Weaning Mass Research Articles

Mass changes of grey seal Halichoerus grypus pups on Sable Island: differential maternal investment reconsidered

Theory predicts that where variance in reproductive success differs between sexes, as in many sexually dimorphic species, mothers should invest more in male than in female offspring. In pinnipeds, parental investment is the sole responsibility of the mother. Both size at birth and subsequent mass gain during lactation are measures of that investment. We studied mass gain of grey seal pups, a sexually dimorphic species, during lactation and mass loss during the first 13 days of the postweaning fast using longitudinal data obtained on Sable Island, Canada. A mixed‐effects repeated measures model was used to account for the serial correlation in these longitudinal data. We found no significant difference in the birth mass of male (16.6 ± 0.45 kg) and female (15.6 ±0.74 kg) pups. Rate of mass gain by males (3.0 ± 0.13 kg/d) and females (2.7 ± 0.12 kg/d) also did not differ significantly during the lactation period. Grey seal pups on Sable Island tended to be larger at birth and gain mass more rapidly (70%–100%) during lactation than those in the United Kingdom. Mass loss of weaned pups was curvilinear over time. Over the first 10 days of the fast, pups lost 22% of their weaning mass. In both males and females, large pups lost mass more slowly than small ones during the postweaning fast. Based on our results and a review of previous studies, we found little evidence of differential maternal investment in male and female grey seal pups.

Mass-transfer efficiency between hooded seal (Cystophora cristata) mothers and their pups in the Gulf of St. Lawrence

We investigated the efficiency of mass transfer in hooded seals (Cystophora cristata) through serial mass measurements on mother – pup pairs during lactation. Data on birth mass, weaning mass, pup growth, lactation duration, mass loss during the postweaning fast, and adult female mass were collected during the breeding seasons of 1988 – 1991. Pups weighed 24.4 ± 2.6 kg (mean ± SD, N = 19) at birth; males (25.3 ± 2.3 kg, N = 7) did not differ statistically from females (24.0 ± 2.7 kg, N = 12). During the nursing period pups grew at a rate of 6.9 ± 1.2 kg (N = 28) per day. Weaning took place at 3.8 ± 0.5 days of age (N = 19). Mass at weaning was not related to mass at birth. Pups were weaned at 47.1 ± 6.7 kg (N = 25). The mean value for weaning mass of males (47.6 ± 7.1 kg, N = 10) was not significantly different from that of females (46.7 ± 6.8 kg, N = 15). Ten percent of weaned pups stole milk from females after their own mothers had departed. Weaners, which consistently lost mass, did so at a rate of 1.3 ± 0.8 kg per day during the early part of the postweaning fast. At parturition, mean maternal body mass was 236.5 ± 35.5 kg (range 172 – 306 kg, N = 19). Mean maternal mass loss per day was 10.1 ± 2.6 kg. Efficiency of mass transfer from females to their pups was 63.2 ± 12.8% (N = 26).

Observations On Nursing Behaviour of Hooded Seals, Cystophora Cristata

Abstract This study reports the first quantitative data on nursing behaviour of hooded seals which have a four-day nursing period, the shortest known for any mammal. Twenty mother pup-pairs were observed at a whelping patch off the coast of Newfoundland, Canada during March, 1990. A total of 38 nursing sessions were recorded in 19 hours of observations. Pups nursed for an average duration of 5.5 min and at a frequency of approximately 2.4 bouts/ hour. Morning and afternoon rates were similar (x = 2.5 bouts/hr and x = 2.4 bouts/hr, respectively) and nocturnal nursing was witnessed. Pups were nursing for 18% of the total observation time which, assuming no diurnal pattern, would total 4.3 hr per day, the highest daily nursing duration reported for any phocid. We concluded that hooded seal nursing behaviour is another important factor in the unique lactation strategy attributed to a particularly unstable environment. It helps to ensure that pups attain sufficient weaning mass, double their birth weights, in the four-day nursing period.

A note on the early calving of beef heifers

The Nguni, the smallest beef breed in South Africa, was used !o investigate the advantages of mating beef heifers early. A group of 43 heifers was mated at 13 - 15 months of age, in contrast to the normal practice of mating heifers at 25 -27 months of age. No significant differences were found in calving percentage, fecundity percentage or mature cow mass between the two groups. However, there were significant differences in birth mass (24,8 versus 26,0) and weaning mass (156,3 versus 174,4) of the progeny produced by the two groups during the entire experiment" The main reason for the differences in weaning mass seems to be a lower milk production in the early calving group due to reduced udder development. The results suggested that without additional inputs early mating may not be a feasible proposition"

Finnsheep and their utilization in crosses with the Merino under range conditions of South-Africa

Two field trials were performed at two localities in a semiarid region to evaluate the performance of Finn (F) x Merino(M) crossbred females. The trials involved 781 F x M ewes and 657 M ewes. Ile de France, S.A. Mutton Merino, Dohne Merino, M, and F x M rams were used for matings. The F x M ewes were superior to M ewes in lambing-%, especially after mating as lambs, and the fecundities were 187and 107 %, resp. Multiple lambs of F x M ewes had better survival rates than those of M ewes. Lambs born from F x M ewes grew faster, had a larger weaning mass, over 10 % longer stables, ca. 2 mm thicker fibres, 30 % lower clean fleece weights, and a little less crimps/25 mm than those born from M ewes. Thus, F x M seemed to provide a suitable and acceptable composite showing remarkable adaptability to harsh environmental conditions. The results from the F x M wool and its special qualities can be regarded as useful attributes. Establishment of a composite F x M female line appeared well-founded.

Patterns of Postnatal Growth in a Laboratory Colony of Peromyscus leucopus

Phenotypic variation in postnatal growth was examined in 52 litters of Peromyscus leucopus. Male and female growth trajectories were similar during the preweaning period, but diverged during the postweaning period, and partial compensatory growth was exhibited with smaller weanlings growing more rapidly during the postweaning period. Litter size was not related to growth form, but the sex ratio of a litter affected the growth trajectory, with increasing proportion of males in a litter associated with decreased male growth during the preweaning period and lower male mass at weaning. Maternal mass also was correlated with offspring growth; larger females had offspring that grew rapidly during the postweaning period and attained a higher breeding mass. In addition, loss of mass by mothers during the late preweaning period was correlated with heavier neonate and weaning mass, and faster offspring growth during the early preweaning period. Maternal mass also was associated with litter frequency; heavier females were more likely to become pregnant at postpartum estrus.

Maternal Investment and Neonatal Growth in Phocid Seals

(1) This paper draws together information on neonatal size at birth, weaning mass, growth rates during the nursing period and duration of lactation of phocid seals in order to examine similarities and differences in these aspects of life-history patterns within the group. Broader interspecific comparisons are also made in order to evaluate the adaptive developmental responses of phocid seals during the period of maternal investment in contrast to terrestrial carnivores and to mammals generally. (2) Individual phocid offspring of most species are large and precocial, but female phocid seals as a group do not invest more energy per litter than many other carnivores and not substantially more than mammals generally at the time of parturition. (3) The relative mass of individual phocid seals at weaning is more uniform within the group than is mass at birth. This similarity is achieved by compensatory variation of growth rates and the duration of lactation. (4) Although data are limited, it appears that maternal investment differs between the sexes in all species which are sexually dimorphic with respect to body size.

Fitting Sigmoidal Equations to Mammalian Growth Curves

Three sigmoidal growth equations were tested for their usefulness in fitting mammalian growth curves. The von Bertalanffy, Gompertz, and logistic equations were fitted to growth data by nonlinear regression techniques. The residual sum of squares and deviations of predicted neonate, weaning, and adult masses from observed values were used as criteria to choose among the models. The von Bertalanffy equation provided the smallest residual sum of squares, while the Gompertz equation fitted equally well by this criterion. The logistic equation overestimated neonate mass and underestimated adult mass, the Gompertz overestimated neonate mass, and the von Bertalanffy overestimated weaning mass. The Gompertz model was chosen to fit a sample of 331 species; growth rate constants, K , for these species are presented. The relationship of K to adult mass was calculated and was found to have a slope similar to that of altricial birds. K -values were found to be comparable to those reported by Case (1978) and consistently higher than those of Millar (1977). Species having differing rates from those reported by Case or Millar were also identified; ground squirrels had faster growth rates and seals had slower growth rates when rate of growth was estimated by the Gompertz equation.

The efficiency of Afrikaner, Bonsmara, Simmentaler and hereford cattle in a sub-tropical environment

Norms for the performance of 4 breeds of cattle were studied. Bonsmara cows (434.8±3.5 kg) were the heaviest, followed by Simmentaler (418.7±3.9 kg), Afrikaner (411.6±4.0 kg) and Herefords (385.6±4.5 kg). Breeds differed significantly in terms of the preweaning growth of their calves. Simmentaler (212.3±2.6 kg) and Bonsmara (216.2±2.5 kg) were superior. A breed x age of cow interaction in terms of preweaning growth of the calf was established. Actual weaning mass of the calves appeared to have the most important influence on cow efficiency apart from weaning percentage.

Beef production systems and sales strategies in an extensive ranching region in South Africa

Rainfall variability and stocking rate in extensive ranching regions in the Northwestern Transvaal, South Africa, can have substantial influence on feed availability per animal and thus on beef production. A simulation model was developed to compare the degree of variability of revenues from four beef production systems, ranging from inflexible weaner marketing to marketing of 3-year-old oxen. Regression equations relating stocking rate and rainfall to calving percentage and weaning mass, and actual rainfall data over a period of 54 years were used in the analysis. Results indicated a lower mean revenue with a low income variation for the more intensive weaner system as compared to the more flexible 26–28-months and 39–42-months oxen production systems. Thus, in this area, characterised by low and rather variable rainfall, superior economic results can be obtained by choosing flexible production systems and marketing strategies.

Continuous grazing oncenchrus ciliaris

Abstract Breeding cattle grazed Cenchrus ciliaris continuously for four years. Excellent calving percentages (mean 95,25%) and good weaning masses (mean 245 kg) were obtained, the A.D.G.’s being 0,963 kg for heifers and 1,075 kg for bulls. The system was planned to eliminate grazing management as a factor.

The development of a production system for beef animals onCenchrus ciliarispasture : Part II

Abstract Thee years’ results from a trial designed to develop a production system for a breeding herd of beef animals are presented. The trial, located in the northern Transvaal, comprised 30 ha of dryland Cenchrus ciliaris grazed by 30 cows and their calves. During the 1973/74, 1974/75 and 1975/76 seasons the pasture produced 283, 262 and 207 grazing days/ha as well as 2,7, 1,8 and 4,1 tonnes of hay/ha respectively. Average 205‐day corrected weaning masses of the heifer calves were 189, 196 and 184 kg, and that of the bull calves 200, 208 and 188 kg respectively.