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Individual differences among mature boars in T-maze preference for estrous or non-estrous sows
Applied Animal Behaviour Science, 17 (1987) 77-82 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
77
I n d i v i d u a l D i f f e r e n c e s a m o n g M a t u r e B o a r s in TM a z e P r e f e r e n c e for E s t r o u s or N o n - e s t r o u s S o w s JOHN J. McGLONE and JULIE L. MORROW
Animal Science Department, Texas Tech University, Lubbock, TX 79409 (U.S.A.) ( Accepted for publication 26 June 1986)
ABSTRACT
McGlone, J.J. and Morrow, J.L., 1987. Individual differences among mature boars in T-maze preference for estrous or non-estrous sows. Appl. Anim. Behav. Sci.,17: 77-82. Two experiments were conducted to evaluate the ability of boars to identify estrous sows. The preference of 11 mature boars for estrous or non-estrous sows was tested using a T-maze in Experiment 1. Boars were given a feed test on Days 1 and 4 and on Days 2, 3, 5 and 6; estrous and nonestrous sows were alternated in the right and left arms of the T-maze. The time (rain) boars spent near four sets of estrous and non-estrous sows was recorded during each 5 min test. Yorkshire, Duroc, Landrace and Hampshire boars were tested in a random order on each day. Three boars (called target boars) spent more time (P<0.05) near estrous rather than non-estrous sows. No boar preferred non-estrous sows. In Experiment 2, the time (min) that 8 crossbred sows (Yorkshire, Duroc, Landrace and Hampshire crosses) spent near target boars was determined using a 5-rain T-maze preference test. None of the 8 estrous sows tested showed a preference for any of the 3 target boars (P> 0.50). We conclude that some individual boars have the ability to distinguish between estrous and non-estrous sows. The target boars' ability to detect an estrous sow is not determined by feedback from the behavior of estrous sows.
INTRODUCTION Sexual b e h a v i o r in t h e b o a r m a y be released by a n e s t r o u s female or a v a r i e t y of i n a n i m a t e objects. T h e p r i m a r y stimulus which elicits m o u n t i n g was r e p o r t e d to be visual ( S i g n o r e t e t al., 1975). S i g n o r e t (1970) r e p o r t e d e x p e r i m e n t s in w h i c h he t e s t e d b o a r s in a T - m a z e a n d f o u n d t h a t b o a r s were as a t t r a c t e d to e s t r o u s as to n o n - e s t r o u s sows. T h e c o n c l u s i o n t h a t b o a r s c a n n o t d i s t i n g u i s h b e t w e e n e s t r o u s a n d n o n - e s t r o u s sows m a y n o t be true for e a c h individual boar. S i g n o r e t (1970) also f o u n d t h a t m o u n t i n g a t t e m p t s b y t h e b o a r w h e n in with a g r o u p o f e s t r o u s gilts c o n s t i t u t e d 6.6% o f all social i n t e r a c t i o n s , while 11.7% of social i n t e r a c t i o n s were b o a r s m o u n t i n g a n e s t r o u s gilts. T h e r e f o r e , t h e logical conclusion was m a d e t h a t b o a r s do n o t have t h e ability to distinguish estrous f r o m n o n - e s t r o u s females, t h a t t h e y o p e r a t e m a i n l y b y trial a n d error, a n d t h a t
0168-1591/87/$03.50
© 1987 Elsevier Science Publishers B.V.
78 the stimulus for mounting is primarily an immobile object (Craig, 1981; Houpt and Wolski, 1982 ). The objective of this work was to determine if individual boars prefer, in a T-maze test, to spend time near estrous sows. Out empirical observation of wide variation in individual boar sexual behavior and ability drove us to investigate Signoret's (1970) findings in more depth. MATERIALS AND METHODS
Experiment I Eleven mature, experienced boars (1-3 years of age ) were evaluated for their ability to distinguish between estrous and non-estrous sows using a T-maze. The alley into the T-maze was 1.22 m wide and 4.88 m long. Each arm of the T-maze was 1.83 × 1.52 m. Within each arm, stimulus animals were kept in an area approximately 1.1 X 1.83 m. Four mid-gestation, non-estrous sows were paired with four estrous sows of similar weight. Four of the boars were housed indoors in individual pens between pens of sows, while the remaining 7 boars were housed outside in individual pens. Sows were placed in the arms of the T-maze behind an open wire-mesh panel. Boars had short-distance visual, auditory and olfactory contact with stimulus sows. Tactile and very-close-range olfactory communication between boars and sows was not possible. Estrous sows were alternated in the left and right arms of the T-maze on each test day. Yorkshire, Duroc, Landrace and Hampshire boars were tested in a random order on each test day. There were 6 test days. During the 1st and 4th days (called feed tests), rubber feed troughs containing a small a m o u n t of feed were placed in each arm of the maze. Six weeks separated Test Days 3 and 4, while other tests were on consecutive days. On the 2nd, 3rd, 5th and 6th test days, estrous and nonestrous sows were in each arm of the maze. On Test Days 2 and 6 the estrous sow was in the left arm, on Days 3 and 5 the estrous sow was in the right arm. Each test sow was used once to test each boar. Estrous sows were bred to confirm estrus after all boars were tested. The duration of each test was 5 min per boar. The time (min) boars spent in left, right and neutral areas of the T-maze was recorded with an electronic event recorder. On all test days, the direction of the boars' initial turn (right or left) was recorded. Percentage data were normalized using an angular transformation (square root and arcsine). Transformed percentage time boars spent with estrous and non-estrous sows was analyzed using analysis of variance procedures ( S.A.S., 1981 ). The split-plot, randomized complete block model included boar effects (blocks), time near estrous or non-estrous sow ( sow effect), boar by sow interaction (used to test boar and sow effects), test day effects (sub-plot), day by
79 boar interaction, day by sow interaction and the residual error term. Differences among means were separated by the predicted difference procedure within the general linear models programs (S.A.S., 1981 ).
Experiment 2 The possibility exists that estrous sows ( as used in Experiment 1 ) are only stimulated by certain boars (perhaps, for example, these target boars could have a stronger pheromone output). If the estrous sows used in Experiment 1 showed enhanced proceptive behavior towards only some boars, then the estrous sows would actually have been initiating the boars' enhanced sexual behavior. Therefore, this second study was designed to determine if estrous sows prefer to spend time near certain boars. Eight crosbred sows (Yorkshire, Landrace, Duroc and Hampshire breeds) were evaluated for their preference in a T-maze for either a boar (the target boar) that could distinguish between estrous and non-estrous sows or one that could not. Target boars were the Yorkshire, Landrace and Duroc boars that spent significantly more time near the estrous sows in Experiment 1. All sows tested were in full standing estrus. Sows were bred at the end of each test day to further confirm estrus. The same T-maze as in Experiment 1 was utilized to test the sows. The target boar was alternated in the left and right arms of the T-maze and was matched with a boar of similar size and breed. A feed test was performed on all 8 sows on Day 1, the day before sows were anticipated to be in standing heat. Sows were tested with the boars three times, on the morning and afternoon of Day 2 (the first day of full standing estrus) and on the morning of Day 3. The duration of each test was 5 min per sow, and the duration each sow spent in the left, right and neutral areas was recorded with an electronic event recorder. The percentage data were normalized using an angular transformation and analyzed using analysis of variance procedures ( S.A.S., 1981 ). The split-plot, randomized complete block model included boar and sow effects (which were tested by the boar by sow interaction), test day effects, day by boar interaction, day by sow interaction and the residual error term. RESULTS
Experiment I Boars 2, 3 and 4 ( hereafter called target boars) spent more time ( P < 0.05) near estrous rather than non-estrous sows (Table I). The boar by sow interaction was significant ( P < 0.03). No boar preferred non-estrous sows. Equal time was spent in the right and left arms of the T-maze during the feed tests, but boars, on average, showed a preference for making an initial right turn when they entered the maze. In the first feed trial, 8 boars turned right and 3
8O TABLE I Percentage time individual boars spent near estrous and non-estrous sows (4 tests per boar). Data are arithmetic means. Analysis was performed on angular transformed data. Boar No.
1 23 33 43 5 6 7 8 9 10 11
Breed I
L Y L D Y H D H H D Y
SE
T i m e near estrous sow
T i m e near nonestrous sow
(%)
(%)
38.92 45.77 43.00 73.42 39.47 37.00 27.90 31.60 37.12 33.47 34.02
20.60 12.25 14.87 7.22 27.82 25.22 36.80 31.90 17.12 32.60 33.80
9.63
9.63
P value 2
0.81 0.01 0.04 0.01 0.43 0.39 0.56 0.99 0.13 0.96 0.93
1L = Landrace; Y = Yorkshire; D = Duroc; H = Hampshire. 2From comparison of transformed data on percentage of time near estrous or non-estrous sows. 3Referred to as "Target Boars".
turned left, while in the second feed trial, 9 boars turned right and 2 turned left.
Experiment 2 None of the 8 sows tested showed a preference for any of the 3 target boars (Table II, P > 0.5). Equal time was also spent in the right and left arms of the T-maze during the sow feed test. More sows also initially turned right when TABLE II Time ( % ) estrous sows ( N = 8 sows per boar) spent near target a n d n o n - t a r g e t ' boars. Target boar No.
Time estrous sow spent near target' boar
Time estrous sow spent near other boar
SE
P value 2
2 3 4
33.65 39.59 33.65
34.60 36.05 34.60
10.25 9.5 12.8
> 0.50 > 0.50 > 0.50
~Target boars were those which could distinguish estrous from non-estrous sows in E x p e r i m e n t 1. 2From comparison of angular t r a n s f o r m e d data on time near target or other boar.
81
they entered the T-maze during the feed test. Five sows turned right while 3 turned lefton the feed test day. DISCUSSION
Three boars showed the abilityto detect estrous sows in Experiment 1. Boars showing a preference for estrous sows were of three different breeds (Yorkshire, Landrace and Duroc). Therefore, no evidence was collected to suggest that the ability to distinguish estrous from non-estrous sows was genetically endowed. All three target boars were, however, housed inside the breeding barn between pens of sows. This housing regime m a y be a factor in the abilityof the boars to distinguish between estrous and non-estrous sows. Alternatively,these particular boars m a y have been housed indoors because the herdsmen were aware of these boars' abilities. Learning may also be an important factor in the development of individual boar preferences for estrous sows. The initialright-turn preference shown by boars and sows in the T-maze m a y have been reinforced by always making a right turn as they did when entering the breeding pen. Although most boars and sows initiallyturned right, the amount of time (rain) boars or sows spent in either arm of the T-maze on the respective test days was similar on feed test days. Sows are bred in a hand-mating management system and none of the boars had any pen-mating experience. None of the boars used in Experiments I and 2 was trained for semen collection from a dummy. Three of the boars tested were occasionally used for semen collection where boars mounted a sow. The Yorkshire target boar was used for semen collection once every 2 or 3 months. The type of mating system used m a y influence the abilityof the boar in detecting an estrous sow. Since all boars tested are routinely used to breed sows in a hand-mating system, differences in boar ability as influenced by the type of mating system could not be assessed. Signoret (1970) showed that estrous sows were attracted to boars, but at other times they were equally interested in pigs of either sex. Craig (1981) has suggested that proceptive sexual behavior on the part of the sow may increase the boar's responsiveness to her. The boar's detailed behavioral response was not evaluated in Experiment 2. Although feedback between estrous sows and boars m a y take place, sows did not choose to spend more time near target boars. The proceptive behavior shown by a sow may therefore be an important part of courtship behavior sequence and influence the boar's reproductive behavior and overall success as a breeder. The 8 estrous sows showed proceptive behavior by standing near one or the other boar in the arm of the T-maze, but no preference for target over non-target boars was shown. The sow's response suggests that the target boar's abilityto detect an estrous sow is not determined by the preferences of the sow for males which can detect estrous sows.
82 CONCLUSIONS
The ability to quickly locate an estrous sow by an individual boar could be a factor in further increasing breeding efficiency. The herdsman's time might be saved by use of boars which have the sensory ability to detect estrous sows. If boars also showed normal sexual behavior and if they required little or no herdsman assistance, boars which could identify estrous sows would be the most desirable boars. The T-maze paradigm is a tool which showed that some boars have the ability to, and were motivated to, spend more time near estrous sows. Boars which showed no such preference, we conclude, were not motivated to indicate that preference. Whether they have the ability to discriminate estrous from non-estrous sows cannot be ascertained by this T-maze test. Such non-responding boars either (1) would show their ability to distinguish estrous from non-estrous sows in a different paradigm, or (2) never learned such a skill, or (3) were not genetically endowed with the ability to identify estrous sows. ACKNOWLEDGEMENTS
We thank Daniel Stephens for care of experimental animals and John Drezek for typing the manuscript. We are grateful to James Clark for suggesting Experiment 2. Texas Tech University Paper No. T-5-203.
REFERENCES Craig,J.V.,1981.Domestic Animal Behavior: Causes and ImplicationsforAnimal Care and Management. Prentice-Hall,New Jersey,p. 277. Houpt, K.A. and Wolski, T.R., 1982. Domestic Animal Behavior for Veterinariansand Animal Scientists.Iowa State UniversityPress,Ames, IA, pp. 131-132. S.A.S.,1981. StatisticalAnalysis Systems User's Guide. S.A.S. Institute,Cary, NC, Signoret,J.P.,1970. Reproductive behavior in pigs.J. Reprod. Fertil.,Suppl.,11: 105-117. Signoret,J.P.,Baldwin, B.A., Fraser, D., and Hafez, E.S.E., 1975. The behaviour of swine. In: E.S.E. Hafez (Editor),The Behaviour of Domestic Animals. 3rd edn. Williams and Wilkins, Baltimore,pp. 302-311.
77
I n d i v i d u a l D i f f e r e n c e s a m o n g M a t u r e B o a r s in TM a z e P r e f e r e n c e for E s t r o u s or N o n - e s t r o u s S o w s JOHN J. McGLONE and JULIE L. MORROW
Animal Science Department, Texas Tech University, Lubbock, TX 79409 (U.S.A.) ( Accepted for publication 26 June 1986)
ABSTRACT
McGlone, J.J. and Morrow, J.L., 1987. Individual differences among mature boars in T-maze preference for estrous or non-estrous sows. Appl. Anim. Behav. Sci.,17: 77-82. Two experiments were conducted to evaluate the ability of boars to identify estrous sows. The preference of 11 mature boars for estrous or non-estrous sows was tested using a T-maze in Experiment 1. Boars were given a feed test on Days 1 and 4 and on Days 2, 3, 5 and 6; estrous and nonestrous sows were alternated in the right and left arms of the T-maze. The time (rain) boars spent near four sets of estrous and non-estrous sows was recorded during each 5 min test. Yorkshire, Duroc, Landrace and Hampshire boars were tested in a random order on each day. Three boars (called target boars) spent more time (P<0.05) near estrous rather than non-estrous sows. No boar preferred non-estrous sows. In Experiment 2, the time (min) that 8 crossbred sows (Yorkshire, Duroc, Landrace and Hampshire crosses) spent near target boars was determined using a 5-rain T-maze preference test. None of the 8 estrous sows tested showed a preference for any of the 3 target boars (P> 0.50). We conclude that some individual boars have the ability to distinguish between estrous and non-estrous sows. The target boars' ability to detect an estrous sow is not determined by feedback from the behavior of estrous sows.
INTRODUCTION Sexual b e h a v i o r in t h e b o a r m a y be released by a n e s t r o u s female or a v a r i e t y of i n a n i m a t e objects. T h e p r i m a r y stimulus which elicits m o u n t i n g was r e p o r t e d to be visual ( S i g n o r e t e t al., 1975). S i g n o r e t (1970) r e p o r t e d e x p e r i m e n t s in w h i c h he t e s t e d b o a r s in a T - m a z e a n d f o u n d t h a t b o a r s were as a t t r a c t e d to e s t r o u s as to n o n - e s t r o u s sows. T h e c o n c l u s i o n t h a t b o a r s c a n n o t d i s t i n g u i s h b e t w e e n e s t r o u s a n d n o n - e s t r o u s sows m a y n o t be true for e a c h individual boar. S i g n o r e t (1970) also f o u n d t h a t m o u n t i n g a t t e m p t s b y t h e b o a r w h e n in with a g r o u p o f e s t r o u s gilts c o n s t i t u t e d 6.6% o f all social i n t e r a c t i o n s , while 11.7% of social i n t e r a c t i o n s were b o a r s m o u n t i n g a n e s t r o u s gilts. T h e r e f o r e , t h e logical conclusion was m a d e t h a t b o a r s do n o t have t h e ability to distinguish estrous f r o m n o n - e s t r o u s females, t h a t t h e y o p e r a t e m a i n l y b y trial a n d error, a n d t h a t
0168-1591/87/$03.50
© 1987 Elsevier Science Publishers B.V.
78 the stimulus for mounting is primarily an immobile object (Craig, 1981; Houpt and Wolski, 1982 ). The objective of this work was to determine if individual boars prefer, in a T-maze test, to spend time near estrous sows. Out empirical observation of wide variation in individual boar sexual behavior and ability drove us to investigate Signoret's (1970) findings in more depth. MATERIALS AND METHODS
Experiment I Eleven mature, experienced boars (1-3 years of age ) were evaluated for their ability to distinguish between estrous and non-estrous sows using a T-maze. The alley into the T-maze was 1.22 m wide and 4.88 m long. Each arm of the T-maze was 1.83 × 1.52 m. Within each arm, stimulus animals were kept in an area approximately 1.1 X 1.83 m. Four mid-gestation, non-estrous sows were paired with four estrous sows of similar weight. Four of the boars were housed indoors in individual pens between pens of sows, while the remaining 7 boars were housed outside in individual pens. Sows were placed in the arms of the T-maze behind an open wire-mesh panel. Boars had short-distance visual, auditory and olfactory contact with stimulus sows. Tactile and very-close-range olfactory communication between boars and sows was not possible. Estrous sows were alternated in the left and right arms of the T-maze on each test day. Yorkshire, Duroc, Landrace and Hampshire boars were tested in a random order on each test day. There were 6 test days. During the 1st and 4th days (called feed tests), rubber feed troughs containing a small a m o u n t of feed were placed in each arm of the maze. Six weeks separated Test Days 3 and 4, while other tests were on consecutive days. On the 2nd, 3rd, 5th and 6th test days, estrous and nonestrous sows were in each arm of the maze. On Test Days 2 and 6 the estrous sow was in the left arm, on Days 3 and 5 the estrous sow was in the right arm. Each test sow was used once to test each boar. Estrous sows were bred to confirm estrus after all boars were tested. The duration of each test was 5 min per boar. The time (min) boars spent in left, right and neutral areas of the T-maze was recorded with an electronic event recorder. On all test days, the direction of the boars' initial turn (right or left) was recorded. Percentage data were normalized using an angular transformation (square root and arcsine). Transformed percentage time boars spent with estrous and non-estrous sows was analyzed using analysis of variance procedures ( S.A.S., 1981 ). The split-plot, randomized complete block model included boar effects (blocks), time near estrous or non-estrous sow ( sow effect), boar by sow interaction (used to test boar and sow effects), test day effects (sub-plot), day by
79 boar interaction, day by sow interaction and the residual error term. Differences among means were separated by the predicted difference procedure within the general linear models programs (S.A.S., 1981 ).
Experiment 2 The possibility exists that estrous sows ( as used in Experiment 1 ) are only stimulated by certain boars (perhaps, for example, these target boars could have a stronger pheromone output). If the estrous sows used in Experiment 1 showed enhanced proceptive behavior towards only some boars, then the estrous sows would actually have been initiating the boars' enhanced sexual behavior. Therefore, this second study was designed to determine if estrous sows prefer to spend time near certain boars. Eight crosbred sows (Yorkshire, Landrace, Duroc and Hampshire breeds) were evaluated for their preference in a T-maze for either a boar (the target boar) that could distinguish between estrous and non-estrous sows or one that could not. Target boars were the Yorkshire, Landrace and Duroc boars that spent significantly more time near the estrous sows in Experiment 1. All sows tested were in full standing estrus. Sows were bred at the end of each test day to further confirm estrus. The same T-maze as in Experiment 1 was utilized to test the sows. The target boar was alternated in the left and right arms of the T-maze and was matched with a boar of similar size and breed. A feed test was performed on all 8 sows on Day 1, the day before sows were anticipated to be in standing heat. Sows were tested with the boars three times, on the morning and afternoon of Day 2 (the first day of full standing estrus) and on the morning of Day 3. The duration of each test was 5 min per sow, and the duration each sow spent in the left, right and neutral areas was recorded with an electronic event recorder. The percentage data were normalized using an angular transformation and analyzed using analysis of variance procedures ( S.A.S., 1981 ). The split-plot, randomized complete block model included boar and sow effects (which were tested by the boar by sow interaction), test day effects, day by boar interaction, day by sow interaction and the residual error term. RESULTS
Experiment I Boars 2, 3 and 4 ( hereafter called target boars) spent more time ( P < 0.05) near estrous rather than non-estrous sows (Table I). The boar by sow interaction was significant ( P < 0.03). No boar preferred non-estrous sows. Equal time was spent in the right and left arms of the T-maze during the feed tests, but boars, on average, showed a preference for making an initial right turn when they entered the maze. In the first feed trial, 8 boars turned right and 3
8O TABLE I Percentage time individual boars spent near estrous and non-estrous sows (4 tests per boar). Data are arithmetic means. Analysis was performed on angular transformed data. Boar No.
1 23 33 43 5 6 7 8 9 10 11
Breed I
L Y L D Y H D H H D Y
SE
T i m e near estrous sow
T i m e near nonestrous sow
(%)
(%)
38.92 45.77 43.00 73.42 39.47 37.00 27.90 31.60 37.12 33.47 34.02
20.60 12.25 14.87 7.22 27.82 25.22 36.80 31.90 17.12 32.60 33.80
9.63
9.63
P value 2
0.81 0.01 0.04 0.01 0.43 0.39 0.56 0.99 0.13 0.96 0.93
1L = Landrace; Y = Yorkshire; D = Duroc; H = Hampshire. 2From comparison of transformed data on percentage of time near estrous or non-estrous sows. 3Referred to as "Target Boars".
turned left, while in the second feed trial, 9 boars turned right and 2 turned left.
Experiment 2 None of the 8 sows tested showed a preference for any of the 3 target boars (Table II, P > 0.5). Equal time was also spent in the right and left arms of the T-maze during the sow feed test. More sows also initially turned right when TABLE II Time ( % ) estrous sows ( N = 8 sows per boar) spent near target a n d n o n - t a r g e t ' boars. Target boar No.
Time estrous sow spent near target' boar
Time estrous sow spent near other boar
SE
P value 2
2 3 4
33.65 39.59 33.65
34.60 36.05 34.60
10.25 9.5 12.8
> 0.50 > 0.50 > 0.50
~Target boars were those which could distinguish estrous from non-estrous sows in E x p e r i m e n t 1. 2From comparison of angular t r a n s f o r m e d data on time near target or other boar.
81
they entered the T-maze during the feed test. Five sows turned right while 3 turned lefton the feed test day. DISCUSSION
Three boars showed the abilityto detect estrous sows in Experiment 1. Boars showing a preference for estrous sows were of three different breeds (Yorkshire, Landrace and Duroc). Therefore, no evidence was collected to suggest that the ability to distinguish estrous from non-estrous sows was genetically endowed. All three target boars were, however, housed inside the breeding barn between pens of sows. This housing regime m a y be a factor in the abilityof the boars to distinguish between estrous and non-estrous sows. Alternatively,these particular boars m a y have been housed indoors because the herdsmen were aware of these boars' abilities. Learning may also be an important factor in the development of individual boar preferences for estrous sows. The initialright-turn preference shown by boars and sows in the T-maze m a y have been reinforced by always making a right turn as they did when entering the breeding pen. Although most boars and sows initiallyturned right, the amount of time (rain) boars or sows spent in either arm of the T-maze on the respective test days was similar on feed test days. Sows are bred in a hand-mating management system and none of the boars had any pen-mating experience. None of the boars used in Experiments I and 2 was trained for semen collection from a dummy. Three of the boars tested were occasionally used for semen collection where boars mounted a sow. The Yorkshire target boar was used for semen collection once every 2 or 3 months. The type of mating system used m a y influence the abilityof the boar in detecting an estrous sow. Since all boars tested are routinely used to breed sows in a hand-mating system, differences in boar ability as influenced by the type of mating system could not be assessed. Signoret (1970) showed that estrous sows were attracted to boars, but at other times they were equally interested in pigs of either sex. Craig (1981) has suggested that proceptive sexual behavior on the part of the sow may increase the boar's responsiveness to her. The boar's detailed behavioral response was not evaluated in Experiment 2. Although feedback between estrous sows and boars m a y take place, sows did not choose to spend more time near target boars. The proceptive behavior shown by a sow may therefore be an important part of courtship behavior sequence and influence the boar's reproductive behavior and overall success as a breeder. The 8 estrous sows showed proceptive behavior by standing near one or the other boar in the arm of the T-maze, but no preference for target over non-target boars was shown. The sow's response suggests that the target boar's abilityto detect an estrous sow is not determined by the preferences of the sow for males which can detect estrous sows.
82 CONCLUSIONS
The ability to quickly locate an estrous sow by an individual boar could be a factor in further increasing breeding efficiency. The herdsman's time might be saved by use of boars which have the sensory ability to detect estrous sows. If boars also showed normal sexual behavior and if they required little or no herdsman assistance, boars which could identify estrous sows would be the most desirable boars. The T-maze paradigm is a tool which showed that some boars have the ability to, and were motivated to, spend more time near estrous sows. Boars which showed no such preference, we conclude, were not motivated to indicate that preference. Whether they have the ability to discriminate estrous from non-estrous sows cannot be ascertained by this T-maze test. Such non-responding boars either (1) would show their ability to distinguish estrous from non-estrous sows in a different paradigm, or (2) never learned such a skill, or (3) were not genetically endowed with the ability to identify estrous sows. ACKNOWLEDGEMENTS
We thank Daniel Stephens for care of experimental animals and John Drezek for typing the manuscript. We are grateful to James Clark for suggesting Experiment 2. Texas Tech University Paper No. T-5-203.
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