and a 2% increase in interest rate for Holstein-Friesians and
Jerseys .
variable Change Pro�lt Econo.ic value/ba
/ha /cow Protein Milk�at Lactose Voluae Live-
weight (') ( $ ) ( $ ) ( kg) ( kg) ( kg ) ( kg ) ( kg ) Bolstein- Friesian Base .odel 0 1 , 989 876 1 0 . 53 4 . 19 -1 . 30 -0 . 09 -1 . 10 Variable +10 1 , 970 868 10 . 55 L 21 -1 . 29 -0 . 09 -1 . 08 costs Interest rate + 2 1 , 969 867 10 . 55 4 . 22 -1 . 28 -0 . 09 -1 . 08 stock prices +10 1 , 977 871 1 0 . 54 4 . 21 -1 . 29 -0 . 09 -1 . 09 Jersey Base model 0 2 , 171 8 4 0 1 1 . 8 4 4 . 51 - 1 . 61 -0 . 10 -1 . 37 Variable +10 2 , 150 8 3 2 11 . 85 4 . 54 -1 . 60 -0 . 10 -1 . 3 4 costs Interest rate + 2 2 , 152 833 1 1 . 8 5 4 . 54 -1 . 60 -0 . 10 -1 . 35 stock prices +10 2 , 159 836 1 1 . 85 4 . 53 -1 . 60 -0 . 10 -1 . 36
Variation in stock prices had the least effect on profit per
cow , profit per ha and on economic values . Hi storica l l y ,
prices for mature cows and r i sing "2 year old i n-cal f hei fers changed in accordance with variations in the price for milk
or mi lkfat . The returns per kg mi lkfat can be multipl ied by
110 to arrive at a reasonable estimate for the cost price for dairy cows ( Rayne , 1 9 8 9 ; Lincoln University , 1 9 9 1 ) . However , using actual prices for the last three years and a l l owing for a price d i fferential between Jerseys and Holstein-Friesians the factor was c loser to 150 for Holstein-Friesians and 1 3 0 for Jerseys . Thi s close rel ationship between the returns for mi lkfat and the cost price of dairy cows has a stabi l i s ing effect on net f a rm i ncome .
Chapter 5, Aspects ot selection tor econoaic .erit in dairy cattle - G. Ahlborn, 1994 1 7 2
An increase in i nput costs h a d only a relativel y sma l l effect
on economic values . An increase in costs per cow increased
the economic values for milk components and decreased the economic value for l iveweight s l ightly .
General ly , the effect of increased costs was sma l l for both Holstein-Fri e s i ans and Jerseys . Interest rates and variable costs had a s l ightly greater effect on profit per cow and profit per ha than on stock prices .
5 . 2 . Biologica l variables
One of the general characteristics of biological variables is their inherent underlying variation . Thus , the mean of each variable i s the most l ikely value , but a range of possible values i s encountered for all variables . The variation i s
traditiona l l y described by the second moment of the f requency
distribution for the variable . However , the standard
deviation is not known for a number of biological variables partly due to the d i f ficulty and relatively high cost of
measurement . Consequently , the effect of l ikely changes i n
the values of the biological variables was evaluated by
assuming a coefficient of -variation of 1 0 % for these
variables . Thi s was calculated using the basel ine value as
a mean resulting in an approximate standard deviation for these vari ables :
Range for variable ( ± ) = ( � * 1 0 ) / 100
In addition , some biological variables such as energy ef ficiency are estimates only with an associated l arge standard error requiring the eval uation of a wide range of values to arrive at a reasonable approximation of thei r effects on net farm i ncome .
The results from this sensitivity analys is i ndicated
Chapter 5, Aspects of selection for economic merit in dairy cattle - G. Ahlborn , 1994
173
in the biological variables . the reasons for this were
either i nherent to biological variation or poor estimation accuracy .
5 . 2 . 1 .
Metabo l isable energy ava i l ableThe amount of energy available f rom pasture for feeding dairy cattle per annum is one of the most variable factors in this dairy production system and i s l argely determined by the management of the farm . Bes ides the appl ication of fert i l i zer to i ncrease the amount of OM grown , uti l i zation and energy content of the OM inf 1 uence the amount of metabo l isable energy avai lable for cows .
The effect of changes in these variables , and thus the amount of ava i l abl e metabo l isable energy , on economic values was evaluated . Results are shown in Table 5 . 1 0 . for the base situation and changes of one ( energy content of OM ) and two ( kg OMjha grown ) standard deviations above and below the mean . As fi rst and second moments were not avai l able for the proportion of f eed uti l ised thi s variable was decremented from 8 7 . 8 % in 1 0 % steps .
The amount of metabo l i s able energy ava i l able affected both stocking rate and total farm prof it , resulting in differing
economic values per ha . However , the relati vi ty between
economic values for the various traits and economic values per cow rema i ned the same as prof it was defined as the difference between revenues and costs . The minimal effect of management pol ic i es on economic values per cow was reported by Oekkers ( 1 9 9 1 ) after an analysis of the effect of less than optimal management pol icies on economic values for dairy
cattle . Groen ( 1 9 8 9 ) a l so concl uded that production levels
and feed qual i ty have no noteworthy influence on the economic
Values for m i l k and beef production traits . However , both
Chapter 5, Aspects ot selection tor economic merit in dairy cattle - G. Ahlborn , 199.