meat breeds; namely, the Texel, Suffolk and German Merino. The comparison focused on the following:
Ž .
Ø the effects of the presence of the gene F q vs. qq ;
Ž
B C
. Ø
the effects of genes of different origin Fec vs.
Fec ; and Ž
Ø the effects of crossing a gene in different local breeds BT vs. BGM, Cambridge =
Ž .
. Cambridge CC vs. CT vs. CS .
A unique feature of this study is that the Booroola and Cambridge crossings were observed simultaneously in similar experimental conditions.
2. Materials and methods
2.1. Animals Ž
. The experiment was performed during the breeding season September–October at
Ž
X X
. the Ovine Research Centre, Faulx-les-Tombes 50825 North and 582 East , Belgium.
Ž .
All ewes were multiparous. Ten purebred Cambridge ewes CC and different cross- Ž
. Ž
. breeds, 11 Cambridge = Texel CT , 10 Cambridge = Suffolk CS , 12 Booroola = Texel
Ž .
Ž .
BT and 10 Booroola = German Mutton Merino BGM were investigated. For each Ž
. Ž
. type of crossbred, five to six adult aged 2.5–5 years carriers F q and non-carriers
Ž .
qq were used; they were previously selected on the basis of OR and prolificacy. During the experiment, the animals were housed indoors under natural lighting. They
received water and hay ad libitum enriched with 300 g of concentrate composed of cereal, beet pulp and soya.
2.2. Experimental design Follicular growth during the oestrous cycle of the ewe presents three distinct waves
characterized by a period of recruitment of small follicles, their growth and atresia, except in the 3rd wave where one or some follicles escape atresia and ovulate. This
Ž .
study focused on the 3rd wave, beginning on days 12–13 day of ovulation s Day 0 . Ž
. Daily laparoscopies Fig. 1 allowed mapping of the follicles at the ovarian surface and
the tracing of their individual events, size, growth and atresia or ovulation. Every ewe was initially synchronized with two intramuscular injections of 100 mg of
Ž
w
. prostaglandin F
PGF 0.4 ml Estrumate , Coopers with an interval of 10 days
2 a 2 a
Ž .
Days y13 and y3 to ensure that all the ewes were at the same stage of the oestrous Ž
cycle at the beginning of the experiment. The presumed day of ovulation 3 days after .
the 2nd injection of PGF was considered as Day 0. The 1st laparoscopic examination
2 a
was carried out on Day 6 to determine the OR by counting the number of corpora lutea.
Fig. 1. Treatment protocol.
Ž .
Ž .
From Days 13 Day y4 to 17 Day 0 of the following oestrous cycle , laparoscopies were performed daily to monitor the growth and atresia of every ovarian follicle. The
Ž .
position and the diameter of every follicle diameter G 2.0 mm on the ovarian surface were mapped. Healthy follicles showed a continuing pattern of growth and reached a
steady size or ovulated. In the former case, they became atretic and began to regress until disappearing.
In order to determine whether the repetitive laparoscopic examinations affected any of the reproductive processes, the OR was also determined on Day 21. Thereafter, the
ewes had a 2nd session of synchrony for a 3rd evaluation of OR.
2.3. Laparoscopy Each laparoscopic examination was performed using a 5-mm optic fibre and manipu-
Ž .
lation probe Richard Wolf endoscope
engraved with a millimetric scale. Local Ž
. anaesthesia 1 ml of 2 xylocaine was injected subcutaneously at two places: 3–4 cm
anterior the udder and 4–5 cm either side of the midcentral line. The endoscope and the manipulation probe were inserted into the peritoneal cavity at the injection sites. A
preliminary study showed that laparoscopy examination of the ovaries allowed the
Ž follicles visible on the ovarian surface to be accurately monitored Noel et al., 1992;
¨
. 1993 .
2.4. Presentation of results Ž
. Follicles were ranked into three size classes: small diameter 2–3.5 mm , medium-
Ž .
Ž .
sized diameter 3.5–5.0 mm and large diameter 5.0 mm . The following features of follicular growth were calculated: mean number of small, medium-sized and large
follicles; maximal size attained by the largest follicles before regression or ovulation; atresia rate; and, OR. The atresia rate was defined as the percentage of shrinking
follicles between two size classes.
2.5. Statistical analysis The data are expressed as means S.E. They were analyzed using GLM procedures
Ž .
Statistical Analysis System, 1985 . A three-way analysis of variance was used to determine whether OR and follicular parameters differed among crossbreds and between
Fec carriers and non-carriers. In the model, the crossbred type and the fecundity-gene status were considered as fixed-crossed effects, and the ewe was taken as a random
Ž .
effect Dagnelie, 1975 . The Scheffe test was used to compare group means when the
´
Ž .
main or interaction effects were significant P - 0.01 and P - 0.05 . Values relating to OR and the rate of follicle atresia were logarithmically transformed before analysis.
3. Results
