Discriminating spontaneous locomotor play of dairy calves using accelerometers.

Play behavior is a promising welfare indicator in dairy calves because it decreases in negative situations such as pain or hunger and increases in positive contexts such as in appropriate social environments. Directly measuring play is time consuming because it is performed in irregular bouts and can be inconsistent over days. To facilitate automatic recording of play, previous studies fitted triaxial accelerometers to the hind legs of calves and measured the velocity of movements in large arenas; high correlations were reported between vertical axis peak duration and the duration of locomotor play. The current study aimed to validate accelerometers for recording spontaneous locomotor play in calves' home pens over longer periods. Data were collected from 48 Holstein Friesian calves, housed in groups of 3 in pens of 10 m2, at either 4 or 8 wk of age. Acceleration at the vertical axis of the hind leg was recorded at a rate of 1 Hz. One active time period for each calf was randomly selected (mean duration ± standard deviation = 34 ± 9 min). From video of the corresponding time period, the frequency of locomotor play events, consisting of run, turn, and buck/buck-kick, was recorded using behavior sampling. Combined counts of play events were highly correlated (Pearson r = 0.91) with counts of acceleration peaks. However, for calves with higher levels of locomotor play, this method underestimated the extent of play. Alternatively, run, turn, and buck events obtained from video were transformed by creating intervals of 10 s and then classifying each 10-s interval as comprising events of play ("play") or not comprising events of play ("no play"). The corresponding accelerometer data for all 10-s periods, equaling 10 consecutive readings each, were classified into play or no play by using quadratic discriminant analysis; 79% of periods with locomotor play were correctly classified. Counts of observed play intervals correlated with the counts of play periods from accelerometers (r = 0.87), but the discriminant analysis consistently overestimated play. In conclusion, accelerometer measurements at 1 Hz (in 1-s intervals) and at the vertical axis cannot be used alone to exactly quantify absolute levels of locomotor play in the home pen. However, counts of peak accelerations can provide a rough estimate of inter-individual differences in play events, and discriminant analysis can be used as a proxy for one-zero sampling of inter-individual differences in locomotor play.

Individual stability in vocalization rates of preweaning piglets.

Piglet vocalization rates are used as welfare indicators. The emission rates of the two gross categories of piglet calls, namely low frequency calls ("grunts") and high frequency calls ("screams"), may contain different information about the piglet's internal state due to differing communicative functions of the two call types. More knowledge is needed about the sources of variation in calling rates within and between piglets. We examined to what extent the emission rates of the two call types are codetermined by individual and litter identity, i.e., whether the rates are repeatable within individuals and similar between littermates. We recorded frequency of grunts and screams in one mildly negative (short-term Isolation) and one moderately negative (manual Restraint) situation during the first week (week 1) and the 4th week (week 4) of life and asked the following questions: 1) Are within-individual vocalization rates stable across the suckling period? 2) Are within-individual vocalization rates stable across the two situations? 3) Is there within-litter similarity in vocalization rates? 4) Does this within-litter similarity increase during the suckling period? Within-individual vocalization rates were stable between week 1 and week 4 (grunts in Restraint P < 0.05; grunts in Isolation P < 0.001; screams in Restraint P < 0.001; screams in Isolation P < 0.001). Across the two situations at the same age, the vocalization rates were not stable for grunts but were stable for screams at week 1 and week 4 (P < 0.05). Vocalization rates were more similar between littermates than between piglets belonging to different litters (grunts in Restraint P < 0.001; grunts in Isolation P < 0.01; screams in Restraint P < 0.001; screams in Isolation P < 0.001). This litter effect did not grow stronger from week 1 to week 4 as the within-litter coefficient of variance did not decrease between the two ages. Sex of the piglet had no influence on vocalization rates while greater body weight was associated with lower screaming rates in the Restraint situation (P < 0.05). In conclusion, our study demonstrates that both individuality of the piglet and litter identity affect the vocalization rates of piglets in negatively valenced situations. For screams, the repeatability of individual vocalization rates holds even across situations, while for grunts, the rates are repeatable during ontogeny within the situations, but not across situations.

Higher dominance position does not result in higher reproductive success in female beef cattle.

The aim of this study was to investigate whether beef cows that achieve higher dominance status than their age-mates have prolonged reproductive life, increased number of offspring born and weaned, and/or heavier BW of the offspring. We also assessed whether maternal dominance rank affects the offspring sex ratio. We recorded data on 309 potential deliveries of female beef cows with known dominance status in a seasonally pastured herd over a 14-yr period and linked them with yearly records of dominance status of the cows assessed around feeding. We did not find any effect of age-corrected dominance index on cow reproductive success measured as delivery or weaning success, calf birth weight or weaning weight, survival of the cow to the following reproductive season, or sex of the conceived calf (generalized linear models, > 0.05). In conclusion, the results indicate that in a typical situation of pastured beef cattle, there might be no selection for individual striving to achieve higher dominance status.

Weaning reactions in beef cattle are adaptively adjusted to the state of the cow and the calf.

Abrupt weaning as practiced in beef cattle husbandry is stressful for both the cow and her offspring. However, the reaction to weaning varies among individuals. Based on the theory of maternal care allocation, we derived and tested the following hypotheses: 1) cow reaction to weaning will be stronger if the calf is young, if the calf is a female, and if the calf had higher daily weight gain; 2) cows in a higher parity and cows that are not concurrently pregnant will react more on weaning; and 3) young and female calves, and also calves with higher daily weight gain will respond more to weaning. We recorded frequency of vocalization and time spent moving in 50 cow-calf pairs (27 males and 23 females) immediately after weaning at 151 to 274 d of age. The recordings were made at 0 to 2 h, 6 to 8 h, and 24 to 26 h after the separation of the calves from the cows. Linear mixed models were used to test the predictions. In cows, age of the calf had the strongest effect with mothers of younger calves vocalizing more ( < 0.05). Frequency of vocalization was higher in mothers of calves with higher daily weight gain ( < 0.01) and in nonpregnant mothers ( < 0.01). Frequency of the moving was higher in younger cows ( < 0.05). Sex of the calf had no effect. In calves, females vocalized ( < 0.001) and moved ( < 0.01) more than males and calves with higher daily weight gain also called more ( < 0.01). The relationships between the 2 behaviors and their time courses were different in cows and calves. In cows, vocalization and movement were correlated ( < 0.001) and both increased until 6 to 8 h and then plateaued or declined ( < 0.001). In calves, vocalizations steadily increased until 24 to 26 h ( < 0.001) whereas movement remained unchanged in time and was uncorrelated with vocalizations. These differences indicate that vocalization may be a more sensitive indicator of weaning stress than movement. Our results document that the ability to adaptively adjust mother-young interactions has been preserved in domesticated beef cattle.

The effect of age at separation from the dam and presence of social companions on play behavior and weight gain in dairy calves.

Play behavior positively affects welfare of farm animals, yet impoverished social environment during early ontogeny may limit the opportunity or motivation to play. This study investigated the independent and the combined effects of the presence of the dam during the colostrum feeding period and subsequent group housing on play behavior and growth in dairy calves. Forty female calves were allocated to 1 of 4 treatments according to a 2×2 factorial design. The treatments were with or without mother during the 4d after birth and companion housing (single pens or grouped housing in pens of 4 calves between 1 and 8wk of age). After 8wk of age all calves were housed in groups of 4 calves. Play behavior of the calves was observed at 2, 5, and 12wk of age in the following situations: 6 h of spontaneous behavior in the home pen, a 15-min open-field test, and a 15-min social test with an unfamiliar calf. Additionally, play behavior after grouping or relocation at 8wk of age was recorded during two 2-h sessions. There were no significant effects of the mother by companion interaction either on the amount of play behavior in any of the tests or on the body weights of the calves. Presence of the mother after birth did not increase later playfulness, with the exception of higher spontaneous play at 12wk of age. When calves were housed in groups of 4, they played more in the home pen on wk 2 and 5 than individually housed calves of the same age. In contrast, individually housed calves were more playful during open-field tests and social tests on wk 2 and 5. At 8wk, single calves that were placed in a new pen with 3 unfamiliar calves played more than twice as much as grouped calves that were just moved to a new pen with familiar companions. These results show that single-housed calves are deprived of natural levels of play, as demonstrated by both their lower spontaneous play behavior and the higher rebound effect when they are exposed to larger spaces or larger spaces plus companions. Calves that stayed with their mothers for 4d postpartum grew much better until the end of the second week. After that, grouped calves grew better until wk 10 and they tended to be heavier for at least 2wk after relocation or mixing at wk 8. The study shows that brief maternal rearing and group housing independently improve different aspects of performance and welfare of dairy calves.

Fluctuating asymmetry as an animal welfare indicator -- a review of methodology and validity.

It has been suggested that fluctuating asymmetry (FA) reflects an animal's ability to cope with the sum of challenges during its growing period and, thus, is a potential welfare indicator. In this review we investigate the evidence of associations between FA and other welfare indicators measured at the level of the individual and of effects of welfare-relevant environmental conditions on FA in populations of captive birds and mammals including humans. As the question of validity cannot be treated independently from the quality of the available data, first a checklist for the proper measurement and analysis of FA is drafted and used to evaluate the methodological quality of the various studies. We recommend this checklist to be used as a standard for future FA studies. We found 17 relevant studies on associations between FA and other welfare indicators, and 36 studies on effects of welfare-relevant factors on FA. Frequent methodological shortcomings or insufficient methodological information allow for only cautious conclusions. The proportion of significant results supporting the link between higher FA and poorer welfare is only moderately high. Independent from statistical significance, almost all studies found the relationship between FA and welfare to be prevailingly in the expected direction. FA is a promising measure of animal welfare, despite a great number of open questions, e.g. relating to the ontogeny of FA or its sensitivity to various stressors. The considerable potential of FA as a welfare indicator makes it worthwhile to pursue more intensely validation studies as well as applied studies. These studies should pay particular attention to an appropriate methodological approach.

Begging for milk: evolution of teat massaging in suckling pigs.

We present a model that simulates the evolution of teat massaging (begging) by suckling piglets (Sus scrofa) and milk distribution among teats (provisioning) by their mothers. Contrary to previous begging models, this one incorporates an ontogenetic dimension in that the inherited begging and provisioning rules are repeatedly allowed to interact, and their consequences for milk intake, growth and death probability are assessed, during each nursing. We test the model under three selection regimes differing in the relative importance of the between-litter selection component. We show that the selection regime with the strongest between-litter selection component leads to lowest begging levels and most effective milk utilization, thus supporting the hypothesis that selection based on whole litters may attenuate sibling competition.

Computer-aided method for calculating animal configurations during social interactions from two-dimensional coordinates of color-marked body parts.

In an experiment investigating the impact of preweaning social experience on later social behavior in pigs, we were interested in the mutual spatial positions of pigs during paired social interactions. To obtain these data, we applied a different colored mark to the head and back of each of 2 pigs per group and videotaped the pigs' interactions. We used the EthoVision tracking system to provide x,y coordinates of the four colored marks every 0.2 sec. This paper describes the structure and functioning of a FoxPro program designed to clean the raw data and use it to identify the mutual body positions of the 2 animals at 0.2-sec intervals. Cleaning the data was achieved by identifying invalid data points and replacing them by interpolations. An algorithm was then applied to extract three variables from the coordinates: (1) whether the two pigs were in body contact; (2) the mutual orientation (parallel, antiparallel, or perpendicular) of the two pigs; and (3) whether the pig in the "active" position made snout contact in front of, or behind, the ear base of the other pig. Using these variables, we were able to identify five interaction types: Pig A attacks, Pig B attacks, undecided head-to-head position, "clinch" resting position, or no contact. To assess the reliability of the automatic system, a randomly chosen 5-min videotaped interaction was scored for mutual positions both visually (by 2 independent observers) and automatically. Good agreement was found between the data from the 2 observers and between each observer's data and the data from the automated system, as assessed using Cohen's kappa coefficients.

Mammalian play: training for the unexpected.

In this review, we present a new conceptual framework for the study of play behavior, a hitherto puzzling array of seemingly purposeless and unrelated behavioral elements that are recognizable as play throughout the mammalian lineage. Our major new functional hypothesis is that play enables animals to develop flexible kinematic and emotional responses to unexpected events in which they experience a sudden loss of control. Specifically, we propose that play functions to increase the versatility of movements used to recover from sudden shocks such as loss of balance and falling over, and to enhance the ability of animals to cope emotionally with unexpected stressful situations. To obtain this "training for the unexpected," we suggest that animals actively seek and create unexpected situations in play through self-handicapping; that is, deliberately relaxing control over their movements or actively putting themselves into disadvantageous positions and situations. Thus, play is comprised of sequences in which the players switch rapidly between well-controlled movements similar to those used in "serious" behavior and self-handicapping movements that result in temporary loss of control. We propose that this playful switching between in-control and out-of-control elements is cognitively demanding, setting phylogenetic and ontogenetic constraints on play, and is underlain by neuroendocrinological responses that produce a complex emotional state known as "having fun." Furthermore, we propose that play is often prompted by relatively novel or unpredictable stimuli, and is thus related to, although distinct from, exploration. We present 24 predictions that arise from our new theoretical framework, examining the extent to which they are supported by the existing empirical evidence and contrasting them with the predictions of four major alternative hypotheses about play. We argue that our "training for the unexpected" hypothesis can account for some previously puzzling kinematic, structural, motivational, emotional, cognitive, social, ontogenetic, and phylogenetic aspects of play. It may also account for a diversity of individual methods for coping with unexpected misfortunes.

Consequences of a modified putative substrate-activation site on catalysis by yeast pyruvate decarboxylase.

Earlier, it had been proposed in the laboratories at Halle that a cysteine residue is responsible for the hysteretic substrate activation behavior of yeast pyruvate decarboxylase. More recently, this idea has received support in a series of studies from Rutgers with the identification of residue C221 as the site where substrate is bound to transmit the information to H92, to E91, to W412, and finally to the active center thiamin diphosphate. According to steady-state kinetic assays, the C221A/C222A variant is no longer subject to substrate activation yet is still a well-functioning enzyme. Several further experiments are reported on this variant: (1) The variant exhibits lag phases in the product formation progress curves, which can be attributed to a unimolecular step in the pre-steady-state stage of catalysis. (2) The rate of exchange with solvent deuterium of the thiamin diphosphate C2H atom is slowed by a factor of 2 compared to the wild-type enzyme, suggesting that the reduced activity that results from the substitutions some 20 A from the active center is also seen in the first key step of the reaction. (3) The solvent (deuterium oxide) kinetic isotope effect was found to be inverse on V(max)/K(m) (0.62), and small but normal on V(max) (1.26), virtually ruling out residue C221 as being responsible for the inverse effects reported for the wild-type enzyme at low substrate concentrations. The solvent kinetic isotope effects are compared to those on two related enzymes not subject to substrate activation, Zymomonas mobilis pyruvate decarboxylase and benzoylformate decarboxylase.

Dimensions of maternal behaviour characteristics in domestic and wildxdomestic crossbred sows.

We examined the maternal behaviour of seven domestic and seven wildxdomestic primiparous sows during 10 days post partum to investigate two questions: (1) Did maternal behaviour change during domestication? (2) Can the interindividual variability of maternal behaviour be subsumed into a few dimensions of maternal temperament? We recorded: (a) willingness to leave the nest for food on Day 2; (b) reaction to a playback of squeezed piglet distress vocalisation on Day 2; (c) spontaneous nursing behaviour and spontaneous lying-down behaviour on Day 5 (from an overnight video recording); (d) reactions to playbacks of various piglet distress vocalisations on Day 6 and (e) reactions to a human in the 'nest' with piglets on Day 9. Moreover, data on baseline cortisol saliva concentration and its increase during a brief transportation period and novel environment challenge at the age of 5 months were available. Crossbred sows did not differ from domestic ones in any aspect of maternal behaviour except for a higher tendency to terminate final massage during nursings and a higher frequency of changing posture from lying to standing and back during the night. Factor analysis (based on correlation matrix of 11 behaviour and cortisol variables calculated for all 14 sows after removing the effect of breed) indicated that 82% of the variability in the data could be explained by three factors: first, 'calmness' on which low night time frequency of major posture changes, carefulness of lying-down behaviour and high propensity to remain in nursing position after milk ejection loaded positively while cortisol concentrations during challenge loaded negatively; second, 'protectiveness' with high loadings of the reaction scores to the playbacks of piglet distress calls and the human presence near the piglets; and third, 'nursing activity' which was strongly positively associated with nursing frequency, and negatively with the proportion of nutritive nursings and baseline cortisol values. The results indicate that most aspects of pig maternal behaviour have not been significantly changed by domestication and that substantial variability in maternal behaviour exists between sows, perhaps in the form of several behaviour characteristics which encompass both behaviour and endocrine profiles of the sows.

Prolactin and insulin levels in lactating sows in relation to nursing frequency.

It has been established that sows up- or down-regulate their milk production as the frequency of nursings is changed. The amount of udder massage by piglets might also influence milk production. To investigate whether these effects are associated with changes in prolactin or insulin levels, we enforced five sows each to nurse either every 35 min (MIN35) or every 70 min (MIN70) over a 26- to 28-hr period. Milk production was measured during the first 24 hr of this period. During the last three to four nursings, blood was collected every 5 min. Plasma prolactin levels increased after milk ejection (P < 0.05), whereas insulin levels increased only briefly in MIN70 sows. Sows nursing every 35 min had lower basal (P < 0.001) and maximal (P < 0.05) concentrations of insulin than MIN70 sows. There were no differences between the two groups in prolactin levels. Nursings with a postejection udder massage longer than 90 s tended to induce a higher increase in prolactin (P < 0.1) than nursings with a shorter massage. When the effects of imposed nursing frequency were removed, there was an across-sows positive residual correlation between average prolactin levels (P < 0.05) and the duration of post-ejection udder massage during the preceding 24 hr. We conclude that when milk production of a sow is changed by altering the nursing frequency within natural limits, the necessary alteration in catabolic state of energy metabolism may be associated with altered insulin levels. The duration of udder massage in a single nursing might have only a slight immediate impact on prolactin levels, but may influence prolactin levels more substantially if increased for a period of 24 hr.

Activation of thiamin diphosphate in enzymes.

Activation of the coenzyme ThDP was studied by measuring the kinetics of deprotonation at the C2 carbon of thiamin diphosphate in the enzymes pyruvate decarboxylase, transketolase, pyruvate dehydrogenase complex, pyruvate oxidase, in site-specific mutant enzymes and in enzyme complexes containing coenzyme analogues by proton/deuterium exchange detected by 1H-NMR spectroscopy. The respective deprotonation rate constant is above the catalytic constant in all enzymes investigated. The fast deprotonation requires the presence of an activator in pyruvate decarboxylase from yeast, showing the allosteric regulation of this enzyme to be accomplished by an increase in the C2-H dissociation rate of the enzyme-bound thiamin diphosphate. The data of the thiamin diphosphate analogues and of the mutant enzymes show the N1' atom and the 4'-NH2 group to be essential for the activation of the coenzyme and a conserved glutamate involved in the proton abstraction mechanism of the enzyme-bound thiamin diphosphate.

Activation of thiamin diphosphate and FAD in the phosphatedependent pyruvate oxidase from Lactobacillus plantarum.

The phosphate- and oxygen-dependent pyruvate oxidase from Lactobacillus plantarum is a homotetrameric enzyme that binds 1 FAD and 1 thiamine diphosphate per subunit. A kinetic analysis of the partial reactions in the overall oxidative conversion of pyruvate to acetyl phosphate and CO2 shows an indirect activation of the thiamine diphosphate by FAD that is mediated by the protein moiety. The rate constant of the initial step, the deprotonation of C2-H of thiamine diphosphate, increases 10-fold in the binary apoenzyme-thiamine diphosphate complex to 10(-2) s-1. Acceleration of this step beyond the observed overall catalytic rate constant to 20 s-1 requires enzyme-bound FAD. FAD appears to bind in a two-step mechanism. The primarily bound form allows formation of hydroxyethylthiamine diphosphate but not the transfer of electrons from this intermediate to O2. This intermediate form can be mimicked using 5-deaza-FAD, which is inactive toward O2 but active in an assay using 2,6-dichlorophenolindophenol as electron acceptor. This analogue also promotes the rate constant of C2-H dissociation of thiamine diphosphate in pyruvate oxidase beyond the overall enzyme turnover. Formation of the catalytically competent FAD-thiamine-pyruvate oxidase ternary complex requires a second step, which was detected at low temperature.

The role of nursing frequency in milk production in domestic pigs.

We conducted three experiments to assess how nursing frequency affects milk output in early pig lactation. In Exp. 1, nursing behavior of 12 individually penned sows was recorded on d 1 through 3 postpartum. The milk output was measured using the weigh-suckle-weigh method. The spontaneous changes in the nursing frequency between d 1 and 2 were positively correlated with the changes in milk output (rS = .64), and the same was true for changes between d 2 and 3 (rS = .77). In Exp. 2, we forced sows, 7 to 8 d after parturition, to nurse every 35 min (10 sows) or every 70 min (eight sows) for 24 h. Sows nursing at short intervals had more nursings without milk ejection, but they gave 27% more milk and their litters gained 44% more weight during the experimental 24 h than sows nursing at long intervals. Litters nursed at long intervals massaged the udder longer after milk ejection. In Exp. 3, milk output was measured after intervals of 35, 50, and 70 min imposed in varied order on 11 experimental sows in the second week of lactation. In a separate recording of two 50-min nursings, we measured milk output from teats that were, or were not, sucked at the first nursing (i.e., giving within-sow comparison of 50 or 100 min). The milk output after 35, 70, and 100 min did not differ from that after 50 min, although there was a tendency for a slight increase with longer intervals. The results suggest that glands are refilled early after milk ejection and that the increase in milk available with prolonged intervals is only slight. As a result, it is the nursing frequency that plays a crucial role in adjusting the milk output.

Molecular mechanism of regulation of the pyruvate dehydrogenase complex from E. coli.

The pyruvate dehydrogenase multienzyme complex from E. coli shows a sigmoidal dependency of the reaction rate on the substrate concentration when product formation is followed in the presence of physiological concentrations of the cofactor thiamin diphosphate. To elucidate the molecular mechanism of this regulation, the influence of the substrate pyruvate on the coenzyme-protein interaction has been investigated using several coenzyme analogues. The observed binding constants of all coenzymatically active analogues are increased in the presence of the substrate pyruvate, whereas those of all coenzymatically inactive analogues are not altered in the presence of pyruvate. This points to an increased binding affinity of a reaction-intermediate-coenzyme complex to the protein. Since cofactor binding and dissociation at physiological concentrations of thiamin diphosphate are slow compared to the catalytic reaction, a slow transition to the active state of the enzyme occurs. After lowering the pyruvate concentration, the opposite effect, a dissociation of the thiamin diphosphate from the enzyme is observed. This slow substrate dependent enhancement of cofactor binding enables efficient regulation of the pyruvate dehydrogenase complex by its substrate pyruvate.

The effect of time of day on sperm competition and male reproductive success in laboratory rats.

The study was designed to test the hypothesis that siring success of male rats depends on when during the receptivity period the matings occur. In Experiment 1, females were mated with pairs of males differing in coat colour genetic marker. The males copulated with the female successively, either about 1 hour apart at dusk (schedule AA) or about 1 hour apart around midnight (BB) or one at dusk and the other around midnight (AB). The males mating first had lesser siring success under the schedule AB than under the other two schedules. In Experiment 2, females were mated under the same regimen as in Experiment 1. One male of each competing pair had its spermatozoa labeled by 3H-thymidine. The proportions of spermatozoa of the labeled males were identified in samples from uterine horns and oviducts. Balanced contributions of both males were recorded in uterus in all groups. No definitive conclusion concerning oviductal sperm composition could be reached. In both experiments, night-mating males copulated more quickly. It is suggested that copulation at about midnight is advantageous in intermale reproductive competition and that the function of the diurnal variation in the speed of male sexual behaviour might be clarified on this ground.

Different outcomes of sperm competition in right and left sides of the female reproductive tract revealed by thymidine-3H-labeled spermatozoa in the rat.

We attempted to record directly the results of sperm competition between two male rats in samples from female reproductive tracts. Gametes of 7 male rats were labeled in vivo by repeated injections of thymidine-6-3H. 33 females were mated successively with one of the injected males and with a noninjected male, or vice versa. Samples of the resulting sperm mixtures were recovered from both the uterine horns and the oviducts of the females. Pure samples of the injected males' sperm were obtained from uterine horns of females mated solely to them. Smears of samples were evaluated autoradiographically. Except for one male, the injections resulted in a broad peak of sperm labeling with maximum intensity on days 56-58 postinjection. This labeling enabled the assessing of contribution of either male to uterine and tubal sperm in the competitive matings. The injections did not influence competitive ability of male gametes in terms of sperm transport to horns or oviducts. The outcomes of sperm competition were significantly different in the right and left sides in most female subjects. Nevertheless, the outcomes were usually similar in a horn and a tube on the same side of the body. In vivo sperm labeling appears to be a useful method in the study of rodent sperm competition.

Role of the medial preoptic area in sexual behaviour of the male rat: a study using repeated cycloheximide infusions.

The effect of cycloheximide (CHX), an inhibitor of proteosynthesis, on sexual behaviour was studied in adult male rats in which it was infused into the medial preoptic area of the hypothalamus (MPOA). Sexual interaction took place under control and modification of the precopulatory behaviour of the female. Among the various bilaterally infused amounts of CHX--20 micrograms in 1 microliter, 40 micrograms in 1 microliter, 80 micrograms in 2 microliters--the effect of the largest dose corresponded to a hypothetical state of copulatory readiness of the males; 2 h after administration the males were not capable of initiating copulatory behaviour with a passively receptive female, but did so successfully with a highly soliciting female. The dependence of copulatory readiness of the males on the precopulatory behaviour of the females was confirmed repeatedly after this dose of CHX. At the same time, the precopulatory activity of the males towards a passively receptive female was unimpaired. The effect of CHX was reversible; 48 h after infusion the males displayed high copulatory readiness. Only half the males (n = 7) given bilateral infusions of 80 micrograms CHX fulfilled criterion of copulatory performance. Histological control demonstrated that the MPOA was affected bilaterally by CHX infusion in 10 males out of 14. The results are discussed from the aspect of participation of the MPOA in the regulation of male sexual behaviour. The method allows changes in sexual behaviour to be studied in the same individual in a chronic experiment.

Transition from precopulatory to copulatory behaviour in male rats with lesions in medial preoptic area: dependence on precopulatory pattern of female.

In the present study, both the precopulatory behaviour and the copulatory readiness of male rats following the bilateral medial preoptic area lesions was compared with their intact states. In behavioural testing, the intensity of female precopulatory behaviour was used as an experimental variable. The results showed that the natural threshold of copulatory readiness of males was increased in the lesioned state, the animals were more dependent on the soliciting patterns of the female. However, all the males exhibited conspicuous precopulatory behaviour towards the stimulus females used. Apparently, further brain structures participate in the regulation of sexual behaviour of males, above all, in activation or maintenance of precopulatory activity.