Variation In Reproductive Performance Research Articles

Visual monitoring of reproduction in dairy herds

Two complementary approaches to produce visual information from reproduction records are described and exemplified. The Event Display shows all reproductive events, over a year, for all cows in a herd, by symbols placed in an array with columns representing calendar weeks and rows representing individual cows. The Reproduction Monitor consists of graphs of insemination and pregnancy rates evaluated weekly with a Bayesian technique. These visual monitoring tools are well suited to explore temporal variation in reproductive performance, they provide a quick overview of herd performance, and they provide information about individual animals.

Importance of Rabbits in the Diet and Reproductive Success of Black Kites in Southwestern Spain

The rabbit Oryctolagus cuniculus is the most common prey of many predators in Mediterranean ecosystems, but how its abundance affects the productivity of its predators has been poorly studied. The Black Kite Milvus migrans is a generalist predator, but in our study area eats mainly rabbits. There was considerable year to year variation in the proportions of the nine prey types examined in the diet. The abundance of young and sick rabbits seemed to determine the consumption rate of rabbits by Black Kites. Interannual variation in reproductive performance (chick starvation mortality, fledging weight and length of the nestling period) was related to the proportion of rabbits in the diet, a year of high performance coinciding with a high proportion of rabbits in the diet. Some factors explaining the importance of rabbits for the reproductive success of this raptor are discussed.

Genetic basis of variation in reproductive performance. (2) Genetic correlation between gestation length and prolificacy in sheep

This study was based on analysis of records of gestation length, prolificacy, multiple birth, body weight and total birth weight for 7,083 ewes of the Arcotts (Canadian, Outaouais and Rideau; three synthetic strains developed at the Animal Research Centre, Ottawa, Canada), Suffolk and Finnish Landrace (Finnsheep) breeds. Sheep were housed indoors, in a controlled environment. Ewes divided into two flocks with equal contribution of genetic material were bred in January, May and September months at the end of a period of short days, to lamb alternately at 4-month intervals under an 8-month breeding cycle. Breed, prolificacy, year and breeding season has significant effects on gestation length of the ewe. The Canadian Arcott and Suffolk ewes, both meat-type sire breeds, had gestation lengths of 147 and 146 days, respectively, compared to 145 days for Outaouais and Rideau Arcott ewes and 144 days for Finnsheep ewes, all fecund-type dam breeds. There was a progressive reduction of gestation length within breed as prolificacy increased from ewes bearing single to quintuplet lambs. Though significant, the magnitude of the breeding season effects was negligible. Sex of lamb, age and body weight of the ewe had no influence on gestation length ( P>0.05). Heritability based on paternal half-sib estimates for both gestation length and prolificacy was 0.18. The estimates of genetic and phenotypic correlations between gestation length and prolificacy were 0.09 and 0.06, respectively. Although the frequency of multiple birth is highly variable, its heritability estimate of 0.04 and its positive genetic correlation with gestation length of 0.43, indicates multiple birth would not be a useful selection criterion for reducing gestation length. Selection for prolificacy, despite its 40–43% variability, would have little effect on gestation length because of the poor correlation between the two traits. Therefore, to reduce a 21-week gestation length by one week, despite the 2% variability in gestation length, direct selection for shorter gestation appears to be the best option. It is doubtful that there would be any economic advantage in reducing gestation length by selection in view of the limited reduction achievable.

Effect of pod zone moisture content on reproductive growth in three cultivars of peanut (Arachis hypogaea)

Very little research has been done to investigate the effect of a dry podding zone on reproductive development in peanut plants that are otherwise well hydrated via subsoil moisture extraction. The influence of podding zone moisture content on reproductive development and growth of three peanut cultivars (McCubbin, Gajah and Robut 33-1) was investigated in pots grown in the glasshouse. In two cultivars (McCubbin and Gajah) seed yield was reduced in a dry (air-dry) compared to a wet (field capacity) podding zone. Seed yield of Robut 33-1 was unaffected by podding zone moisture content, indicating that cultivar variation in reproductive performance in response to podding zone moisture may exist.

Genetic basis of variation in reproductive performance. I. Ewe lambs treated with fluorogestone acetate and PMSG in a controlled environment

This study involved records on fertility, prolificacy, multiple birth, fecundity, body weight and age at breeding of 2380 ewe lambs from 432 sires of three synthetic strains developed at the Animal Research Centre, Ottawa, Canada. Ewes were divided into two equal flocks which were bred to lamb alternately at 4-month intervals under an 8-month breeding cycle. Lambs were housed indoors, in a controlled environment, on expanded metal mesh floors in windowless barns and were bred in January, May and September at the end of a period of short days. Ewes that lambed were generally heavier and slightly older at breeding as were ewes that lambed to mating at the synchronised estrus. Though not significant, trends demonstrating seasonal differences in the heritabilities of all reproductive traits were observed. Paternal half-sib estimates showed fertility, prolificacy, multiple births and fecundity were non-heritable in ewes lambing to matings at the synchronized estrus. Heritability estimates for prolificacy and multiple birth were 0.22 and 0.13, respectively, in ewes lambing to matings at the synchronized plus follow-up estrus, suggesting that slow genetic progress can be achieved in these traits from selection. Heritability estimates ranged from 0.03 to 0.22 for body weight and from 0.28 to 0.54 for age at breeding. Ewes that lambed showed lower values than all ewes exposed. Phenotypic correlations between reproductive traits and either body weight or age at breeding were low and ranged from 0.04 to 0.09. There were higher estimates of genetic correlation of prolificacy (and multiple birth) with either body weight or age at breeding in ewes lambing to matings at the combined estruses. Indirect selection of ewe lambs based on age and body weight at breeding may be an effective alternative to direct selection for genetic improvement of prolificacy and multiple birth.

Effect of PMSG dosage on the reproductive performance of adult ewes and ewe lambs bred at a progestagen-PMSG synchronized estrus

The effect of dose of pregnant mares' serum gonadotropin (PMSG) on the reproductive performance of adult ewes and ewe lambs and lamb survival at birth after treatment with fluorogestone acetate (FGA)-impregnated intravaginal sponges and PMSG (250 IU or 500 IU) to synchronize estrus was evaluated. Ewes were exposed to rams for breeding at the synchronized and subsequent estrous cycles. The flock, comprised of three synthetic strains and two control breeds, was maintained in a controlled environment and exposed to an artificial light regimen which alternated at 4-mo intervals from 16h of light daily to 9h of light daily. Trials were conducted during January, May and September at the end of a 9-h daylength cycle. Adult ewes were bred in May and 8 mo later in January. Ewe lambs were bred in September at 6.5 to 7.5 mo of age. The overall reproductive performance of the adult ewes was similar at the two breedings: fertility ∼90%, prolificacy ∼2.7, fecundity ∼240% and lambs born alive ∼2.4. Dosage of PMSG had no effect. Reproductive performance of ewe lambs was lower and there was a strain × treatment interaction, suggesting greater variability in response. The results indicate there is no advantage to using a higher dose of PMSG in ewes with a natural relatively high fecundity. Moreover, the use of the artificial photoperiod appears to overcome the natural seasonal variation in reproductive performance.

Reproduction in Stephens' Woodrat: The Wages of Folivory

The reproductive pattern of Stephens' woodrat ( Neotoma stephensi ) reflects strong selection for energy conservation. We hypothesize that the major selective force is this woodrat's dietary specialization on juniper foliage, a food rich in defensive, digestibility-reducing chemicals. Compared to most other rodents, and to other species of woodrats, Stephens' woodrat has small litters (usually a single young); each litter comprises a small percentage of the mother's weight (8%), young grow slowly and are weaned late, and there is broad temporal overlap of suckling and feeding on solid food. In addition, females attain reproductive maturity late (typically at some 10 months of age), commonly suffer severe weight losses during lactation, and many individuals recover this weight slowly after lactation. Most natality occurs in the period from March through May; of the females that live to reproduce, only 15% survive to reproduce a second season. Dietary selectivity—the use of foliage from specific trees with relatively low levels of defensive chemicals—is probably learned in the long pre-weaning period and may allow females to maximize milk production, growth rates and survival of her young, and, by minimizing lactation weight losses and the time necessary to regain weight, may shorten the interval between litters. Wide variation in reproductive performance among females may be associated with differences among den sites with respect to access to junipers with low levels of defensive compounds.

Grading and rotational crossbreeding of beef cattle. I. Reproductive performance.

Purebred Angus (A), Polled Hereford (PH) and Santa Gertrudis (SG) bulls were mated to grades, two-breed and three-breed rotational crosses of these breeds (seven herds) to produce three generations (G1, G2 and G3) of calves. The grade A and PH cows were higher in A and PH breeding, respectively, than grade SG cows were in SG breeding. Reproductive performance among grade and rotational-cross herds was evaluated for herd differences, heterosis and effects of various genetic components. For cows that produced G1 calves, the proportion of cows that calved, had a live calf and weaned a calf was higher (P less than .01) for those that calved compared with those that failed to calve the previous year. For cows that produced G2 and G3 calves, previous year's calving status did not affect (P greater than .05) reproductive performance. Grade A and PH were similar (P greater than .05) in reproductive performance during G1, G2 and G3. As generations advanced, SG decreased in reproductive performance. Except for the PH-SG rotational cross in G3, the A, PH and all two-breed rotational crosses and the three-breed rotational cross generally were similar (P greater than .05) for the three reproductive traits during each generation. Within generations, reproductive performance was similar (P greater than .05) between rotations within each of the two-breed rotational cross herds. For the three-breed rotational cross herd, differences due to rotation generally were not significant during G1 and G2, but for G3, the SG sires were associated with lower (P less than .05) reproductive performance for each of the three reproductive traits compared with A and PH sires. Heterosis percentages generally were positive but not significant for each of the three reproductive traits. On the basis of additive and maternal effects of A and SG expressed as deviations from PH, the only genetic component that significantly affected reproductive performance was the detrimental additive effect of SG in G2 and G3 for each of the three reproductive traits. Also, there was a consistent negative relationship between breed additive and maternal components for each of the three reproductive traits during each generation. Only 4 to 7% of the variation in reproductive performance was accounted for in the analyses that included breed additive, breed maternal, heterosis and average maternal heterosis effects. Averaged over generations, from .1 to .4% additional variation was due to factors that may have included specific maternal heterosis, epistasis and linkage.

The effect of cereal growth stage and feeding site on the reproductive activity of the bird‐cherry aphid, Rhopalosiphum padi

SUMMARYApterous Rhopalosiphum padi on the first leaf of cereal plants, developed faster and were more fecund at seedling to stem extension of barley, at tillering to earing of oats and at stem extension and earing of wheat. Feeding site on a mature plant also affected the rate of development and fecundity of the aphids; the largest and most fecund developed on the stems of oat and wheat plants. The consequences of these variations in reproductive performance are discussed in relation to the population dynamics of R. padi and its possible pest status in Britain.

Variations in reproductive performance among certain strains of inbred Syrian hamsters.

Variations in reproductive performance among certain strains of inbred Syrian hamsters.

Selection among males for the genetic improvement of female fertility.

The quantitative physiological study of genetic variation in reproductive performance has shown that differences in the litter size and incidence of lambing in sheep are associated with variation in the release of LH. This variation is detectable in young animals of both sexes, and the injection of LHRH may aid its recognition. In the male it is associated with variation in mating behavior and testis growth. The ovarian activity of both sheep and mice has been shown to change following selection for testis growth. The use of measures of testis growth as criteria for selection to improve the reproductive performance of females is discussed.

A survey of reproductive performance in herds of beef cattle from 13 properties in Victoria

An analysis of the reproductive, performance of beef cattle based on 5840 records of performance from thirteen properties in Victoria was made. Traits analysed included calving rate, twinning rate, mortality of calves, age at first calving interval. When all data were pooled, mean age at first calving was 863.5 days, calving interval 361 days, calving rate 88.7 per cent, mortality rate at birth of the calves 4.3 per cent, pre-weaning mortality 1.5 per cent, post-weaning mortality 0.3 per cent and twinning rate 1.5 per cent. Wide variation in reproductive performance was observed between properties. As found in other studies, age of dam was the main factor affecting reproductive performance and adjustments to take account of this variation are necessary when comparing the performance of different animals.

Variations in the fertility over the joining period of ewes on hill country

Abstract The cumulative data from 9 flocks of sheep over the period 1967 to 1973, representing 2427 2-year-old and 5443 3- to 5-year-old (mature) ewe-matings, were analysed for variation in reproductive performance between ewe ages and among those mated by entire rams in each of 4 successive 14-day periods. Joining with the entire rams began on the 15 to 20 March and lasted 8 weeks. The percentage lambs weaned per ewes present at lambing was 71 % for 2-year-olds and 93% for mature ewes. This difference was mainly associated with the lower multiple birth rate of 2-year-olds (15% v. 31%). Only 37% of 2-year-olds and 61 % of mature ewes were mated in the first period of joining, and the conception rate for ewes mated in this period was respectively 12% and 6% lower than for those mated in the second period. The percentage of ewes lambing to mating in a single period was at a maximum (62%) for all ewes mated in period 2 and declined for those mated in periods 3 and 4. The multiple birth rate was a maximum of 21 % for the 2-year-olds conceiving in period 1 and declined to 10% in period 4. In mature ewes the multiple birth rate was 33% for those conceiving in periods 1 and 2, and 23% in periods 3 and 4.

Mammalian Reproductive Data Fitted to a Mathematical Model

If intervals between successive births were identically and independently distributed, a model for reproductive performance could be put in terms of a renewal process, in which reproductive performance is predicted from known distributions of the intervals. For a sample of mice, expected reproductive performance was estimated, according to such a model, from observed distributions of intervals between litters. A graphical comparison of expected and observed results indicated that the variance of the cumulative number of litters born by termination of the experiment exceeded that in the model. The mean number of litters was a less sensitive indicator than the variance. Because of oscillations inherent in such data, a fit cannot be attempted to values observed for only a single day, such as at the end of the experiment. It is felt that this method warrants further exploration as an approach to studying variation in reproductive performance.

Sources of variation in reproductive performance in selected herds of beef cattle in north-eastern Australia.

SummaryThis paper contains observations of several sources of variation in reproductive performance on 13 herds of beef cattle in north‐eastern Australia. Nearly 15,000 cows were examined, man, on more than one occasion. Variation between herds in pregnancy rate in June or September 1964, was 44 to 75 per cent. Lactating heifers had lower pregnancy rates than lactating cows, which in turn had lower rates than non‐lactating animals. Within classes, cows in poor body condition had lower fertility than those in forward‐store or fat condition. Losses of calves between pregnancy tests and branding ranged from 6 to 40 per cent in a sample of herds. In herds where year‐to‐year data were avail‐able, the majority of cattle had one calf every two years, or two calves every three years. In one herd, cows that calved before February reared more calves than those that calved later.The main conclusion was that improved nutrition of lactating heifers and cows would be expected to increase pregnancy rates substantially.

Seasonal variation in reproductive performance of Merino ewes in northern New South Wales

Two groups of Merino ewes were observed for five years to determine the variation within years and to make comparisons between years in the numbers of ewes exhibiting oestrus, in fertility, and in lamb birth weights. A group of 35 ewes (continuous), was run constantly with vasectomized rams and services were recorded. From the other (changing) group, a fresh sub-group of 15 ewes was joined with fertile rams every four to six weeks; services were recorded, together with lambing performance and lamb birth weights.Distinct breeding and anoestrous seasons similar to those shown by other workers were observed in both groups of ewes. However, the onset of oestrous activity was a month earlier in the changing ewes than in the continuous ewes.Fertility was low during spring and early summer and reached a maximum in autumn.The birth weight of the lambs appeared to be predominantly influenced by the ewes' nutrition during pregnancy.