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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

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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)