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Effect of follicle size on bovine oocyte morphology and embryo yield following maturation, fertilization and culture in vitro
THERIOGENOLOGY
EFFECT OF FOLLICLE SIZE ON BOVINE OOCYTE MORPHOLOGY AND EMBRYO YIELD FOLLOWING MATURATION, FERTILIZATION AND CULTURE IN VITRO P. Lonergan, H. Sharif, P. Monaghan, H. Wahid, M. Gallagher and I. Gordon Department of Animal Science and Production, University College Dublin, Lyons Estate, Newcastle, Co. Dublin, IRELAND The aim of the present study was to investigate the effect of follicle size on the type of bovine oocyte obtained for in vitro maturation (IVM) and to assess the ability of oocytes from follicles of different size categories to become fertilized and undergo cleavage and early embryonic (2-6mm, >6mm) development in vitro. Primary bovine oocytes were obtained from slaughterhouse ovaries following the isolation and subsequent rupture of vesicular follicles >2mm in diameter. On recovery, oocytes were classified according to the morphology of their surrounding cumulus cells as: (1) denuded; (2) expanded; (3) with 2-3 layers; (4) with 4-5 layers; and (5) with many layers of cumulus cells. The total number of oocytes recovered as well as the number in each category were recorded and are presented in Table 1. A representative number of good quality oocytes (category 5) from both follicle size categories were put through the IVM/IVF/IVC procedure (Lu -* et al 9 1987, Vet. Record, 121:259; 122:539) and the cleavage rate (no. eggs cleaved/no. 1988, Vet. Record, inseminated), cleavage index (no. eggs cleaved beyond the 2-cell stage/total no. cleaved) and embryo yield (no. blastocysts/no. eggs cleaved) were recorded (Table 2). Table
1: Effect
of
Follicle
Size
on the
Type of
Oocyte
Obtained
for
Follicle Size(mm)
Oocytes Recovered
Denuded
Expanded
2-3 Layers
3-4 Layers
Many Layers
2-6
87.7Xa (186/212)
3.8Xe (7/186)
14.5Xa (27/186)
12.9%* (24/186)
22.oxa (41/186)
46.8XL (87/186)
>6
77.O%b (104/135)
1.9X8 (2/104)
11.6’Xa (12/104)
6.7Xe (7/104)
9.69Lb (10/104)
70.2Xb (73/104)
X2
P
NS
NS
P
P
Table
2:
Follicle Size(mm)
Effect
of
Follicle
NS Size
on Embryo Yield
Cleavage Rate
Index
Yield
86.9X8
Following
Blastocyst Hatching
IVH/IVF/IVC.
Rate
90.8Xa (99/109)
(86/99)
34.3%a (34/99)
85. 2Xa (29/34)
>6
92.9x* (91/98)
82 * 4Xa (75/91)
65.9Xb (60/91)
71.7XE (43/60)
X2
NS
P
NS
2-6
NS
IVM.
Significantly more oocytes with many layers of cumulus cells and a significantly higher proportion of morula/blastocyst-stage embryos were obtained from follicles >6mm in diameter ( X: 65.9%) compared to 2-6mm follicles (X: 34.3%). This study demonstrates a clear relationship between follicle size and oocyte quality. It is possible that improved oocyte quality arises from the action of growth factors present in the larger follicles. These results also suggest, however, that the IVF and IVC systems employed are adequate and that low results in terms of embryo yield result from the quality of the oocyte selected for IVM.
248
JANUARY
1992 VOL. 37 NO. 1
EFFECT OF FOLLICLE SIZE ON BOVINE OOCYTE MORPHOLOGY AND EMBRYO YIELD FOLLOWING MATURATION, FERTILIZATION AND CULTURE IN VITRO P. Lonergan, H. Sharif, P. Monaghan, H. Wahid, M. Gallagher and I. Gordon Department of Animal Science and Production, University College Dublin, Lyons Estate, Newcastle, Co. Dublin, IRELAND The aim of the present study was to investigate the effect of follicle size on the type of bovine oocyte obtained for in vitro maturation (IVM) and to assess the ability of oocytes from follicles of different size categories to become fertilized and undergo cleavage and early embryonic (2-6mm, >6mm) development in vitro. Primary bovine oocytes were obtained from slaughterhouse ovaries following the isolation and subsequent rupture of vesicular follicles >2mm in diameter. On recovery, oocytes were classified according to the morphology of their surrounding cumulus cells as: (1) denuded; (2) expanded; (3) with 2-3 layers; (4) with 4-5 layers; and (5) with many layers of cumulus cells. The total number of oocytes recovered as well as the number in each category were recorded and are presented in Table 1. A representative number of good quality oocytes (category 5) from both follicle size categories were put through the IVM/IVF/IVC procedure (Lu -* et al 9 1987, Vet. Record, 121:259; 122:539) and the cleavage rate (no. eggs cleaved/no. 1988, Vet. Record, inseminated), cleavage index (no. eggs cleaved beyond the 2-cell stage/total no. cleaved) and embryo yield (no. blastocysts/no. eggs cleaved) were recorded (Table 2). Table
1: Effect
of
Follicle
Size
on the
Type of
Oocyte
Obtained
for
Follicle Size(mm)
Oocytes Recovered
Denuded
Expanded
2-3 Layers
3-4 Layers
Many Layers
2-6
87.7Xa (186/212)
3.8Xe (7/186)
14.5Xa (27/186)
12.9%* (24/186)
22.oxa (41/186)
46.8XL (87/186)
>6
77.O%b (104/135)
1.9X8 (2/104)
11.6’Xa (12/104)
6.7Xe (7/104)
9.69Lb (10/104)
70.2Xb (73/104)
X2
P
NS
NS
P
P
Table
2:
Follicle Size(mm)
Effect
of
Follicle
NS Size
on Embryo Yield
Cleavage Rate
Index
Yield
86.9X8
Following
Blastocyst Hatching
IVH/IVF/IVC.
Rate
90.8Xa (99/109)
(86/99)
34.3%a (34/99)
85. 2Xa (29/34)
>6
92.9x* (91/98)
82 * 4Xa (75/91)
65.9Xb (60/91)
71.7XE (43/60)
X2
NS
P
NS
2-6
NS
IVM.
Significantly more oocytes with many layers of cumulus cells and a significantly higher proportion of morula/blastocyst-stage embryos were obtained from follicles >6mm in diameter ( X: 65.9%) compared to 2-6mm follicles (X: 34.3%). This study demonstrates a clear relationship between follicle size and oocyte quality. It is possible that improved oocyte quality arises from the action of growth factors present in the larger follicles. These results also suggest, however, that the IVF and IVC systems employed are adequate and that low results in terms of embryo yield result from the quality of the oocyte selected for IVM.
248
JANUARY
1992 VOL. 37 NO. 1