New Zealand Journal of Agricultural Research abstracts
Influence of year, age, and geographical location on induced oestrus in ewes
early in the breeding season
L. S. FENTON1
G. H. SHACKELL1a
M. L. RAMSAY1
K. G. DODDS1
P. J. REID2
B. J. McLEOD1
1AgResearch Invermay
Private Bag 50034
Mosgiel, New Zealand
2AgResearch Woodlands
RD 1, Invercargill
New Zealand
Abstract Oestrous activity was monitored at two locations
(Invermay in Otago and Woodlands in Southland) in ewe flocks of similar age
structure, synchronised at the beginning of the breeding season each year for 5
years (1991-95). After an 11-day CIDR treatment, interval to oestrus, duration
of oestrus, and ovulation rate were measured. Age of ewe affected the mean
interval to oestrus (32.4-41.0 h), with 2-tooths commencing up to 10 h later
than older ewes (
P < 0.05). There was a significant location effect
in 1992 when oestrus commenced 8.6 h later at Woodlands than at Invermay (41.0
versus 32.4 h;
P < 0.05). Duration of oestrus differed significantly
between some years (
P < 0.05) at Woodlands but not at Invermay. There
was also a difference between locations whereby Woodlands animals had a longer
oestrus (23.4-34.2 h), by 7.4-17.5 h (
P < 0.001), than those at
Invermay (15.0-18.1 h). This difference did not occur in 1995, when both flocks
were located at Woodlands. Mean ovulation rate (1.9-2.2) was not significantly
different either within or between locations. These data suggest that even in
the same flock, age of ewe, year, and location may influence oestrous activity
in ewes treated to manipulate the oestrous cycle at the beginning of the
breeding season.
Keywords location; seasonality; onset of oestrus; duration of
oestrus; synchronisation; sheep
New Zealand Journal of Agricultural Research, 1997, Vol. 40: 69-74
0028-8233/97/4001-0069 $2.50/0 (c) The Royal Society of New Zealand
1997
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