Prof Hassen: Grass and forage crops Flashcards
1
Q
What is a roughage?
A
- Feedstuff with >18% CF or >20% ADF >30% NDF
- High in fibre and low in energy
- Used by ruminants and nonruminants
- Nutrient in roughages are made available by microbial digestion
- examples are pasture grass and other forage crops, silages, hay, straws and chaff.
2
Q
What is the major enzyme involved in photosynthesis?
A
Ribulose biphosphate carboxylase
3
Q
Define herbage
A
Plant material, except seeds and roots that can be utilized as food by animals.
4
Q
Roughage normally include_____
A
herbage or forage, but is not restricted to plants grown for animal consumption(forage plants)
5
Q
Forage is devided into_____
A
Native and cultivated species
6
Q
Name the types of pasture:
A
1) Temporary pasture, limited life span (1-4Years), consists of a single sown plant species, ex. italian rye and lucerne
2) Permanent pastures: Life span more than 4 years.
7
Q
Practically what could be the reasons that there is not sufficient intake of nutrients during the growing season?
A
- Nutritave value falls
- soil and climatology may be unsuited
- grazing management system may fail
8
Q
Name the advantages of grass as food for grazing animals:
A
- Most are palatable when immature
- Very few are toxic
- Grows in all environments where grazing animals can survive
9
Q
Describe the pattern of growth for grasses
A
- temperate grass starts to grow in spring when soil temp. is 4-6 degrees
- once growth starts, the pattern of growth is the same for all grass species
- This includes rapid leaf growth, increased stem growth, ultimate emergence of the flowering head, formation of seeds.
10
Q
What promotes development of vegetative tillers?
A
Removing the seed head
11
Q
The storage carbohydrates of temperate grasses is ____, while in tropical and sub-tropical grasses it is _____
A
Fructans, starch
12
Q
When is grass growth very rapid?
A
During the autumn wet season
13
Q
Growth rates of grasses is dependant on___
A
- Environment
- Nutrient availability
- Amount of leaf within the sward
14
Q
What does the rate of re-growth in grasses depend on?
A
Maturity of the crop at the time of harvesting
15
Q
What is the growth range for temperate pastures?
A
40-100 kg DM/ha/day in spring
16
Q
Name the factors which influence the nutritive value of herbage:
A
- Stage of growth
- Species
- Soils and fertilizer treatments
- Grazing systems
17
Q
What is the moisture content of grasses?
A
750-850g/kg in DM
Falls to 650 when the plant matures
18
Q
What is the CP ranges of grass
A
30 -300 g/kg DM
19
Q
What is the composition of grass DM dependant on?
A
Relative proportion of cell walls and cell contents
20
Q
What is the acid detergent fiber ranges of grasses?
A
200-450 g/kg DM
21
Q
What is included in the cell walls of grasses?
A
- Water soluble carbs ( fructans, glucose, fructose, raffinose and stachyose) that range from 25-300g/kg DM.
- Protein
- Cellulose 200-300g/kg DM
- Hemicellulose 100-300g/kg DM
- lignin
22
Q
True protein accounts for ____% of N
A
80%, but protein content decreases with maturity
23
Q
_______ constitutes more than 50% of the cellular protein in grasses.
A
Ribulose biphosphate carboxylase
24
Q
Grasses are rich in the following amino acids?
A
Arginine, glutamic acid and lysine
25
What are the first 2 limiting amino acids in grasses?
Methionine and isoleucine
26
CP of tropical grass is ___ than the CP of temperate grass.
Lower
27
What does ADIN stand for
Acid detergent insoluble nitrogen
28
What are the main components of NPN
- Amino acids
- Amides
- Nitrate
29
What is the ether extract fraction in grasses ?
It is low and does not exceed 60 g/kg DM
30
The ether extract includes:
- triacylglycerols
- glycolipids
- waxes
- phospholipids
sterols
31
What is the main fatty acid in grasses?
- Linolenic acid, makes up 60-75% of total FA's
| - Linoleic and palmitic acids are the next 2 most abundant FA's
32
The mineral composition of grasses depends on?
- species
- stage of growth
- soil type
- cultivation condition
- fertilizer application
33
What is the precursor for vitamin A?
Beta-carotene, Grass herbage is rich in this. In green crops= 550mg/kg DM. In green crops the conc. of vit A is 100 times higher than what is needed by a cow.
34
Except for Vit A, what are the other vitamins presents in green forage crops?
Vit E, many Vit B's like riboflavin, Vit D is present more in mature herbage.
35
Why do diets of grazing animals vary?
- There can be a variation in botanical composition
- Plant growth is diffirent at diffirent times of the year
- Plant growth rates differ
- Plant maturities can differ
36
Name the 4 growth stages of grasses:
leafy, boot, heading, bloom
37
Name the 4 growth stages of legumes:
leafy, prebud, bud, bloom
38
Proteins may be indigestible, why ?
Because most of the proteins are bound to fiber.
39
As a plant grows, what happens to its nutritave values?
- The structural carbohydrates increase, these include cellulose, lignin and hemicellulose
- Conc. of protein and total ash decrease
- digestibility of organic matter decrease
40
What determines the digestibility of a plant?
- Plant anatomy
- Age, as plant matures the digestibility will decrease except in spring where digestibility stays the same for a month.
- Digestibility of grass is also influenced by leaf:stem ratio, in young grass stems are more easily digested that leaves, but over time this changes
41
A low NE value of a mature herbage is due to:
- low organic matter digestibility
| - high concentration of cellulose
42
What are the six important tribes of grasses?
- Agrosteae
- Aveneae
- Festuceae
- Eragrosteae
- Andropogoneae
- Paniceae
43
Why can it be negative for grasses to grow more quickly ?
In arm climates, grasses mature rapidly. This means their protein and phosphorus levels fall to a very low levels quickly and they have a high fiber content.
44
Why do C3 and C4 species have diffirent nutritive values?
Due to their differences in photosynthetic pathways
45
C4 plants hav inherently low N content,why?
Due to their adaptability to low soil fertility
46
Anatomically, how do temperate and tropical species differ
- There are more there are more vascular and thick wall bundle sheaths and lignin in tropical plants
- The mesophyl cells are more densely packed in tropical species that temperate species
- Lower intracellular space in tropcal species than temperate species.
47
The anatomical diffirences between temperate and tropical species mean that_______
- Tropical grasses have a higher tensile strength, which means retarded mechanical and microbial degradation in the rumen.
- Tropical grasses have lower digestibility and lower voluntary dry matter intake
48
What should the selection of pasture species be based on ?
- Agronomic (persistency and productivity)
| - Nutritive value characteristics
49
How do plants react to a mineral deficiency in the soil?
- Limit their growth
| - Reduce the conc. of minerals in their tissue
50
Sulpher deficiency leads to
reduced digestibility of herbage in sheep
51
What does the application of N fertilisers help with?
- Increase leaf area and photosynthesis rate
- Increase the CP content and frequently the amide and nitrate contents
- Depresses the water soluble carb content of temperate grasses.
- Alters the botanical composition and nutritive value of swards.
52
Name the 3 types of grazing systems:
- Cut and carry, grass is cut and taken to a kraal, this has the best control over an animals diet.
- Continuous, animals kept on the same pasture through the year
- Rotational, pastures are grazed for short periods with high stocking rate and grazing pressure
53
What is the connection between the amount of grass eaten by animals and the root growth of that grass?
- With 50% of the plant eaten, roots will not stop growing.
- If 70% of the plant is eaten, 50% of the roots will stop growing for 17 days
- If 90% of the plant is eaten, 100% of the roots will stop growing for 17days.
54
What are the nutritional disorders associated with grasses?
- nitrate poisoning
- mycotoxicosis
- grass sickness
- grass tetany
55
What causes the toxic effect of nitrogen in ruminants?
Reduction of nitrate to nitrite, nitrate oxidises the ferrous iron of haemoglobin to the ferric state producing the brown pigment methaemoglobin which cannot transport oxygen to the body.
56
What are the toxic signs of nitrate poisoning?
- Trembling
- Staggering
- Rapid respiration
- Death
57
What is the lethal dose of nitrate in herbage?
2.2 g/kg DM
58
What is mycotoxicoses?
A disorder of grazing animals caused by the invasion of grasses by fungi ( fungi produces mycotoxins)
59
Which fungi causes rye grass staggers?
Acremonium loliae, which produces the neurotoxin alkaloid lolitrem B.
60
Which fungi causes Paspalum staggers?
Claviceps paspali, which is relted to the ergot fungus
61
Tall fescu is infected by the fungi ______
Acremonium coenophalium, which produces an ergot alkaloid ergovaline. Ergovaline causes the condition fescue foot.
62
Which micotoxin is produces by Pithomyces chartarum?
Sporidesmin, which causes liver damage in grazing animals. This causes the release into the circulation of bile and the chrolophyll breakdown product phylloerythrin, which causes the disorder called facial exzema.
63
The control of mycotoxicoses is based on ______
- Use of fungicides on pasture
- selection of resistant plants and animals
- modification of grazing practices to avoid consumption of infected herbage.
64
What is the scientific name of grass sickness and what is grass sickness?
- Equine dysautonomia
- Happens when horses graze on pasture after a dry period and involves the toxin botulinum. Damage occurs to the autonomic nervous system.
65
Grass sickness (equine dysautonomia) is characterised by _______.
- Muscular tremors
- Loss of weight
- Abnormal stance
- difficulty to swallow
- impaction of the colon
- regurgitation of stomach contents
66
The main sugar in clover is ____
sucrose
67
What is the conc. of starch in clovers?
50g/kg DM
68
Give 3 examples of efforts to introduce legumes in the pasture system:
1) Centrosema pubescens into pasture of the wet tropical
2) Macroptilium atropurpurium into drier areas
3) Medicago staiva into warm temperate areas and in many tropical and sub-tropical areas.
69
What are egyptian clovers valued for?
Rapid growth in the winter season in sub-tropics and for its good recovery after cutting or grazing.
70
What is the protein in foliage of leguminous trees
200-300g/kg DM
