Associations between hepatic metabolism of propionate and palmitate in liver slices from transition dairy cows.

Multiparous Holstein cows (n=95) were used to evaluate changes in hepatic propionate and palmitate metabolism and liver composition over time during the transition period, along with the relationships of these variables with cumulative increases in nonesterified fatty acids and ß-hydroxybutyrate during the periparturient period. Data from 3 previous experiments were used to address the study objectives, accounting for a total of 95 multiparous Holstein cows. Liver slices from biopsies on d -21, 1, and 21 relative to parturition were used to determine conversion of [1-(14)C]palmitate to CO2 and esterified products (EP) and the conversion of [1-(14)C]propionate to CO2 and glucose. Hepatic glycogen content was highest on d -21 and was 26.9 and 36.5% of prepartum values on d 1 and 21, respectively. Liver triglyceride content was lowest at d -21 and was 271 and 446% of prepartum values on d 1 and 21, respectively. We detected no difference in the capacity for the liver to oxidize [1-(14)C]palmitate to CO2 between d -21 and d 1; however, on d 21, oxidation was 84% of prepartum values. The capacity of the liver to convert [1-(14)C]palmitate to EP was 148 and 139% of prepartum values on d 1 and 21, respectively. The capacity of liver to convert [1-(14)C]propionate to CO2 was 127 and 83% of prepartum values on d 1 and 21, and the capacity of liver to convert [1-(14)C]propionate to glucose was 126 and 85% of prepartum values on d 1 and 21, respectively. Correlation relationships suggest that overall, cows with elevated prepartum liver triglyceride content had elevated triglycerides throughout the transition period along with increased [1-(14)C]palmitate oxidation and conversion to EP and a decreased propensity to convert [1-(14)C]propionate to glucose. Cows with increased [1-(14)C]propionate oxidation had increased conversion of [1-(14)C]propionate to glucose throughout the transition period. Overall, conditions that lead to impairments in fatty acid metabolism during the transition period appear to be associated with impaired postpartum hepatic propionate metabolism.

Feeding 2-hydroxy-4-(methylthio)-butanoic acid to periparturient dairy cows improves milk production but not hepatic metabolism.

Forty-eight Holstein cows, entering second or later lactation, were utilized to determine the effects of 2-hydroxy-4-(methylthio)-butanoic acid (HMB) on milk production, hepatic lipid metabolism, and gluconeogenesis during the periparturient period. Cows were fed one of 3 diets as TMR starting 21 d before expected calving. These diets contained 0 (the basal diet), 0.09 (+HMB), or 0.18 (++HMB)% HMB. From parturition to 84 DIM, cows were fed diets that contained 0, 0.13, or 0.20% HMB. Prepartum and postpartum dry matter intakes were similar among cows fed the basal diet, +HMB and ++HMB. There was a quadratic effect on milk yield such that cows fed +HMB had the greatest milk yield; yields of milk by cows fed the basal diet and ++HMB were similar. This led to trends for increased yields of 3.5% fat-corrected milk and total solids when cows were fed +HMB. Percentages of fat, protein, and total solids in milk were not affected by treatment. Despite differences in milk yield, calculated energy balance was not affected by treatment. Plasma concentrations of NEFA, beta-hydroxybutyrate, and glucose were not different among treatments. Liver triglyceride content was similar among treatments on d 1 postpartum and was increased for cows consuming +HMB on d 21 postpartum compared with the other dietary treatments. Capacities for metabolism of [1-14C]palmitate by liver slices in vitro were not affected by treatment; however, conversion of [1-14C]propionate to CO2 and glucose decreased as the amount of HMB consumed by cows increased on d 21 postpartum. Cows consuming +HMB had greater days to first ovulation compared with cows consuming the basal diet and ++HMB as measured by plasma progesterone concentrations. These data suggest that adding HMB to low Met diets to achieve a predicted Met supply of approximately 2.3% of metabolizable protein supply is beneficial for increasing milk production but does not appear to benefit hepatic energy metabolism during early lactation.

Effects of propylene glycol or fat drench on plasma metabolites, liver composition, and production of dairy cows during the periparturient period.

Forty-eight Holstein cows were used to determine the effects of short-term oral drenches of propylene glycol (PG) and Ca-soaps of palm oil fatty acids (fat) on plasma concentrations of key metabolites, liver composition, and milk production during the first 3 wk of lactation. Treatments (2 x 2 factorial arrangement) given orally once daily for the first 3 d postpartum were water (control), 500 ml of PG, 454 g of fat, or 500 ml of PG plus 454 g of fat. All treatments were administered as a total volume of 1.9 L. Administration of PG decreased concentrations of nonesterified fatty acids (NEFA) in plasma during the first 7 d and the first 21 d postpartum and tended to decrease concentrations of beta-hydroxybutyrate during the first 7 d postpartum. Concentrations of insulin in plasma were not affected by treatment. Administration of either PG or fat increased plasma glucose and liver glycogen concentrations compared to the control or PG plus fat treatments. Concentrations of triglycerides in liver were not affected by treatment. Administration of PG did not affect dry matter intake or milk yield and composition during the first 3 wk postpartum; however, cows drenched with fat tended to have lower dry matter intake and milk yield during the first 3 wk of lactation. Short-term drenching of PG effectively decreased NEFA concentrations in plasma during early lactation; however, data do not support administration of fat via drench to early lactation cows and concurrent administration of dietary fat appears to blunt the metabolic response of cows to PG.

Liver metabolism and production of cows fed increasing amounts of rumen-protected choline during the periparturient period.

Forty-eight multiparous Holstein cows were fed treatments consisting of either 0, 45, 60, or 75 g/d of a rumen-protected choline (RPC) source in a completely randomized design from 21 d before expected calving to 63 d postpartum to determine whether choline supplementation to the diet would affect hepatic fatty acid and glucose metabolism, key metabolites in plasma, and cow performance. Dry matter intake (DMI), milk yield, body condition score, and body weights (BW) were similar for cows receiving the four treatments. Feeding RPC tended to increase yields of milk fat, 3.5% fat-corrected milk, and total solids. Plasma concentrations of nonesterified fatty acids and beta-hydroxybutyrate were not different among cows fed the four treatments. Concentrations of triglycerides in liver were similar, but concentrations of glycogen in liver increased as cows consumed increasing amounts of RPC. Hepatic capacity for storage of [1-(14)C]palmitate as esterified products within liver slices tended to decrease as the amount of RPC consumed by cows increased; however, effects of treatment on hepatic capacity for oxidation of [1-(14)C]palmitate to CO2 were not significant. These data imply that choline may increase the rate of very low density lipoprotein synthesis and secretion of esterified lipid products from liver. Hepatic capacities for conversion of [1-(14)C] propionate to CO2 and to glucose in liver were similar among cows fed the four treatments. Collectively, these results suggest that hepatic fatty acid metabolism and cow performance are responsive to increasing the supply of choline during the periparturient period.

Systems to evaluate the protein quality of diets fed to lactating cows.

Ten multiparous and 5 primiparous cows (62 +/- 33 d in milk) were used in a replicated 5 x 5 Latin square design to investigate three dietary protein evaluation systems for lactating cows: milk protein score, Cornell Net Carbohydrate and Protein System, and an increase in Lys and Met to supply 15 and 5% of the predicted total essential amino acids (AA) in duodenal digesta, respectively. Five isonitrogenous diets were evaluated differently by the three systems. The milk protein score indicated that formulations of diets 2, 3, 4, and 5 were of equal quality and better for milk protein synthesis than was diet 1. The Cornell Net Carbohydrate and Protein System indicated that diets 3, 4, and 5 contained adequate AA, but diets 1 and 2 were deficient in Lys and Met. The increase in Lys and Met supply indicated that only diets 3 and 5 provided adequate Lys and Met. The dry matter intake, energy-corrected production, and fat production were lower, and 3.5% fat-corrected milk production tended to be lower, for cows consuming diets 4 and 5 than for cows consuming diets 2 and 3. Cows consuming diet 1 had lower percentages of crude protein, true protein, and casein N in their milk than did with cows consuming all other diets. Cows fed diets 3 and 5 had higher percentages of protein in milk than did cows fed other diets. Protein production was greater, and casein N tended to be greater, for cows consuming diet 3 than for cows consuming diet 2. Although all three systems had validity, the system by which Lys and Met were increased most accurately predicted milk protein percentages and production.

Ruminal degradation, amino acid composition, and estimated intestinal digestibilities of four protein supplements.

Blood meal, canola meal, corn gluten meal, and menhaden fish meal were weighed into dacron bags for incubation in the rumens of two ruminally cannulated Holstein cows on 3 d for 0, 3, 6, 12, 18, and 24 h. Both the original feeds and the residues remaining after 12 h were analyzed for amino acid (AA) content. Canola meal was degraded the most extensively in the rumen, and blood meal was degraded the least extensively. Intestinal digestibilities estimated using an enzymatic in vitro technique were all high; canola meal was estimated to have the lowest intestinal digestibility, and corn gluten meal was estimated to have the highest intestinal digestibility. The AA profile of the 12-h residues differed only slightly from the AA profile of the original protein supplements. A comparison of the AA profiles of feed residues with milk protein showed that isoleucine was the first-limiting AA in blood meal, canola meal, and fish meal, and lysine was the first-limiting AA in corn gluten meal. Although canola meal was extensively degraded in the rumen, its 12-h residue still provided an estimated AA profile to the intestinal tract that was closest to the AA profile of milk protein. Blood meal and corn gluten meal are good sources of ruminally undegradable protein but are deficient in some AA and should probably be fed only in combination with other protein sources that complement their AA profiles.

Evaluation of corn distillers grains and ruminally protected lysine and methionine for lactating dairy cows.

Twelve multiparous Holstein cows averaging 57 d (36 to 77 d) postpartum at the start of the experiment were utilized in a replicated 4 x 4 Latin square design. Dietary protein supplements were 1) soybean meal, 2) soybean meal plus ruminally protected Lys and Met, 3) corn distillers grains, and 4) corn distillers grains plus ruminally protected Lys and Met. Dry matter intakes were lower for cows fed diets containing soybean meal than for cows fed diets containing corn distillers grains. Milk yield increased with the corn distillers grains (34.3, 34.0, 35.3, and 36.7 kg/d for cows fed diets 1 through 4, respectively), especially when supplemented with ruminally protected Lys and Met. Milk protein yield and percentage were increased by amino acid supplementation. Milk fat yield and percentage were unaffected by diet. The only milk protein fraction affected was nonprotein N, which was lower in the milk of cows fed corn distillers grains. Lysine, Met, and Phe were indicated as the most limiting amino acids for all diets when using amino acid extraction efficiency and transfer efficiency to indicate limiting amino acids. When corn distillers grains were supplemented with ruminally protected Lys and Met, milk yield and milk protein yield and percentage increased because the diet containing corn distillers grains was probably deficient in Lys.

Response of cows fed a low crude protein diet to ruminally protected methionine and lysine.

Ten cows (mean = 128 DIM) were utilized in a replicated 5 x 5 Latin square design and fed diets formulated to supply adequate (18% CP) or inadequate (14% CP) Met and Lys. A prototype supplement of ruminally protected Met and Lys was added to the 14% CP diet to provide 0, 50, 100, and 150% of the predicted deficiency of Met and Lys. The DMI; yields of milk, 3.5% FCM, total N, protein N, and whey N; plasma concentrations of Arg, Cit, His, Ile, Leu, Orn, Phe, Pro, Tyr, Val, and urea N were greater for cows fed the 18% CP diet. Supplementing ruminally protected Met and Lys to the 14% CP diet did not affect DMI or yields of milk, 3.5% FCM, milk CP, and milk SNF. Milk fat yield was affected quadratically because it was greater when 0 or 150% of the deficiency of Met and Lys was supplied. Percentages of CP and casein N in milk increased linearly as cows were fed increasing amounts of ruminally protected Met and Lys. Plasma concentrations of urea N, Met, and Lys increased when ruminally protected Met and Lys were fed; however, other nutrients probably were limiting for synthesis of milk and milk protein when cows were fed a 14% CP diet because yields of each were not increased by ruminally protected Met and Lys.