This study assessed relative bioavailability of guanidinoacetic acid (GAA) in cattle. Seven ruminally cannulated Holstein steers (initial body weight of 280 kg) were used in an experiment with a 5 × 5 Latin square design; the 2 additional steers received a treatment sequence identical to 2 steers in the Latin square. Treatments were: control (no GAA, water infusion), ruminal infusion of 10 or 20 g/d GAA, and abomasal infusion of 10 or 20 g/d GAA, with all infusions delivered continuously. Periods were 7 d in length, and on d 7 blood and urine samples were collected to determine concentrations of GAA and its associated metabolites. Plasma creatine concentrations increased linearly (P < 0.01) with GAA infusion to the abomasum and tended to increase linearly (P = 0.06) when GAA was infused ruminally. Urinary creatine concentrations increased linearly with increasing amounts of GAA infused in the abomasum (P < 0.01) and the rumen (P < 0.05). There were no significant effects of GAA infusion to either the abomasum or rumen on plasma or urinary concentrations of GAA. Plasma creatinine concentrations were not affected by GAA infusion to the abomasum or rumen. Urinary creatinine concentrations decreased when GAA was infused abomasally (P < 0.05). Because plasma and urinary creatine concentrations yielded the statistically strongest linear responses, they were selected as the primary response criteria for quantifying ruminal escape of GAA. Calculated by slope-ratio methodology, estimates for ruminal escape of GAA based on plasma creatine and urinary creatine concentrations were 47% and 49%, respectively. Ruminally infused GAA was about half as effective as abomasally infused GAA in elevating plasma and urinary concentrations of creatine.

Six ruminally cannulated Holstein steers (256 ± 14 kg) were used in a 6 × 6 Latin square design to assess effects of guanidinoacetic acid (GAA) supplementation on N retention and methionine (Met) methyl group flux in growing cattle fed corn-based diets. Factorial treatments were 2 levels of Met (0 or 5 g/d) and 3 levels of GAA (0, 7.5, or 15 g/d) delivered by continuous abomasal infusion. Periods were 10 d in length and included 6 d of treatment adaptation, 3 d for total fecal and urine collections, and 1 d for blood sampling and flux measurements. Urinary N linearly increased (P < 0.01) with GAA supplementation and decreased (P < 0.05) with Met supplementation. Fecal N excretion was unaffected (P ≥ 0.42) by treatment. Retained N was not affected by GAA supplementation, but it was increased (P < 0.01) by Met supplementation. Use of methionine for transmethylation reactions, as well remethylation of homocysteine, was not affected by GAA supplementation when Met was not supplemented, but tended to be linearly increased by GAA supplementation when Met was supplemented (GAA-linear × Met interaction; P = 0.07), with the increases matching the amount of GAA provided. This response suggests that methylation reactions for compounds other than GAA were reduced by GAA supplementation when Met supply was deficient. Plasma concentrations and urinary excretion of creatine increased linearly (P = 0.03 and P = 0.06, respectively) when GAA was supplemented. There was a linear increase (P < 0.01) in urinary GAA excretion with GAA supplementation. Neither plasma concentration nor urinary excretion of creatinine was affected (P ≥ 0.17) by treatment. No treatment differences (P ≥ 0.13) were observed for plasma haptoglobin concentrations. Plasma urea-N linearly increased (P < 0.05) with GAA supplementation. Concentrations of Met and taurine increased (P < 0.05) when Met was supplemented. Plasma arginine was greatest at the intermediate level of supplemental GAA (quadratic, P < 0.05). The increase in N retention when Met was supplemented demonstrates Met was limiting in the corn-based diet. Supplementation of GAA alone or with Met as a methyl donor did not increase N retention in growing steers, perhaps because creatine production was favored over protein deposition as a use for Met.

Objective Objective: This study was conducted to evaluate the ability of supplemental methionine to improve health, inflammation status, and performance of receiving cattle. Study Description Study Description: A group of 384 crossbred heifers (initial weight 489 lb) of Tennessee origin were used in a 45-day receiving trial with limit-feeding to evaluate the effects of supplemental methionine (Smartamine M; Adisseo, Alpharetta, GA) on health, inflammation, and performance. Cattle received either 0 (control) or 10 grams/day Smartamine M, a ruminally protected methionine product. Plasma haptoglobin levels measured on days 0, 14, and 45 were used as a biomarker of inflammation. The Bottom The Bottom Line: Line: Supplemental methionine supplied by Smartamine M does not improve performance but reduces inflammation and possibly improves immune function in receiving heifers.

Methionine supplementation can improve immune function in transition dairy cattle. Our objective was to determine if supplemental methionine could reduce acute phase protein responses in newly received growing cattle. 384 crossbred heifers (222 kg initial BW; southeastern U.S. origin) were received in 4 truckloads (blocks) over 9 d. BW was measured at arrival. The following day (d 0) cattle were vaccinated for viral and clostridial diseases, received Draxxin (2.5 mg tulathromycin/kg BW), and were stratified within block by arrival BW to 1 of 8 pens containing 12 animals each. Cattle (in 32 total pens) were limit-fed at 2.2% of BW daily (DM basis) a ration containing 40% Sweet Bran, 34.5% dry-rolled corn, 10% corn silage, 7.5% supplement, 4% alfalfa hay, and 4% prairie hay. Within blocks, pens were assigned to 1 of 2 treatments: 0 (control) or 10 g/d Smartamine M (SM) to provide 6 g/d metabolizable methionine. Pen weights were collected weekly to adjust feed offered the following week. Individual BW and tail-vein blood samples were collected on d 0, 14, and 45. Plasma haptoglobin was measured to assess acute phase protein response. Incidences of morbidity (1.6% for control, 2.6% for SM) and mortality (0.5% for both control and SM) were low. Between d 0 and 45, no differences were observed for ADG (1.24 vs. 1.27 kg/d; control vs. SM, P = 0.55) or G:F (0.107 vs. 0.110, P = 0.28), but DMI was 1.3% greater (P < 0.01) for control than SM due to differences in diet DM. An interaction between treatment and linear effect of day was detected for plasma haptoglobin (P < 0.05); over time, haptoglobin increased more for control (2.15, 2.28, and 2.95 mg/mL at 0, 14, and 45 d) than for SM (2.35, 2.37, and 2.58 mg/mL). Supplemental methionine may alleviate acute phase protein responses in stressed receiving cattle.

Objective: This study was conducted to determine if leucine supplementation could improve protein deposition and lysine utilization in growing steers.Study Description: Ruminally cannulated Holstein steers (380 lb) were provided treatments of postruminal infusions of 0 or 0.212 oz/day of lysine, and 0, 0.529, or 1.058 oz/day of leucine, with all 6 combinations tested. Ruminal infusions of volatile fatty acids and abomasal infusions of glucose provided energy, and all essential amino acids, except lysine, were infused abomasally to make lysine the sole limiting amino acid. Urine and fecal collections were used to measure nitrogen retention (protein deposition).The Bottom Line: Supplementation with leucine did not affect protein deposition of growing steers when lysine was a limiting amino acid, suggesting that, at the levels included in this study, leucine did not stimulate protein synthesis.