New Zealand Journal of Agricultural Research abstracts
Nitrogen fertiliser effects on milk yield and composition, pasture intake,
nitrogen and energy partitioning, and rumen fermentation parameters of dairy
cows in early lactation
T. R. MACKLE
C. R. PARR
A. M. BRYANT
Dairying Research Corporation
Private Bag 3123
Hamilton, New Zealand
Abstract The effects of nitrogen (N) fertiliser on milk
production and composition, voluntary dry matter intake (DMI), and aspects of
rumen fermentation and N and energy partitioning were studied in early
lactation. Twenty Jersey and 12 Friesian cows were individually offered freshly
cut pastures that had received either 100-150 kg N/ha (HN) or 25 kg N/ha (LN)
as urea, either ad libitum or restricted to 70% of ad libitum. Treatments were
imposed for two consecutive 14-day periods during September and October 1993.
The main effects of higher rates of N fertiliser (LN versus HN) were to
decrease milk protein yield (0.58 versus 0.56 kg/cow per day; P <
0.05), milk protein content (36.0 versus 35.1 g/1000 g; P < 0.01),
and DMI for cows on ad libitum pasture allowance (14.6 versus 14.0 kg DM/cow
per day; P < 0.01). Dry matter and organic matter digestibilities,
microbial N production, and N and energy balance were unaffected by N
fertiliser. The proportion of ingested N retained in milk was reduced slightly
(19.8 versus 21%; P < 0.01) whereas milk urea N and milk non-protein
N as a proportion of total N were increased by HN (0.21 versus 0.19 g/kg,
P < 0.0001; and 7.0 versus 6.6%, P < 0.05). HN tended to
increase rumen ammonia concentration and pH levels while foremilk urea levels
were unchanged. There were no clear effects of N fertiliser on rumen volatile
fatty acid concentrations. Effects of N fertiliser on the chemical and
botanical composition of pasture were minor. We conclude that the application
of N fertiliser in winter/early spring had only minor effects on pasture intake
and milk composition in early lactation.
Keywords nitrogen fertiliser; cows; dry matter intake; milk;
protein; rumen; lactation
New Zealand Journal of Agricultural Research, 1996, Vol. 39: 341-356
0028-8233/96/3903-0341 $2.50/0 (c) The Royal Society of New Zealand
1996
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