Changes in the muscle fibre properties of the mouse temporal muscle after weaning

To clarify changes in the muscle fibre properties of the temporal muscle related to the start of masticatory movement, we immunohistochemically investigated myosin heavy chain (MyHC) isoform protein expression using pre-weaning and post-weaning mice. In addition, we examined the expression of a gene coding for those MyHC proteins. Immediately after weaning, isoforms with fast and potent contractility were frequent. This suggests that the temporal muscle plays an important role in a marked functional change in the oral cavity from lactation to mastication, contributing to oral function in cooperation with other masticatory muscles.     

The nuclei innervating digastric muscle do not project to the hypoglossal nucleus in the rat

We employed the retrograde neural tracing method using the pseudorabies virus bartha strain (PRV-Ba) to investigate the projection from accessory trigeminal nucleus (Acc5) or accessary facial nucleus (Acc7) to hypoglossal nucleus (HP). After injection of PRV-Ba into the bellies of the digastric muscle, the PRV-Ba containing neurones were observed in Acc5 of the cranial belly injected rats and Acc7 of caudal belly injected rats ipsilaterally, but not in HP. These results suggest that Acc5 and Acc7 may not project to HP and that movements of the digastric muscle are not related to cooperation with tongue movements during mastication.     

Characteristics of myofibres in the masseter muscle of mice during postnatal growth period

Functional maturation of muscles is related to the constitutional proportion of muscle protein isoforms during development and growth. Although the mouse masseter muscle (MS) is classified as a fast limb muscle, its functions are different from those of a limb muscle. This study investigated the differentiation of myosin heavy chain (MHC) isoforms during the postnatal development periods in mouse MS and mouse tibialis anterior (TA), which is a fast limb muscle. Many anti-MHC slow-type-positive fibres were observed in neonatal MS and TA; these fibres decreased during development. Adult MS was composed of anti-MHC fast-type-positive fibres. MHC isoforms in MS were composed of MHC-2a and MHC-2d soon after birth. MHC-2b was expressed, but MHC-2a was not seen after 21 days. Expression of MHC-2b agreed with the weaning period, that is 2-3 weeks after birth. This fact suggested that the transformation from suckling to mastication changed the MHC isoforms during this period. In this study, the expressions of MHC-2b agree with the weaning period.     

Relationship between weaning and secretion of luteinizing hormone, cortisol and transcortin in beef cows

The effects of suckling on secretion of luteinizing hormone, cortisol and transcortin were investigated in anovulatory postpartum cows. On d 35 postpartum, calves were separated from 12 cows to prevent suckling and eight calves continued to suckle their dams ad libitum. Between 35 and 41 d postpartum, samples of jugular blood were collected every 15 min for two periods of 6 h/d. In non-suckled cows, frequency of pulses and basal luteinizing hormone increased but amplitude of pulses did not change. Concentrations of total cortisol in serum of cows were not altered during 3 d after weaning calves and did not differ among intervals before, during and after a suckling event. Affinity of transcortin for cortisol was not affected by postpartum interval or treatment. Capacity of transcortin to bind cortisol tended to increase after weaning. We found no evidence to support the hypothesis that suckling reduces binding capacity of transcortin or increases unbound cortisol. Differences in preovulatory secretion of luteinizing hormone between suckled and non-suckled cows could not be accounted for by differences in secretion of cortisol. In beef cows that are fed to satisfy requirements for energy and have average body condition, we conclude that negative modulation of luteinizing hormone by suckling is not mediated by cortisol.     

Variations in the concentrations of the immunoglobulins IgG1, IgG2, IgM and IgA in sheep. 2. Changes in the blood of lambs of different breeds and crossbreeds during the course of the rearing period

The sera of 188 lambs from seven breed groups were analyzed for the concentrations of IgG1, IgG2, IgM and IgA by radial immunodiffusion using monospecific antibodies. From each lamb, 14 blood samples were drawn before and 5 samples after weaning. The following results were obtained: 1. Immunoglobulins could not be detected in sera drawn before the first intake of colostrum. 2. In normally suckling lambs, the peak concentrations of maternal immunoglobulins are attained at 0-18 hrs after birth. They can be assessed in a single blood sample drawn between 18 and 24 hrs. 3. The half-life times of maternal immunoglobulin in lamb sera are 11 days for IgG1, 7 days for IgG2, 6 days for IgM and 18 hours for IgA. 4. The absolute peak heights relate to the amounts of colostrum ingested before 12-18 hrs after birth. 5. The decline of maternal immunoglobulins in lamb sera over-laps with the onset of lamb immunoglobulin synthesis. Renewed rises of concentrations are observed for IgG2 after week 2, for IgM after week 3 and for IgG1 after week 7. The concentrations of IgA remain at the low levels characteristic for the serum of grown sheep. 6. The role of immunoglobulin synthesis in suckling lambs is only briefly and to a small extent reduced after weaning.     

Postweaning growth check in pigs is markedly reduced by intermittent suckling and extended lactation

The objective of this study was to determine whether intermittent suckling (IS) combined with an extended lactation can reduce postweaning growth check in pigs. Three weaning regimens [conventional weaning (CW), IS with 6-h separation intervals (IS6), and IS with 12-h separation intervals (IS12)] were compared. In CW (n = 17 litters), litters had continuous access to the sow until weaning (d 21, d 0 = farrowing). In IS6 and IS12, litters were separated from the sow for 12 h/d, beginning at d 14 and lasting until weaning (d 41 to 45). Litters were with the sow from 1400 to 2000 and from 0200 to 0800 (IS6, n = 14) or between 2000 and 0800 (IS12, n = 14). Litter size was standardized within 2 d after farrowing by crossfostering, resulting in an average litter size of 10.9 +/- 1.8 piglets. Piglets had ad libitum access to creep feed from d 7 onward. One week after the onset of IS (d 20), creep feed intake was increased in litters from both IS groups compared with CW litters (P < 0.05). Both IS groups consumed considerable amounts of creep feed before weaning (d 41 to 45). Total feed intake before weaning was greater (P = 0.004) in IS12 (3,808 +/- 469 g/piglet) than in IS6 (2,717 +/- 404 g/piglet). In comparison, CW litters consumed 18 +/- 9 g/piglet before weaning (d 21). Irrespective of weaning regimen, total feed intake of litters before weaning was highly correlated with post-weaning feed intake (P < 0.001). Furthermore, in all treatment groups, total preweaning feed intake was correlated with postweaning growth (P < 0.10). Irrespective of treatment, piglets suckling anterior teats grew faster than piglets suckling middle or posterior teats during the first 2 wk of lactation. Body weights at the end of the experiment (d 55) were similar among weaning regimens. Onset of IS induced a growth check in both IS groups (34% for IS12 and 22% for IS6). Only a mild growth check was observed after weaning of IS litters (14% for both IS groups). However, a serious growth check (98%) was observed after weaning of CW litters. Results of the current study indicate that IS stimulated feed intake during lactation, providing a more gradual transition to weaning. Because the IS6 regimen did not prevent the growth check after the onset of IS and is rather laborious, we suggest that IS12 might be preferable for a practical implementation of IS.     

The muscles of mastication in the caspian seal (Phoca caspica)

The muscles of mastication and their related skull characters in the Caspian seal (Phoca caspica) were anatomically examined and compared with those of the Baikal (Phoca sibirica) and ringed (Phoca hispida) seals. A well-developed masseter muscle was observed in the Caspian seal, whereas the temporal muscle consisted of thin bundles. The skull of the Caspian seal possessed the same thin frontal bone and the dorso-ventrally developed zygomatic arch found in the Baikal seal that are required to install the enlarged eyeball into the orbit. The temporal bone was not robust, and the digastric muscle was well-developed in the ventral space of the auditory bulla. The present results suggest that the skull form of the Caspian seal has changed morphologically from its ringed seal-like ancestors, and suggest that the evolutionary strategy of the muscles of mastication in the Caspian seal is principally consistent with that of the Baikal seal.     

Correlation between villous height and the disaccharidase activity in the small intestine of piglets from nursing to growing

Early weaning induces villous atrophy in the small intestine. Reduction in villous height in the small intestine after weaning is associated with reductions in brush‐border enzyme activity. Body weight gain after weaning is, therefore, correlated with villous height. This evidence suggested that the maintenance of small intestinal structure and function after weaning is important for the growth of young pigs. On the other hand, the relationship between villous height and the activity of the digestive enzymes in the small intestine has not been studied with piglets from the suckling to the growing period. Five suckling piglets, four piglets in the proximal stage of weaning, four pigs in the distal stage of weaning and four growing pigs were used. The activities of lactase (LA), sucrase (SA) and maltase (MA) were determined. LA showed a positive correlation with villous height in weaning. SA and MA were positively correlated with villous height from suckling to growing. In a previous study, non‐infectious dyspeptic diarrhea was frequently observed in growing piglets on Japanese swine farms. The maintenance of villous height to retain disaccharidase activity may prevent dyspepsic diarrhea in this stage.     

Insulin sensitivity and muscle characteristics in calves at different levels of physical activity

This study was undertaken to investigate insulin sensitivity and muscle characteristics in calves at different levels of physical activity. Ten male calves of the Swedish Holstein breed were allocated to either an exercise or a non-exercise group. The exercise group performed light work on a treadmill, 5-15 min at 10-12 occasions during 4-5 weeks. The treadmill speed varied from 0.6 to 1.5 m/s. At the beginning and end of the experimental period, the hyperinsulinemic euglycemic clamp technique was used to assess insulin sensitivity and gluteus medius muscle biopsies specimens were obtained for histochemical and biochemical analyses. There were no significant differences in insulin sensitivity, muscle fibre types, enzyme activities or glycogen content between the groups before or after the experimental period. The areas of type I, IIA, IIB fibres and mean muscle fibre area increased significantly in both groups during the experimental period. Muscle fibre characteristics and insulin sensitivity varied among the calves. Insulin sensitivity correlated positively to the percentage of type I fibres at the start of the experiment, and negatively to the mean muscle fibre area at the end of the experimental period. The results indicate that insulin sensitivity in young calves is associated with the change seen in muscle fibre areas with growth, but not by a short period of light physical activity.     

Quantification of mammary gland tissue size and composition changes after weaning in sows

The objectives of this study were to characterize the tissue compositional changes in porcine mammary glands after weaning and to determine whether administration of estradiol alters the profile of these tissue changes. Forty-five primiparous sows were assigned randomly to one of two treatment groups after weaning, control or estrogen treated. Estrogen-treated sows received twice-daily injections of estradiol-17beta (0.125 mg/kg of BW); control sows received vehicle injections. Sows were weaned at d 21 of lactation and killed on either d 0 (d of weaning; n = 5) or on d 2, 3, 4, 5, or 7 after weaning (n = 4 per treatment on each day). Teat order relative to suckling behavior was observed on the day before weaning to determine which mammary glands the piglets suckled. Suckled and non-suckled glands were identified from the teat order observation, and individual mammary glands were collected at slaughter. Mammary glands were trimmed of skin and extraneous fat pad, individually weighed, and bisected to measure cross-sectional area. The remaining half of each gland was ground and stored at -20 degrees C for chemical analyses. Frozen tissue was used for measuring tissue DNA, DM, protein, fat, and ash contents. Suckled mammary glands of sows undergo significant and dramatic changes during the initial 7 d after weaning, with significant changes occurring even by d 2 after weaning. Mean cross-sectional area of parenchymal tissue in suckled mammary glands decreased from 59.7 +/- 2.1 cm2 on the day of weaning to 26.8 +/- 2.3 cm2 by d 7 after weaning (P < 0.0001). Mammary gland wet weight decreased from 485.9 +/- 22.0 g on the day of weaning to 151.5 +/- 24.8 g by d 7 after weaning (P < 0.0001), whereas DNA decreased from 838.8 +/- 46.2 g on the day of weaning to 278.4 +/- 52.5 g by d 7 after weaning (P < 0.0001). The changes in gland wet weight and DNA during the period of mammary gland involution in the sow represent loses of over two-thirds of the parenchymal mass and nearly two-thirds of the cells that were present on the day of weaning. Estrogen treatment did not affect overall mammary involution during the first 7 d after weaning. Mammary glands that were not suckled during lactation had no further loss of parenchymal tissue during the first 7 d after weaning. Mammary gland involution in the sow is a rapid process and is probably irreversible within 2 or 3 d after weaning.     

Suckling behaviour in captive Dendrohyrax arboreus (Mammalia: Hyracoidea)

The suckling behaviour in four consecutive litters of a captive female Dendrohyrax arboreus is described. The young showed teat constancy which was established by day four of age without aggressive interactions, and maintained until weaning in all multiple litters. A preference for the more productive inguinal teats was apparent. Frequency of suckling bouts decreased with time but their duration increased. Most suckling occurred shortly after dawn and before dusk. The female showed decreasing maternal care in each successive litter.     

Studies on improving the fertility of aged sows. 3. Results of histological studies on puerperal involution and regeneration processes in the endometrium of lactating sows and sows after extremely early weaning]

Involution and regeneration following parturition was studied in 48 sows allowed to suckle their piglets normally, or from which the piglets were taken away at 5-8 days of age. Samples of uterus were obtained by biopsy 4, 8, 11, 14, 17, 20, 30, 32 and 40 days after parturition. In lactating sows, endometrial changes similar to those of oestrus in a normal cycle were present 32 days after parturition. This fact seems to justify the removal of piglets at 21-28 days of age. After very early weaning (5-8 days), incomplete oestrus-like changes in the endometrium were seen on the 17th day after parturition. The observed involutionary and regenerative changes in the puerperal uterus suggest that early weaning after 10-12 days of suckling is feasible, but it may be advisable to use drugs that would accelerate uterine involution.     

Age and exercise effects on mitochondrial density and capillary fibre ratio in bird leg muscle

1. Muscle fibre composition, capillary-fibre ratio and mitochondrial density of the Iliotibialis lateralis muscle were monitored during growth from the age of 8 weeks to sexual maturity (24 weeks) in sedentary birds and in birds subjected to regular treadmill exercise. 2. The Iliotibialis lateralis muscle consists almost exclusively of type IIA and IIB fibres with a small percentage of "unclassified" fibres. Over the 16-week period of growth there was no change in fibre composition but a marked fibre hypertrophy linked with a fall in the capillary-fibre ratio. Mitochondrial volume density increased with age but this was not significant. 3. Exercise significantly increased the IIA:IIB fibres ratio from 0.77 to 1.1 but had no significant effect on any other measured characteristics. 4. It is concluded that exercise at the intensity and duration employed (10-15 min daily, ca. 70-80% maximum oxygen consumption) has little effect on the growth and development of avian skeletal muscle although there was evidence of an increased oxidative capacity of the muscle.     

Desmotomy of the Accessory Ligament of the Superficial Digital Flexor Muscle in Equine Cadaver Limbs

Effects of longitudinal compression before and after transection of the accessory ligament of the superficial digital flexor (SDF) muscle were measured in eight equine cadaver forelimbs. When compression was increased from 890 N to 3115 N, the metacarpophalangeal (MCP) and carpal joints hyperextended 20 degrees and 4 degrees, respectively, and strain in the SDF and deep digital flexor tendons was increased 3.5% and 1.4%, respectively. The accessory ligament did not elongate. Immediately after transection of the accessory ligament at 3115 N load, a 2.8 mm gap formed between the transected ends of the accessory ligament, and the muscle belly of the SDF elongated and moved distad. The MCP joint hyperextended 15.8% further and strain of the SDF tendon increased 11.2% further. These results show that the accessory ligament transferred load in the SDF musculotendinous unit away from the muscle belly and that desmotomy altered this function. Decrease in the MCP joint angle indicated that the accessory ligament contributed to the support of the MCP joint under load. Increase in SDF strain after desmotomy was probably influenced by the change in the moment about the MCP joint and increased length of the SDF musculotendinous unit.     

Plasma protein profiles of neonatal pigs before and after suckling

Absorption of colostral proteins ingested by neonatal piglets within 24 to 36 h after birth is generally considered to be non-selective. Nevertheless, the transfer of colostral proteins, except immunoglubulins, from gut to bloodstream after natural suckling is still poorly characterized. The purpose of this study was to investigate the changes in 2-dimensional electrophoretic plasma protein profiles of neonatal piglets before and after suckling, in order to characterize the gastrointestinal absorption of colostral proteins into the neonatal bloodstream. As expected, the most significant change in plasma after suckling is the presence of a large amount of immunoglobulin. However, while the concentration of a few proteins was mildly increased in post-suckling plasma, the evidence of absorption of colostral non-immunoglobulin proteins by neonatal piglets was not detected in this study.     

Dietary fibre enrichment of supplemental feed modulates the development of the intestinal tract in suckling piglets

Background: Commercial pre-weaning diets are formulated to be highly digestible and nutrient-dense and contain low levels of dietary fibre. In contrast, pigs in a natural setting are manipulating fibre-rich plant material from a young age. Moreover, dietary fibre affects gastrointestinal tract(GIT) development and health in older pigs. We hypothesised that supplemental diets that contain vegetal fibres are accelerating GIT development in suckling piglets in terms of size and functionality. From d 2 of life, sow-suckled piglets had access to a low fibre diet(CON),a diet with a fermentable long-chain arabinoxylan(lc-AXOS), a diet with a largely non-fermentable purified cellulose(CELL), or a diet containing both fibres. During the initial 2 weeks, the control diet was a high-density milk replacer,followed by a dry and highly digestible creep meal. Upon weaning at 25 d, 15 piglets from each treatment group,identified as eaters and originating from six or seven litters, were sacrificed for post-mortem examination of GIT morphology, small intestinal permeability and metabolic profile of the digesta. The microbiota composition of the mid-colon was evaluated in a sub-set of ten piglets.Results: No major statistical interactions between the fibre sources were observed. Piglets consumed the fibrecontaining milk supplements and creep diets well. Stomach size and small intestinal permeability was not affected.Large intestinal fill was increased with lc-AXOS only, while relative large intestinal weight was increased with both fibre sources(P 0.050). Also, CELL decreased ileal pH and tended to increase ileal DM content compared to CON(P 0.050). Moreover, the concentration of volatile fatty acids was increased in the caecum(P 0.100) and midcolon(P 0.050) by addition of CELL. lc-AXOS only stimulated caecal propionate(P 0.050). The microbiota composition showed a high individual variation and limited dietary impact. Nonetheless, CELL induced minor shifts in specific genera, with notable reductions of Escherichia-Shigella.Conclusions: Adding dietary fibres to the supplemental diet of suckling piglets altered large intestinal morphology but not small intestinal permeability. Moreover, dietary fibre showed effects on fermentation and modest changes of microbial populations in the hindgut, with more prominent effects from the low-fermentable cellulose.     

Association between butyrate and short-chain fatty acid concentrations in gut contents and faeces in weaning piglets

The concentration and composition of short-chain fatty acids (SCFA) in gastrointestinal and faecal samples were studied in weaning pigs fed different amounts and composition dietary fibre (DF). In Trial 1 a total of 50 castrated piglets were fed five experimental diets with varying contents of citrus pectin (soluble fibre) and barley hulls (insoluble fibre) and gastrointestinal contents were collected at euthanasia 9 days after weaning. In Trial 2, 120 pair-wise penned piglets were allocated to the same experimental diets as in Trial 1 (24 piglets per treatment), and fresh faecal samples were collected 5 and 32 days after weaning.

There was no difference in the concentrations of SCFA caused by dietary treatments, but across treatments there was a correlation between concentration of SCFA and the proportion of butyrate. The correlation was lowest in the caecum (r² = 0.22, P = 0.0007) and highest in the distal colon (r² = 0.45, P = 0.0001). In faeces there was no relationship 5 days after weaning (r² = 0.004. P = 0.64) but a correlation of r² = 0.25 (P = 0.0001) 32 days after weaning. The results suggest that adaptive changes and differences between piglets in fermentative capacity immediately after weaning are associated not only with a higher concentration of SCFA but also a changed fermentation profile.     

Feeding and growth in a captive-born bottlenose dolphin Tursiops truncatus

The feeding and growth of a captive-born bottlenose dolphin Tursiops trunÄtus calf were studied for 30 months post partum. Changes in the behaviours associated with suckling were monitored and suggested that the mammary glands need tactile stimulation before the calf can feed. The calf exhibited no teat preference and mean duration of each suckling bout (4 s) remained constant throughout the suckling period. Suckling frequency declined rapidly during the first two months and continued decreasing steadily for the remainder of the study. A reduced growth rate from seven months suggests that nutrition obtained only from milk is insufficient; however, growth rate increased from 11 months, after the calf started feeding on fish. Solid food intake increased rapidly until completion of the study, by which time the calf was eating 16 kg of fish daily. Short-term reductions in food intake after weaning resulted in corresponding reductions in weight, but appeared to have no effect on linear growth.     

Effects of lamb sucking on the bacterial flora of teat duct and mammary gland of ewes.

We aimed (i) to determine differences in bacterial flora of teat duct and mammary gland of ewes before and after suckling, (ii) to evaluate factors potentially affecting those. We collected samples of teat duct material and mammary secretion from 11 ewes immediately before and after sucking by lambs, as well as 120 min later. We processed samples bacteriologically and compared changes in infection by the Sign Test. We isolated bacteria from 3.5% duct and 1.5% secretion samples before suckling. Respective figures post-suckling were 10.6% and 2.0%, and 120 min later 6.8% and 1.5%. We recorded differences in infection of duct samples before and after suckling in 40 cases; bacteria were isolated before suckling from six samples, whereas after it from 34 (p < 0.001). Also, we recorded differences in samples collected after suckling and 120 min later in 12 cases; bacteria were isolated immediately post-suckling from eight samples, whereas 120 min later from four (p = 0.375). No significant changes were seen for secretion. We found neither difference between ewes with single or twin lambs, nor among stages of lactation. Mostly, we isolated staphylococci: 70% of isolates before suckling, 80% of isolates after it, 91% of isolates 120 min later. After suckling we also isolated two Mannheimia haemolytica strains. Suckling predisposes to entrance of bacteria into the teat; however, increased teat infections did not result in mammary infections. Isolation of M. haemolytica post-suckling indicates that lambs act as source of infection for this pathogen.