Future dairy farming in New Zealand will require increases in milksolids production and reduced impact on the environment. Cows which are more feed conversion efficient (FCE) and nitrogen use efficient (NUE) will help achieve these targets. In March 2010, eight High breeding worth (BW = 198), High production worth (PW = 319) and eight Low BW (57) PW (10) cows were housed in metabolism stalls and fed low quality perennial ryegrass-based herbage (metabolisable energy = 9.87 MJ/kg DM; crude protein = 15.2 g/100g DM). High BW cows had higher dry matter intakes (DMI) (16.0 vs 14.8 kg DM/cow/d, P <0.05) and produced more milksolids (1.32 vs 1.03 kg MS/cow/d, P <0.001). Due to their higher DMI, the High BW cows also had a higher feed N intake than the Low BW cows (388 vs 360 g N/cow/d, P <0.05), and partitioned more of their intake N to milk (22.0 vs 18.5 %, P <0.01) and less to urine (39.7 vs 46.2%, P <0.01). Overall, the High BW cows were more FCE (82.7 vs 70.2 g MS/kg DMI, P <0.01) and more NUE (22.0 vs 18.5 %, P <0.01) when fed low quality herbage in late lactation.
Proceedings of the New Zealand Society of Animal Production, Volume 71, Invercargill, 109-113, 2011
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