Molecular Structures and Metabolic Characteristics of Protein in Brown and Yellow Flaxseed with Altered Nutrient Traits

The objectives of this study were to investigate the chemical profiles; crude protein (CP) subfractions; ruminal CP degradation characteristics and intestinal digestibility of rumen undegraded protein (RUP); and protein molecular structures using molecular spectroscopy of newly developed yellow seeded flax (Linum usitatissimum L.). Seeds from two yellow flaxseed breeding lines and two brown flaxseed varieties were evaluated. The yellow-seeded lines had higher contents of oil (44.54 vs 41.42 per cent  dry matter (DM)) and CP (24.94 vs 20.91 per cent  DM) compared to those of the brown-seeded varieties. The CP in yellow seeds contained lower contents of true protein subfraction (81.31 vs 92.71 per cent  CP) and more extensively degraded (70.8 vs 64.9 per cent  CP) in rumen resulting in lower content of RUP (29.2 vs 35.1 per cent  CP) than that in the brown seeded varieties. However, the total supply of digestible RUP was not significantly different between the two seed types. Regression equations based on protein molecular structural features gave relatively good estimation for the contents of CP , soluble CP , RUP , and intestinal digestibility of RUP. In conclusion, molecular spectroscopy can be used to rapidly characterize feed protein molecular structures and predict their nutritive value. (Authors abstract)

In the last two decades, the use of full fat flaxseed in dairy ration has been increased due to its known positive effects on animal fertility and reproductive health,  fatty acid composition of milk,  and as a consequence on long term human health. Increasing the oil content of flaxseed, and the proportion of C18:3n 3 in the total oil, has been the focus of recent flax breeding in Canada. As a result, yellow flaxseed breeding lines with a high content of oil and C18:3n 3 have been recently developed by the Crop Development Centre (CDC), University of Saskatchewan (Saskatoon, SK, Canada). The
yellow flaxseed has a larger seed size and thinner seed coat compared to those of the brown flaxseed varieties, resulting in higher contents of oil and CP, and lower content of NDF in the seeds. A higher content of CP and lower content of NDF have been reported for yellow seeded canola meal and carinata seeds compared to those of their brown seeded counterparts.  Moreover, the CP in flaxseed contains a high fraction of soluble protein (SP; 76 per cent  CP) compared to other oilseeds such as canola (22 per cent  CP) and carinata (49 per cent  CP).  As a consequence, flaxseed derived CP rapidly and extensively degrades in the rumen,  causing lower fermentation efficiency and losses of gaseous N to the environment. The objectives of the present study were to investigate the (1) chemical profile; (2) CP subfractions according to Cornell Net Carbohydrate and Protein System (CNCPS); (3) ruminal CP degradation characteristics and intestinal digestibility of rumen nondegraded protein (RUP); and (4) the protein’s molecular structural features using Fourier transform per infrared-attenuated total reflectance (FT/IR ATR) molecular spectroscopy of newly developed CDC yellow flaxseed in comparison with that of brown flaxseed. The fifth objective was to quantify the relationship between the protein’s molecular structural features and their chemical profiles and digestive behavior in the rumen and intestine of dairy cattle.

On average, the yellow seeded lines had higher contents of EE (44.54 vs 41.42 per cent  DM) and CP (24.94 vs 20.91 per cent  DM) compared to those of the brown seeded varieties. The higher contents of CP and EE in the yellow seeded lines could be related to their larger seed size and thinner and translucent seed coat that results in a relatively greater proportion of oil and protein containing mass (cotyledons and endosperm) and smaller proportion of fiber containing mass (seed coat) compared to those of the brown seeded varieties.  In agreement with our findings, higher contents of CP and EE have been reported for yellow seeded canola meal compared to that of its brown seeded counterpart.   Within the yellow seeded lines, FO8425 had a higher content of EE; and within the brown seeded varieties, CDC Bethune had a higher content of EE and CP. The latter findings suggest some genotype differences in the chemical profiles of flaxseed within the yellow and brown seed types. The CP chemical profile revealed that on average the CP in yellow flaxseed lines had a higher content of ADIP (7.80 vs 3.38 per cent  CP). The ADIP is believed to be non degradable in rumen and non digestible in the postruminal tract. In contrast to our findings, previous studies have reported lower contents of ADIP in yellow seeded carinata strains and canola meal compared to their brown seeded counterparts.  This discrepancy may be related to the inherent genetic variation in these seeds. Compared to brown seeded varieties, the content of NDIP was lower (16.45 vs 11.44 per cent  CP) in the yellow seeded lines, which is in line with literature findings.  Among the yellow seeded lines, the content of ADIP was higher  in F08 times 425, whereas no significant differences were observed in the CP chemical profile among the brown seeded varieties. Overall, the results of chemical profiles showed that the yellow seeded lines had higher contents of EE and CP; however, the CP in the yellow-seeded lines may not be optimally utilized by dairy cows due to the relatively high proportion of rapidly degradable SP (data not shown) and nondigestible ADIP fractions.

Results of the CNCPS CP subfractions of the brown seeded and yellow seeded flax are presented. The contents of all CP subfractions varied among the four genotypes. The yellow seeded lines had significantly higher contents of the nonprotein fractions, namely, the instantaneously solublilized (PA) fraction (10.88 vs 3.91 per cent  CP). The yellow seeded lines contained a high content of nonavailable (PC) fraction (7.80 vs 3.38 per cent  CP) compared to that in brown seeded varieties. As a consequence of high PA and PC fractions, the true protein fraction of the yellow seeded lines was markedly lower ( 81.31 vs 92.71 per cent  CP) than that in the brown seeded varieties. The PA fraction very rapidly (200 per cent per h) 31 degrades to NH3 N in the rumen and often contributes to NH3 N losses in the environment. Whereas, the PC fraction neither degrades in the rumen nor is digested in the postruminal tract and excreted in feces to the environment.  These results suggest that CP in the yellow flaxseed genotypes is not optimally digested and utilized in the gastrointestinal tract of dairy cows compared brown flaxseed varieties. However, the brown flaxseed varieties had a markedly higher (13.13 vs 3.65 per cent  CP) PB3 subfraction. The PB3 slowly (0.06 to 0.55 per cent per h) degrades in the rumen, and a large fraction of PB3 bypasses the rumen and is digested in the small intestine.  Among the brown-seeded varieties, CDC Sorrel had lower PB1 and higher PB2 and PB3 fractions, suggesting that CP in CDC Sorrel will be more gradually broken down to NH3 N in the rumen and that a higher fraction of CP will bypass the rumen. (Editors comments)