows were randomly assigned in a 4 × 4 Latin square experiment involving 5-d treatment periods and abomasal infusion of 1) ethanol (control), 2) a 9, 11 CLA mix (containing 32% trans-9, cis-11, 29% cis-9, trans-11, and 17% trans-9, trans-11), 3) a trans-9, trans-11 CLA supplement, and 4) a trans-10, cis-12 CLA supplement (positive control). The trans-9, trans-11 CLA and trans-10, cis-12 CLA supplements were of high purity (>90%), and all supplements were infused at a rate to provide 5 g/d of the CLA isomer of interest. Milk yield and dry matter intake did not differ among treatments. Compared with the control treatment, milk fat yield was reduced by 15% for the 9, 11 CLA mixture and by 27% for the trans-10, cis-12 CLA treatment. We also found that trans-9, trans-11 CLA had no effect on milk fat yield, and previous research has shown that milk fat yield is unaltered when cows are infused with cis-9, trans-11 CLA. When all treatments were considered, results suggested that trans-9, cis-11 was the CLA isomer in the 9, 11 CLA mix responsible for the reduction in milk fat synthesis, although the magnitude was less than that observed for trans-10, cis-12 CLA. Interestingly, trans-9, trans-11 CLA altered the milk fat desaturase index, further demonstrating that alterations in desaturase can occur independently of effects on milk fat synthesis. Overall, our investigations identified that an increase in milk fat content of trans-9, cis-11 CLA was associated with diet-induced MFD and provided evidence of a role for this isomer in MFD based on the 15% reduction in milk fat yield with abomasal infusion of a CLA enrichment that supplied 5 g/d of trans-9, cis-11 CLA.     

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.     

Distinct blood and milk 18-carbon fatty acid proportions and buccal bacterial populations in dairy cows differing in reticulorumen pH response to dietary supplementation of rapidly fermentable carbohydrates

Nine Holstein dairy cows were fed diets with increasing proportions of rapidly fermentable carbohydrates (RFCH) to investigate the effect on reticular pH, milk fat content (MFC), 18-carbon fatty acid proportions in blood plasma and milk, and bacterial community in buccal swab samples. Inter-animal variation was expected in terms of reticular pH response upon higher RFCH proportions, which would be reflected in the occurrence or not of milk fat depression (MFD). Moreover, this variation in occurrence of MFD was hypothesized to be related to differences in blood and milk fatty acid proportions and in the bacterial community in buccal samples. Cows were fed a total mixed ration throughout the experiment, which consisted of 4 periods: adaptation (d 0–4) and low (d 5–18), increasing (d 19–24), and high RFCH (d 25–28). During the increasing RFCH period, the standard concentrate (211 g of starch/kg of dry matter) was gradually and partly replaced by a concentrate high in RFCH (486 g of starch/kg of dry matter). The reticular pH was measured using a bolus and the time below pH 6.00 was calculated on a daily basis. On d 13, 14, 25, 27, and 28, plasma and milk samples were collected and analyzed for 18-carbon fatty acid proportions, and buccal swabs were collected for bacterial community analysis based on 16S rRNA gene amplicon sequencing. Inter-animal variation was observed in terms of reticular pH, which allowed us to divide the cows into 2 groups: tolerant (time below pH 6.00 ≤ 0.1 h/d) and susceptible cows (time below pH 6.00 ≥ 1.26 h/d). The lower reticular pH of susceptible cows was accompanied by lower MFC. Both groups already differed in reticular pH and MFC during the low-RFCH period. Furthermore, higher RFCH amounts did not decrease the reticular pH in either of the 2 groups. Nevertheless, MFD was observed in both groups during the high-RFCH period compared with the low-RFCH period. Lower MFC in animals with lower reticular pH or during the high-RFCH period was associated with a shift in 18-carbon fatty acids toward trans-10 at the expense of trans-11 intermediates, which was observed in plasma as well as in milk samples. Moreover, lower MFC was accompanied by shifts in the relative abundance of specific bacteria in buccal samples. Genera Dialister, Sharpea, Carnobacterium, Acidaminococcus, and uncultured genera belonging to the Betaproteobacteria were more abundant in situations with greater trans-10 proportions.     

Principal component and multivariate analysis of milk long-chain fatty acid composition during diet-induced milk fat depression

The objective of this study was to assess the relationship between individual milk fatty acids (FA) and diet-induced milk fat depression (MFD) using principal component analysis (PCA) and multivariate analysis (MA). Cow treatment observations (n = 63) from 3 published feeding experiments with lactating dairy cows were used in the analyses. In the PCA, principal component loading plots 1 (PC1) and 2 (PC2) described 55.9% of the total variation in milk FA and fat concentrations. Saturated FA (14:0, 16:0, and 17:0) and milk fat percentage showed negative loading for PC1. Trans-18:1 isomers (trans-6+7+8 to trans-15), trans-7, cis-9 conjugated linoleic acid (CLA), and trans-10, cis-12 CLA showed positive (opposite) loading, suggesting a negative relationship between these isomers and milk fat percentage. Cis-11, trans-13 CLA and cis-9, trans-11 CLA were associated with the PC2 axes (neutral), indicating that they were not associated with MFD. Multivariate analysis with milk fat percentage as the dependent variable and individual PC1 positive loading variables showed a breakpoint relationship for trans-6+7+8-, trans-9-, trans-10-, and trans-13+14-18:1 and a linear relationship for trans-11-, trans-12-, trans-15-18:1, trans-10, cis-12 CLA, and trans-7, cis-9 CLA. Subsequent MA was conducted on 41 treatment means from 12 independent experiments from the literature, in which concentrations of trans-6+7+8-, trans-9-, trans-10-, and trans-11-18:1, and cis-9 trans;-11, and trans-10, cis-12 CLA were reported. Significant negative effects of trans-9-18:1, trans-10-18:1, and trans-10, cis-12 CLA on milk fat percentage were observed. In this study, the PCA and MA showed that among trans-18:1 isomers, trans-10-18:1 was the most negatively correlated to milk fat percentage. However, the threshold concentration related to maximum MFD indicated that the relative potency was greatest for trans-6+7+8- and lowest for trans-10-18:1. These results suggested that trans-6+7+8-18:1 might be more important than trans-10-18:1 in MFD. Principal component analysis also showed that trans-10, cis-12 and trans-7, cis-9 CLA were the isomers most negatively correlated to milk fat percentage, implying a possible role of trans-7, cis-9 CLA in MFD. Additional experiments are needed to establish whether trans-7-18:1 is involved in MFD or that its effects are mediated via the endogenously synthesized trans-7, cis-9 CLA.     

Seasonal variation in the positional distribution of fatty acids in bovine milk fat

The aim of this study was to determine the seasonal variation in the positional distribution of fatty acids (FA) in bovine milk fat. Bovine milk samples were collected from May 2017 to April 2018 in the Netherlands, and the FA composition in the sn-2 position was determined by using sn-1(3)-selective transesterification of Candida antarctica lipase B. The majority of the FA showed significant variation at sn-2 and sn-1(3) positions between different seasons. The seasonal variation in sn-2 position was higher than the sn-1(3) positions. Parallel to the changes in the diet of the cows throughout a year, we observed an increase in blood-derived FA (i.e. C18:0, C18:1 cis-9) concentrations and a decrease in de novo–synthesized FA during summer. In winter, more saturated FA were esterified in sn-2 position of milk fat. Highest concentrations of palmitic acid, C16:0, was observed in sn-2 position in winter, whereas the amount of unsaturated FA at this position was highest in summer. These results showed that the FA compositions in different regiospecific positions changed due to season; however, the proportions of a specific FA within the 3 positions of the triacylglycerols in milk fat did not change upon seasonal variation.     

Short communication: Effects of lysolecithin on milk fat synthesis and milk fatty acid profile of cows fed diets differing in fiber and unsaturated fatty acid concentration

Thirteen multiparous Holstein cows were used in a crossover design that tested the effect of lysolecithin in diets differing in neutral detergent fiber (NDF) and unsaturated fatty acid (FA) concentrations. Experimental periods were 20 d in length and included two 10-d phases. A standard fiber and lower fat diet was fed the first 10 d (30.5% NDF, no added oil, lower-risk phase) and a lower NDF and higher oil diet was fed during the second 10 d (29.0% NDF and 2% oil from whole soybeans and soybean oil, high-risk phase). Treatments were control and 10 g/d of lysolecithin (LYSO) extended in a ground corn carrier. Milk was sampled on d 0, 5, and 10 of each phase for determination of fat and protein concentration and FA profile. We found no effect of treatment or treatment by time interaction for dry matter intake, milk yield, or milk protein concentration. A treatment by time interaction was observed for milk fat concentration and yield. Milk fat concentration was higher in LYSO on d 5 of the lower-risk phase, but decreased progressively in both treatments during the high-risk phase. Milk fat yield was not different among treatments during the lower-risk phase, but was lower in LYSO on d 15 and tended to be lower on d 20 during the high-risk phase. Concentrations of milk de novo FA decreased and preformed FA increased during the high-risk phase, but we found no effect of treatment or treatment by time interactions. We noted an effect of time, but no treatment or treatment by time interactions for milk trans FA isomers. Briefly, trans-11 C18:1 and cis-9,trans-11 conjugated linoleic acid progressively decreased as trans-10 C18:1 and trans-10,cis-12 conjugated linoleic acid progressively increased during the high-risk phase. The LYSO increased milk fat concentration when feeding a higher fiber and lower unsaturated FA diet, but decreased milk fat yield when feeding a lower fiber and higher unsaturated FA diet, although biohydrogenation pathways and capacity did not appear to be modified. The effect of lysolecithin on rumen fermentation warrants further investigation, but is not recommended when feeding lower fiber and higher unsaturated fat diets.     

Effects of intravenous infusion of conjugated diene 18:3 isomers on milk fat synthesis in lactating dairy cows

It has been previously established that trans-10, cis-12 conjugated linoleic acid plays an important role in milk fat depression (MFD). However, in many situations of dietary induced MFD, the reduction in milk fat synthesis is much greater than what would be predicted based on the milk fat concentration of trans-10, cis-12 18:2. These observations suggest that other biohydrogenation intermediates could be implicated in MFD. The objective of this study was to evaluate the effects on milk fat synthesis of an intravenous administration of 2 conjugated diene 18:3 isomers (cis-9, trans-11, cis-15 and cis-9, trans-13, cis-15 18:3), which are intermediates in ruminal biohydrogenation of α-linolenic acid. Three multiparous Holstein dairy cows (days in milk = 189 ± 37 d; body weight = 640 ± 69 kg; mean ± standard deviation), fitted with indwelling jugular catheters, were randomly assigned to a 3 × 3 Latin square design. For the first 5 d of each period, cows were infused intravenously with a 15% lipid emulsion providing 1) cis-9, trans-11, cis-15 18:3 + cis-9, trans-13, cis-15 18:3 + trans-10, cis-12 18:2 (CD18:3 + CLA); 2) cis-9, cis-12, cis-15 18:3 + cis-9, cis-12 18:2 as a control (ALA + LA); or 3) cis-9, cis-12, cis-15 18:3 + trans-10, cis-12 18:2, as a positive control (ALA + CLA). Milk production was recorded, and milk was sampled daily at each milking for analyses of fat, protein, lactose, milk urea nitrogen, and somatic cell count. Dry matter intake, milk yield, and milk protein were not affected by treatment. Over the experimental period, milk fat content was decreased by 7% for cows that received either ALA + CLA or CD18:3 + CLA compared with ALA + LA. The temporal pattern of milk fat content showed a linear decrease during the infusion period for ALA + CLA and CD18:3 + CLA treatment groups. The transfer efficiencies of conjugated diene 18:3 isomers into milk fat averaged 39 and 32% for cis-9, trans-11, cis-15 18:3 and cis-9, trans-13, cis-15 18:3, respectively. The CD18:3 + CLA treatment had no effect on milk fat concentration beyond that attributable to its trans-10, cis-12 18:2 content. In conclusion, results from the current study offered no support for a role of either cis-9, trans-11, cis-15 18:3 or cis-9, trans-13, cis-15 in MFD.