A few figures for different facts and groups are presented
here:
Av.Gest.for 9353 heifers, which calved under 2 years: 267,5 days

y i " 63912 cows (2.parturition and more): 278,2 days
" " m 19602 heifers, which calved over 2 years: 278,23 days
The incidence of twins born was in 30,000 heifers: 0,8%
and in 64,000 cows: 4 ,8%

Significant differences were found between Service-Sires, with
regard of the gestation length of their offspring carried in
utero, as the following figures demonstrate:

No.of Partur. Length of No.of Partur. Length of

Bire of heifers Gestation of cows Gestation
Usi A 275,4 days 35750 275,9 days
Adi 35153 2B 260 b3
Thor 139 27942 =¥ 3 871 REOSIN M
Hamdan 615 28054800 740 281358 Y
Hashuv 143 281, 20mt 260 2824 .t

3. SEX RATIOS IN SIRE PRCGENIES.

In 1966 R. Bar-Anan published Israeli data, showing that
certain bulls sire offspring of a sex ratio, significantly diffe-
rent from the average. Present data, accumulated over three years,
confirm these findings, as the following figures demcnstrate.

Number of Parturitions by cows only and percentage of males born:

Y All % Sire % Deviation |Sire % Deviation
qer Sires males N. males from mean B. males from mean
1964/5 | 20779 50 341 58 +8% 1318 52 +2%
1965/6 | 21341 49 1289 52 +3% 1043 53 +4%
1966/7 | 21801 50 2213 54 +4% 2y 53 +3%

The total deviations from the mean sex ratio for each of these
two Sires, repeated each year are significant by 0,05. There
appear to be certain bulls, which sire offspring of a sex ratio,
consistently different than the average.

4. TRENDS OF EARLY AND LATE MATURING IN PROGENIES OF SIRES OF
THE SAME BREED.

Progeny testing for milk-production is carried out prelimi-
narily for the first 122 days and finally for the 305 days
lactations. The contemporary comparison method is used on actual
heifer-yields, and their within herd-year-season weighted devia-
tions from stablemate heifer yields are computed. These are
separately carried out for heifers, which calved under 24 months
of age and for those over 24 months old. These progeny-tests,
within age groups, revealed (Bar—Anan, 1967), that within the
friesian breed there are Sires, whose young daughters (under 2

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