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Effect of time to first cleavage on hatching rate of bovine embryos in vitro
THERIOGENOLOGY
EFFECT OF TIlME TO FIRST CLEAVAGE ON HATCHING RATE OF BOVINE EMBRYOS IN VITRO
L. Plante and W. A. King Department of Biomedical Sciences, Ontario Veterinary College University of Guelph, Guelph, Ontario, Canada, NlG 2Wl. Although bovine oocyte nuclear maturation is relatively synchronous in vitro (85% MI1 after 24 h), cleavage after IVF may extend over a 24 to 40 h period. The present study was undertaken to determine whether the length of time between insemination and cleavage is related to an embryo’s subsequent developmental potential and hatching in vitro. Following oocyte maturation and fertilization in vitro, 539 presumptive zygotes (18-20 h post-fertilization; hpi) were cultured with oviductal cells in Menezo-82 medium supplemented with 10% estrous cow serum. At 24, 30, 40, 48, or 62 hpi, cleaved zygotes were removed from the original culture and grouped according to cleavage stage in separate drops of the same medium. The average rate of cleavage was 57.7% (range 46-75%). Hatching occurred between Days 8 and 15 after fertilization. The results were as follows: Subsequent develoument Time of Cleavage Number Blasto. Hatched B/n H/n &z&on 24
(hui)
s&e __
(n)
(B)
0
0
__
__
__
__
30
2-cell 4-cell
108 26
71 12
55 7
65.7%’ 46.1%b
50.9%a 26.9%b
40
2-cell 4-cell 8-cell
61 59 5
23 21 2
16 11 0
37.7%’ 35.6%’ 0%’
26.2%= 18.6%” O%a
48
2-cell 4-cell B-cell
13 16 1
0 6 0
0 2 0
0%’ 37.5%b O%a
0%’ 12.5%b O%=
62
2-cell 4-cell 8-cell
3 9 3
0 3 1
0 2 1
O%a 33.3%’ 33.3%’
o%a 22.2%= 33.3%a
> 62
2-cell 4-cell 8-cell
1 1 1
0 0 0
0 0 0
0% 0% 0%
0% 0% 0%
Values with different superscripts (p < 0.05)
within the same time of selection are statistically different
The results show that most zygotes cleave between 24 and 48 hpi. While embryos that were at the 2-tell stage by 30 hpi gave the highest rate (p < 0.05) of blastocysts (65.7%) and hatching (50.9%), a few that cleaved between 48 and 62 hpi also developed and hatched. Some embryos had short second and/or third cell cycles, passing from l- to 8-cells in 8-15 h, but few of these (l/9) hatched. Hatching within all groups was distributed over 5 to 8 days. (Supported by NSERC, CAAB, PCTF and United Breeders Inc.).
274
JANUARY
1992 VOL. 37 NO. 1
EFFECT OF TIlME TO FIRST CLEAVAGE ON HATCHING RATE OF BOVINE EMBRYOS IN VITRO
L. Plante and W. A. King Department of Biomedical Sciences, Ontario Veterinary College University of Guelph, Guelph, Ontario, Canada, NlG 2Wl. Although bovine oocyte nuclear maturation is relatively synchronous in vitro (85% MI1 after 24 h), cleavage after IVF may extend over a 24 to 40 h period. The present study was undertaken to determine whether the length of time between insemination and cleavage is related to an embryo’s subsequent developmental potential and hatching in vitro. Following oocyte maturation and fertilization in vitro, 539 presumptive zygotes (18-20 h post-fertilization; hpi) were cultured with oviductal cells in Menezo-82 medium supplemented with 10% estrous cow serum. At 24, 30, 40, 48, or 62 hpi, cleaved zygotes were removed from the original culture and grouped according to cleavage stage in separate drops of the same medium. The average rate of cleavage was 57.7% (range 46-75%). Hatching occurred between Days 8 and 15 after fertilization. The results were as follows: Subsequent develoument Time of Cleavage Number Blasto. Hatched B/n H/n &z&on 24
(hui)
s&e __
(n)
(B)
0
0
__
__
__
__
30
2-cell 4-cell
108 26
71 12
55 7
65.7%’ 46.1%b
50.9%a 26.9%b
40
2-cell 4-cell 8-cell
61 59 5
23 21 2
16 11 0
37.7%’ 35.6%’ 0%’
26.2%= 18.6%” O%a
48
2-cell 4-cell B-cell
13 16 1
0 6 0
0 2 0
0%’ 37.5%b O%a
0%’ 12.5%b O%=
62
2-cell 4-cell 8-cell
3 9 3
0 3 1
0 2 1
O%a 33.3%’ 33.3%’
o%a 22.2%= 33.3%a
> 62
2-cell 4-cell 8-cell
1 1 1
0 0 0
0 0 0
0% 0% 0%
0% 0% 0%
Values with different superscripts (p < 0.05)
within the same time of selection are statistically different
The results show that most zygotes cleave between 24 and 48 hpi. While embryos that were at the 2-tell stage by 30 hpi gave the highest rate (p < 0.05) of blastocysts (65.7%) and hatching (50.9%), a few that cleaved between 48 and 62 hpi also developed and hatched. Some embryos had short second and/or third cell cycles, passing from l- to 8-cells in 8-15 h, but few of these (l/9) hatched. Hatching within all groups was distributed over 5 to 8 days. (Supported by NSERC, CAAB, PCTF and United Breeders Inc.).
274
JANUARY
1992 VOL. 37 NO. 1