Effects of commercially available palmitic and stearic acid supplements on nutrient digestibility and production responses of lactating dairy cows

Chromium and Palmitic Acid Supplementation Modulate Adipose Tissue Insulin Sensitivity in Postpartum Dairy Cows

Periparturient dairy cows exhibit intense lipolysis driven by reduced dry matter intake, enhanced energy needs, and the loss of adipose tissue (AT) insulin sensitivity. Extended periods of low insulin sensitivity and negative energy balance induce lipolysis dysregulation, leading to increased disease susceptibility and poor lactation performance. Chromium (Cr) supplementation improves systemic insulin sensitivity, while palmitic acid (PA) increases energy availability for milk production. However, the effect of supplementing Cr and PA alone or in combination on insulin sensitivity in AT is unknown. Thirty-two multiparous cows were used in a randomized complete block design experiment and randomly assigned to one of 4 diets fed from 1 to 24 DIM. Diets included: control, no supplementation (CON, n = 8); Cr (Cr-propionate at 0.45 ppm Cr/kg DM, n = 8); PA (1.5% DM, n = 8); or Cr+PA (n = 8). Plasma samples were collected at -13 ± 5.1 d prepartum (PreP), and 14.4 ± 1.9d (PP1) and 21 ± 1.9d (PP2) after calving for albumin, BHB, BUN, calcium, cholesterol, glucose, nonesterified fatty acids (NEFA), total protein, iron, transferrin, triglycerides, and oxylipids quantification. Subcutaneous AT (SCAT) explants were collected at PreP, PP1 and PP2 and incubated in the presence of the lipolytic agent isoproterenol (ISO = 1 µM, BASAL = 0 µM) for 3 h. The antilipolytic effect of insulin (1µL/L) on SCAT explants was evaluated during ISO stimulation (IN+ISO). Lipolysis was quantified by glycerol release in the media (nmol glycerol/mg AT). Macrophage infiltration and adipocyte size were measured using hematoxylin and eosin-stained AT sections and immunohistochemistry. Cr tended to reduce postpartum NEFA concentrations when compared with CON, PA, and Cr+PA. Likewise, Cr increased the percentage of large adipocytes (>9000 µm2) postpartum compared with other diets. In line with higher lipid content, Cr-fed cows had higher ex-vivo BASAL lipolysis at PP2 when compared with PA and Cr+PA. ISO induced higher lipolysis at PP1 and PP2 but it was not affected by Cr and PA. IN+ISO reduced lipolysis by 29.91 ± 11% in Cr compared with ISO. In contrast, IN+ISO did not affect ISO lipolysis in CON, PA, and Cr+PA. Plasma transferrin was reduced by Cr. At PP2, PA cows had 3.3-fold higher macrophage infiltration in SCAT when compared with CON and Cr. Plasma 9-HODE and 9-oxoODE were increased by Cr+PA. PA increased plasma 13-oxoODE and Cr increased the ratio of 13-HODE:13-oxoODE. PA increased 5-iso Prostaglandin F2α-VI. Our results demonstrate that supplementing Cr during the immediate postpartum enhances SCAT insulin sensitivity and lipid accumulation. Further studies should determine the effects and mechanisms of action of Cr and PA on AT lipogenesis, adipogenesis, and their impact on lactation performance.

Effects of raw and roasted high oleic soybeans on milk production of high-producing dairy cows

Processing method of soybeans has the potential to influence dairy cow production performance, therefore we determined the effect feeding raw or roasted, ground high oleic acid soybeans (HOSB) on production responses of high-producing dairy cows. Thirty-six multiparous Holstein cows (45.6 ± 6.22 kg/d of milk; 110 ± 61 DIM) were randomly assigned to treatment sequences in a 4 × 2 Truncated Latin square design with 35-d periods. Treatments were: 1) control diet containing soybean meal and soybean hulls (CON), 2) 16% roasted and ground HOSB (RST), 3) 16% raw and ground HOSB (RAW-D), and 4) 16% raw and ground HOSB + additional rumen by-pass protein (RAW-U). High oleic acid soybeans replaced conventional soybean meal and hulls in the control diet and rumen by-pass protein replaced soybean meal in RAW-U to maintain diet nutrient composition (%DM) of ∼28.0% NDF, 21.3% forage NDF, 27.3% starch, and 17.8% CP. Fatty acid content of CON, RST, RAW-D, and RAW-U was 1.60, 4.30, 4.36, and 4.34%DM, respectively. Pre-planned contrasts included the overall effect of HOSB inclusion {CON vs. HOSOY [1/3 (RST + RAW-D + RAW-U)]}, the effect of soybean processing {RST vs. RAW [1/2 (RAW-D + RAW-U)]}, and the effect of increasing RUP content within the raw HOSB treatments (RAW-D vs RAW-U). For most variables tested, there were significant interactions between treatment and week, as HOSOY increased production variables compared with CON and RST increased production responses compared with RAW, with only the magnitude of difference varying between weeks. Overall, HOSOY increased DMI and yields of milk, 3.5% FCM, ECM, and milk fat, but did not affect milk protein yield. RST did not impact DMI but increased yields of milk, 3.5% FCM, ECM, milk fat, and milk protein. Compared with RAW-D, RAW-U increased yields of milk and milk protein and tended to increase ECM. Overall, HOSB inclusion of 16% DM increased production responses in high-producing dairy cows, but roasted HOSB had a greater impact than raw HOSB, and the addition of rumen-bypass protein positively affected milk protein response.

Effects of saturated fatty acids with lysophospholipids on production and nutrient digestibility in lactating cows

The objective of the experiment was to determine the effects of supplemental SFA sources, lysophospholipids (LPL), and their interaction on production and nutrient digestibility in lactating dairy cows. The experiment was conducted with 48 cows in a randomized complete block design. Cows were blocked (12 blocks total) by parity and days in milk and randomly assigned to 4 dietary treatments in each block (2 × 2 factorial arrangement), i.e., 2 sources of fat supplements, C16:0 (PA)- or C18:0 (SA)-enriched fat, and with or without LPL. The experiment was conducted for 6 wk to measure daily dry matter intake, milk yield, and weekly milk composition. During the last week of the experiment, spot fecal and urine samples were collected to determine total-tract nutrient digestibility. Milk samples in the last week were also collected to analyze the milk fatty acid (FA) profile. All data were analyzed using the MIXED procedure of SAS, where block was used as a random effect and FA, LPL, and the interaction of FA by LPL were used as fixed effects. Week and interactions of week by FA or LPL were included for production measures. Different sources of SFA did not affect dry matter intake and milk yield. However, the PA treatment increased (39.7 vs. 36.8 kg) energy-corrected milk compared with SA due to increased milk fat yield. No effect of LPL on production measures was observed. Total-tract digestibilities of dry matter, organic matter, crude protein, and total FA were not different between the PA and SA groups, but PA increased (41.4% vs. 38.8%) neutral detergent fiber digestibility compared with SA. Supplementation of LPL increased (64.7% vs. 60.5%) total FA digestibility, especially 18-carbon FA (74.1% vs. 68.2%). An interaction of SFA by LPL was found for 16-carbon FA digestibility. The PA diet increased the concentration of 16-carbon FA in milk fat and SA increased the concentration of preformed FA (≥18 carbons). Supplementation of LPL decreased the concentration of trans-10 C18:1. No difference in N utilization and excretion among treatments was observed. In conclusion, the PA diet was more effective in improving milk fat yield of lactating cows compared with SA. Supplementation of LPL increased digestibility of total FA, especially 18-carbon FA but did not affect production.

High oleic soybean oil maintains milk fat and increases apparent total-tract fat digestibility and fat deposition in lactating dairy cows

Due to the bioactive properties of oleic acid, the objective of this study was to feed high oleic soybean oil (HOSO) to lactating cows and evaluate milk production, body composition, and apparent total-tract digestibility variables. Thirty Holstein cows (n = 16 primiparous, n = 14 multiparous at 87 ± 26 DIM at the start of the trial) were used in a crossover design with periods lasting 21 d. The treatments were a control (CON) diet with no added soybean oil and a HOSO diet with 1.5% diet DM of high oleic soybean oil. Dry matter and milk production data were collected the last 7 d of each period, and milk composition was collected the last 3 d of each period. Fecal samples were collected 6 times during the last 3 d of each period. Body weights were collected on the last 3 d of each period after the morning milking and ultrasound scans of the longissimus dorsi on the last day of each period. Compared with CON, HOSO did not affect DMI, milk production, and milk component yields. However, a parity effect was observed with multiparous cows having increased DMI (5.9 kg/d), milk production (11.2 kg/d), and component yields, with no treatment by parity interactions. Milk fat concentration tended to be greater for HOSO cows. Body weight data tended to have an interaction between treatment and parity, with multiparous HOSO cows having increased BW compared with CON and no effect on primiparous cows. Similar treatment by parity effects were observed for BCS. Compared with CON, HOSO increased fat depth by 0.44 mm and apparent total-tract fat digestibility by 12 percentage units. The results of this study indicated no detrimental effects of HOSO on milk production parameters with an increase in milk fat concentration, fat digestibility, and deposition compared with a control diet.

Effects of increasing dietary inclusion of high oleic acid soybeans on milk production of high-producing dairy cows

Recent research has highlighted the importance of dietary fatty acid profile of fatty acid supplements on production responses of high-producing dairy cows. Conventional soybeans contain ∼15% oleic acid and ∼50% linoleic acid whereas high oleic acid soybeans (HOSB) contain ∼70% oleic acid and ∼7% linoleic acid. We determined the effect of increasing dietary inclusion of roasted and ground HOSB on production responses of high-producing dairy cows. Twenty-four multiparous Holstein cows (50.7 ± 4.45 kg/d of milk; 122 ± 57 DIM) were randomly assigned to treatment sequences in a replicated 4 × 4 Latin square design with 21-d periods. Treatments were increasing doses of HOSB at 0, 8, 16, and 24% DM. The HOSB replaced conventional soybean meal and hulls to maintain similar diet nutrient composition (% DM) of 27.4 - 29.4% (NDF), 20.6% forage NDF, 27.5% starch, and 15.9 - 16.5% CP. Total fatty acid content of treatments was 1.65, 3.11, 4.52, and 5.97% DM, respectively. Pre-planned polynomial orthogonal contrasts included the linear, quadratic, and cubic effects of increasing HOSB. Increasing dietary inclusion of HOSB linearly decreased DMI and milk urea nitrogen and increased yields of milk, 3.5% fat corrected milk, energy corrected milk, and milk fat, and quadratically increased milk protein. The increased response to milk fat was due to an increase in preformed milk fatty acids. Due to the increase in milk component yields and decrease in DMI, there was an increase in feed efficiency. Increasing HOSB inclusion linearly decreased plasma BUN concentration and tended to decrease plasma insulin. Increasing HOSB had no effect on BW change or BCS change. In summary, increasing dietary inclusion of HOSB up to 24% DM increased production responses of high-producing dairy cows and did not affect body reserves.

Effect of increasing dietary inclusion of whole cottonseed on nutrient digestibility and milk production of high-producing dairy cows

We determined the effects increasing dietary inclusion of whole cottonseed (WCS) on nutrient digestibility and milk production responses of high-producing dairy cows. Twenty-four multiparous Holstein cows (mean ± SD; 52.7 ± 2.63 kg/d of milk; 104 ± 23 DIM) were randomly assigned to treatment sequences in a replicated 4 × 4 Latin square design with 21-d periods. Treatments were increasing doses of WCS at 0, 8, 16, and 24% DM, with WCS replacing soybean meal and hulls to maintain similar diet nutrient composition (%DM) of NDF (32%), forage NDF (21%), starch (27%), and CP (17%). Total fatty acid (FA) content of each treatment was 1.70, 2.96, 4.20, and 5.40%DM, respectively. Three preplanned contrasts were used to test the linear, quadratic, and cubic effects of increasing dietary WCS. Increasing dietary WCS from 0 to 24% DM quadratically influenced intakes of DM and NDF, with the highest value being for the 8% WCS, and intakes of 16- and 18-carbon, and total FA, with maximum values obtained up to 24% WCS. Increasing dietary WCS affected digestibility of DM (cubic) and NDF (quadratic), with the lowest values being for the 8% WCS. Increasing WCS increased 16-carbon digestibility (quadratic) but decreased digestibility of 18-carbon and total FA (both quadratic), with highest and lowest values for the 24% WCS, respectively. Increasing dietary WCS quadratically increased absorbed 16- and 18-carbon, and total FA, with maximum values obtained for 24% WCS. Increasing dietary WCS quadratically increased yields of milk, milk fat, milk protein, milk lactose, 3.5% fat corrected milk, and energy corrected milk, and linearly increased body weight gain. The source of milk FA was affected by dietary WCS, with a quadratic decrease in the yield of de novo and mixed milk FA and a quadratic increase in preformed milk FA. Increasing dietary WCS linearly increased trans-10 C18:1 milk FA content. As dietary WCS increased, plasma insulin linearly decreased, and plasma gossypol levels linearly increased. Despite the decrease in total FA digestibility, increasing dietary WCS from 0 to 24% DM increased FA absorption. Increasing dietary inclusion of WCS up to 16% DM increased milk production responses and DM intake. Under the current dietary conditions, high-producing dairy cows benefited best from a diet containing 8-16% DM inclusion of WCS.

Increasing palmitic acid and reducing stearic acid content of supplemental fatty acid blends improves production performance of mid-lactation dairy cows

We determined the effects of altering the ratio of palmitic (C16:0) and stearic (C18:0) acids in supplemental fatty acid (FA) blends on production responses of mid-lactation dairy cows. Twenty-four multiparous Holstein cows (mean ± standard deviation; 47.1 ± 5.8 kg of milk yield, 109 ± 23 DIM) were randomly assigned to treatment sequences in a replicated 4 × 4 Latin square design with 21-d periods. Treatments were a control diet not supplemented with FA (CON), and 3 diets incorporating 1.5% of dry matter (DM) FA supplement blends containing 30% C16:0 + 50% C18:0, 50% C16:0 + 30% C18:0, and 80% C16:0 + 10% C18:0. Additionally, the FA blends were balanced to contain 10% of oleic acid (cis-9 C18:1). The FA blends replaced soyhulls in the CON diet. Diets were formulated to contain (% of DM) 31.0% neutral detergent fiber, 27.0% starch, and 16.9% crude protein. The statistical model included the random effect of cow within square and the fixed effects of period, treatment, and their interaction. Preplanned contrasts included CON versus overall effect of FA supplementation and the linear and quadratic effects of increasing C16:0 in FA blends. Overall FA treatment had no effect on dry matter intake (DMI), but increasing C16:0 linearly increased DMI. Compared with CON, overall FA treatment increased yields of milk, 3.5% of fat-corrected milk, energy-corrected milk, and milk fat but did not affect milk protein yield. Increasing C16:0 linearly increased milk fat yield and tended to linearly increase the yields of 3.5% of fat-corrected milk and energy-corrected milk. Fatty acid supplementation decreased the yield of de novo milk FA but increased yields of mixed and preformed milk FA compared with CON. Increasing C16:0 in FA treatments did not affect the yield of de novo milk FA, linearly increased the yield of mixed, and decreased the yield of preformed milk FA. In summary, feeding FA supplements containing C16:0 and C18:0 increased milk production responses with no effect on DMI compared with a control diet. Mid-lactation cows producing ∼40 to 50 kg/d milk yield responded best to increasing supplemental C16:0 in FA supplements, demonstrating that FA supplements higher in C16:0 and limited in C18:0 improves production responses.

Altering palmitic acid and stearic acid ratios in the diet of early-lactation Holsteins under heat stress: Feed intake, digestibility, feeding behavior, milk yield and composition, and plasma metabolites

The objective of this study was to evaluate the effects of varying the ratio of dietary palmitic (C16:0; PA) and stearic (C18:0; SA) acids on nutrient digestibility, production, and blood metabolites of early-lactation Holsteins under mild-to-moderate heat stress. Eight multiparous Holsteins (body weight = 589 ± 45 kg; days in milk = 51 ± 8 d; milk production = 38.5 ± 2.4 kg/d; mean ± standard deviation) were used in a duplicated 4 × 4 Latin square design (21-d periods inclusive of 7-d data collection). The PA (88.9%)- and SA (88.5%)-enriched fat supplements, either individually or in combination, were added to diets at 2% of dry matter (DM) to formulate the following treatments: (1) 100PA:0SA (100% PA + 0% SA), (2) 66PA:34SA (66% PA + 34% SA), (3) 34PA:66SA (34% PA + 66% SA), and (4) 0PA:100SA (0% PA + 100% SA). Diets offered, in the form of total mixed rations, were formulated to be isonitrogenous (crude protein = 17.2% of DM) and isocaloric (net energy for lactation = 1.69 Mcal/kg DM), with a forage-to-concentrate ratio of 40:60. Ambient temperature-humidity index averaged 72.9 throughout the experiment, suggesting that cows were under mild-to-moderate heat stress. No differences in DM intake across treatments were detected (mean 23.5 ± 0.64 kg/d). Increasing the dietary proportion of SA resulted in a linear decrease in total-tract digestibility of total fatty acids, but organic matter, DM, neutral detergent fiber, and crude protein digestibilities were not different across treatments. Decreasing dietary PA-to-SA had no effect on the time spent eating (340 min/d), rumination (460 min/d), and chewing (808 min/d). As dietary PA-to-SA decreased, milk fat concentration and yield decreased linearly, resulting in a linear decrease of 3.5% fat-corrected milk production and milk fat-to-protein ratio. Feed efficiency expressed as kg 3.5% fat-corrected milk/kg DM intake decreased linearly with decreasing the proportion of PA-to-SA in the diet. Treatments had no effect on milk protein and lactose content. A linear increase in de novo and preformed fatty acids was identified as the ratio of PA to SA decreased, while PA and SA concentrations of milk fat decreased and increased linearly, respectively. A linear reduction in blood nonesterified fatty acids and glucose was detected as the ratio of PA to SA decreased. Insulin concentration increased linearly from 10.3 in 100PA:0SA to 13.1 µIU/mL in 0PA:100SA, whereas blood β-hydroxybutyric acid was not different across treatments. In conclusion, the heat-stressed Holsteins in early-lactation phase fed diets richer in PA versus SA produced greater fat-corrected milk and were more efficient in converting feed to fat-corrected milk.

Altering the ratio of palmitic, stearic, and oleic acids in dietary fat affects nutrient digestibility, plasma metabolites, growth performance, carcass, meat quality, and lipid metabolism gene expression of Angus bulls

This study evaluated the effects of changing the ratio of palmitic, stearic, and oleic acids in dietary fat on nutritional metabolism, growth performance, and meat quality of finishing Angus bulls. Bulls received the following three treatments: (1) a control diet without fat supplement (CON), (2) CON + mixed fatty acid supplement (58% C16:0 + 28% cis-9 C18:1; MIX), (3) CON + saturated fatty acid supplement (87% C16:0 + 10% C18:0; SFA). In summary, both fat treatment diets simultaneously increased saturated fatty acids C16:0 (P = 0.025), C18:0 (P < 0.001) and total monounsaturated fatty acids (P = 0.008) in muscle, thus balancing the ratio of unsaturated to saturated fatty acids in muscle. MIX diet increased the digestibility of dry matter (P = 0.014), crude protein (P = 0.038), and ether extract (P = 0.036). SFA diet increased the daily gain (P = 0.032) and intramuscular fat content (P = 0.043). The high content of C16:0 and C18:0 in the SFA diet promoted weight gain and fat deposition of beef cattle by increasing feed intake, up-regulating the expression of lipid uptake genes and increasing deposition of total fatty acids, resulting in better growth performance and meat quality.

The form more than the fatty acid profile of fat supplements influences digestibility but not necessarily the production performance of dairy cows

The form of a lipid supplement, its degree of saturation, and its fatty acid (FA) profile greatly influence digestibility and cow productive response. The objective in this study was to examine the effect of fat supplements that differ in their form or FA profile on nutrient digestibility and cow performance. Forty-two mid-lactation cows (128 ± 53 d) were assigned to 3 treatment groups according to milk yield, days in milk, and body weight. For 13 wk, the cows were fed rations that contained (on a dry matter basis) (1) 2.4% of calcium salts of fatty acids (CSFA) consisting of 45% palmitic acid (PA) and 35% oleic acid (OA; CS45:35); (2) 2.4% of CSFA consisting of 80% PA and 10% OA (CS80:10); or (3) 2.0% of free FA consisting of 80% PA and 10% OA (FF80:10). Rumen samples were taken to measure the ammonia and volatile FA concentrations, and fecal samples were taken to measure the digestibility. Preplanned comparisons were CS45:35 versus CS80:10 to assess 2 CSFA supplements with different FA profiles, and CS80:10 versus FF80:10 to assess similar FA profiles in different forms. Compared with CS45:35, CS80:10 decreased the milk yields, increased the fat percentage, and tended to increase the energy-corrected milk (ECM) yields. The fat percentage of milk was highest in the FF80:10 cows (4.02%), intermediate in the CS80:10 cows (3.89%), and lowest in the CS45:35 cows (3.75%). Compared with CS80:10, FF80:10 increased milk yields (50.1 vs. 49.4 kg/d, respectively), tended to increase fat percentage, and increased 4% fat-corrected milk (4% FCM; 49.1 vs. 47.7 kg/d, respectively) and ECM yields (49.5 vs. 48.2 kg/d, respectively). Treatment had no effect on dry matter intake (DMI), and compared with CS80:10 cows, the calculated energy balance was lower in the FF80:10 cows. The 4% FCM/DMI and ECM/DMI ratios were higher in the FF80:10 group compared with the CS80:10 group. Compared with the CS80:10 cows, the FF80:10 cows had a lower rumen pH, higher propionate, lower acetate/propionate ratio, and higher total VFA. Compared with CS45:35 cows, the apparent total-tract digestibilities of neutral detergent fiber and acid detergent fiber were higher in CS80:10 cows; whereas, the apparent total-tract digestibilities of dry matter, organic matter, protein, neutral detergent fiber, and acid detergent fiber were higher in the CS80:10 cows compared with the FF80:10 cows. Compared with the CS80:10 group, the apparent digestibility of total FA was 13.0 percentage points lower in the FF80:10 cows (79.1 vs. 66.1%, respectively), and similarly, the digestibilities of 16-carbon and 18-carbon FA were lower in the FF80:10 cows than in the CS80:10 cows. In conclusion, the form, more than the FA profile of fat supplements, influenced digestibility. Further, the CSFA supplements were more digestible than the free fatty acids, regardless of the FA profile. However, energy partitioning toward production appeared to be higher in the FF80:10 cows, although the digestibility of nutrients was lower than in the CSFA product with a similar FA profile.

Effects of esterification, saturation and amount of fatty acids infused into the rumen or abomasum in lactating dairy cows

Our objective was to determine the effects of chemical structure, amount, and site of infusion of long-chain fatty acids (LCFA) in lactating dairy cows. Six multiparous Holstein cows were used in a 6 × 6 Latin square design with 21-d periods. During d 1 to 14, 250 g/d of LCFA and during d 15 to 21, 500 g/d of LCFA were infused continuously into either the rumen or abomasum. Treatments were 1) Control (CONT); 200 g/d of meat solubles plus 12 g/d of Tween 80 in 10 L of water, administered half in the rumen and half in abomasum; 2) control plus mostly saturated LCFA into the abomasum (SFAA); 3) control plus mostly saturated LCFA into the rumen (SFAR); 4) control plus soy (mostly unsaturated LCFA) free fatty acids (FFA) into the abomasum (UFAA); 5) control plus soy triglycerides (TG) into the abomasum (TGA); and 6) control plus soy TG into the rumen (TGR). The first 10 d of each period were for adaptation and washout from the previous treatment. The diet consisted of 30% (dry matter basis) corn silage, 20% alfalfa silage and 50% concentrate. Cows infused with UFAA had lower dry matter intake and milk yield than those infused with SFAA or TGA and reductions were greater at the higher infusion amount. Milk fat yield was decreased by UFAA relative to other treatments. Unsaturated LCFA decreased milk fat yield more than saturated LCFA. All LCFA treatments decreased short- and medium-chain FA in milk relative to CONT, with greatest decreases for UFAA. Apparent total tract digestibilities of nutrient fractions were decreased by UFAA compared with TGA and SFAA and tended to be lower at the higher infusion amount. Apparent digestibility of total fatty acids (FA) was greater for SFAR than for SFAA. Plasma glucagon-like peptide-1 was greater for cows infused with UFAA than SFAA or TGA and increased at the higher amount. Plasma cholecystokinin was greater for cows infused with LCFA compared with CONT. Postruminal unsaturated FFA reduced intake and digestibility of nutrients and FA compared with postruminal TG infusion; saturated FA did not decrease dry matter intake or disrupt nutrient digestion. Glucagon-like peptide-1 may be involved in regulation of feed intake by long-chain fatty acids.

Abomasal infusion of different exogenous emulsifiers alters fatty acid digestibility and milk fat yield of lactating dairy cows

We evaluated the effects of abomasal infusion of emulsifiers on fatty acid (FA) digestibility and milk production of lactating dairy cows. All emulsifiers examined were polysorbates, nonionic surfactants, consisting of a polyethoxylated sorbitan esterified with FA. The polysorbates tested in this study consisted of the same polyethoxylated sorbitan base but differed by the FA esterified to it. Eight rumen-cannulated multiparous cows (89 ± 13 d in milk) were assigned to a treatment sequence in 4 × 4 Latin squares with 18-d periods consisting of 7 d of washout and 11 d of infusion. Treatments were abomasal infusions of water only (CON) or 30 g/d of different emulsifiers as follows: polysorbate-C16:0 (T40), polysorbate-C18:0+C16:0 (T60), and polysorbate-C18:1 (T80). Emulsifiers were dissolved in water and delivered at 6-h intervals (total daily infusion was divided into 4 equal infusions per day). Cows were fed the same diet that contained (% diet dry matter) 32.1% neutral detergent fiber, 15.7% crude protein, 25.8% starch, and 3.32% FA (including 1.92% FA from a saturated FA supplement containing 34.2% C16:0 and 47.7% C18:0). The T80 treatment increased total FA digestibility compared with CON (5.40 percentage units) and T60 (3.90 percentage units) and tended to increase it compared with T40. Also, T40 tended to increase and T80 increased (4.80 percentage units) 16-carbon FA digestibility compared with CON. The T80 treatment increased 18-carbon FA digestibility compared with the other treatments. The T40 treatment tended to increase and T80 increased total FA absorption compared with CON (53 g/d) and T60 (52 g/d). Both T40 and T80 increased the absorption of 16-carbon FA compared with CON and T60. The T60 treatment did not differ from CON for any digestibility variable. Both T40 and T80 increased the yields of milk fat, 3.5% fat-corrected milk, and de novo, mixed, and preformed milk FA compared with CON. In conclusion, not all emulsifiers increased FA digestibility. Compared with CON, T80 increased the digestibility and absorption of total, 16-, and 18-carbon FA. The T40 treatment tended to increase and T80 increased total FA absorption and the yields of milk fat and 3.5% FCM compared with CON. Milk fat yield was increased by increases in de novo, mixed, and preformed milk FA. In our short-term infusion study, results suggest that the predominant FA present in the polysorbate affects its ability to improve FA digestibility. Overall, FA digestibility and absorption were improved the most when cows received the T80 treatment.

Nutrient digetibility and production responses of lactating dairy cows when saturated free fatty acid supplements are included in diets: A meta-analysis

Our objective was to perform a series of meta-analyses to evaluate the effects of diets supplemented with saturated free fatty acid (FA) supplements (SFAA) compared with nonfat supplemented control diets (CON) on nutrient digestibility and production responses of lactating dairy cows and to determine whether experimental design affects responses to SFFA. We divided SFFA into C16:0-enriched supplements (PALM, FA supplements with ≥80% C16:0) and C16:0+C18:0-enriched supplements (MIX, FA supplements with ≥80% C16:0+C18:0). The database was formed from 32 peer-reviewed publications with SFFA supplemented at ≤3% diet dry matter (DM). We completed 3 different meta-analyses to meet our objectives. We analyzed the interaction between experimental design (continuous vs. change-over) and treatments (CON vs. SFFA; Meta.1). Regardless of experimental design, we evaluated the effect of treatment (CON vs. PALM vs. MIX; Meta.2) and the effect of 1-percentage-unit increase of MIX and PALM in diet DM (Meta.3). In Meta.1, there was no interaction between treatments and experimental design for any variable. In Meta.2, compared with CON, MIX had no effect on NDF digestibility, milk protein yield and energy corrected milk (ECM), increased the yields of milk (1.20 kg/d) and milk fat (0.04 kg/d), and decreased FA digestibility (5.20 percentage units). Compared with CON, PALM increased NDF digestibility (4.50 percentage units), the yields of milk (1.60 kg/d), milk fat (0.10 kg/d), milk protein (0.04 kg/d), and ECM (2.00 kg/d), and had no effect on FA digestibility. Compared with MIX, PALM tended to increase FA digestibility (3.20 percentage units), increased NDF digestibility (3.50 percentage units), milk fat yield (0.06 kg/d), and ECM (1.20 kg/d). In Meta.3, for each 1-percentage-unit increase of supplemental FA in diet DM, MIX had no effect on NDF digestibility, decreased FA digestibility, increased the yields of milk and milk fat, had no effect on milk protein yield, ECM and milk fat content, and decreased milk protein content. For each 1-percentage-unit increase of supplemental FA in diet DM, PALM increased NDF digestibility, had no effect on FA digestibility, increased the yields of milk, milk fat, ECM and milk fat content, tended to increase milk protein yield, and had no effect on milk protein content. Our results indicate no reason for the restrictive use of change-over designs in saturated FA supplementation studies and meta-analyses. Lactating dairy cows responded better to a FA supplement enriched in C16:0 compared with one containing C16:0 and C18:0.

Dietary fatty acid and starch content and supplemental lysine supply affect energy and nitrogen utilization in lactating Jersey cows

The effects of dietary fatty acid (FA) and starch content as well as supplemental digestible Lys (sdLys) on production, energy utilization, and N utilization were evaluated. Each factor was fed at 5 different amounts, and factor limits were as follows: 3.0 to 6.2% of dry matter (DM) for FA; 20.2 to 31.3% of DM for starch, and 0 to 17.8 g/d of sdLys. Dietary FA and starch were increased by replacing soyhulls with supplemental fat and corn grain, respectively, and sdLys increased with rumen-protected Lys. Fifteen unique treatments were fed to 25 Jersey cows (mean ± SD; 80 ± 14 d in milk) across 3 blocks in a partially balanced incomplete block design. Each block consisted of 4 periods of 28 d, where the final 4 d were used to determine milk production and composition, feed intake, energy utilization (via total collection and headbox-style indirect calorimetry), and N utilization (via total collection). Response surface models were used to evaluate treatment responses. Increasing dietary FA decreased DM intake and milk protein yield. When dietary starch was less than 24%, milk protein concentration increased with increasing sdLys, but when dietary starch was greater than 26% milk protein concentration decreased with increasing sdLys. Digestibility of FA increased when dietary FA increased from 3.0 to 4.2% and decreased as FA increased beyond 4.2%. Although neutral detergent fiber digestibility decreased as dietary starch increased, energy digestibility increased. As dietary FA increased, metabolizable energy (ME) content quadratically increased. Supply of ME increased as dietary FA increased from 3.0 to 4.2% and decreased as FA increased beyond 4.2%. Increasing dietary FA and starch decreased CH₄ production and urinary energy. Increasing dietary starch increased the efficiency of utilizing dietary N for milk N. Increasing sdLys quadratically decreased N balance as sdLys increased from 0 to 8 g/d and increased N balance as sdLys increased from 8 to 18 g/d. Increasing dietary FA can increase ME content, however, at high dietary FA, decreased DM intake and FA digestibility resulted in a plateau in ME content and a decrease in ME supply. Our results demonstrate that sdLys supply is important for milk protein when dietary starch is low, and some Lys may be preferentially used for muscle protein synthesis at the expense of milk protein when sdLys is high.

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.

Dynamics of Bacterial and Fungal Communities and Metabolites During Aerobic Exposure in Whole-Plant Corn Silages With Two Different Moisture Levels

The study was aimed to investigate the effect of moisture content on microbial communities, metabolites, fermentation quality, and aerobic stability during aerobic exposure in whole-plant corn silages preserved long time to improve the quality and aerobic stability of the silage during feed-out. Corn plants with two different moisture levels (high-moisture content, 680 g/kg; low-moisture content, 620 g/kg) were harvested at one-third and two-thirds milk-line stages, respectively, ensiled in laboratory-scale silos, and then sampled at 350 day after ensiling and at 2 and 5 day after opening to investigate bacterial and fungal communities, metabolites, and aerobic stability. High-moisture content increased aerobic stability and pH and decreased lactic acid and microbial counts in silages (P < 0.05). During aerobic exposure, the low-moisture silages had higher pH and lactic acid bacterial count and lower lactic acid than the high-moisture silages (P < 0.05); Acinetobacter sp. was the most main bacterial species in the silages; Candida glabrata and unclassified Candida had an increasing abundance and negatively correlation with aerobic stability of high-moisture silages (P < 0.05), while C. glabrata, Candida xylopsoci, unclassified Saccharomycetaceae, and unclassified Saccharomycetales negative correlated with aerobic stability of low-moisture silages (P < 0.05) with a rising Saccharomycetaceae; the silages had a reducing concentration of total metabolites (P < 0.05). Moreover, the high-moisture silages contained greater total metabolites, saturated fatty acids (palmitic and stearic acid), essential fatty acids (linoleic acid), essential amino acids (phenylalanine), and non-essential amino acids (alanine, beta-alanine, and asparagine) than the low-moisture silages at 5 day of opening (P < 0.05). Thus, the high-moisture content improved the aerobic stability. Acinetobacter sp. and Candida sp. dominated the bacterial and fungal communities, respectively; Candida sp. resulted in the aerobic deterioration in high-moisture silages, while the combined activities of Candida sp. and Saccharomycetaceae sp. caused the aerobic deterioration in low-moisture silages. The greater aerobic stability contributed to preserve the palmitic acid, stearic acid, linoleic acid, phenylalanine, alanine, beta-alanine, and asparagine during aerobic exposure.

Effect of palmitic acid-enriched supplements containing stearic or oleic acid on nutrient digestibility and milk production of low- and high-producing dairy cows

We evaluated the effects of fatty acid (FA) supplement blends containing 60% palmitic acid (C16:0) and either 30% stearic acid (C18:0) or 30% oleic acid (cis-9 C18:1) on nutrient digestibility and milk production of low- and high-producing dairy cows. Twenty-four multiparous Holstein cows [118 ± 44 d in milk (DIM)] were divided into 2 blocks by milk production and then randomly assigned to treatment sequence in four 3 × 3 Latin squares within production level, balanced for carryover effects in three consecutive 21-d periods. Cows were blocked by milk yield and assigned to 1 of 2 groups (n = 12 per group): (a) low group (42.5 ± 3.54 kg/d; 147 ± 42 DIM) and (b) high group (55.8 ± 3.04 kg/d; 101 ± 34 DIM). Commercially available fat supplements were combined to provide treatments that consisted of the following: (1) control (CON; diet with no supplemental FA), (2) FA supplement blend containing 60% C16:0 and 30% C18:0 (PA+SA), and (3) FA supplement blend containing 60% C16:0 and 30% cis-9 C18:1 (PA+OA) The FA blends were fed at 1.5% of dry matter (DM) and replaced soyhulls from CON. Preplanned contrasts were (1) overall effect of FA treatments [CON vs. the average of the FA treatments (FAT); 1/2 (PA+SA + PA+OA)], and (2) effect of FA supplement (PA+SA vs. PA+OA). Regardless of production level, overall FAT reduced DMI compared with CON. Also, regardless of level of milk production, PA+OA increased total-tract FA digestibility compared with PA+SA. Treatment by production level interactions were observed for neutral detergent fiber (NDF) digestibility, total FA intake, and the yields of 3.5% fat-corrected milk (FCM), energy-corrected milk (ECM), and milk fat. In low-producing cows, FAT increased DM and NDF digestibility compared with CON. In high-producing cows PA+SA increased DM and NDF digestibility compared with PA+OA. In low-producing cows, PA+SA increased 3.5% FCM, ECM, and milk fat yield compared with PA+OA. However, in high-producing cows PA+OA tended to increase 3.5% FCM compared with PA+SA. In conclusion, low-producing cows responded better to a FA blend containing 60% C16:0 and 30% C18:0, whereas high-producing dairy cows responded more favorably to a FA blend containing 60% C16:0 and 30% cis-9 C18:1. However, further research is required to validate our observations that higher-yielding cows have improved production responses when supplemented with cis-9 C18:1 compared with C18:0.

Effects of fat supplements containing different levels of palmitic and stearic acid on milk production and fatty acid digestibility in lactating dairy cows

Fat supplements based on palmitic acid (PA) or stearic acid (SA) are expected to have different effects on milk production and nutrient metabolism in lactating dairy cows. In this study, the effects of prilled fat supplements containing different levels of PA and SA were tested in 12 high-producing multiparous cows (pretrial milk yield = 53.4 ± 8.7 kg/d; mean ± SD) arranged in a 4 × 4 Latin square design with 21-d periods. Treatments were control (CON; no supplemental fat), an enriched PA supplement (HP; 91% C16:0), an enriched SA supplement (HS; 92.5% C18:0), and a blend of PA and SA (INT) fed at 1.95% of diet dry matter. All supplements contained oleic acid at approximately 5% of fatty acids. The HP treatment decreased dry matter intake (DMI) by 1.9 kg/d and 1.1 kg/d compared with SA and CON, respectively. Milk yield was not changed by treatment, but INT increased energy-corrected milk by 2.7 kg/d compared with HS. The HP and INT treatments increased milk fat yield by 0.11 and 0.14 kg/d compared with CON, respectively. Additionally, HP decreased yield of <16 carbon fatty acids (FA; de novo synthesized) by 44 g/d and 43 g/d compared with INT and CON, respectively. The HP treatment increased 16-carbon FA (mixed source) by 155 g/d compared with CON and 64 g/d relative to INT. No effect of treatment on apparent total-tract digestibility of dry matter, organic matter, or neutral detergent fiber was detectable. The INT and HS treatments decreased total-tract digestibility of 16-carbon FA by 10.3 and 10.5 percentage units compared with HP, respectively. Total-tract digestibility of 18-carbon FA was lowest in the HS diet and highest with HP. In conclusion, supplementing PA increased milk fat yield compared with control and SA, but supplementing a mixture of PA and SA increased energy-corrected milk without decreasing intake. The FA profile of fat supplements influences their digestibility and effects on DMI and milk and milk fat synthesis.

Altering the ratio of dietary palmitic and oleic acids affects nutrient digestibility, metabolism, and energy balance during the immediate postpartum in dairy cows

This article is the second from an experiment that determined the effects of altering the dietary ratio of palmitic (C16:0) and oleic (cis-9 C18:1) acids on digestibility, production, and metabolic responses of dairy cows during the immediate postpartum. This article elaborates on the effect of these diets on nutrient digestibility, energy balance, and metabolism. Fifty-six multiparous cows were used in a randomized complete block design and randomly assigned to 1 of 4 treatments fed from 1 to 24 d in milk. The treatments were: (1) control (CON) diet not supplemented with fatty acids (FA); (2) diet supplemented with a FA blend containing 80% C16:0 and 10% cis-9 C18:1 (80:10); (3) diet supplemented with a FA blend containing 70% C16:0 and 20% cis-9 C18:1 (70:20); and (4) diet supplemented with a FA blend containing 60% C16:0 and 30% cis-9 C18:1 (60:30). The FA supplement blends were added at 1.5% of diet dry matter by replacing soyhulls in the CON diet. Three preplanned contrasts were used to compare treatment differences: (1) CON versus FA-supplemented diets, (80:10 + 70:20 + 60:30)/3; (2) the linear effect of cis-9 C18:1 inclusion in diets; and (3) the quadratic effect of cis-9 C18:1 inclusion in diets. The FA-supplemented diets increased digestibility of dry matter, neutral detergent fiber, 18-carbon FA, and total FA compared with CON. We observed a tendency for an interaction between treatment and time for the digestibility of 18-carbon and total FA because the difference in digestibility between CON and 60:30 treatments tended to increase over time. Increasing dietary cis-9 C18:1 increased linearly the digestibility of dry matter, neutral detergent fiber, 16-carbon, 18-carbon, and total FA. Interestingly, total absorbed FA was positively related to milk, milk fat yield, energy-corrected milk, plasma insulin, and albumin, and negatively related to plasma nonesterified FA (NEFA) and body weight loss. The FA-supplemented diets increased intake of digestible energy, metabolizable energy, and net energy for lactation compared with CON. Compared with CON, FA-supplemented diets increased milk energy output and tended to increase negative energy balance. Increasing dietary cis-9 C18:1 increased intake of digestible energy, metabolizable energy, and net energy for lactation. Although increasing dietary cis-9 C18:1 did not affect milk energy output and energy for maintenance, increasing dietary cis-9 C18:1 improved energy balance. Compared with CON, FA-supplemented diets increased plasma insulin, but we did not observe differences between CON and FA-supplemented diets for NEFA and albumin. Increasing cis-9 C18:1 in FA treatments linearly decreased plasma NEFA and tended to linearly increase insulin and β-hydroxybutyrate. During the carryover period, no treatment differences in blood metabolites were observed. Our results indicate that feeding FA supplements containing C16:0 and cis-9 C18:1 during the immediate postpartum period increased nutrient digestibility, energy intake, and milk energy output compared with a non-fat-supplemented control diet. Increasing dietary cis-9 C18:1 increased energy intake, reduced markers of body fat mobilization, and improved energy balance during the immediate postpartum.

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

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

Advances in fatty acids nutrition in dairy cows: from gut to cells and effects on performance

High producing dairy cows generally receive in the diet up to 5-6% of fat. This is a relatively low amount of fat in the diet compared to diets in monogastrics; however, dietary fat is important for dairy cows as demonstrated by the benefits of supplementing cows with various fatty acids (FA). Several FA are highly bioactive, especially by affecting the transcriptome; thus, they have nutrigenomic effects. In the present review, we provide an up-to-date understanding of the utilization of FA by dairy cows including the main processes affecting FA in the rumen, molecular aspects of the absorption of FA by the gut, synthesis, secretion, and utilization of chylomicrons; uptake and metabolism of FA by peripheral tissues, with a main emphasis on the liver, and main transcription factors regulated by FA. Most of the advances in FA utilization by rumen microorganisms and intestinal absorption of FA in dairy cows were made before the end of the last century with little information generated afterwards. However, large advances on the molecular aspects of intestinal absorption and cellular uptake of FA were made on monogastric species in the last 20 years. We provide a model of FA utilization in dairy cows by using information generated in monogastrics and enriching it with data produced in dairy cows. We also reviewed the latest studies on the effects of dietary FA on milk yield, milk fatty acid composition, reproduction, and health in dairy cows. The reviewed data revealed a complex picture with the FA being active in each step of the way, starting from influencing rumen microbiota, regulating intestinal absorption, and affecting cellular uptake and utilization by peripheral tissues, making prediction on in vivo nutrigenomic effects of FA challenging.

Milk production responses to altering the dietary ratio of palmitic and oleic acids varies with production level in dairy cows

We evaluated the effects of altering the dietary ratio of palmitic (C16:0; PA) and oleic (cis-9 C18:1; OA) acids on production responses of cows with a wide range of milk production (32 to 65 kg/d) in a crossover design experiment with a preliminary period. Thirty-two multiparous Holstein cows (144 ± 54 d in milk) were assigned randomly to a treatment sequence. Treatments were diets supplemented with fatty acid (FA) blends (1.5% of diet dry matter) that provided 80% C16:0 + 10% cis-9 C18:1 (PA) and 60% C16:0 + 30% cis-9 C18:1 (PA+OA). The corn silage and alfalfa-based diets contained 20.0% forage neutral detergent fiber (NDF), 28.5% starch, and 17.1% crude protein. Treatment periods were 21 d with the final 5 d used for data and sample collection. Treatment did not affect dry matter intake (DMI), milk yield, energy-corrected milk (ECM), body weight, or body weight change. The PA+OA diet increased total, 16-carbon, and 18-carbon FA digestibility compared with the PA diet. Compared with PA+OA, PA increased fat yield (1.97 vs. 1.91 kg/d) and protein yield (1.61 vs. 1.55 kg/d). The PA diet also increased the yield of de novo (448 vs. 428 g/d) and mixed (749 vs. 669 g/d) milk FA and decreased the yield of preformed FA (605 vs. 627 g/d) compared with PA+OA. Interactions were detected between treatment and preliminary milk yield for DMI, total FA intake, 16-carbon FA intake, ECM, 3.5% fat-corrected milk (linear interaction), and a tendency for milk yield (linear interaction); lower-producing cows (<45 kg/d) had increased DMI and ECM on the PA diet, whereas higher-producing cows (>55 kg/d) had increased DMI and ECM on the PA+OA diet. A linear interaction was detected between treatment and preliminary milk yield for mixed milk FA yield (linear interaction) and a tendency for de novo milk FA yield (linear interaction). Our results demonstrate that feeding a fat supplement containing more cis-9 C18:1 replacing C16:0 increased production responses (DMI, milk yield, and ECM) in higher-producing cows, but decreased production responses in lower-producing cows.