The effect on ruminal fermentation and milk production of increasing the proportion of non-structural carbohydrate (NSC) in a pasture diet was investigated in early (Trial 1) and late (Trial 2) lactation. Twenty four cows in Trial 1 and 15 cows in Trial 2 were offered pasture (P), 85% P plus 15% protein/NSC mixture (PR), and P+10% (Trial 1) or P+15% (Trial 2) NSC (PE) in a latin square design. All diets were isonitrogenous and P and PR were isoenergetic. PE but not PR increased microbial protein synthesis and decreased rumen ammonia and milk urea levels compared to P in both trials. In Trial 1, neither PE nor PR increased milk yield or milk solids output compared to P. Nitrogen but not dry matter digestibility was reduced on PR and PE compared to P. Ruminal degradation of casein, but not of pasture, was increased on PR and PE compared to P. In Trial 2 the milk yields of cows offered PE and PR were greater than those offered P, and greater on PE than PR. Increasing the ratio of carbohydrate to protein was more effective in improving nitrogen utilisation in the rumen than was increasing the proportion of NSC.

VR, Carruthers, PG Neil, and DE Dalley

Proceedings of the New Zealand Society of Animal Production, Volume 56, , 255-259, 1996
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