Recognising the limits to live weight-reproduction relationships
in ewes
L. RUTHERFORD, A.M. NICOL AND C.M. LOGAN
Animal and Food Sciences Division, Lincoln University, PO Box
84, Lincoln University, Canterbury
E-Mail:
NZSAP 2003 Abstract No. 34
Proceedings of the New Zealand Society of Animal Production
63: 140-143
The relationship between joining live weight and ovulation rate
and number of lambs born was examined in a composite flock of small- and
large-framed ewes. Approximately equal numbers of small- (n = 315) and
large (n = 305) framed, mixed-age ewes of equal average condition score,
selected in the same proportion from 9 commercial flocks (mainly
Coopworth), were managed together from early March to pre-lambing. The
average pre-joining live weight (±SD) of small-framed ewes (61.3
±6.35 kg). was significantly (P<0.001) lower than that of
large-framed ewes (71.1±6.58 kg). Ewes were joined with 14
Coopworth ram hoggets fitted with ram harnesses on 8 April. Ewes marked
by rams were temporarily removed from the flock every 7 days for 21 days
and ovulation rate (0, 1, 3, 4) recorded by laparoscopy the following
day after fasting. Pregnancy status (0, 1, 2 or more) was recorded by
ultrasonography on 4 July. Ewes were fully recorded at lambing. The mean
ovulation rate (OR) of small-framed ewes was significantly lower (1.76,
P<0.05) than that of large-framed ewes (1.92). The regression of OR
on joining live weight (jLW) was significant (P<0.001) for small-
ewes (OR = 0.0216 x jLW + 0.463) but there was no relationship between
OR and jLW in large-framed ewes. Maximum OR (1.92) was predicted to
occur at 67.5 kg jLW. The results of this study indicate an upper limit
to the live weight ovulation rate relationship. Compared on the basis of
equal ewe live weight per ha, OR per ha was 12% higher for small- than
large-framed ewes.
Keywords: NZSAPAB;
ewes; frame size; ovulation rate, joining live weight
Last Updated 8/07/2004
