ABSTRACTS 381
The quality of the semen will depend upon the methods of collection and preserva-
tion. For semen obtained directly from the penis of the stallion after natural inter-
course the quality is low as it contains secretions of the vagina of the mare and may be a
medium through which disease is spread. Semen collected by the artificial vagina, if the
procedure has been properly carried out under the most sanitary conditions, will be of
very good quality and may keep well. The semen is preserved by first allowing it to stand
a few minutes. One part is then mixed with two parts of preserving diluent and the
mixture is cooled by packing in cracked ice. It is then stored at 8°-10°F. until used.
[J. N. W.]
Inheritance of horns in sheep. B. L. WARWICK AND P. B. DUNKLE (1939).
J. Heredity 30, 325.
I N many breeds of domestic sheep the rams have horns. They may be relatively small
or as large as those of the Rocky Mountain Bighorn, a wild species. In any species
the horns of the female, when present, are much smaller than those of the male. One
of the big horned domestic breeds is the Dorset Horn.
In the most widely distributed breed or type of domestic sheep, the Merino (including
the Rambouillet), the males of most strains have horns while the females are hornless.
The females do have knobs, however, ordinarily less than one inch high, resembling
horn cores. In some cases they have horn-like coverings called scurs which are easily
distinguished from the horns of the Dorset female by their small size and irregular shape.
Some strains of Merino and Rambouillet as well as many other breeds of domestic
sheep, such as the Shropshire, Southdown, Cotswold and Suffolk, are hornless in both
sexes. They not only lack horns but have depressions in the skull instead of horn cores.
In 1905 and 1909 Wood crossed the Dorset Horn and Suffolk breeds and interpreted
the inheritance of horns in sheep as dominant in the male and recessive in the female.
His results have, however, been interpreted differently by later workers. Arkell proposed
another hypothesis in 1912 which involved a sex-linked inhibitor, but this explanation
has since been discarded. An intermediate horn in Wood's F 1 generation might have
suggested dominance of hornlessness in both sexes with this dominance incomplete in the
male. On the basis of present evidence this seems to be a valid explanation of horn
inheritance in sheep.
Wood's F 1 ewes all had depressions. At two or three years of age, however, scurs
appeared. Arkell studied crosses of hornless breeds with the Dorset Horns as well as
those of hornless breeds with the Merino and Rambouillets.
The authors suggested in 1931 that the horns of Rambouillet males and the knobs
of the females were due to one principal pair of recessive genes. Recent experiments
confirm this in their opinion. They now think that scurs may be due to additional
minor genes but their tests are incomplete. They have, however, confirmed the mono-
factoral basis for the inheritance of hornlessness and horned in this stock.
Commercial crossing of Dorset Horn rams with Merino ewes is common in certain
areas. All F 1 ewes, whose dam was a Merino with knobs, have horns. ' When homo-
zygous hornless Rambouillet rams, ' as identified by breeding tests, ' or rams of pure
hornless breeds
are crossed with Merino or Rambouillet ewes, the F 1 female
progeny are invariably hornless (with depressions). '
Hornless female progeny are always produced when Dorset, which is horned in both
sexes, and Merino or Rambouillet, in which the male is horned and the female is knobbed,
are respectively bred to a pure hornless type.
When the Dorset and the Merino or
Rambouillet are crossed with each other, horned females of the Dorset parental type are
obtained. ' These facts suggested the hypothesis that the genes for hornless, Dorset
horns, and Merino horns constitute an allelic series. ' In confirmation of this, backcrosses
of an F 1 Dorset × Rambouillet ram to a Rambouillet or Meri o ewe with knobs were
made. Female progeny were horned and knobbed, as expected, in a 1:1 ratio. If, how-
ever, instead of being allelic the horns of the Dorset and Merino were due to different
pairs of genes, such back crosses should have given horned, knobbed and hornless female
progeny in a ratio of 1:2:1.
The genes are indicated thus ; hornlessness H, Dorset horns H' and Merino or Ram-
bouillet horns h. They are considered allelic.
[J. N. W.]