4. nutritional; value of pasture and concentrates
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4. Nutritional; value of pasture and concentrates
ANIM 3028Tom Cowan
Tropical Dairy Research Centre, UQ, Gatton
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Forages for rapid expansion• 40% of milk is in tropics/subtropics• 3.9% annual growth• Forage base is
• pasture (~15%)• cut grass• crop byproduct (rice straw, banana leaves, sugar cane)
• Pasture and forage crops are predominant in northern Australia
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Chronological development in northern Australia
1960 Native pasture Oats 0.5t
1970 Grass-legume Oats 0.5
1980 Grass+N Ryegrass+irrigation 0.8
1990 +Maize/lucerne Ryegrass/clover 1.5
2000 +Maize/lucerne Ryegrass/clover 2.5
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Adaptation to the environment
• Grasses in the tropics and subtropics adapted
• high fibre, drought tolerance, rapid growth and flowering
• breeding has given grasses of higher leaf content
• but other characters remain
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Growth rates(kg DM/ha/day)
0
10
20
30
40
50
60
70
80
5 15 25 35
Tropical grassTemperate grass
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Grass types
• Cut and carry• erect growth• high DM yield• Napier (Elephant),
Panicum spp, Sorghum, millets
• Grazing• many have stolons or
rhizomes• signal, kikuyu,
Rhodes, couch
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Leaf vs. stemParameter Leaf Stem
- crude protein- in vitro dry matter digestibility- acid detergent fibre (ADF)- neutral detergent fibre (NDF)- phosphorus- potassium
Rumen- retention time (h)
Energy expenditure- chewing (No.g-1 DMI)
- selection index *
Intake- grazed - long term (kg cow-1day-1)
9.4-16.359-6938630.211.63
24
5.5
2-6
9.8
3.0-12.743-5844720.222.08
32
10.1
0.3-1.0
1.3
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Grass yield and cow intake
• Cows select for leaf• For maximum intake yield is high (I.e.
leaf+stem)• 35 kg DM/cow/day• 2500 kg DM/ha
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Grazing effort
• Low leaf density• small bite size (0.3
g/bite)• limits to bite number
(36,000)• limit to time spent
grazing (12h)
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Grass nutritive value
• 4 week regrowth of tropical grass– 20% CP– 60% NDF– 28% ADF– 10% WSC
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Nutritive value of tropical grasses
• 4 week regrowth– 20% CP– 60% NDF– 28% ADF– 10% WSC– 65% DOMDM
• 12 week regrowth– 10% CP– 70% NDF– 40% ADF– 1%WSC– 45% DOMDM
WSC
6am 6pm 6am
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Minerals in grasses
• Often low in tropical grasses• especially P, Ca and Na• N fertiliser reduces P content• kikuyu very low in Ca and Na• setaria high in oxalate, cause Ca deficiency• normally supplement with P, Ca and Na
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Pasture growth• Nitrogen is a key limiting nutrient• ~4t with nil N• ~12t with 300 N• 23kg DM/kg N average
– irrigation 31 kg DM/kg N
• response reduced where no ground cover of grass
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Milk production
• Tropical grass = 12L milk/cow/day• Tropical grass + legume = 13.5L
milk/cow/day
Days of lactation0 300
Milk/cow
Winter calving
Summer calving
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Stocking rate
• Stocking rate very important to production• with Nitrogen fertiliser and water can be
increased– 7 to 8 cows/ha– 14000 to 20000L milk/ha
• N, water and stocking rate are main drivers of production
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Grazing management
• High farmer interest, limited impact on production
• need a rotation for cow/people management• 10 to 12 paddocks common for tropicals• temperate pastures are strip grazed
(rationed)
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Strip grazing of tropicals
Grazing rotationOpen * Rotational
Mulching post grazing - + - +Leaf - pasture content (%DM) Milk yield (kg cow-1 day-1)
44a
15.0b
57c
14.9b
47b
13.6a
59d
16.7c
* Two paddock system, one week grazing, one week spelling.
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Concentrates
• Concentrates = grain+protein meal+minerals+ other (e.g. buffers)
• or energy/protein rich byproducts (e.g. molasses, coconut meal)
• have become “complementary”, not “supplementary” feeds
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Sources of nutrients in concentrates
• Energy - grains, molasses, fats
• Protein - cotton seed, coconut and copra meals, urea
• Minerals - limestone, DCP, salt, premixes
• Other - buffers (e.g. sodium bicarbonate), additives (e.g. rumensin)
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Responses to concentrates
Duration of feeding
Amount fed Milkresponse
Short term
Longer term
(weeks)
1.5-8
24-40
(kg d-1)
2.7-4.0
2.5-6.0
(L kg-1 DM)
0.4-0.5
0.8-1.1
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Level of concentrate feeding
• A guide is L milk/3• less at milk yields below 18L/day
• Lower levels cause economic inefficiencies (cow, labour, capital)
• Higher levels require more nutritional control (acidosis, pasture utilisation)
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