|Abstract or Summary
- Genetic and environmental factors affecting age of first estrus,
wool production, reproduction and lamb production were examined in
eight groups of crossbred ewe lambs from two birth years. The 399
ewe lambs whose first year production was analyzed were from eight
crossbred groups resulting from mating North Country Cheviot, Dorset,
Finnsheep and Romney rams to Suffolk or whiteface Columbia-type range
ewes. The ewe lambs were born January through March of both 1973 and
1974, and were raised to weaning on western Oregon hill pastures.
They were summered and maintained through the breeding season on
irrigated pastures. At the end of the breeding season each year,
ewes within each of the eight groups were randomly divided between
hill pasture and irrigated valley pasture management systems. After
lambing in common facilities, they were returned to the appropriate
management environment where they remained throughout lactation.
Average age at first estrus for the 90 percent of ewes which did
cycle their first fall was 205 days. Age at estrus between years differed by 18 days (P<.01). Sire breed and the sire x dam breed
interaction were not significant effects, but ewes with Suffolk dams
cycled ten days earlier than ewes with Columbia dams (P<.01). Also
a greater proportion of ewes with Columbia dams failed to cycle their
first fall (18 percent versus 2 percent for ewes with Suffolk dams).
None of the birth year interactions was significant. The regression
of age at estrus on birth date of ewe was -.85 days per day (P<.01).
The regression of age at estrus on ewe weight at first estrus (estimated
by interpolation between bracketing weights) was 0.39 days per
pound (P<.01). The unexpected signs of the two regression coefficients
probably resulted from shortened day length in the fall triggering
estrus at a fairly constant calendar time but at varying ages and
weights, depending upon when the lamb was born the previous spring
Breed of the ewe's dam significantly affected wool grade with
Columbia crosses having finer wool. Staple length was longest and
about equal for Finn and Romney sired ewes; Dorset crosses produced
the shortest wool. Columbia cross wool was longer than Suffolk cross
wool only in Finn and Dorset cross ewes. Grease fleece weight of
Columbia crosses was consistently heavier than that of Suffolk crosses.
Romney sired ewes had the heaviest fleeces followed by Cheviot, Dorset
and Finn sired ewes. Observable medullation was most severe in the
two Cheviot crossbred groups, with a tendency for slightly greater
medullation in Suffolk than in Columbia crosses. Romney x Columbia
ewes generated the most wool income, due to heavy fleece weight and high value per pound of clean wool. Ewes with Columbia dams generated
higher wool income than did those with Suffolk dams.
The reproductive performance of ewes with Finn sires was superior
to that of ewes with Dorset, Cheviot or Romney sires, while ewes with
Suffolk dams were superior to ewes with Columbia dams. Finn crossbreds
had the greater percentage of ewes lambing per ewe bred (72 percent),
while Romney x Columbia ewes were lowest (18 percent). Finn sired
crossbred ewes averaged 1.62 lambs born per ewe lambing compared to
1.18 for the average of the other crosses. Finn cross ewes excelled
for total weight of lamb weaned, followed by Dorset, Cheviot and
Romney sired ewes. The greater lamb production of the Suffolk cross
ewes more than compensated for their lower wool production. They
generated $6.00 more total gross income than did Columbia crosses.
Also for gross income, ewes with Finn sires were highest followed by
Dorset, Cheviot and Romney sired ewes.