- Email: [email protected]
The influence of boar stimulation on puberty attainment in tethered and group penned gilts
THERIOGENOLOGY
THE INFLUENCE OF BOAR STIMULATION ON PUBERTY ATTAINMENT IN TETHERED AND GROUP PENNED GILTS A. Prunier and M.C. Meunier-Salatin Station de Recherches Porcines, I.N.R.A. Saint Giies, 35590 L’Hermitage, France Received for publication: February 22, 1989 Accepted: October 14, 1989
ABSTRACT The objective of this experiment was to determine the influence of boar exposure on sexual development of tethered and group penned gilts. At 140 d of age, a total of 120 Large White gilts were moved into four stalls, each for one treatment, during three successive replicates. Gilts in treatments TB and T were tethered, and those in treatments GB and G were penned in groups of five animals. Two weeks later, females in treatments TB and GB were exposed to a mature boar for 20 min twice daily, while those in treatments T and G remained isolated from the male. From that age, all gilts were checked daily for estrus with the back pressure test and controlled weekly for ovulation by measuring progesterone concentration in plasma. Recording of social interactions between the male and the females was carried out in the second replicate at 6 and 7 mo of age. Estrone excretion was estimated just before and after relocation and 4 wk after boar introduction in the first and second replicates. Boar exposure advanced puberty attainment of gilts whatever the type of housing (median age at puberty = 233, 260, 215, 264 in treatments TB, T, GB and G, respectively, P
INTRODUCTION Since the work of Brooks and Cole in 1970 (1) which showed that the introduction of a mature boar to prepubertal gilts advances the onset of puberty, many authors have studied this effect (2 to 27). However, in all except three studies (16, 19, 25), authors used crossbred females which are known to attain puberty earlier than purebred gilts (28,29) and therefore could be more sensitive to the “boar effect”. Moreover, the influence of the female housing system on the efficacy of the male to induce puberty has been poorly studied. Acknowledgments The authors are thankful to A.M. Mounier, F. Giovanni, J. Lebost, J.C. Hulii and M. Massard (I.N.R.A. Saint Gilles) for their skillful1technical assistance.
DECEMBER 19B9VOL. 32 NO. 6
949
THERIOGENOLOGY
Thus, the main purpose of this study was to evaluate the influence of the boar introduction on puberty attainment in tethered and group penned gilts from Large White breed. Since urinary estrone excretion has been shown to increase during sexual development of the gilt (30), influence of treatment on this parameter was researched. In order to investigate any possible difference in the level of tactile stimulation provided by the two housing systems, behavioral observations of the interactions between the male and the females were carried out.
MATERIALS AND METHODS Around 100 d of age, 120 Large White gilts from 42 litters were randomly assigned within litter by weight to one of four treatments of 10 animals in three replicates (Table 1). From that age until the end of the experiment, artificial light was provided for 16 h per day. Until relocation, all females of one replicate were gathered in a single stall where no boar was allowed to enter. They were penned in groups of five according to treatment.
Table 1. Birth date, mean age at relocation, urine collections, first blood sampling and boar introduction in the different replicates
Birth date
Replicate 1
Replicate 2
Replicate 3
10/l-28/85
5/286/11/86
3/22-4/S/87
Age at allotment
94
112
95
Age at first urine collection
143
133
Age at relocation
145
135
Age at second urine collection
150
140
Age at boar introduction (TB and BG)
163
153
161
Age at first blood sampling
167
157
164
Age at third urine collection
178
168
146
Around 140 d of age and 72 kg live weight, gilts were moved into the same building in four different stalls according to their treatment. Animals in Treatments T and TB were tethered with a belt around the belly; those in Treatments G and GB remained in groups of five with their original penmates. Tethered gilts were placed side by side in two rows of five, facing in the opposite direction. The gilts were separated by a dung area 0.9 m wide (Figure 1). Net area per animal was, respectively, 2.8 m2 and 1.3 m2 in group and tethered stalls. Fifteen to 19 d after relocation, a mature boar was introduced twice daily from Monday to Friday and once daily on Saturday and Sunday with females in Treatments TB and GB. The boar was placed into the dung area with tethered gilts and in each pen with group-penned gilts, and remained in each stall for 20 mm. Even with tethered gilts, “nose to nose” contacts were possible (Figure 2). No boar was allowed to enter the stalls of females in Treatments T and G.
960
DECEMBER 1969 VOL. 32 NO. 6
THERIOGENOLOGY Au animals were fed with the same diet containing 12.93 IvlJ DE/kg food, 17.3 % protein and 0.83 % lysine. They received 1.75 to 2.7 kg/d between 40 and 100 kg live weight and were restricted at 2.5 kg/d thereafter. Live weight was recorded at allotment, at 14-d intervals throughout the experiment and at slaughter. [n Replicates 1 and 2, samples of urine were collected in the morning on three consecutive days, before and after relocation and after boar introduction (Table 1). The samples were stored at -20°C until assayed for creatinine and estrone.
Dung
area
Tra
Figure 1. Plan of the experimental stalls
Figure 2. Female and boar contact in a tethered stall
DECEMBER 1989 VOL. 32 NO. 6
951
THERIOGENOLOGY
Behavioral recordings were carried out in the second replicate at 6 and 7 mo of age, beginning at 2 min after the boar was introduced into the stall (Treatment TB) or a pen (Treatment GB), and lasted 20 mitt in each treatment. Recordings were repeated on two consecutive days, beginning alternately with each treatment. Social interactions of the male towards the females and vice versa were recorded. Nose-to-head and nose-to-body, ano-genital sniffmg, and mounting attempts were recorded. Reaction of the gilt to male contact was observed and recorded as “negative” when the female tried to knock into or bite the male or to escape from hhn. From 160 d of age, es&us was checked twice daily from Monday to Friday and once daily on Saturday and Sunday. The back pressure test (31) was used either in the presence of the boar (Treatments TB and GB) or not (Treatments T and G). To control age at tirst ovulation, blood samples were collected once a wk and assayed for progesterone. Animals were slaughtered either at 4 wk after ovulation was detected with a concentration of progesterone higher than 5 @ml (=positive blood sample) or at 300 d of age. Five gilts were eliminated before the end of the experiment due to error (one gilt) or to health problems. Ovaries were dissected to determine the number of corpora lutea (CL) and corpora albicans. Adrenal glands were also collected, separated from the fat and weighed. Concentration of creatinine was measured using the Jaffe method (32). Estrone concentration was measured using a radioimmunoassay previously described (30). Plasmas were analyzed in a direct radioimmunoassay to determine whether the concentration was higher than 5 q/ml, as described previously (33). Since we have previously shown (34) that in 20 to 125 kg Large White gilts, the amount of creatinine excreted in urine/24 h (Qc) increased linearly with live weight (W): Qc=O.O%S*W-0.503 (r=0.97, n=30); the amount of estrone excretedD4 h (Qoe) can be estimated atier measurement of the concentrations of estrone (CEl) and creatinine (Ccr): QOE=(CEl/Ccr)*(O.O558W-0.503). For each female with at least two urine samples in the same series, the mean amount of estrone per series was then calculated. Age at puberty was determined according to estrus detection and a progesterone test. It was age at first estrus when these data were in agreement, and age at first positive blood sample minus 6 d (mean duration between estrus and positive sample in females in which first estrus was detected) in females in which estrus was not detected. Gilts which had not ovulated before slaughter at 300 d were nominally ascribed a pubertal age of 301 d. Analysis of variance followed by the Scheffe test was used to establish the effect of treatment and replicate on live weight, ages at relocation, at 100 kg of weight and at slaughter. Analysis of covariance, with live weight or age as covariates, was used for ovulation rate at the second estrous cycle and weight of the adrenal glands. The Mann and Whitney test was used to analyze differences in age at puberty and behavioral data. Effect of treatments on percentage of females with silent estrus was assessed by Chi-square. Correlation between age at 100 kg and age at puberty was calculated with the method of Spearman.
952
DECEMBER 1989 VOL. 32 NO. 6
THERIOGENOLOGY
RESULTS
Age and live weight at relocation as well as age at 100 kg were similar in the four treatments, while signiticant variations were observed between replicates (Table 2). Females were younger and lighter at relocation in the second replicate than in the others, and they were older at 100 kg of weig:ht in the first replicate than in the later ones. Age and live weight at slaughter were higher in the treatments without boar introduction and lower in Replicate 2 than in Replicates 1 and 3. Table 2. Effect of replicates on mean age (d) and live weight (kg) at relocation and at slaughter and, on mean age at 100 kg Replicate
Treatment -
Residual standard deviation
TB
T
GB
G
1
2
3
Age at relocation
142
142
142
142
145 lr
135 v
146 u
56
Weight at relocation
73
73
71
73
73v
6Sw
80”
11
Age at 100 kg
180
186
184
182
189 u
182v
180v
12
Age at slaughter
264 b
282 a
247 c
291a
281 u
263 v
270 uv
21
Weight at slaughter
138 b
145 a
133 b
152 a
148u
134 v
144u
13
28
30
29
28
38
39
38
Number of gilts
al b, c Mean values in the same row with different letters diier between treatments at P
Table 3. Effect of treatment and replicate on mean weight (g) of adrenal glands
TB
T
GB
G
1
2
3
Residual standard deviation
5.3
5.4
4.9
5.2
5.1
5.4
5.1
0.8
Replicate
Treatment
Adrenal weight
Variation in estrone excretion between the period preceding and that following relocation differed between treatments and was positive only in treatment T (Table 4). It was similar in Replicates 1 and 2 and (Table 4). Variation from the period preceding and that following male introduction was not influenced by the treatment or by the replicate.
DEC:EMBER 1989 VOL. 32 NO. 6
953
THERIOGENOLOGY
Table 4. Influence of treatment and replicate on mean variation in 24-hour estrone excretion @g/24 h) between the period preceding and that following relocation and between the period preceding and that following boar introduction Treatment
dQOE due to relocation No of gilts dQOE due to boar No of gilts
TB
T
GB
G
1
2
Residual standard deviation
-1.9 ab
+2.3 a
-2.4 b
-2.6 b
-0.3
-1.1
4.8
Replicate
13
19
18
16
30
36
7.7
+5.3
+7.4
+4.4
+4.9
+I.2
12
19
18
18
33
34
+4.2
apb Mean values in the same row with different letters diier at P~0.05.
The total number of interactions initiated by the male towards the females was not influenced by the type of housing (P>O.l). The number of nose-to-nose and nose-to-body was higher when females were in penned group than when they were tethered, while interactions directed to the ano-genital region were less numerous for penned groups than for tethered gilts (Table 5). However, differences were significant only at 7 mo of age. The number of mounting attempts did not diier between the two types of housing. More than 50% of the interactions performed by the male received a negative response from the females. This proportion was lower in tethered than in group-penned gilts (Table 5). The number of social interactions initiated by the females towards the male was much lower when they were tethered, whatever their age (P~0.05).
Table 5. Influence of the housing system on behavioral interactions between the male and the females. Minimum and maximum values are given in parentheses Tethered gilts
Group penned gilts 6 months of age
Male to female interactions : - Nose-to-head and nose-to-body - Ano-genital region snifftng - Mounting attempts Female to male interactions : - Nose-to-head and nose-to-body - Ano-genital region sniffing - Negative response (%)
12.5 (S-26) 6 (4-12) 1 (O- 5)
15.5 (3-54) 2 (1-18) 2 (O-20)
0.5 (o-12) b 0 (0) 61.5 (46-95)
12 (2-28) a 0.5 (O-12) 83 (50-100) 7 months of age
Male to female interactions : - Nose-to-head and nose-to-body - Ano-genital region sniffing - Mounting attempts Female to male interactions : - Nose-to-head and nose-to-body - Ano-genital region sniffing - Negative response (%)
11.5 (4-19) b 18 (10-24) a 3 (O-14)
19.5 (8-40) a 7 (4-21) b 2 (5-10)
o (o-1) b 0 (0) b 69.5 (25-88) b
11 (O-25) a 4 (1-13) a 86.5 (59-95) a
a, b Median values in the same row with different letters differ at P~0.05.
954
DECEMBER 1969 VOL. 32 NO. 6
THERIOGENOLOGY
Table 6. Influence of the housing system and boar introduction on reproductive performance of the gilt. Minimum and maximum female values are given in parentheses
TB
T
GB
G
Total
Mediig age at puberty id) Replicate 1
294 b,u (228305)
(1!??235)
305 au (305)
291 u
$57305)
Replicate 2
205 bpv (190-305)
(2;4:;5)
217 b (188-246)
246 a,v (226-305)
228”
Replicate 3
229 b,v (188251)
255 a (177-291)
220 b (183-255)
258 a,v (248-282)
246”
233 b
260a
215 c
264a
Total
Mean ovulation rate at the second cycle Total
14.7
Total
26 b
14.8
14.9
Y;,“\ti with silent estr 17
15.5
Residual standard deviation 3.2
59 a
39
al bp c Median values in the same row with diierent letters diier between treatments at PcO.05. ut ” median values in the same column with diierent letters differ between replicates at PcO.05. Significant differences in age at puberty were observed between treatments and replicates (Table 6). Age at puberty was significantly higher in the first than in the two subsequent replicates. In fact, this effect was mainly due to Treatments TB and G. Boar introduction advanced puberty attainment in group-penned gilts whatever the replicate, while it was efficient in two of the three replicates when gilts were tethered. The housing system had a sign&ant influence only in the first replicate: puberty was delayed in tethered compared to group-penned gilts in presence of the boar. Whithin treatment correlations between age at 100 kg and age at puberty were low (r=-0.11 to +0.31, P>O.O5).Age, live weight and treatment had no effect on ovulation rate at the second estrous cycle #(P>O.l; Table 5). The percentage of gilts with silent estrus was lower in treatments with boar introduction, whatever the type of housing (Table 5). DISCUSSION Tethering has been supposed to cause stress that could alter reproductive function (35-40). Experimental results concerning the influence of tethering on adrenal activity are not conclusive. We found no effect on adrenal weight unlike to Jensen et al. (35), who observed hypertrophy of the adrenals in tethered compared with group-penned gilts. Moreover, it has been shown that cortisol concentration is increased only during the first week after tethering ovariectomized gilts (36), while free and total corticosteroids are not altered in long-term tethered cyclic gilts, and these females show few inappropriate stereotyped behaviours such as champing, biting and excessive drinkink (37). However, in pregant sows tethered for several weeks, plasma-free corticosteroid level is increased in comparison with group-penned sows (38) and the number of stereotyped behaviours is also higher (39). Concerning reproductive function, it has been shown that tethered pregnant sows have normal littersize (35,40), but a longer farrowing duration (39). We observed a delayed puberty
DECEiMBER 1989 VOL. 32 NO. 6
955
THERIOGENOLOGY
in gilts submitted to boar intluence, as reported in a previous study (35). However, in this latter experiment as in our, the effect of tethering on sexual development varied between replicates, suggesting that other environmental parameters interact with this factor. Filly, in gilts isolated from the male, our experiment demonstrates that type of housing has no influence on age at puberty probably because puberty attainment could not be delayed any further. The results of our study conftrm the importance of boar exposure for the stimulation of puberty in the gilt Moreover, this effect interacts with other experimental factors such as type of housing. When gilts are penned in groups, boar introduction always reduces age at puberty, while when gilts are tethered, the boar effect is variable. Thus, we can suppose that when gilts are tethered, contacts with the boar are not sufficient to overcome the negative effect of other environmental factors. This could reflect a lesser influence of the male under this condition, since it has been shown that full physical contact by the male with the gilts gave better results for puberty attainment than limited contact (13, 17). In our experiment, the number of mounting attempts and total number of interactions performed by the male were similar in the two types of housing, but they were not directed to the same body part of the female. Moreover, the number of interactions initiated by the gilts towards the male are decreased appreciably when they were tethered. Finally, fewer male interactions induced a negative response in the tethered females, probably in relation to the restriction of movement and the impossibility of escaping from the male. Inadequate stimulation provided by the male and/or the altered behavioral response of the females could explain the lower efficacy of the boar in stimulating the occurrence of puberty in tethered condition. That the male touched and sniffed the ano-genital part of tethered gilts rather than their heads and bodies was to be expected since the male could hardly reach the front portions of tethered female bodies. The low number of interactions performed by tethered gilts towards the boar was also not surprising since tethering reduced movement. However, what was unexpected was that we observed that more than half of the contacts initiated by the male induced a reaction of defence or avoidance whatever the type of housing. Despite these negative behavioral reactions of the gilts, the boar was effective in stimulating puberty attainment. The importance of this female behavior in the efficacy of the boar effect needs to be evaluated Variation in estrone excretion due to the relocation of 140-d gilts was low, and did not seem to be influenced by the type of housing. Between 140 and 175 d of age, estrone excretion increased, as in previous data (30, 41), but this variation was not affected by boar introduction and type of housing. Thus, estrone excretion can not be recommanded for evaluating boar efficacy or the deleterious effect of an environmental factor. Variation in age at puberty between replicates within the two treatments reflects the influence of environmental factors other than type of housing and boar introduction. Duration of daylenght was not involved, since all gilts were lighted 16/24 h from three mo of age until the end of the experiment. An effect of season of birth was also not a convincing factor: puberty was delayed in our autumn born gilts, while in previous experiments the opposite (3, 20) or no effect (42,43) was shown. Difference in growth rate was probably not involved, even though gilts in the replicate with the slowest puberty attainment were older at 100 kg than their counterparts. However, the correlation between ages at 100 kg and at puberty was very low. Other factors might be involved. Ovulation rate was not influenced by the type of housing and boar introduction, as in previous experiments (7-11, 16, 17, 27,32). Efficacy of estrus detection in the presence of the male was close to 80 % as in other experiments (19, 28); however, contrary to them, we found a decrease of efficacy in the absence of the boar. This discrepancy could be due to the fact that these authors inspected the vulva in addition to performing the back pressure test. Moreover, it has been shown that only 48 % of the cyclic gilts having a lordosis reaction to the male still show it in the absence of the male (31). The type of housing had no influence on efficacy of estrus detection as shown by previous data (35,37). In conclusion, our experiment shows that the effect of boar introduction is more important for puberty attainment of the gilt than the type of housing used. However, there is an interaction between these two factors. In tethered gilts there is a risk that boar introduction may become
DECEMBER 1989 VOL. 32 NO. 6
THERIOGENOLOGY
ineffective when other negative factors are present. Inadequate boar stimulation and/or altered behavioral response of tethered gilts could explain this phenomenon. Additional environmental facta’rs influencing sexual development of the gilts remain to be identified. REFERENCES 1. Brooks, P.H. and Cole, DJ.A. The effect of the presence of a boar on the attainment of puberty in gilts. J. Reprod. Fertil., 23:435-440 (1970). 2. Hughes, P.E. and Cole, DJ.A. Reproduction in the gilt. 3. The influence of gilt age at boar introduction on the attainment of puberty. Anim. Prod. 2:89-94 (1976). 3. Mavrogenis, A.P. and Robison, O.W. Factors affecting puberty in swine. J. Anim. Sci 9:12511255 (1976). 4. Hughes, P.E. and Cole, DJ.A. Reproduction in the gilt 3. The effect of exogenous oestrogen on the attainment of puberty and subsequent reproductive performance. Anim. Prod. z:ll-20 (1978). 5. Thompson, LH. and Savage, J.S. Age at puberty and ovulation rate in gilts in confinement as influenced by exposure to boar. J. Anim. Sci. 47:1141-1144 (1978). 6. Kirkwood. R.N. and Hushes. P.E. The influence of age at first boar contact on 1 ~ubertv , attainment ‘inthe gilt. An& Prod. 2:231-238 (1979). 0 7. Kirkwood, R.N. and Hughes, P.E. A note on the efficacy of continuous versus limited boar exposure on puberty attainment in the gilt. Anim. Prod. 2:205-207 (1980). 8. Kirkwood, R.N. and Hughes, P.E. A note on the influence of “boar effect “component stimuli” on puberty attainment in the gilt Anim. Prod. 31:209-211 (1980). 9. Paterson, A.M. and Lindsay, D.R. Induction of puberty. 1. The effects of rearing conditions on reproductive performance and response to mature boars after early puberty. Anim. Prod. 3_1:291-297 (1980). 10. Kirkwood, R.N. and Hughes, P.E. A note on the influence of boar age on its ability to advance puberty in the gilt. Anim. Prod. 32:211213 (1981). 11. Kirkwood, 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. J Reprod. Fertil. 6&193-l% (1981). 12. Hemsworth, P.H., Cronin, G.M. and Hansen, C. The influence of social restriction during rearing on the sexual behavior of the gilt. Anim. Prod. 35:35-40 (1982). 13. Karlbom, I. Attainment of puberty in females pigs: influence of boar stimulation. Anim. Reprod. Sci. $313-319 (1982). 14. Cronin, G.M. The effect of early contact with mature boars on reproductive efficiency in the gilt. Anim. Reprod. Sci. 6:51-57 (1983). 15. Kirkwood, R.N. and Hughes, P.E. The influence of boar-related odours on puberty attaiment in gilts. Anim. Prod. 3@131-136 (1983). 16. Booth, W.D. A note on the significance of boar salivary pheromones to the male-effect on puberty attainment in gilts. Anim. Prod. 39:149 152 (1984).
DECEMBER
1989 VOL.
32 NO. 6
THERIOGENOLOGY
17. Deligeorgis, S.G., Lunney, D.C. and English, P.R. A note on the efficacy of complete versus partial boar exposure on puberty attainment in the gilt Anim. Prod. 39:145-147 (1984). 18. Eastham, P.R, Dick, G.W. and Cole, DJA. Reproduction in the gilt. 5. The effect of the presence of the mature male during rearing on puberty attainment. Anim. Prod. 2:277-282 (1984). 19. Walton, J.S. A note on the effect of exposure to a boar on the development of the reproductive system of immature gilts. Anim. Prod. 39483-486 (1984). 20. Pearce, G.P. and Hughes, P.E. The influence of daily movement of gilts and the environment in which boar exposure occurs on the efficacy of boar-related precocious puberty in the gilt. Anim. Prod. 4j:161-167 (1985). 21. Walton, J.S. A note on the effect of exposing gilts to a mature boar at 140 d of age. Anim. Prod. +123-126 (1985). 22. Walton, J.S. A note on the effect on puberty in gilts of exposure to a boar between 140 and 160 d of age. Anim. Prod. %:127-129 (1985). 23. Eastham, P.R, Dick, G.W. and Cole, DJ.A. Reproduction in the gilt. 6. The effect of various degrees of mature boar contact during rearing on puberty attainment. Anii. Prod. 4&343-349 (1986). 24. Eastham, P.R., Dick, G.W. and Cole, DJ.A. The effect of age at stimulation by relocation and first mature boar contact on the attainment of puberty in the gilt. Anim. Reprod. Sci. g:31-38 (1986). 25. Booth, W.D. A note on the influence of a Gottingen miniature boar on puberty attainment in Large White gilts. Anim. Prod. fi:165-168 (1987). 26. Pearce, G.P. and Hughes, P.E. The intluence of boa-component in the gilt. Anim. Prod. *:293-402 (1987).
stimuli on puberty attainment
27. Van Lunen, T.A. and Aherne, F.X. Intluence of method of boar exposure on age at puberty of gilts. Can. J. Anim. Sci. g:553-556 (1987). 28. Christenson, RK. and Ford, JJ. Puberty and estrus in confiment reared gilts. J. Anim. Sci. 49:743-751 (1979). 29. Legault, C. Determinisme genetique de la pr&ocitC sexuelle, du taux d’ovulation, et du nombre d’embryons chez la truie primipare: heritabiiite, effet d’heterosis. Journees Rech. Porcine en France 2:147-153 (1973). 30. Camous, S., Prunier, A. and Pelletier, J. Plasma prolactin, LH, FSH and estrogen excretion pattern in gilts during sexual development. J. Anim. Sci., g:1308-1317 (1985). 31.
Signoret, J.P. Contribution a I’etude des mecanismes ethologiques et endocriniens comportement sexuel de la truie (Sus scrofa L.). These d’Etat. Universite Paris VI, 1972.
du
32. Hodgen, G.D., Erb, R.E. and Plotka, E.D. Estimating creatinine excretion in sheep. J. Anim. Sci. 26:58f+589 (1%7) 33. Terqui, M. and Thimonier, J. Nouvelle methode radioimmunologique rapide pour l’estimation du niveau de progesterone plasmatique. Application pou le diagnostic pr&zoce de gestation. C. R. Acad. Sci. Paris, -279:11091112 (1974).
966
DECEMBER 1989 VOL. 32 NO. 6
THERIOGENOLOGY
34. Prunier, A. Mise en place de la fonction de reproduction chez la truie: Evolution des s&r&ions hypophysaires et ovariennes. These Yme cycle. Universite Paris VI, 1984. 35. Jensen, AH., Yen, J.T., Gehriig, M.M., Baker, D.H., Becker, D.E. and Harmon, B.G. Effects of space restriction and management on pre and postpuberal response of female swine. J. Anim. Sci. 31:745-750 (1970). 36. Becker, B.A., Ford, JJ., Christenson, R.K., Manak, RC., Hahn, G.L. and DeShazer, J.A. Cortisol response of gilts in tether stalls. J. Anim. Sci. g:264- 270 (1985). 37. Elarnett, J.L., Cronin, G.M., Wield, C.G. and Dewar, AM. The welfare of adult pigs: the effects of five housing treatments on bchaviour, plasma corticosteroids and injuries. Appl. Anim. Behav. Sci. g:209232 (1984). 38. Elarnett, J.L., Winfield, C.G., Cronin, G.M., Hemsworth, P.H. and Dewar, A.M. The effect of individual and group housing on behavioral and physiological responses related to the welfare of pregnant pigs. Appl. Anim. Behav. Sci. 14:149-161 (1985). 39. Hansen, LL. and Vestergaard, K. Tethered versus loose sows: ethological observations and measures of sow productivity. II. Production results. Ann. Rech. Vet. Q:185-191 (1984). 40. Vestergaard, K. and Hansen, L.L. Tethered versus loose sows: ethological observations and measures of sow productivity. I. Ethological observations during pregnancy and farrowing. ,4nn. Rech. Vet. @245-256. (1984). 41.
Schlenker, G., Koppe, D. and Siefert, H. Die pdpuberale und praovulatorische Gstrogenausscheidung in Beziehung zur Fortpflanzungsregulation weiblicher Scheme. Arch. Exp. Vet. Med. 27 H6:881-889 (1973).
42. Sorensen, A.M., Thomas, W.B. and Gossett, J.W. A further study of the influence of level of energy intake and season on reproductive performance of gilts. J. Anim. Sci. g:347-349 l(l%l). 43.
Prunier, A., Bonneau, M. and Etienne, M. Effects of Jive weight and age on the sexual development of gilts and boars fed two planes of nutrition. Reprod. Nutr. Develop. 21689-700 1:1987).
DECEMBER 1989 VOL. 32 NO. 6
969
THE INFLUENCE OF BOAR STIMULATION ON PUBERTY ATTAINMENT IN TETHERED AND GROUP PENNED GILTS A. Prunier and M.C. Meunier-Salatin Station de Recherches Porcines, I.N.R.A. Saint Giies, 35590 L’Hermitage, France Received for publication: February 22, 1989 Accepted: October 14, 1989
ABSTRACT The objective of this experiment was to determine the influence of boar exposure on sexual development of tethered and group penned gilts. At 140 d of age, a total of 120 Large White gilts were moved into four stalls, each for one treatment, during three successive replicates. Gilts in treatments TB and T were tethered, and those in treatments GB and G were penned in groups of five animals. Two weeks later, females in treatments TB and GB were exposed to a mature boar for 20 min twice daily, while those in treatments T and G remained isolated from the male. From that age, all gilts were checked daily for estrus with the back pressure test and controlled weekly for ovulation by measuring progesterone concentration in plasma. Recording of social interactions between the male and the females was carried out in the second replicate at 6 and 7 mo of age. Estrone excretion was estimated just before and after relocation and 4 wk after boar introduction in the first and second replicates. Boar exposure advanced puberty attainment of gilts whatever the type of housing (median age at puberty = 233, 260, 215, 264 in treatments TB, T, GB and G, respectively, P
INTRODUCTION Since the work of Brooks and Cole in 1970 (1) which showed that the introduction of a mature boar to prepubertal gilts advances the onset of puberty, many authors have studied this effect (2 to 27). However, in all except three studies (16, 19, 25), authors used crossbred females which are known to attain puberty earlier than purebred gilts (28,29) and therefore could be more sensitive to the “boar effect”. Moreover, the influence of the female housing system on the efficacy of the male to induce puberty has been poorly studied. Acknowledgments The authors are thankful to A.M. Mounier, F. Giovanni, J. Lebost, J.C. Hulii and M. Massard (I.N.R.A. Saint Gilles) for their skillful1technical assistance.
DECEMBER 19B9VOL. 32 NO. 6
949
THERIOGENOLOGY
Thus, the main purpose of this study was to evaluate the influence of the boar introduction on puberty attainment in tethered and group penned gilts from Large White breed. Since urinary estrone excretion has been shown to increase during sexual development of the gilt (30), influence of treatment on this parameter was researched. In order to investigate any possible difference in the level of tactile stimulation provided by the two housing systems, behavioral observations of the interactions between the male and the females were carried out.
MATERIALS AND METHODS Around 100 d of age, 120 Large White gilts from 42 litters were randomly assigned within litter by weight to one of four treatments of 10 animals in three replicates (Table 1). From that age until the end of the experiment, artificial light was provided for 16 h per day. Until relocation, all females of one replicate were gathered in a single stall where no boar was allowed to enter. They were penned in groups of five according to treatment.
Table 1. Birth date, mean age at relocation, urine collections, first blood sampling and boar introduction in the different replicates
Birth date
Replicate 1
Replicate 2
Replicate 3
10/l-28/85
5/286/11/86
3/22-4/S/87
Age at allotment
94
112
95
Age at first urine collection
143
133
Age at relocation
145
135
Age at second urine collection
150
140
Age at boar introduction (TB and BG)
163
153
161
Age at first blood sampling
167
157
164
Age at third urine collection
178
168
146
Around 140 d of age and 72 kg live weight, gilts were moved into the same building in four different stalls according to their treatment. Animals in Treatments T and TB were tethered with a belt around the belly; those in Treatments G and GB remained in groups of five with their original penmates. Tethered gilts were placed side by side in two rows of five, facing in the opposite direction. The gilts were separated by a dung area 0.9 m wide (Figure 1). Net area per animal was, respectively, 2.8 m2 and 1.3 m2 in group and tethered stalls. Fifteen to 19 d after relocation, a mature boar was introduced twice daily from Monday to Friday and once daily on Saturday and Sunday with females in Treatments TB and GB. The boar was placed into the dung area with tethered gilts and in each pen with group-penned gilts, and remained in each stall for 20 mm. Even with tethered gilts, “nose to nose” contacts were possible (Figure 2). No boar was allowed to enter the stalls of females in Treatments T and G.
960
DECEMBER 1969 VOL. 32 NO. 6
THERIOGENOLOGY Au animals were fed with the same diet containing 12.93 IvlJ DE/kg food, 17.3 % protein and 0.83 % lysine. They received 1.75 to 2.7 kg/d between 40 and 100 kg live weight and were restricted at 2.5 kg/d thereafter. Live weight was recorded at allotment, at 14-d intervals throughout the experiment and at slaughter. [n Replicates 1 and 2, samples of urine were collected in the morning on three consecutive days, before and after relocation and after boar introduction (Table 1). The samples were stored at -20°C until assayed for creatinine and estrone.
Dung
area
Tra
Figure 1. Plan of the experimental stalls
Figure 2. Female and boar contact in a tethered stall
DECEMBER 1989 VOL. 32 NO. 6
951
THERIOGENOLOGY
Behavioral recordings were carried out in the second replicate at 6 and 7 mo of age, beginning at 2 min after the boar was introduced into the stall (Treatment TB) or a pen (Treatment GB), and lasted 20 mitt in each treatment. Recordings were repeated on two consecutive days, beginning alternately with each treatment. Social interactions of the male towards the females and vice versa were recorded. Nose-to-head and nose-to-body, ano-genital sniffmg, and mounting attempts were recorded. Reaction of the gilt to male contact was observed and recorded as “negative” when the female tried to knock into or bite the male or to escape from hhn. From 160 d of age, es&us was checked twice daily from Monday to Friday and once daily on Saturday and Sunday. The back pressure test (31) was used either in the presence of the boar (Treatments TB and GB) or not (Treatments T and G). To control age at tirst ovulation, blood samples were collected once a wk and assayed for progesterone. Animals were slaughtered either at 4 wk after ovulation was detected with a concentration of progesterone higher than 5 @ml (=positive blood sample) or at 300 d of age. Five gilts were eliminated before the end of the experiment due to error (one gilt) or to health problems. Ovaries were dissected to determine the number of corpora lutea (CL) and corpora albicans. Adrenal glands were also collected, separated from the fat and weighed. Concentration of creatinine was measured using the Jaffe method (32). Estrone concentration was measured using a radioimmunoassay previously described (30). Plasmas were analyzed in a direct radioimmunoassay to determine whether the concentration was higher than 5 q/ml, as described previously (33). Since we have previously shown (34) that in 20 to 125 kg Large White gilts, the amount of creatinine excreted in urine/24 h (Qc) increased linearly with live weight (W): Qc=O.O%S*W-0.503 (r=0.97, n=30); the amount of estrone excretedD4 h (Qoe) can be estimated atier measurement of the concentrations of estrone (CEl) and creatinine (Ccr): QOE=(CEl/Ccr)*(O.O558W-0.503). For each female with at least two urine samples in the same series, the mean amount of estrone per series was then calculated. Age at puberty was determined according to estrus detection and a progesterone test. It was age at first estrus when these data were in agreement, and age at first positive blood sample minus 6 d (mean duration between estrus and positive sample in females in which first estrus was detected) in females in which estrus was not detected. Gilts which had not ovulated before slaughter at 300 d were nominally ascribed a pubertal age of 301 d. Analysis of variance followed by the Scheffe test was used to establish the effect of treatment and replicate on live weight, ages at relocation, at 100 kg of weight and at slaughter. Analysis of covariance, with live weight or age as covariates, was used for ovulation rate at the second estrous cycle and weight of the adrenal glands. The Mann and Whitney test was used to analyze differences in age at puberty and behavioral data. Effect of treatments on percentage of females with silent estrus was assessed by Chi-square. Correlation between age at 100 kg and age at puberty was calculated with the method of Spearman.
952
DECEMBER 1989 VOL. 32 NO. 6
THERIOGENOLOGY
RESULTS
Age and live weight at relocation as well as age at 100 kg were similar in the four treatments, while signiticant variations were observed between replicates (Table 2). Females were younger and lighter at relocation in the second replicate than in the others, and they were older at 100 kg of weig:ht in the first replicate than in the later ones. Age and live weight at slaughter were higher in the treatments without boar introduction and lower in Replicate 2 than in Replicates 1 and 3. Table 2. Effect of replicates on mean age (d) and live weight (kg) at relocation and at slaughter and, on mean age at 100 kg Replicate
Treatment -
Residual standard deviation
TB
T
GB
G
1
2
3
Age at relocation
142
142
142
142
145 lr
135 v
146 u
56
Weight at relocation
73
73
71
73
73v
6Sw
80”
11
Age at 100 kg
180
186
184
182
189 u
182v
180v
12
Age at slaughter
264 b
282 a
247 c
291a
281 u
263 v
270 uv
21
Weight at slaughter
138 b
145 a
133 b
152 a
148u
134 v
144u
13
28
30
29
28
38
39
38
Number of gilts
al b, c Mean values in the same row with different letters diier between treatments at P
Table 3. Effect of treatment and replicate on mean weight (g) of adrenal glands
TB
T
GB
G
1
2
3
Residual standard deviation
5.3
5.4
4.9
5.2
5.1
5.4
5.1
0.8
Replicate
Treatment
Adrenal weight
Variation in estrone excretion between the period preceding and that following relocation differed between treatments and was positive only in treatment T (Table 4). It was similar in Replicates 1 and 2 and (Table 4). Variation from the period preceding and that following male introduction was not influenced by the treatment or by the replicate.
DEC:EMBER 1989 VOL. 32 NO. 6
953
THERIOGENOLOGY
Table 4. Influence of treatment and replicate on mean variation in 24-hour estrone excretion @g/24 h) between the period preceding and that following relocation and between the period preceding and that following boar introduction Treatment
dQOE due to relocation No of gilts dQOE due to boar No of gilts
TB
T
GB
G
1
2
Residual standard deviation
-1.9 ab
+2.3 a
-2.4 b
-2.6 b
-0.3
-1.1
4.8
Replicate
13
19
18
16
30
36
7.7
+5.3
+7.4
+4.4
+4.9
+I.2
12
19
18
18
33
34
+4.2
apb Mean values in the same row with different letters diier at P~0.05.
The total number of interactions initiated by the male towards the females was not influenced by the type of housing (P>O.l). The number of nose-to-nose and nose-to-body was higher when females were in penned group than when they were tethered, while interactions directed to the ano-genital region were less numerous for penned groups than for tethered gilts (Table 5). However, differences were significant only at 7 mo of age. The number of mounting attempts did not diier between the two types of housing. More than 50% of the interactions performed by the male received a negative response from the females. This proportion was lower in tethered than in group-penned gilts (Table 5). The number of social interactions initiated by the females towards the male was much lower when they were tethered, whatever their age (P~0.05).
Table 5. Influence of the housing system on behavioral interactions between the male and the females. Minimum and maximum values are given in parentheses Tethered gilts
Group penned gilts 6 months of age
Male to female interactions : - Nose-to-head and nose-to-body - Ano-genital region snifftng - Mounting attempts Female to male interactions : - Nose-to-head and nose-to-body - Ano-genital region sniffing - Negative response (%)
12.5 (S-26) 6 (4-12) 1 (O- 5)
15.5 (3-54) 2 (1-18) 2 (O-20)
0.5 (o-12) b 0 (0) 61.5 (46-95)
12 (2-28) a 0.5 (O-12) 83 (50-100) 7 months of age
Male to female interactions : - Nose-to-head and nose-to-body - Ano-genital region sniffing - Mounting attempts Female to male interactions : - Nose-to-head and nose-to-body - Ano-genital region sniffing - Negative response (%)
11.5 (4-19) b 18 (10-24) a 3 (O-14)
19.5 (8-40) a 7 (4-21) b 2 (5-10)
o (o-1) b 0 (0) b 69.5 (25-88) b
11 (O-25) a 4 (1-13) a 86.5 (59-95) a
a, b Median values in the same row with different letters differ at P~0.05.
954
DECEMBER 1969 VOL. 32 NO. 6
THERIOGENOLOGY
Table 6. Influence of the housing system and boar introduction on reproductive performance of the gilt. Minimum and maximum female values are given in parentheses
TB
T
GB
G
Total
Mediig age at puberty id) Replicate 1
294 b,u (228305)
(1!??235)
305 au (305)
291 u
$57305)
Replicate 2
205 bpv (190-305)
(2;4:;5)
217 b (188-246)
246 a,v (226-305)
228”
Replicate 3
229 b,v (188251)
255 a (177-291)
220 b (183-255)
258 a,v (248-282)
246”
233 b
260a
215 c
264a
Total
Mean ovulation rate at the second cycle Total
14.7
Total
26 b
14.8
14.9
Y;,“\ti with silent estr 17
15.5
Residual standard deviation 3.2
59 a
39
al bp c Median values in the same row with diierent letters diier between treatments at PcO.05. ut ” median values in the same column with diierent letters differ between replicates at PcO.05. Significant differences in age at puberty were observed between treatments and replicates (Table 6). Age at puberty was significantly higher in the first than in the two subsequent replicates. In fact, this effect was mainly due to Treatments TB and G. Boar introduction advanced puberty attainment in group-penned gilts whatever the replicate, while it was efficient in two of the three replicates when gilts were tethered. The housing system had a sign&ant influence only in the first replicate: puberty was delayed in tethered compared to group-penned gilts in presence of the boar. Whithin treatment correlations between age at 100 kg and age at puberty were low (r=-0.11 to +0.31, P>O.O5).Age, live weight and treatment had no effect on ovulation rate at the second estrous cycle #(P>O.l; Table 5). The percentage of gilts with silent estrus was lower in treatments with boar introduction, whatever the type of housing (Table 5). DISCUSSION Tethering has been supposed to cause stress that could alter reproductive function (35-40). Experimental results concerning the influence of tethering on adrenal activity are not conclusive. We found no effect on adrenal weight unlike to Jensen et al. (35), who observed hypertrophy of the adrenals in tethered compared with group-penned gilts. Moreover, it has been shown that cortisol concentration is increased only during the first week after tethering ovariectomized gilts (36), while free and total corticosteroids are not altered in long-term tethered cyclic gilts, and these females show few inappropriate stereotyped behaviours such as champing, biting and excessive drinkink (37). However, in pregant sows tethered for several weeks, plasma-free corticosteroid level is increased in comparison with group-penned sows (38) and the number of stereotyped behaviours is also higher (39). Concerning reproductive function, it has been shown that tethered pregnant sows have normal littersize (35,40), but a longer farrowing duration (39). We observed a delayed puberty
DECEiMBER 1989 VOL. 32 NO. 6
955
THERIOGENOLOGY
in gilts submitted to boar intluence, as reported in a previous study (35). However, in this latter experiment as in our, the effect of tethering on sexual development varied between replicates, suggesting that other environmental parameters interact with this factor. Filly, in gilts isolated from the male, our experiment demonstrates that type of housing has no influence on age at puberty probably because puberty attainment could not be delayed any further. The results of our study conftrm the importance of boar exposure for the stimulation of puberty in the gilt Moreover, this effect interacts with other experimental factors such as type of housing. When gilts are penned in groups, boar introduction always reduces age at puberty, while when gilts are tethered, the boar effect is variable. Thus, we can suppose that when gilts are tethered, contacts with the boar are not sufficient to overcome the negative effect of other environmental factors. This could reflect a lesser influence of the male under this condition, since it has been shown that full physical contact by the male with the gilts gave better results for puberty attainment than limited contact (13, 17). In our experiment, the number of mounting attempts and total number of interactions performed by the male were similar in the two types of housing, but they were not directed to the same body part of the female. Moreover, the number of interactions initiated by the gilts towards the male are decreased appreciably when they were tethered. Finally, fewer male interactions induced a negative response in the tethered females, probably in relation to the restriction of movement and the impossibility of escaping from the male. Inadequate stimulation provided by the male and/or the altered behavioral response of the females could explain the lower efficacy of the boar in stimulating the occurrence of puberty in tethered condition. That the male touched and sniffed the ano-genital part of tethered gilts rather than their heads and bodies was to be expected since the male could hardly reach the front portions of tethered female bodies. The low number of interactions performed by tethered gilts towards the boar was also not surprising since tethering reduced movement. However, what was unexpected was that we observed that more than half of the contacts initiated by the male induced a reaction of defence or avoidance whatever the type of housing. Despite these negative behavioral reactions of the gilts, the boar was effective in stimulating puberty attainment. The importance of this female behavior in the efficacy of the boar effect needs to be evaluated Variation in estrone excretion due to the relocation of 140-d gilts was low, and did not seem to be influenced by the type of housing. Between 140 and 175 d of age, estrone excretion increased, as in previous data (30, 41), but this variation was not affected by boar introduction and type of housing. Thus, estrone excretion can not be recommanded for evaluating boar efficacy or the deleterious effect of an environmental factor. Variation in age at puberty between replicates within the two treatments reflects the influence of environmental factors other than type of housing and boar introduction. Duration of daylenght was not involved, since all gilts were lighted 16/24 h from three mo of age until the end of the experiment. An effect of season of birth was also not a convincing factor: puberty was delayed in our autumn born gilts, while in previous experiments the opposite (3, 20) or no effect (42,43) was shown. Difference in growth rate was probably not involved, even though gilts in the replicate with the slowest puberty attainment were older at 100 kg than their counterparts. However, the correlation between ages at 100 kg and at puberty was very low. Other factors might be involved. Ovulation rate was not influenced by the type of housing and boar introduction, as in previous experiments (7-11, 16, 17, 27,32). Efficacy of estrus detection in the presence of the male was close to 80 % as in other experiments (19, 28); however, contrary to them, we found a decrease of efficacy in the absence of the boar. This discrepancy could be due to the fact that these authors inspected the vulva in addition to performing the back pressure test. Moreover, it has been shown that only 48 % of the cyclic gilts having a lordosis reaction to the male still show it in the absence of the male (31). The type of housing had no influence on efficacy of estrus detection as shown by previous data (35,37). In conclusion, our experiment shows that the effect of boar introduction is more important for puberty attainment of the gilt than the type of housing used. However, there is an interaction between these two factors. In tethered gilts there is a risk that boar introduction may become
DECEMBER 1989 VOL. 32 NO. 6
THERIOGENOLOGY
ineffective when other negative factors are present. Inadequate boar stimulation and/or altered behavioral response of tethered gilts could explain this phenomenon. Additional environmental facta’rs influencing sexual development of the gilts remain to be identified. REFERENCES 1. Brooks, P.H. and Cole, DJ.A. The effect of the presence of a boar on the attainment of puberty in gilts. J. Reprod. Fertil., 23:435-440 (1970). 2. Hughes, P.E. and Cole, DJ.A. Reproduction in the gilt. 3. The influence of gilt age at boar introduction on the attainment of puberty. Anim. Prod. 2:89-94 (1976). 3. Mavrogenis, A.P. and Robison, O.W. Factors affecting puberty in swine. J. Anim. Sci 9:12511255 (1976). 4. Hughes, P.E. and Cole, DJ.A. Reproduction in the gilt 3. The effect of exogenous oestrogen on the attainment of puberty and subsequent reproductive performance. Anim. Prod. z:ll-20 (1978). 5. Thompson, LH. and Savage, J.S. Age at puberty and ovulation rate in gilts in confinement as influenced by exposure to boar. J. Anim. Sci. 47:1141-1144 (1978). 6. Kirkwood. R.N. and Hushes. P.E. The influence of age at first boar contact on 1 ~ubertv , attainment ‘inthe gilt. An& Prod. 2:231-238 (1979). 0 7. Kirkwood, R.N. and Hughes, P.E. A note on the efficacy of continuous versus limited boar exposure on puberty attainment in the gilt. Anim. Prod. 2:205-207 (1980). 8. Kirkwood, R.N. and Hughes, P.E. A note on the influence of “boar effect “component stimuli” on puberty attainment in the gilt Anim. Prod. 31:209-211 (1980). 9. Paterson, A.M. and Lindsay, D.R. Induction of puberty. 1. The effects of rearing conditions on reproductive performance and response to mature boars after early puberty. Anim. Prod. 3_1:291-297 (1980). 10. Kirkwood, R.N. and Hughes, P.E. A note on the influence of boar age on its ability to advance puberty in the gilt. Anim. Prod. 32:211213 (1981). 11. Kirkwood, 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. J Reprod. Fertil. 6&193-l% (1981). 12. Hemsworth, P.H., Cronin, G.M. and Hansen, C. The influence of social restriction during rearing on the sexual behavior of the gilt. Anim. Prod. 35:35-40 (1982). 13. Karlbom, I. Attainment of puberty in females pigs: influence of boar stimulation. Anim. Reprod. Sci. $313-319 (1982). 14. Cronin, G.M. The effect of early contact with mature boars on reproductive efficiency in the gilt. Anim. Reprod. Sci. 6:51-57 (1983). 15. Kirkwood, R.N. and Hughes, P.E. The influence of boar-related odours on puberty attaiment in gilts. Anim. Prod. 3@131-136 (1983). 16. Booth, W.D. A note on the significance of boar salivary pheromones to the male-effect on puberty attainment in gilts. Anim. Prod. 39:149 152 (1984).
DECEMBER
1989 VOL.
32 NO. 6
THERIOGENOLOGY
17. Deligeorgis, S.G., Lunney, D.C. and English, P.R. A note on the efficacy of complete versus partial boar exposure on puberty attainment in the gilt Anim. Prod. 39:145-147 (1984). 18. Eastham, P.R, Dick, G.W. and Cole, DJA. Reproduction in the gilt. 5. The effect of the presence of the mature male during rearing on puberty attainment. Anim. Prod. 2:277-282 (1984). 19. Walton, J.S. A note on the effect of exposure to a boar on the development of the reproductive system of immature gilts. Anim. Prod. 39483-486 (1984). 20. Pearce, G.P. and Hughes, P.E. The influence of daily movement of gilts and the environment in which boar exposure occurs on the efficacy of boar-related precocious puberty in the gilt. Anim. Prod. 4j:161-167 (1985). 21. Walton, J.S. A note on the effect of exposing gilts to a mature boar at 140 d of age. Anim. Prod. +123-126 (1985). 22. Walton, J.S. A note on the effect on puberty in gilts of exposure to a boar between 140 and 160 d of age. Anim. Prod. %:127-129 (1985). 23. Eastham, P.R, Dick, G.W. and Cole, DJ.A. Reproduction in the gilt. 6. The effect of various degrees of mature boar contact during rearing on puberty attainment. Anii. Prod. 4&343-349 (1986). 24. Eastham, P.R., Dick, G.W. and Cole, DJ.A. The effect of age at stimulation by relocation and first mature boar contact on the attainment of puberty in the gilt. Anim. Reprod. Sci. g:31-38 (1986). 25. Booth, W.D. A note on the influence of a Gottingen miniature boar on puberty attainment in Large White gilts. Anim. Prod. fi:165-168 (1987). 26. Pearce, G.P. and Hughes, P.E. The intluence of boa-component in the gilt. Anim. Prod. *:293-402 (1987).
stimuli on puberty attainment
27. Van Lunen, T.A. and Aherne, F.X. Intluence of method of boar exposure on age at puberty of gilts. Can. J. Anim. Sci. g:553-556 (1987). 28. Christenson, RK. and Ford, JJ. Puberty and estrus in confiment reared gilts. J. Anim. Sci. 49:743-751 (1979). 29. Legault, C. Determinisme genetique de la pr&ocitC sexuelle, du taux d’ovulation, et du nombre d’embryons chez la truie primipare: heritabiiite, effet d’heterosis. Journees Rech. Porcine en France 2:147-153 (1973). 30. Camous, S., Prunier, A. and Pelletier, J. Plasma prolactin, LH, FSH and estrogen excretion pattern in gilts during sexual development. J. Anim. Sci., g:1308-1317 (1985). 31.
Signoret, J.P. Contribution a I’etude des mecanismes ethologiques et endocriniens comportement sexuel de la truie (Sus scrofa L.). These d’Etat. Universite Paris VI, 1972.
du
32. Hodgen, G.D., Erb, R.E. and Plotka, E.D. Estimating creatinine excretion in sheep. J. Anim. Sci. 26:58f+589 (1%7) 33. Terqui, M. and Thimonier, J. Nouvelle methode radioimmunologique rapide pour l’estimation du niveau de progesterone plasmatique. Application pou le diagnostic pr&zoce de gestation. C. R. Acad. Sci. Paris, -279:11091112 (1974).
966
DECEMBER 1989 VOL. 32 NO. 6
THERIOGENOLOGY
34. Prunier, A. Mise en place de la fonction de reproduction chez la truie: Evolution des s&r&ions hypophysaires et ovariennes. These Yme cycle. Universite Paris VI, 1984. 35. Jensen, AH., Yen, J.T., Gehriig, M.M., Baker, D.H., Becker, D.E. and Harmon, B.G. Effects of space restriction and management on pre and postpuberal response of female swine. J. Anim. Sci. 31:745-750 (1970). 36. Becker, B.A., Ford, JJ., Christenson, R.K., Manak, RC., Hahn, G.L. and DeShazer, J.A. Cortisol response of gilts in tether stalls. J. Anim. Sci. g:264- 270 (1985). 37. Elarnett, J.L., Cronin, G.M., Wield, C.G. and Dewar, AM. The welfare of adult pigs: the effects of five housing treatments on bchaviour, plasma corticosteroids and injuries. Appl. Anim. Behav. Sci. g:209232 (1984). 38. Elarnett, J.L., Winfield, C.G., Cronin, G.M., Hemsworth, P.H. and Dewar, A.M. The effect of individual and group housing on behavioral and physiological responses related to the welfare of pregnant pigs. Appl. Anim. Behav. Sci. 14:149-161 (1985). 39. Hansen, LL. and Vestergaard, K. Tethered versus loose sows: ethological observations and measures of sow productivity. II. Production results. Ann. Rech. Vet. Q:185-191 (1984). 40. Vestergaard, K. and Hansen, L.L. Tethered versus loose sows: ethological observations and measures of sow productivity. I. Ethological observations during pregnancy and farrowing. ,4nn. Rech. Vet. @245-256. (1984). 41.
Schlenker, G., Koppe, D. and Siefert, H. Die pdpuberale und praovulatorische Gstrogenausscheidung in Beziehung zur Fortpflanzungsregulation weiblicher Scheme. Arch. Exp. Vet. Med. 27 H6:881-889 (1973).
42. Sorensen, A.M., Thomas, W.B. and Gossett, J.W. A further study of the influence of level of energy intake and season on reproductive performance of gilts. J. Anim. Sci. g:347-349 l(l%l). 43.
Prunier, A., Bonneau, M. and Etienne, M. Effects of Jive weight and age on the sexual development of gilts and boars fed two planes of nutrition. Reprod. Nutr. Develop. 21689-700 1:1987).
DECEMBER 1989 VOL. 32 NO. 6
969