This experiment investigated whether increased crude protein concentration in
turnips fertilised with nitrogen would improve milk production. Dairy cows
were offered a basal diet of silage, hay and 5 kg dry matter barley
supplemented with 5 kg dry matter turnips fertilised with nitrogen
(n = 12) or 5 kg dry matter control turnips
(n = 12) over 14 days. The effect of providing a
diet isonitrogenous with the nitrogen-fertilised turnip diet and with rumen
degradable protein on milk production was also investigated by replacing 1 kg
barley with 1 kg lupins; 12 cows were offered 4 kg (dry matter) barley, 1 kg
lupins with 5 kg control turnips.
The control cows (offered control turnips with barley) consumed 17.8 kg dry
matter, 2.34 kg crude protein and 187 MJ metabolisable energy. In comparison
with the control cows, cows offered nitrogen-fertilised turnips with barley
had lower (P<0.05) daily dry matter and metabolisable
energy intakes and higher (P<0.05) crude protein
intake whereas cows offered control turnips with barley and lupins had similar
daily dry matter intake and higher (P<0.05) intakes
of metabolisable energy and crude protein.
The cows offered nitrogen-fertilised turnips with barley produced similar
yields of milk and milk constituents to those of the control cows (19.6 L milk
with 855 g fat, 625 g protein and 951 g lactose daily), reflecting the lower
intakes of dry matter and metabolisable energy by the cows offered
nitrogen-fertilised turnips with barley compared with that of the control
cows. Cows offered control turnips with barley and lupins had a greater
(P<0.05) daily yield of milk fat and protein than did
the other groups of cows; milk yield was increased by 0.5 L when 1 kg dry
matter barley was replaced with 1 kg dry matter lupins. It is economical for
farmers to feed turnips in conjunction with barley and lupins to overcome
summer shortages of high-quality feeds.
Effect of Dietary Crude Protein Concentration on Ruminal Nitrogen Metabolism in Lactating Dairy Cows