The reactivity of neonatal rabbits to the mammary pheromone as a probe for viability

Newborn rabbits depend on a daily nursing interaction with the mother to gain milk and to survive. During this interaction, they localise and seize the nipples displaying a typical behaviour triggered by maternal odour cues. The mammary pheromone constitutes such a signal in domestic rabbits: it elicits sucking-related movements in more than 90% of the pups. However, some newborns remain unresponsive to the presentation of the pheromone, even pups apparently healthy and highly motivated to suck. The main goal of the present study was therefore to explore the link between the unresponsiveness of rabbit pups to the mammary pheromone and their growth and survival in breeding conditions. To that end, 293 newborns from 30 litters were tested for their head searching-oral grasping responses to the mammary pheromone on days 1 and 3, and their milk intake and mortality were followed up from days 1 to 21. It was hypothesised that unresponsive newborns would have subsequent difficulties in finding nipples, sucking and surviving. Early weight and success in milk intake were further considered as mediating factors in growth and viability. The results showed that pups that were unresponsive to the mammary pheromone on day 1 were less successful in gaining milk and had a higher rate of mortality than the responsive pups. However, this impact was modulated by the weight of pups: it appeared only in the lightest newborns. Moreover, this impact vanished on day 3. On the other hand, the pup weight and sucking success on days 1 to 3 strongly influenced viability and growth during the period extending from days 1 to 21. Taken together, the results show that the day-1 responsiveness of rabbit pups to the mammary pheromone can be considered as an indicator of individual viability in pups having a small weight (<48 g on day 1). The predictive validity of the pups’ pheromonal reactivity seems however time-limited as it works only during the first, but crucial, postnatal days.     

Transformation of Escherichia coli in foodstuffs.

The plasmid transfer by transformation of Escherichia coli in 12 foods was investigated under conditions commonly found in processing and storage of food. Transformation occurred in all foods with frequencies of at least 10(-8) when a simplified standard transformation protocol with non-growing cells was applied. Higher rates (ca. 10(-7)) were found in milk, soy drink, tomato and orange juice. Furthermore, E. coli became transformed at temperatures below 5 degrees C, i.e. under conditions highly relevant in storage of perishable foods. In soy drink this condition resulted in frequencies which were even higher than those determined after application of a temperature shift to 37 degrees C. The transformation of cells growing in milk and carrot juice at a constantly kept temperature of 37 degrees C provides evidence for the potential of E. coli to become transformed naturally. With purified DNA frequencies were determined in these substrates of ca. 2.5 x 10(-7) and 2.5 x 10(-8), respectively. Similar frequencies were also obtained in milk containing the crude nucleic acids of homogenised cell suspensions of E. coli (pUC18). Moreover, the release of plasmid DNA from E. coli during food processing and the subsequent uptake of this DNA by growing E. coli cells was shown to take place after homogenisation in milk indicating a horizontal plasmid transfer by transformation of E. coli.     

Leptin treatment during lactation increases transfer of iodine through the milk

We have previously shown that protein restriction during lactation is associated with changes in iodine secretion into the milk and that a pup's serum leptin concentration was increased at the end of lactation. So, here we evaluate whether leptin treatment during lactation affects iodine transfer through the milk to the pups. Lactating rats were divided into two groups: the leptin (Lep) group, single injected with recombinant rat leptin (8 microg/100g of body weight, daily for 3 consecutive days), and the control (C) group that received the same volume of saline. We studied iodine transfer to the pups through the milk on Days 4, 12 and 21 of lactation. In those days, the dams were separated from their pups for 4 h. Then, the mothers received an injection of 131I (2.22x10(4) Bq ip) and the pups were allowed to nurse for 2 h. The animals were sacrificed 2 h later. Leptin, total serum T3 and total serum T4 concentrations were higher (P<.05) in pups of Lep mothers only on Day 4, suggesting a higher transfer of leptin through the milk at this period, probably with a direct stimulatory effect on thyroid hormone secretion. In other periods, however, even without a detectable increase in a pup's serum leptin concentration, maternal leptin administration increased the pup's thyroid iodine uptake (Day 12, 39%; Day 21, 34%), probably caused by a higher transfer of iodine through the milk, since they had a higher gastric content of 131I on Days 12 (31%) and 21 (128%).     

Nickel deficiency alters nickel flux in rat everted intestinal sacs

This study was conducted to determine nickel absorption in nickel-deficient rats. Jejunal segments obtained from dietary nickeldepleted (13 μg nickel/kg diet) and nickel-control (1 mg nickel/kg diet) adult rats from the first generation, and suckling pups from the second offspring were used. The nickel transfer across the intestinal epithelium and nickel uptake into the intestine were measured by use of everted jejunal sacs using a wide range of nickel concentrations administered on the luminal side (1.1 x 10^-8 M til 1.0 x 10^-4 M). Both the intestinal nickel transfer and nickel uptake were influenced by the dietary nickel supply in rat offspring, but not in the adult rats from the first generation. However, in nickel-deficient offspring, the nickel transfer across the small intestine was higher than in nickelcontrol offspring. This difference was greater using low intraluminal nickel concentrations than high nickel concentrations, and was significant at 1.1 x 10^-8 M, 6.1 x 10^-8 M, 5.1 x 10^-7 M, 1.0 x 10^-6 M, and 5.0 x 10^-6 M. Also, nickel uptake into the intestine was somewhat greater in nickel-deficient rat pups than in nickel-control pups, and significant using 1.1 x 10^-7 M and 1.0 x 10^-6 M nickel. A definite saturation type kinetic for the intestinal nickel absorption in relation to the intraluminal nickel concentration could not be observed.     

Cyclic 3', 5'-AMP relay dictyostelium discoideum. V. Adaptation of the cAMP signaling response during cAMP stimulation

In dictyostelium discoideum, extracellular cAMP activates adenylate cyclase, which leads to an increase in intracellular cAMP and the rate of cAMP secretion. The signaling response to a constant cAMP stimulus is terminated after several minutes by an adaptation mechanism. The time- course of adaptation stimuli of 10(-6) or 10(-7) M cAMP was assessed. We used a perfusion technique to deliver defined cAMP stimuli to [(3)H]adenosine-labeled amoebae and monitored their secretion of [(3)H]cAMP. Amoebae were pretreated with 10(-6) or 10(-7) M cAMP to periods of 0.33-12 minutes, and then immediately given test stimuli of 10(-8) M to 2.5 x 10(-7) M cAMP. The response to a given test stimulus was progressively attenuated and finally extinguished as the duration of the pretreatment stimulus increased. During concentration of the test stimulus. The responses to test stimuli of 10(-8), 5 x 10(-8), 10(-7), or 2.5 x 10(-7) M cAMP were extinguished after approximately 1, 2.25,2.5, and 10 min, respectively. 1.5 min of stimulation with 10(-7) M cAMP was necessary to extinguish the response of a test stimulus of 10(-8) M cAMP. Our data suggest that adaptation begins within 20 s of stimulation, rises rapidly for approximately 2.5 min, and reaches a plateau after approximately 10 min. The absolute rate of rise was faster during pretreatment with 10(-6) than with 10(-7) M cAMP. These results support a working hypothesis in which the occupancy of surface cAMP receptors leads to changes in two opposing cellular processes, excitation and adaptation, that control the activity of D. discoideum adenylate cyclase.     

Polygalacturonase enzyme production from bacterial isolated from raw milk and green and black olives

Forty microbial strains isolated from raw milk samples and black and green olives were grown in MP5 (mineral pectin 5) medium containing 0.5% lemon pectin. All strains synthesized an extracellular polygalacturonase. Rhodotorula sp. ONRh9 (0.44 U x mL(-1)) and Leuconostoc sp. LLn1 (0.16 U x mL(-1)), which had a more active polygalacturonase in MP5 medium, were studied in MAPG5 medium containing polygalacturonic acid. Highest biomass and polygalacturonase production by these two strains were observed for polygalacturonic acid concentrations of 10 g x L(-1) (Rhodotorula sp. ONRh9) and 5 g x L(-1) (Leuconostoc sp. LLn1) and for initial pH values of 6 (Rhodotorula sp. ONRh9) and 5.5 (Leuconostoc sp. LLn1). The two strains grown in fermenters in MAPG5 medium generated the following results: with controlled initial pH, Rhodotorula sp. produced maximum biomass (DO) and polygalacturonase (PG) after 20 h (DO, 3.86; PG, 0.24 U x mL(-1)) of growth, and this level was sustained until the end of the culture; Leuconostoc sp. LLn1 synthesized more cells and polygalacturonase between 4 h (DO, 1.80; PG, 0.17 U x mL(-1)) and 24 h (DO, 3.90; PG, 0.27 U x mL(-1)) of culture. With uncontrolled initial pH, the cultures produced maximum biomass and polygalacturonase after 20 h (DO, 3.30; PG, 0.26 U x mL(-1)) for Rhodotorula sp. ONRh9 and 10 h (DO, 2.84; PG, 0.17 U x mL(-1)) for Leuconostoc sp. LLn1.     

Influence of centrifugation and different extenders on post-thaw sperm quality of ram semen

Using a 2-step extension methodology to freeze ram semen, 2 freezing protocols (P1 and P2) and 3 extenders were evaluated in a split-sample experiment. The freezing protocols were tested in combination with Extenders A and B (Experiment 1), and B and C (Experiment 2). Protocol 1 included centrifugation before filling the straws to reconcentrate the diluted semen to a calculated sperm concentration of 800 x 10(6) cells/mL. Protocol 2 involved appropriate ejaculate extension to yield 800 x 10(6) cells/mL as in P1, albeit avoiding centrifugation. Extenders A and B were milk-based and were supplemented with 5% egg yolk and fructose. Extender B was clarified by centrifugation (twice at 3310 g/20 min). Extender C was based on TRIS-citrate-fructose supplemented with 20% egg yolk and clarified as described for Extender B. Final glycerol concentration was 7% for all 3 extenders. Post-thaw parameters studied were subjective motility, computer assisted sperm motility analysis (CASA), membrane integrity (SYBR-14/P1), and capacitation status (chlortetracycline assay, CTC). The overall sperm concentration (x 10(6)/straw) differed (P<0.001) between P1 (mean+/-SD, 138.1+/-14.8) and P2 (216.5+/-13.9). Despite centrifugation, P1 appeared to be less harmful for spermatozoa than P2, yielding higher percentages of subjective motility, linearity, membrane integrity and uncapacitated spermatozoa. Due to the difference in concentrations obtained between P1 and P2, the total calculated numbers of spermatozoa having desirable characteristics were higher in samples processed as P2. In Experiment 1, P1 resulted in lower calculated numbers x 10(6) in the Aldose of subjective motility (87.2+/-5.1 vs 125.3+/-5.1; P<0.05), linearity (70.6+/-4.3 vs 79.8+/-4.3; NS), intact-membrane (77.4+/-5 vs 108.5+/-5.1; P<0.001), and uncapacitated (36.5+/-2.5 vs 46.5+/-2.5; P<0.05) spermatozoa, than P2. In Experiment 2, calculated sperm numbers (x 10(6)/straw) were lower in P1 than in P2 for subjective motility (80.8+/-5.4 vs 92.0+/-5.4; NS), linearity (63.3+/-5.6 vs 73.1+/-5.6; NS), membrane integrity (77.7+/-3.6 vs 101.0+/-3.6; P<0.001), and uncapacitated spermatozoa (28.3+/-3.24 vs. 4.1+/-3.2; P<0.01). Extender B (clarified milk extender) was consistently better than Extender A (nonclarified milk extender) for all parameters studied, but the difference was only statistically significant for linearity after 1 h of incubation at 38 degrees C (44.0+/-2.4 vs 36.2+/-2.4; P<0.05). Extender B was also better than Extender C (TRIS-citrate-fructose) for percentage of uncapacitated (49.7+/-2.2 vs 34.4+/-2.3; P<0.001), subjective motile (57.5+/-2.7 vs 43.8+/-2.7; P<0.01), and linear motile (46.5+/-2.8 vs 33.7+/-2.8; P<0.01) spermatozoa, but not for membrane integrity (51.6+/-1.5 vs 51.7+/-1.5). It was concluded that exclusion of centrifugation, as in P2, yielded higher sperm numbers with desirable characteristics per straw. Clarification of milk-based extender (B) resulted in better post-thaw sperm quality, especially compared with TRIS-based extender (C).     

Possible role for phosphatidylinositol 3-kinase in regulating meiotic maturation of bovine oocytes in vitro

In this study 2 phosphatidylinositol 3-kinase (PI 3-kinase)-specific inhibitors, wortmannin and 2-[4-Morpholinyl]-8-phenyl-4H-1-benzopyran-4-one (LY294002), were used to investigate whether PI 3-kinase is involved in the signal transduction that leads to bovine oocyte maturation. Bovine follicular oocytes were cultured in vitro for 24 h in a basic medium consisting of tissue culture medium-199 supplemented with LH, FSH, fetal cow serum, Na-pyruvate and gentamicin. The oocytes were then examined for the stage of meiotic progression and degree of cumulus expansion. In Experiment 1, in cumulus-oocyte complexes (COCs), wortmannin, at any level tested (10(-8) M, 10(-7) M or 10(-6) M), had no effect on resumption of meiosis as judged by germinal vesicle breakdown and progression to prometaphase I or metaphase I. However, wortmannin significantly (P < 0.01) decreased the proportion of oocytes developing to metaphase II in a dose-dependent manner. In Experiment 2, when denuded oocytes were cultured with wortmannin at 0, 10(-7) M and 10(-6) M concentrations, the same pattern of response for COCs was observed, with no effect on meiotic resumption and a significant (P < 0.01) decrease in the proportion of oocytes reaching metaphase II. In Experiment 3, half of the recovered COCs were denuded and both denuded and intact COCs were cultured in the presence of 0, 2.5 x 10(-5) M, 5.0 x 10(-5) M and 7.5 x 10(-5) M LY 294002 before being examined for meiotic progression. Whereas LY294002, at any examined level, had no effect on the percentage of oocytes developing to metaphase I, it significantly (P < 0.01) decreased the proportion of metaphase II oocytes when used at 5.0 x 10(-5) or 7.5 x 10(-5) M for both intact COCs and denuded oocytes. In Experiment 4, no significant difference in the degree of cumulus expansion was scored after the COCs were cultured in the presence of wortmannin or LY294002 or in the absence of either treatment. These results provide indirect evidence for a role of PI 3-kinase in the bovine oocyte itself in regulating meiotic progression beyond metaphase I.     

Dietary trans-vaccenic acid (trans11-18:1) increases concentration of cis9,transll-conjugated linoleic acid (rumenic acid) in tissues of lactating mice and suckling pups

Lactating mice were fed trans-vaccenic acid (trans 11-18:1, TVA) to assess desaturation of TVA to cis9,trans11-conjugated linoleic acid (9/11CLA). Diets contained 30 g x kg(-1) 18:2n-6 (LA) or 20 g LA plus 10 g 18:0 (SA), TVA, or a CLA mixture (MCLA). Compared with SA, feeding TVA increased 9/11CLA concentrations in blood plasma phospholipid, triglyceride, and free fatty acid fractions. However, concentrations of 9/11CLA in plasma fractions were greater when MCLA was fed compared with SA or TVA. No 9/11CLA was detected in liver of mice fed SA, and it was only 1 mg x g(-1) of total fatty acids in the carcass. In contrast, 9/11CLA content of liver (5 mg x g(-1)) and carcass (6 mg x g(-1)) of mice fed TVA was similar to liver (5 mg x g(-1)) and carcass (7 mg x g(-1)) of mice fed MCLA. Mammary tissue of SA-fed mice had no detectable 9/11 CLA, compared with 5 or 14 mg x g(-1) for TVA or MCLA-fed mice. Stearoyl-CoA desaturase activity in mammary tissue from TVA-fed dams was 14% greater compared with SA. Activity of this enzyme in liver tissue was similar among treatments. In pups nursing TVA-fed dams, 9/1 ICLA accounted for 3 mg x g(-1) in liver but no 9/11CLA was detected in the carcass. In pups nursing MCLA-fed dams, however, 9/11CLA accounted for 8 and 6 mg x g(-1) in liver and carcass. Results indicated TVA desaturation enhanced 9/11CLA in tissues and milk fat.     

The ACTH/MSH(4-9) analogue ORG 2766 stimulates microtubule formation in axons of central neurons of the snail Lymnaea stagnalis.

Central nervous systems of the pond snail Lymnaea stagnalis were incubated in vitro in different concentrations of ORG 2766 (10(-9)-2.5 x 10(-4) M) for 10 and 20 h. Quantitative ultrastructural study of cross sections of the cerebral commissure showed that the number of microtubules in large axons had increased after 10 h of incubation by approximately 50% (Experiment 1) and 30% (Experiment 2), respectively. No further increase was observed after 20 h of incubation. (The higher concentrations were studied.) Maximal stimulation was already found at a concentration of 10(-8) M. At a concentration of 10(-9) M control levels were observed. It is concluded that ORG 2766 stimulates microtubule formation already at very low concentrations. It is not clear whether the compound stimulates synthesis of tubulin, induces assembly of microtubules, or causes an increase in stability of microtubules. Nevertheless, ultrastructural data on the morphology of the glial cells indicate that these cells are activated by ORG 2766 treatment, which suggest that ORG 2766 has general trophic effects.     

Optimisation of initial cell concentration enhances freeze-drying tolerance of Pseudomonas chlororaphis

The freeze-drying tolerance of Pseudomonas chlororaphis, an antifungal bacterium used as biocontrol agent was investigated. P. chlororaphis is freeze-drying sensitive and the viability drops more than 3 log units in the absence of protective freeze-drying medium. Of the freeze-drying media tested, lactose, sucrose, trehalose, glutamate, sucrose with glutamate, skimmed milk, and skimmed milk with trehalose, skimmed milk gave the lowest survival (0.6+/-0.2%) and sucrose the highest (6.4+/-1.2%). Cellular accumulation of sucrose from the freeze-drying medium and the protective effect of sucrose were dependent on sucrose concentration. The effect of initial cell concentration, from 1 x 10(7) to 5 x 10(10) CFU/ml, on survival after freeze-drying was studied for carbon starved cells with sucrose as freeze-drying medium. The highest freeze-drying survival values, 15-25%, were obtained for initial cell concentrations between 1 x 10(9) and 1 x 10(10) CFU/ml. For cell concentrations outside this window more than 10 times lower survival values were observed. P. chlororaphis was cultivated to induce stress response that could confer protection against freeze-drying inactivation. Carbon starvation and, to a lesser extent, heat treatment enhanced freeze-drying tolerance. By combining optimal cell concentration, optimal sucrose concentration and carbon starvation the survival after freeze-drying was 26+/-6%.     

Serum albumin-lipid membrane interaction influencing the uptake of porphyrins

It is frequently observed in pharmaceutical practice that entrapped substances are lost rapidly when liposomes are used as carriers to introduce substances into cells. The reason for the loss is the interaction of serum components with liposomes. To elucidate the mechanism of this phenomenon the partition of mesoporphyrin (MP) was systematically studied in model systems composed of various lipids and human serum albumin (HSA). As surface charge is an important factor in the interaction, neutral (1, 2-dimyristoyl-sn-glycero-3-phosphatidylcoline, DMPC) and negatively charged (1,2-dimyristoyl-sn-glycero-3-phosphatidylcoline/1, 2-dimyristoyl-sn-glycero-3-phosphatidylglycerol, DMPC/DMPG = 19/1 w/w) lipids were compared. The liposome/apomyoglobin system was the negative control. The size distribution of sonicated samples was carefully analyzed by dynamic light scattering. Constants of association of MP to the proteins and to the liposomes were determined: K(p,1) = (2.5 +/- 0.7) x 10(7) M(-1), K(p,2) = (1.0 +/- 0.7) x 10(8) M(-1), K(L,1) = (1.3 +/- 0.3) x 10(5) M(-1), and K(L,2) = (3.2 +/- 0.6) x 10(4) M(-1) for HSA, apomyoglobin, DMPC, and DMPC/DMPG liposomes, respectively. These data were used to evaluate the partition experiments. The transfer of MP from the liposomes to the proteins was followed by fluorescence spectroscopy. In the case of apomyoglobin, the experimental points could be interpreted by ruling out the protein-liposome interaction. In the case of HSA, the efflux of MP from the liposomes was strongly inhibited above a critical HSA concentration range for negatively charged vesicles. This effect was interpreted as the result of HSA coat formation on the liposome surface. This direct interaction is significant for small liposomes. The interpretation is fully supported by differential scanning calorimetry experiments.     

Melatonin in rat milk and the likelihood of its role in postnatal maternal entrainment of rhythms

The rhythm of melatonin in rat milk and the capacity of pups to synthesize and metabolize melatonin were studied. Melatonin was undetectable in milk in the light (< 21 pM), but increased rapidly 2-4 h after dark to peak at 357 +/- 66 pM at mid-dark. Oral or subcutaneous administration of melatonin to 5- and 10-day-old pups resulted in peak plasma melatonin levels 30 min after administration and rapid metabolism. Increases in pineal and plasma melatonin levels at night were detected at 5 and 6 days of age, respectively. Isoproterenol administration (2 microg/g body wt) at mid-light to day 10 pups increased plasma melatonin from 312 +/- 40 pM to 1,298 +/- 160 pM, whereas propranolol (2 microg/g body wt) suppressed nocturnal melatonin secretion from 1,270 +/- 128 pM to 395 +/- 66 pM. The rise of pineal and plasma melatonin in day 10 pups occurred 1 and 2 h after dark onset, respectively, preceding the onset in dams by 3 and 4 h, respectively. Propranolol administration to 2- and 5-day lactating dams inhibited plasma and milk melatonin at night but had no effect on their suckling pups. Transfer of melatonin via the milk is unlikely to provide an entraining signal for rat pups.     

Binding of transferrin-iron to the plasma membrane of a lactating rabbit mammary gland cell

1. Cells isolated from a lactating rabbit mammary gland have been investigated for transferrin-iron receptors. The existence of these structures has been demonstrated through a specific binding with a competitor non-labelled rabbit transferrin. 2. The interaction of iron-receptor complex depends on the concentration of [59Fe]transferrin, the number of cells and the time. 3. Scatchard's plot of data indicates two classes of receptor sites: one with a binding capacity 6.48 x 10(-9) g Fe per cell and affinity constant 2.48 x 10(10) M-1 and another with 1.06 x 10(-8) g Fe per cell and 4.66 x 10(11) M-1 respectively. 4. The probable mechanism of the iron transport from blood to milk through the lactating cell was discussed.     

3,5,3'-Triiodothyronine administered to rat dams during lactation increases milk yield and triglyceride concentration and hastens pups growth

It is known that lactation induces a mild hypothyroid state in rats and other mammals while thyroid hormone administration increases milk secretion in ruminants. The aim of this study was to investigate the effects of a moderate dose of 3,5,3'-triiodothyronine (T3), administered to rat dams during lactation on pups' growth and milk yield and composition. Primiparous Wistar rats with litters adjusted to 10 pups per dam received either tap water or T3 (75 microg/kg x day) in their drinking water from parturition till weaning. Food and water intake of dams and body weight of dams and pups were measured daily. In other groups of rats with similar treatments, milk yield of dams, macronutrient milk composition, and mammary arteriovenous differences for triglycerides (TG) and glucose were also determined. Dams treated with T3 ingested more food and their pups gained more weight than controls. Milk yield, milk TG concentration and glucose extraction by mammary glands were also higher in T3 treated dams. The results show that compensation of the mild hypothyroidism of the lactating rat may contribute to an increase in milk production and lipid levels, leading to an increase in growth of pups.     

Suckling ability and maternal prolactin levels in hypothyroid rats

Long-Evans rats and their offspring were made hypothyroid by addition of the antithyroid goitrogen 6-N-propylthiouracil (PTU) to the drinking water (0.1%) from the day of parturition. Serum concentrations of prolactin (PRL), thyroid-stimulating hormone (TSH) and thyroxine (T4) were determined by double radioimmunoassay (RIA). From the fifth postnatal day, body weight of PTU-treated pups was significantly lower than that of control rats, and a strikingly elevated serum TSH level and nondetectable amount of T4 were measured both in PTU-exposed mothers and their offspring at Day 10 postpartum. To test the youngs' suckling capability and the amount of maternal milk production, 10- and 15-day-old normal and PTU-treated pups were separated from their mothers for 4 hr in the morning and then reunited and allowed to suckle. Normal pups gained body weight at the end of both the first and second hour postreunion, while PTU pups gained only during the first hour and lost weight in the second hour of testing. When the pups were exchanged between normal and PTU mothers, opposite results were obtained, indicating that the reduced gain in hypothyroid rats was not due to impaired suckling capability, or insufficient sensory stimulation for milk secretion but to a decreased milk production of PTU mothers. In accordance with this, in lactating hypothyroid rats both the basal (presuckling) level and the suckling-induced rise of serum PRL were found significantly depressed.     

Competition for Milk in the Domestic Rabbit: Survivors Benefit from Littermate Deaths

We sought evidence for postnatal resource limitation among littermates of the domestic rabbit Oryctolagus cuniculus , and asked whether deaths of indi~vidual pups benefit survivors by increasing their share of milk. Milk ingestion, growth and mortality of 10 chinchilla-breed captive litters were recorded between birth and age 21 d. That milk limits growth and survival was indicated by larger litters showing lower weight gain and higher mortality, and by a significant positive correlation between milk ingested by individual pups and weight increase. Within litters, pups with higher birth weights grew faster, and weight hierarchies became increasingly stable over the 3 weeks, suggesting that advantages accrued during gestation were progressively consolidated during lactation. After individual pups died, the total daily milk weight obtained by the litter was generally unaffected but per capita milk consumption and growth of surviving pups increased, and increases in per capita consumption were greater in smaller litters. The most successful competitors for milk apparently benefit from the deaths of their littermates by obtaining an increased share of an undiminished daily food supply. This relationship has not previously been demonstrated in any vertebrate.     

Weaning and Parent-Offspring Conflict in the Domestic Dog

Weaning and signs of a parent-offspring conflict were studied in four females of the Swedish Dachsbracken breed of domestic dog and their pups. The animals were observed from the second to the seventh week of age of the pups. In addition to regular weighing, measurements of milk and solid food intake per pup and meal were also made, and samples of milk from the mothers were collected and analysed. The most important mechanism for weaning seemed to be on the behavioural level. The time that the mother spent with her pups decreased continuously from week 2 to week 7, as did the number of sucklings per hour. Furthermore, both duration of suckling and the number of sucklings initiated by the mother decreased during the period, while the proportion of sucklings where the mother was standing increased steadily. The weights of mothers stayed rather constant during the period and there was no difference in the amount of milk given per suckling or in the composition of milk between the early and late weeks of lactation. Consequently, costs for the mother, in terms of loss of weight, were negligible as she was able to compensate for the increased energy demand of lactation with an increased food intake. There was a tendency for care-giving behaviour to decrease and aggression from the mother to increase at the same time as there was a tendency for care-seeking and contact-seeking behaviour from the pups to increase. These changes, together with the less frequent initiation of suckling by the mother, could perhaps be seen as signs of conflict. Conflict was defined according to TRIVERS' theory (1974) and referred to the disagreement between the female and her pups about the amount of care given. However, although the animals were kept in a way that allowed them to perform as much as possible of their natural behaviour, the good nutritional conditions, one of the characteristics of captive life, may have reduced overt parent-offspring conflict.     

Demonstration of a quiescent period for feeding controls in the developing rat

Feeding behaviour of rats during development was assessed by weighing pups before and after a 4 h feeding session. During the first postnatal week, fasted pups gained significantly more weight than fed pups. This difference disappeared during the second week, but reappeared during the third week and persisted through the fourth week. In another series, pups were weighed at 2 and 4 h after beginning feeding. This showed that fasted pups aged 6 days compensate by suckling longer than fed pups. At 10 and 14 days of age there were no differences between fed and fasted pups at either 2 or 4 h, but from 16 days onward, fasted pups had eaten significantly more than fed pups at both times. A control experiment showed that the lack of compensation by fasted pups aged 10-14 days did not reflect lack of availability of milk. Video-analysis of suckling behaviour at ages 6, 10 and 15 days provided further evidence for lack of feeding controls during the second postnatal week: at 6 and 15 days fasted pups spent more time actively sucking than did fed pups. Whereas at 10 days, there were no differences between fed and fasted pups. It is concluded that feeding controls are present during the first postnatal week, become quiescent during the second week and reappear during the third week.     

Effect of macromolecule supplementation during in vitro maturation of goat oocytes on developmental potential

In vitro maturation (IVM) of goat oocytes with serum-supplemented media results in oocytes with reduced developmental potential. The objective of this study was to develop a defined medium for IVM of goat oocytes that better supports subsequent embryonic development. Cumulus oocyte complexes (COC) were matured for 18-20 hr in: Experiment (1), tissue culture medium 199 (TCM199) with 10% (v/v) goat serum or modified synthetic oviduct fluid maturation medium (mSOFmat) with 2.5, 8.0, or 20.0 mg/ml bovine serum albumin (BSA); Experiment (2), mSOFmat with 4.0, 8.0, 12.0, or 16.0 mg/ml BSA; or Experiment (3), 1.0 mg/ml polyvinyl alcohol (PVA; control), 4.0 mg/ml BSA, 0.5 mg/ml hyaluronate plus 0.5 mM citrate, or hyaluronate, citrate, and BSA. Mature COC were coincubated for 20-22 hr with 12-15 x 10(6) sperm/ml in modified Brackett and Oliphant (mBO) medium. Embryos were cultured for a total of 7 days in G1/2, and evaluated for cleavage, and blastocyst development, hatching, and total cell numbers. In the first experiment, more (P < 0.05) blastocysts developed per cleaved embryo following maturation in mSOFmat with 2.5 or 8.0 mg/ml BSA than with 20.0 mg/ml BSA or TCM199 with 10% goat serum. The various concentrations of BSA used in the second experiment did not affect (P > 0.05) any of the developmental endpoints examined. In the third experiment, developmental potential of oocytes matured with PVA or hyaluronate with citrate was not different (P > 0.05) from oocytes matured in the presence of BSA. These results demonstrate that developmentally competent goat oocytes can be matured under defined conditions.