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Effects of repeated superovulation and flushing on reproductive performance of Bos indicus cows
THERIOGENOLOGY
EFFECTS OF REPEATED SUPEROVULATION AND FLUSHING ON REPRODUCTIVE PERFORMANCE OF BOS INDICUS COWS1'2 P. Bastidas and R. D. Randel
Texas A&M University Agricultural Research & Extension Center Overton, Texas 75684 Received for publication: November 2, 1986 Accepted: September 25, 1987
ABSTRACT To determine the effect of repeated superovulation and flushing in Bos indicus cows, 1,841 embryo collection records of 813 Brahman donor cows were analyzed using least-squares methods. Number of flushes affected total number of ova collected per donor (P < 0.07); number of transferable embryos (P < O.OOl)> pregnancy rate in the recipient (P < 0.03); number of embryos collected per donor (P < 0.003); number of morulas (P < 0.10); and number of blastocysts (P < 0.10). Total ova recovered decreased from 9.4 at the first flush to 2.9 at the fifth flush. Least-squares means (LSM) of transferable embryos per flush ranged from 5.3 for the first flush to 2.2 on the fifth flush. Pregnancy rate in the recipient was higher (44.2%) during the fourth flush and then decreased (38.8%) after six or more flushes. LSM of number of embryos collected ranged from 6.8 during the first flush to 3.0 for the fifth flush. Embryo production was (P < 0.003) higher (6.5) during the first flush than during the second flush (5.0). Number of blastocysts recovered per donor was higher (3.9) during the first flush and lower (2.2) during the fifth flush. Repeatabilities of the ovarian response to superovulation ranged from 0.10 to 0.17. These low levels of repeatability do not encourage any cull:.ng program upon ovarian response to based strictly superovulation. These data establsih that repeated superovulation and flushing have a detrimental effect on embryo parameters, especially after the fourth flush, in Brahman donor cows. Keywords:
superovulation, Bos indicus, embryo transfer, flushing
Acknowledgements 1 2Journal paper TA 21975, Texas Agricultural Experiment Station. This study was a contribution to Western Regional Project W-112, Reproductive Performance in Domestic Ruminants.
DECEMBER
1987 VOL. 28 NO. 6
827
THERIOGENOLOGY
INTRODUCTION
cows superovulated once produced more embryos per collection that cows superovulated two or three times. Data analyzed from approximately 1,000 Holstein cows and heifers have shown that fertilization rate and embryo numbers decrease after 10 repeated superovulations (5). The repeated production of a large number of ova by the cow appears to be restrained by two factors: one due to the repetition of treatment and the other due to the lack of response of some animals to any superovulatory treatment. The large variations of superovulatory responses have been ascribed to individual differences in the follicular population of the ovaries, both in terms of numbers and stage of development (6). Atretic follicles could be stimulated to grow but not to ovulate. Factors influencing the superovulatory response in BOS indicus cattle are not currently known. Further, the endocrine differences at the hypothalamic-pituitary-gonadal level (7,8,9) may produce differential between Bos taurus and Bos indicus effects on both the superovulatory response and embryo production. Embryo transfer, therefore, relies upon the production of large fertilized numbers of ova which become and are recovered as transferable embryos. Little has been reported delineating repeated superovulation and flushing. Therefore, the basic objectives of this study were to: 1) determine effects of repeated superovulation and flushing on embryo transfer results, and 2) analyze repeatability of the ovarian response to successive superovulation of Brahman cows. MATERIALS
AND METHODS
Embryo collection records were obtained from two embryo transfer units located in Central Texas for 2,015 nonsurgical embryo donor collections from 813 Brahman cows over a period of seven years (1978 1984). The embryos were evaluated and embryo transfer pregnancy results were recorded. All animals were maintained under the same management and embryo collection procedures at both embryo transfer units.
828
DECEMBER
1987 VOL. 28 NO. 6
THERIOGENOLOGY
Animals All donor animals utilized in the superovulation and embryo collection regimens were nonlactating, purebred Brahman cows and heifers. Recipient females were of diverse genetic background. All donor females were examined by palpation per rectum for evidence of possible reproductive problems, and at least two estrous periods were observed prior to any superovulation treatment (x = 64 + 5 d). Procedures for superovulation techniques were as previously described util:.zing FSH-P in a five day decreasing dose schedule (10). All donor recipient cows were also provided with an and adequate nutrr.tional provision according to NRC standards (11). Evaluation
of Embryos
The stage of development of embryos was determined by examination of embryonic morphology according to procedures previously described Only morphologically were normal embryos transferred to (10). recipient cows. Embryos that showed gross structural abnormalities, degeneration, or fragmentation and embryos that were retarded in development as well as unfertilized ova were discarded. Statistical
Analyses
Statistical analyses were performed using least-squares methods The basic model included the for unequal subclass numbers (12). effects of month of collection, year of collection, number of flushes, and the two-way interactions of month and year. Only the effects of flushing on embryo transfer results will be discussed. A companion paper (13) has previously dealt with seasonal effects. Preliminary analysis indicated two-factor interactions small that were and non-significant; the interactions were deleted from the therefore, final statistical applied estimating model. The analysis for repeatability of ovarian response and ova collected per flush was the least-squares means procedure (12). Repeatability was estimated by intraclass correlation using the variance components for cows and residual.
Total
Ova,
Transferable
RESULTS
AND DISCUSSION
Embryos
and Total
Embryos
Number of flushes affected total number of ova collected (P < and number of number of transferable emrbyos (P < 0.001): 0.07); embryos collected (P < 0.003) per donor. The effect of repeated superovulation, as reflected by total ova and embryos recovered per and subsequent flush, showed that after four repeated superovulatirns flushes ovarian response decreased in Brahman donor cows (Figure 1). relating similar or different No other data are currently available trends in Bos indicus cattle. However, data reported in Bos taurus cattle (2,14) have shown that the number of ovulations decreases after the second and fourth flush. Monniaux et al. (6) have suggested that the variations in the ovulatory response to superovulation are due to
DECEMBER
1987 VOL. 28 NO. 6
829
THERIOGENOLOGY
differences in the follicular populations of the ovaries, both in terms of number and stage of development. No data are currently available regarding the mechanisms that control follicular population dynamics in Bos indicus cattle. Brahman cattle however, seem to be more sensitive to exogenous gonadotropins than European cattle (15). Information regarding modification of the normal process of folliculogenesis and the modifications induced by superovulation as well as the long term effect of exogenous gonadotropin on ovarian function in Bos indicus cattle is not available. However, Halley et al. (10) suggested that a 40 to 43 mg total dose of FSH-P was quite effective in superovulating the Brahman cows, but the effects of this superovulatory treatment on subsequent ovarian response was not evaluated.
12 TOTAL OVA TRANsFERABLEEMBRlos TOTAL EmYCX
2 0 1
2
3
4
5
5+
FLUSHES Figure 1. Least-squares means and standard enors of total ova, transferable embrvos and total embryos recovered per donor per flush.
The number of transferable embryos also decreased with number of flushes (Figure 1). The estimated least-squares means of transferable embryos per flush ranged from a high of 5.3 for the first flush to a low of 1.8 on the fifth flush. Similar studies in Bos indicus cows are not currently available. Donaldson and Perry (5) reported that Bos taurus beef cows superovulated once produced more transferable embryos than cows superovulated two or three times. Similarly, Hasler et al. (14) pointed out that fertilization rate decreased after five superovulations in Holstein donor cows. Furthermore, when the average of transferable embryos obtained after the fourth flush in Brahman donor cows is compared with those reported in Bos taurus (5,131, the decrease is more dramatic in Bos indicus. It is possible that breed differences in sensitivity to superovulation could be involved in this pattern exhibited by the Brahman donor cow.
830
DECEMBER
1987 VOL. 28 NO. 6
THERIOGENOLOGY
Number of embryos recovered decreased with subsequent flushes (Figure 1). After the fourth flush the number of‘embryos recovered declined rapidly. The least-squares means of number of embryos recovered ranged from a high of 6.8 for the first flush to a low of 3.0 for the fifth flush. Similarly, when data from donor cows with one and two flushes were analyzed separately, the number of embryos recovered was higher (6.5) for cows flushed once than for cows flushed twice (5.0). These results are similar to those reported by others in Bos taurus cattle (5,141. Embryo production at the first collection was higher than it was from cows superovulated three or more times. Donaldson and Perry (5) found that increasing the dose of gonadotropin did not halt the decline in embryo production. Further, they also reported that the predictability of embryo production from cows that were selected to remain in the embryo transfer unit and that were super-ovulatedseveral times did not increase. Pregnancy Rate per Donor Pregnancy rate per donor cow was affected by number of flushes (P < 0.03). Number of flushes per donor affected pregnancy rate in the recipients (Figure 2). Pregnancy per donor cow increased from the first to the fourth collection, but it tended to decrease after the fourth flush. This trend is explained by the fact that both total embryos and number of transferable embryos recovered decrease with repeated flushing of Brahman donor cows. Comparable data quantifying the maximum number of flushes per Bos indicus donor and evaluating subsequent pregnancy rates in the recipient cows are not available.
50 T @ w
(PcO.03)
40
1
2
3 FLU&S
5
6+
Figure 2. Least-squares means and standard errors of pregnancy rate per donor per flush.
DECEMBER 1987 VOL. 28 NO. 6
831
THERIOGENOLOGY
of Blastocysts
and
of flushes affected number blastocysts (P and number morulas (P cow 3). The number blastocysts decreases the fourth Similarly, the number morulas recovered per donor repeated flushes. The of recovered during the first second were (1.5 1.2, than the flush A tendency previously in number embryos per cow. repeated in donor seems have detrimental on embryo and of recovered flush.
0 1
2
3FLUSH&
5
6+
Figure 3. Least-squares means and standard errors of number of blastocysts and morulas recovered par donor per flush
Number
of Unfertilized
Ova
Number of unfertilized ova recovered per donor was affected by number of flushes (P < 0.04). Number of unfertilized ova tended to decrease with repeated flushing (Figure 4). In addition, significant were detected between the first and second (P < 0.011 differences flush. Number of unfertilized ova was higher (2.5) during the first flush than during the second flush (1.7). It is not possible to ascertain from these results the extent to which the number of unfertilized ova recovered tended to decrease after repeated flushing. Number of unfertilized ova recovered did show variation among years. Least-squares means ranged from a low (0.6) during 1978 to a high (3.0) during 1983.
832
DECEMBER
1987 VOL. 28 NO. 6
THERIOGENOLOGY
1
3FLUSH&
2
5
6+
Figure 4. Least-squares means and standard enors of unfertilized ova recovered per donor per flush. Repeatability
of Ovarian
Response
Repeatabilities of the ovarian response to superovulation as measured by number of ova recovered in each collection were estimated. The range of repeatabilities obtained was between 0.10 and 0.17 (Table
Table
1.
Estimates of repeatability of the ovarian measured by total ova recorded
Var.iable
response
Repeatability
SEM
0.10 0.17 0.11 0.10 0.03 0.11 0.18
0.03 0.03 0.03 0.03 0.03 0.03 0.03
Pregnancy Rate Total Ovulations Total Embryos No. Blastocysts No. Morulas Transferable Embryos Unfertilized Ova -
total ova produced was 0.17 and the The repeatability of repeatability of pregnancy rate obtained by the total number of Likewise, low embryos transferred from each collection was 0.10. repeatabilities obtained in the other characteristics were all With this level of repeatability, a evaluating the ovarian response. culling program based upon ovarian response would not be advisable. strictly on response to Further, a selection scheme based evaluating genetic superovulation is not justified. Data the variation on ovarian response to superovulation are lacking for both it becomes important to Bos taurus and Bos indicus cows. Therefore,
DECEMBER
1987 VOL.
28 NO. 6
833
l-HERIOGENOLOGY
identify the source of variation and the course of selection of the ovarian response to superovulation that would be the most rational from a genetic and economic perspective. In summary, the number of flushes had a significant effect on total ova recovered per donor cow. Number of ova recovered decreased rapidly after the fourth superovulation and flush. Least-squares means of number of ova ranged from a high (9.4) during the first flush to a low (2.9) during the fifth flush. Likewise, number of flushes affected number of transferable embryos. Consistent with the results obtained on total ova recovered, number of transferable embryos was higher (5.3) during the first flush than during the fifth flush (2.2). Total embryos recovered were significantly affected by number of Embryo production per donor decreased with repeated flushes. flushing. The number of embryos recovered declined rapidly after the fourth flush. Higher recoveries of embryos were achieved during the first flush (6.8) and lower ones during the fifth flush (3.0). Qualitatively, the number of blastocysts and number of morulas recovered decreased with number of flushes. The least-squares means of number of blastocysts ranged from a high (3.9) during the first flush to a low (2.2) during the fifth flush. A similar trend was observed for number of morulas recovered per flush. Repeatability of the ovarian response to superovulation was estimated in this study. Levels of repeatability of ovarian response to superovulation were low; therefore, it indicates that genetic selection of potential donors based strictly upon selection according to the ovarian response to superovulation is not feasible at this time. To conclude, a definite effect of repeated flushing was detected in all parameters evaluated in this study. Brahman donor cows had the regard to ovarian responsiveness to lowest performance with superovulation during the fourth flush as reflected by number of ovulations and number of transferable embryos per flush. This effect was consistent with lower pregnancy rates in the recipient. Number of blastocysts and number of morulas recovered per flush decreased after the fourth flush. These findings suggest that Brahman donor cows tend to have a decrease in embryo quality after the fourth flush. Further, these results show that both the number and the viability of embryos are affected by repeated superovulation in Brahman donor cows. REFERENCES
834
1.
Seidel, Jr., G.E. and Seidel, S.M. The embryo transfer industry. In: Brackett, B.G., Seidel, Jr., G.E. and Seidel, S.M., teds.). New Technologies in Animal Breeding. Academic Press, New York, 1982.
2.
Saumande, J. and Chupin, D. Superovulation: A limit to egg transfer in cattle. Theriogenology 7:141-149 (1977).
3.
Nelson, L.D., Seidel, Jr., G.E. and Elsden R.P. Superovulation of cows using follicle stimulating hormone and prostaglandin F2 alpha. Theriogenology -11:104 abstr. (1979).
DECEMBER
1987 VOL. 28 NO. 6
THERIOGENOLOGY
4.
Dziuk, P.J., Donker, J.D., Nichols, J.R. and Petersen, W.W. Problems associated with the transfer of ova between cattle. Tech. Bull. Minn. Agric. Exp. Sta. No. 222 pp. 75 (1958).
5.
Donaldson, L. E. and Perry, B. superovulation of commercial -20:163-168 (1983).
6.
Monniaux, D., Chupin, D. and Saumande, J. Superovulatory responses of cattle. Theriogenology 19:55-87 (1983).
7.
Harrison, L.M., Hansen, T.R. and Randel, R.D. Evidence for seasonal and nutritional modification of ovarian and pituitary function in crossbred heifers and Brahman cows. J. Anim. Sci. 55:649-656 (1982). -
8.
Randel, R.D., Moseley, W.M. Serum luteinizing hormone surge and progesterone near estrus in Brahman compared to Brahman x Hereford and Hereford heifers. J. Anim. Sci. -37:199 (Abstr.). (1977).
9.
Randel, R. D. Reproductive endocrinology of Brahman cattle. Colloques de 1'INRA. -20:159-188 (1983).
Embryo production by repeated donor Theriogenology cows.
Les
10.
Halley, S.M., Rhodes, III, R.C., McKellar, L.D. and Randel, R.D. Successful superovulation nonsurgical collection and transfer of 12:97-108 (1979). embryos from Brahman cows. Theriogenology -
11.
NCR. Nutrient Requirements of Domestic Animals, No. 4. Requirements of Beef Cattle. National Research Washington, DC. (1976).
12.
Harvey, W.R. Least-squares analysis of data with unequal subclass numbers. ARS H-4. USDA, Washington, DC (1975).
13.
Bastidas, P. and Randel, R.D. Seasonal effects on embryo transfer results in Brahman cows. Theriogenology (1987) (Submitted).
14.
Hasler, J.F., McCauley, A-D., Schermerhorn, E.C. and Foote, R.H. Theriogenology Superovulatory responses of Holstein cows. 19:83-99 (1983). -
15.
Massey, J.M. and Oden, A.J. No seasonal effect on embryo donor performance in the southwest region of the USA. Theriogenology -21:196-217 (1984).
D:ECEMBER
1987 VOL. 28 NO. 6
Nutrient Council,
835
EFFECTS OF REPEATED SUPEROVULATION AND FLUSHING ON REPRODUCTIVE PERFORMANCE OF BOS INDICUS COWS1'2 P. Bastidas and R. D. Randel
Texas A&M University Agricultural Research & Extension Center Overton, Texas 75684 Received for publication: November 2, 1986 Accepted: September 25, 1987
ABSTRACT To determine the effect of repeated superovulation and flushing in Bos indicus cows, 1,841 embryo collection records of 813 Brahman donor cows were analyzed using least-squares methods. Number of flushes affected total number of ova collected per donor (P < 0.07); number of transferable embryos (P < O.OOl)> pregnancy rate in the recipient (P < 0.03); number of embryos collected per donor (P < 0.003); number of morulas (P < 0.10); and number of blastocysts (P < 0.10). Total ova recovered decreased from 9.4 at the first flush to 2.9 at the fifth flush. Least-squares means (LSM) of transferable embryos per flush ranged from 5.3 for the first flush to 2.2 on the fifth flush. Pregnancy rate in the recipient was higher (44.2%) during the fourth flush and then decreased (38.8%) after six or more flushes. LSM of number of embryos collected ranged from 6.8 during the first flush to 3.0 for the fifth flush. Embryo production was (P < 0.003) higher (6.5) during the first flush than during the second flush (5.0). Number of blastocysts recovered per donor was higher (3.9) during the first flush and lower (2.2) during the fifth flush. Repeatabilities of the ovarian response to superovulation ranged from 0.10 to 0.17. These low levels of repeatability do not encourage any cull:.ng program upon ovarian response to based strictly superovulation. These data establsih that repeated superovulation and flushing have a detrimental effect on embryo parameters, especially after the fourth flush, in Brahman donor cows. Keywords:
superovulation, Bos indicus, embryo transfer, flushing
Acknowledgements 1 2Journal paper TA 21975, Texas Agricultural Experiment Station. This study was a contribution to Western Regional Project W-112, Reproductive Performance in Domestic Ruminants.
DECEMBER
1987 VOL. 28 NO. 6
827
THERIOGENOLOGY
INTRODUCTION
cows superovulated once produced more embryos per collection that cows superovulated two or three times. Data analyzed from approximately 1,000 Holstein cows and heifers have shown that fertilization rate and embryo numbers decrease after 10 repeated superovulations (5). The repeated production of a large number of ova by the cow appears to be restrained by two factors: one due to the repetition of treatment and the other due to the lack of response of some animals to any superovulatory treatment. The large variations of superovulatory responses have been ascribed to individual differences in the follicular population of the ovaries, both in terms of numbers and stage of development (6). Atretic follicles could be stimulated to grow but not to ovulate. Factors influencing the superovulatory response in BOS indicus cattle are not currently known. Further, the endocrine differences at the hypothalamic-pituitary-gonadal level (7,8,9) may produce differential between Bos taurus and Bos indicus effects on both the superovulatory response and embryo production. Embryo transfer, therefore, relies upon the production of large fertilized numbers of ova which become and are recovered as transferable embryos. Little has been reported delineating repeated superovulation and flushing. Therefore, the basic objectives of this study were to: 1) determine effects of repeated superovulation and flushing on embryo transfer results, and 2) analyze repeatability of the ovarian response to successive superovulation of Brahman cows. MATERIALS
AND METHODS
Embryo collection records were obtained from two embryo transfer units located in Central Texas for 2,015 nonsurgical embryo donor collections from 813 Brahman cows over a period of seven years (1978 1984). The embryos were evaluated and embryo transfer pregnancy results were recorded. All animals were maintained under the same management and embryo collection procedures at both embryo transfer units.
828
DECEMBER
1987 VOL. 28 NO. 6
THERIOGENOLOGY
Animals All donor animals utilized in the superovulation and embryo collection regimens were nonlactating, purebred Brahman cows and heifers. Recipient females were of diverse genetic background. All donor females were examined by palpation per rectum for evidence of possible reproductive problems, and at least two estrous periods were observed prior to any superovulation treatment (x = 64 + 5 d). Procedures for superovulation techniques were as previously described util:.zing FSH-P in a five day decreasing dose schedule (10). All donor recipient cows were also provided with an and adequate nutrr.tional provision according to NRC standards (11). Evaluation
of Embryos
The stage of development of embryos was determined by examination of embryonic morphology according to procedures previously described Only morphologically were normal embryos transferred to (10). recipient cows. Embryos that showed gross structural abnormalities, degeneration, or fragmentation and embryos that were retarded in development as well as unfertilized ova were discarded. Statistical
Analyses
Statistical analyses were performed using least-squares methods The basic model included the for unequal subclass numbers (12). effects of month of collection, year of collection, number of flushes, and the two-way interactions of month and year. Only the effects of flushing on embryo transfer results will be discussed. A companion paper (13) has previously dealt with seasonal effects. Preliminary analysis indicated two-factor interactions small that were and non-significant; the interactions were deleted from the therefore, final statistical applied estimating model. The analysis for repeatability of ovarian response and ova collected per flush was the least-squares means procedure (12). Repeatability was estimated by intraclass correlation using the variance components for cows and residual.
Total
Ova,
Transferable
RESULTS
AND DISCUSSION
Embryos
and Total
Embryos
Number of flushes affected total number of ova collected (P < and number of number of transferable emrbyos (P < 0.001): 0.07); embryos collected (P < 0.003) per donor. The effect of repeated superovulation, as reflected by total ova and embryos recovered per and subsequent flush, showed that after four repeated superovulatirns flushes ovarian response decreased in Brahman donor cows (Figure 1). relating similar or different No other data are currently available trends in Bos indicus cattle. However, data reported in Bos taurus cattle (2,14) have shown that the number of ovulations decreases after the second and fourth flush. Monniaux et al. (6) have suggested that the variations in the ovulatory response to superovulation are due to
DECEMBER
1987 VOL. 28 NO. 6
829
THERIOGENOLOGY
differences in the follicular populations of the ovaries, both in terms of number and stage of development. No data are currently available regarding the mechanisms that control follicular population dynamics in Bos indicus cattle. Brahman cattle however, seem to be more sensitive to exogenous gonadotropins than European cattle (15). Information regarding modification of the normal process of folliculogenesis and the modifications induced by superovulation as well as the long term effect of exogenous gonadotropin on ovarian function in Bos indicus cattle is not available. However, Halley et al. (10) suggested that a 40 to 43 mg total dose of FSH-P was quite effective in superovulating the Brahman cows, but the effects of this superovulatory treatment on subsequent ovarian response was not evaluated.
12 TOTAL OVA TRANsFERABLEEMBRlos TOTAL EmYCX
2 0 1
2
3
4
5
5+
FLUSHES Figure 1. Least-squares means and standard enors of total ova, transferable embrvos and total embryos recovered per donor per flush.
The number of transferable embryos also decreased with number of flushes (Figure 1). The estimated least-squares means of transferable embryos per flush ranged from a high of 5.3 for the first flush to a low of 1.8 on the fifth flush. Similar studies in Bos indicus cows are not currently available. Donaldson and Perry (5) reported that Bos taurus beef cows superovulated once produced more transferable embryos than cows superovulated two or three times. Similarly, Hasler et al. (14) pointed out that fertilization rate decreased after five superovulations in Holstein donor cows. Furthermore, when the average of transferable embryos obtained after the fourth flush in Brahman donor cows is compared with those reported in Bos taurus (5,131, the decrease is more dramatic in Bos indicus. It is possible that breed differences in sensitivity to superovulation could be involved in this pattern exhibited by the Brahman donor cow.
830
DECEMBER
1987 VOL. 28 NO. 6
THERIOGENOLOGY
Number of embryos recovered decreased with subsequent flushes (Figure 1). After the fourth flush the number of‘embryos recovered declined rapidly. The least-squares means of number of embryos recovered ranged from a high of 6.8 for the first flush to a low of 3.0 for the fifth flush. Similarly, when data from donor cows with one and two flushes were analyzed separately, the number of embryos recovered was higher (6.5) for cows flushed once than for cows flushed twice (5.0). These results are similar to those reported by others in Bos taurus cattle (5,141. Embryo production at the first collection was higher than it was from cows superovulated three or more times. Donaldson and Perry (5) found that increasing the dose of gonadotropin did not halt the decline in embryo production. Further, they also reported that the predictability of embryo production from cows that were selected to remain in the embryo transfer unit and that were super-ovulatedseveral times did not increase. Pregnancy Rate per Donor Pregnancy rate per donor cow was affected by number of flushes (P < 0.03). Number of flushes per donor affected pregnancy rate in the recipients (Figure 2). Pregnancy per donor cow increased from the first to the fourth collection, but it tended to decrease after the fourth flush. This trend is explained by the fact that both total embryos and number of transferable embryos recovered decrease with repeated flushing of Brahman donor cows. Comparable data quantifying the maximum number of flushes per Bos indicus donor and evaluating subsequent pregnancy rates in the recipient cows are not available.
50 T @ w
(PcO.03)
40
1
2
3 FLU&S
5
6+
Figure 2. Least-squares means and standard errors of pregnancy rate per donor per flush.
DECEMBER 1987 VOL. 28 NO. 6
831
THERIOGENOLOGY
of Blastocysts
and
of flushes affected number blastocysts (P and number morulas (P cow 3). The number blastocysts decreases the fourth Similarly, the number morulas recovered per donor repeated flushes. The of recovered during the first second were (1.5 1.2, than the flush A tendency previously in number embryos per cow. repeated in donor seems have detrimental on embryo and of recovered flush.
0 1
2
3FLUSH&
5
6+
Figure 3. Least-squares means and standard errors of number of blastocysts and morulas recovered par donor per flush
Number
of Unfertilized
Ova
Number of unfertilized ova recovered per donor was affected by number of flushes (P < 0.04). Number of unfertilized ova tended to decrease with repeated flushing (Figure 4). In addition, significant were detected between the first and second (P < 0.011 differences flush. Number of unfertilized ova was higher (2.5) during the first flush than during the second flush (1.7). It is not possible to ascertain from these results the extent to which the number of unfertilized ova recovered tended to decrease after repeated flushing. Number of unfertilized ova recovered did show variation among years. Least-squares means ranged from a low (0.6) during 1978 to a high (3.0) during 1983.
832
DECEMBER
1987 VOL. 28 NO. 6
THERIOGENOLOGY
1
3FLUSH&
2
5
6+
Figure 4. Least-squares means and standard enors of unfertilized ova recovered per donor per flush. Repeatability
of Ovarian
Response
Repeatabilities of the ovarian response to superovulation as measured by number of ova recovered in each collection were estimated. The range of repeatabilities obtained was between 0.10 and 0.17 (Table
Table
1.
Estimates of repeatability of the ovarian measured by total ova recorded
Var.iable
response
Repeatability
SEM
0.10 0.17 0.11 0.10 0.03 0.11 0.18
0.03 0.03 0.03 0.03 0.03 0.03 0.03
Pregnancy Rate Total Ovulations Total Embryos No. Blastocysts No. Morulas Transferable Embryos Unfertilized Ova -
total ova produced was 0.17 and the The repeatability of repeatability of pregnancy rate obtained by the total number of Likewise, low embryos transferred from each collection was 0.10. repeatabilities obtained in the other characteristics were all With this level of repeatability, a evaluating the ovarian response. culling program based upon ovarian response would not be advisable. strictly on response to Further, a selection scheme based evaluating genetic superovulation is not justified. Data the variation on ovarian response to superovulation are lacking for both it becomes important to Bos taurus and Bos indicus cows. Therefore,
DECEMBER
1987 VOL.
28 NO. 6
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l-HERIOGENOLOGY
identify the source of variation and the course of selection of the ovarian response to superovulation that would be the most rational from a genetic and economic perspective. In summary, the number of flushes had a significant effect on total ova recovered per donor cow. Number of ova recovered decreased rapidly after the fourth superovulation and flush. Least-squares means of number of ova ranged from a high (9.4) during the first flush to a low (2.9) during the fifth flush. Likewise, number of flushes affected number of transferable embryos. Consistent with the results obtained on total ova recovered, number of transferable embryos was higher (5.3) during the first flush than during the fifth flush (2.2). Total embryos recovered were significantly affected by number of Embryo production per donor decreased with repeated flushes. flushing. The number of embryos recovered declined rapidly after the fourth flush. Higher recoveries of embryos were achieved during the first flush (6.8) and lower ones during the fifth flush (3.0). Qualitatively, the number of blastocysts and number of morulas recovered decreased with number of flushes. The least-squares means of number of blastocysts ranged from a high (3.9) during the first flush to a low (2.2) during the fifth flush. A similar trend was observed for number of morulas recovered per flush. Repeatability of the ovarian response to superovulation was estimated in this study. Levels of repeatability of ovarian response to superovulation were low; therefore, it indicates that genetic selection of potential donors based strictly upon selection according to the ovarian response to superovulation is not feasible at this time. To conclude, a definite effect of repeated flushing was detected in all parameters evaluated in this study. Brahman donor cows had the regard to ovarian responsiveness to lowest performance with superovulation during the fourth flush as reflected by number of ovulations and number of transferable embryos per flush. This effect was consistent with lower pregnancy rates in the recipient. Number of blastocysts and number of morulas recovered per flush decreased after the fourth flush. These findings suggest that Brahman donor cows tend to have a decrease in embryo quality after the fourth flush. Further, these results show that both the number and the viability of embryos are affected by repeated superovulation in Brahman donor cows. REFERENCES
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Seidel, Jr., G.E. and Seidel, S.M. The embryo transfer industry. In: Brackett, B.G., Seidel, Jr., G.E. and Seidel, S.M., teds.). New Technologies in Animal Breeding. Academic Press, New York, 1982.
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