At the start of the planning period, the farm had a higher level of pasture cover and the herd was in better condition than the previous year (Table 1 ). Milk production was the same as last season (1 .39 kg MS/cow/day), and the case farmer had a similar level of silage on hand (1 03 versus 1 00 bales). An additional 1 .0 ha of forage crop had been planted, but the farmer had about 900 less bales of hay on-hand. The silage and hay had been cut later than last year and this would result in reduced pasture growth rates if the season turned dry. The case farmer was carrying an extra four cows, but had an additional 4.0 ha in the milking area. January was cool and wet like the previous year, but pasture growth was higher and the farm had a higher pasture cover on February first than the previous year (1 800 versus 1 350 - 1 400 kg OM/ha). Conditions started to turn dry at the end of January. Pasture growth rates were very low during February and gradually declined through the month as conditions remained dry with the farm only receiving some 21 mm of rainfall. In contrast, the farm experienced good growing conditions over February in the previous year. The difference in growing conditions is reflected in the change in average pasture cover. I n the first season, the average pasture cover remained constant throughout February, whereas this year, it fell some 500 kg OM/ha over the month.
March was cooler than normal, and rainfall was about average. In contrast, pasture growth rates had been above average during the previous March. Pasture cover declined slightly through March, whereas last season, it increased by almost 1 00 kg OM/ha. Ouring April, pasture growth rates were about average and pasture cover increased slightly during the month. In the previous season, pasture growth rates were above average during the first half of April, but declined rapidly as conditions became cold and dry.
Table 1 . Comparison of years one and two.
Factor Year 2 Year 1
25th December cover 1 800 1 700 Cow condition 4.8 Milk 1 .39 1 .39 Cow numbers 1 50 1 40 Rotation 30 30 Effective area 52 48? 1 st cover 1 800 1 650 Cow condition 4.8 4.5+ Milk 1 .39 1 .39 Cow numbers 1 44 1 40 area 3.0 2.0 1 03 1 00 1 488 2400 Rotation 30 30 1 st cover 1 800 1 400 Cow condition 4.8 4.5 Milk 1 .39 1 .39 Cow numbers 1 44 1 38 Rotation 28 - 30 29 - 30
Farmer A -Summary of Year Two 1 53
Factor. Year 2 Year 1
March cover 1 300 1 350 - 1 400 Cow condition 4.8 4.5 Milk 1 .04' 1 . 1 3 - 1 .22 Cow numbers 142 1 38 Rotation 25 - 28 24 - 29 Date started 1 0/21xx 3 1 /1 /xx Date terminated 23/3/xx 1 /3/xxc Date started 1 5/3/xx Date terminated 29/3/xx
Amount fed 17 bales
1 st cover 1280 1 445 Cow condition 4.5 4.5 Milk 1 .04 1 . 1 3 - 1 . 1 7 Cow numbers 1 26 1 38 Rotation 24 - 25 25 - off date 28/4/xx 29/4/xx
Cow numbers at off 1 1 9 1 299
Milk 0.84 1 . 1 3
Condition score 4.5 4.5
cover 1 332 1 392
Date herd on 1 3/4/xx
Rotation at off 25 28
Urea for winter 1 .5 tonnes 0.0 tonnes
e The young stock were given 3.0 ha because they were short of feed as a result of late hay and silage crops. h Average herd condition increased to 5.0 condition score units on the 24th March, and then declined to 4.8
condition score units.
i Milk production held at 1 .22 kg MS/cow/day through most of February. When the herd went onto the second
forage crop on the 28th February, the case farmer reduced milk production to 1 .04 kg MS/cow/day.
a The rotation length is the range over the previous month, and the figure in brackets is the rotation length at the end of the month.
f Second forage crop of 1 .5 ha fed on the 28th February.
c The crop was not grazed for 5 days during this period due to muddy conditions. d Not fed until the herd were dried off.
9 The case farmer put 9 cull cows on waste ground on the 5th April and milked them until the 1 8th April when they were sold to the works.
The plan
Planning horizon
The data from year two confirms that the summer planning period starts at Xmas and goes through to mid March when the autumn rains are expected. This planning horizon is chosen because it is a period when the farm is in feed deficit. It moves from a feed surplus position in late spring to a feed deficit situation in early summer. Termination of the planning horizon occurs when the autumn rains arrive in mid March. The rains cause a flush of growth and the farm experiences a period of feed surplus conditions. Mid March is also near a critical decision, drying off, which has a major influence on next season's production.
Hierarchies of plans
There were two plans that dominated the period of the study, one over the summer (Xmas - April 1 st), and another from April 1 st to calving. Shorter planning periods were encapsulated within these two plans and related to events, e.g. pre-forage crop, forage crop, post-forage crop to April 1 st, April 1 st to drying off.
Values, goals and targets
As with last season, the case farmer's goal over the summer-autumn was to maximise the number of milking cows on-hand at mid March. To achieve this goal, the farmer had several important intermediate targets. He aimed to maintain the herd on a 25 - 30 day rotation. The case farmer's milk production target in early January (pre-forage crop) was to maintain milk production at the post-Xmas level (1 .39 kg MS/cow/day in this year) for as long as possible. This goal was not identified last year. It appears the case farmer tries to hold milk production at a particular level for as long as possible. The case farmer has no absolute level in mind, but the aim is to prevent a downward trend in milk production. This is achieved through reducing the rotation length. Normally, the case farmer then introduces a target of 1 . 1 3 kg MS/cow/day which is used to Signal that it is time to introduce the forage crop. Once introduced to the forage crop, the milk production target for the herd is 1 .04 kg MS/cow/day. Post-forage crop, the case farmer's targets are to maintain the herd on a 25 - 30 day rotation and ensure the condition of individual cows does not fall below 3.5 condition score units.
This year, the case farmer changed the forage crop milk production target to 1 .1 3 kg MS/cow/day with an introduction target of 1 .22 kg MS/cow/day. The herd went onto the forage crop at 1 .22 kg MS/cow/day, but the case farmer then increased the forage crop milk production target from 1 .1 3 kg MS/cow/day to 1 .22 kg MS/cow/day because of the good feed situation and the state of the herd. Conditions deteriorated through February, and the case farmer revised the forage crop milk production target downwards to 1 .04 kg MS/cow/day when he placed the herd on the second forage crop in early March.
In early April, the primary goal of the case farmer for the autumn period was to maintain herd condition at 4.5 condition score units. The case farmer prefers to maintain the condition of the herd at the level he will calve at rather than take condition off the herd in late lactation and put it back on during the winter. This is because it is more difficult to increase herd condition over the winter months. The case farmers other goal was to maintain milk production at 1 .04 kg MS/cow/day. This target was used because the case farmer knew that if milk production fell below this level, the herd would be losing condition.
Farmer A - Summary of Year Two 1 55 The case farmer also used the average pasture cover targets he had calculated from his feed budget. He analysed six scenarios which comprise three drying off dates and for each of these scenarios, with and without winter nitrogen options. The case farmer developed a 3 x 2 matrix (Table 2) which showed the average pasture cover target required at drying off for each of the six options. The case farmer used the same average pasture cover (2200 kg OM/ha) and cow condition targets (4.5 condition score units) for calving as last year.
Table 2. Pasture cover targets the case farmer must dry off at for different dates, with and without urea.
Off Date With Urea Without Urea
1 5th 1 250 1 450
20th 1 287 1 487
30th 1 325 1 525
The case farmer had an annual production target of 26,000 kg MF. In early March he had produced 22,500 kg MF and believed that if he could maintain milk production at 1 .04 kg MS/cow/day through March, he would produce 25,000 kg MF by the end of the month and would only need to produce 1 000 kg MF in April to meet target. This target did not influence decision making.
Planning method
At the start of summer, the case farmer assessed the state of the farm (average pasture cover, pasture growth rates, forage crop, silage yield, cow intake, condition and milk production). He then used this information to undertake a mental simulation (rough feed budget) from Xmas to mid March to assess whether his typical plan would work. Importantly, the case farmer believed a climatic shift had occurred and that wet summers had become the norm. He therefore used higher than average pasture growth rates in his mental simulation. This and the good feed position suggested his "typical" plan was too conservative. Therefore he modified the planning heuristics and increased his milk production targets by 0.085 kg MS/cow/day. This in effect increased cow intakes, and initiated forage crop grazing at an earlier date. The ''typical" plan was modified in two other ways. First, because a strategic decision had been made to replace the summer silage with 1 .0 ha of forage crop, this second crop replaced the silage in the plan. This also meant the plan included a second paddock of new grass that was to be sown before mid April. The other modification was because of a tactical problem with reproductive performance in the previous spring (very cold and wet). As such the case farmer planned to delay removing the bull for two weeks to allow later cycling cows to be mated. This in turn meant he had to shift pregnancy testing two weeks later. These modifications were pre-set before the case farmer tested the feasibility of this modified ''typical'' plan. The case farmer did not undertake a formal feed budget once the forage crop was grazed to assess the amount of silage to be fed as was undertaken last year. This was because the initially the case farmer did not intend to use silage.
As with last year, once the pregnancy test information was obtained, the case farmer completed a formal feed . budget with monthly time intervals for the period April 1 st to calving. The first step was to estimate the average pasture cover he required on the farm at May 1 st to achieve his average pasture cover and cow condition targets at calving. His targets at calving (20th July) were 2200 kg OM/ha and an average herd condition of 4.5 condition score units. After entering cow numbers, feed requirements, supplements and average pasture growth rates into the equation, the case farmer estimated that he needed
an average pasture cover of 1 600 kg OM/ha on May 1 st. The case farmer then estimated the extra average pasture cover he could grow if he applied 1 .5 tonnes of urea during autumn-winter. This allowed him to reduce his May 1 st target to 1 400 kg OM/ha. Average pasture cover was 1 300 kg OM/ha in early April. The case farmer then estimated the pasture cover targets he needed to achieve for different drying off dates, with and without urea (Table 2). The plan the case farmer developed had no allowance in it for increasing cow condition. Therefore, his main concern at that point in time was the condition of the herd.
The case farmer used a partial budget to estimate the costs of the urea, and the income generated from extending the lactation. This analysis showed nitrogen was economic to use. Although the case farmer had previously mentioned bought-in hay as another option for extending the lactation, this was not analysed.
The case farmer stated that he would not use nitrogen if the autumn flush occurred because he did not believe he would get a response under these conditions. This argument was based on his experience with spring nitrogen. He believed that if he used urea at the same time, it would upset the nutrient balance, and this would lead to reduced pasture growth later in the winter. He has experienced a lag effect in spring after applying urea. Pasture growth rates used in the planning process come from previous experience. The case farmer only completed one feed budget before drying off. Rather than recalculate another feed budget after each farm walk, he just compared his actual average pasture cover to the targets he had calculated that are shown in Table 2. This reduced the amount of effort the case farmer had to put into the planning process.
Planning rules
Analysis of the data identified several planning rules used by the case farmer to develop his plan (Table 3). The reasons given by the farmer for these rules is also specified.
Table 3. Decision rules for the summer plan.
Decision Rule Reason
Selection of summer- I F date = Xmas, At Xmas the case farmer aims to take as
autumn stocking rate THEN identify cull cows not many cows as possible through the
considered suitable for milking summer-autumn period. He identifies
through the summer-autumn and culls that he thinks are not suitable to take se" them and milk the remainder through this period, and sells them at, or
through the period. soon after Xmas. These culls are cows
with mastitis or a dangerous
Drying off the herd or Do not dry off part of the herd and The case farmer has a policy of keeping part of the herd continue to milk the remainder. the herd together as a unit. Therefore he
does not dry off part of the herd and
continue the remainder.
Culling empty cows IF a cow is empty, The case farmer prefers to continue
THEN retain the cow until near milking empty cows rather than cull them
drying off. immediately because they are the best producing animals. Without a developing
fetus, empty cows produce more milk
than cows.
Milk production target Do not use a milk production target The case farmer has used a milk for supplement that will result in poor utilisation of production target when feeding
feeding supplements or pasture. supplements (forage crop. silage) that
has ensured a high level of utilisation. This target also ensures the level of
Farmer A -Summary of Year Two 1 57
Decision Rule Reason
quality is maintained. The case farmer
believes that if he used a milk production target of 1 .39 kg MS/cow/day when
feeding supplements, both supplement and pasture utilisation would be poor. Therefore, supplement and pasture
utilisation determine the upper limit of the milk production target over the summer Forage crop grazing Introduce the forage crop when milk The forage crop is introduced to the herd
production falls to 1 .22 kg relatively early so that the change in diet
MS/cow/day. is relatively gradual. This also allows the
forage crop to last for longer than if it was introduced later and made up a larger
proportion of the herd's diet. Data from
this season suggests that if the proportion of pasture in the diet is too low, metabolic
problems can occur when feeding the
forage crop. The case farmer thought
year two was going to be a wet summer
and increased the milk production target
by 0.085 kg MS/cow/day to take
advantage of the expected above
rates.
The amount of forage Feed sufficient forage crop to The case farmer thought that year two crop fed to the herd maintain milk production at 1 .1 3 kg was going to be another wet summer, and
MS/cow/day. so he increased the milk production target
0.085 kg MS/cow/day in order to take
advantage of the expected higher then
average pasture growth rates. He had leamt in the previous wet summer that the herd could produce at high levels over the
summer had sufficient feed.
Forage crop nutrition The case farmer admits that one of the
problems with the forage crop is that
unlike maize, it does not put condition on
his herd. Instead, it is used to produce
milk. However, if the level of pasture the
herd is consuming reaches low levels
while feeding the forage crop, the herd
will lose condition.
Forage crop maturity Feed the forage crop at its maturity Forage crop quality tends to decline after
date. its maturity date is reached. The case
farmer attempts to minimise this effect by
planting the forage crop at a date that ensures maturity coincides with the period
when the forage crop is likely to be grazed. However, forage crop maturity
has little effect on the case farmer's
decision making at the actual time of Forage crop removal Graze the forage crop such that the The date by which the new grass must be
and new grass new grass can be sown by mid sown is reasonably flexible. For example,
sowing date April. the first crop was sown in late March,
while the second crop was sown in mid April. In year one, the impression was gained that the new grass had to be sown
mid March.
Rotation length Maintain rotation length between 25 The case farmer's choice of maximum
- 30 day round. rotation length relates to the impact of the stocking rate/cow concentration effect. Above a thirty day round, cow density per
hectare is such that there is insufficient
pre-grazing mass to fully feed the herd.
Decision Rule Reason
insufficient to achieve the pre-grazing
residuals the case farmer needs to fully
feed the herd at the next grazing. On a
longer rotation, pasture cover can get too
long (> 2000 kg OM/ha) and reduce pasture growth rates. At the other extreme, the case farmer does not want a rotation length of less than 25 days
because at this rate, average pasture cover declines too quickly, and pasture
is reduced.
Plan
The case farmer's plan for year two is summarised in Table 4. At Xmas he planned to carry 1 44 cows through the summer-autumn. The case farmer planned to maintain a rotation of 25 - 30 days and hold production at some level for as long as possible. The forage crop was to be fed when milk production fell to 1 .22 kg MS/cow/day in late