Agriculture Reference
In-Depth Information
or knowledge of the nutrient contents of availa-
ble feeds, more precise formulation and feeding
of animal diets is a good option for improving
animal management.
With the goal of maximizing milk produc-
tion, the replacement rate of the milking herd
has increased in recent years (CDIC, 2011). This
requires the production of more replacement
heifers to maintain the herd, which requires
more feed production and increased manure
handling. A long-term management option may
be to improve the longevity of the milking ani-
mals through genetic improvement or better
animal care. This option was modelled by reduc-
ing the replacement rate of the milking herd to
30% and the number of replacement heifers
raised on the farm to 2000.
This change in animal management had a
similar effect on N losses as the reduction in pro-
tein feeding just described (Table 10.1).
Ammonia emission was reduced by about 7%,
nitrate leaching by 10% and the reactive N foot-
print by 6%. Maintaining fewer replacement
animals had little effect on P runoff loss, but the
accumulation of excess P and K were reduced.
Net greenhouse gas emission and carbon foot-
print were also reduced about 9%. Increasing
longevity in lactation was also beneficial to the
producer. Farm income was reduced slightly due
to fewer cull cows sold, but this was offset by
reduced production costs increasing annual
farm profitability by US$75 per cow. Therefore,
improved animal management to reduce the
replacement rate of the herd is beneficial to both
the environment and the producer when it is
done without sacrificing milk production.
Through improved animal genetics and
feeding management, milk production per ani-
mal has steadily improved for many years and
this trend continues (NASS, 2011). Producing
more milk with the same or fewer animals can
provide both environmental and economic ben-
efits. This is illustrated by increasing the milk
production level of the herd to 11,000 kg per
cow (Table 10.1). To produce the additional milk,
feed and nutrient intakes are increased, which
increases nutrient excretion in manure (Rotz
et al
., 2011b). This creates a small increase in
ammonia emission with a 6% increase in nitrate
leaching. Considering the greater amount of
milk produced, the total reactive N loss per unit
of milk is reduced by 6%. An environmental
concern though, is that the long-term increase in
soil P and K is increased, which could lead to
greater nutrient runoff losses in the future.
Greenhouse gas emissions are also increased
about 4% but the carbon footprint (emission per
unit of milk produced) decreased 4%. Increased
milk production is of great benefit to the pro-
ducer. Increased feed and manure-handling costs
were offset by increased milk sales increasing
annual farm profit by over US$200 per cow.
Manure handling
The effects of four manure-handling options are
illustrated using a smaller dairy farm in central
Pennsylvania. The dairy herd consisted of 100
Holstein cows and 80 replacement heifers with
an annual replacement rate of 35% and milk
production of 9500 kg per cow. All animals were
fed total mixed rations to meet their nutrient
requirements. Free stall barns were used to house
animals with manure removed daily by scraping.
Crops included 40 ha of lucerne, 50 ha of maize
and 10 ha of oats produced on gently sloping
clay loam soil. Small amounts of N, phosphate
and potash fertilizers were used to meet crop
nutrient requirements along with all manure
nutrients produced on the farm. Lucerne and
maize silage stored in bunker silos provided all of
the forage needed to feed the herd. The remaining
maize and oats were harvested, stored in a tower
silo and fed as high moisture grain. With this
cropping strategy, 87% of the total feed require-
ment was produced on the farm. Straw from the
oat crop was also used for bedding.
For the first manure-handling option, daily
hauling and field application of manure was
used (Table 10.2). Manure was scraped from the
free stall barns, loaded on a spreader and applied
to cropland each day. The manure was broadcast
on the field surface without incorporation into
the soil. As a second option, a concrete tank was
used to store manure for field application in the
spring and autumn, and manure was incorpo-
rated into the soil by a tillage operation within
2 days of application. Compared with the daily
hauling practice, use of long-term manure stor-
age increased ammonia emission by 32% but
decreased nitrate leaching and denitrification
losses by 14% (Table 10.2). Overall, the total loss
of reactive N was increased 9%. Energy use was
