Milk fat depression, the glucogenic theory, and trans-C18:1 fatty acids

Effects of dietary palmitic acid and oleic acid ratio on milk production, nutrient digestibility, blood metabolites, and milk fatty acid profile of lactating dairy cows

Adequate energy supply is a crucial factor for maintaining the production performance in cows during the early lactation period. Adding fatty acids (FA) to diets can improve energy supply, and the effect could be related to the chain length and degree of saturation of those FA. This study was conducted to evaluate the effect of different ratios of palmitic acid (C16:0) to oleic acid (cis-9 C18:1) on the production performance, nutrient digestibility, blood metabolites, and milk FA profile in early lactation dairy cows. Seventy-two multiparous Holstein cows (63.5 ± 2.61 days in milk) blocked by parity (2.39 ± 0.20), body weight (668.3 ± 20.1 kg), body condition score (3.29 ± 0.06), and milk yield (47.9 ± 1.63 kg) were used in a completely randomized design. Cows were divided into 3 groups with 24 cows in each group. Cows in the 3 treatment groups were provided iso-energy and iso-nitrogen diets, but the C16:0 to cis-9 C18:1 ratios were different: (1) 90.9% C16:0 + 9.1% cis-9 C18:1 (90.9:9.1); (2) 79.5% C16:0 + 20.5% cis-9 C18:1 (79.5:20.5); and (3) 72.7% C16:0 + 27.3% cis-9 C18:1 (72.7:27.3). Fatty acids were added at 1.3% on a dry matter basis. Although the dry matter intake fat-corrected milk yield and energy-corrected milk yield were not affected, the milk yield, milk protein yield, and feed efficiency increased linearly with increasing cis-9 C18:1 ratio. The milk protein percentage and milk fat yield did not differ among treatments, whereas the milk fat percentage tended to decrease linearly with the increasing cis-9 C18:1 ratio. The lactose yield increased linearly and lactose percentage tended to increase linearly with increasing cis-9 C18:1 ratio, but the percentage of milk total solids and somatic cell count decreased linearly. Although body condition scores were not affected by treatments, body weight loss decreased linearly with increasing cis-9 C18:1 ratio. The effect of treatment on nutrient digestibility was limited, except for a linear increase in ether extract and neutral detergent fiber digestibility with increasing cis-9 C18:1 ratio. There was a linear increase in the concentration of plasma glucose, but the triglyceride and nonesterified FA concentrations decreased linearly with increasing cis-9 C18:1 ratio. As the cis-9 C18:1 ratio increased, the concentration of de novo FA decreased quadratically, but the mixed and preformed fatty acids increased linearly. In conclusion, increasing cis-9 C18:1 ratio could increase production performance and decrease body weight loss by increasing nutrient digestibility, and the ratio that had the most powerful beneficial effect on early lactation cows was 72.7:27.3 (C16:0 to cis-9 C18:1).

Concentrate allowance and corn grain processing influence milk production, body reserves, milk fatty acid profile, and blood metabolites of dairy cows in the early postpartum period

The study goal was to determine the effects of a fast (FAS) or slow (SLW) incremental rate of concentrate feeding and corn processing method during the early postpartum period on lactational performance, body reserves, blood metabolites, and milk fatty acid (FA) profile. Forty multiparous Holstein cows were used in a randomized block design with a 2 × 2 factorial arrangement of treatments. Treatment diets were either a FAS [1.0 kg of dry matter (DM)/d] or SLW (0.25 kg of DM/d) incremental rate of concentrate feeding (up to 12 kg of DM/d) with either dry ground corn (DGC) or steam-flaked corn (SFC) as the primary starch source in concentrate. Treatments were fed from 5 to 64 d postpartum. The basal diet consisted of forage, soybean meal, and 5 kg/d concentrate in the postpartum period. Throughout the experiment, dry matter intake (DMI) and milk yield were measured daily, and milk components, body condition score, and body weight were recorded at 16-d intervals, whereas blood metabolites and milk FA profile were measured at 16 and 32 d in milk. The incremental rate of concentrate feeding interacted with corn processing method to affect plasma concentration of glucose with greater glucose in SFC treatment compared with DGC in cows fed with the FAS strategy. Cows fed FAS and SFC had a greater total DMI than those fed SLW and DGC counterparts (22.8 versus 22.1 kg and 22.7 versus 22.1 kg, respectively), and also SFC increased yield of actual milk compared with the DGC counterpart (42.7 versus 41.6 kg). The milk fat and energy-corrected milk yields were not different among treatments whereas milk protein yield was greater when SFC was fed. Greater incremental rate of concentrate feeding tended to increase milk lactose yield during the first 64 d of lactation. The loss of body condition score increased when cows were fed SLW for the entire period and plasma nonesterified fatty acids and β-hydroxybutyrate concentrations increased with the SLW strategy. The proportions of total trans 18:1 and trans-11 18:1 FA in milk fat were higher in cows fed FAS. However, feeding SLW enhanced milk de novo and mixed FA proportions compared with FAS, whereas the proportions of milk FA were not affected by corn grain processing method. The incremental rate of concentrate feeding had significant effects on DMI, milk yield, and body reserve changes. Although feeding SFC instead of DGC had benefits on DMI and milk yield at 48 and 64 d postpartum, treatments did not interact to affect production responses when cows were fed with the SLW strategy.

Gene function adjustment for carbohydrate metabolism and enrichment of rumen microbiota with antibiotic resistance genes during subacute rumen acidosis induced by a high-grain diet in lactating dairy cows

The high-grain diets fed to ruminants generally alters the structure and function of rumen microbiota, resulting in variations of rumen fermentation patterns and the occurrence of subacute rumen acidosis (SARA). To clarify the microbial mechanism for carbohydrate metabolism during SARA, 8 ruminally cannulated Holstein cows in mid lactation were selected for a 3-wk experiment. The cows were randomly divided into 2 groups, fed either a conventional diet (CON; 40% concentrate; dry matter basis) or a high-grain diet (HG; 60% concentrate; dry matter basis). Compared with the CON diet, the HG diet reduced average daily pH (5.71 vs. 6.13), acetate concentration (72.56 vs. 78.44 mM), acetate ratio (54.81 vs. 65.24%), and the ratio of the concentrations of acetate to propionate (1.87 vs. 3.21) but increased the concentrations of total volatile fatty acids (133.03 vs. 120.22 mM), propionate (41.32 vs. 24.71 mM), and valerate (2.46 vs. 1.68 mM) and the propionate ratio (30.51 vs. 20.47%). Taxonomic analysis indicated that the HG cows had a higher relative abundance of Ruminococcus, Eubacterium, Selenomonas, Ruminobacter, Succinimonas, Methanomicrobium, and Methanocaldococcus accompanied by a lower relative abundance of unclassified Firmicutes, unclassified Bacteroidetes, Bacteroides, Fibrobacter, Alistipes, Candidatus Methanoplasma, Methanomassiliicoccus, and Methanolobus. Carbohydrate-active enzyme annotation suggested that there was enriched abundance of glycosyltransferases (GT) 2, glycoside hydrolase (GH) 13, GH24, carbohydrate-binding module (CBM) 26, GH73, GH25, CBM12, GH23, GT8, CBM50, and GT9 and reduced abundance of GH78, GH31, S-layer homology, GH109, carbohydrate esterase 1, GH3, carbohydrate esterase 10, and GH43 in the HG group. Functional profiling revealed that the HG feeding mainly downregulated the pentose phosphate pathway of carbohydrate catabolism, acetate metabolism, propionate metabolism (succinate pathway), and methane metabolism, whereas it upregulated the Embden-Meyerhof-Parnas and Entner-Doudoroff pathways of glycolysis and the citrate cycle. Additionally, the HG feeding promoted the abundance of various antibiotic resistance genes and antimicrobial resistance gene families. These results elucidated the structure and function adjustment of rumen microbiota for carbohydrate metabolism and summarized the enrichment of rumen antibiotic resistance genes under the HG feeding, which expands our understanding of the mechanism underlying the response of rumen microbiota to SARA in dairy cattle.

Effect of dietary fat supplements on levels of n-3 poly-unsaturated fatty acids,transacids and conjugated linoleic acid in bovine milk

The effects of three fat supplements on milk yield and composition were measured using 12 mid-lactation in-calf Hoistein-Friesian cows in a balanced incomplete change-over design over three periods each of 3 weeks. All cows received a basal diet consisting of 36 kg/day grass silage (dry matter (DM) 270 g/kg, metabolizable energy (ME) 11·6 MJ/kg DM) and 7 kg/day o f a concentrate mixture containing (g/kg) rolled barley (501), molassed sugar-beet pulp shreds (277), soya-bean meal (208) and a standard cow mineral supplement (14). Treatments were CON (control-no supplement); LIN and FISH (250 gl day of either linseed oil or marine oil, providing approximately 0·046 of ME intake) or TOA (95 glday of tuna orbital oil, providing 0·018 of total ME intake).

There were no significant effects on silage DM intake or milk yield (means 9·25 and 17·2 kg/day respectively). The FISH and TOA treatments depressed (F < 0·05) milk fat concentration (45·4, 44·6, 34·5 and 41·6 (s.e.d. 1·08) g/kg for CON, LIN, FISH and TOA respectively; note — the same treatment order is used for all results quoted). Compared with values for CON, yield of f at (glday) was significantly (F < 0·05) greater for LIN and significantly lower for FISH (739, 808, 572 and 732, s.e.d. 28·7). All three oil supplements reduced (F < 0·05) milk protein content (33·6, 32·5, 30·6 and 32·4 (s.e.d. 0·43) g/kg) but, apart from a small increase for LIN, protein yield (glday) was unaffected (545, 586, 510 and 574, s.e.d. 20·2).

The concentrations (g/100 g) of short-chain fatty acids (< C14) and C16 : 0 in milk f at were lower (F < 0·05) for LIN than for the other treatments. All supplements increased the concentrations ofC18:1 (F < 0·05), the value for LIN being greater (F < 0·05) than for the other treatments (21·0, 27·2, 25·3 and 23·7, s.e.d. 0·74). The FISH and TOA treatments increased (F < 0·05) the concentrations of long chain (< C2O) (n-3) poly-unsaturated fatty acids (PUFA), (0·19, 0·17, 0·49 and 0·27, s.e.d. 0·026) but less than proportionately 0·03 of dietary intake of these acids was transferred to milk, probably because they were found to be mostly in the phospholipid and cholesterol ester fractions of plasma. The FISH and TOA treatments increased (F < 0·05) the percentages of total trans fatty acids in milk fat (1·13, 2·19, 10·26 and 3·62, s.e.d. 0·728) whilst a significant (F < 0·05) increase in conjugated linoleic acid (CLA) was observed only for FISH (0·16, 0·28, 1·55, and 0·52, s.e.d. 0·154). Concentrations of CLA and total trans acids in milk were highly correlated (r = 0·91, no. =36, F < 0·001) whilst trans acids in milk were inversely correlated with milk fat content (r = -0·63, no. = 36, F < 0·001) supporting the theory that milk fat depression may be caused by increased supply of trans fatty acids to the mammary gland. The health implications of these changes in milk fat composition are discussed.

Effect of fish-oil supplementation on levels of (n-3) poly-unsaturated fatty acids in the lipoprotein fractions of bovine plasma

Eight mid-lactation Holstein-Friesian dairy cows were used in an experiment to investigate whether poor transfer to milk of (n-3) long chain (≥C20) poly-unsaturated fatty acids (n-3 LCPUFA), from diets containing fish oil, is related to their mode of transport in plasma lipoproteins. The cows were split into two groups of four, each of which was housed with 24 other cows which did not provide blood data in this experiment. All cows received a basal diet ad libitum consisting of (kg/t dry matter) silage (539), grain distillers’ grains (148), rolled barley (248) and soya (65). All cows also received a mid-day meal of 2·76 kg per cow per day of molassed sugar-beet shreds. The control group (C) received no oil supplement but those in the treatment group (F) received 300 g per cow per day of fish oil absorbed onto the sugar-beet shreds. Fish oil inclusion progressively depressed milk fat concentration of the four cows from each group over the 3 weeks of the experiment so that levels were approximately 20 g/kg lower for cows in treatment F than for those in C (P < 0·05). Mean concentrations over all cows of the long-chain (≥C20, n-3) poly-unsaturated fatty acids in milk fat (g/100 g) were 0·12 and 0·54 for treatments C and F respectively, whilst corresponding output in milk (g/day) increased from 116 to 3·91, an average efficiency of transfer of 4·6%. The fatty acid compositions of the lipoproteins were measured in plasma samples from the four cows from each group after 3 weeks on the experimental diets The proportions (g/100 g fatty acids) of C20: 5 (n-3) in cholesteryl (CE) and phospholipid (PL) of high-density lipoprotein (HDL) in the plasma were respectively increased from 0·97 to 4·39 (P < 0·05) and from 1·15 to 4·74 (P < 0·01) by the fish-oil supplementation. For C22: 6 (n-3), the proportions in CE and PL of HDL respectively increased (P < 0·001) from 0·02 to 0·23 and from 0·16 to 2·18 as a result of the supplementation. The mean proportions (g/100 g fatty acids) of C20: 5 (n-3) and C22: 6 (n-3) in the triglyceride fraction of very low-density lipoprotein were 1·05 and 2·3 respectively and were not significantly altered by fish-oil supplementation (P > 0·05). It is suggested that the low transfer efficiency of (n-3) LCPUFA to the milk is partly due to their transport in the plasma largely as components of HDL lipids which are unavailable to the mammary gland.

Effect of oil supplementation of a diet containing a high concentration of starch on levels of trans fatty acids and conjugated linoleic acids in bovine milk

Sixteen Holstein Friesian cows were offered ad libitum a forage mixture of three parts (dry-matter (DM) basis) maize silage (starch and neutral-detergent fibre (NDF) 324 and 395 g/kg DM) and one part grass silage (NDF 518 g/kg DM) in a 4 ✕ 4 Latin-square change-over design experiment using four periods each of 4 weeks. Cows were housed in a cubicle house, bedded on sand and given food through Calan gates. The four supplement treatments were control (no oil supplement, C); 1·5 kg/day processed crushed linseed (PL); 1·5 kg/day crushed linseed (L) and 0·6 kg/day marine algae (A) providing 0, 440, 423 and 109 g/day of oil respectively. Cows also received a pelleted concentrate in three equal meals (12·0, 10·5, 10·5 and 11·2 kg/day for C, PL, L and A respectively) containing (g/kg DM) 260, 203, 288 and 74 of crude protein, NDF, starch and water-soluble carbohydrate respectively. Oil supplementation depressed (P < 0·05) forage intake (11·2, 10·3, 10·1 and 10·1 kg DM per day) but milk yield was unaffected (P > 0·05) by treatment (mean 35·9 kg/day). Milk fat concentrations were low and further depressed (P < 0·05) by algal supplementation (33·5, 32·3, 32·3 and 25·6 g/kg). Algal supplementation caused a three-fold increase in the concentrations of (n-3) long chain (>C20) polyunsaturated fatty acids in milk fat (to 0·51 g/100 g fat) representing a transfer efficiency from diet to milk of ca. 5%. Oil supplementation increased levels of all trans monoenes in milk but the effect was much greater for treatment A (P < 0·05) and for trans-10 C18: 1 (1·52, 1·94, 1·72 and 6·12 g/100 g milk fat for C, PL, L and A respectively). Trans-10 C18: 1 was the predominant trans monoene in milk fat for all treatments (47·7, 45·2, 45·6 and 67·4% of total). Treatment A also caused the greatest increases (P < 0·05) in conjugated linoleic acid (CLA to 0·54, 0·69, 0·65 and 0·97 g/100 g milk fat). Although mainly cis-9, trans-11, a small proportion (4·8 to 5·5%) of the CLA was identified as the trans-10, cis-12 isomer for all treatments. This pattern of isomers of trans monoenes and CLA, which may have implications for the health properties of the milk, may be related to effects on rumen function caused by the high starch intakes (5·75, 5·09, 5·11 and 5·27 kg/day).

Lipopolysaccharide derived from the rumen down-regulates stearoyl-CoA desaturase 1 expression and alters fatty acid composition in the liver of dairy cows fed a high-concentrate diet

Background

Dairy cows are often fed a high-concentrate diet to meet lactating demands, yet long-term concentrate feeding induces subacute ruminal acidosis (SARA) and leads to a decrease in milk fat. Stearoyl-CoA desaturase1 (SCD1) participates in fatty acid biosynthesis in the liver of lactating ruminants. Here, we conducted this study to investigate the impact of lipopolysaccharide derived from the rumen on SCD1 expression and on fatty acid composition in the liver of dairy cows fed a high-concentrate diet. Eight multiparous mid-lactating Holstein cows (455 ± 28 kg) were randomly assigned into two groups in the experiment and were fed a low-concentrate diet (LC) or high-concentrate diet (HC) for 18 weeks.

Results

The results showed that the total volatile fatty acids and lactic acid accumulated in the rumen, leading to a decreased rumen pH and elevated lipopolysaccharides (LPSs) in the HC group. The long chain fatty acid profile in the rumen and hepatic vein was remarkably altered in the animals fed the HC diet. The triglyceride (TG), non-esterified fatty acid (NEFA) and total cholesterol (TCH) content in the plasma was significantly decreased, whereas plasma glucose and insulin levels were increased. The expression of SCD1 in the liver was significantly down-regulated in the HC group. In regards to transcriptional regulators, the expression of sterol regulatory element binding transcription factors (SREBF1c, SREBF2) and SREBP cleavage activating protein (SCAP) was down-regulated, while peroxisome proliferator-activated receptor α (PPARα) was up-regulated.

Conclusions

These data indicate that lipopolysaccharide derived from the rumen down-regulates stearoyl-CoA desaturase 1 expression and alters fatty acid composition in the liver of dairy cows fed a high-concentrate diet.

Interactions of monensin with dietary fat and carbohydrate components on ruminal fermentation and production responses by dairy cows

Variation in milk fat percentage resulting from monensin supplementation to lactating dairy cows could be due to altered ruminal fermentation with interactions of monensin with ruminal biohydrogenation of fat and ruminal carbohydrate availability. The objective of the study was to determine the effects of feeding monensin as Rumensin (R) in diets differing in starch availability (ground or steam-flaked corn), effective fiber (long or short alfalfa hay, LAH or SAH), and 4% fat (F) from distillers grains, roasted soybeans, and an animal-vegetable blend on ruminal fermentation characteristics and milk production in lactating dairy cows. Six ruminally cannulated lactating Holstein cows were used in a balanced 6×6 Latin square design with 21-d periods. The cows were fed 6 diets: (1) C=control diet with ground corn and LAH, (2) CR=C plus R, (3) CRFL=CR plus F, (4) CRFS=ground corn, R, F, and SAH, (5) SRFL=steam-flaked corn, R, F, and LAH, and (6) SRFS=steam-flaked corn, R, F, and SAH. Mean particle size of LAH was 5.00 mm and 1.36 mm for SAH. All diets were formulated to have 21% forage NDF and 40% NFC. The R tended to decrease DMI, decreased milk fat yield, and numerically lowered milk fat percentage (3.41 vs. 2.98%). Addition of F to R diets did not affect milk fat percentage. By feeding diets containing R and F, SAH tended to increase milk fat percentage for the ground-corn diet, but SAH tended to decrease milk fat percentage with steam-flaked corn (CRFL+SRFS vs. CRFS+SRFL). The steam-flaked corn increased total-tract NDF digestibility (CRFL + CRFS vs. SRFL+SRFS; 51.1 vs. 56%). Addition of F with R decreased total VFA concentration and increased rumen pH. Fat addition with R decreased rumen NH3N and MUN (12.8 vs. 13.9 mg/dL), and SFC decreased NH3N concentration compared with ground corn. Although R caused milk fat depression, addition of F did not further exacerbate milk fat depression. Fatty acid analysis did not implicate any particular biohydrogenation intermediate as the causative factor for the milk fat depression.

Selection of barley grain affects ruminal fermentation, starch digestibility, and productivity of lactating dairy cows

The objective of this study was to evaluate the effects of 2 lots of barley grain cultivars differing in expected ruminal starch degradation on dry matter (DM) intake, ruminal fermentation, ruminal and total tract digestibility, and milk production of dairy cows when provided at 2 concentrations in the diet. Four primiparous ruminally cannulated (123 +/- 69 d in milk; mean +/- SD) and 4 multiparous ruminally and duodenally cannulated (46 +/- 14 d in milk) cows were used in a 4 x 4 Latin Square design with a 2 x 2 factorial arrangement of treatments with 16-d periods. Primiparous and multiparous cows were assigned to different squares. Treatments were 2 dietary starch concentrations (30 vs. 23% of dietary DM) and 2 lots of barley grain cultivars (Xena vs. Dillon) differing in expected ruminal starch degradation. Xena had higher starch concentration (58.7 vs. 50.0%) and greater in vitro 6-h starch digestibility (78.0 vs. 73.5%) compared with Dillon. All experimental diets were formulated to supply 18.3% crude protein and 20.0% forage neutral detergent fiber. Dry matter intake and milk yield were not affected by treatment. Milk fat concentration (3.55 vs. 3.29%) was greater for cows fed Dillon compared with Xena, but was not affected by dietary starch concentration. Ruminal starch digestion was greater for cows fed high-starch diets compared with those fed low-starch diets (4.55 vs. 2.49 kg/d), and tended to be greater for cows fed Xena compared with those fed Dillon (3.85 vs. 3.19 kg/d). Ruminal acetate concentration was lower, and propionate concentration was greater, for cows fed Xena or high-starch diets compared with cows fed Dillon or low-starch diets, respectively. Furthermore, cows fed Xena or high-starch diets had longer duration that ruminal pH was below 5.8 (6.6 vs. 4.0 and 6.4 vs. 4.2 h/d) and greater total tract starch digestibility (94.3 vs. 93.0 and 94.3 vs. 93.0%) compared with cows fed Dillon or low-starch diets, respectively. These results demonstrate that selection of barley grain can affect milk fat production and rumen fermentation to an extent at least as great as changes in dietary starch concentration.

Effect of forage type and proportion of concentrate in the diet on milk fatty acid composition in cows given sunflower oil and fish oil

Based on the potential benefits ofcis-9,trans-11 conjugated linoleic acid (CLA) for human health there is a need to develop effective strategies for enhancing milk fat CLA concentrations. In this experiment, the effect of forage type and level of concentrate in the diet on milk fatty acid composition was examined in cows given a mixture of fish oil and sunflower oil. Four late lactation Holstein-British Friesian cows were used in a 4 × 4 Latin-square experiment with a 2 × 2 factorial arrangement of treatments and 21-day experimental periods. Treatments consisted of grass (G) or maize (M) silage supplemented with low (L) or high (H) levels of concentrates (65 : 35 and 35 : 65; forage : concentrate ratio, on a dry matter (DM) basis, respectively) offered as a total mixed ration at a restricted level of intake (20 kg DM per day). Lipid supplements (30 g/kg DM) containing fish oil and sunflower oil (2 : 3 w/w) were offered during the last 14 days of each experimental period. Treatments had no effect on total DM intake, milk yield, milk constituent output or milk fat content, but milk protein concentrations were lower (P< 0.05) for G than M diets (mean 43.0 and 47.3 g/kg, respectively). Compared with grass silage, milk fat contained higher (P< 0.05) amounts of C12:0, C14:0, trans C18:1and long chain ≥ C20 (n-3) polyunsaturated fatty acids (PUFA) and lower (P< 0.05) levels of C18:0and trans C18:2when maize silage was offered. Increases in the proportion of concentrate in the diet elevated (P< 0.05) C18:2(n-6) and long chain ≥ C20 (n-3) PUFA content, but reduced (P< 0.05) the amount of C18:3(n-3). Concentrations oftrans-11 C18:1in milk were independent of forage type, but tended (P< 0.10) to be lower for high concentrate diets (mean 7.2 and 4.0 g/100 g fatty acids, for L and H respectively). Concentrations oftrans-10 C18:1were higher (P< 0.05) in milk from maize compared with grass silage (mean 10.3 and 4.1 g/100 g fatty acids, respectively) and increased in response to high levels of concentrates in the diet (mean 4.1 and 10.3 g/100 g fatty acids, for L and H, respectively). Forage type had no effect (P> 0.05) on total milk conjugated linoleic acid (CLA) (2.7 and 2.8 g/100 g fatty acids, for M and G, respectively) orcis-9,trans-11 CLA content (2.2 and 2.4 g/100 g fatty acids). Feeding high concentrate diets tended (P< 0.10) to decrease total CLA (3.3 and 2.2 g/100 g fatty acids, for L and H, respectively) andcis-9,trans-11 CLA (2.9 and 1.7 g/100 g fatty acids) concentrations and increase milktrans-9,cis-11 CLA andtrans-10,cis-12 CLA content. In conclusion, the basal diet is an important determinant of milk fatty acid composition when a supplement of fish oil and sunflower oil is given.

Fatty acid synthase effects on bovine adipose fat and milk fat

A quantitative trait locus (QTL) was identified by linkage analysis on bovine Chromosome 19 that affects the fatty acid, myristic acid (C14:0), in subcutaneous adipose tissue of pasture-fed beef cattle (99% level: experiment-wise significance). The QTL was also shown to have significant effects on ten fatty acids in the milk fat of pasture-fed dairy cattle. A positional candidate gene for this QTL was identified as fatty acid synthase (FASN), which is a multifunctional enzyme with a central role in the metabolism of lipids. Five single nucleotide polymorphisms (SNPs) were identified in the bovine FASN gene, and animals were genotyped for FASN SNPs in three different cattle resource populations. Linkage and association mapping results using these SNPs were consistent with FASN being the gene underlying the QTL. SNP substitution effects for C14:0 percentage were found to have an effect in the opposite direction in adipose fat to that in milk fat. It is concluded that SNPs in the bovine FASN gene are associated with variation in the fatty acid composition of adipose fat and milk fat.

Rates and efficiencies of reactions of ruminal biohydrogenation of linoleic acid according to pH and polyunsaturated fatty acids concentrations

Data from a previous study about the effects of pH and of linolenic acid (C18:3n-3) and linoleic acid (C18:2n-6) concentrations on C18:2n-6 biohydrogenation in ruminal cultures were used to calculate the rates and efficiencies of the three reactions of C18:2n-6 biohydrogenation (isomerisation of C18:2n-6 to CLA; reduction of CLA to trans-octadecenoic acids; reduction of trans-octadecenoic acids to stearic acid). First, low pH was confirmed to inhibit isomerisation and was shown to inhibit the second reduction, leading to an accumulation of vaccenic acid. This later effect had only been observed in some in vivo studies using high concentrate diets, because in in vitro experiments, the very low pH frequently used depresses isomerisation which consequently generates very low amount of substrates for reductions whose variations become difficult to ascertain. Second, C18:2n-6 at high concentration was confirmed to saturate its own isomerisation and the increase of CLA production due to high initial C18:2n-6 was shown to inhibit the two subsequent reductions. Third, C18:3n-3 at high concentrations was confirmed to inhibit C18:2n-6 isomerisation. Moreover, the second reduction was shown to be saturated, probably by all trans-octadecenoic acids intermediates of C18:2n-6 and C18:3n-3 biohydrogenation, leading to an accumulation of trans-octadecenoic acids, especially vaccenic acid. This fatty acid is partly desaturated into CLA in the mammary gland, which explains the synergy between C18:2n-6 and C18:3n-3 for milk CLA noticed by others in vivo. This approach helped explain the actions of pH and of C18:2n-6 and C18:3n-3 concentrations on C18:2n-6 biohydrogenation and allows some explanations about differences noticed between studies.

Effect of Varying Dietary Ratios of Alfalfa Silage to Corn Silage on Production and Nitrogen Utilization in Lactating Dairy Cows

Twenty-eight (8 ruminally cannulated) lactating, multiparous Holstein cows were blocked by DIM and randomly assigned to 7 replicated 4 x 4 Latin squares (28-d periods) to investigate the effects of different dietary ratios of alfalfa silage (AS) to corn silage (CS) on production, N utilization, apparent digestibility, and ruminal metabolism. The 4 diets contained (dry matter basis): A) 51% AS, 43% rolled high-moisture shelled corn (HMSC), and 3% solvent soybean meal (SSBM); B) 37% AS, 13% CS, 39% HMSC, and 7% SSBM; C) 24% AS, 27% CS, 35% HMSC, and 12% SSBM; and D) 10% AS, 40% CS, 31% HMSC, and 16% SSBM. Dietary crude protein contents were 17.2, 16.9, 16.6, and 16.2% for diets A, B, C, and D. All 4 diets were high in energy, averaging 49% nonfiber carbohydrates and 24% neutral detergent fiber. Intake of dry matter, yield of milk, 3.5% fat-corrected milk and fat, milk fat content, and apparent digestibility of neutral detergent fiber and acid detergent fiber all decreased linearly when CS replaced AS. Effects on fiber digestion and milk fat may have been due to increasing fluctuation in ruminal pH and time the pH remained < 6.0 when CS replaced AS. Milk protein content increased linearly with increasing CS, but there were no differences in protein yield. There were linear increases in apparent N efficiency and decreases in N excreted in urine and feces when CS replaced AS. Production was depressed on the diet highest in CS. Quadratic analysis indicated that milk and protein yields were maximal at dietary AS:CS ratios of, respectively, 37:13 and 31:19. No diet minimized N excretion without negatively affecting production. Diet C, with an AS:CS ratio of 24:27, was the best compromise between improved N efficiency and sustained production. Because CS is complementary with AS, it is recommended that CS be fed in AS-based diets to maintain milk yield while improving N utilization.

Effect of safflower oil, flaxseed oil, monensin, and vitamin E on concentration of conjugated linoleic acid in bovine milk fat

Conjugated linoleic acid (CLA) refers to a mixture of conjugated octadecadienoic acids of predominantly ruminant origin. The main isomer in bovine milk fat is the cis-9, trans-11 CLA. Interest in CLA increased after the discovery of its health-promoting properties, including potent anticarcinogenic activity. Two experiments were conducted to evaluate dietary strategies aimed at increasing the concentration of CLA in bovine milk fat. Both experiments were organized as a randomized complete block design with a repeated measures treatment structure. In Experiment 1, 28 Holstein cows received either a control diet or one of 3 treatments for a period of 2 wk. The control diet consisted of 60% forage (barley silage, alfalfa silage, and alfalfa hay) and 40% concentrate on a dry matter (DM) basis, fed as a total mixed ration (TMR). The concentrate was partially replaced in the treatment groups with 24 ppm of monensin (MON), 6% of DM safflower oil (SAFF), or 6% of DM safflower oil plus 24 ppm of monensin (SAFF/M). Average cis-9, trans-11 CLA levels in milk fat after 2 wk of feeding were 0.45, 0.52, 3.36, and 5.15% of total fatty acids for control, MON, SAFF, and SAFF/M, respectively. In Experiment 2, 62 Holstein cows received either a control diet or one of 5 treatment diets for a period of 9 wk. The control diet consisted of 60% forage (barley silage, alfalfa silage, and alfalfa hay) and 40% concentrate on a DM basis, fed as a TMR. The concentrate was partially replaced in the treatment groups with 6% of DM safflower oil (SAFF), 6% of DM safflower oil plus 150 IU of vitamin E/kg of DM (SAFF/E), 6% of DM safflower oil plus 24 ppm of monensin (SAFF/M), 6% of DM safflower oil plus 24 ppm of monensin plus 150 IU of vitamin E/kg of DM (SAFF/ME), or 6% of DM flaxseed oil plus 150 IU of vitamin E/kg of DM (FLAX/E). Average cis-9, trans-11 CLA levels during the treatment period were 0.68, 4.12, 3.48, 4.55, 4.75, and 2.80% of total fatty acids for control, SAFF, SAFF/E, SAFF/M, SAFF/ME, and FLAX/E, respectively. The combination of safflower oil with monensin was particularly effective at increasing milk fat CLA. The addition of vitamin E to the diet partially prevented the depression in milk fat associated with oilseed feeding, but had no significant effect on the concentration of CLA in milk.

Relationship Among Trans and Conjugated Fatty Acids and Bovine Milk Fat Yield Due to Dietary Concentrate and Linseed Oil

Effects on fatty acid profiles and milk fat yield due to dietary concentrate and supplemental 18:3n-3 were evaluated in 4 lactating Holstein cows fed a low- (35:65 concentrate:forage; L) or high- (65:35; H) concentrate diet without (LC, HC) added oil or with linseed oil (LCO, HCO) at 3% of DM. A 4 x 4 Latin square with four 4-wk periods was used. Milk yield and dry matter intake averaged 26.7 and 20.2 kg/d, respectively, across treatments. Plasma acetate and beta-hydroxybutyrate decreased, whereas glucose, nonesterified fatty acids, and leptin increased with high-concentrate diets. Milk fat percentage was lower in cows fed high-concentrate diets (2.31 vs. 3.38), resulting in decreases in yield of 11 (HC) and 42% (HCO). Reduced yields of 8:0-16:0 and cis9-18:1 fatty acids accounted for 69 and 17%, respectively, of the decrease in milk fat yield with HC vs. LC (-90 g/d), and for 26 and 33%, respectively, of the decrease with HCO vs. LCO (-400 g/d). Total trans-18:1 yield increased by 25 (HCO) and 59 (LCO) g/d with oil addition. Trans10-18:1 yield was 5-fold greater with high-concentrate diets. Trans11-18:1 increased by 13 (HCO) and 19 (LCO) g/d with oil addition. Trans13+14-18:1 yield increased by 9 (HCO) and 18 (LCO) g/d with linseed oil. Yield of total conjugated linoleic acids (CLA) in milk averaged 6 g/d with LC or HC compared with 14 g/d with LCO or HCO. Cis9,trans11-CLA yield was not affected by concentrate level but increased by 147% in response to oil. Feeding oil increased yields of trans11,cis13-, trans11,trans13-, and trans,trans-CLA, primarily with LCO. Trans10,cis12-CLA yield (average of 0.08 g/d) was not affected by treatments. Yield of trans11,cis15-18:2 was 1 g/d in cows fed LC or HC and 10 g/d with LCO or HCO. Yields of cis9,trans11-18:2, cis9,trans12-18:2, and cis9,trans13-18:2 were positively correlated (r = 0.74 to 0.94) with yields of trans11-18:1, trans12-18:1, and trans13+14-18:1, respectively. Plasma concentrations of biohydrogenation intermediates with concentrate or linseed oil level followed similar changes as those in milk fat. Milk fat depression was observed when HC induced an increase in trans10-18:1 yield. A correlation of 0.84 across 31 comparisons from 13 published studies, including the present one, was found among the increase in percentage of trans10-18:1 in milk fat and decreased milk fat yield. We observed, however, more drastic milk fat depression when HCO increased yields of total trans-18:1, trans11,cis15-18:2, trans isomers of 18:3, and reduced yields of 18:0 plus cis9-18:1.

Milk Fat Responses to a Change in Diet Fermentability Vary by Production Level in Dairy Cattle

The effects of dietary starch fermentability on plasma metabolites and hormones, milk production, and milk fatty acid profile were evaluated in a crossover study. Thirty-two multiparous Holstein cows (121 +/- 48 d in milk, 41 +/- 9 kg/d 3.5% fat-corrected milk [FCM]; mean +/- SD) were randomly assigned to treatment sequence and were fed a diet intermediate to the treatments during an initial 21-d period. Treatments were dry ground corn grain (DG) and high moisture corn (HM) harvested from the same field. Treatment periods were 14 d, with the final 4 d used for data and sample collection. Diets included corn silage and alfalfa haylage at a 2:1 ratio and were ~26% neutral detergent fiber, 16.5% crude protein, 32% starch, and 3.5% fatty acids. High moisture corn increased plasma glucose, nonesterified fatty acid, and triglyceride concentrations, but treatment had no consistent effect on yield of milk or FCM. High moisture corn increased trans C(18:1) concentrations at an increasing rate as production level decreased across cows, and milk fat depression was evident in cows below approximately 40 kg/d FCM yield. In contrast, production level had little influence on milk trans C(18:1) concentration for DG. Milk trans C(18:1) concentration was negatively correlated with milk fat concentration, as was trans-9 C(18:1), trans-10 C(18:1), and cis-9, trans-11 C(18:2). Concentration of trans-10, cis-12 C(18:2) was not correlated with milk fat concentration. Production level may influence biohydrogenation patterns and trans C(18:1) production because of differences in rumen environment; rumen pH and dilution rate can alter metabolism and populations of rumen microbes. Diets with highly fermentable starch sources and without supplemental dietary polyunsaturated fatty acids can induce milk fat depression in lower-producing cows, likely because of increased production of trans C(18:1) fatty acids.

Effects of Substrate, Passage Rate, and pH in Continuous Culture on Flows of Conjugated Linoleic Acid and Trans C18:1

A dual-flow continuous culture system consisting of 4 fermenters was used in a 4 x4 Latin square design. The objective of the research was to evaluate the effects of solid dilution rate (SDR), pH, and concentration of linoleic acid (LA) in the feed mixture on the production of conjugated linoleic acid (CLA) and trans-C18:1. The 4 treatments were 1) control = pH 6.5, 1% LA, 4%/h SDR; 2) high solid dilution rate (HSDR) = pH 6.5, 1% LA, 8%/h SDR; 3) high linoleic acid (HLA) = pH 6.5, 3% LA, 4%/h SDR; and 4) low pH (LPH) = pH 5.8, 1% LA, 4%/h SDR. Inoculum was collected 6 h after feeding from a cow fed 40% alfalfa hay and 60% grain. Liquid dilution rate was held at 0.12/h. All treatments except HLA contained 2% tallow. The LA was dissolved in buffer and continuously infused into the fermenters. The CLA flows were 16.5, 20.4, 23.2, and 25.2 mg/d for control, HSDR, HLA, and LPH, respectively. Compared with control, LPH increased flows of CLA, cis-C18:1, and C18:2, and decreased flow of C18:0. The neutral detergent fiber (NDF) and acid detergent fiber (ADF) digestibilities were not affected by pH. The HSDR tended to increase CLA flow compared to control, possibly because a shorter solid retention time led to incomplete biohydrogenation (BH). The NDF and ADF digestibilities and bacterial numbers were reduced by HSDR. With more LA available as a substrate for CLA, HLA resulted in a higher flow of CLA than control. The HLA resulted in the highest acid detergent fiber and fatty acid digestibilities, bacterial numbers, and BH. Increasing solids passage rate, reducing pH, and increasing dietary LA appears to increase in vitro CLA production.

Variations of trans octadecenoic acid in milk fat induced by feeding different starch-based diets to cows

The impact of starch sources differing in their velocities of ruminal degradation on the milk fat of dairy cows was studied. The animals received diets containing a slowly degradable (potatoes) or rapidly degradable (wheat) starch concentrate (40% of the dry matter) in a total mixed diet. Milk fat was the only animal performance factor affected: Cows produced significantly less milk fat when fed the wheat diet than the potato diet (-3.3 g/kg, -122 g/d; P < 0.05). With the wheat diet, milk fat was poorer in short-chain FA and richer in unsaturated long-chain FA, especially in trans octadecenoic acid (4.4 vs. 2.7% of the total FA, P < 0.05). A very large increase in the isomer trans-10 18:1 (+1.46% of the total FA) was observed. Because no difference in volatile FA concentrations in the rumen was revealed, the increase in trans octadecenoic acids, and particularly the isomer trans-10 18:1, was associated with the larger postprandial drop in ruminal pH with wheat. Similar concentrate levels and FA profiles in both diets indicated that the decrease in milk fat was due to changes in the ruminal environment. Quicker degradation of wheat starch, and hence a greater drop in pH with this diet associated with the absence of any effect on volatile FA, strengthen the hypothesis developed in the literature of enzyme inhibition via increased levels of trans octadecenoic acids, especially the trans-10 isomer. Hence, milk fat can be decreased with rapidly degradable starch sources and not only with high levels of concentrates in the diet or added fat. More detailed work is necessary to elucidate the microorganisms involved and to determine whether metabolic pathways similar to those reported for high-concentrate diets are involved.

Nutritional regulation of milk fat synthesis

Certain diets cause a marked reduction in milk fat production in ruminants. Commonly referred to as milk fat depression (MFD), the mechanism involves an interrelationship between rumen microbial processes and tissue metabolism. Numerous theories to explain this interrelationship have been proposed and investigations offer little support for theories that are based on a limitation in the supply of lipogenic precursors. Rather, the basis involves alterations in rumen biohydrogenation of dietary polyunsaturated fatty acids and a specific inhibition of mammary synthesis of milk fat. The biohydrogenation theory proposes that under certain dietary conditions, typical pathways of rumen biohydrogenation are altered to produce unique fatty acid intermediates that inhibit milk fat synthesis. Trans-10, cis-12 conjugated linoleic acid (CLA) has been identified as one example that is correlated with the reduction in milk fat. Investigations with pure isomers have shown that trans-10, cis-12 CLA is a potent inhibitor of milk fat synthesis, and similar to diet-induced MFD, the mechanism involves a coordinated reduction in mRNA abundance for key enzymes involved in the biochemical pathways of fat synthesis. A more complete identification of these naturally produced inhibitors of fat synthesis and delineation of cellular mechanisms may offer broader opportunities for application and understanding of the regulation of lipid metabolism.

Influence of Corn Silage Particle Length on the Performance of Lactating Dairy Cows Fed Supplemental Tallow

The objective of this study was to determine if the length of chop of processed corn silage influences the impact of supplemental fat on rumen fermentation and performance of dairy cows. We hypothesized that increasing forage particle length may alleviate the interference of fat on rumen fermentation. Sixteen Holstein cows averaging 120 d in milk were used in a replicated 4 x 4 Latin square design with 21-d periods. Treatments were arranged as a 2 x 2 factorial with 0 or 2% tallow (dry matter basis), and corn silage harvested at either 19 or 32 mm theoretical length of cut. The forage:concentrate ratio was 50:50, and diets were formulated to contain 18% crude protein and 32% neutral detergent fiber (dry matter basis). Cows were allowed ad libitum consumption of diets that were fed twice daily as a total mixed ration. Fat supplemented cows had lower dry matter intake and produced less milk fat relative to nonsupplemented cows. No effect of corn silage particle length was observed for dry matter intake and milk fat production. Proportion of trans-10 C18:1 and of trans-10, cis-12 conjugated linoleic acid was highest in milk fat of cows fed 2% supplemental tallow. Rumen pH was not affected by feeding tallow, and tended to be highest for cows eating the 32-mm theoretical length of chop corn silage diets. No effect of treatments was observed for rumen acetate-to-propionate ratio or rumen ammonia concentration. In this study, tallow supplementation had a negative impact on performance of dairy cows regardless of the corn silage particle length. Feeding tallow increased formation of trans-fatty acids in the rumen in the absence of significant changes in the rumen environment.

Effects of tallow in diets based on corn silage or alfalfa silage on digestion and nutrient use by lactating dairy cows

Six multiparous Holstein cows (average 31 days in milk; 36.3 kg/d of milk) fitted with ruminal cannulas were used in a 6 x 6 Latin square with 21-d periods to investigate the effects of diets that varied in forage source and amount of supplemental tallow. Isonitrogenous diets in a 2 x 3 factorial arrangement were based on either high corn silage (40:10 corn silage to alfalfa silage, % of dry matter) or high alfalfa silage (10:40 corn silage to alfalfa silage, % of dry matter) and contained 0, 2, or 4% tallow. Intakes of dry matter and total fatty acids were lower when cows were fed the high corn silage diet. Tallow supplementation linearly decreased dry matter intake. Milk yield was unaffected by diet; yields of milk fat and 3.5% fat-corrected milk were higher for the high alfalfa silage diet but were unaffected by tallow. Milk fat percentage was higher for the high alfalfa silage and tended to decrease when tallow was added to the high corn silage diet. Contents of trans-C18:1 isomers in milk fat were increased by high corn silage and tallow, and tended to be increased more when tallow was fed in the high corn silage diet. Ruminal pH and acetate:propionate were lower when high corn silage was fed. Ruminal acetate:propionate decreased linearly as tallow increased; the molar proportion of acetate was decreased more when tallow was added to the high corn silage diet. Ruminal liquid dilution rates were higher for the alfalfa silage diet; ruminal volume and solid passage rates were similar among diets. Total tract apparent digestibilities of dry matter, organic matter, crude protein, starch, energy, and total fatty acids were unaffected by diet. Digestibilities of neutral detergent fiber, acid detergent fiber, hemicellulose, and cellulose were lower when high corn silage was fed. The high alfalfa silage diet increased intakes of metabolizable energy and N, and increased milk energy and productive N. Tallow decreased the amount of N absorbed but had few other effects on utilization of energy or N. Tallow linearly increased concentrations of nonesterified fatty acids and cholesterol in plasma; cholesterol was increased by high alfalfa silage. Overall, forage source had more pronounced effects on production and metabolism than did tallow supplementation. Few interactions between forage source and tallow supplementation were detected except that ruminal fermentation and milk fat content were affected more negatively when tallow was fed in the high corn silage diet.

Whole linted cottonseed as a forage substitute fed with ground or steam-flaked corn: digestibility and performance

Six ruminally and duodenally cannulated Holstein cows were used in a 6 x 6 Latin square design. The objective was to evaluate any potential interactions in site of nutrient digestion when neutral detergent fiber (NDF) from cottonseed was incrementally substituted for forage NDF (FNDF) from alfalfa silage and when starch availability was varied by feeding ground (G) or steam-flaked (SF) corn. Iso-NDF diets were forage control with G corn (21% FNDF), 5% whole cottonseed (WCS) with G or SF corn (18% FNDF), 10% WCS with G or SF corn (15% FNDF), and 15% WCS with G corn (12% FNDF). Ruminal or total tract digestibilities of organic matter (OM) or nonstructural carbohydrate (NSC) were unaffected, but efficiency of microbial protein synthesis decreased as WCS increased. Ruminal NDF digestibility was not affected despite a linear decrease in pH, but postruminal NDF digestibility decreased with increasing WCS. Ruminal digestibilities of OM and NSC were higher for SF than G corn but did not affect efficiency of microbial N synthesis. Dry matter intake increased quadratically with increasing level of WCS but decreased when SF replaced G corn. Milk yield did not differ across treatments. Milk fat percentage was affected quadratically and milk protein increased linearly with increasing WCS. Milk fat percentage decreased but milk protein was not affected when SF replaced G corn. Lack of an interaction between corn source and level of WCS substitution suggests that WCS was equally effective in maintaining ruminal fermentation and digestibility in diets varying in ruminal starch availability.

The effect of oilseeds in diets of lactating cows on milk production and methane emissions

Thirty-six lactating multiparous Holstein cows were assigned to diets that contained 2.3, 4.0, and 5.6% fat for an entire lactation to determine the effect of oilseeds on milk composition, production, and methane emissions. The diets were formulated so that whole cottonseeds and canola oilseeds provided equal amounts of added fat. Methane emissions were measured every 3 mo from two replicates of four cows per treatment using a room tracer approach. Dry matter intakes and yields of milk and FCM were greater for cows fed the diets containing oilseeds. Although the concentration of protein in milk was reduced, yields of both protein and fat tended to be increased by the addition of fat. Within the milk fat, the concentrations of C10, C12, C14:0, and C16:0 were reduced and concentrations of C18, C18:1, and trans-C18:1 were increased in response to dietary oilseeds. In serum, urea-N was increased by the dietary oilseeds. Supplementation of diets with oilseeds did not affect methane emissions but tended to increase the efficiency of milk produced per unit of methane emitted. A 1.7% addition of fat to the control diet from a combination of oilseed types increased yields of milk without reducing methane emission rates. The strategy of using unsaturated fats from oilseeds to substantially reduce methane emissions was ineffective, although yield of milk was increased.

Effect of supplemental tallow on performance of dairy cows fed diets with different corn silage:alfalfa silage ratios

A study was conducted to investigate the response to supplemental tallow of lactating cows fed basal diets with different alfalfa silage:corn silage ratios. We postulated that supplemental tallow will have decreasing negative effects on rumen fermentation, dry matter intake (DMI), and milk fat percentage as the dietary ratio of alfalfa silage:corn silage is increased. Eighteen Holstein cows averaging 134 +/- 14 d in milk were used in a replicated 6 x 6 Latin square design with 21-d periods. Treatments were arranged as a 2 x 3 factorial with 0 or 2% tallow (DM basis) and three forage treatments: 1) 50% of diet DM as corn silage, 2) 37.5% corn silage and 12.5% alfalfa silage, and 3) 25% corn silage and 25% alfalfa silage. Cows were allowed ad libitum consumption of a total mixed ration. Diets were formulated to contain 18% crude protein and 32% neutral detergent fiber. No fat x forage treatment interactions were observed. Fat supplemented cows had lower DMI and produced more milk with less milk fat content relative to non-supplemented cows. Concentration of trans-octadecenoic acids was higher in milk fat of tallow-supplemented cows. Tallow supplementation had no effect on ruminal pH and acetate:propionate ratio, but tended to decrease total volatile fatty acid (VFA) concentration in the rumen. Increasing the proportion of alfalfa silage increased DMI, milk fat percentage, and milk fat yield regardless of the fat content of the diet. Total VFA concentration and acetate:propionate ratio in the rumen were increased in response to higher levels of alfalfa in the diets. These results suggest that replacing corn silage with alfalfa silage did not alleviate the negative response of dairy cows to tallow supplementation at 2% of diet DM.

The composition of bovine milk lipids: January 1995 to December 2000

Data from recent publications on bovine milk lipids are presented and discussed. This includes extraction of lipids, triacylglycerols, phospholipids, other complex lipids, sterols, isoflavones, and fatty acids. Improved gas-liquid and high performance liquid chromatography were used. Data on the trans and cis isomers of fatty acid and of conjugated linoleic acids are given, and the analyses are described. Papers about the lipids in milks and dairy products from the United States are few; where with the exception of trans-fatty acid isomers and conjugated linoleic acids, almost no research has been reported.

Effect of type and level of dietary fat on rumen fermentation and performance of dairy cows fed corn silage-based diets

The objective of this study was to investigate the effects of tallow and choice white grease (CWG) fed at 0, 2, and 4% of the diet dry matter (DM) on rumen fermentation and performance of dairy cows when corn silage is the sole forage source. Fifteen midlactation Holstein cows were used in a replicated 5 x 5 Latin square design with 21-d periods. Treatments were 0% fat (control), 2% tallow, 2% CWG, 4% tallow, and 4% CWG (DM basis). The forage:concentrate ratio was 50:50, and diets were formulated to contain 18% crude protein and 32% neutral detergent fiber (DM basis). Cows were allowed ad libitum consumption of diets fed twice daily as total mixed rations. Cows fed supplemental fat had lower DM intake and produced less milk and milk fat than cows fed the control diet. Feeding 4% fat reduced milk production and milk fat yield relative to feeding 2% fat. Treatments had little effect on the concentration of trans-octadecenoic acids in milk fat. Total trans fatty acids were poorly related to changes in milk fat percentage. Ruminal pH and total volatile fatty acids concentration were not affected by supplemental fat. The acetate:propionate ratio, NH3-N, and numbers of protozoa in the rumen were significantly decreased when fat was added to the diets. Source of dietary fat did not affect rumen parameters. There was no treatment effect on in situ corn silage DM and neutral detergent fiber disappearance. Including fat in corn silage-based diets had negative effects on milk production and rumen fermentation regardless of the source or level of supplemental fat.

Effects of postrumen starch infusion on milk production and energy metabolism in dairy cows

Two experiments were conducted to determine effects of postrumen starch infusion on milk production and energy and nitrogen utilization in lactating dairy cows. In experiment 1, four cows in early lactation fed grass silage and concentrates were continuously infused into the duodenum with water or 700, 1400, or 2100 g of purified maize starch daily for 10 to 12 d in a 4 x 4 Latin square design with 2-wk periods. Starch infusion increased milk yield linearly and decreased milk fat concentration in a quadratic manner such that increases in fat-corrected milk and calculated milk energy yield were minimal except at the highest rate of infusion. Changes in milk energy output suggest that even at the highest infusion rate metabolizable energy supplied by infused starch was used for tissue energy or oxidized. In experiment 2 energy and nitrogen balance were measured in four cows in late lactation fed a mixture of dehydrated lucerne, grass silage, and concentrates during the last 6 d of 2-wk abomasal infusions of 1200 g of purified wheat starch daily or water in a balanced switchback design with 5-wk periods. Measurements of fecal starch concentration indicated nearly all the starch infused was digested, but decreased fecal pH and apparent nitrogen digestion suggested an increase in hindgut starch fermentation. Starch infusion decreased urine nitrogen output in part because of increased tissue nitrogen retention but had no effect on milk nitrogen output. In absolute terms, numerical decreases in feed energy intake and energy digestion reduced the recovery of starch energy infused as digestible and metabolizable energy, but in terms of changes in total energy supply with starch infusion, 79% was recovered as metabolizable energy. Starch infusion had no effects on heat or milk energy but increased net energy for lactation due to a numerical increase in tissue energy, implying that in late-lactation cows, starch digested postruminally was used with high efficiency for tissue energy retention as protein and fat.

Dairy goat performance with different dietary concentrate levels in late lactation

Alpine yearling doelings (22; 44+/-1.0kg) and mature does (25; 59+/-1.7kg) were used in an experiment with 16 weeks in late lactation, 8-13 weeks dry and 12 weeks in the subsequent lactation. Diets of 20, 35, 50 or 65% concentrate and 2.18, 2.34, 2.49 and 2.62Mcal/kg ME, respectively (20C, 35C, 50C and 65C treatments, respectively), were consumed ad libitum in late lactation, with a 35% concentrate diet (2.18Mcal/kg ME) in the first 4 weeks of the dry phase and 50% concentrate (2.65Mcal/kg ME) until kidding. Other goats consuming 20 or 35% concentrate in late lactation received 65 (2.65Mcal/kg ME) or 50% concentrate, respectively, in the dry phase (20A and 35A treatments, respectively). All goats consumed a 50% concentrate diet (2.42Mcal/kg ME) in the subsequent early lactation. DM intake in late lactation was similar among treatments (1.95, 2.21, 2.17, 2.10, 1.99 and 2.00kg per day for 20C, 35C, 50C, 65C, 20A and 35A, respectively; S.E.=0.098) and greater (P<0.05) for does versus doelings (2.16 versus 1.98kg per day; S.E.=0.058); DM intake in the dry phase was similar among treatments. Relative to BW, DM intake was greater (P<0.05) for doelings than for does in late lactation (4.16 versus 3.43% BW) and early lactation (4.56 versus 3.80% BW). The effect of dietary treatment on milk production in late lactation varied with parity (P<0.05); milk production by doelings was 1.39, 1.49, 1.43, 1.57, 1.29 and 1.52kg per day and by does was 1.01, 1.89, 2.38, 1.63, 1.17 and 1.34kg per day for 20C, 35C, 50C, 65C, 20A and 35A, respectively; S.E.=0.200). BW change during the entire 16 weeks late lactation phase was greater (P<0.05) for 65C than for other treatments except 50C (6.9, 5.6, 9.1, 10.4, 5.8 and 4.0kg for 20C, 35C, 50C, 65C, 20A and 35A, respectively; S.E.=1.28), although BW at kidding and litter weight were similar among treatments. BW, DM intake and milk production in the first 12 weeks of the subsequent lactation were not affected by dietary treatment or parity. In conclusion, with moderate to high quality forage in late lactation and a moderate level of concentrate in the dry period, the level of concentrate fed in late lactation and in the dry period may not affect subsequent lactation performance regardless of parity. Milk production by doelings in late lactation appears relatively less responsive to dietary concentrate level than that by does.

Influence of carbohydrate source and buffer on rumen fermentation characteristics, milk yield, and milk composition in late-lactation Holstein cows

The effects of concentrate-to-forage ratio and buffer on rumen fermentation and production parameters were examined in four rumen-cannulated cows (240 +/- 18 d in milk) fed a total mixed ration ad libitum in a 4 x 4 Latin square design. The treatments were a 50:50 concentrate to forage ratio with [1.2% of dry matter, (DM)] and without (0% of DM) buffer and a 75:25 concentrate to forage ratio with (1.2% of DM) and without (0% of DM) buffer. Rumen pH declined in response to increased concentrate but was not influenced by buffer. In the absence of the buffer, rumen acetate declined and propionate was elevated at the higher level of concentrate inclusion. The milk fat concentration was lower for cows fed the high concentrate diet without buffer; however, the addition of buffer to the diet prevented the milk fat depression. Milk fat depression was associated with elevated trans-C18:1 fatty acids in milk, which provides additional support for an inhibitory effect of these fatty acids on mammary fat synthesis. We concluded that the potential of nutrition as a tool to alter milk composition is greater in later lactation as these animals are better able to cope with the negative effects of high grain diets, and the treatment response is greater than in early lactation.

Mammary lipogenic enzyme activity, trans fatty acids and conjugated linoleic acids are altered in lactating dairy cows fed a milk fat-depressing diet

The objectives of the present study were to examine the effect of a milk fat-depressing (MFD) diet on: 1) the activity of mammary acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), 2) ACC mRNA relative abundance and 3) distributions of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA) in milk fat. Twelve lactating Holstein cows were used in a single reversal design. Two diets were fed: a control diet (60:40% forage/concentrate) and an MFD diet (25:70% forage/concentrate, supplemented with 5% soybean oil). The MFD diet decreased (P: < 0 0.001) milk fat by 43% and ACC and FAS activity by 61 and 44%, respectively. A reduced ACC mRNA relative abundance (P: < 0.001) corresponded with the lower ACC activity. The fatty acids synthesized de novo were decreased (P: < 0. 002), whereas tFA were increased from 1.9 to 15.6% due predominantly to a change in trans-10-18:1 isomer (P: < 0.001). With the MFD diet, the trans-7, cis-9 and trans-10, cis-12 CLA isomers were elevated (P: < 0.001), in contrast to the decrease in trans-11-18:1 (P: < 0. 001) and cis-9, trans-11-18:2. The data were consistent with a dietary effect on mammary de novo FA synthesis mediated through a reduction in ACC and FAS activity and in ACC mRNA abundance. The results were compatible with a role of trans-10, cis-12 CLA in milk fat depression, but alterations noted in tFA and other CLA isomers suggest that they also may be important during diet-induced milk fat depression.

Effects of brown midrib 3 mutation in corn silage on productivity of dairy cows fed two concentrations of dietary neutral detergent fiber: 1. Feeding behavior and nutrient utilization

The effects of digestibility of corn silage neutral detergent fiber (NDF) and dietary NDF content on feeding behavior, dry matter intake (DMI), and energy utilization were evaluated with eight multiparous high producing dairy cows in a duplicated 4 x 4 Latin square design with 21-d periods. Experimental diets contained corn silage from a brown midrib (bm3) hybrid or its isogenic normal control at two concentrations of dietary NDF (29 and 38%). Both low NDF diets and bm3 corn silage treatments increased DMI and milk yield. However, an interaction between corn silage treatment and dietary NDF content was observed for meal size and for interval between meals, implying that different mechanisms regulating DMI dominate depending on the fermentation characteristics of diets. The bm3 treatment depressed milk fat concentration when fed in a low NDF diet. The bm3 corn silage increased solids-corrected milk yield, but did not affect daily body weight gain compared with control, whereas low NDF diets increased daily body weight gain, but did not affect solids-corrected milk yield compared to high NDF diets. Both bm3 treatments and low NDF diets reduced ruminal pH, but low NDF treatments increased fluctuation of ruminal pH and bm3 treatments did not. Feeding bm3 corn silage increased the energy utilized for milk production, possibly because of a consistent supply of metabolic fuels from the rumen. The beneficial effects of bm3 corn silage on productivity of lactating cows were greater for the cows fed a high NDF diet.

The effects of time of disease occurrence, milk yield, and body condition on fertility of dairy cows

The associations between occurrence of diseases, milk yield, and body condition score on conception risk after first artificial insemination (AI) were analyzed in an observational study on a convenience sample of 43 farms participating in a herd health program. Data were taken from 9369 lactations, from 4382 cows inseminated between 20 and 180 d in milk from 1990 to 1996. Two logistic regression models, one containing data from all lactations and a subset containing data from 1762 lactations with body condition scoring, were used to determine pregnancy risk at first AI. The effects of herd deviation in test-day milk yield, body condition score loss, and milk fat to protein ratio changes in early lactation were significant predictors of pregnancy risk, independent of disease; days in milk; farm; and seasonal factors. Three different methods of disease parameterization (incidence rates, binomial classes dependent on the interval in days since last occurrence with respect to AI, and a linear variable weighted for this interval) produced similar results. Metritis, cystic ovarian disease, lameness, and mastitis gave odds ratios for pregnancy risk ranging from 0.35 to 1.15, largely dependent on the interval in days from final disease occurrence to first AI. Displaced abomasum, milk fever, and retained fetal membranes resulted in odds ratios for pregnancy risk of 0.25, 0.85, and 0.55, respectively. These diseases showed little relationship between fertility and the number of days since last occurrence. Results of this study confirm the negative effects of milk yield, body score condition loss, and disease on dairy cow fertility. The effects of some diseases on first service conception were strongly dependent on the interval since last disease occurrence. This was especially valid for clinical mastitis, which has an extremely weak effect on conception if occurring prior to AI and is associated with > 50% reduction in pregnancy risk if occurring in the 3 wk directly after AI.

Influence of carbohydrate source and buffer on rumen fermentation characteristics, milk yield, and milk composition in early-lactation Holstein cows

The effects of concentrate to forage ratio and sodium bicarbonate (buffer) supplementation on intake, ruminal fermentation characteristics, digestibility coefficients, milk yield, and milk composition were examined in 4 cannulated Holstein cows (100 +/- 20 d in milk). A 4 x 4 Latin square design with 2 x 2 factorial arrangement of treatments was implemented for 3-wk experimental periods. The 4 treatments were a 50:50 concentrate to forage ratio with 1.2% of dry matter (DM) and without added buffer and a 75:25 concentrate to forage ratio with (1.2% of DM) and without (0% of DM) buffer. The forage component of the ration was a 50:50 mixture of alfalfa and barley and triticale silage, and diets were fed ad libitum as a total mixed ration. Although feed intake was not influenced by treatments, substantial treatment differences were observed for milk yield and milk composition. Cows fed high-concentrate diet had lower ruminal pH, ruminal acetate, and butyrate concentrations, whereas propionate concentrations were significantly elevated. The addition of buffer, at both levels of concentrate inclusion, resulted in elevated total volatile fatty acids and acetate concentrations. We concluded that altering the forage concentrate ratio in the diet of lactation cows influenced milk yield and milk composition, but the addition of buffer to the diet prevented the elevation in trans-C18:1 fatty acids in milk fat, and related milk fat depression, associated with feeding high-concentrate diets.

High-fat dairy product consumption increases delta 9c,11t-18:2 (rumenic acid) and total lipid concentrations of human milk

Conjugated octadecadienoic acids (18:2, conjugated linoleic acids) have been shown to be anticarcinogenic and may influence growth and nutrient partitioning. The delta 9c,11t-18:2 isomer (rumenic acid, RA) is most common in both food sources and human tissues. To determine if maternal diet can influence milk RA concentration, breastfeeding women (n = 16) were enrolled in a 3-wk crossover study. Women initially consumed minimal amounts of food containing RA during week 1, then were assigned randomly to consume diets rich in high-fat dairy foods (and thus RA) during week 2 or 3. Milk was collected by complete breast expression twice during each experimental week. Current and chronic RA intakes were estimated by 3-d dietary records and food frequency questionnaires, respectively. Estimated chronic RA intakes ranged from 49 to 659 mg/d. Dietary RA intake was greater during the high compared to the low dairy period (291 +/- 75 vs. 15 +/- 24 mg/d, respectively; P < 0.0001). Milk contained more RA during the high than the low dairy period (13.5 +/- 0.1 vs. 8.2 +/- 0.4 mumol/g lipid, respectively; P < 0.0001). Milk lipid concentration was influenced by diet, such that lipid concentration was greater during the high than the low dairy period (46.6 +/- 5.0 vs. 38.3 +/- 1.6 mg/g milk, respectively; P < 0.05). Additionally, multiple regression analyses suggested that body mass index was the primary predictor of milk RA and lipid concentrations. In summary, these data indicate that both lipid and RA concentrations of human milk can be influenced by diet.