Crowing and mating behaviors in lines of chickens selected for mating frequency

The frequency and relationship of crowing to several mating behaviors were determined in lines selected for high and low cumulative number of completed matings, and in the unselected random-bred population from which the selected lines originated. A diurnal rhythm in crowing frequency was observed, with birds crowing more at 09.00 h than at 13.00 and 16.00 h. The frequency of crowing increased from 24 to 68 weeks of age in the high mating line which was in contrast to decreases in the low mating and unselected control lines. Significant positive correlations were obtained between crowing at the various ages and between crowing and courting at 68 weeks of age. Implications of these findings to the backyard flocking situation are discussed.     

Testosterone determinations in lines of chickens selected for differential mating frequency

This study was designed to evaluate the relationship between plasma testosterone titers and mating behavior in lines of chickens that had undergone bidirectional selection for high and low mating frequency and in the unselected population from which the selected lines originated. Plasma testosterone (T) concentrations were determined by radioimmunoassay procedures. Also measured were packed blood cell volumes (PCV) and two behaviors, courtship and completed matings. Significant differences were found among lines for all measures with the high mating line ranking above the low mating line and the unselected control line being intermediate to the selected lines for all measures. Also found was a positive correlated response of plasma T titers to selection for the cumulative number of completed matings.     

Androgen influence on mating behavior in selected lines of Japanese quail

Bidirectional selection for high and low mating behavior has resulted in lines of Japanese quail that differ significantly in mating frequency. To evaluate the effects of this selection on the endocrine aspects of mating behavior, exogenous testosterone cypionate (TC) was administered to caponized and intact males from selected and control lines. Dosages of TC, administered as a single injection, were 0, 5.0, and 10.0 mg for the caponized and 1.25, 2.5, and 5.0 mg for the intact males. Mating performance was measured by testing each male individually with a series of female tester-flocks for eight 8-min periods.Capons mated within 3 to 4 days postinjection, with the period of peak activity occurring between the eighth and twelfth days. Hypertrophy of the cloacal gland followed a similar pattern. At no TC level was the mating frequency of caponized males from the low mating line equal to that of males from the high mating line. Furthermore, exogenous TC at these dosages failed to stimulate capons from the high and low mating lines to mate as frequently as the intact males of their respective lines. Exogenous TC had a depressing effect upon the mating frequency of intact males from the high mating and control lines but had no influence on those from the low mating line.     

Testosterone-induced precocious sexual behavior in chickens differing in adult mating frequency

Precocious adult sexual behavior was determined for chicks from two lines of chickens selected bidirectionally for adult mating frequency. Three-day-old chicks were injected with either 0 or 12.5 mg testosterone cypionate (TC) in sesame oil, and their sexual responses to a hand thrust test (HTT) measured at 10, 12, 14, 16 and 18 days of age. TC stimulated copulation in both the high and low mating line, while birds receiving injections of the vehicle only, failed to copulate. There were differences in precocious sexual behavior between lines at this young age, although further differential maturation of neural tissues mediating mating behavior may occur.Courts, mounts, treads and matings were determined for these same birds at 7 weeks of age, following treatment with 25 mg TC. Differences were found between the lines, with high mating line birds scoring higher than low mating line birds for all behaviors measured. Early treatment with TC, however, had no direct effect on sexual behaviors at this age. Correlations between 7-week behaviors and HTT scores were determined and their possible meanings discussed.     

Genetic control of the immune response in lines of chickens selected for graft-versus-host competences

The immune response of chickens to goat erythrocytes has been examined. The H line selected for high competence of graft-versus-host reaction (GVHR) showed higher immune responses than the L line selected for low GVHR competence. It appeared also that immune responses were controlled by the B blood group locus, which is the major histocompatibility locus in chickens. The relative immune responsiveness of B genotypes were B ¹¹/¹¹> B ⁹/ B ¹¹> B ⁹/B⁹.
Treatment of antiserum with 2-mercaptoethanol (2-ME) proved that the difference in immune responses between lines was due mainly to the 2-ME resistant antibody and that the difference between the B genotypes was due to the 2-ME sensitive antibody.     

Expression profiles of somatotropic axis genes in lines of chickens divergently selected for 56-day body weight

The objective of this study was to evaluate mRNA expression of somatotropic axis genes in chickens divergently selected for high (HWS) or low (LWS) body weight at 56 days of age. Gene expression was measured on days 16, 18, and 20 of incubation, day of hatch, and days 3, 7, 28, and 56 posthatch. Pituitary growth hormone mRNA raised from prehatch to posthatch, with a similar profile in both lines. Liver growth hormone receptor (GHR) mRNA was high during embryogenesis, declined to low levels at day 3 posthatch, and then increased to day 56. Expression of liver insulin-like growth factor 1 (IGF-1) mRNA increased sharply by day 28 in line HWS and day 56 in line LWS. Pectoralis major muscle GHR mRNA was greater in line LWS than HWS. Muscle IGF-1 mRNA declined during embryogenesis, increased posthatch, and declined after day 7. IGF-1 mRNA was 1,000-fold greater in embryonic muscle than embryonic liver. Muscle IGF-1 receptor mRNA was greater in line LWS than HWS posthatch. These results demonstrate that genetic selection for high or low body weight has altered the expression profiles of somatotropic axis genes in a line-, age-, and tissue-specific manner.     

Differential feed intake responses to central corticotrophin releasing factor in lines of chickens divergently selected for low or high body weight

Effects of intracerebroventricular (ICV) injection of corticotrophin releasing factor (CRF) on feed intake were evaluated in two lines of White Plymouth Rock chickens that have been selected from a common base population for high (HWS) or low (LWS) juvenile body weight. Both lines responded with reduced feed intake after ICV CRF; however, the threshold of response was lower in line LWS than HWS. Additionally, the effects of two receptor antagonists, astressin and alpha-helical CRF (9-41; alpha-CRF), and the effect of CRF fragment 6-33, (which displaces CRF from its binding protein), were evaluated in these lines. Although all three antagonists increased feed intake in line LWS but not line HWS, they attenuated the appetite-reducing effects of CRF only in line HWS. Peripheral plasma corticosterone concentrations after an acute stressor were higher in line LWS than in line HWS. These data support the thesis of correlated responses in the CRF system to selection for high or low juvenile body weight. These differences may contribute to differential feed intake, and hence altered body weights.     

Line and crossing effects in a diallel mating system with highly inbred lines of White Leghorn chickens

Summary Seven highly inbred lines of White Leghorn chickens were used in a near complete diallel mating plan during eight years. The lines originated from three different base populations selected for egg weight. Average inbreeding coefficients of parents of chicks hatching in successive years were 0.75, 0.80, 0.84, 0.86, 0.89, 0.91, 0.93 and 0.94. The composition of line, specific combining ability and reciprocal effects and their estimated values are given. These effects were estimated for age at first egg (AFE), average weight of all eggs laid to 40 weeks (EW40), body weight at 40 weeks (BW40), number of eggs to 40 weeks (EP40) and number of eggs between 41 and 60 weeks (EP60). Records of 3247 hens surviving to 40 weeks and of 3133 birds to 60 weeks could be used. Large differences between line effects could be found in all traits. They were only partly due to the preceding selection in the base populations. All specific combining effects were in the expected direction, negative for AFE and positive for EW40, BW40, EP40 and EP60. Recovery of inbreeding depression inflated these effects rather substancially. Average heterosis, defined as the relative superiority of a line combination over the mid parent value, was –11.3%, 5.8%, 7.8%, 45.1% and 35.8% for AFE, EW40, BW40, EP40 and EP60 respectively. One line showed a relative superiority in AFE of -19.3% compared to about –7.9% for all other combinations. Reciprocal or sex-linked effects were generally smaller in all traits than specific combining effects, they were considerably smaller in AFE, EP40 and EP60. General reciprocal effects could be found for several lines in one or more traits. Offspring of two lines, when used as sire lines, showed a negative correlation between reciprocal effects of egg weight and body weight.     

Sexual behavior of dwarf and normal genotypes in divergent growth lines of chickens

Comparisons of several reproductive factors were made among dwarf, heterozygous and normal chickens in lines selected for high (HW) and low (LW) juvenile body weight. Semen concentration was significantly greater in the HW than in the LW line, and was greater for the normals than for the heterozygous or dwarf males. HW males had a significantly lower percentage of normal spermatozoa than the LW males, while there were no differences among dwarf genotypes. Fertility, as measured by A.I., was higher for LW than for HW females, whereas there were no differences among male genotypes. Mating behavior of males was measured in flocks where the pullets were of the same genotype, and where several genotypes were intermingled. The number of courts, mounts, treads, completed matings and crouches elicited was less for HW than for LW males. Although morphological and behavioral pre-mating barriers among populations were not complete, there was a tendency toward preferential mating between dwarf genotypes within the LW line which resulted in a male genotype-female genotype interaction. Matings among other genotypes were random, with an expression of passive dominance of males over females.     

Differential feeding responses to central alpha-melanocyte stimulating hormone in genetically low and high body weight selected lines of chickens

This study was conducted to compare the effects of central alpha-MSH, a potent anorexigenic signal, in lines of chickens that have undergone long-term divergent selection for low (LWS) or high (HWS) body weight. Chicks from both lines were centrally injected with 0, 24, 120 or 600 pmol alpha-MSH and feed and water intake were concurrently measured thereafter for a total of 180 min. The LWS line responded to all doses of alpha-MSH with a similar potent decrease in feed intake at all observation times. The HWS line only responded to 600 pmol alpha-MSH with decreased feed intake. alpha-MSH did not influence water intake in either line. To determine if differential hypothalamic signaling was associated with the anorexigenic effect, c-Fos immunoreactivity was measured in appetite-related hypothalamic nuclei after 600 pmol central alpha-MSH injections. c-Fos immunoreactivity was increased in the dorsomedial hypothalamus, paraventricular nucleus (PVN) and ventromedial hypothalamus in both lines after alpha-MSH; however, the magnitude of increase was greater in LWS than in HWS chicks at the PVN (136% vs. 47% increase over controls, respectively). Based on behavior observations, the number of feeding and exploratory pecks is decreased with greater magnitude after alpha-MSH in the LWS line. Additionally, alpha-MSH was associated with increased deep rest in both lines, and may be a secondary effect to reduced ingestion. These data support that the LWS line has a lower threshold for the anorexigenic effect of central alpha-MSH while in the HWS line this threshold is higher, and that this difference may be associated with differential hypothalamic signaling. Genetic variation exists in the threshold of anorexigenic response for central alpha-MSH in LWS and HWS lines of chickens with possible implications to other species including humans.     

Reciprocal relationships between pulsatile androgen secretion and the expression of mating behavior in adult male ferrets

The pulsatile secretion of androgen was similar over a 12-hr period in breeding male ferrets implanted with jugular catheters which either achieved an intromission with an estrous female or received no socio-sexual contact. This negative result contrasts with the previous demonstration (Carroll, Erskine, and Baum, 1987, Endocrinology 121, 1349-1359) of a significant, delayed rise in mean plasma androgen concentrations in breeding male ferrets 5-12 hr after mating. Males used in that previous study had lower initial mean plasma levels of androgen and smaller testis diameters than the present males. We therefore asked whether differences in circulating androgen levels, characteristic of males in different phases of the seasonal breeding cycle, might affect the expression of mating behavior. Castrated males given 0, 0.2, 2.0, or 5.0 mg/kg of testosterone propionate (TP) showed dose-related increases in the expression of different components of sexual behavior, including neck gripping, mounting, and intromitting. Surprisingly, intromissive performance was significantly better in intact breeding males than in castrates given even the highest dosage of TP. These results suggest that ferrets' mating performance may vary with seasonal variations in androgen availability, and that the ability of males to exhibit a postcoital increase in the testicular secretion of androgen may be limited to the beginning or end of the breeding season, when circulating levels of androgen are relatively low. Mating-induced increments in androgen secretion at these times may enhance subsequent reproductive success by facilitating males' intromissive capacity, which is required for the induction of ovulation and optimal sperm transport in female partners.     

Responses of chickens subjected to thyroid hormone depletion-repletion

The purpose of this experiment was to determine the relationship between lipid metabolism and the expression of specific genes in chickens fed methimazole to produce hypothyroidism. Male, broiler chickens growing from 14 to 28 days of age were fed diets containing 18% crude protein and either 0 or 1 g methimazole per kg of diet. At 28 days, these two groups were further subdivided into groups receiving 18% crude protein diets containing either 0 or 1 mg triiodothyronine (T(3)) per kg. Birds were sampled at intervals from 0 to 120 h. Measurements taken included in vitro lipogenesis (IVL), malic enzyme (ME), isocitrate dehydrogenase (ICD-NADP), aspartate aminotransferase (AAT) activities and the expression of the genes for ME, fatty acid synthase (FAS), NADP-ICD, AAT and acetyl coenzyme carboxylase (ACC). Gene expression was estimated with real time RT-PCR assays. Expression rates were noted as C(t)'s. Dietary methimazole decreased IVL and ME at 28 days of age. T(3) and supplementation for 1 day restored both IVL and ME. Paradoxically, continuing T(3) replenishment for a longer period decreased IVL without affecting ME activity. Although methimazole decreased ME gene expression, there was only a transitory relationship between enzyme activity and gene expression when plasma T(3) was replenished with exogenous T(3). These data explain the apparent dichotomies in lipid metabolism elicited by changes in the thyroid state of animals. Most metabolic changes in response to feeding T(3) occurred within a short period of time, suggesting that changes in intermediary metabolism preceded morphological changes. Furthermore, the thyroid state of the animal will determine responses to exogenous T(3).     

Exogenous androgen during development alters adult partner preference and mating behavior in gonadally intact male rats

In the rat, neonatal administration of testosterone propionate to a castrated male causes masculinization of behavior. However, if an intact male is treated neonatally with testosterone (hyper-androgen condition), male sexual behavior in adulthood is disrupted. There is a possibility that the hyper-androgen treatment is suppressing male sexual behavior by altering the male's partner preference and thereby reducing his motivation to approach the female. If so, this would suggest that exposure to supra-physiological levels of androgen during development may result in the development of male-oriented partner preference in the male. To test this idea, male rats were treated either postnatally or prenatally with testosterone, and partner preference and sexual behavior were examined in adulthood. The principal finding of this study was that increased levels of testosterone during early postnatal life, but not prenatal, decreased male sexual behavior and increased the amount of time a male spent with a stimulus male, without affecting the amount of time spent with a stimulus female during partner preference tests. Thus, the reduction in male sexual behavior produced by early exposure to high levels of testosterone is not likely due to a reduction in the male's motivation to approach a receptive female.     

Organ growth of selected lines of chickens and their F1 crosses to a common body weight or age

Summary Organ growth of male chickens selected for high and low 56-day body weight and their reciprocal F₁ crosses was compared at a common age (56 days) or at a common body weight (180 g). Organs that differed at a common body weight included weights of proventriculus, small intestine, lungs, feathers and abdominal fat and length of esophagus. Organ weights that differed at a common age included esophagus, gizzard, heart, liver, lungs, breast, legs, feathers and abdominal fat, and lengths of shank, esophagus and small intestine. Heterosis for most organs was less than 15%. Those exhibiting heterosis greater than 30% included weights of fat depots and feathers, plus lengths of the esophagus, small intestine and shank. Heterosis for these traits, however, varied depending on whether comparisons were made at common body weight or age. These results imply that biological functions of organs at specific ages may not reflect the situations at common body weights and suggest differences in resource allocations among populations.     

The aetiology of hypoxaemia in chickens selected for rapid growth

In comparison to other classes of chickens, broilers selected for rapid growth tend to be hypoxaemic, and many develop congestive heart failure (CHF). In order to explain the physiological mechanisms associated with hypoxaemia in fast-growing broiler chickens (Gallus gallus), this study examined several basic physiological parameters including the blood gas profile in arterial [left atrial (LA)] and mixed venous [right atrial (RA)] blood, systemic oxygen extraction ratio, and intrapulmonary shunt fraction. These parameters were further studied in the context of blood flow in the pulmonary circulation, structural characteristics of the lungs, and cardiac function [measured as cardiac index (CI)]. Overall, broilers had lower arterial and mixed venous blood pO(2) levels and higher pCO(2) levels compared to leghorns. The cardiac index was lower in fast-growing and CHF broilers compared to leghorn chickens or feed-restricted broilers. Systemic oxygen extraction ratio (ER) and intrapulmonary shunt fraction were significantly higher in fast-growing broilers and birds with CHF (all P<0.01). Lungs of all broilers, but not leghorns, contained ectopic, irregular nodular formations located within air spaces. Broilers with clinical signs of hypoxaemia revealed the highest number of these formations in their lung. Taken together, the present findings indicate that key factors associated with the development of hypoxaemia in fast-growing broilers include: (1) high demand for oxygen as evidenced by high oxygen ER; (2) inadequate cardiac output (CO) to fulfill the higher oxygen demands, leading to severe depletion of O(2) in mixed venous blood; and (3) elevated intrapulmonary shunt fraction and possibly dead space associated with specific pathological and anatomical characteristics within the lung.     

Physiological responses to salinity in selected lines of wheat

Two selections of bread wheat, Triticum aestivum L., differing in their relative salt resistance, were grown in salinized solution culture, and relative growth rates, osmotic adjustment, ion accumulation, and photosynthesis were monitored to study the responses of the plants to salinity.

Differences in water relations were minimal and were only apparent for 3 days following salinization. The lines differed substantially in their relative growth rates and photosynthetic responses for several weeks following salinization, despite full osmotic adjustment. Concentrations of major cations and Cl⁻ in the plant organs were remarkably similar in both lines, indicative of minimal differences in gross ion absorption and translocation.

The authors interpret these results to suggest that the major difference between these two lines of wheat was their response to specific ion effects, at the level of the organ, tissue, cell, and subcellular entities. Superior compartmentation of toxic ions by the more salt-tolerant line, presumably in the vacuole, might have enabled it to maintain its cytoplasmic metabolic apparatus in a stabler and more nearly normal state than the sensitive line was able to do; a measure of true cytoplasmic toleration of salt may also be a factor.

     

Heart rate variability in domestic chicken lines genetically selected on feather pecking behavior

Domestic chicken lines of the White Leghorn type differing in their level of feather pecking were developed by divergent genetic selection specifically on feather pecking behavior. We determined parameters of heart rate variability to elucidate the relative activation of the sympathetic and parasympathetic nervous systems during rest and stressful situations. A total of 48 hens were tested in 8 batches. Segments of 2 min were extracted from electrocardiograms recorded by radio-transmitter implants, before (basal undisturbed conditions) and during physical restraint and a social test. Under basal conditions mean distance between R-waves were shorter in the low and high lines compared to the control. During physical restraint, stress reactions [reduced root of the mean squares of successive differences (RMSSD), reduced high frequency (HF), high low frequency (LF/HF) and low vagal-sympathetic effect (VSE) compared to basal levels] were significant in all lines. During the physical restraint the high feather pecking (HFP) line reacted significantly stronger than control (CON) and low feather pecking (LFP) line. During social test the LFP line reacted different than the other two lines. Seemingly birds from LFP conceived the social test as less stressful than birds from the CON and HFP lines. From this it follows that (1) physical restraint generally induced higher stress reactions than the social test and (2) genetic selection for higher levels of feather pecking increased the autonomic nervous system reaction to physical restraint whereas selection against feather pecking has reduced the response to increased social contact.     

The mating behavior and reproduction performance in a multi-sire mating system for pigs

An important aim of organic animal production is to allow natural animal behaviour. Regarding reproduction techniques, artificial insemination is permitted but natural mating is preferred. The outdoor multi-sire system, where the sows are placed in large paddocks with a group of boars, is one example of a service system, which complies well with the organic ideals of facilitating natural animal behavior. However, very little knowledge is available about such system. Seven groups of in total of 47 sows and 31 boars were observed to study the mating behavior in an outdoor multi-sire mating system and the subsequent reproduction results. The time of start of courtship, behavior and the cause of disruption if the courtship was terminated, were recorded each time a boar courted a sow. All aggressive interactions between the boars were also recorded to estimate the boar ranking order. The observations revealed numerous poor quality matings, a huge variation in the number of times sows are mated, and overworked boars. Only 35% of all copulations lasted 2 min or more and 63% of all copulations were disrupted, mainly by competitor boars. The higher social status of the boar, the more copulations did it disrupt (p < 0.05). The outcome was an unacceptable variation in reproduction results. Only 71% of all estrus sows conceived, corresponding to a pregnancy rate of 77% of all mated sows. A large inter-group variation in reproduction performance was observed, indicating scope for improvements. In some groups all sows showed estrus and all sows conceived. Recommendations for improvement of the system are proposed.