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Response to synthetic gonadoliberin (GnRH) in anestrous cows
THERIOGENOLOGY
lW3POBSE TO SYNTHETIC GONiDOLIl3E~ (GtiH) IN ANESTftoUSCOWS R.L. Bhoble aml S.K. Gupta
Divisionof Animu Reproduction Indian VOterinsryF&SearchInStitUt8 Izatnagar243 122 (U.P.) Received
for publication: Accepted:
June 12, 1985 April 16, 1986
ABSTRQCT Fifty-threeanestrousCOWS of Harisnacrossedwith Holstein,Friesian,Brown Swiss or Jersey half-br88dcrosses were treadedwith Buserelinacetateaqueoussolution0.0042 mg/ml, administered as a singleintrsmuscular (i..m.) dose of 21ng. Tw8lve (22.64%)animalsexhibitedcompletefollicular d8velopment, ovulationand behaviourslexpressionof oestrus. Twenty-eight(52.83s)cows showedonly partial folliculardevelopmentwith no ovulationor oeskous manifestations. Thirteen(24.53%)animalsdid not respond. Of eight controlanimals,three (3?.3o(;e, showedpartialfollicular developmentand no owlation or symptomsof oestrus while five (62.5%) did not respond. In GnRH-treated cows showingfolliculardevelopment, oestrousmanifestation, and ovulation,nine animalsresponded between 4 to 10 d after administration.Three animals took from 14 to I.55d. The mean time from treatmentto response for this group was 22.17 d. In animalsshowingpartial follic?lardevelopmentand no oestrousbehaviour,the intsrval d in 28 animals.In tha controlgroup, to 11 was three animalsshowedpartialfolliculardevelopmenton 94 d of GnBB in anestrosts cows promoaverag+ The administration ted thetievelopment of folliclesto a certainstage as evident from th8 clinicalobservations, but the folliclesfailedto grow beyonda particularstage. The reasonsfor failureof folliculardevelopmentbeyonda particularstaBein GnRRtreatedanimalsare not clear. It appearedthat the response to GnRH may be expectedto peak by the eleventhday and a seconddose may then be tried for a favourableresponse. Kciywords: Gonadoliberin,anestroUs cows,follicles
The authorsare thankfulto Hoechst,Frankfurt,Germany, for their gift of Recsptal(GnRH), which has enabledus to pursue this work, We are erateful to the Director,I.V.R.I., Isatnagar,for providingexperimental materialfor this study. JUNE1986VOL.25N0.6
759
THERIOGENOLOGY
liWRODUCTlOM
Synthetic:gonadoliberin compounds (GnRH) have recently been used in the management of reproductive problems in cows and are considered useful for improving conception rates (l), treating ovarian cysts (23, reducing post-partum estrus intervsls (31, and inducing ovarian activity in anestrous animals (4&U. It is commonly reported that heifers, even after reachingthe age of maturity and attaining desired body weight, have not shown e,strusor estrous behaviour. Similarly, animals after ealving failed to show heat for a long tlrnefor no apparent reason. This delay in ovariancyclicityin
heifersand in postpartumanima3.s resultsin heavy economic losses in terms of management expenses, longer interval between calving to conception, and prolonged calving interval. The purpose of this study was to assess ovarian response to the administration of the synthetic analogue of GnRH in anestrous cows as judged by development of follicles or corpus luteum (CL5 on the ovary by clinico-gynaecologicalexamination, estrous expression, behavioursl manifestations of estrus, ovulation, or conception. This study also assessed the inter-, ma4 from treatment to onset of clinical response. MATERIALS AHI3 EHODS Fifty-three anestroushalf-bredcows of Harianacrossed with Holstein,Friesfan,Brown Swiss,or Jersey stockwere used. A balancednutritionaldiet includinggreens,dry fodder rendconcentrate mixturewas fed to these animals, All cows tested for brucellosisand tuberculosis were negativeand maintained under barn management. Ovarianstatuswas assessed by examinationper rectum at periodicintervalsbeforeand after treatment. ISach&al was examinedtwice at an interval of 10 d beforethe treatmentand a minimumof three to four examinationswas made at 3- to 4-d intervalsafter treatment.
The syntheticanaloue of GnRH used in the study was Receptalaqueoussolutiont .0042 me/ml. The compound was administered in a &ml (21 ng) Lm. dose aseptically. Schedule of examination for evidence of ovarian activity included obser vationsof ovaries. The degreeof follicular developmentwas graded as Fl , F2, or F3 and the corporaluteawere gradedas CLl, CL2 or CL3. Folliclesless than 0.5 cm were designated
Fl; 0.5 cm to 1 cm,F2;mature follicle,Ffj. Ovarianexaminationsbeforeend after treatmentwere used to detectpossible
760
JUNE 1986VOL.25N0.6
THERIOGENOLOGY palpablechangeson the ovariansurface. Detectionof estrusin a herd was done twice a day with a teaserbull and was apparentlythoroughenoughto includeshortestrous periods. The crossbredcows includedin this study did not show any follicularor luteal structureon the ovary before treatment. Observationsof mountingbehaviour,discharge from the vulva,conception,and folliculardevelopmentwere graded as follows: 1. Response1 - Rxpressionof estruswith or without conceptfon 2. Response2 - E9oexpressionof estrusbut with follicular developmentof differingdegrees 3. No response
In 53 treatedanimals,12(22.6&j, 23 (52,$3$),and 13 l24.53;$) showedresponses1, 2 and no responserespectively, while out of eight controlanimals, three (37.50$)end five (62.50$)showedresponse2 end no responserespectively as shown in Table 1. of anestrouscows Table 1. Responsedistribution
Response1 Response2 No response Total GnRR-treated
53 @2%$)
(52:3%1
C?z53%1
(37.&Q
(6&X$)
Control
JUNE1986VOL.25NO.6
8
761
THERIOGENOLOGY
The GnRR-treated cows showing response 1 averaged 29.17 d to respond as shown in Table 2. Of these 12 animals, nine responded between 4-10 d following treatment. The remaining three animals took from 14 to 155 d. Al.122 GnRR-treated cows responded within 3-U. d after treatment. Thirteen cows showed no response to GnRR treatment. Three of the eight control auimals showed response 2 on 94 d average, one animal responded on Day 8 and the other two after 111 and I!53d. Rone of the three exhibited external symptoms of estrus. Five animals in the control group did not respond. The response distribution of GnRH-treated cows indicatesa majority of animals exhibited follieular development without behavioural manifestations of heat (response 2). Next in frequency were animals that showed no response by behavioursl expression of heat and conception. None of the control animals showed response 1. Table 3 reflects that of the 12 cows showing response 1 seven cows conceived while five did not conceive. These five cows showed the presence of cyclic corpus luteum on one of the ovaries. In cows showing.response2, 15 cows showed the presence of Fl follicles and X3 cows exhibited F2 follicles during follow-up examinations. Of three cows in the control group showing response 2,two showed I?2follicles and one showed an Fl follicle.
Table 2. Mean interval in days ld> from administration of GnRH anslogue to response in anestrous cows
Response 1 GnRR-treated
Contzol
29.17 (12ja 4-10 d (9) 14-155 d (3)
Response 2 6.32 (23) 3-11 a 94.00 (3) 3-163 (d1
Total 40
3
Figures in parentheses indicate number of animals.
762
JUNE
1986 VOL. 25 NO. 6
THERIOGENOLOGY
Table 3. _-.
_
~.
ResDonse
1
Pregnant
7
Details of cows showing different degrees of follicular development ~~
Man-pregnant
5
R nonse2 F1 follicles F2 follicles
15
3.3
A long time period was necessary to prQiloteresponse 1 in GnFCH-treatedcows. The ovarian stimulation was triggered only partly and no manifestation of external symptoms of estrus occurred in the majority of animals.
Several reports in the literature pertaining to the use of GnRh in cows indicate possible reasons for variations in GnFB response. Eaoconception rate difference was found between GnRH-treated cows and controls. Females with small, hard follicles did not conceive even after treatment with LHRF (1). hone of the GnBH treatments reduced the service peribd lagth (6). GnBH treatment increased the per cent of cows exhibiting oestrus but reproductive performance during breeding season did not differ among groups (3). There was no significant difference between GnRH-treated cows and controls in either the interval from parturition to first oestrus or the calving interval (7). Little difference was found in the occurrence of oestrus between LHRIItreated groups and control groups of postpartum cows (8). The results of this study on follicular development in GnRHtreated cows with response 2 are similar to the result cited above. GnRH-induced ovulation in postpartum dairy cows resulted when large follicles were present at the time of treatment (9). LH release in response to GnRH was shown to be abrupt and biphasic and failed to induce normal ovarian activity in animals with reproductive disorders (10, 11).
JUNE1986VOL.25NO.6
763
THERIOGENOLOGY
In the present study administration of CnRH in cows has promoted development of follicles upto a certain stage as indicated by the majority of animals showing response 2. The ovarian follicle in response to GnRH treatment has developed to a certain point and then failed to grow further or ovulate. The failure of follicular development beyond a particular stage in GnRH-treated animals iS unexplained. Presensitization of the reproductive tract with steroids frau a previous cycle (as in ewes) (12) may be necessary for adequate response,or some unidentified factor may be responsible.
GnRH analogue in the treatment of anestrous cows was found less effective between control and treated group (5). LRRH was also used in the treatment of postparttrmanestms in cows and its successful*application was discussed (13). In our study GriRHadministration has promoted development of follicles but not ovulation or behavioural manifestations (response 2) in the majority of cows treated. This may be due to an inadequate GnRH dose or to the need for episodic administration or to the need for closer examination or observations, etc. The examination of the ovaries beforetreat ment is not predictive of the response and other paraneters should be considered. Response monitoring through hormonal. levels and further studies supported by ciinico-gynaecological evaluations of cows are necessary before therapeutic applications of GnRH can be proposed.
1. Gunzler, O., Schatzle, ti.,and Schmidt, L.A. Studies with LKRF in cattle. Theriogenology_&:129-I.30 (1974). 2. Christl, H.C. Studies with a synthetic gonadotrophin releasing hormone in treatuent in infertility. Vet. Bul. *:897 (19751. 3. Fonseca, F.A., Rritt, J.H., Kosugiyama, W.,Ritchie, H.D., and Pillard, E.U. Ovulation,ovarian function and reproductive performance after treatment with GnRR in post partum suckled COWS. Theriogenology2:171-X31 (1980). 4. Kaneda, H., Kamomae, H., Domeki, I., and Nakahara, T. Response of quiescent ovaries to gonadotrophins and an LHRH anslogue in grazing heifers. Japanese Journal of Animal Reproduction&:89-94(l979).
764
JUNE 1986VOL. 25N0.6
THERIOGENOLOGY
5. Holtemoller, B. Investigations on the use of synthetic GnRH in cattle. Thesis Fachbereich Veterinarmedizin und Tierzucht UnfverLitat Giessen, German Federal Republic (1975). 6. Bulman, D.C. end Wood, P.D.P. Abnormal patterns of ovarian activity in dairy cows and their relationships with reproductive performance. Animal Production a:1770188 (1980). 7. Holness, D.H., and Hale, D.H. The response of lactating Africander cows to treatment with a progesterone releasing intravagillaldevice or injection of synthetic GnRE. animal Reproduction Science &181-X38 (1980). Ovarian activity in post-partum beef COWS* 8. Peters, A.& In lath International Congress on Diseases of Cattle, Tel-Aviv, 20-23 October, 1980. Reports and Summaries, Part 2. Israel, Israel Association for Buiatrics. 801-805 (1980). 9. Garverick, H.A., urnore, R.C., Vaillancourt, D.H., and Sharp, A.J. Ovarian response to GnRH in postpartum dairy COWS. Am. J. Vet. Res. &&:l582-I588 (1980). 10. Madej, A., Barcikowski, B., Stupnicki, R., Kula, E., and Binienda, A. LH response to injection of synthetic GnRH or infusion of oestradiol 17-P in heifers. Anti. Breed, Abstr. *:5290 (1980). 11. Webb, R., Lamming, G.E., Haynes, N.B., Hats, H-D., and Nanns, J.G. Response of cyotic and post-partun suckled cows to injections of synthetic LHRH. J. Reprod. Fertil. B:133-143 (1977). 12, Frandle, $.A., Kinder, J.E., Coy, D.H., Schally, A.V., Reeves, J.J., and Estergreed, V.L. Plasma progestlns in anestrousewes treated with D-Leu 6-desgly LH 210LHRH ethylamide. J. Anim. sci. a:486 (1977). 13. Humblot, P. Study of postpartum fertility in the cow. Etude de la fecondite post-partum chez la vache. Elevage et Insemination No. 171, 14-24 (1979).
JUNE 1986 VOL. 25 NO. 6
765
lW3POBSE TO SYNTHETIC GONiDOLIl3E~ (GtiH) IN ANESTftoUSCOWS R.L. Bhoble aml S.K. Gupta
Divisionof Animu Reproduction Indian VOterinsryF&SearchInStitUt8 Izatnagar243 122 (U.P.) Received
for publication: Accepted:
June 12, 1985 April 16, 1986
ABSTRQCT Fifty-threeanestrousCOWS of Harisnacrossedwith Holstein,Friesian,Brown Swiss or Jersey half-br88dcrosses were treadedwith Buserelinacetateaqueoussolution0.0042 mg/ml, administered as a singleintrsmuscular (i..m.) dose of 21ng. Tw8lve (22.64%)animalsexhibitedcompletefollicular d8velopment, ovulationand behaviourslexpressionof oestrus. Twenty-eight(52.83s)cows showedonly partial folliculardevelopmentwith no ovulationor oeskous manifestations. Thirteen(24.53%)animalsdid not respond. Of eight controlanimals,three (3?.3o(;e, showedpartialfollicular developmentand no owlation or symptomsof oestrus while five (62.5%) did not respond. In GnRH-treated cows showingfolliculardevelopment, oestrousmanifestation, and ovulation,nine animalsresponded between 4 to 10 d after administration.Three animals took from 14 to I.55d. The mean time from treatmentto response for this group was 22.17 d. In animalsshowingpartial follic?lardevelopmentand no oestrousbehaviour,the intsrval d in 28 animals.In tha controlgroup, to 11 was three animalsshowedpartialfolliculardevelopmenton 94 d of GnBB in anestrosts cows promoaverag+ The administration ted thetievelopment of folliclesto a certainstage as evident from th8 clinicalobservations, but the folliclesfailedto grow beyonda particularstage. The reasonsfor failureof folliculardevelopmentbeyonda particularstaBein GnRRtreatedanimalsare not clear. It appearedthat the response to GnRH may be expectedto peak by the eleventhday and a seconddose may then be tried for a favourableresponse. Kciywords: Gonadoliberin,anestroUs cows,follicles
The authorsare thankfulto Hoechst,Frankfurt,Germany, for their gift of Recsptal(GnRH), which has enabledus to pursue this work, We are erateful to the Director,I.V.R.I., Isatnagar,for providingexperimental materialfor this study. JUNE1986VOL.25N0.6
759
THERIOGENOLOGY
liWRODUCTlOM
Synthetic:gonadoliberin compounds (GnRH) have recently been used in the management of reproductive problems in cows and are considered useful for improving conception rates (l), treating ovarian cysts (23, reducing post-partum estrus intervsls (31, and inducing ovarian activity in anestrous animals (4&U. It is commonly reported that heifers, even after reachingthe age of maturity and attaining desired body weight, have not shown e,strusor estrous behaviour. Similarly, animals after ealving failed to show heat for a long tlrnefor no apparent reason. This delay in ovariancyclicityin
heifersand in postpartumanima3.s resultsin heavy economic losses in terms of management expenses, longer interval between calving to conception, and prolonged calving interval. The purpose of this study was to assess ovarian response to the administration of the synthetic analogue of GnRH in anestrous cows as judged by development of follicles or corpus luteum (CL5 on the ovary by clinico-gynaecologicalexamination, estrous expression, behavioursl manifestations of estrus, ovulation, or conception. This study also assessed the inter-, ma4 from treatment to onset of clinical response. MATERIALS AHI3 EHODS Fifty-three anestroushalf-bredcows of Harianacrossed with Holstein,Friesfan,Brown Swiss,or Jersey stockwere used. A balancednutritionaldiet includinggreens,dry fodder rendconcentrate mixturewas fed to these animals, All cows tested for brucellosisand tuberculosis were negativeand maintained under barn management. Ovarianstatuswas assessed by examinationper rectum at periodicintervalsbeforeand after treatment. ISach&al was examinedtwice at an interval of 10 d beforethe treatmentand a minimumof three to four examinationswas made at 3- to 4-d intervalsafter treatment.
The syntheticanaloue of GnRH used in the study was Receptalaqueoussolutiont .0042 me/ml. The compound was administered in a &ml (21 ng) Lm. dose aseptically. Schedule of examination for evidence of ovarian activity included obser vationsof ovaries. The degreeof follicular developmentwas graded as Fl , F2, or F3 and the corporaluteawere gradedas CLl, CL2 or CL3. Folliclesless than 0.5 cm were designated
Fl; 0.5 cm to 1 cm,F2;mature follicle,Ffj. Ovarianexaminationsbeforeend after treatmentwere used to detectpossible
760
JUNE 1986VOL.25N0.6
THERIOGENOLOGY palpablechangeson the ovariansurface. Detectionof estrusin a herd was done twice a day with a teaserbull and was apparentlythoroughenoughto includeshortestrous periods. The crossbredcows includedin this study did not show any follicularor luteal structureon the ovary before treatment. Observationsof mountingbehaviour,discharge from the vulva,conception,and folliculardevelopmentwere graded as follows: 1. Response1 - Rxpressionof estruswith or without conceptfon 2. Response2 - E9oexpressionof estrusbut with follicular developmentof differingdegrees 3. No response
In 53 treatedanimals,12(22.6&j, 23 (52,$3$),and 13 l24.53;$) showedresponses1, 2 and no responserespectively, while out of eight controlanimals, three (37.50$)end five (62.50$)showedresponse2 end no responserespectively as shown in Table 1. of anestrouscows Table 1. Responsedistribution
Response1 Response2 No response Total GnRR-treated
53 @2%$)
(52:3%1
C?z53%1
(37.&Q
(6&X$)
Control
JUNE1986VOL.25NO.6
8
761
THERIOGENOLOGY
The GnRR-treated cows showing response 1 averaged 29.17 d to respond as shown in Table 2. Of these 12 animals, nine responded between 4-10 d following treatment. The remaining three animals took from 14 to 155 d. Al.122 GnRR-treated cows responded within 3-U. d after treatment. Thirteen cows showed no response to GnRR treatment. Three of the eight control auimals showed response 2 on 94 d average, one animal responded on Day 8 and the other two after 111 and I!53d. Rone of the three exhibited external symptoms of estrus. Five animals in the control group did not respond. The response distribution of GnRH-treated cows indicatesa majority of animals exhibited follieular development without behavioural manifestations of heat (response 2). Next in frequency were animals that showed no response by behavioursl expression of heat and conception. None of the control animals showed response 1. Table 3 reflects that of the 12 cows showing response 1 seven cows conceived while five did not conceive. These five cows showed the presence of cyclic corpus luteum on one of the ovaries. In cows showing.response2, 15 cows showed the presence of Fl follicles and X3 cows exhibited F2 follicles during follow-up examinations. Of three cows in the control group showing response 2,two showed I?2follicles and one showed an Fl follicle.
Table 2. Mean interval in days ld> from administration of GnRH anslogue to response in anestrous cows
Response 1 GnRR-treated
Contzol
29.17 (12ja 4-10 d (9) 14-155 d (3)
Response 2 6.32 (23) 3-11 a 94.00 (3) 3-163 (d1
Total 40
3
Figures in parentheses indicate number of animals.
762
JUNE
1986 VOL. 25 NO. 6
THERIOGENOLOGY
Table 3. _-.
_
~.
ResDonse
1
Pregnant
7
Details of cows showing different degrees of follicular development ~~
Man-pregnant
5
R nonse2 F1 follicles F2 follicles
15
3.3
A long time period was necessary to prQiloteresponse 1 in GnFCH-treatedcows. The ovarian stimulation was triggered only partly and no manifestation of external symptoms of estrus occurred in the majority of animals.
Several reports in the literature pertaining to the use of GnRh in cows indicate possible reasons for variations in GnFB response. Eaoconception rate difference was found between GnRH-treated cows and controls. Females with small, hard follicles did not conceive even after treatment with LHRF (1). hone of the GnBH treatments reduced the service peribd lagth (6). GnBH treatment increased the per cent of cows exhibiting oestrus but reproductive performance during breeding season did not differ among groups (3). There was no significant difference between GnRH-treated cows and controls in either the interval from parturition to first oestrus or the calving interval (7). Little difference was found in the occurrence of oestrus between LHRIItreated groups and control groups of postpartum cows (8). The results of this study on follicular development in GnRHtreated cows with response 2 are similar to the result cited above. GnRH-induced ovulation in postpartum dairy cows resulted when large follicles were present at the time of treatment (9). LH release in response to GnRH was shown to be abrupt and biphasic and failed to induce normal ovarian activity in animals with reproductive disorders (10, 11).
JUNE1986VOL.25NO.6
763
THERIOGENOLOGY
In the present study administration of CnRH in cows has promoted development of follicles upto a certain stage as indicated by the majority of animals showing response 2. The ovarian follicle in response to GnRH treatment has developed to a certain point and then failed to grow further or ovulate. The failure of follicular development beyond a particular stage in GnRH-treated animals iS unexplained. Presensitization of the reproductive tract with steroids frau a previous cycle (as in ewes) (12) may be necessary for adequate response,or some unidentified factor may be responsible.
GnRH analogue in the treatment of anestrous cows was found less effective between control and treated group (5). LRRH was also used in the treatment of postparttrmanestms in cows and its successful*application was discussed (13). In our study GriRHadministration has promoted development of follicles but not ovulation or behavioural manifestations (response 2) in the majority of cows treated. This may be due to an inadequate GnRH dose or to the need for episodic administration or to the need for closer examination or observations, etc. The examination of the ovaries beforetreat ment is not predictive of the response and other paraneters should be considered. Response monitoring through hormonal. levels and further studies supported by ciinico-gynaecological evaluations of cows are necessary before therapeutic applications of GnRH can be proposed.
1. Gunzler, O., Schatzle, ti.,and Schmidt, L.A. Studies with LKRF in cattle. Theriogenology_&:129-I.30 (1974). 2. Christl, H.C. Studies with a synthetic gonadotrophin releasing hormone in treatuent in infertility. Vet. Bul. *:897 (19751. 3. Fonseca, F.A., Rritt, J.H., Kosugiyama, W.,Ritchie, H.D., and Pillard, E.U. Ovulation,ovarian function and reproductive performance after treatment with GnRR in post partum suckled COWS. Theriogenology2:171-X31 (1980). 4. Kaneda, H., Kamomae, H., Domeki, I., and Nakahara, T. Response of quiescent ovaries to gonadotrophins and an LHRH anslogue in grazing heifers. Japanese Journal of Animal Reproduction&:89-94(l979).
764
JUNE 1986VOL. 25N0.6
THERIOGENOLOGY
5. Holtemoller, B. Investigations on the use of synthetic GnRH in cattle. Thesis Fachbereich Veterinarmedizin und Tierzucht UnfverLitat Giessen, German Federal Republic (1975). 6. Bulman, D.C. end Wood, P.D.P. Abnormal patterns of ovarian activity in dairy cows and their relationships with reproductive performance. Animal Production a:1770188 (1980). 7. Holness, D.H., and Hale, D.H. The response of lactating Africander cows to treatment with a progesterone releasing intravagillaldevice or injection of synthetic GnRE. animal Reproduction Science &181-X38 (1980). Ovarian activity in post-partum beef COWS* 8. Peters, A.& In lath International Congress on Diseases of Cattle, Tel-Aviv, 20-23 October, 1980. Reports and Summaries, Part 2. Israel, Israel Association for Buiatrics. 801-805 (1980). 9. Garverick, H.A., urnore, R.C., Vaillancourt, D.H., and Sharp, A.J. Ovarian response to GnRH in postpartum dairy COWS. Am. J. Vet. Res. &&:l582-I588 (1980). 10. Madej, A., Barcikowski, B., Stupnicki, R., Kula, E., and Binienda, A. LH response to injection of synthetic GnRH or infusion of oestradiol 17-P in heifers. Anti. Breed, Abstr. *:5290 (1980). 11. Webb, R., Lamming, G.E., Haynes, N.B., Hats, H-D., and Nanns, J.G. Response of cyotic and post-partun suckled cows to injections of synthetic LHRH. J. Reprod. Fertil. B:133-143 (1977). 12, Frandle, $.A., Kinder, J.E., Coy, D.H., Schally, A.V., Reeves, J.J., and Estergreed, V.L. Plasma progestlns in anestrousewes treated with D-Leu 6-desgly LH 210LHRH ethylamide. J. Anim. sci. a:486 (1977). 13. Humblot, P. Study of postpartum fertility in the cow. Etude de la fecondite post-partum chez la vache. Elevage et Insemination No. 171, 14-24 (1979).
JUNE 1986 VOL. 25 NO. 6
765