Submitted to: Amino Acids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 12, 2012
Publication Date: May 7, 2012
Repository URL: http://handle.nal.usda.gov/10113/56107
Citation: Waterman, R.C., Ujazdowski, V.L., Petersen, M.K. 2012. Effects of rumen-protected methionine on plasma amino acid concentrations during a period of weight loss for late gestating beef heifers. Amino Acids 43:2165-2177. Interpretive Summary: Late gestating heifers grazing Northern Great Plains rangelands often require supplementation in order to meet their nutritional requirements. However, the proper balance of amino acids (AA) still may not be met since AA requirements for pregnant beef heifers are not well defined. Supplement formulation is inexact, and some supplements are utilized less effectively. Research indicates that the first limiting AA is most likely methionine, especially when rumen microbial protein is the key supplier of AA to the small intestine. Dietary proteins in range forages and other feedstuffs can be extensively degraded in the rumen, incorporated into microbial protein, flow to the small intestine to be potentially used as metabolizable protein, which becomes the primary AA source for the host ruminant. The objectives of this study were to determine if plasma AA concentrations were altered in response to inclusion of rumen-protected, DL-MET into the diet of late gestation heifers grazing mixed grass prairie during winter and to identify if methionine is a prospective limiting AA in ruminants experiencing body weight loss. An additional objective was to determine if inclusion of rumen-protected, DL-MET would enhance ruminal disappearance of organic matter (OM) and neutral detergent fiber (NDF) and if the combined effects of each objectives would minimize body weight loss. By supplementing rumen-protected, DL-MET, we hypothesize that heifers will likely improve utilization of other non-limiting or less limiting AA. In conclusion, first calf heifers grazing dormant rangelands in late gestation had improved AA utilization when rumen protected methionine was offered. Furthermore, this research indicates that methionine was a limiting AA in late gestating heifers experiencing body weight loss. The benefit of supplying additional methionine in a form that is rumen protected such as M85 to the rumen appears to be dependent upon passage rate since detectable difference were emerging after only 24 hours. This benefit can encourage greater utilization of the dormant forage as observed with improved OM disappearance at 24 h of in situ incubation. The results of this study did not show any improvements in heifer BW, BCS or calf birth weight when Met was fed. Future work is needed to elucidate the potential of other co-limiting amino acids and their interaction with heifers in late gestation and when experiencing body weight loss.
Technical Abstract: This study determined changes in plasma amino acid concentration in late-gestating (beginning 58 ± 1.02 d prior to calving), primiparous, winter-grazing range heifers receiving wheat middling based supplement without (CON) or with rumen-protected methionine (MET) to provide 15 g DL- MET each day. Plasma was collected on d -2 and d 0 (start of MET supplementation just prior to individually receiving supplement at 0700 h). Plasma was sampled again on d 40, 42 and 44 prior to supplementation at 0700 h and 1100 h (4 h after receiving daily supplement). Data were analyzed with cow as the experimental unit. Continuous variables were analyzed by the main effects of treatment, date, or time and their interaction when appropriate. Comparable BW (P = 0.32) and BCS (P = 0.83) over the 44-d metabolism trial were found between both CON- and MET-fed heifers. MET-supplemented heifers had greater (P < 0.0001) plasma concentrations of methionine indicating that the rumen-protection technology successfully delivered methionine to the small intestine. Supplementation with rumen-protected DL-MET caused a significant supplement × date interaction for glutamine (P = 0.03), glycine (P = 0.02), methionine (P < 0.0001), and serine (P = 0.05). In addition, trends for supplement × date interactions were detected for leucine (P = 0.07), threonine (P = 0.09), valine (P = 0.08), total amino acids (TAA; P = 0.08), non essential amino acids (NEAA; P = 0.08), branched chain amino acids (BCAA; P = 0.08), and glucogenic amino acids (GLUCO; P = 0.08). These results suggest that the BCAA Branched chain AA (leucine, and valine) were utilized more efficiently with MET supplemented heifers compared to CON supplemented heifers. Plasma AA concentrations for glutamic acid (P = 0.0005), histidine (P = 0.01), tyrosine (P = 0.0001), and EAA (P = 0.0022), all decreased throughout the study. These results further confirm methionine is a limiting amino acid in forage fed late-gestating heifers and further suggests the limitation when grazing dormant range forages as shown by improved utilization of other plasma amino acids when supplemental methionine was provided.