Dietary fat and ruminally protected amino acids for high producing dairy cows

Eight early lactation Holstein cows, used in a replicated 4 x 4 Latin square design, were fed the following diets: control; control plus ruminally protected amino acids (15 g methionine and 20 g lysine); control plus added fat (.32 kg 60:40 animal and vegetable blend and .36 kg of Ca salts of fatty acids); control plus ruminally protected amino acids plus added fat. The objective was to examine the effect of ruminally protected forms of lysine and methionine and dietary fat on milk yield and composition. Cows were fed for ad libitum consumption of total mixed diets consisting of 50% forage and 50% concentrate on a DM basis. Added fat increased milk, fat, and 4% FCM yield but decreased milk protein percentage. Ruminally protected amino acids increased milk protein percentage. The combined effect of fat and ruminally protected acids increased milk fat percentage and yield more than the sole addition of either supplement. Added fat increased the percentage and yield of long-chain fatty acids in milk. Plasma free fatty acids were also increased by fat addition. Adding ruminally protected amino acids to fat-supplemented diets may help alleviate the milk protein depression found with added fat.     

Ruminant fat volatiles as affected by diet. A review

Volatile compounds in meat have been widely studied for their favourable or undesirable effects on meat flavour, or for their potential use in tracing the animal feeding system. To date, the chemical mechanisms causing the appearance of volatile compounds in meat have been largely understood. Several variables are involved in the accumulation of volatiles in animal tissues and among them animal diet plays a key role. The purpose of the present review is to highlight the effects of different dietary regimes (concentrate, green grass and fat-enriched diets) on the appearance of fat volatile compounds in ruminant meat. Grain-based diets induce greater accumulations in meat of branched-chain fatty acids, some aldehydes, and lactones while meat fat from grazing animals contains high levels of phenols, terpenes, indoles and sulphur compounds. Fat-enriched diets exert their effect mainly on those volatiles which originate from polyunsaturated fatty acids. Cooking procedures have been considered for their contribution to fat volatiles in meat by reactions induced by high temperatures.     

Production responses of dairy cows when fed supplemental fat in low- and high-forage diets

Intake of net energy for lactation (NE_L) is often the limiting factor for milk production and is affected by stage of lactation and dietary concentrations of forage and fat. Because of the mechanisms involved, interactions are likely between those 2 diet components and stage of lactation. We conducted an experiment with 72 Holstein cows starting at 21 and ending at 126 d in milk (DIM). Cows were fed diets (dry matter basis) with 40 or 60% forage (67% corn silage, 33% alfalfa silage) each with 0 or 2.25% added saturated free fatty acids. The high- and low-forage diets contained 25 and 17% forage neutral detergent fiber and 30 and 33% total neutral detergent fiber, respectively; the low-forage diets contained several byproducts. Diets with and without fat contained approximately 5.2 and 3.2% long-chain fatty acids, respectively. Feeding fat or low-forage diets increased NE_L intake, but no interaction was observed. The increase in NE_L intake by cows fed low-forage diets was caused by increased dry matter intake, and the increase in NE_L intake by cows fed fat was caused by increased energy density of the diet. Interactions between fat and forage were observed for energy utilization. When high-forage diets were supplemented with fat, the increased NE_L intake went toward body energy reserves as measured by higher body condition scores with no change in milk yield. However, when low-forage diets were supplemented with fat, milk yield increased (2.6 kg/d) with no change in body condition. The differential partitioning of NE_L may have been caused by nutrients other than NE_L limiting milk production in cows fed the high-forage diets. With low-forage diets, intake of other nutrients was greater (i.e., greater dry matter intake). At 35 DIM, dietary treatments had little effect on milk fatty acids composition but in later lactation (125 DIM), feeding supplemental fatty acids or feeding low-forage diets increased long-chain fatty acids and decreased short-chain fatty acids. However, treatment did not have marked effects on concentrations of total fat or protein in milk. The amount of forage in a diet influences cow responses to supplemental fat and should be considered when diets are formulated.     

Relationships between meat quality measurements in rabbits fed with three diets of different fat type and content

Two hundred and eighty-four, genetically similar (a three-way cross), young rabbits were fed ad libitum, from weaning, either a commercial diet (group C, ether extract 2.6%) or a diet containing vegetable fat (group V, ether extract, 9.9%) or animal fat (group A, ether extract 11.7%). A principal component (PC) analysis was performed with the variables: ultimate pH at 24 h post mortem measured in the longissimus dorsi (LD) and in the biceps femoris (BF) muscles, colour measured on the surface of the loin, fatty acid composition of perirenal fat, meat fat content of the hind leg, water holding capacity and cooking losses of the meat, and sensory variables determined by a trained panel test. The four first PC explained 62% of the total variation (27, 13, 11 and 11%, respectively). The first PC grouped the fatty acids, the second PC grouped the sensorial variables, and the third and fourth PCs grouped the pHs and the water holding capacity. The projection of the data in the first two PCs showed three separate groups of points. Animals fed with diet V were on the left side of the graph, where the variable C18:2 lies, whereas animals fed with diets A and C lay on the right side of the graph, where the saturated acids were grouped. These were slightly separated by the higher content of oleic acid in the animals fed with diet A. The second PC, where the sensorial variables were grouped, did not separate the animals fed with diets A, V and C. The diets used in this experiment had only a slight influence on the organoleptic characteristics of rabbit meat.     

A relationship between bovine fat colour and fatty acid composition

Subcutaneous adipose tissue was obtained from pasture-grazed (n = 13) and short-term (70 days) grain-fed (n = 13) cattle. The yellow colour of the adipose tissue was assessed by Minolta b(?) value readings and by determination of total carotenoids and the two measurements gave a correlation coefficient of 0·79 (P < 0·01). The fatty acid composition of the samples varied with fat colour. As the b(?) value and the carotenoid content of the fat increased, there was a significant increase in the total percentage of cis mono-unsaturated fatty acids and a decrease in saturated fatty acids (P < 0·01). Consequently, the ratio of cis mono-unsaturated to saturated fatty acids was found to be higher in those samples exhibiting a greater yellow colour.     

Effect of increasing amounts of a linoleic-rich dietary fat on the fat composition of four pig breeds. Part I: Backfat fatty acid evolution

Four diets prepared, respectively, with 0%, 2%, 4% and 8% of a high-linoleic added fat were administered (76 days of treatment) to a sample of 112 pigs of four breeds (Landrace, Large White, Duroc and a crossbreed Landrace × Duroc). The effects of diet and breed on the evolution of the fatty acid composition of backfat were examined by taking biopsies. Over time, a continuous increase in stearic, palmitic and oleic acids throughout the pig’s life was observed. Oleic acid showed the smallest differences among the four diets at the end of the experiment, while stearic and palmitic acid showed higher differences according to the increase in the percentage of dietary fat. Stearic acid showed the highest rate of increase over time, according to the increasing intake of linoleic acid (diets 1–4). These increases were compensated by a decrease in linoleic acid, although this decrease tended to stabilize according to a higher percentage of added fat and also, for diet 4 (8% fat), an increase in linoleic acid was observed at the end of the experiment. Among the minor fatty acids, arachidonic acid showed a clear decrease over time, although higher levels at the end of the experiment were observed for diets including 4% and 8% of added fat, compared to the other two diets including lower amounts of linoleic acid. Moreover, a significant effect was observed for the factor breed. So, Duroc pigs showed the highest rate of deposit of linoleic acid and the lowest of stearic acid, while the other three breeds showed similar rates.     

Effect of dietary fat in isocaloric rations on the nitrogen content of milk from Holstein cows

Effects of dietary fat on milk composition, particularly milk N, were evaluated using 12 lactating Holstein cows in a replicated 4 X 4 Latin-square design. Four complete mixed diets were formulated to contain either 0 or 3.5% added fat (grease) and either 1.6 or 1.7 Mcal NE1 (0, 1.6; 0, 1.7; 3.5, 1.6; and 3.5, 1.7). Diets were fed for ad libitum intake, and periods were 21 d. Adding fat to the diet depressed total milk N, casein N, and whey protein N concentration compared with no added fat at both energy densities. The proportion of total N in the casein fraction was not affected by dietary fat, whereas the proportion of N associated with the NPN fraction was increased with diets containing added fat. The high concentration diet (0, 1.7) contained the highest content of milk N and casein N. Added dietary fat increased the proportion of long-chain fatty acids (C18 and C18:1) in milk fat and decreased the proportion of short-chain fatty acids (C8 to C16). Daily milk yield was higher for the high energy fat diet (3.5, 1.7) than for the other three diets, which were similar. Blood concentrations of triglycerides, nonesterified fatty acids, and cholesterol were increased by diets containing added fat.     

Evaluation method for firmness and stickiness of porcine perirenal fat

The firmness and stickiness of chilled porcine fat at 4°C were evaluated with an Instron compression tester and compared with fatty acid composition. Firmness of cylindrical adipose samples was measured at a force producing a 70% deformation. Firmness values were correlated with refractive index data (r=-0.67), melting point data (r=0.77), and saturated fatty acids concentration data (r=0.72) of the extracted lipid, and with sensory scores data (r=0.89). The firmness value correlated with the concentration of C18:0 (r=0.73). The stickiness of comminuted fat samples was evaluated with the Instron using a fixed load at a compression force of 20N and crosshead speed of 1.5mm/s. Single regression analyses showed that the stickiness parameters, stretch and adhesiveness correlated negatively with the concentration of the saturated fatty acids data (r=-0.64, -0.52) but positively and weakly with the monounsaturated fatty acids data (r=0.28, 0.34). Multiple regression analysis improved their relationships. These results indicate that mechanical evaluation may be used to predict porcine fat texture and saturated fatty acids concentration.     

Influence of dietary fat on pork eating quality

This study compared the influence of dietary fat sources on meat quality, fatty acid composition and sensory attributes in pork. The experiment was conducted with 43 entire male pigs (Pietrain×(Landrace×Large White)) which were fed a basal diet without added fat (control diet) or supplemented with different sources of fat: animal fat (1%, AF1; 3%, AF3), soyabean oil (1%, SBO1) and calcium soaps of palm oil (1%, CaSPO1). Dietary fat supplementation did not significantly affect ultimate pH, colour, Warner-Bratzler shear force values, sensory attributes or SFA. Pigs fed SBO1 had the lowest proportion of MUFA and the highest of PUFA. In conclusion, these dietary fat sources could be recommended for inclusion in diets, at these levels, with no detrimental effect on eating quality. Despite finding no significant differences, the PCA afforded a comprehensive view of the predominating attributes of pork from animals fed the different fats.     

The effect of nonstructural carbohydrate and addition of full fat extruded soybeans on the concentration of conjugated linoleic acid in the milk fat of dairy cows

Conjugated linoleic acid (CLA), a naturally occurring anticarcinogen found in dairy products, is a byproduct of incomplete ruminal biohydrogenation of unsaturated fatty acids. Our objective was to determine the effect of nonstructural carbohydrate sources, addition of full fat extruded soybeans as a source of unsaturated fatty acids, and possible interactions on the milk fat content of CLA. Cows (n = 20) were assigned to a 4 x 4 Latin square involving two sources of nonstructural carbohydrate, high starch (corn) or high pectin (citrus pulp), with or without addition of extruded soybeans. Milk yield was not affected by nonstructural carbohydrate source, but milk production was increased by 7.8 to 10.5% with dietary additions of extruded soybeans. Milk fat content did not differ between treatments, but fatty acid composition was affected. Cows fed extruded soybean diets had reduced concentrations of C8 to C16 fatty acids and increased concentrations of octadecenoic acids. Diets with extruded soybeans also resulted in more than a doubling in milk fat concentration and yield of CLA. Nonstructural carbohydrate source had only minor effects on CLA, and there was no interaction with extruded soybeans. Milk fat content of trans-C18:1 and CLA were closely related (r2 = 0.77). However, variation among cows was about threefold for each of the diets and rank order of individual cows differed among diets. Overall, we demonstrated that diet modification can be used to alter CLA content of milk fat, but there was substantial individual cow variation for all diets.     

The value of different fat supplements as sources of digestible energy for lactating dairy cows

The effects of fat supplements that differed in fatty acid composition (chain length and degree of saturation) and chemical form (free fatty acids, Ca salts of fatty acids, and triacylglyceride) on digestible energy (DE) concentration of the diet and DE intake by lactating cows were measured. Holstein cows were fed a control diet [2.9% of dry matter (DM) as long-chain fatty acids] or 1 of 3 diets with 3% added fatty acids (that mainly replaced starch). The 3 fat supplements were (1) mostly saturated (C18:0) free fatty acids (SFA), (2) Ca-salts of fatty acids (CaFA), and (3) triacylglyceride high in C16:0 fatty acids (TAG). Cows fed CaFA (22.8 kg/d) consumed less DM than cows fed the control (23.6 kg/d) and TAG (23.8 kg/d) diets but similar to cows fed SFA (23.2 kg/d). Cows fed fat produced more fat-corrected milk than cows fed the control diet (38.2 vs. 41.1 kg/d), mostly because of increased milk fat percentage. No differences in yields of milk or milk components were observed among the fat-supplemented diets. Digestibility of DM, energy, carbohydrate fractions, and protein did not differ between diets. Digestibility of long-chain fatty acids was greatest for the CaFA diet (76.3%), intermediate for the control and SFA diets (70.3%), and least for the TAG diet (63.3%). Fat-supplemented diets had more DE (2.93 Mcal/kg) than the control diet (2.83 Mcal/kg), and DE intake by cows fed supplemented diets was 1.6 Mcal/d greater than by cows fed the control, but no differences were observed among the supplements. Because the inclusion rate of supplemental fats is typically low, large differences in fatty acid digestibility may not translate into altered DE intake because of small differences in DM intake or digestibility of other nutrients.     

Transfer of dietary zinc and fat to milk--evaluation of milk fat quality, milk fat precursors, and mastitis indicators

The present study demonstrated that the zinc concentration in bovine milk and blood plasma is significantly affected by the intake of saturated fat supplements. Sixteen Holstein cows were used in a 4 × 4 Latin square design with 4 periods of 12 d, and 4 dietary treatments were conducted. A total mixed ration based on corn silage, grass-clover silages, and pelleted sugar beet pulp was used on all treatments. A high de novo milk fat diet was formulated by adding rapeseed meal and molasses in the total mixed ration [39 mg of Zn/kg of dry matter (DM)], and a low de novo diet by adding saturated fat, fat-rich rapeseed cake, and corn (34 mg of Zn/kg of DM). Dietary Zn levels were increased by addition of ZnO to 83 and 80 mg of Zn/kg of DM. Treatments did not affect daily DM intake, or yield of energy-corrected milk, milk fat, or milk protein. The high de novo diet significantly increased milk fat percentage and milk content of fatty acids with chain length from C6 to C16, and decreased content of C18 and C18:1. Treatments did not influence milk free fatty acids at 4°C at 0 or 28 h after milking. The average diameter of milk fat globules was significantly greater in milk from cows offered low de novo diets. Furthermore, the low de novo diet significantly increased the concentration of nonesterified fatty acids and d-β-hydroxybutyrate in blood plasma, the latter was also increased in milk. Treatments did not affect the enzyme activity of lactate dehydrogenase and N-acetyl-β-d-glucosaminidase in milk or the activity of isocitrate dehydrogenase and malate dehydrogenase in blood plasma. The low de novo diet significantly increased plasma Zn and milk Zn content, whereas dietary Zn level did not in itself influence these parameters. This indicates that the transfer of fat from diet to milk might facilitate transfer of Zn from diet to milk.     

Effects of hard fats on in vitro and in vivo rumen fermentation, milk production and reproduction in dairy cows

Adding 0, 5, 15, and 20% of substrate as prilled or unprilled fatty acids [palmitic (47 to 48%), stearic (36 to 37%), and oleic (14%) acids] to an in vitro rumen fermenter had no effect on total VFA production. Acetate:propionate ratio was reduced by fatty acid concentrations of 15 and 20% (prilled and unprilled). In a 4 x 4 Latin square, increasing dietary prilled fatty acids (0, 3, 6, or 9% of DM) decreased DM intake, increased percentage of milk fat, and had no effect on percentage of milk protein. Milk volume and FCM increased with 3% but decreased with 6 and 9% dietary fatty acids. Rumen fluid acetate:propionate decreased with increasing dietary fatty acids. Holstein cows in three herds in Pennsylvania and Friesian cows in an Israeli herd were assigned randomly to receive, from 0 to 110 to 150 d postcalving, diets containing 0 or 2% of DM prilled fat. In Israel, dietary fat increased milk yield, FCM, and fat percentage during the first 90 d postcalving. In Pennsylvania, prilled fat had variable effects on milk composition and little effect on milk yield and FCM. Conception rate was improved in cows consuming rations containing prilled fat: first service, 59.1 versus 42.6%; all services, 59.3 versus 40.7%. The inclusion of prilled fat at 2% of DM in dairy cattle rations had slight effects on rumen fermentation, variable effects on milk yield and composition, and beneficial effects on conception rate.     

Lactational responses of dairy cows fed unsaturated dietary fat and receiving bovine somatotropin.

Feeding unsaturated dietary fat to lactating dairy cows receiving bST may effectively alter the fatty acid composition of milk fat. This was tested using 16 Holstein cows assigned to one of four treatments during midlactation. Treatments were control, control diet with 15.5 mg of bST/d per cow, dietary fat from sunflower seeds and bST, or dietary fat from safflower seeds and bST. Diets were formulated to contain 19% CP and contained 25% corn silage, 25% alfalfa hay, and 50% concentrate mix on a DM basis. Milk yield was not significantly higher when bST was administered and increased with added fat diets (29.5, 32.7, 40.0, and 34.1 kg/d for the control, control with bST, sunflower seed with bST, and safflower seed with bST treatments, respectively). Percentage of milk fat was similar for all treatments. Concentrations of long-chain and unsaturated fatty acids in milk were increased slightly by bST and substantially with added fat. Milk protein percentages were not influenced by bST but were reduced by approximately .2 unit with added fat. Added unsaturated dietary fat coupled with bST increased milk yield and produced a greater concentration of unsaturated fatty acids in milk.     

Effect of dietary fat type on meat quality and fatty acid composition of various tissues in growing-finishing swine

Thirty-six castrated male growing pigs were used to study the effect of dietary beef tallow (BT) versus sunflower oil (SO) on meat quality and fatty acid composition of various tissues. The diets used contained either 5% (w/w) of the variable fat source. The fat type had no significant effect on carcass traits (carcass weight, back-fat thickness, fat-lean ratio) and meat quality (colour, pH(1), pH(U), drip losses, cooking losses, shear force, sacromere length, loin moisture, loin marbling). The diet with SO instead of BT significantly increased the incorporation of polyunsaturated fatty acids in adipose tissues, loin and liver at the expense of the sum of saturated and monounsaturated fatty acids. In erythrocytes, the diet containing SO raised the contents of saturated and polyunsaturated fatty acids and lowered that of monounsaturated fatty acids. In particular, the SO diet produced an increase in the content of linoleic acid (C18:2n-6) in the various tissues. It is concluded that feeding a diet with SO instead of BT altered the fatty acid composition of tissues without simultaneously affecting various characteristics of meat quality.     

Effect of dietary lipid source on conjugated linoleic acid concentrations in milk fat

Conjugated linoleic acids (CLA) found in ruminant milk fat are a byproduct of incomplete biohydrogenation of lipids by ruminal bacteria. We examined the effect of different dietary fat supplements and processing methods on CLA. In trial 1, dietary supplements of Ca salts of fatty acids from canola oil, soybean oil, and linseed oil increased CLA content of milk fat by three- to fivefold over the control diet. Trials 2 and 3 examined the effect of processing methods for heat treatment of full fat soybeans. In trial 2, extrusion, micronizing, and roasting resulted in two- to threefold greater concentrations of CLA in milk fat than the control diet (raw ground soybeans). In trial 3, different temperatures of extrusion (120, 130, and 140 degrees C) increased the CLA content of milk fat to a similar extent; CLA averaged 19.9 mg/g of fatty acids for the extrusion treatments compared with 4.2 mg/g of fatty acids for the control diet (raw ground soybeans). Fish oil (200 and 400 ml/d) was examined in trial 4 and both levels resulted in CLA concentrations in milk fat that were about threefold greater than the control diet. In trial 5, grain and silage from a high oil corn hybrid increased the CLA content of milk fat; however, responses were modest with the CLA concentration (mg/g of fatty acids) averaging 4.6 and 2.8 for diets with high oil hybrid and normal hybrid, respectively. Similarly, dietary supplements of animal fat byproducts (tallow plus yellow grease; trial 6) resulted in modest increases in the CLA content of milk fat. Overall, several dietary manipulations involving lipid sources and processing methods were identified that allow for a marked increase in the conjugated linoleic acid content of milk fat.     

Performance and fat quality of heavy pigs fed maize differing in linoleic acid content

Maize shows wide differences in linoleic acid due both to total lipid content and to fatty acid profile. Therefore, diets containing the same high maize percentage (up to 55%) can differ in linoleic acid content and lead to subcutaneous fats of differing suitability for raw ham curing. Two trials were performed on heavy pigs; in the first, 60 pigs (body weight 48.7 ± 5.1 kg) were fed three diets made using three maize batches differing in linoleic acid due to different total lipid content, in the second trial, 40 pigs (live weight 70.4 ± 3.4 kg) were fed two diets made using two maize batches differing in linoleic acid due to their fatty acid profile. Pigs were slaughtered at 170 kg of live weight. In both trials, the growth and slaughtering performance did not differ. In the first trial the three diets lead to a different content of linoleic acid both in subcutaneous (low linoleic vs medium linoleic vs high linoleic P  0.01) and intramuscular fat (low linoleic vs high linoleic P  0.05). In the second trial different linoleic acid content was observed for subcutaneous fat (P  0.01) but not for intramuscular fat. To formulate diets for heavy pigs, it is crucial to know the linoleic acid content of the maize used, because differences of only 0.3% can lead to significant differences in fatty acids composition of depot fats.     

Effect of added dietary fat and bovine somatotropin on the performance and metabolism of lactating dairy cows

Four early lactation Holstein cows (44 to 105 d postpartum) were used in a 4 X 4 Latin square experiment in a 2 X 2 factorial arrangement of treatments to study effects of added dietary fat and/or bovine somatotropin on performance and metabolism. Treatments were: 1) control diet plus placebo injection; 2) 5% added dietary fat (hydrolyzed blend of animal and vegetable fat) + placebo injection; 3) control diet + 50 IU bovine somatotropin/d; and 4) 5% added dietary fat + 50 IU bovine somatotropin/d. Dietary fat reduced dry matter intake (21.6 vs. 22.7 kg/d) and elevated plasma triglycerides (34.7 vs. 29.2 mg/100 ml). Injection of somatotropin lowered blood urea nitrogen, increased plasma free fatty acids, and increased plasma somatotropin. Milk production, milk fat percent, and 4% FCM production were increased by the injection of somatotropin. Milk protein percent was decreased (3.30 vs. 3.44%) with added fat and tended to be lower with somatotropin. The percentage of short-chain fatty acids (C6 to C14) in milk fat decreased with added fat while the percentage of stearic and oleic acids in milk fat increased. Production responses for fat plus somatotropin and somatotropin treatments were similar. Under the conditions of this study, the addition of dietary fat with injection of somatotropin had little effect on production parameters compared with that found with somatotropin alone.     

Responses of milk fat composition to dietary fat or nonstructural carbohydrates in Holstein and Jersey cows

Milk fat from Jersey cows contains less oleic acid (cis-C18:1) and more short- and medium-chain fatty acids than does milk fat from Holstein cows. The objective of this experiment was to determine responses in milk fat composition when Jersey and Holstein cows were fed diets either high (37% of dry matter) or low (27% of dry matter) in content of nonstructural carbohydrates (NSC) and supplemented with either 0 or 2.5% (of dry matter) of a mostly saturated fat source. Four Holstein cows and four Jersey cows were used in a Latin square design with 28-d periods; diets were in a 2 x 2 factorial arrangement. Fat supplementation decreased contents of fatty acids synthesized de novo within the mammary gland and increased contents of C18:0 and cis-C18:1. Low-NSC diets tended to increase C16:0 and to decrease C18:0, cis-C18:1, and C18:3. Despite the differences in fatty acid composition between breeds, both breeds generally responded similarly to dietary treatments. An interaction of breed and fat indicated that the content of cis-C18:1 in milk fat was increased more by supplemental fat in Holsteins than in Jerseys. Interactions of breed x fat and breed x carbohydrate type showed that the ratio of cis-C18:1 to C18:0 decreased when Jerseys were supplemented with fat but increased for Holsteins, and decreased when Jerseys were fed the low-NSC diet but increased when Holsteins were fed low NSC. The data are consistent with the hypothesis (Beaulieu and Palmquist, 1995, J. Dairy Sci. 78:1336-1344) that mammary activity of stearoyl-coenzyme A desaturase is lower in Jerseys than in Holsteins.     

Dietary fat and nitrogen composition of milk from lactating cows

Effects of dietary fat on milk composition, particularly milk N, were evaluated in lactating dairy cows at two stages of lactation. Complete mixed diets containing 0, 3.5, or 7% of the diet DM as animal fat were fed to 12 cows in a 3 X 3 Latin square. Cows were divided into two status categories based on stage of lactation resulting in two squares of early and two of late lactation cows. Percentages of fat, solids, lactose, and protein were decreased and ash increased in the milk of cows fed the 7% fat diet. Percent of casein N was elevated while nonprotein N was depressed by fat fed in diet. Percentage of solids and protein was higher and lactose lower for cows in late lactation than for those in early lactation. Dietary fat reduced the proportion of short-chain fatty acids in milk fat and increased C18:0 and C18:1 fatty acids. Digestibility of DM, energy, and fiber was not significantly affected by dietary fat, but estimates decreased with increased dietary fat. Cows in late lactation had a higher digestibility of dietary fractions than early lactation cows even though intakes of DM were similar.