EVALUATION OF DAIRY HERD FERTILITY
In order to evaluate the fertility status of a herd it is necessary first of all
to quantify certain reproductive values, and in order to do this it is
necessary to have access to records of reproductive events. The
minimum information required is identity of cow; last calving date; first
and subsequent service or insemination dates; confirmation of
pregnancy.
The following measurements of fertility can be made:
Number of services or inseminations per conception: The number of
services should not exceed 2 services, if exceeds than this number, the
herd suffers from reproductive problems like repeat breeder
(conception failure).
Calving interval and calving index (CI):The calving interval is the
interval (in days)between two successive calvings; for an individual cow
the calving index is the mean calving interval of all the cows in a herd
at a specific point in time.
These two measurements have been used traditionally as a measure of
fertility, since they indicate how closely the individual cow or herd
approximates to the accepted optimum of365 days.
The calving interval (or index, CI) is the sum of two components, the
interval from the last calving date to the date of conception (a) and the
length of gestation (b).
Thus:
CI = a + b
Therefore:
CI = 85 days + 280 days = 365 day.
Calving to conception interval (CCI): The calving to conception interval
(CCI) is calculated by counting the number of days from calving to the
service that resulted in pregnancy.
The CCI is a useful measurement of fertility but requires a positive
diagnosis of pregnancy to be made. The CCI can be expressed thus:
mean CCI = c + d
Where c is the mean calving to first service interval and d is the mean
first service to conception interval.
Therefore:
Mean CCI = 65 days + 20 days = 85 day.
Days open: This is defined as the interval, in days, from calving to the
subsequent effective service date of those cows that conceive, and from
calving to culling or death for those cows that did not conceive.
Numerically, it will always be greater than the mean CCI unless all cows
that are served conceive in which case it would be the same.
The average days are (85 -110days).
Overall pregnancy rate: which is calculated by dividing of the cows
calving to the cows inseminated.100
The overall pregnancy rate would be50%.
The pregnancy rate is influenced by:
●The correct timing of artificial insemination which will be dependent
particularly on the accuracy of estrus detection.
● Correct artificial insemination technique, and handling and storage of
semen.
● Good fertility of the bull if natural service is used.
● Adequate nutritional status of cows and heifers at the time of service
and afterwards. The overall pregnancy rate is very useful measures of
fertility; it is used to calculate the reproductive efficiency of the herd.