The responses of grazing animals to specific plant secondary compounds were examined in trials in which dairy cows grazed spaced plants of either birdsfoot trefoil (Lotus corniculatus L.) with high and low concentration of extractable condensed tannins (2.54 and 0.62 % in the DM respectively for high and low tannin genotypes), or red clover (Trifolium pratense L.) with high and low formononetin concentration (0.68 and 0.29 % in the DM respectively for high and low formononetin genotypes). Plants were established in 4 linear sequences of 26, each providing three blocks (replicates) of balanced sets of 2 plant species, 2 concentrations of test components, and plants either not trimmed or trimmed to minimise physical differences between genotypes within species. The sequences were grazed by four trained cows and selective behaviour was determined by the number of grazing bites per plant. Observations were repeated in March (P1) and April (P2). On average, animals grazed more on non-trimmed than on trimmed plants (7.6 vs 3.1 ± 0.711 bites/plant in P1, P=0.0001; and 8.4 vs 3.6 ± 0.858 bites/plant in P2, P=0.0002), but did not show clear discrimination between red clover and lotus (6.3 vs 4.4 ± 0.711 bites/plant in P1, P=0.053; and 6.3 vs 5.7 ± 0.858 bites/plant in P2, P=0.620). However, though the distribution of bites between red clover plants with high and low formononetin was similar (7.2 vs 5.5 ± 0.76 bites/plant in P1, P= 0.130; and 7.3 vs 5.3 ± 1.08 bites/plant in P2, P= 0.191), they showed strong preference for low condensed tannin concentration in lotus ( 2.1 vs 6.6 ± 1.11 bites/plant in P1, P= 0.0068; and 3.9 vs 11.1 ± 1.35 bites/plant in P2, P= 0.069).
Proceedings of the New Zealand Society of Animal Production, Volume 58, , 110-112, 1998
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