Age Groups Of Sheep Research Articles

Correlative variation of economically valuable traits in South Kazakh Merino.

Fine-fleeced sheep are distinguished by numerous economically valuable traits that constitute the foundation for productive distinctions among breeds, populations, lines, and individuals. Many of these traits have already been mentioned or thoroughly examined during studies on the correlative variability of productivity indicators, blood parameters, characteristics of pulmonary gas exchange, histological structures of the skin, and features of the experimental sheep's coat. The objective of our research was to investigate the correlative variability of key economically valuable traits that characterize the overall functional state of sheep organisms under varying environmental conditions. The study was conducted at the "Sharbulak" breeding farms and the "Samat" peasant farms in the Kazygurt district of the Turkestan region. Our findings reveal that one-year-old rams surpass ewes in terms of live weight by 32-37% and in terms of unwashed wool shearing by 21-23%. Two-year-old rams outperform ewes in live weight by 2.15-2.17 times and in unwashed wool shearing by 2.38-2.44 times. The highest phenotypic variability in relative terms (as indicated by the coefficient of variation) is observed in the shearing of pure wool, with an average coefficient of variation of 18.1% across all sex and age groups of sheep. This is followed by the wool coefficient (17.4%) and the yield of pure fiber (12.5%). For each group of animals, the most substantial phenotypic correlation coefficients were observed between the live weight of sheep and the shearing of unwashed wool. On average, across all groups of sheep at the "Sharbulak" breeding farm, this phenotypic correlation reaches +0.411 ± 0.077. Correspondingly, for the sheep herd at the "Samat" peasant farm, it is +0.326 ± 0.075. The second-highest phenotypic correlation pertains to the cut of unwashed wool and the length of wool (with correlation coefficients of +0.156 ± 0.058 and +0.145 ± 0.057, respectively, for the herds). The third-highest correlation involves live weight and wool length (+0.131 ± 0.085 and +0.105 ± 0.078, respectively). No statistically significant differences were identified in the average correlation coefficients between the live weight of sheep, the shearing of unwashed wool, and the length of the staple among the flocks of sheep at the "Sharbulak" breeding farm and the "Samat" peasant farm.

Molecular evaluation of Cryptosporidium spp. in sheep in southern Xinjiang, China.

Cryptosporidium spp. are diarrheagenic intestinal parasites with multiple hosts worldwide. A total of 1252 fresh fecal samples of sheep were collected from 10 large-scale farms in southern Xinjiang. Based on the small subunit ribosomal (SSU rRNA) gene of Cryptosporidium, 100 Cryptosporidium-positive samples (8.0%, 100/1252) were detected by PCR. Nine out of 10 farms were positive for Cryptosporidium, with the highest infection rate being 18.4% (23/125) on farm 9 in Qira. The infection rates of Cryptosporidium in pre-weaned lambs, weaned lambs, fattening sheep, and adult sheep were 20.3% (61/301), 10.3% (34/329), 0.9% (3/327), and 0.7% (2/295), respectively. Three Cryptosporidium species were identified, namely, C. xiaoi (n=61), C. parvum (n=22), and C. ubiquitum (n=17). Of them, C. xiaoi was detected on all positive farms and in different age groups of sheep. The subtypes of C. parvum and C. ubiquitum were identified by PCR at the 60 kDa glycoprotein (gp60) gene. Two C. parvum subtypes were identified: IIdA19G1 (n = 21) and IIdA15G1 (n = 1). One C. ubiquitum subtype was identified with XIIa (n = 17). These results indicated the common transmission and genetic diversity of Cryptosporidium in sheep in southern Xinjiang, and further investigations are needed on the zoonotic potential of C. parvum and C. ubiquitum in this region.

Parameters of breeding traits of sheep of the new breed Artlukhsky merino

The planned breed for breeding in the Republic of Dagestan is Dagestan mountain breed. However, from sheep of this breed fine merino wool is not obtained, and the breeding of special merino breed for mountain and transhumant breeding system is an urgent problem. The purpose of the research was to characterize the main breeding traits in different sex and age groups of sheep of the new breed Artlukhsky merino, such as live weight, wool shearing and its qualitative parameters. Artlukhsky merino breed was bred by using Dagestan mountain breed on the ewes at the beginning stage of the rams of Stavropol breed, and at the final stage – Manych merino breed. The research of the parameters of the breeding traits has been made on elite and class I animals in the breeding farm of the APC “Krasny Oktyabr” in the Kazbekovsky area in the Republic of Dagestan. The live weight of sheep of different sex and age groups of the tested breed was 45–97 kg. The average fineness of wool fibers in adult rams was 23,3 microns (60 quality), in ewes – 22,9 microns (64 quality), in rams aged 12 months – 22,1 microns and young ewes – 20,9 microns (64 quality). The difference in the fineness of the wool on the side and thigh did not exceed one quality. The length of the wool fibers on the side on average in adult rams was at least 9,9 cm, in ewes – 9,4 cm, in young ewes – 10,2 cm and young rams – 10,4 cm. The yield of washed wool in the herd was at the level of 64 %, the fertility of ewes was 125 to 135 %. Thus, the indicators of the main selected traits in sheep of the new breed Artlukhsky merino are at the level of the best domestic breeds, such as Volgograd and Vyatka.

Spreading bowel paraziteies (Eimerii, Cryptosporidium)in sheep in the south regions of Azerbaijan

In 2018–2019 in order to study the dynamics of the spread of protozoan intestinal parasites, scatological studies of various age groups of sheep were carried out in private sheep-breeding farms in Masalli and Astara regions of the southern region of Azerbaijan. It was found out that in the farms of the Masalli region, the infection of sheep with eimeria is 30.7%, with cryptosporidium - 29.3%; in the farms of Astara region, respectively, 27.1 and 24.2%.

Application o f Inn ovative Aerospace Technologies f or Pastoral Farming o f Sheeps

Development of an innovative system of livestock husbandry based on the use of digital aerospace technologies and telemetry is a new modern direction in the development of the livestock industry, designed to solve the many problems of restoring fertility of soil and pasture for animals. To develop a methodology for remote assessment of pasture fertility, we used the technological capabilities of using unmanned aerial vehicles and satellite service, which allows us to study the dynamics of the NDVI (Normalized Difference Vegetation Index) of various pasture plots in the Stavropol Territory of the Russian Federation. The analysis of literary sources shows that the main problems associated with the complex automation of forecasting processes for complex objects are not technical, but methodological in nature and are caused by the lack of a theoretical base that should form the basis for creating the corresponding model and algorithmic support. A comparison of the results of a prognostic assessment of the nutritional value of fodder plants obtained from unmanned aerial vehicle (UAV) images, space services with actual nutritional values obtained from studies of the zoochemical composition of feeds showed a high degree of correlation. The UAV capabilities were recognized as promising for assessing the ethological characteristics of the Manych merino sheep, which allows to optimize the acquisition of groups of animals consolidated by forage activity. The article considers the issues of assessing the nutritional value of pasture feed and the vegetation index when raising sheep of the Jalgin merino breed in the conditions of the steppe regions of the Stavropol Territory. The introduction of remote assessment methods in pastoral livestock can optimize the cultivation of various sex and age groups of sheep and reduce the time to achieve production parameters by 5-8%.

Seasonal variability of palatability and nutrient intake in different age groups of range sheep

ABSTRACT The study was designed to analyze the seasonal dynamics of the nutritive value of endemic plant species (Berberis lycium, Indigofera heterentha, Parrotiopsis jacquemontiana, Rosa macrophylla and Rosa webbiana) and composite pasture grasses in different age groups of sheep using double indicator method. Twenty Kashmir Merino sheep from the two age groups in each season of summer (June) and autumn (October) were selected and divided into Group I (about 4 months of age) and Group II (1–2 years of age) in a 2 × 2 factorial design. The metabolizable energy (ME) of plants and composite grasses range from 10.11 to 12.60 and 7.32 to 9.94 MJ/kg, respectively, across different seasons. The quality of plants and the composite grass samples, measured in terms of total digestible nutrients, ME, crude protein and fiber content deteriorated with the advancement of the season. Palatability, nutrient and mineral intake, D and relative feed quality values were better during the summer than the autumn season. ME intake in younger sheep (Group I) was deficient by 32.5% compared to maintenance requirements during the autumn season. It was found that adult sheep tend to optimize their energy requirements from pastures while younger sheep fail to do so. Abbreviations: ADF: Acid Detergent Fiber; ADL: Acid Detergent Lignin; Ca: Calcium; CP: Crude Protein; D value: Digestible organic matter in dry matter; DCP: Digestible Crude Protein; DMI: Dry Matter Intake; EE: Ether Extract; ME: Metabolizable Energy; NDF: Neutral Detergent Fiber; OM: Organic Matter; P: Phosphorus; RFI: Relative Feed Index; TDN: Total Digestible Nutrients

English

A preliminary survey was conducted to determine the prevalence of some tick-borne haemoparasitic diseases (TBHDs) and their effects on the haematological parameters of sheep and goats in Maiduguri abattoir. A total of 200 blood samples were collected from sheep (n = 100) and goats (n = 100) from November 2015 to May 2016. Giemsa stained blood smears were prepared and examined under light microscope, to screen for haemoparasites. Packed cell volume (PCV) was determined by microhaematocrit centrifugation technique while haemoglobin (Hb) concentration was determined by Sahli’s method. The total white blood cell (WBC) and red blood cell (RBC) counts were estimated with Neubauer hemocytometer while erythrocyte indices were calculated. The results showed 13.5% overall prevalence of tick-borne haemoparasitic diseases in sheep 13 (6.5%) and goats 14 (7.0%). There was no significant (p>0.05) differences in prevalence of haemoparasites between sexes and age groups of sheep and goats. Anaplasma ovis and Babesia ovis were identified in the study of which A. ovis [23 (11.5%)] was higher (p<0.05) than B. ovis [2 (1.0%)]. A single co-infection of A. ovis and B. ovis was encountered in sheep. The mean values of PCV, Hb and RBC counts of infected sheep were lower (p<0.05) than the uninfected sheep. Similarly, the mean values of Hb and WBC of were significantly (p<0.05) lower in infected goats. This stud has reports important tick-borne haemoparasitic diseases in sheep and goats. We recommend tick control using suitable acaricides, periodic screening and treatment of small ruminants in Maiduguri. Key words: Anaemia, Anaplasma ovis, Babesia ovis, haemoglobin, packed cell volume, white blood cell count.

Electrocardiographic Analysis of ST-Segment Duration and Morphology in Sheep and Goats: Effect of Species, Breed, Age and Sex

The importance of obtaining normal values of ST-segment for specific breeds of animals besides the high variability of indices in small ruminant has been emphasized. The animals were assigned into 4 groups (G1-4), according to their age: G1<3 months, 3 months ≤G2< 1 year, 1 year≤G3<3 years, and G4 ≥ 3 years old. There were 34 animals in each study group. The animals were assigned to two comprising groups: sheep, goat, male and female. Also, the animals were divided into three groups according to their breed, including: Kermani sheep, Saanen and Cashmere (Raini) goats. The present study showed that sex, age and breed had no effect on ST-segment in sheep and goats and the obtained data can provide a good basis for judging the ST-segment length and morphology in difference sexes, breeds and age groups of sheep and goats.

Coenurus cerebralis and its pathology in an organized farm of Tamil Nadu.

Coenurosis is a disease of the central nervous system in sheep. A survey was carried out to assess the occurrence of Coenurus cerebralis in Madras red sheep. A prevalence rate of 12.30% observed when 122 slaughtered Madras red sheep were examined in an organized farm during 2002 to 2007 at Livestock Research Station, Kattupakkam, Tamil Nadu, India. The skulls of the animals were opened to know the prevalence of Coenurus cyst in the brain. Out of 12.30%, only 3.28% sheep showed clinical signs while the remaining were apparently healthy (9.02%). C. cerebralis cysts were observed in cerebrum, cerebellum and on spinal cord, averaging 66.67, 26.67 and 6.66%, respectively. Among different age groups of sheep, highest infection rate was observed in rams (20.69%) followed by ewes (10.00%), young males (9.09%) and young females (8.33%). Males (17.50%, 7/40) were more infected compared to the female sheep (9.76%, 8/82). Grossly, ventral cerebrum was congested and depression in sulci was noticed. Posterior portion of the skull showed severe congestion and haemorrhage. Severe congestion was also noticed on the gyri of right cerebral hemisphere.

Prevalence of Hydatid Cysts in Slaughtered Animals from Different Areas of Libya

The present study reports on the infection rates of hydatid cysts in both sexes and different age groups of sheep, camels and cattle from government abattoirs in different parts of Libya. An infection rate of 10.06% was recovered among 32,971 all ruminants (sheep, camels and cattle). Out 25314 of sheep, 2659 (10.52%) were infected. Out 7496 of camels, 940 (12.54%) were infected. Out 161 of cattle, 17 (10.56%) were infected. As regards to the infected organs, liver was seen to be the most commonly infected organ in sheep and cattle (46.03%; 52.94%, respectively), but in camels, it was the lung (55.21%). The fertility rates of hydatid cysts were 80% in sheep, 84% in camels and 0% in cattle. In sheep, the fertility rate of liver hydatid cysts was higher than that in other organs (53.85%), but in camels, the fertility rate in the lung was higher than that of other infected organs (66.7%). Thus, the incidence of echinococcosis in slaughtered livestock is noticeably high and denotes some hazards in control measures in Libyan abattoirs.

Periparturient transmission of Cryptosporidium xiaoi from ewes to lambs

The mechanism for the maintenance of Cryptosporidium infection in sheep between yearly lambing periods is not clear. Previously, periparturient shedding of oocysts as the result of stress from lambing was suspected to be a mechanism for the initiation of Cryptosporidium infection in lambs, but this has never been verified by genotyping studies. In this study, fecal specimens from four age groups of sheep in Inner Mongolia, China were examined for Cryptosporidium spp. by PCR-restricted fragment length polymorphism and sequence analyses of the small subunit (SSU) rRNA gene, including 59 ewes 1 week before parturition, 154 ewes at parturition, 87 lambs of 3–4 weeks, and 75 lambs of 15–16 weeks. The Cryptosporidium infection rate in ewes at parturition (7.8%) was significantly higher than at 1 week before parturition (1.7%). Higher infection rates were found in lambs (18.4% and 26.7% for 3–4-week-old and 15–16-week-old lambs, respectively). Most (10/13) Cryptosporidium-positive ewes were shedding Cryptosporidium xiaoi, which was also the dominant species (15/16) in neonatal lambs of 3–4 weeks in age (15/16). The less common species in ewes, Cryptosporidium ubiquitum, was not found in lambs of 3–4 weeks but was the dominant species (14/20) in lambs of 15–16 weeks. The major zoonotic Cryptosporidium species, C. parvum (of the IIaA15G2R1 subtype), was only found in one lamb. These data support the occurrence of periparturient transmission of Cryptosporidium spp., especially C. xiaoi, from ewes to lambs.

A Survey of Seasonal Infestation with Przhevalskiana Larvae in Slaughtered Goats and Sheep in South-western Iran

In this research slaughtered sheep and goats were investigated during August 2003-July 2004 at a slaughterhouse in Masjed-Soleyman, South-Western Iran. The number of infested animals with Przhevalskiana larvae and their age and sex was recorded. Collected larvae from infested animals were stored in Alcohol-Glycerin solution and were studied to determine their morphological properties and species. The data was analyzed by the chi-square test. Rate of infestation was 0.2 and 5.3% in sheep and goats, respectively. Infestation rate in male and female goats and sheep was significantly different (p<0.05). Prevalence of hypodermosis in sheep was significantly different in spring and winter, while infestation prevalence in goats was significantly different in four seasons of the year. Myiasis was seen more frequent in 2-3 and 1-2-year-old age groups of sheep and goats, respectively. The causative agents of goat and sheep hypodermosis were Przhevalskiana aegagri and Przhevalskiana crossii. The onset of fly activity was from late June to mid July.

Determination of prevalence and risk factors for infection with Babesia ovis in small ruminants from Turkey by polymerase chain reaction

In this study, PCR and thin blood smear-based diagnostic methods were used to assess the frequency of Babesia infection in small ruminants. A total of 300 sheep and 100 goats from 37 randomly selected herds located in eight locations of eastern Turkey were examined for the presence of Babesia infection and any tick species on the body of the animals. Of 400 blood samples examined, 6 (1.5%) were positive for Babesia spp. piroplasms upon microscopic examination, whereas 33 (8.25%) were positive for the presence of B. ovis by PCR. The prevalence of babesiosis in small ruminants detected by PCR was significantly higher than obtained in microscopic examination of thin blood smears (P < 0.05). Thirty-three animals produced the DNA fragment specific for Babesia ovis of which 32 (10.66%) were sheep and 1 (1%) was goat. The difference between the prevalence of Babesia infection in sheep and goats were statistically significant (P < 0.05). The prevalence of Babesia infection in different age groups of sheep were statistically non-significant (P > 0.05). The frequency of B. ovis infection was higher in herds with tick burden than no tick burden (P < 0.05). Seven amplicons (six from sheep and one from goat) were sequenced. The resulting sequences were identical to the recently reported nucleotide sequence of B. ovis. A total of 510 ticks belonging to the Rhipicephalus spp. were collected from sheep. Ticks were identified to be R. bursa and R. turanicus on the basis of morphological features.

Prevalence of Theileria spp. infection in sheep in South Khorasan province, Iran

The prevalence of Theileria spp. infection was studied in sheep in the South Khorasan province in Iran from 2003 to 2004. A total of 840 sheep from 34 flocks were clinically examined and investigated for the presence of Theileria spp. in the appropriate blood smears and any tick species on the body of the animals. In this study, 11.9% of sheep were infected with Theileria spp., with a parasitemia of 0.02–0.1%. Differences in the infection rates were statistically significant among different areas of the South Khorasan province. The highest prevalence was found in the Ferdows area (31.4%) and the lowest rate in the Nehbandan area (0.7%). The prevalence of Theileria spp. infection in males and females and between different age groups of sheep were not statistically significant. Seasonally, the prevalence of Theileria spp. infection in sheep reached its highest level in June (26.3%), whereas it decreased in July and August. It was found that 50.5% of the animals harbored Rhipicephalus sanguineus, 48.5% harboured Hyalomma anatolicum and 0.89% harboured Hyalomma dromedari.

Longitudinal study of the spread of ovine Johne's disease in a sheep flock in southeastern New South Wales

The aim of this study was to apply whole flock testing over time to determine the prevalence, distribution and spread of infection in a recently infected flock, with a view to planning intervention strategies for disease control. Serology, pooled faecal culture (PFC) and histology were used to determine the distribution and persistence of infection in a sheep flock in south east New South Wales between 1997 and 2002. Partial flock testing was done up to June 2000, after which annual whole flock testing, using PFC was performed. Faecal shedding of M a paratuberculosis was not detected in home-bred sheep until 7 years after the introduction of infected sheep in 1993. For at least 7 years there was clustering of infection and shedding within two age groups only. The infected groups appeared to have been exposed to infection (mycobacterial contamination) at an early age (<12 months) and commenced shedding at 5 years of age or older. Groups that were exposed to contamination as adults did not shed detectable amounts of M a paratuberculosis during the study period. Clustering of detectable infection in age groups of sheep that were exposed as lambs was a feature on this farm, providing indirect evidence of finite duration of survival of M a paratuberculosis on pasture and the influence of age on the susceptibility of sheep to develop detectable M a paratuberculosis infection. Spread of infection occurred very slowly and was probably related to the long incubation period (exposure to shedding interval) of 5 years observed on this farm. The findings suggest that partial flock culling, selective grazing management and vaccination could lead to a reduction in mycobacterial contamination on farm to a level at which patent infection no longer occurs. Better understanding of disease spread within flocks over time through flock profiling using PFC will help in devising surveillance strategies (including testing protocols for market assurance testing) to detect infected flocks where there has been clustering and slow spread of infection.

Body measurements in Bergamasca sheep

To investigate the evolution of Bergamasca sheep breed in the last two decades body measurements recently taken were compared with the breed standard (BMST) and with those from a previous study conducted in 1984 (BM84). Height at withers (HW), height at rump (HR), depth of body (DB), width at shoulders (WS), hearth girth (HG), anterior pelvic width (APW), middle pelvic width (MPW), body length (BL), distance from the front to the back margin (HOCK1) and from the lateral to the medial margin (HOCK2) of hock were measured on 495 Bergamasca sheep (466 ewes and 29 rams) from 14 flocks (seven sedentary and seven transhumance systems). Animals were grouped into 12–24 months and >24 months of age for the study. In general, a reduction of all body dimensions was observed compared to BMST and the largest decreases were for BL, APW and MPW. Compared to BM84, sheep older than 24 months were wider, with a slight increase in DB, HG and WS. Variations among these body measurements suggest that the breed standard need to be updated. Husbandry system (sedentary and transhumance) and age divided into 10 age classes of 6 months were also investigated as possible sources of variation for body measurements in females. Ewes raised in a transhumance system were taller, longer and showed a wider hock. On the contrary, ewes raised in a sedentary system were wider at chest and rump. Body measurements varied with increasing age: the smallest were for 12–18 months old ewes, whereas little variation was observed after 18 months of age. A factor analysis was used to study the interdependence among body measurements of young and adult sheep in each husbandry system. Two and four factors were retained in young and adult sheep in a sedentary system, whereas for both age groups of sheep in a transhumance system three factors were retained. In general, with the exception of young sheep in a sedentary system, the first and second factor showed largest positive association between variables and factors for measures concerning the width and height and the third was associated with body development. Since variation in body width was not associated with body height, body shape could possibly be improved to establish a tall animal with characteristic meat animal traits.

An epidemiological study on Babesia infection in small ruminants in Mashhad suburb, Khorasan province, Iran

The prevalence of Babesia infection was studied in sheep and goats in Mashhad area from 1998 to 2000. A total of 391 sheep and 385 goats from 77 flocks were clinically examined for the presence of Babesia blood smears and any tick species on the body of the animals. The study revealed that 26.1% of sheep and 14.8% of goats were infected with Babesia. The prevalence of Babesia ovis and Babesia motasi in sheep and goats were 23.5%, 0.5% and 14%, 0.5%, respectively. Double (mixed) infections occurred in 10 sheep (2.5%) and 1 goat (0.25%). The prevalence of Babesia infection between male and female and between different age groups of sheep and goats were statistically non-significant. Seasonally, the prevalence of Babesia infection in sheep reached highest level in August (56%), while a decrease was observed in September reaching the lowest level In February and March. The monthly prevalence of Babesia in goats was not significant. The clinical signs of Babesiosis were observed in 8% of infected sheep and 6.8% of infected goats. The percentage of infected sheep with higher parasitemia was more than infected goats. In this study, five ixodid species were collected from sheep and goats. The Rhipicephalus sanguineus and Hyalomma marginatum, were the most common species in sheep and goats. Other tick species encountered were Dermacentor daghestanicus in goats and Hyalomma anatolicum, Hyalomma asiaticum in sheep. The attachment sites of R. sanguineus and H. marginatum, H. anatolicum were around the anus, but D. daghestanicus was in the shoulder region.

The relationship between coccidal and helminth infections in sheep and goats in Kenya

Studies on prevalence of coccidian oocysts and their infection levels (oocysts g-1, OPG) were carried out among various age groups of sheep and goats from different geographical locations in Kenya. Prevalent species of Eimeria were identified and levels of infection with strongyle eggs (eggs g-1, EPG) examined. A significant difference was found in the EPG levels between various farms but not in the OPG levels; this was attributed to the relative susceptibility of various preparasitic stages of helminths to adverse climatic conditions, especially desiccation, compared with coccidian oocysts. There was a negative correlation between OPG levels and the age of animals as a result of acquired immunity. Between OPG and EPG values there was a positive correlation which is in tandem with the role of contamination in the acquisition of both types of infection. Sheep were found to shed significantly more oocysts and helminth eggs than goats; this could be related to the differences in their mode of feeding, i.e. grazing and browsing respectively. Young age (under 1 year) and confinement were found to contribute to high prevalence of oocysts in faecal samples. In sheep, a total of ten species of Eimeria were identified, the most prevalent being E. ovina (43%) and E. ovinoidalis (16.5%). In goat samples, eight species were identified, the commonest being E. arloingi (37.5%) and E. ninakohlyakimovae (35.2%).

Age-related respiratory responses to substance P in normal sheep

The in vivo effects of substance P ( SP) on respiratory parameters in four different age groups of sheep were examined. Intravenous sP (10 −8 to 5×10 −6 mol kg −1 bodyweight) caused a dose-dependent reduction in dynamic compliance and increase in respiratory resistance in all four groups. The bronchoconstrictor response was age-related, with the greatest response occurring in the youngest age group (four to six months). In the oldest group (over four years) there was minimal bronchomotor response to sP, but a dose-dependent apnoea was present. These findings indicate that there is an age-related alteration in the respiratory response to SP in sheep.

Convergence in mammalian nucleus of solitary tract during development and functional differentiation of salt taste circuits

To determine the type and extent of neural rearrangements that are made during functional differentiation of circuits for salt taste processing, we determined receptive field size and salt response characteristics of second-order taste cells in 3 age groups of sheep. Neurophysiological recordings were made from single cells in the nucleus of the solitary tract (NST) in fetal, perinatal, and postnatal sheep. Responses to NH4Cl, NaCl, and KCl were measured, and location and number of fungiform papillae in the receptive field were determined by stimulating individual papillae with anodal electrical current. The data are compared with previous, parallel measures from chorda tympani nerve afferent taste fibers to permit conclusions about convergence or divergence onto second-order cells. Receptive field size of second-order taste neurons increases during development, in contrast to the decrease in field size observed previously for chorda tympani nerve fibers during the same period. Furthermore, receptive fields of second-order cells are significantly larger than those of first-order fibers at perinatal and lamb ages, but not fetal. Thus, there is convergence of first-order taste afferents onto brain-stem neurons, and the convergence increases remarkably between fetal and perinatal periods. Associated with the increase in convergence are increased salt response frequencies relative to afferent fibers for NaCl in perinatal animals and lambs, and for KCl in lambs. The increase in frequencies occurs before NST neurons are functionally mature, as indicated by the rapid response adaptation of many cells in young animals. Convergence in NST during development apparently functions to maximize gain for processing neural responses to NaCl. In the periphery, response frequencies to NaCl are very low in fetuses, and increase progressively during development. In the NST, NaCl response frequencies are high even in fetuses, and remain high. The process of convergence onto second-order cells is accomplished with maintenance of order in afferent projections because receptive fields of NST neurons are composed of fungiform papillae that are clustered together, not dispersed over the tongue. Our quantification of taste receptive field size at 2 neural levels provides strong evidence for increasing convergence in the NST during development. Altering patterns of afferent neural input and geometry of second-order neurons may have a role in establishing convergence. The convergence has an apparently special function: to increase gain for NaCl taste sensation. Therefore, neural rearrangements during differentiation of salt taste pathways result in specific functional outcomes.