Effects of magnesium source and monensin on nutrient digestibility and mineral balance in lactating dairy cows.

The interaction of monensin and 2 supplemental Mg sources (MgO and MgSO4) on total-tract digestion of minerals and organic nutrients and milk production was evaluated in lactating dairy cattle. Eighteen multiparous Holstein cows (139 ± 35 DIM) were used in a split-plot experiment with 0 or 14 mg/kg diet DM of monensin as the whole-plot treatments and Mg source as split-plot treatments. During the entire experiment (42 d), cows remained on the same monensin treatment but received a different Mg source in each period (21 d) of the Latin square. Diets were formulated to contain 0.35% Mg with about 40% of that provided by MgO or MgSO4. Diets were formulated to have similar concentrations of major nutrients and K concentrations were elevated (2.1% of DM) with K2CO3 to create antagonism to Mg absorption. Apparent digestibility was measured by total collection of urine and feces. Supplemental MgSO4 decreased DMI (26.9 vs. 25.7 kg/d) and tended to decrease milk yield (40.2 vs. 39.3 kg/d), but increased the digestibility of OM (68.3 vs. 69.2%) and starch (91.9 vs. 94.4%) compared with MgO. Feeding MgSO4 with monensin decreased NDF digestibility compared with other treatments (46.7 vs. 50.2%). That diet also had decreased apparent absorption of Mg compared with diets without monensin (15.6 vs. 19.2%), whereas MgO with monensin had greater apparent absorption of Mg (23.0%) than other treatments. Cows consuming MgSO4 had increased apparent Ca absorption (32.2 vs. 28.1%) and balance. A diet with MgSO4 without monensin increased the concentration of long-chain fatty acids in milk, suggesting increased mobilization of body fat or decreased de novo fatty acid synthesis in the mammary gland. Overall, when dietary Mg was similar, MgO was the superior Mg source for lactating dairy cattle, but inclusion of monensin in diets should be considered when evaluating Mg sources.

Effect of including canola meal and supplemental iodine in diets of dairy cows on short-term changes in iodine concentrations in milk.

The dietary requirement for iodine is based on thyroxine production, but data are becoming available showing potential improvements in hoof health when substantially greater amounts of I are fed. Feeding high amounts of I, however, can result in the milk having excessive concentrations of I. Canola meal contains goitrogenic compounds that reduce the transfer of I into milk. We hypothesized that including canola meal in diets would allow high supplementation rates of I without producing milk with unacceptable concentrations of I. Thirty midlactation Holstein cows were fed a diet with all supplemental protein from soybean meal (0% of diet dry matter as canola meal) or with all supplemental protein from canola meal (13.9% canola meal). A third treatment has a mix of soybean meal and canola meal (3.9% canola meal). Within canola-meal treatment, cows were fed 0.5 or 2.0mg of supplemental I per kilogram of diet dry matter from ethylenediamine dihydroiodide. Cows were maintained on the canola treatment for the duration of the experiment but were changed from one I treatment to the other after 13d of receiving the treatment. Milk I concentration before the treatments started (cows fed 0.5mg/kg of I) averaged 272µg/L and increased within 22h after cows were first fed diets with 2mg/kg of I. As inclusion rate of canola meal increased, the concentration of I in milk decreased linearly. After 12d of supplementation, milk from cows fed 0.5mg/kg of I had 358, 289, and 169µg of I/L for the 0, 3.9%, and 13.9% canola-meal treatments. For cows fed 2.0mg/kg of I, milk I concentrations were 733, 524, and 408µg/L, respectively. Concentrations of I in serum increased with increased I supplementation, but the effect of canola meal was opposite of what was observed for milk I. Cows fed the highest canola-meal diets had the highest serum I whether cows were fed 0.5 or 2.0mg/kg of I. Feeding dairy cows diets with 13.9% canola meal maintained milk I concentrations below 500µg/L when diets were supplemented with 2mg/kg of I.

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.

Varying forage type, metabolizable protein concentration, and carbohydrate source affects manure excretion, manure ammonia, and nitrogen metabolism of dairy cows.

Effects of forage source, concentration of metabolizable protein (MP), and type of carbohydrate on manure excretion by dairy cows and production of ammonia from that manure were evaluated using a central composite experimental design. All diets (dry basis) contained 50% forage that ranged from 25:75 to 75:25 alfalfa silage:corn silage. Diets contained 10.7% rumen-degradable protein with variable concentrations of undegradable protein so that dietary MP ranged from 8.8 to 12%. Starch concentration ranged from 22 to 30% with a concomitant decrease in neutral detergent fiber. A total of 15 diets were fed to 36 Holstein cows grouped in 6 blocks. Each block was a replicated 3 x 3 Latin square resulting in 108 observations. Manure output (urine and feces) was measured using total collection, and fresh feces and urine were combined into slurries and incubated for 48 h to measure NH3-N production. Feces, urine, and manure output averaged 50.5, 29.5, and 80.1 kg/d, respectively. Manure output increased with increasing dry matter intake (approximately 3.5 kg of manure/kg of dry matter intake), increased concentrations of alfalfa (mostly via changes in urine output), and decreased concentrations of starch (mostly via changes in fecal output). The amount of NH3-N produced per gram of manure decreased with increasing alfalfa because excreted N shifted from urine to feces. Increasing MP increased NH3-N produced per gram of manure mainly because of increased urinary N, but increased fecal N also contributed to the manure NH3. Manure NH3-N production per cow (accounts for effects on manure production and NH3-N produced per unit of manure) was least and milk protein yields were maximal for diets with high alfalfa (75% of the forage), moderate MP (11% of diet dry matter), and high starch (30% of diet dry matter).

Relative bioavailability of all-rac and RRR vitamin E based on neutrophil function and total alpha-tocopherol and isomer concentrations in periparturient dairy cows and their calves.

The objective of this experiment was to determine whether source of supplemental alpha-tocopherol fed to periparturient dairy cows affects neutrophil function and vitamin E status of the cow and the neonatal calf. Starting 14 d before anticipated calving and continuing until 14 d post-parturition, cows were fed diets with no supplemental vitamin E or with 2,500 IU/d of vitamin E from all-rac alpha-tocopheryl acetate or RRR alpha-tocopheryl acetate. All-rac alpha-tocopherol contains equimolar amounts of all 8 stereoisomers, whereas the RRR contains only the RRR isomer. Concentrations of alpha-tocopherol in cow plasma, colostrum, milk, and blood neutrophils were greatest for the RRR treatment, intermediate for all-rac, and lowest for cows fed no supplemental vitamin E. The concentration of alpha-tocopherol in plasma of newborn calves was very low and not affected by treatment but after 6 feedings of their dam's colostrum or milk, concentrations in calf plasma followed the same treatment pattern as cow plasma. The number of bacteria phagocytized was greater by neutrophils from cows fed all-rac vitamin E than for the other 2 treatments, which resulted in a greater number of bacteria being killed. For cows fed all-rac vitamin E, the RRR isomer comprised about 20% of the alpha-tocopherol consumed but approximately 60% of the alpha-tocopherol in plasma and milk. This enrichment was caused mostly by an almost complete discrimination against the 2S isomers. Because all-rac alpha-tocopherol is 50% 2S isomers, these data suggest that 1 g of all-rac tocopheryl acetate is equivalent to 0.5 g of RRR tocopheryl acetate.

Effect of feeding propionibacteria on milk production by early lactation dairy cows.

This experiment was conducted to determine the effect of a direct-fed microbial agent, Propionibacterium strain P169 (P169), on rumen fermentation, milk production, and health of periparturient and early-lactation dairy cows. Starting 2 wk before anticipated calving, cows were divided into 2 groups and fed a control diet or the control diet plus 6 x 10(11) cfu/d of P169. Cows were changed to a lactation diet at calving, and treatments continued until 119 d in milk. Rumen fluid samples were taken about 1 wk before calving, and at 1 and 14 wk after calving. Cows fed P169 had lower concentrations of acetate (mol/100 mol of total volatile fatty acids) at all time points, greater concentrations of propionate on the first and last sampling points, and greater concentrations of butyrate on the first 2 time points. Concentrations of glucose in plasma and milk and plasma concentrations of beta-hydroxybutyrate were not affected by treatment. Cows fed P169 had greater concentrations of plasma nonesterified fatty acids on d 7 of lactation. The high nonesterified fatty acids at that time point was probably related to the high production of milk during that period by cows fed the additive. Cows fed P169 during the first 17 wk of lactation produced similar amounts of milk (44.9 vs. 45.3 kg/d, treatment vs. control) with similar composition as cows fed the control diet. Calculated net energy use for milk production, maintenance, and body weight change was similar between treatments, but cows fed the P169 consumed less dry matter (22.5 vs. 23.5 kg/d), which resulted in a 4.4% increase in energetic efficiency.

Effect of corn silage hybrid and metabolizable protein supply on nitrogen metabolism of lactating dairy cows.

This experiment was conducted to determine the effects of corn silage hybrid and supply of metabolizable protein (MP) on manure excretion and N metabolism by lactating dairy cows. Eight Holstein cows in midlactation (replicated 4 x 4 Latin square with 21-d periods) were fed 1 of 4 treatments, arranged factorially. Diets contained 55% corn silage made from a dual-purpose hybrid or a brown midrib (BMR) hybrid, and 45% concentrate that contained either a low or high concentration of rumen undegradable protein (altered by the addition of fish meal and treated soybean meal). Crude protein averaged 14.0 and 17.5% and supply of MP averaged 2,360 and 2,990 g/d for the low and high MP treatments (not affected by hybrid). Increasing supply of MP greatly increased urine output and tended to increase total manure output, whereas diets with BMR silage tended to reduce manure output. Increased MP supply increased daily excretion of manure N by 25% (465 vs. 374 g/d), fecal N by 27 g, and urinary N by 64 g. When the effect of N intake was removed, cows fed BMR silage excreted about 15 g/d less N via manure than cows fed the other silage. Rumen ammonia, volatile fatty acid concentrations, and pH were not affected by treatment. Dry matter intake (overall mean = 24.9 kg/d) tended to be increased with increased MP but was not affected by hybrid. Milk production for cows fed BMR was higher than for cows fed the dual-purpose hybrid (36.9 vs. 35.3 kg/d), but because of changes in fat concentration, yield of energy-corrected milk was not affected by treatment. The only interaction observed was increased yield of milk protein when BMR silage was combined with increased supply of MP.

Macromineral digestion by lactating dairy cows: estimating phosphorus excretion via manure.

Data from 8 experiments involving 39 diverse dietary treatments and 162 Holstein cows were used to derive equations that estimate manure excretion of P by lactating dairy cows. Within an experiment, diets were formulated to have similar P concentrations and to meet or slightly exceed standard recommendations for P. The data were generated from total collection digestion trials. The only sources of supplemental P used were dicalcium phosphate and monosodium phosphate. The concentration of dietary P ranged from 0.34 to 0.45% of dry matter (DM). Cows varied in milk production (8 to 59 kg/d), DM intake (12.4 to 30.5 kg/d), and P intake (45 to 133 g/d). Apparent digestibility of P averaged 40.4%, fecal output of P averaged 47 g/d, and apparent P retention averaged 4 g/d. Two equations were derived to estimate excretion of P via manure (g/d): 1) Manure P = -2.5 + 0.64 x P intake, and 2) Manure P = 7.5 + 0.78 x P intake - 0.702 x Milk; where P intake is in g/d and milk is kg/d. Both equations were evaluated using literature data, and both equations had acceptable accuracy for field use. The requirements for P of lactating dairy cows from the National Research Council (NRC) were also evaluated, and for most diets, those requirements were adequate based on retention of P.

Digestible energy values of diets with different fat supplements when fed to lactating dairy cows.

A total collection digestion trial using high producing lactating cows (average milk yield = 40.7 kg/d) was conducted to measure the effect of different fat supplements on dietary digestible energy (DE) concentrations and to calculate the DE value of the supplements. A diet with no supplemental fat, 2 diets with 1.75 or 3.5% (dry basis) Ca salts of palm fatty acids (Ca-PFA), and 2 diets with 1.6 or 3.2% hydrogenated triacylglycerides from palm oil (HPO) were fed in a 5 x 5 Latin square experiment with 28-d periods. Concentrations of supplemental long-chain fatty acids in the diets were 1.7 and 3.4% for the 2 supplementation rates. Dry matter intake was reduced when cows were fed the high concentration of Ca-PFA, but cows fed Ca-PFA produced more milk than cows fed the control diet or diets with HPO. The type or amount of fat supplementation did not affect measures of rumen fermentation or in situ fiber digestibility. Digestibility of energy, dry matter, and organic matter were higher for diets with Ca-PFA than for diets with HPO, mainly because of increased fatty acid digestibility. The dietary concentration of DE was similar between the control diet and diets with HPO (2.97 Mcal/kg), but it increased as the concentration of Ca-PFA increased (3.04 and 3.16 Mcal/kg for low and high supplementation rates). The calculated DE concentrations of the supplements averaged 7.3 and 3.1 Mcal/kg for Ca-PFA and HPO. The 2001 National Research Council dairy model accurately estimated DE concentrations in all diets (<1% difference).

Effect of dietary fat and vitamin E on alpha-tocopherol in milk from dairy cows.

Diets with different fat treatments and with 25, 125, or 250 IU of supplemental vitamin E (all-rac alpha-tocopheryl acetate)/kg of dry matter (DM) were fed for 28 d to midlactation Holstein cows to determine factors affecting concentrations of alpha-tocopherol in milk. Diets contained no supplemental fat or 2.25% added fat from roasted soybeans or tallow. Vitamin E treatment had no effects on production, but fat supplementation increased milk yield (37.2 vs. 35.1 kg/d). Cows fed RSB ate more DM (24.0 vs. 21.9 kg/d) and produced more milk fat than cows fed tallow. Supplemental fat increased plasma concentrations of alpha-tocopherol and cholesterol. Increased intake of alpha-tocopherol linearly increased concentrations of alpha-tocopherol in plasma but the rate of increase was 1.9 times greater when fat was fed. Plasma alpha-tocopherol concentrations were linearly related to concentrations in milk, but a change in plasma alpha-tocopherol resulted in a smaller change in milk alpha-tocopherol when fat was fed than when it was not. Fat treatment did not affect plasma alpha-tocopherol expressed relative to plasma cholesterol (mg alpha-tocopherol/g cholesterol) or relationships between plasma alpha-tocopherol/g of cholesterol and milk alpha-tocopherol. These data suggest that concentrations of alpha-tocopherol in milk are a function of the alpha-tocopherol enrichment of the plasma lipid fraction and enrichment of that fraction is saturable.

Effects of feeding diets based on silage from corn hybrids that differed in concentration and in vitro digestibility of neutral detergent fiber to dairy cows.

A dual-purpose hybrid and a hybrid selected for high neutral detergent fiber (NDF) concentration were harvested as corn silage. The dual-purpose silage (DPCS) had 42% NDF and 35.4% in vitro (30 h) NDF digestibility and the high fiber silage (HFCS) had 49% NDF and 40.1% in vitro NDF digestibility. Two diets (dry matter basis) had 45% DPCS or HFCS and 46% corn grain-based concentrate (dietary NDF was 29 and 32%, respectively), a third diet had 33% HFCS and 58% corn-based concentrate (27% dietary NDF), and a fourth diet had 33% DPCS and 58% concentrate that contained soybean hulls (32% dietary NDF). All diets contained 9% alfalfa silage. Diets were fed to eight midlactation Holstein cows in a 4 x 4 Latin square with 28 d periods. No differences among treatments were observed for milk yield (34.1 kg/d), dry matter intake (23.7 kg/d), and yield and concentration of milk protein. Cows fed the diet with 33% HFCS tended to have lower milk fat percentage than cows fed the 45% DPCS diet. Total digestible nutrients (measured using total collection) tended to be lower for the 33% DPCS diet than for the 45% DPCS diet. In vivo digestibility of NDF tended to be lower for the 33% HFCS diet than the 45% DPCS diet, but digestibility of starch in the two diets with HFCS was higher than the 45% DPCS diet. The lack of any substantial differences in responses suggest that the HFCS was equal to the DPCS when fed at 45% of the diet dry matter (53.5% total forage). When HFCS replaced DPCS so that NDF was similar between diets, milk fat percentage was reduced and ruminal propionate was increased. Increasing dietary NDF by adding soybean hulls to a diet based on DPCS reduced digestibility of dry matter, organic matter, and protein, and resulted in lower energy balance than the 45% DPCS diet.

Effect of oil content and kernel processing of corn silage on digestibility and milk production by dairy cows.

Corn silages were produced from a high oil corn hybrid and from its conventional hybrid counterpart and were harvested with a standard silage chopper or a chopper equipped with a kernel processing unit. High oil silages had higher concentrations of fatty acids (5.5 vs. 3.4% of dry matter) and crude protein (8.4 vs. 7.5% of dry matter) than the conventional hybrid. Processed silage had larger particle size than unprocessed silage, but more starch was found in small particles for processed silage. Dry matter intake was not influenced by treatment (18.4 kg/d), but yield of fat-corrected milk (23.9 vs. 22.6 kg/d) was increased by feeding high oil silage. Overall, processing corn silage did not affect milk production, but cows fed processed conventional silage tended to produce more milk than did cows fed unprocessed conventional silage. Milk protein percent, but not yield, was reduced with high oil silage. Milk fat percent, but not yield, was higher with processed silage. Overall, processed silage had higher starch digestibility, but the response was much greater for the conventional silage hybrid. The concentration of total digestible nutrients (TDN) tended to be higher for diets with high oil silage (71.6 vs. 69.9%) and tended to be higher for processed silage than unprocessed silage (71.7 vs. 69.8%), but an interaction between variety and processing was observed. Processing conventional corn silage increased TDN to values similar to high oil corn silage but processing high oil corn silage did not influence TDN.