The effects on germination of seeds subjected to mechanical and chemical damage caused by ruminant digestion.

Seeds dispersal by livestock is being studied as a factor which contributes to changes in natural and agricultural landscapes by establishing new species over different habitats, affecting the ecosystem and leading to a search for better management practices. Grazing and manure distribution as fertilizer are means of spreading both desirable and problematic species across the land, therefore understanding how aspects such as seed viability and germination are affected by ruminant digestion will help on the development of more efficient methods for preserving and increasing the quality of rangelands and pastures.   

The capacity of forage species to maintain its morphological and physiological characteristics after being subjected to physical and chemical damage exerted by livestock will determine on which extent the seeds will successfully spread and grow over the land, conserving and enriching the habitat. The dissemination of weed species can happen by the same means, the difference is that weeds are usually more resilient when compared to forages. Undesirable plants usually have a greater capacity of adjustment, adapting more easily under unfavorable conditions due to specific evolutionary attributes that among others include seed size and seed coat hardness. These attributes often help the seeds go through the digestion process unharmed, preserving viability and germination power.

The objective of this research was to determine how the germination of important forages and problematic weeds species in cropping systems is affected by physical damage caused by mastication and chemical damage caused by rumen digestion.  

The experiment consisted of three treatments: mastication simulation, rumen digestion and mastication following exposure to rumen digestion. The species used were: Eastern Gamagrass (Tripsacum dactyloides), Johnsongrass (Sorghum halepense), Lambsquarter (Chenopodium album), Palmer Amaranth (Amaranthus palmeri), Redroot Pigweed (Amaranthus retroflexus), Sicklepod (Senna obtusifolia), Black Locust (Robinia pseudoacacia), Switchgrass (Panicum virgatum), Texas Panicum (Panicum texanum) and Velvetleaf (Abutilon theophrasti). The main goal was to analyze which of the treatments would have the greatest effect on germination. A chewing simulator was built utilizing simple materials to recreate the mastication process: a “T” bar with a velcro wrapped on the tip served as the teeth and gum of the animal. A PVC pipe containing the seeds and stuck onto a piece of wood served as the mouth. For rumen digestion, fiber bags containing the seeds were placed into cannulated steers and treated in situ (fistulated cow) during 48 hours.

The responses varied according to the species. Eastern Gamagrass showed a reduction of 3,3% on germination for mastication following rumen digestion, a 2,7% reduction when exposed only to rumen digestion and a 2,1% reduction for mastication. Mastication and rumen digestion increased germination on Switchgrass by 9,1% and 0,8% respectively with mastication following rumen digestion decreasing it by 12,2%. Palmer Amaranth, Redroot Pigweed, Texas Panicum and Velvetleaf were negatively affected by all treatments with Palmer Amaranth presenting the highest average reduction per treatment: 62,9%. Johnsongrass, Sicklepod, Black Locust  and Lambsquarter were favored by the process, ending with a higher germination rate for most of the treatments. Black Locust raised its germination by 25,1% (mastication following rumen digestion), 7,4%(rumen digestion) and 12,7%  Dormancy can be addressed as the reason for these variations. Digestion is going to damage the seed coat, enabling exchange of light, water and gases with the environment, breaking dormancy.

Understanding how forage and weed species respond to ruminant digestion is essential in order to improve current management practices and increase conservation of grasslands and pastures.