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Influence of the presence of a mature female on puberty attainment in gilts
THERIOGENOLOGY
INJXUENCE
OF TEE PRESENCE OF A MATURE FEMALE ON PUBERTY ATTAINMENT IN GILTS A. Pnmier and A.M. Mounler
Station de Recherches Porcines, I.N.R.A., St-Giies, 35590 l’Hermitage, France Received for publication: Accepted:
March 6, JuZy 29,
1991 1991
ABSTRACT At 90 days of age, 40 Large White gilts were assigned to one of two treatments. At 155 days, a mature female which was left intact (Treatment I) or ovariectomized (Treatment 0) was placed in each pen of five experimental gilts. From 180 days, estrus was checked daily with the back pressure test, and the occurrence of ovulation was detected by measuring the concentration of plasma progesterone at vrieekly intervals. From 240 days, a mature boar was introduced, for 5 minutes daily, into each pen during esttus detection. Gilts were slaughtered within 12 days after ovulation or at 270 days of age if they were not cyclic earlier. The percentage of gilts reaching puberty before 225 days of age was significantly higher in Treatment I (7/19) than in Treatment 0 (O/19) even though the average age at puberty was similar (I, 231 +. 24 days; 0,243 f 12 days; mean + SD). Age at puberty and the number of days between mature female introduction and puberty differred significantly between the pens of gilts in Treatment 0 but not in Treatment I. Ovarian weights, ovulation rate and percentage of gilts with silent estms were similar in the two treatments. Thus, the occurrence of pubertal estrus may be influenced by contact with an older, cyclic female or with other contemporary females raised in the same pen Key words: puberty, gilt, female stimulation, progesterone
EWRODUCTION It is well known that exposure of prepubertal gilts to a mature boar advances significantly the onset of puberty (1,2). This effect has also been observed in mice and the cow (3,4). Other social factors can interfere with sexual maturation, and the influence of contacts with other females, contemporary or mature, has been reported. In mice, puberty is delayed when females are reared in young groups or in the presence of a mature female (5). In the gilt, puberty is Acknowledgments The authors thank B. Car&ant, J. Chevalier, G. Conseil, F. Giovanni, F. Legouevec, M. Lemarie and J. Portanguen for their skillfull technical assistance.
OCTOBER 1991 VOL. 36 NO. 4
537
THERIOGENOLOGY
delayed in individual females compared with group penned females (6). and the size of the group may influence age at puberty (7). Moreover, Den Hartog and Noordewier (8) have reported lower within-pen than between-pen variances for females belonging to the same treatment group. In addition, Delcmix et al. (9) have shown that ovarian activity in wild sows belonging to the same social group is closely synchronized both in the presence and in the absence of a male. In order to determine the influence of a cyclic female on sexual maturation of the domestic gilts, we compared the attahnnent of puberty among gilts raised in the presence of a mature intact female or an ovariectomized one.
MATERIALS AND METHODS Around 90 days of age, 40 Large White females, born in April 1989 from 20 litters, were assigned within litter by weight to one of two treatments. The gilts were housed in the same building under natural conditions of lighting, with one stall used for each treatment. In both stalls, experimental females were kept in groups of five in adjacent pens with the same pen mates throughout the experiment. In each stall nonexperimental growing pigs, immature females, or castrated males were present. When experimental gilts were 155 rt: 3 days of age (mean + SD), a mature female 208 to 246 days of age was placed in each pen. The mature female was either ovariectomized (Treatment 0) or left intact (Treatment I). From 240 + 3 days of age, a mature boar was introduced daily for 5 minutes into each pen. This boar was housed in a separate stall of the same building. Animals were fed a standard diet containing 12.93 MJ DE/kg food, 17.3% protein and 0.83% lysine. They received 1.2 to 3.1 kg/day between 40 and 100 kg of live weight and were restricted to 2.9 kg/day until reaching 120 kg and to 2.7 kglday thereafter. Live weights were recorded at allotment, at ICday intervals throughout the experiment, and at slaughter. From 155 days of age, estrus was checked daily. The back pressure test (10) was used both in the absence (before 240 days of age) and in the presence of the boar (after 240 days of age). To detect ovulation, blood samples were collected once a week from 176 days of age. A direct radioimmunoassay (11) was performed on plasma in order to determine whether the concentration of progesterone was higher than 5 nglml (positive sample), which indicates that ovulation has occurred. Determination of age at puberty was based on estrus detection and on the progesterone test as described previously (12). Females were slaughtered 7 to 12 days after a positive blood sample or at 9 months of age (between 271 and 273 days). One female from each treatment was slaughtered before the end of the experiment due to an error (one female) and to a health problem (one female), and these two females, which were not pubertal, were eliminated from the analysis. Ovarian weights were recorded and ovaries were dissected to determine the number of corpora lutea (CLs). For both treatment groups, sample variances of age at puberty, interval between mature female introduction and puberty, ovarian weight and number of CLs were calculated, and the comparisons between the two treatments were carried out using the Fisher test (13). These data were also subjected to nonparametric analyses: the test of Mann and Whimey (14) to assess differences between treatment groups and the test of Kruskall and Wallis (14) to assess
636
OCTOBER 1991 VOL. 36 NO. 4
THERIOGENOLOGY differences between pens within each treatment. Comparison of percentages of females attaining puberty or having a silent estrus (ovulation without detected estms) was achieved using the Chi-square test (14).
RESULTS Puberty occurred early (before 225 days of age) in mote Treatment I (7/19) than Treatment 0 (O/19) gilts (P < 0.01). However, at 240 days of age, just before boar introduction, this difference was no longer significant: 1 l/19 for Treatment I and 9/19 for Treatment 0 (P > 0.1; Figure 1). At the end of the experiment, percentage of females which were not pubertal was similar in both groups (Treatment I, l/19; Treatment 0,2/19; P > 0.1). TREATMENT 0
TREATMENT I r
t
3
2
-I
2
1
J 110
9
3
.
-;
.1 ..-
.. 0
j.-
.
0
70
6
. I
-..*-
5
4
0 I .
_1
i-.
__ .O
300~ I
I
Boar Introduction
I
!
.o* I .
ioo*I
!
50
30
10 /
_-l-L
Figure 1. Timetable of the occurrence of the first estrus (
0
silent estrus, @detected e&us).
Age at puberty and number of days between the introduction of the mature female and puberty were more variable in Treatment I than in Treatment 0 (Table 1). Within Treatment I, age at puberty and number of days from introduction of the mature female to puberty were similar in all four pens, while within Treatment 0 them were significant differences between pens (P c 0.05; Figure 1). Finally, residual standard deviation of the number of days between introduction of the mature female and puberty when the pen effect is removed was much higher within Treatment I (23.2) than within Treatment 0 (6.4).
OCTOBER 1991 VOL. 36 NO. 4
THERIOGENOLOGY
Table 1. Influence of treatment on sexual development of gilts (means + SD) I
0
Comparison of variancesa
Ovarian weight (grams)
14.1 + 3.9
14.0 + 3.4
>O.l
Corpora lutea (number)
14.7 + 3.7
14.2 f. 2.4
0.05
Treatment
Interval from female intoduction to puberty (days)
76+25
85 + 13
0.005
Pubertal age (days)
231+24
243 + 12
0.005
Number of gilts
17
18
a Level of significance of the Fisher test, The percentage of gilts with silent esttus was similar in the two groups of females both before (Deatment I, l/7; Treatment 0, l/9; P > 0.1) or after male introduction (Treatment I, 4/l 1; Treatment 0, 5/8; b 0.1). The percentage was much higher when the back pressure test was performed in the absence of the boar than in the presence of the boar (without boar, 9/19; with boar, 2/16; P < 0.01). Variances in the ovarian weights were similar between the two groups of females, while the number of CLs was more variable in Treatment I than in Treatment 0 (Table 1). Ovarian weights and the number of CLs were similar in the two groups of gilts.
DISCUSSION This experiment indicates that contact with a cyclic female may stimulate puberty I attainment in the gilt: the percentage of gilts reaching puberty before 225 days of age was higher upon introduction of an intact cyclic female than an ovariectomized one. However, only a minority of the females were responsive to the contact with a cyclic gilt, so that attainment of puberty was more variable in this group, and the average age at puberty did not differ significantly between the two treatment groups. Our results show that ovulation can be synchronized in a group of domestic gilts attaining puberty regardless of the presence of a mature male as has been shown for mature wild sows recovering from seasonal anesnus (9). This result is also similar to that of Den Hat-tog and Noordewier (8), showing that variabliiity of age at first estrus is lower within pen than between pens of gilts. Such synchrony of ovarian cyclicity has been observed in the human (15), baboon (16), laboratory rat (17) and red deer (18). The mechanisms responsible for this phenomenon are not known. Pheromonal communication is probably involved, since it has been shown in the laboratory rat that estrus is synchronized by pheromones from cyclic, pregnant or lactating females (17, 19). Moreover, pheromones seem to be components of the boar effect on puberty
640
OCTOBER 1991 VOL. 36 NO. 4
THERIOGENOLOGY attainment in the domestic gilt (20-22). Our study shows that this synchronization of ovulation is delicate in domestic gilts and can be disrupted by the introduction of a cyclic female. The mere introduction of an older female into the group is not sufficient; the female must be cyclic. Thus, a modification of the social structure of a group is not sufficient in itself to disrupt the synchronization of ovulation. The ovulation rate at puberty was not influenced by the introduction of a cyclic rather than an dvariectomized gilt Efficacy of estrus detection was not influenced by the type of mature gilt introduced, while the presence of a male had a great influence. The effect of the boar could be confused with a possible effect of the female age. However, previous experiments have shown that the efficacy of estrus detection using the back pressure test is two or three times better in the presence rather than in the absence of a boar (10,12). In conclusion, present study provides evidence of an influence of contact with other females on the occurrence of pubertal estrus in the gilt. The optimal benefit from tbis effect remains to be determined.
REFERENCES 1. Brooks, P.H. and Cole, D.J.A. The effect of the presence of a boar on the attainment of puberty in gilts. J. Reprod. Fertil. a:435440 (1970). 2. Prunier, A. Influence de la presentation Prod. Anim. 2:65-72 (1989).
au verrat sur l’age a la pubert6 des truies. INRA
3. Vandenbergh, J.G. Male odor accelerates female sexual maturation in mice. Endocrinology &658-660 (1969). 4. Izard, M.K. and Vanderbergh, J.G. The effects of bull mine on puberty and calving date in crossbred beef heifers. J. Anim. Sci. s:1160-1168 (1982). 5. Vanderbergh, J.G., Drickamer, L.C. and Colby, J.R. Social and dietary factors in the sexual maturation of female mice. J. Reprod. Fertil. z:397-405 (1972). 6. Mavrogenis, A.P. and Robison, O.W. Factors affecting puberty in swine. J. Anim. Sci. Q:1251-1255 (1976). 7. Christenson, R.K. Influence of number of gilts per pen on estrous traits in confinementreared gilts. Theriogenology 2: 313-320 (1984). 8. Den Hartog, L.A. and Noordewier, G.J. The effect of energy intake on age at puberty in gilts. J. agtic. Sci. 2:263-280 (1984). 9. Delcroix, I., Maugct, R and Signoret, J.P. Existence of synchronization of reproduction at the level of the social group of the European wild boar (sl?s scrof& J. Repmd. Fertil.
OCTOBER 1991 VOL. 36 NO. 4
THERIOGENOLOGY
B:613-617
(1990).
10. Sigooret, J.P. Contribution Zi 1’Etude des M&nismes Ethologiques et Endocriniens du Compoltement Sexuel de la Truie (&s & L.). Thi?se d’Etat. Universite Paris VI, 1972. 11. Terqui, M. and Thimonier, J. Nouvelle m&ode pour l’estimation du niveau de progestkrone plasmatique. Application pour le diagnostic de gestation. C. R. Acad. Sci. Paris 229:1X@-1112 (1974). 12. Pnmier, A. and Meunier-Salati, M.C. The influence of boar stimulation on pubelty attainment in tethered and group penned gilts. Theriogenology 2:949-959 (1989). 13. Snedecor, G.W. and Co&ran, Ames, IA, USA, 1957.
G. Statistical Methods. The Iowa State University Press.
14. Siegel, S. Non Parametric Statistics for the Behavioral Sciences. International Edition. MacGraw-Hill Book Co., New York, 1956, pp. 116-184.
Student
15. MacClintock, M.K. Menstrual synchrony and suppression. Nature 22p:244 (1971). 16. Rowe& T. Social Behavior of Monkeys. Kingsport Press, Kingsport, TN, 1972. 17. MacClintock, M.K. communication m
Estrous n-d.
synchrony and its mediation by airborne Horm. and Behav. l&264-276 (1978).
chemical
18. Iason, R.I. and Guiness, F.E. Synchrony of oestrus and conception danhus L.). Anim. Behav. B:1169-1174 (1985).
in red deer (Cervus,
19. MacClintock, M.K. Modualtion of the oestrous cycle by pheromones lactating rats. Biol. Repmd. a:823-829 (1983).
from pregnant and
20. Khlcwood, R.N., Forbes, J.M. and Hughes, P.E. Influence of boar contact on attainment of puberty in gilts after removal of the olfactory bulbs. I. Reprod. Fertil. fi:193-196 (1981). 21. Kirkwood, R.N., Hughes, P.E. and Booth, W.D. The influence of boar-related odours on puberty attainment in gilts. Anim. Prod. %131-136 (1983). 22. Pearce, G.P. and Hughes, P.E. The influence of boar-component attainment in the gilt. Anim. Prod. &293-302 (1987).
stimuli on puberty
OCTOBER 1961 VOL. 36 NO. 4
INJXUENCE
OF TEE PRESENCE OF A MATURE FEMALE ON PUBERTY ATTAINMENT IN GILTS A. Pnmier and A.M. Mounler
Station de Recherches Porcines, I.N.R.A., St-Giies, 35590 l’Hermitage, France Received for publication: Accepted:
March 6, JuZy 29,
1991 1991
ABSTRACT At 90 days of age, 40 Large White gilts were assigned to one of two treatments. At 155 days, a mature female which was left intact (Treatment I) or ovariectomized (Treatment 0) was placed in each pen of five experimental gilts. From 180 days, estrus was checked daily with the back pressure test, and the occurrence of ovulation was detected by measuring the concentration of plasma progesterone at vrieekly intervals. From 240 days, a mature boar was introduced, for 5 minutes daily, into each pen during esttus detection. Gilts were slaughtered within 12 days after ovulation or at 270 days of age if they were not cyclic earlier. The percentage of gilts reaching puberty before 225 days of age was significantly higher in Treatment I (7/19) than in Treatment 0 (O/19) even though the average age at puberty was similar (I, 231 +. 24 days; 0,243 f 12 days; mean + SD). Age at puberty and the number of days between mature female introduction and puberty differred significantly between the pens of gilts in Treatment 0 but not in Treatment I. Ovarian weights, ovulation rate and percentage of gilts with silent estms were similar in the two treatments. Thus, the occurrence of pubertal estrus may be influenced by contact with an older, cyclic female or with other contemporary females raised in the same pen Key words: puberty, gilt, female stimulation, progesterone
EWRODUCTION It is well known that exposure of prepubertal gilts to a mature boar advances significantly the onset of puberty (1,2). This effect has also been observed in mice and the cow (3,4). Other social factors can interfere with sexual maturation, and the influence of contacts with other females, contemporary or mature, has been reported. In mice, puberty is delayed when females are reared in young groups or in the presence of a mature female (5). In the gilt, puberty is Acknowledgments The authors thank B. Car&ant, J. Chevalier, G. Conseil, F. Giovanni, F. Legouevec, M. Lemarie and J. Portanguen for their skillfull technical assistance.
OCTOBER 1991 VOL. 36 NO. 4
537
THERIOGENOLOGY
delayed in individual females compared with group penned females (6). and the size of the group may influence age at puberty (7). Moreover, Den Hartog and Noordewier (8) have reported lower within-pen than between-pen variances for females belonging to the same treatment group. In addition, Delcmix et al. (9) have shown that ovarian activity in wild sows belonging to the same social group is closely synchronized both in the presence and in the absence of a male. In order to determine the influence of a cyclic female on sexual maturation of the domestic gilts, we compared the attahnnent of puberty among gilts raised in the presence of a mature intact female or an ovariectomized one.
MATERIALS AND METHODS Around 90 days of age, 40 Large White females, born in April 1989 from 20 litters, were assigned within litter by weight to one of two treatments. The gilts were housed in the same building under natural conditions of lighting, with one stall used for each treatment. In both stalls, experimental females were kept in groups of five in adjacent pens with the same pen mates throughout the experiment. In each stall nonexperimental growing pigs, immature females, or castrated males were present. When experimental gilts were 155 rt: 3 days of age (mean + SD), a mature female 208 to 246 days of age was placed in each pen. The mature female was either ovariectomized (Treatment 0) or left intact (Treatment I). From 240 + 3 days of age, a mature boar was introduced daily for 5 minutes into each pen. This boar was housed in a separate stall of the same building. Animals were fed a standard diet containing 12.93 MJ DE/kg food, 17.3% protein and 0.83% lysine. They received 1.2 to 3.1 kg/day between 40 and 100 kg of live weight and were restricted to 2.9 kg/day until reaching 120 kg and to 2.7 kglday thereafter. Live weights were recorded at allotment, at ICday intervals throughout the experiment, and at slaughter. From 155 days of age, estrus was checked daily. The back pressure test (10) was used both in the absence (before 240 days of age) and in the presence of the boar (after 240 days of age). To detect ovulation, blood samples were collected once a week from 176 days of age. A direct radioimmunoassay (11) was performed on plasma in order to determine whether the concentration of progesterone was higher than 5 nglml (positive sample), which indicates that ovulation has occurred. Determination of age at puberty was based on estrus detection and on the progesterone test as described previously (12). Females were slaughtered 7 to 12 days after a positive blood sample or at 9 months of age (between 271 and 273 days). One female from each treatment was slaughtered before the end of the experiment due to an error (one female) and to a health problem (one female), and these two females, which were not pubertal, were eliminated from the analysis. Ovarian weights were recorded and ovaries were dissected to determine the number of corpora lutea (CLs). For both treatment groups, sample variances of age at puberty, interval between mature female introduction and puberty, ovarian weight and number of CLs were calculated, and the comparisons between the two treatments were carried out using the Fisher test (13). These data were also subjected to nonparametric analyses: the test of Mann and Whimey (14) to assess differences between treatment groups and the test of Kruskall and Wallis (14) to assess
636
OCTOBER 1991 VOL. 36 NO. 4
THERIOGENOLOGY differences between pens within each treatment. Comparison of percentages of females attaining puberty or having a silent estrus (ovulation without detected estms) was achieved using the Chi-square test (14).
RESULTS Puberty occurred early (before 225 days of age) in mote Treatment I (7/19) than Treatment 0 (O/19) gilts (P < 0.01). However, at 240 days of age, just before boar introduction, this difference was no longer significant: 1 l/19 for Treatment I and 9/19 for Treatment 0 (P > 0.1; Figure 1). At the end of the experiment, percentage of females which were not pubertal was similar in both groups (Treatment I, l/19; Treatment 0,2/19; P > 0.1). TREATMENT 0
TREATMENT I r
t
3
2
-I
2
1
J 110
9
3
.
-;
.1 ..-
.. 0
j.-
.
0
70
6
. I
-..*-
5
4
0 I .
_1
i-.
__ .O
300~ I
I
Boar Introduction
I
!
.o* I .
ioo*I
!
50
30
10 /
_-l-L
Figure 1. Timetable of the occurrence of the first estrus (
0
silent estrus, @detected e&us).
Age at puberty and number of days between the introduction of the mature female and puberty were more variable in Treatment I than in Treatment 0 (Table 1). Within Treatment I, age at puberty and number of days from introduction of the mature female to puberty were similar in all four pens, while within Treatment 0 them were significant differences between pens (P c 0.05; Figure 1). Finally, residual standard deviation of the number of days between introduction of the mature female and puberty when the pen effect is removed was much higher within Treatment I (23.2) than within Treatment 0 (6.4).
OCTOBER 1991 VOL. 36 NO. 4
THERIOGENOLOGY
Table 1. Influence of treatment on sexual development of gilts (means + SD) I
0
Comparison of variancesa
Ovarian weight (grams)
14.1 + 3.9
14.0 + 3.4
>O.l
Corpora lutea (number)
14.7 + 3.7
14.2 f. 2.4
0.05
Treatment
Interval from female intoduction to puberty (days)
76+25
85 + 13
0.005
Pubertal age (days)
231+24
243 + 12
0.005
Number of gilts
17
18
a Level of significance of the Fisher test, The percentage of gilts with silent esttus was similar in the two groups of females both before (Deatment I, l/7; Treatment 0, l/9; P > 0.1) or after male introduction (Treatment I, 4/l 1; Treatment 0, 5/8; b 0.1). The percentage was much higher when the back pressure test was performed in the absence of the boar than in the presence of the boar (without boar, 9/19; with boar, 2/16; P < 0.01). Variances in the ovarian weights were similar between the two groups of females, while the number of CLs was more variable in Treatment I than in Treatment 0 (Table 1). Ovarian weights and the number of CLs were similar in the two groups of gilts.
DISCUSSION This experiment indicates that contact with a cyclic female may stimulate puberty I attainment in the gilt: the percentage of gilts reaching puberty before 225 days of age was higher upon introduction of an intact cyclic female than an ovariectomized one. However, only a minority of the females were responsive to the contact with a cyclic gilt, so that attainment of puberty was more variable in this group, and the average age at puberty did not differ significantly between the two treatment groups. Our results show that ovulation can be synchronized in a group of domestic gilts attaining puberty regardless of the presence of a mature male as has been shown for mature wild sows recovering from seasonal anesnus (9). This result is also similar to that of Den Hat-tog and Noordewier (8), showing that variabliiity of age at first estrus is lower within pen than between pens of gilts. Such synchrony of ovarian cyclicity has been observed in the human (15), baboon (16), laboratory rat (17) and red deer (18). The mechanisms responsible for this phenomenon are not known. Pheromonal communication is probably involved, since it has been shown in the laboratory rat that estrus is synchronized by pheromones from cyclic, pregnant or lactating females (17, 19). Moreover, pheromones seem to be components of the boar effect on puberty
640
OCTOBER 1991 VOL. 36 NO. 4
THERIOGENOLOGY attainment in the domestic gilt (20-22). Our study shows that this synchronization of ovulation is delicate in domestic gilts and can be disrupted by the introduction of a cyclic female. The mere introduction of an older female into the group is not sufficient; the female must be cyclic. Thus, a modification of the social structure of a group is not sufficient in itself to disrupt the synchronization of ovulation. The ovulation rate at puberty was not influenced by the introduction of a cyclic rather than an dvariectomized gilt Efficacy of estrus detection was not influenced by the type of mature gilt introduced, while the presence of a male had a great influence. The effect of the boar could be confused with a possible effect of the female age. However, previous experiments have shown that the efficacy of estrus detection using the back pressure test is two or three times better in the presence rather than in the absence of a boar (10,12). In conclusion, present study provides evidence of an influence of contact with other females on the occurrence of pubertal estrus in the gilt. The optimal benefit from tbis effect remains to be determined.
REFERENCES 1. Brooks, P.H. and Cole, D.J.A. The effect of the presence of a boar on the attainment of puberty in gilts. J. Reprod. Fertil. a:435440 (1970). 2. Prunier, A. Influence de la presentation Prod. Anim. 2:65-72 (1989).
au verrat sur l’age a la pubert6 des truies. INRA
3. Vandenbergh, J.G. Male odor accelerates female sexual maturation in mice. Endocrinology &658-660 (1969). 4. Izard, M.K. and Vanderbergh, J.G. The effects of bull mine on puberty and calving date in crossbred beef heifers. J. Anim. Sci. s:1160-1168 (1982). 5. Vanderbergh, J.G., Drickamer, L.C. and Colby, J.R. Social and dietary factors in the sexual maturation of female mice. J. Reprod. Fertil. z:397-405 (1972). 6. Mavrogenis, A.P. and Robison, O.W. Factors affecting puberty in swine. J. Anim. Sci. Q:1251-1255 (1976). 7. Christenson, R.K. Influence of number of gilts per pen on estrous traits in confinementreared gilts. Theriogenology 2: 313-320 (1984). 8. Den Hartog, L.A. and Noordewier, G.J. The effect of energy intake on age at puberty in gilts. J. agtic. Sci. 2:263-280 (1984). 9. Delcroix, I., Maugct, R and Signoret, J.P. Existence of synchronization of reproduction at the level of the social group of the European wild boar (sl?s scrof& J. Repmd. Fertil.
OCTOBER 1991 VOL. 36 NO. 4
THERIOGENOLOGY
B:613-617
(1990).
10. Sigooret, J.P. Contribution Zi 1’Etude des M&nismes Ethologiques et Endocriniens du Compoltement Sexuel de la Truie (&s & L.). Thi?se d’Etat. Universite Paris VI, 1972. 11. Terqui, M. and Thimonier, J. Nouvelle m&ode pour l’estimation du niveau de progestkrone plasmatique. Application pour le diagnostic de gestation. C. R. Acad. Sci. Paris 229:1X@-1112 (1974). 12. Pnmier, A. and Meunier-Salati, M.C. The influence of boar stimulation on pubelty attainment in tethered and group penned gilts. Theriogenology 2:949-959 (1989). 13. Snedecor, G.W. and Co&ran, Ames, IA, USA, 1957.
G. Statistical Methods. The Iowa State University Press.
14. Siegel, S. Non Parametric Statistics for the Behavioral Sciences. International Edition. MacGraw-Hill Book Co., New York, 1956, pp. 116-184.
Student
15. MacClintock, M.K. Menstrual synchrony and suppression. Nature 22p:244 (1971). 16. Rowe& T. Social Behavior of Monkeys. Kingsport Press, Kingsport, TN, 1972. 17. MacClintock, M.K. communication m
Estrous n-d.
synchrony and its mediation by airborne Horm. and Behav. l&264-276 (1978).
chemical
18. Iason, R.I. and Guiness, F.E. Synchrony of oestrus and conception danhus L.). Anim. Behav. B:1169-1174 (1985).
in red deer (Cervus,
19. MacClintock, M.K. Modualtion of the oestrous cycle by pheromones lactating rats. Biol. Repmd. a:823-829 (1983).
from pregnant and
20. Khlcwood, R.N., Forbes, J.M. and Hughes, P.E. Influence of boar contact on attainment of puberty in gilts after removal of the olfactory bulbs. I. Reprod. Fertil. fi:193-196 (1981). 21. Kirkwood, R.N., Hughes, P.E. and Booth, W.D. The influence of boar-related odours on puberty attainment in gilts. Anim. Prod. %131-136 (1983). 22. Pearce, G.P. and Hughes, P.E. The influence of boar-component attainment in the gilt. Anim. Prod. &293-302 (1987).
stimuli on puberty
OCTOBER 1961 VOL. 36 NO. 4