Week 4

Roughages

Factors Influencing Forage Nutritional Value

Text Transcript

Follow along with the audio...

• Factors influencing nutrient content, digestibility, and subsequent nutritional value of forage
• In this section and others of the module
• Data presented to illustrate trends
• Actual values vary with conditions
• Forage maturity at harvest
• Primary factor influencing nutritional value
• Table 8.1 – Developmental stages of legumes and grasses

Table 8.1 - Developmental Stages of Legumes and Grasses

Stages of maturity	Definition*
Legumes
Late vegetative	No visible buds, flowers, or seed pods. Stem at least 12 inches tall
Early bud	Visible flower buds on at least one stem (1%)
Mid bud	50% of the stems have at least one bud
Late bud	75% of the stems have at least one bud, no visible flowers
First bloom	Flowers on at least one stem (1%)
1/10 bloom	10% of the stems have at least one flower
Mid bloom	50% of the stems have at least one flower
Full bloom	75% of the stems have at least one flower, no visible seed pods
Grasses
Vegetative	Leaves only, stems not elongated
Stem elongation	Stems elongating. Specify early or late jointing.
Boot	Flower head is enclosed in flag leaf sheath and not showing
Heading	Flower head emerging or emerged from flag sheath but not shedding pollen
Anthesis	Flowering stage, anthers shedding pollen
Milk stage	Seed immature, endosperm milky
Dough stage	Well-developed seed, endosperm doughy
Ripe seed	Seed ripe, leaves green to yellow brown
*Randomly select 100 stems from the field and determine the percentage of stems at the most mature stage of development.

• Associations with maturation
• Decrease in nutrient content, digestibility, and subsequent nutritional value
• Decrease in water, protein, nonstructural carbohydrates (i.e. energy), minerals, and vitamins
• Increase in structural carbohydrates and lignin
• Lignin
• In part, responsible for decrease in digestibility
• Indigestible complexes with cellulose, hemicellulose, and proteins
• Legumes > warm-season grasses > cool-season grasses
• Legumes: <6 - >10%
• Grasses: <3 - >7%
• Rate and magnitude dependent on number of factors including species and environmental conditions
• Data
  • Table 8.2 – Stage of maturity and range of CP and NDF for legumes and grasses

Table 8.2 - Stage of Maturity and Range of CP and NDF for Legumes and Grasses

	Composition, % DM
Stage of Maturity	CP*	NDF**
Grasses
Pre head	>18	<55
Early head	13-18	55-60
Head	8-12	61-65
Post head	<8	>65
Legumes
Pre bloom	>19	<40
Early bloom	17-19	40-46
Mid bloom	13-16	47-51
Full bloom	<13	>51
*CP = Crude protein; **NDF = Neutral detergent fiber

• Table 7-6 on page 125 of text – Seasonal changes in CHO, lignin, and cell solubles for four species of grasses
• Table 7-9 on page 128 of text – Effect of maturity on CP of grasses (mean of eight grasses)
• Alfalfa – NRC publications
• Early vegetative to full bloom
• CP
• 23% to 15%
• TDN
• 63% to 55%
• Table 7-3 on page 121 of text – Effect of maturity on digestibility of alfalfa
• Figure 8.10 – Stage of maturity to maximize digestible DM yield for legumes and grasses



• Additional data in literature for other species and parameters
• Digestibility and dry-matter intake
• As digestibility decreases, dry-matter intake decreases
• DMI
• Essential for nutrient intake
• Rationale
• As digestibility decreases, digestion and passage rates decrease
• DMI limited by physical volume required to contain feedstuff prior to passage
• Not effective method to accurately relate forage digestibility to dry-matter intake
• Additional factors
• Plant species
• Between grasses and legumes
• Within classifications of grasses and legumes
• Environmental conditions
• Progression rate of season
• Temperature and moisture levels and patterns
• Soil conditions
• For grasses, N fertilization
• Increase CP and DM yield
• For grass-legume systems
• Excess N fertilization may result in loss of legumes
• Additional associations suggested
• Leaf to stem ratio
• In general, nutritional value of leaves greater than of the stems
• As plant mature, ratio of leaves to stems decreases
• Decreasing nutritional value of forage
• Extent of leaf loss greater in legumes versus grasses
• Table 8.3 – Stage of maturity and percentage of leaves for legumes and grasses

Table 8.3 - Stage of Maturity and Percentage of Leaves for Legumes and Grasses

Stage of Maturity	Percentage of Leaves
Grasses
Pre head	>50
Early head	40-50
Head	30-40
Post head	20-30
Legumes
Pre bloom	40-50
Early bloom	35-45
Mid bloom	25-40
Full bloom	<30

• Effective management will increase nutritional value of forage system
• Examples
• Selection of forage species
• Fertilization practices
• Stage of maturity at harvest
• Maintenance of forage at vegetative state