Balancing diets for lysine (Lys) and methionine (Met) in dairy rations is becoming a regular practice in today’s industry. In order to be able to use rumen-protected AA (RPAA) in those diets a method to assess the efficacy and bioavailability needs to be proposed. The objective of the following studies was to propose the acceptance of the plasma free AA dose-response technique as a standardized methodology for evaluating RPAA in lactating dairy cows. Thirteen dose-response Latin square studies using ruminally-cannulated multiparous Holstein cows were conducted. Regression analysis of the slopes against the difference between plasma Lys concentration of basal and highest infusion amount, plasma Lys concentration at highest infusion amount, basal plasma Lys concentration, days in milk, milk yield, milk true protein concentration and yield, and dry matter intake, indicated the factor that most affected the magnitude of the slope, and hence the technique’s precision, was the difference between plasma Lys concentration of basal and highest infusion amount. It was concluded that the plasma free AA dose-response technique is sensitive to increasing amounts of absorbed Lys, and therefore is an appropriate technique for evaluating RP-Lys supplements.
The objectives of the second study were: 1) to confirm linearity in plasma Met response by infusion or rumen protected Met (RP-Met) from Smartamine ® M ( Adisseo, Alpharetta, GA) 2) to determine if using the plasma concentration of Met or total sulfur AA (TSAA) expressed in micromolar basis is the more accurate response parameter, and 3) to determine if expressing the plasma concentrations of Met and TSAA as percentages of total AA concentration (subtracted from Met or TSAA concentration, respectively) would reduce the variability of estimating Met bioavailability. Ten rumen-cannulated Holstein cows were fed a Met-deficient basal diet and assigned to a replicated 5 × 5 Latin square design with 7-d experimental periods. Treatments were 0, 12, and 24 g/d of abomasally infused Met and 15 and 30 g/d of fed Met from a RP-Met supplement. Slopes for infused and fed Met were 1.40 and 1.04 for plasma Met expressed on a micromolar basis, and 0.066 and 0.049 for plasma Met expressed as a percentage of total AA. Corresponding values for plasma TSAA were 2.00 and 1.64 on a micromolar basis, and 0.104 and 0.084 when expressed as a percentage of total AA. Estimates of bioavailability for the RP-Met supplement ranged from 74.4 to 81.8%. We conclude that the plasma free AA dose-response technique is precise, and as Met is a precursor to other sulfur AA, the concentration of TSAA expressed as a percentage of total AA should be used when calculation bioavailability of RP-Met products.
Determination of bioavailability for RPAA using the plasma free AA dose-response method has relied on blood sampling 2, 4, 6, and 8 h after the morning feeding the last 3 d of each period in Latin square experiments with cows fed every 8 h. The objective of the third study was to determine if this sampling protocol captured the diurnal variation in plasma Met concentrations that exists and adequately measures the bioavailability of Met in a RP Met supplement Smartamine M. Five multiparous lactating Holstein cows were used in a 5 × 5 square design with 7-d periods. Treatments were 0, 12, and 24 g/d of abomasally infused Met and 15 and 30 g/d of fed Met from a RP-Met. Blood samples were collected via jugular catheters every 2 h starting at 0700 h on d 5, 6, and 7 of each period. There was no diurnal variation in plasma Met concentrations (P = 0.18). Plasma Met concentrations were averaged across days for the 2-8, 10-16, 18-24, and 2-24 h blood sampling periods. The bioavailabilities of Met in RP-Met averaged 84.7, 84.4, 90.0, and 84.6% for the 2-8, 10-16, 18-24, and 2-24 h sampling periods, respectively. The similarity in estimates of bioavailability for RP-Met for the 2-8 and 2-24 h sampling periods indicates that our original blood sampling protocol (i.e., 2-8 h) is adequate for determining the bioavailability of RP-Met.
The objective of the fourth study was to use the plasma free AA dose-response method to compare the bioavailability of Met in Smartamine M (Adisseo, Antony, France) from the new (SM1) and original (SM2) production plants along with 2 additional commercially available RP-Met products, Mepron (MPN; Evonik Ind., Kennesaw, GA) and AminoShure-M (ASM; Balchem Corp., New Hampton, NY). Ten multiparous lactating Holstein cows, fed Met-deficient diets, were used in a replicated 5 × 5 Latin square design with 7-d periods. Treatments included a negative control with no added RP-Met (CON) or 30 g of Met supplied by the 4 RP-Met products. Plasma total sulfur AA concentrations (µM) were greatest for cows fed SM1 and SM2 and intermediate for MPN and ASM compared to CON. Based on the published bioavailability of Met in SM2 (80%), the calculated bioavailabilities of Met in SM1, MPN, and ASM were 80, 23, and 17%.
|Commitee:||Brito, Andre, Erickson, Peter, Lapierre, Helene, Schwab, Charles, Sloan, Brian|
|School:||University of New Hampshire|
|Department:||Animal and Nutritional Sciences|
|School Location:||United States -- New Hampshire|
|Source:||DAI-B 78/07(E), Dissertation Abstracts International|
|Subjects:||Animal sciences, Nutrition|
|Keywords:||Amino acids, Bioavailability, Lysine, Methionine, Protected, Ruminant|
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