Effect of food restriction on reproduction and lactation in house mice mated post partum

Primiparous, post-partum mated BALB/c bom inbred mice were allowed to raise litters of 6 young until Day 22 of lactation: 11 of 25 females were restricted to 60% of food consumption of ad-libitum fed dams after stud male removal at Day 2 of lactation. Since weight gain of restricted females during lactation was not inhibited and infanticidal behaviour was not enhanced, food deprivation can be considered to have been relatively mild. However, none of the food-restricted dams gave birth to a second litter whereas 12 of the 14 ad-libitum fed mice littered. This pregnancy failure is suggested to be due to implantation failure or abortion shortly after implantation, which is attributed to maternal manipulation rather than to immediate consequences of energetic demands of lactated young. The dynamics of the weight changes of dams and young suggest that milk production in suckling house mice drops most markedly between Days 17 and 18 of lactation, irrespective of whether the dams are non-pregnant, pregnant, or food-restricted.     

The effect of Ca-transport inhibitors on the excitability of the pregnant and post partum rabbit uterus

To continue an earlier study, a total of 54 uterine strips were excised from 25 days pregnant and post partum rabbits. These muscles were examined under a variety of experimental conditions to further define functionally their “activator-Ca” (A-Ca) which couples excitation with contraction under these two extreme regulatory states of the uterus. As in earlier studies, increasing the stimulus strength in graded steps from 2 to 80 V/5 cm revealed two distinct “peaks” of excitability, one at ～12 V/5 cm and another at ～60 V/6 cm, separated by a zone of inhibition. Knowing that effective “first peak” stimulation demands intact membrane function and the availability of A-Ca, while the “second peak” stimulation probably bypasses the membrane process and activates the contractile system directly by mobilizing Ca bound to intracellular structures, the effects on the strength-tension curve of normal and Ca-free KRB, excess KCl, Verapamil, Ruthenium-red and MnCl₂ were examined. These studies exposed again the different states of the A-Ca in the uteri of pregnant and post partum rabbits, which partly explain the functional differences of the myometrium under these two extreme regulatory conditions.     

Effect of season on luteal activity during the post partum period of dairy cows in temperate areas

Seasonal effects on luteal activity during post partum were evaluated in two consecutive studies in 253 dairy cows in Northern Italy. In study 1, plasma progesterone concentrations were determined on days 14, 21, 28, 35, 42, 49 and 56 post partum and in study 2 cows were synchronized and inseminated at a fixed time using two regimes based on the 'Ovsynch' protocol. Study 1: Animals were classified as luteal (progesterone >1.5 ng/ml in at least two consecutive samples) or non-luteal (progesterone <1.5 ng/ml in all samples). The proportion of cows without luteal activity from calving to day 56 post partum was 47/253 (18.5%). Of the 47 cows without luteal activity, 42 (89%) were detected during the warm months of the year and five were detected during the cold months of the year, and the effect of season was highly significant (P < 0.001). Study 2: Three study groups were established; control (CONT, untreated cows, n = 92), GPG (cows receiving gonadotropin-releasing hormone (GnRH) on day 0, PGF2α on day 7 followed by a second dose of GnRH 24 h later, n = 80); and HPH (the same as the GPG group, but with human chorionic gonadotropin (hCG) substituted for GnRH, n = 81). In the GPG and HPH groups, cows were inseminated 16 to 22 h after the second GnRH or hCG injection. Untreated cows were inseminated at first estrus after a voluntary weaning period. Because the effects of the GPG and HPH regimes on pregnancy rate were not significantly different, data were pooled into a single treatment group (TREAT). Pregnancy rates during the warm months of the year were 16% and 15% at first service and 65% and 66% at day 135 post partum for CONT and TREAT groups, respectively. Pregnancy rates during the cold months of the year were 36% and 38% at first service and 72% and 76% at day 135 post partum for CONT and TREAT groups, respectively. There was an effect of season (P < 0.05) but not of treatment on pregnancy rate. Treatment reduced the number of days from calving to conception during both the cold (101 ± 3.2 v. 121 ± 3.1 days; P < 0.001) and warm seasons (122 ± 3.2 v. 145 ± 3.1 days; P < 0.001). In conclusion, the present study shows that (i) heat stress during the warm season can compromise luteal activity and (ii) that regimes based on the Ovsynch protocol did not improve pregnancy rate at first service or by 135 post partum, but they had a positive effect on the calving-to-conception interval.     

The effect of lactation length on greenhouse gas emissions from the national dairy herd

Many governments have signed up to greenhouse gas emission (GHGE) reduction programmes under their national climate change obligations. Recently, it has been suggested that the use of extended lactations in dairy herds could result in reduced GHGE. Dairy GHGE were modelled on a national basis and the model was used to compare emissions from lactations of three different lengths (305, 370 and 440 days), and a current ‘base’ scenario on the basis of maintaining current milk production levels. In addition to comparing GHGE from the average ‘National Herd’ under these scenarios, results were used to investigate how accounting for lactations of different lengths might alter the estimation of emissions calculated from the National Inventory methodology currently recommended by Intergovernmental Panel on Climate Change. Data for the three lactation length scenarios were derived from nationally recorded dairy performance information and used in the GHGE model. Long lactations required fewer milking cows and replacements to maintain current milk yield levels than short ones, but GHGEs were found to rise from 1214 t of CO₂ equivalent (CE)/farm per year for lactations of 305 days to 1371 t CE/farm per year for 440-day lactations. This apparent anomaly can be explained by the less efficient milk production (kg milk produced per kg cow weight) found in later lactation, a more pronounced effect in longer lactations. The sensitivity of the model to changes in replacement rate, persistency and level of milk yield was investigated. Changes in the replacement rate from 25% to 20% and in persistency by −10% to +20% resulted in very small changes in GHGE. Differences in GHGE due to the level of milk yield were much more dramatic with animals in the top 10% for yield, producing about 25% less GHGE/year than the average animal. National Inventory results were investigated using a more realistic spread of lactation lengths than recommended for such calculations using emissions calculated in the first part of the study. Current UK emission calculations based on the National Inventory were 329 Gg of methane per year from the dairy herd. Using the national distribution of lactation lengths, this was found to be an underestimate by about 10%. This work showed that the current rise in lactation length or a move towards calving every 18 months would increase GHGE by 7% to 14% compared with the current scenario, assuming the same milk yield in all models. Increased milk yield would have a much greater effect on reducing GHGE than changes to lactation length, replacement rate or persistency. National Inventory methodology appears to underestimate GHGE when the distribution of lactation lengths is considered and may need revising to provide more realistic figures.     

The influence of days post partum on chloramphenicol absorption from the bovine uterus

Chloramphenicol at a single dose of 5.5 mg/kg of body weight was administered by intrauterine infusion to 12 normal cows at varying lengths of time ranging from 14 to 90 days post partum. At approximately 45 days following intrauterine infusion of the drug, chloramphenicol was administered intravenously to 10 of the same cows, again at a single dose of 5.5 mg/kg of body weight. Serum concentrations at various time intervals following the two routes of administration were then compared to determine the fraction of chloramphenicol absorbed from the uterus to the systemic circulation. Cows less than or equal to 60 days post partum absorbed an average of 27.4% of the dose from the uterus over a 48 hour period, while those greater than 60 days post partum absorbed 54.6% of the dose. However, this difference was not statistically significant when evaluated using the t-test at the 0.05 level of significance. The half-life (t (1 2 )) of chloramphenicol in serum was only 80 minutes. The data collected indicates extensive distribution of chloramphenicol to the tissues following intrauterine infusion and suggests the need for a two compartment model in describing chloramphenicol pharmacokinetics and for calculation of the fraction reaching the systemic circulation.     

Three-stage stochastic epidemic model: an application to AIDS.

A three-stage stochastic epidemic model extending the so-called classical epidemic process to one that includes time-dependent transition probabilities is described, and a solution to the appropriate set of forward differential-difference equations is given. When an individual can move from being a susceptible to one infected with the HIV virus to one diagnosed as having AIDS, we can use this general model to describe an AIDS epidemic process. We obtain expressions for the mean and variance of the number of AIDS cases for some special cases. By comparing these with actual data, it is suggested that, for some categories of cases (in particular, children), this model might be a plausible model to describe the underlying mechanism of the AIDS epidemic.     

The “activator-Ca” of the pregnant and post partum rabbit uterus

From 25 days pregnant and post partum rabbits, a total of 133 uterine strips were excised and studied $\text{in}$$\text{vitro}$ under a variety of experimental conditions, to define functionally the regulatory state of the “activator-Ca” (ACa) which couples excitation with contraction in these two extreme regulatory conditions of the uterus. Using Verapamil and Ruthenium-red (both of which inhibit Ca-influx), MnCl₂ (which, in addition, displaces Ca from binding sites), or EGTA (a chelating agent), excitability and ⁴⁵Ca-efflux, were measured. The studies showed that in the progesterone-dominated pregnant uterus the ACa is more strongly bound than in the progesterone-deficient post partum uterus and that extracellular-Ca plays a greater role in the activation of the latter than in that of the former. The effects on excitability of Ca-deficiency and inhibition of Ca-transport indicate that the site of strong binding of the ACa in the pregnant uterus is in or near the plasma membrane, partly accounting for the physiological character of this membrane under progesterone dominance.     

Varieties of stochastic model: a comparative study of the Gompertz effect

A comparative study is made of various models for the Gompertz phenomenon, which is a form of growth rate limitation in population dynamics. Deterministic, Markov birth-death, diffusion and stochastic differential equation models are studied, with a view to assessing their advantages and limitations.     

Establishing a beachhead: a stochastic population model with an Allee effect applied to species invasion

We formulated a spatially explicit stochastic population model with an Allee effect in order to explore how invasive species may become established. In our model, we varied the degree of migration between local populations and used an Allee effect with variable birth and death rates. Because of the stochastic component, population sizes below the Allee effect threshold may still have a positive probability for successful invasion. The larger the network of populations, the greater the probability of an invasion occurring when initial population sizes are close to or above the Allee threshold. Furthermore, if migration rates are low, one or more than one patch may be successfully invaded, while if migration rates are high all patches are invaded.     

The effect of lactation length on the circulating concentrations of progesterone and oestradiol in the early weaned sow

Eighteen crossbred multiparous sows were allocated at random to one of two lactation lengths: 42 or 10 days. All sows were mated at the oestrus after weaning and from mating until day 26 post coitum they were bled every second day. Progesterone and oestradiol concentration in the plasma was determined by radioimmunoassay. Progesterone increased more rapidly between days 4 and 10 post coitum in early weaned sows and the oestradiol surge at mating was abnormally extended for the same group.     

Influence of energy and nutrient supply pre and post partum on performance of multiparous Simmental,Brown Swiss and Holstein cows in early lactation

A study was conducted to evaluate the effects of pre partum (PRE) and post partum (POST) dietary energy and nutrient supply (E) and their interactions on feed intake, performance and energy status in dairy cows of three breeds. In this experiment, the effects of three energy and nutrient supply levels (low (L), medium (M), high (H)), both pre-calving and post-calving, were investigated, using a 3×3 factorial arrangement of treatments. In both phases (84 days pre- and 105 days post-calving) E levels applied to a total of 81 multiparous cows of breeds Simmental (SI), Brown Swiss (BS) and Holstein–Friesian (HF; n=27 for each breed), were 75%, 100% and 125% of recommendations of the German Society of Nutrition Physiology (GfE). Dry matter intake (DMI) was restricted, if energy intake exceeded target values. Pre partum DMI and energy intake were different as designed, liveweight and body condition score (BCS) of SI cows were higher, but EB was lower, compared to BS and HF cows. Milk yield and composition were influenced by all three main experimental factors (E_PRE, E_POST, breed). Energy-corrected milk yield was 25.6, 28.6 and 30.1 kg/day for L_PRE, M_PRE and H_PRE as well as 21.5, 30.1 and 32.6 kg/day for L_POST, M_POST and H_POST, respectively. Numerically, only for milk protein content the interactions E_PRE×E_POST and E_PRE×breed reached significance. Impact of energy supply pre-calving was more pronounced when cows had lower energy supply post-calving and vice versa. On the other hand, milk yield response of cows to energy supply above requirements was greater for cows that were fed on a low energy level pre partum. Impact of energy level pre partum was higher for HF cows, showing that their milk production relies to a greater extent on mobilization of body reserves. Increasing energy supply pre partum led to a more negative energy balance post partum, mainly by increasing milk yield and content, whereas feed intake was slightly reduced. Increasing energy supply post partum enhanced milk yield as well as milk protein and lactose content. Calculated energy balance corresponded well with liveweight and BCS change. Response of milk yield to increasing energy supply followed the principle of diminishing returns, since energy was increasingly partitioned to body retention. Increasing energy supply pre partum enhances milk yield and content post partum, but exacerbates negative energy balance and its consequences.     

Selective changes in gangliosides of human milk during lactation: a molecular indicator for the period of lactation

Gangliosides of human milk from women at various periods of lactation were analyzed. GD3 in colostrum, particularly in the early period of lactation, was the major ganglioside, and the molar ratio of GM3 to GD3 was 0.2-0.3 in the milk at 2-6 days postpartum. In contrast, milk from women at 60-390 days postpartum contained GM3 as the major ganglioside and the molar ratio of GM3 to GD3 was more than 3. Milk at 8-40 days postpartum represented an intermediate stage in terms of the ratio of GM3 to GD3. The selective change in the molar ratio of gangliosides was observed as a phenomenon common to all human milk from different individuals at different periods of lactation, indicating that the periods of lactation can be defined on the basis of the ratio. Since glycolipids in human milk are preferentially localized in the milk fat globule membrane, which is derived from the plasma membrane of epithelial cells in the mammary gland, the changes in the ganglioside composition reported in this communication may reflect a qualitative change of the cells in the mammary gland.     

On the therapy effect for a stochastic growth Gompertz-type model

We consider a diffusion model based on a generalized Gompertz deterministic growth in which carrying capacity depends on the initial size of the population. The drift of the resulting process is then modified by introducing a time-dependent function, called "therapy", in order to model the effect of an exogenous factor. The transition probability density function and the related moments for the proposed process are obtained. A study of the influence of the therapy on several characteristics of the model is performed. The first-passage-time problem through time-dependent boundaries is also analyzed. Finally, an application to real data concerning a rabbit population subject to particular therapies is presented.     

Distribution of births in an abrupt sequence: a stochastic model

A probability model for the distribution of number of births in a time segment (T0, T0 + T), where T0 is a distant time point since the start of the process, has been derived. The provision that birth propensities in the process of human reproduction may change over time has been considered. The model is illustrated with a set of observed data.     

The rat as an animal model for fetoplacental development: a reappraisal of the post-implantation period

Following implantation in rodents, the uterine stromal fibroblasts differentiate into densely packed decidual cells. This process, called decidualization, is well-orchestrated and progresses both antimesometrially and mesometrially, creating two regions with distinctive cellular morphologies. In addition, subsequent placental development is dependent on the invasion of the trophoblast, the process intimately linked to the endometrial tissue remodelling and depending largely on the environment created by the decidua; this phenomenon is crucial for the establishment and maintenance of pregnancy. The key mechanisms underlying the maternal tissue remodelling and trophoblast invasion remain poorly understood. The rat, just like human beings, exhibits a highly invasive type of placental development, the haemochorial placentation. For obvious ethical reasons, the studies of endometrial tissue remodelling throughout pregnancy in humans are greatly limited. Although the rat differs somewhat from humans with regards to the implantation process, it is an appropriate model for studying the mechanisms of decidualization as well as subsequent remodelling of the uterine tissues and fetoplacental development. As decidual remodelling is very closely linked to placentation and the maternal-fetal interactions in the rat show several important similarities to human placentation, the morphological alterations occurring during the post-implantation period in the rat have been addressed in the present review.     

Plasma prolactin concentrations during the ovarian cycle and lactation and their relationship to return of fertility post partum in the common marmoset (Callithrix jacchus)

A heterologous double-antibody radioimmunoassay was used to measure plasma prolactin concentrations in 27 marmosets. The assay was valid for the marmoset because plasma levels of prolactin were increased in response to TRH and metoclopramide and suppressed in response to bromocriptine treatment. During the cycle there were no consistent changes in plasma prolactin concentrations. During lactation mothers suckling single or twin infants had higher prolactin levels than did non-suckling females and levels were highest with twins. No statistically significant delay in the resumption of ovulation post partum was observed for the suckling and non-suckling females; conception occurred in all but one marmoset by 70 days post partum. These results show that neither the suckling stimulus nor high levels of prolactin post partum delay the return of ovulation and fertility in the common marmoset, a result in contrast to that for all other primate species so far investigated.     

Assessment of the post partum Reproductive Performance of the Icelandic Dairy Cow During a 3 Year Period

The time of ovulation, artificial insemination (AI), conception and conception rate were studied in 412 Icelandic dairy cows from 2 different areas during a period of 3 years. To assess these parameters the progesterone level was measured in sequential samples of milk and the status of the genital organs evaluated by monthly rectal palpations. The time and number of AI was recorded and the conception rate calculated and compared with the other parameters. Furthermore, the length of the calving interval and gestation period were determined. The effects of year, season, area, age, herd and parity on these parameters were evaluated. The overall mean for the time of first post partum ovulation was 42 days and varied from 29 to 49 days between herds. This is a considerably longer time than recorded for many other breeds of dairy cows. The effects of season, area and herd were significant for the time of first post partum ovulation. The overall time of first post partum AI and conception were 74 days and 97 days, respectively. In spite of late onset of ovarian activity in Icelandic dairy cows, these two pararmeters are comparable to those of other breeds of cattle. The effects of season, parity and herd were significant for these two parameters. The conception rate to first post partum AI was 59% and the number of AI per conception was 1.6. The time of conception correlated closely (r = 0.5) with the time of first post partum AI, but the conception rate to first AI increased and the number of AI per conception decreased with increasing time of first post partum AI. The calving interval was 382 days and the gestation period was 287 days.