Mammary gland utilization of amino acids and energy metabolites differs when dairy cow rations are isoenergetically supplemented with protein and fat

Mammary gland utilization of AA and other metabolites in response to supplemental energy from protein (PT) and supplemental energy from fat (FT) was tested in a 2 × 2 factorial arrangement using a randomized complete block design. Fifty-six Holstein-Friesian dairy cows were adapted during a 28-d control period to a basal total mixed ration consisting of 34% grass silage, 33% corn silage, 5% grass hay, and 28% concentrate on a dry matter (DM) basis. Experimental rations were fed for 28 d immediately following the control period and consisted of (1) low protein, low fat (LP/LF), (2) high protein, low fat (HP/LF), (3) low protein, high fat (LP/HF), and (4) high protein, high fat (HP/HF). To obtain the high-protein (HP) and high-fat (HF) diets, intake of the basal ration was restricted and supplemented isoenergetically [net energy (MJ/d) basis] with 2.0 kg/d rumen-protected protein (soybean + rapeseed, 50:50 mixture on a DM basis) and 0.68 kg/d hydrogenated palm fatty acids on a DM basis. Arterial and venous blood samples were collected on d 28 of both periods. Isoenergetic supplements (MJ/d) of protein and fat independently and additively increased milk yield, PT increased protein yield, and FT increased fat yield. A PT × FT interaction affected arterial concentration of all essential AA (EAA) groups, where they increased in response to PT by a greater magnitude at the LF level (on average 35%) compared with the HF level (on average 14%). Mammary gland plasma flow was unaffected by PT or FT. Supplementation with PT tended to decrease mammary clearance of total EAA and decreased group 1 AA clearance by 19%. In response to PT, mammary uptake of total EAA and group 2 AA increased 12 and 14%, respectively, with significantly higher uptake of Arg, Ile, and Leu. Energy from fat had no effect on mammary clearance or uptake of any AA group. The mammary gland uptake:milk protein output ratio was not affected by FT, whereas PT increased this ratio for EAA and group 2 AA. Arterial plasma insulin concentration decreased in response to FT, in particular on the HP/HF diet, as indicated by a PT × FT interaction. Arterial concentrations of nonesterified fatty acids, triacylglycerol, and long-chain fatty acids increased in response to FT, and concentrations of β-hydroxybutyrate and acetate decreased in response to FT only at the HP level. Mammary clearance and uptake of triacylglycerol and long-chain fatty acids increased in response to FT. Energy from PT and FT increased lactose yield despite no change in arterial glucose concentration or mammary glucose uptake. Mammary-sequestered glucose with PT or FT was used in the same amount for lactose synthesis, and a positive net mammary glucose balance was found across all treatments. Results presented here illustrate metabolic flexibility of the mammary gland in its use of aminogenic versus lipogenic substrates for milk synthesis.     

Expression of genes related to energy metabolism and the unfolded protein response in dairy cow mammary cells is affected differently during dietary supplementation with energy from protein and fat

Secretory capacity of bovine mammary glands is enabled by a high number of secretory cells and their ability to use a range of metabolites to produce milk components. We isolated RNA from milk fat to measure expression of genes involved in energy-yielding pathways and the unfolded protein response in mammary glands of lactating cows given supplemental energy from protein (PT) and fat (FT) tested in a 2 × 2 factorial arrangement. We hypothesized that PT and FT would affect expression of genes in the branched-chain AA catabolic pathway and tricarboxylic acid (TCA) cycle based on the different energy types (aminogenic versus lipogenic) used to synthesize milk components. We also hypothesized that the response of genes related to endoplasmic reticulum (ER) homeostasis via the unfolded protein response would reflect the increase in milk production stimulated by PT and FT. Fifty-six multiparous Holstein-Friesian dairy cows were fed a basal total mixed ration (34% grass silage, 33% corn silage, 5% grass hay, and 28% concentrate on a dry matter basis) for a 28-d control period. Experimental rations were then fed for 28 d, consisting of (1) low protein, low fat (LP/LF); (2) high protein, low fat (HP/LF); (3) low protein, high fat (LP/HF); or (4) high protein and high fat (HP/HF). To obtain the high-protein (HP) and high-fat (HF) diets, intake of the basal ration was restricted and supplemented isoenergetically (net energy basis) with 2.0 kg/d rumen-protected protein (soybean + rapeseed, 50:50 mixture on dry matter basis) and 0.68 kg/d hydrogenated palm fatty acids on a dry matter basis. RNA from milk fat samples collected on d 27 of each period underwent real-time quantitative PCR. Energy from protein increased expression of BCAT1 (branched-chain amino acid transferase 1) mRNA, but only at the LF level, and tended to decrease expression of mRNA encoding the main subunit of the branched-chain keto-acid dehydrogenase complex. mRNA expression of malic enzyme, a proposed channeling route for AA though the TCA cycle, was decreased by PT, but only at the LF level. Expression of genes associated with de novo fatty acid synthesis was not affected by PT or FT. Energy from fat had no independent effect on genes related to ER homeostasis. At the LF level, PT activated XBP1 (X-box binding protein 1) mRNA. At the HF level, PT increased mRNA expression of the gene encoding GADD34 (growth arrest and DNA damage-inducible 34). These findings support our hypothesis that mammary cells use aminogenic and lipogenic precursors differently for milk component production when dietary intervention alters AA and fatty acid supply. They also suggest that mammary cells respond to increased AA supply through mechanisms of ER homeostasis, dependent on the presence of FT.     

Milk production and efficiency of utilization of nitrogen,metabolizable protein,and amino acids are affected by protein and energy supplies in dairy cows fed alfalfa-based diets

Alfalfa has a lower fiber digestibility and a greater concentration of degradable protein than grasses. Dairy cows could benefit from an increased digestibility of alfalfa fibers, or from a better match between nitrogen and energy supplies in the rumen. Alfalfa cultivars with improved fiber digestibility represent an opportunity to increase milk production, but no independent studies have tested these cultivars under the agroclimatic conditions of Canada. Moreover, decreasing metabolizable protein (MP) supply could increase N use efficiency while decreasing environmental impact, but it is often associated with a decrease in milk protein yield, possibly caused by a reduced supply of essential AA. This study evaluated the performance of dairy cows fed diets based on a regular or a reduced-lignin alfalfa cultivar and measured the effect of energy levels at low MP supply when digestible His (dHis), Lys (dLys), and Met (dMet) requirements were met. Eight Holstein cows were used in a double 4 × 4 Latin square design, each square representing an alfalfa cultivar. Within each square, 4 diets were tested: the control diet was formulated for an adequate supply of MP and energy (AMP_AE), whereas the 3 other diets were formulated to be deficient in MP (DMP; formulated to meet 90% of the MP requirement) with deficient (94% of requirement: DMP_DE), adequate (99% of requirement: DMP_AE), or excess energy supply (104% of requirement; DMP_EE). Alfalfa cultivars had no significant effect on all measured parameters. As compared with cows receiving AMP_AE, the dry matter intake of cows fed DMP_AE and DMP_EE was not significantly different but decreased for cows fed DMP_DE. The AMP_AE diet provided 103% of MP and 108% of NE_L requirements whereas DMP_DE, DMP_AE, and DMP_EE diets provided 84, 87, and 87% of MP and 94, 101, and 107% of NE_L requirements, respectively. In contrast to design, feeding DMP_EE resulted in a similar energy supply compared with AMP_AE, although MP supply has been effectively reduced. This resulted in a maintained milk and milk component yields and improved the efficiency of utilization of N, MP, and essential AA. The DMP diets decreased total N excretion, whereas DMP_AE and DMP_EE diets also decreased milk urea-N concentration. Reducing MP supply without negative effects on dairy cow performance is possible when energy, dHis, dLys, and dMet requirements are met. This could reduce N excretion and decrease the environmental impact of milk production.     

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.     

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.     

Dietary protein oscillation: Effects on feed intake,lactation performance,and milk nitrogen efficiency in lactating dairy cows

Limited research with growing ruminants indicates that oscillating (OS) dietary crude protein (CP) concentration may improve nitrogen use efficiency (NUE). Our aim was to determine if a total mixed ration (TMR) based on OS CP (48-h phases of 13.4% and 16.5% CP, respectively) would increase NUE of lactating dairy cows compared with a static CP TMR (ST; 14.9% CP). The experiment was a randomized complete block design with 50 cows [150 ± 61 (mean ± SD) d in milk]. Cows were blocked by parity, days in milk, and milk protein yield. On average, diets were equal in composition over the total experiment. Cows were milked twice daily, and 8 milk samples were collected in each 4-d period. Each 48 h of low-CP (LP) and high-CP (HP) TMR offered to OS cows corresponded to milk collected at milkings 1 to 4 and 5 to 8, respectively. Dry matter intake (mean = 25.5 kg/d for both treatment groups); yields of milk (mean = 31.5 kg/d for both treatment groups), protein, fat, lactose, and fat- and protein-corrected milk (mean = 33.6 kg/d for both treatment groups); and milk concentration of protein, fat, and lactose did not differ between treatments. However, milk urea concentration was higher for OS compared with ST (12.2 vs. 11.3 mg/dL). Body weight, body condition score, NUE, and feed efficiency were unaffected by OS. Apparent total-tract digestibility of dry matter (695 vs. 677 g/kg), organic matter (714 vs. 697 g/kg), CP (624 vs. 594 g/kg), neutral detergent fiber (530 vs. 499 g/kg), and starch (976 vs. 973 g/kg) were higher for OS than for ST cows. Cows in OS responded transiently, and regression analysis of differences within block over time revealed changes in yield of milk (−531 g/d), milk protein (−25.6 g/d), and milk lactose (−16.7 g/d) in LP. Opposite effects were observed for yield of milk (+612 g/d), milk protein (+28.8 g/d), and milk lactose (+28.0 g/d) during HP. Changes in concentrations of milk protein (−0.050%/d), lactose (+0.030%/d), and urea (−3.0 mg/dL per day) during LP, and in milk lactose (−0.024%/d) and urea (+4.3 mg/dL per day) during HP, were observed. Milk yield, lactose yield, and protein yield were lower for OS than ST cows at the last milking of LP and at the first milking of HP. Milk urea concentration did not show such a lag and was lower in the last 2 milkings of LP, and higher in the last 3 milkings of HP, in OS compared with ST cows. Overall, performance and NUE were unaffected by OS treatment, but apparent total-tract digestibility and milk urea concentration increased, and transient effects on milk yield and composition occurred in OS cows.     

Effect of supplementing rumen-protected methionine on production and nitrogen excretion in lactating dairy cows

Two 4 × 4 Latin square trials (4-wk periods; 16 wk total) were conducted to see whether supplementing rumen-protected Met (RPM; fed as Mepron) would allow feeding less crude protein (CP), thereby reducing urinary N excretion, but without losing production. In trial 1, 24 Holsteins were fed 4 diets as total mixed rations containing [dry matter (DM) basis]: 18.6% CP and 0 g of RPM/d; 17.3% CP and 5 g of RPM/d; 16.1% CP and 10 g of RPM/d; or 14.8% CP and 15 g of RPM/d. Dietary CP was reduced by replacing soybean meal with high-moisture shelled corn. All diets contained 21% alfalfa silage, 28% corn silage, 4.5% roasted soybeans, 5.8% soyhulls, 0.6% sodium bicarbonate, 0.5% vitamins and minerals, and 27% neutral detergent fiber. There was no effect of diet on intake, weight gain, or yields of protein, lactose, and solids-not-fat. However, production was greater at 17.3% CP plus RPM and 16.1% CP plus RPM than on the other 2 diets. Apparent N efficiency (milk N:N intake) was greatest on the lowest CP diet containing the most RPM. Linear reductions in milk urea N and urinary N excretion were observed with lower dietary CP. In trial 2, 32 Holsteins were fed 4 diets as total mixed rations, formulated from ingredients used in trial 1 and containing 16.1 or 17.3% CP with 0 or 10 g of RPM/d. On average, cows were calculated to be in negative N balance on all diets because of lower than expected DM intake. There was no effect of RPM supplementation on any production trait. However, higher CP gave small increases in yields of milk, protein, and solids-not-fat and tended to increase DM intake and lactose yield. Apparent N efficiency was greater, and milk urea nitrogen was lower, on 16.1% CP. In trial 1, feeding lower CP diets supplemented with RPM resulted in improved N efficiency and reduced urinary N excretion. However, in trial 2, reducing dietary CP from 17.3 to 16.1% reduced milk secretion, an effect that was not reversed by RPM supplementation at low DM intakes when cows were apparently mobilizing body protein.     

Effects of reduced dietary protein and supplemental rumen-protected essential amino acids on the nitrogen efficiency of dairy cows

When fed to meet the metabolizable protein requirements of the National Research Council, dairy cows consume an excess of N, resulting in approximately 75% of dietary N being lost to the environment as urine and feces. Reductions in environmental N release could be attained through an improvement in N efficiency. The objective of this study was to determine if the predicted reduction in milk yield associated with feeding a low-protein diet to lactating dairy cows could be avoided by dietary supplementation with 1 or more ruminally protected (RP) AA. Fourteen multiparous and 10 primiparous Holstein cows, and 24 multiparous Holstein × Jersey crossbred cows were used in a Youden square design consisting of 8 treatments and 3 periods. The 8 dietary treatments were (1) a standard diet containing 17% crude protein [CP; positive control (PC)], (2) a 15% CP diet [negative control (NC)], (3) NC plus RP Met (+M), (4) NC plus RP Lys (+K), (5) NC plus RP Leu (+L), (6) NC plus RP Met and Lys (+MK), (7) NC plus RP Met and Leu (+ML), and (8) NC plus RP Met, Lys, and Leu (+MKL). Dry matter intake was not affected by treatment. Crude protein intake was lower for NC and RP AA treatments compared with the PC treatment. No detrimental effect was detected of the low-CP diet alone or in combination with AA supplementation on milk and fat yield. However, milk protein yield decreased for NC and +MKL diets, and lactose yield decreased for the +MKL compared with the PC diet. Milk urea N concentrations were lower for all diets, suggesting that greater N efficiency was achieved by feeding the low-protein diet. Minimal effects of treatments on arterial plasma essential AA concentrations were detected, with only Ile and Val being significantly lower in the NC than in the PC diet. Phosphorylation ratios of signaling proteins known to regulate mRNA translation were not affected by treatments. This study highlights the limitations of requirement models aggregated at the protein level and the use of fixed postabsorptive efficiency to calculate milk protein requirements. Milk protein synthesis regulation by signaling pathways in vivo is still poorly understood.     

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.     

Feeding hydrogenated palm fatty acids and rumen-protected protein to lactating Holstein-Friesian dairy cows modifies milk fat triacylglycerol composition and structure,and solid fat content

The aim of this study was to analyze the effect of fat and protein supplementation to dairy cattle rations on milk fat triacylglycerol (TAG) composition, fatty acid (FA) positional distribution in the TAG structure, and milk solid fat content (SFC). Fifty-six lactating Holstein-Friesian cows were blocked into 14 groups of 4 cows and randomly assigned 1 of 4 dietary treatments fed for 28 d: (1) low protein, low fat, (2) high protein, low fat, (3) low protein, high fat, and (4) high protein, high fat. The high protein and high fat diets were obtained by isoenergetically supplementing the basal ration (low protein, low fat) with rumen-protected soybean meal and rumen-protected rapeseed meal, and hydrogenated palm FA (mainly C16:0 and C18:0), respectively. Fat supplementation modified milk TAG composition more extensively compared with protein supplementation. Fat supplementation resulted in decreased concentrations of the low molecular weight TAG carbon number (CN) 26 to CN34 and medium molecular weight TAG CN40, CN44, and CN46, and increased concentrations of CN38 and the high molecular weight TAG CN50 and CN52. Increased contents of C16:0, C18:0, and C18:1cis-9 in TAG in response to fat supplementation were related to increases in the relative concentrations of C16:0 and C18:0 at the sn-2 position and C18:0 and C18:1cis-9 at the sn-1(3) positions of the TAG structure. Increased concentrations of high molecular weight TAG species CN50 and CN52 in response to fat supplementation was associated with increased milk SFC at 20, 25, and 30°C. Our study shows that important alterations in milk TAG composition and structure occur when feeding hydrogenated palm FA to lactating dairy cattle, and that these alterations result in an increased SFC of milk fat. These changes in milk SFC and TAG composition and structure may improve absorption of both fat and minerals in milk-based products for infants and may affect processing of milk fat.     

Effect of dietary crude protein concentration on milk production and nitrogen utilization in lactating dairy cows

Forty lactating Holstein cows, including 10 with ruminal cannulas, were blocked by days in milk into 8 groups and then randomly assigned to 1 of 8 incomplete 5 × 5 Latin squares to assess the effects of 5 levels of dietary crude protein (CP) on milk production and N use. Diets contained 25% alfalfa silage, 25% corn silage, and 50% concentrate, on a dry matter (DM) basis. Rolled high-moisture shelled corn was replaced with solvent-extracted soybean meal to increase CP from 13.5 to 15.0, 16.5, 17.9, and 19.4% of DM. Each of the 4 experimental periods lasted 28 d, with 14 d for adaptation and 14 d for data collection. Spot sampling of ruminal digesta, blood, urine, and feces was conducted on d 21 of each period. Intake of DM was not affected by diet but milk fat content as well as ruminal acetate, NH₃, and branched-chain volatile fatty acids, urinary allantoin, and blood and milk urea all increased linearly with increasing CP. Milk and protein yield showed trends for quadratic responses to dietary CP and were, respectively, 38.3 and 1.18 kg/d at 16.5% CP. As a proportion of N intake, urinary N excretion increased from 23.8 to 36.2%, whereas N secreted in milk decreased from 36.5 to 25.4%, as dietary protein increased from 13.5 to 19.4%. Under the conditions of this study, yield of milk and protein were not increased by feeding more than 16.5% CP. The linear increase in urinary N excretion resulted from a sharp decline in N efficiency as dietary CP content increased.     

Effects of dietary protein and starch on intake, milk production, and milk fatty acid profiles of dairy cows fed corn silage-based diets

Feed intake, milk production, and milk fatty acid profiles of dairy cows fed corn silage-based diets with different protein and starch concentrations were measured in a 3-period experiment in a changeover design using 12 Holstein cows. Each experimental period lasted for 3 wk. The diet fed as a total mixed ration consisted of 45% corn silage, 5% coarsely chopped wheat straw, and 50% concentrate, on a dry matter (DM) basis. The 4 treatments, formulated to be isoenergetic and to differ in concentrations of dietary crude protein (CP) and starch (DM basis), were as follows: low CP and low starch (LPLS; 14% CP and 15% starch), low CP and high starch (LPHS; 14% CP and 25% starch), high CP and low starch (HPLS; 16% CP and 15% starch), and high CP and high starch (HPHS; 16% CP and 25% starch). The LPLS treatment led to lower DM intake, milk yield, milk protein concentration, and milk lactose yield, probably due to a shortage of both rumen-degradable protein supply to rumen microbes and glucogenic nutrients to the animal. There were no differences between protein-rich diets and LPHS, suggesting that this diet satisfied the rumen-degradable protein requirements of rumen microbes and did not limit feed intake, and the increased supply of glucogenic nutrients spared AA so that the nutrient requirements of mid lactation dairy cows were met. Further increases in CP concentration increased plasma urea concentration and resulted in decreased efficiency of conversion of dietary N into milk N. Milk fatty acid profiles were affected by starch and protein supply, with starch having the largest effect. Additionally, increasing dietary starch concentration decreased the apparent transfer of dietary polyunsaturated fatty acids to milk, suggesting an increased channeling of fatty acids to adipose tissue. The results further suggest that C_15:0 and C_17:0 are synthesized de novo in animal tissues.     

Effect of level of metabolizable protein on milk production and nitrogen utilization in lactating dairy cows

The objective of this study was to investigate the effects of the level of metabolizable protein (MP) on milk production and nitrogen utilization in Chinese Holstein dairy cows. Forty multiparous dairy cows (body weight = 590 kg; days in milk = 135; average milk yield = 30.2 kg/d) were assigned to treatments randomly within groups based on days in milk and milk production. Animals were offered diets with different levels of MP: 8.3% (diet A), 8.9% (diet B), 9.7% (diet C), and 10.4% (diet D) of dry matter. The MP level in diet A was designed to meet the current Chinese National Station of Animal Production and Health guidelines, whereas that in diet D was based on the National Research Council (2001) model. The experiment lasted for 7 wk. Milk yield and milk composition (fat, protein, and lactose) were recorded, and urea nitrogen concentrations in serum, urine, and milk were measured during the experiment. Milk yield and milk protein percentage increased as the MP increased up to 9.7% of dry matter, and then leveled off. Concentrations of nitrogen in urine, serum, and milk increased linearly as the amount of MP was increased, indicating decreased efficiency of nitrogen utilization. Milk lactose percentage and total solids percentage showed no significant differences among the 4 diets. We concluded that the optimal dietary MP level was at 9.6% of dry matter for Chinese Holstein dairy cows producing 30 kg of milk per day.     

Effects of decreasing metabolizable protein and rumen-undegradable protein on milk production and composition and blood metabolites of Holstein dairy cows in early lactation

This study was conducted to evaluate the effects of decreasing dietary protein and rumen-undegradable protein (RUP) on production performance, nitrogen retention, and nutrient digestibility in high-producing Holstein cows in early lactation. Twelve multiparous Holstein lactating cows (2 lactations; 50 ± 7 d in milk; 47 kg/d of milk production) were used in a Latin square design with 4 treatments and 3 replicates (cows). Treatments 1 to 4 consisted of diets containing 18, 17.2, 16.4, and 15.6% crude protein (CP), respectively, with the 18% CP diet considered the control group. Rumen-degradable protein levels were constant across the treatments (approximately 10.9% on a dry matter basis), whereas RUP was gradually decreased. All diets were calculated to supply a postruminal Lys:Met ratio of about 3:1. Dietary CP had no significant effects on milk production or milk composition. In fact, 16.4% dietary CP compared with 18% dietary CP led to higher milk production; however, this effect was not significant. Feed intake was higher for 16.4% CP than for 18% CP (25.7 vs. 24.3 kg/d). Control cows had greater CP and RUP intakes, which resulted in higher concentrations of plasma urea nitrogen and milk urea nitrogen; cows receiving 16.4 and 15.6% CP, respectively, exhibited lower concentrations of milk urea nitrogen (15.2 and 15.1 vs. 17.3 mg/dL). The control diet had a significant effect on predicted urinary N. Higher CP digestibility was recorded for 18% CP compared with the other diets. Decreasing CP and RUP to 15.6 and 4.6% of dietary dry matter, respectively, had no negative effects on milk production or composition when the amounts of Lys and Met and the Lys:Met ratio were balanced. Furthermore, decreasing CP and RUP to 16.4 and 5.4%, respectively, increased dry matter intake.     

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.     

Ruminal biohydrogenation and abomasal flow of fatty acids in lactating cows fed diets supplemented with soybean oil,whole soybeans,or calcium salts of fatty acids

Ruminants have a unique metabolism and digestion of unsaturated fatty acids (UFA). Unlike monogastric animals, the fatty acid (FA) profile ingested by ruminants is not the same as that reaching the small intestine. The objective of this study was to evaluate whole raw soybeans (WS) in diets as a replacer for calcium salts of fatty acids (CSFA) in terms of UFA profile in the abomasal digesta of early- to mid-lactation cows. Eight Holstein cows (80 ± 20 d in milk, 22.9 ± 0.69 kg/d of milk yield, and 580 ± 20 kg of body weight; mean ± standard deviation) with ruminal and abomasal cannulas were used in a 4 × 4 Latin square experiment with 22-d periods. The experiment evaluated different fat sources rich in linoleic acid on ruminal kinetics, ruminal fermentation, FA abomasal flow, and milk FA profile of cows assigned to treatment sequences containing a control (CON), with no fat source; soybean oil, added at 2.68% of diet dry matter (DM); WS, addition of WS at 14.3% of diet DM; and CSFA, addition of CSFA at 2.68% of diet DM. Dietary fat supplementation had no effect on nutrient intake and digestibility, with the exception of ether extract. Cows fed fat sources tended to have lower milk fat concentration than those fed CON. In general, diets containing fat sources tended to decrease ruminal neutral detergent fiber digestibility in relation to CON. Cows fed WS had lower ruminal digestibility of DM and higher abomasal flow of DM in comparison to cows fed CSFA. As expected, diets containing fat supplements increased FA abomasal flow of C18:0 and total FA. Cows fed WS tended to present a higher concentration of UFA in milk when compared with those fed CSFA. This study suggests that under some circumstances, abomasal flow of UFA in early lactation cows can be increased by supplementing their diet with fat supplements rich in linoleic acid, regardless of rumen protection, with small effects on ruminal DM digestibility.     

Interactions of energy and predicted metabolizable protein in determining nitrogen efficiency in the lactating dairy cow

Lactating cows are relatively inefficient in converting dietary N to milk N compared with the efficiency of N use for growth in simple-stomached animals. The majority of productive N losses occur in the postabsorptive system. The aim of the study was to test whether predicted metabolizable protein (MP) and dietary energy exerted independent effects on milk protein synthesis and postabsorptive N efficiency. If true, postabsorptive N efficiency would be expected to be greater when animals are fed high-energy diets. Forty mid-lactation cows (32 multiparous Holstein and 8 primiparous Holstein × Jersey crossbreds) were used in a complete randomized design with a 2 × 2 factorial arrangement of diets. Cows were assigned to 1 of 4 dietary treatments: high-energy, high-protein (HE/HP); high-energy, low-protein (HE/LP); low-energy, high-protein (LE/HP); and low-energy, low-protein (LE/LP). Energy concentrations were 1.55 (HE/HP and HE/LP) or 1.44 (LE/HP and LE/LP) Mcal of net energy for lactation (NE_L)/kg of dry matter (DM). Changes in predicted MP were achieved by feeding diets with 6.6 (HE/HP and LE/HP) or 4.6% (HE/LP and LE/LP) ruminally undegradable protein (DM basis). Ruminally degradable protein was held constant at 10.1% of DM. All cows were fed the HE/HP diet from d 1 to 21 followed by the respective treatments from d 22 to 43 (n = 10). Milk protein yield was reduced as dietary energy was reduced. Milk yield followed a similar pattern as milk protein yield. There was a trend for decreased milk yield as crude protein was reduced. There were no interactions between dietary energy and protein for either milk or protein yield. Plasma amino acid concentrations were not affected by treatment. Milk urea N was affected by energy and protein with a significant interaction (HE/HP = 17.2, HE/LP = 12.2, LE/HP = 21.0, LE/LP = 12.2 mg/dL). Nitrogen efficiency calculated from predicted MP supply was affected by energy and protein supplies with no apparent interaction and ranged from a low of 31% (LE/HP) to a high of 43% (HE/LP). The National Research Council model would predict N efficiency more accurately if a representation of the effects of energy on N efficiency were included in the postabsorptive system.     

Effects of lauric and myristic acids on ruminal fermentation, production, and milk fatty acid composition in lactating dairy cows

The objectives of this experiment were to investigate the effects of lauric (LA) and myristic (MA) acids on ruminal fermentation, production, and milk fatty acid (FA) profile in lactating dairy cows and to identify the FA responsible for the methanogen-suppressing effect of coconut oil. The experiment was conducted as a replicated 3 × 3 Latin square. Six ruminally cannulated cows (95 ± 26.4 DIM) were subjected to the following treatments: 240 g/cow per day each of stearic acid (SA, control), LA, or MA. Experimental periods were 28 d and cows were refaunated between periods. Lauric acid reduced protozoal counts in the rumen by 96%, as well as acetate, total VFA, and microbial N outflow from the rumen, compared with SA and MA. Ruminal methane production was not affected by treatment. Dry matter intake was reduced 35% by LA compared with SA and MA, which resulted in decreased milk yield. Milk fat content also was depressed by LA compared with SA and MA. Treatment had no effect on milk protein content. All treatments increased milk concentration of the respective treatment FA. Concentration of C12:0 was more than doubled by LA, and C14:0 was increased (45%) by MA compared with SA. Concentration of milk FA < C16 was 20% lower for LA than MA. Concentrations of trans 18:1 FA (except trans 12) and CLA isomers were increased by LA compared with SA and MA. Overall, the concentrations of saturated FA in milk fat were reduced, and that of > C16 FA and MUFA were increased, by LA compared with the other treatments. In this study, LA had profound effects on ruminal fermentation, mediated through inhibited microbial populations, and decreased DMI, milk yield, and milk fat content. Despite the significant decrease in protozoal counts, however, LA had no effect on ruminal methane production. Thus, the antimethanogenic effect of coconut oil, observed in related studies, is likely due to total FA application level, the additive effect of LA and MA, or a combination of both. Both LA and MA modified milk FA profile significantly.     

Effect of a high-palmitic acid fat supplement on milk production and apparent total-tract digestibility in high- and low-milk yield dairy cows

The effect of a high-palmitic acid fat supplement was tested in 12 high-producing (mean = 42.1 kg/d) and 12 low-producing (mean = 28.9 kg/d) cows arranged in a replicated 3 × 3 Latin square design. Experimental periods were 21 d, with 18 d of diet adaptation and 3 d of sample collection. Treatments were (1) control (no supplemental fat), (2) high-palmitic acid (PA) supplement (84% C16:0), and (3) Ca salts of palm fatty acid (FA) supplement (Ca-FA). The PA supplement had no effect on milk production, but decreased dry matter intake by 7 and 9% relative to the control in high- and low-producing cows, respectively, and increased feed efficiency by 8.5% in high-producing cows compared with the control. Milk fat concentration and yield were not affected by PA relative to the control in high- or low-producing cows, although PA increased the yield of milk 16-C FA by more than 85 g/d relative to the control. The Ca-FA decreased milk fat concentration compared with PA in high-, but not in low-producing cows. In agreement, Ca-FA dramatically increased milk fat concentration of trans-10 C18:1 and trans-10, cis-12 conjugated linoleic acid (>300%) compared with PA in high-producing cows, but not in low-producing cows. No effect of treatment on milk protein concentration or yield was detected. The PA supplement also increased 16-C FA apparent digestibility by over 10% and increased total FA digestibility compared with the control in high- and low-producing cows. During short-term feeding, palmitic acid supplementation did not increase milk or milk fat yield; however, it was efficiently absorbed, increased feed efficiency, and increased milk 16-C FA yield, while minimizing alterations in ruminal biohydrogenation commonly observed for other unsaturated fat supplements. Longer-term experiments will be necessary to determine the effects on energy balance and changes in body reserves.     

Postruminal infusion of calcium gluconate increases milk fat production and alters fecal volatile fatty acid profile in lactating dairy cows

Gluconic acid is a carboxylic acid naturally occurring in plants and honey. In nonruminant animals, gluconic acid has been shown to increase gastrointestinal butyrate concentrations and improve growth performance, but a ruminant application remains undescribed. This experiment examined the effects of postruminal calcium gluconate (CaG) on milk production, fecal volatile fatty acid concentrations, and plasma metabolite concentrations in lactating dairy cows. Six rumen cannulated multiparous Holstein cows (60 ± 6 d in milk) were randomly assigned to 6 treatment sequences within a 6 × 6 Latin square design in which each experimental period consisted of 5 d of continuous postruminal infusion followed by a 2 d wash-out period. Test treatments included a negative control (CON; 0.90% NaCl wt/vol), positive control (Na-butyrate, 135 g/d), and 4 doses of CaG (44, 93, 140, and 187 g/d). Cows received a total mixed ration (31% corn silage, 28% alfalfa silage, 5% hay, 36% concentrate) with dry matter intake fixed (25.3 ± 1.7 kg/d) throughout the experiment. On d 5 of each infusion period, samples of milk, feces, and blood were collected from each animal. Calcium gluconate treatments increased milk fat concentration, and a tendency was observed for increased milk fat yield and energy-corrected milk yield above levels achieved by CON, with maximal treatment responses of 4.43% (CON 3.81%), 2.089 kg/d (CON 1.760 kg/d), and 51.8 kg/d (CON 47.1 kg/d), respectively. Concentrations of iso-butyric acid in feces were greater in cows infused with CaG (13.3 µmol/g) treatments compared with CON (9.7 µmol/g). Arterial concentrations of glucose and nonesterified fatty acids were lower (glucose: CaG 2.98 mmol/L, CON 3.29 mmol/L and nonesterified fatty acids: CaG 0.130 mmol/L vs. 0.148 mmol/L) and β-hydroxybutyrate higher (CaG 1.703 vs. CON 0.812) in cows infused with CaG than CON. Together, these results suggest that postruminal infusion of CaG may alter metabolic mechanisms to support a milk fat production response.