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Publication Date
1981
Description
This report summarizes the Canadian breeding program to develop a bloat-safe alfalfa (Medicago sativa L.). This program has experienced an evolution of selection methods in attempting to identify bloat-safe alfalfa genotypes. In chronological order, the methods involved selection for fraction I (18S) protein, soluble proteins, foam volume, tannins (flavolans), saponins, initial rate of digestion (IRD), sonication, purified enzymes, gas production, and leaching. Although soluble herbage protein is correlated with the occurrence of pasture bloat, we have experienced slow progress in a selection program to reduce soluble-protein concentration in alfalfa. We have found that foam volume is not correlated with either soluble protein or bloat incidence. After an extensive search of 33 annual and 25 perennial species of Medicago, we have found no tannins. Similarly, a mutation approach to induce flavolan production in alfalfa has failed to reveal tannin (bloat-safe) phenotypes. Seedcoats of alfalfa contain tannins. The saponin theory of bloat has been proven to be invalid. A comparison of bloat-safe and bloat-causing forage legumes revealed slower initial rates of digestion and lower concentrations of intracellular leaf constituents in rumen .fluid when bloat-safe legumes are ingested. Selection is under way to develop contrasting alfalfa synthetics, one with a low initial rate of digestion (bloat-safe synthetic) and another with a high initial rate of digestion. Preliminary data indicate genetic progress for change in initial rate of digestion with no change in overall digestibility as measured by in-vitro dry-matter digestibility. Several new complementary techniques are under development and evaluation to select bloat-safe alfalfa plants. They are all devised to measure basic parameters involved in the etiology of bloat (e.g., cell-wall strength, enzymatic breakdown of cells, microbial degradation, gas production, leaching).
Citation
Goplen, B P.; Howarth, R E.; Lees, G L.; Majak, W; Fay, J P.; and Cheng, K J., "Evolution of Selection Techniques in Breeding for Bloat-Safe Alfalfa" (1981). IGC Proceedings (1981-2023). 16.
(URL: https://uknowledge.uky.edu/igc/1981/section1/16)
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Evolution of Selection Techniques in Breeding for Bloat-Safe Alfalfa
This report summarizes the Canadian breeding program to develop a bloat-safe alfalfa (Medicago sativa L.). This program has experienced an evolution of selection methods in attempting to identify bloat-safe alfalfa genotypes. In chronological order, the methods involved selection for fraction I (18S) protein, soluble proteins, foam volume, tannins (flavolans), saponins, initial rate of digestion (IRD), sonication, purified enzymes, gas production, and leaching. Although soluble herbage protein is correlated with the occurrence of pasture bloat, we have experienced slow progress in a selection program to reduce soluble-protein concentration in alfalfa. We have found that foam volume is not correlated with either soluble protein or bloat incidence. After an extensive search of 33 annual and 25 perennial species of Medicago, we have found no tannins. Similarly, a mutation approach to induce flavolan production in alfalfa has failed to reveal tannin (bloat-safe) phenotypes. Seedcoats of alfalfa contain tannins. The saponin theory of bloat has been proven to be invalid. A comparison of bloat-safe and bloat-causing forage legumes revealed slower initial rates of digestion and lower concentrations of intracellular leaf constituents in rumen .fluid when bloat-safe legumes are ingested. Selection is under way to develop contrasting alfalfa synthetics, one with a low initial rate of digestion (bloat-safe synthetic) and another with a high initial rate of digestion. Preliminary data indicate genetic progress for change in initial rate of digestion with no change in overall digestibility as measured by in-vitro dry-matter digestibility. Several new complementary techniques are under development and evaluation to select bloat-safe alfalfa plants. They are all devised to measure basic parameters involved in the etiology of bloat (e.g., cell-wall strength, enzymatic breakdown of cells, microbial degradation, gas production, leaching).
