BIRTH SPACING AND CHILD MORTALITY: AN ANALYSIS OF PROSPECTIVE DATA FROM THE NAIROBI URBAN HEALTH AND DEMOGRAPHIC SURVEILLANCE SYSTEM

SummaryThe majority of studies of the birth spacing–child survival relationship rely on retrospective data, which are vulnerable to errors that might bias results. The relationship is re-assessed using prospective data on 13,502 children born in two Nairobi slums between 2003 and 2009. Nearly 48% were first births. Among the remainder, short preceding intervals are common: 20% of second and higher order births were delivered within 24 months of an elder sibling, including 9% with a very short preceding interval of less than 18 months. After adjustment for potential confounders, the length of the preceding birth interval is a major determinant of infant and early childhood mortality. In infancy, a preceding birth interval of less than 18 months is associated with a two-fold increase in mortality risks (compared with lengthened intervals of 36 months or longer), while an interval of 18–23 months is associated with an increase of 18%. During the early childhood period, children born within 18 months of an elder sibling are more than twice as likely to die as those born after an interval of 36 months or more. Only 592 children experienced the birth of a younger sibling within 20 months; their second-year mortality was about twice as high as that of other children. These results support the findings based on retrospective data.

Accuracy of simplified sampling procedures for estimating milk composition in dairy ewes

Simplified designs of milk-composition recording, based on information from a single monthly milking, adjusted or not for interval between milkings and for milk yield, were simulated and evaluated for 2553 ewe-test-day records belonging to 155 lactations of Churra dairy ewes. Accuracy of simplified methods was evaluated by comparing estimated trait values (fat, protein, casein and total solid yields) with those observed both in a reference plan, where the two daily milkings were recorded at weekly intervals (A1), and in the official A4 milk recording (monthly records of the two daily milkings). Trait yields per lactation were estimated and adjusted to the only milking period (days in milk 30–120). Estimates of milk component traits were less precise when monthly designs, including the A4 design, were compared with a weekly sampling of both a.m. and p.m. milkings, with fat yield being the most difficult trait to estimate. All options with one daily milking every month were more accurate when the corresponding plan was based on, or began with, the a.m. milking. Adjustment for the preceding interval between milkings or milk yield did not improve sampling accuracy. The design alternating a.m. and p.m. milkings every month, without adjustment, is suggested for recoding milk component traits in dairy ewes.

Losses of precision associated with simplified designs of milk recording for dairy ewes

Simplified designs of milk yield recording based on the yield of a single monthly milking, adjusted or not for interval between milkings and for production level, were simulated and evaluated for 3173 ewe-test-day records belonging to 155 lactations of Churra dairy ewes. Losses of precision associated with simplified methods were evaluated by comparing estimated lactation yields with those observed both in a reference plan, where the two daily milkings were recorded at weekly intervals, and in the official A4 milk recording (monthly records of the two daily milkings). Estimates of lactation yields were less precise when the usual monthly designs were compared with a weekly sampling of both a.m. and p.m. milkings. The losses of precision were high at 9·4–36·2% including the A4 plan. The yield from only the milking period was more predictable than milk yield from the whole lactation (suckling and milking periods) and should consequently be adopted in dairy ewes. All options with one daily milking every month were more accurate when the corresponding plan was based on, or began with, the a.m. milking (loss of precision 14·9–15·8%). There was no evidence of improvement in sampling accuracy by adjusting for the preceding interval between milkings or production level. For practical and economic reasons, the design alternating a.m. and p.m. milkings every month, without adjustment, is suggested for ovine milk recording.

Spatial and temporal variations in pacemaking and conduction in the isolated renal pelvis

In renal pelvis preparations isolated from the sheep, the location of the pacemaker and the pathway of conduction of the electrical impulse in the pelvis were analyzed in detail. An electrophysiological acquisition system was used allowing simultaneous recordings from 240 extracellular electrodes. Reconstruction of the spread of activity showed that the site of the pelvis pacemaker was, in virtually all cases, located at the pelvicalyceal border and never in the body of the pelvis or in the area of the pelviureteric junction. One single pacemaker was responsible for a particular spread of activation, and fusion of activity originating from two or more pacemakers did not place. Furthermore, spontaneous shifts of the pacemaker could occur from one site to another along the pelvicalyceal border. Conduction from the site of the current pacemaker to the pelviureteric junction and the ureter was slow, inhomogeneous, and contorted. Multiple instances of partial or total conduction block were seen at all levels in the pelvis and were not restricted to the pelviureteric junction. The occurrence of the conduction block did not seem to be related to the length of the preceding interval, implying that the refractory period did not play a major role in the genesis of intrapelvic conduction block. In conclusion, high-resolution mapping of the renal pelvis is possible and reveals location and behavior of the pacemaker and documents inhomogeneities in conduction and conduction block.

Temporal Patterns of Feeding Behaviour in Free-Ranging Horses

Feeding was patterned into meals separated by intervals of non-random length. Meal length, which showed a marked circadian rhythm, was positively correlated with the length of the preceding interval (preprandial correlation) in all seasons except the summer. This result implies the existence of a control mechanism which maintained gut-fill high. The organisation of feeding within meals (length of feeding, standing and walking bouts) did not vary consistently between vegetation types, but was strongly influenced by the activity of biting flies.

Nucleolar Development in the Interphase of the Cell Cycle

Stereology of nucleoli at 3 different points of the cell cycle, in the middle of the G1, S and G2 of interphase, was accomplished in a naturally synchronous cell population rendered binucleate and thus ‘labelled’ and made identifiable by 1 h caffeine treatment in root meristems of Allium cepa L. Consistent structural changes were found so that nucleolar parameters by themselves can locate a cell at any interphase period. The growth of the nucleolus in the course of interphase takes place exclusively in its granular portion. The growth rate of this last component was found to be greater in the first half of interphase (5.4 µm5 h-1) than in the second (2.9 µm3 h-1), as calculated for a nucleus with only one fused nucleolus. The changes in volume of the nucleolar components during interphase do not parallel the gene dosage. Nucleolar surface at each point seems to be the factor which determines the growth rate in the preceding interval, since these rates are inverted for fused and unfused nucleoli. The nucleolar volume occupied by lacunae is minimal in the S-period and shows an enormous increase by the middle of G2. We think our data may be the structural basis on which a model for nucleolar functioning in proliferating cells could be built.

Behavior during Extended Exposure to a Multiple Fixed-Interval Adjusting Ratio Schedule of Reinforcement

Three pigeons were exposed to a multiple FI 2 adjusting ratio schedule of reinforcement for periods up to 218 sessions. The ratio requirement was equal to the number of responses in the preceding interval. Ratio response rates varied between those normally found with VR schedules and patterns of responding similar to those produced by FI contingencies.

A Chained Adjusting Ratio Schedule

3 pigeons were exposed to a chained FI 2, adjusting ratio schedule in which the ratio was equal to the number of responses emitted in the preceding interval. When the correlation between the interval output and the following ratio was removed, interval rates declined. A descriptive analysis of sequential interval output suggested an explanation for these findings.

568. The rate of secretion of milk and fat

1. The effects of variations in the length of the milking interval and of the preceding milking interval were measured for five cows.2. The yield of milk increased with the lengths and decreased with the square of the lengths of the milking interval and of the previous milking interval.3. The yield of fat increased with the length of the milking interval and the length of the preceding milking interval and decreased with the square of the length of the milking interval.4. The biological implications of each of the mathematical terms are discussed.5. The effect of the preceding interval was through a direct carry-over of residual milk and also by an effect on the metabolic rate of the alveoli throughout the following interval.6. The rate of secretion of both milk and fat declined with increasing milking interval; there was evidence that the rate of decline for the milk was greater than that for the fat, for the fat percentage of the milk tended to increase.