4. Nutritional; value of pasture and concentrates

1. 4. Nutritional; value of pasture and concentrates ANIM 3028 Tom Cowan Tropical Dairy Research Centre, UQ, Gatton

2. 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

3. Chronological development in northern Australia

4. 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

5. Growth rates(kg DM/ha/day)

6. Cut and carry erect growth high DM yield Napier (Elephant), Panicum spp, Sorghum, millets Grazing many have stolons or rhizomes signal, kikuyu, Rhodes, couch Grass types

7. Leaf vs. stem

8. 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

9. Grazing effort • Low leaf density • small bite size (0.3 g/bite) • limits to bite number (36,000) • limit to time spent grazing (12h)

10. Grass nutritive value • 4 week regrowth of tropical grass • 20% CP • 60% NDF • 28% ADF • 10% WSC

11. 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 Nutritive value of tropical grasses WSC 6am 6pm 6am

12. 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

13. 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

14. Milk production • Tropical grass = 12L milk/cow/day • Tropical grass + legume = 13.5L milk/cow/day Winter calving Milk/cow Summer calving 0 300 Days of lactation

15. 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

16. 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)

17. Strip grazing of tropicals

18. 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

19. 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)

20. Responses to concentrates

21. 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)