P. V. SUKHATME
169
TABLE VI
Comparison between the performance of the foundation stock and their first progeny
Foundation stock
First progeny
t
(1)
Average . .
Standard error
Average . .
Standard error
Number
of
goats
(2)
19
34
Number
of
lactations
(3)
68
130
Total
milk
yield
oz.
(4)
4751.8
198.5
5832.5
210.3
3.3**
Length
of
lactation
days
(5)
176.7
8.4
176.1
5.2
0.1
Average
milk yield
per day of
lactation
oz.
(6)
26.9
1.8
33.1
1.4
2.9**
Number
of
goats
(7)
16
30
Number
of
lactation
(8)
48
110
Length of
kidding
interval
days
(9)
312.5
16.9
291.4
9.5
1.1
Average
milk yield
per day of
kidding
interval
oz.
(10)
16.2
1.5
20.9
0.8
3.5**
The object of this note is to analyse the records
maintained on the Farm with a view to find out the
extent to which the breeding policy followed on the
Farm during the last 10 years has resulted in the
improvement in the milk yield of the herd. The
appropriate method to assess the improvement
would be to compare in successive progenies, the
total milk yield during lactation in relation to the
length of lactation and the length of kidding inter-
val. In other words, we have to compare the per-
formance for total milk yield by standardizing, as it
were, the length of lactation and kidding interval.
This is done by comparing the values for (1) average
milk yield per day of lactation and (2) average milk
yield per day of kidding interval.
Table VI gives the set of comparisons between
the performances of the foundation stock and the
first progeny. Columns (2) and (7) of the table
show the number of goats in the two generations
whose records have been compared. Columns (3)
and (8) give the number of lactations to which the
average performances shown in the other columns
refer. Columns (4), (5), (6), (9) and (10) give the
average values with their standard errors of the
total yield during lactation, the length of lactation
in days, the average daily milk yield during lacta-
tion, the kidding interval, and the average daily
milk yield during the kidding interval respectively.
It will be seen that while there is a slight decrease
in the length of lactation (from 176.7 to 176.1 days)
and the kidding interval (from 312.5 to 291.4 days)
the first progeny has given a higher total milk
yield as also a higher average daily milk yield during
the lactation and the kidding interval. But this
comparison without reference to the errors of the
averages compared is by itself inadequate to sup-
port the conclusion regarding the superiority of
the first progeny over their mothers. For the
averages which have been compared are themselves
variable in the sense that different values for the
performances would have been obtained had there
been different numbers of goats in the two genera-
tions. Before we conclude that the first progeny is
superior to their mothers, it is therefore necessary
to satisfy ourselves that the difference observed
between the performances of the two generations is
larger than the possible difference arising from
variability of the averages. This variability of the
averages is measured by what is called the standard
error and the statistical method to judge whether
the difference observed is due to chance causes is
known as the t test of significance. When the
difference observed cannot be explained on the
grounds of chance, i.e., it is larger than can be
expected on chance causes alone, the difference is
said to be statistically significant. The values for
the standard error have been shown below the
respective averages and the values of t are shown in
the last line of the table. Whenever the observed
difference is found to be significant, the fact is
indicated by asterisks against the corresponding
values of t.
It will be seen from the table that there is no
significant difference between the length of lacta-
tion and kidding interval of the two generations but
that the first progeny has given a statistically
superior performance over their dams in respect
of all the other three characters. This may be
due to several factors: (1) the sires may have had
a real transmitting ability, (2) the better feeding
and herd management right from the birth of the
first progeny in contrast with the environment in
which the dams were reared may also be partly
responsible, (3) the existence of hybrid vigour
which is frequently observed in the progeny of
unrelated animals may also partly offer an, explana-
tion, or (4) there may have been a seasonal effect
arising from the different climatic and disease con-
ditions in the different years in which the dams
and their daughters had their respective lactations.
The better feeding and management at the farm is
expected to have a beneficial effect on the perfor-
mance of the first progeny but it is obviously
impossible to isolate for study the effect of this
factor. We have, however, gone into considerable
detail in regard to factors (1) and (4). Table VII
shows the sirewise comparison of the first progeny
and their mothers.