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Effects of seed size and level of hard-seededness on survival of medic seeds in whole pods fed to sheep or as clean seed exposed in the sheep rumen

F. Squella and E.D. Carter

Plant Science Department,Waite Agricultural Research Institute, University of Adelaide,Glen Osmond SA 5064

Self-regenerating annual medic pasture legumes are used in southern Australia in the cereal livestock zone in a ley-farming system. Inadequate grazing methods, tillage and sowing practices have been responsible for declining medic seed reserves (1). The germinable seed reserve at the break of season in autumn is one of the main determinants of pasture production Ind consequent livestock production. Thus, seed surviving ingestion by animals represents one important factor to be considered. Two studies were carried out at the Waite Research Institute.


The first experiment examined the effects of two seed sizes (from small and large pods) and two evels of hard-seededness (low and high obtained through the use of alternating temperatures) )n survival of Medicago truncatula cv. Paraggio seeds in whole pods fed to sheep. Twenty vlerino wethers were penned individually and each fitted with a faecal-collection harness. tecovery of seed from faeces were recorded daily during 14 days after feeding with pods. Two ;ycles were done to ensure ten sheep replicates (crossover design). The second experiment ;onsidered effects of the ruminal site by use of the nylon bag in sacco technique in four rumen insulated Merino wethers on survival of small and large seeds of Sava and Paraggio cultivars ;elected for 100% soft and 100% hard seeds. Two hundred seeds per treatment (2 cultivars x ?, seed sizes x 2 levels of hard-seededness x 4 replicates) were incubated in the rumen for 48 hours. After treatment, the seeds were tested for germination.

Results and discussion

Zesults from the pen-feeding study (Table 1) show significant effects of the level of hard;eededness and seed size on viable seed (P<0.001 and P<0.005), germinable seed (P<0.001 and '<0.005) ,and hard seed (P<0.001 and P<0.001), respectively.

When the viable seed output was related to the total hard seed input in order to normalize the differences in the original level of hard-seededness between seed category treatments, only significative effect of seed size was obtained (P<0.001).In the second experiment, all seeds from the group selected for 100% soft seed for each cultivar were completely digested, showing a high susceptibility to digestion in the rumen. Opposite results were obtained for hard seed, where the highest softening level achieved was 7.0%. Significant differences (P<0.005) in percentage of viable seed between small and large seed was obtained. The experiments indicate the resistance of hard seed and the susceptibility of soft seed to digestion in the rumen, and suggesting that much of the damage to the hard seed ingested by sheep occurs during the chewing process. It is there, where the size of the hard seed became an important trait for seed survival.


1. Carter, E.D., Wolfe, E.C. and Francis, C.M. 1982. Proc. 2nd Aust.Agron.Conf., Wagga Wagga, pp. 68-82.

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