New Zealand Journal of Agricultural Research abstracts
Milk production and ruminal metabolites from cows offered two pasture diets
supplemented with non-structural carbohydrate
V. R. CARRUTHERS
P. G. NEIL
Dairying Research Corporation
Private Bag 3123
Hamilton, New Zealand
Abstract The effects on milk solids production, ruminal
metabolites, and microbial protein synthesis of four pasture-based diets were
investigated. Two pastures (high or low nitrogen content (HN, LN) each with and
without non-structural carbohydrate supplementation (+NSC, -NSC, at 10% of
metabolisable energy intake) were offered to eight stall held, rumen-fistulated
Friesian cows during four 14-day periods in early to mid lactation in a Latin
square design. HN and LN pastures contained 2.8 and 2.1% N, respectively. Total
daily dry matter intakes averaged 15.6, 14.5, 15.3, and 14.3 kg on HN+NSC,
HN-NSC, LN+NSC, and LN-NSC, respectively. NSC supplementation had no effect on
milk and milk fat yields but increased milk protein yield by 0.04 kg/day on HN
pasture. Yields of milk, fat, and protein were higher on HN than LN pasture but
microbial protein synthesis (MPS, g N/day) was not affected by type of pasture.
MPS and efficiency of MPS (g N/kg digestible organic matter intake) were
increased by NSC supplementation on HN pasture but not on LN pasture. Ruminal
ammonia concentration and total tract N digestibility were reduced by NSC
supplementation on both pastures and were lower on LN compared with HN pasture.
The results indicated that pasture type affected response to NSC
supplementation and that on HN but not LN pasture NSC supplementation improved
N utilisation in the rumen and increased milk protein output.
Keywords dairy cows; pasture; crude protein; non-structural
carbohydrate; ruminal ammonia; rumen fermentation; microbial protein synthesis;
milk yield; milk fat; milk protein; supplementation; nitrogen utilisation
New Zealand Journal of Agricultural Research, 1997, Vol. 40: 513-521
0028-8233/97/4004-0513 $7.00/0 (c) The Royal Society of New Zealand
1997
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