92
SEX MATURITY IN DAIRY CATTLE
[Vol. XXVII, Part III,
In the ' roughage group ' most of the heifers did not come to oestrum at all even
at the age of 5-6 years. Only 3 heifers out of 8 came to heat at the age of 3 years.
Two became pregnant ; the other 6 animals were examined per rectum and it was
found that the genital organs were under-developed.
With a view to eliminate the genetical factors the heifers were grouped accord-
ing to sires. It was found that the heifers from the same sire showed their first
oestrum at a younger age in the concentrate group than those in the roughage group.
DISCUSSION
The longer the animal is unproductive, the greater is the liability of the farmer,
and from this point of view early calvings are advantageous. Early calvers gave
more calves than late calvers [Johansson 1950]. Hartmann [1953] found that fertility
and lifetime production were highest in cows which had their first calving at an
early age and that it did not affect the body size or growth of the animals. It is
the lactation that taxes the heifer and not the burden of pregnancy. The wastage
rate, calculated up to the 5th lactation by the Milk Marketing Board [1953] has
not been affected by the age at first calving. Gethin [1950] thinks that the infor-
mation about the influence of age at first calving on subsequent overall reproduc-
tive efficiency is conflicting and on the whole insufficient. However, his observa-
tions relate to calvings at the age of 27 months and earlier. How early can heifers
be calved without any detriment to future life would depend on the environment
where they are kept and on the individual heifer. This question has been con-
sidered on the basis of the experience gained during these investigations. It appears
that at the Farms all the Hariana heifers should show their first oestrum and con-
ceive at the age between 2 years 6 months to 2 years 9 months. They would, there-
fore, calve at the age of 3½ years. All heifers which do not come to heat at this
age should be regarded as cases of sub-fertility and attention should be paid to them
to avoid economic loss at the farms.
SUMMARY
In a fairly comprehensive survey of a large number of dairy farms in U. P., it
has been observed that the age at first calving is 1538±65 days (approximately 51
months) in Hariana cattle. The earliest age at which the heifer had its first calving
was 895 days (approximately 29½ months). Heifers calving beyond the age of 5
years have been considered as confirmed cases of sub-fertility. The percentage of
such sub-fertile cases to the total population was 12.4 per cent.
The breeding bulls used at the farms have not appreciably influenced this
character. It is explained by assuming that as no selection for this trait was carried
out, the sires studied were of average merit. The procedure to be adopted in
selecting animals for this character, which can be done simultaneously with the
progeny testing of bulls for milk yield, has been indicated.
It has been observed that feeding of balanced ration in general, is favourable
for early maturity. The animals which are fed with a balanced ration consisting
of concentrates, a dry and a little of green roughage, mature much earlier than
those kept in the same plane of nutrition on all roughage (green berseem and bhusa)