23 results on '"F. D. Brien"'
Search Results
2. Litter size at lambing influences genetic evaluation of maternal rearing ability
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Jennifer Smith, Andrew Swan, Kim L Bunter, F. D. Brien, and Daniel Brown
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0301 basic medicine ,Litter (animal) ,Ecology ,media_common.quotation_subject ,Domestic sheep reproduction ,0402 animal and dairy science ,04 agricultural and veterinary sciences ,Heritability ,Biology ,040201 dairy & animal science ,Correlation ,03 medical and health sciences ,030104 developmental biology ,Animal science ,Common mean ,Trait ,Animal Science and Zoology ,Flock ,Reproduction ,Food Science ,media_common - Abstract
The genetic parameters for maternal rearing-ability of ewes were investigated by ignoring or defining the rearing ability trait separately by litter-size class (singles versus multiples) using multi-generational data from three, fully pedigreed Merino flocks differing in prolificacy, production level and environment. Genetic correlations (ra) between litter size (LSIZE) and the percentage of lambs surviving (PLSURV) were more negative with an increasing mean flock litter size (ra: –0.21 ± 0.17 to –0.73 ± 0.08), while the corresponding range in phenotypic correlations (rp) was substantially lower (rp: –0.15 ± 0.01 to –0.33 ± 0.01). Rearing-ability traits defined separately by litter-size class were highly correlated (ra: 0.49 ± 0.19 to 0.64 ± 0.38), but not genetically identical traits in the most prolific flock. Defining rearing-ability traits separately by litter-size class reduced the antagonistic genetic correlations between LSIZE and PLSURV to between –0.39 ± 0.14 and 0.14 ± 0.28, through accommodating the change in mean and variance of PLSURV with LSIZE. Similarly, linear transformation (TSURV) of PLSURV within each litter size to a common mean and variance reduced the antagonistic trend in genetic correlations between LSIZE and TSURV to range between –0.05 ± 0.17 and –0.43 ± 0.13. Since genetic correlations are low to moderate between TSURV and LSIZE, it is possible to select for improvements in both the number of lambs born and lamb survival simultaneously. Defining rearing-ability traits separately by litter-size class and the role of transformation will be investigated further for improving the accuracy of genetic evaluation for rearing ability across a range of flocks, breeds and environmental conditions using more extensive industry data.
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- 2018
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3. Ewe culling and retention strategies to increase reproductive rates in Merino sheep
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Jennifer Smith, F. D. Brien, Sonja Dominik, Rick Tearle, S. Hatcher, J. S. Richards, J. Young, and N. Hermann
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Litter (animal) ,Pregnancy ,Animal breeding ,animal diseases ,media_common.quotation_subject ,Animal production ,0402 animal and dairy science ,04 agricultural and veterinary sciences ,Culling ,Biology ,medicine.disease ,040201 dairy & animal science ,Animal science ,040103 agronomy & agriculture ,medicine ,0401 agriculture, forestry, and fisheries ,Animal Science and Zoology ,Flock ,Reproduction ,Food Science ,media_common - Abstract
The present empirical study of data from three Merino resource flocks of varying genetic backgrounds run in different environments investigated the impact of various selection strategies aimed at culling poor performers (‘passengers’) or retaining good doers (‘performers’) longer, or both, on the flock reproductive performance. Four strategies were investigated and applied either individually or in combination, to quantify their impact on the litter size, rearing type and breeding efficiency (number of lambs weaned per ewe per year) of the whole flock. The main benefit from implementing any of the strategies was a decrease in the proportion of dry ewes in each flock (1–7%). There was little difference between the single strategies of culling twice-dry ewes or culling ewes that twice lambed and lost their lambs. When retaining a cohort of older ewes, it was more efficient to select these on the basis of their lifetime reproductive performance. There was only a marginal benefit gained by combining strategies and, in some cases, a single strategy was still better in terms of breeding efficiency. Commercial producers can improve the reproductive rate of these flocks by culling twice-dry ewes on the basis of their pregnancy scan data.
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- 2018
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4. Variation in physiological profiles may explain breed differences in neonatal lamb thermoregulation
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F. D. Brien, P. I. Hynd, Michelle L. Hebart, and Kate J. Plush
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040301 veterinary sciences ,Ecology ,Cold resistance ,0402 animal and dairy science ,Rectal temperature ,04 agricultural and veterinary sciences ,Thermoregulation ,Biology ,Carbohydrate metabolism ,040201 dairy & animal science ,Breed ,0403 veterinary science ,Animal science ,Environmental management system ,Animal Science and Zoology ,Peak value ,Thermogenesis ,Food Science - Abstract
Ability to adapt rapidly from the uterine environment to self-thermoregulation following birth is a vital requirement for neonatal lamb survival. This investigation reports factors that could explain differences in thermoregulation among breeds that differ in lamb survival. Breeds such as the Merino and Border Leicester have previously been shown to be divergent for birthweight, cold resistance and lamb survival. Cross-bred (Poll Dorset Border Leicester (PDBL, n = 9) and Poll Dorset Merino (PDM, n = 25)) and pure-bred (Border Leicester (BL, n = 35) and Merino (M, n = 46)) lambs were recorded for the thermogenic measures rectal temperature at birth, cold resistance (time for rectal temperature to fall to 35°C while in a cooled water bath) and cold recovery (time to restore rectal temperature after cold exposure) at 1 day of age. In pure-bred lambs, 1 kg increase in weight resulted in a 0.25°C increase in rectal temperature at birth (P < 0.001) and 4.2 min increase in cold resistance (P < 0.001). In contrast, cross-bred lambs did not exhibit any relationship between birthweight and rectal temperature at birth, although they displayed a 3.2 min greater cold resistance for every 1 kg increase in birthweight (P < 0.001). BL-derived lambs were more cold resistant than M lambs (cross-bred: PDBL, 67.1 ± 2.5 min; PDM, 56.4 ± 1.6 min; P < 0.01; and pure-bred: BL, 58.1 ± 1.5 min; M, 53.2 ± 1.3 min; P < 0.01). The quadratic relationship of glucose concentration over time during cold exposure differed with lamb breed. PDBL exhibited higher peak glucose concentrations than did PDM (11.0 mmol/L and 8.9 mmol/L, respectively; P < 0.01). BL took longer to reach peak glucose concentration (50 min) than did M (40 min) and this peak value was higher (BL, 9.4 mmol/L; M, 7.7 mmol/L; P < 0.001). In conclusion, variations in birthweight and glucose metabolism are associated with breed differences in thermogenesis of neonatal lambs.
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- 2016
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5. Effect of previous reproductive performance on current reproductive rate in South Australian Merino ewes
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Raul W. Ponzoni, David O. Kleemann, K. S. Jaensch, Dennis R. Gifford, Simon K. Walker, RJ Grimson, D. H. Smith, F. D. Brien, James R. W. Walkley, and S F Walkom
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0106 biological sciences ,Net reproduction rate ,animal diseases ,media_common.quotation_subject ,Domestic sheep reproduction ,0402 animal and dairy science ,Fertility ,04 agricultural and veterinary sciences ,Biology ,Fecundity ,040201 dairy & animal science ,01 natural sciences ,Animal science ,Environmental management system ,Weaning ,Animal Science and Zoology ,Flock ,Reproduction ,010606 plant biology & botany ,Food Science ,media_common - Abstract
Reproductive performance of ewes in the current year may be influenced by their performance in the previous year and by the ability of seasonal and management conditions to facilitate full recovery before the next breeding cycle. This possibility was tested by analysing reproductive data from 2100 South Australian Merino ewes mated to Merino rams annually from 1991 to 1997. The model fitted to the data included the fixed effects of previous reproductive performance (PRP) (no lambs born; single or multiple lambs born, none reared; single lambs born, singles reared; multiples born, singles reared; multiples born, multiples reared), age of ewe (2.5, 3.5, 4.5 years), year (1992–1997), bloodline (A, B, L, X) and all two-way interactions. Current-year parameters were net reproduction rate (NRR, lambs weaned of ewes joined) and its components of fertility (ewes lambing of ewes joined), fecundity (lambs born of ewes lambing) and lamb survival (lambs weaned of lambs born). Other parameters were lamb liveweight at weaning per ewe joined and pre-mating liveweight. In addition, repeatability values were calculated across ages for these parameters. NRR was higher in the current year for those groups of ewes that reared lambs in the previous year; this was associated with the highly productive multiple-bearing and -rearing groups having a liveweight at the next mating similar compared to that of groups that did not rear lambs. Repeatability values of 0.27 for NRR and 0.40 for fertility suggest there are genetic and permanent environmental components contributing to the differences observed among the PRP groups for NRR, particularly so for fertility. Selecting ewes after their first lambing opportunity on fertility alone at a rate of 90% would give a non-cumulative increase in fertility of 3.4% at subsequent lambing opportunities. Hence, improvements in the current ewe flock for NRR by graziers managing flocks of the South Australian Merino strain are likely to come from (1) identifying and selecting those ewes of high fertility from early records and (2) attending to management factors impacting on fecundity and lamb survival.
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- 2016
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6. Neonatal lamb mortality: factors associated with the death of Australian lambs
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R. van de Ven, F. D. Brien, Geoffrey Hinch, and G. Refshauge
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Starvation ,medicine.medical_specialty ,040301 veterinary sciences ,business.industry ,Obstetrics ,Sire ,0402 animal and dairy science ,Autopsy ,04 agricultural and veterinary sciences ,medicine.disease ,040201 dairy & animal science ,female genital diseases and pregnancy complications ,Birth injury ,0403 veterinary science ,Falling (accident) ,In utero ,medicine ,Animal Science and Zoology ,Flock ,medicine.symptom ,business ,reproductive and urinary physiology ,Food Science ,Cause of death - Abstract
The objective of the present study was to examine the factors associated with the death of neonatal lambs. Postmortem autopsy data were collected from 3198 newborn lambs in the Sheep CRCs Information Nucleus Flock situated in various environments throughout southern Australia. The proportion dying by category from highest to lowest was starvation–mismothering (25%), stillbirth (21%), birth injury (18%), dystocia (9%), death in utero–prematurity (10%), predation (7%), cold exposure (5%), undiagnosed (4%), infection (1%) or misadventure (1%). Factors best explaining the probability of lambs falling into a death category included both birth type and birthweight for dystocia, stillbirth, starvation–mismothering and death in utero–prematurity. The probability of a lamb falling into any category was predicted at the mean birthweight, within birth type. Single-born lambs were more likely to die from dystocia and stillbirth, while twin lambs were more likely to die from birth injury, starvation–mismothering or from undiagnosed causes. Triplet lambs were more likely to die from starvation–mismothering or death in utero–prematurity. Sire type (Merino, maternal or terminal) did not affect the proportions of lambs within any category. The proportions lost to each cause of death were largely consistent among locations, despite the rate of death varying. Dystocia, stillbirth and birth injury, as evidenced by the presence of oedema around the head and neck or by lesions of the central nervous system, accounted for 48% of autopsied lambs. We conclude that for improvements to occur in the rates of lamb survival, the Australian sheep industry must focus on minimising losses due to dystocia, stillbirth, birth injury and starvation.
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- 2016
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7. Thermogenesis and physiological maturity in neonatal lambs: a unifying concept in lamb survival
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P. I. Hynd, Kate J. Plush, F. D. Brien, and Michelle L. Hebart
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0301 basic medicine ,Ecology ,0402 animal and dairy science ,Physiology ,Adipose tissue ,04 agricultural and veterinary sciences ,Thermoregulation ,Biology ,Heritability ,040201 dairy & animal science ,Energy homeostasis ,03 medical and health sciences ,030104 developmental biology ,medicine.anatomical_structure ,Brown adipose tissue ,Shivering ,medicine ,Animal Science and Zoology ,medicine.symptom ,Thermogenesis ,Homeostasis ,Food Science - Abstract
Lamb mortality represents reproductive wastage and an animal welfare concern. While lambs are thought to be at a thermogenic advantage following birth in comparison to other species, death from exposure can still be a major contributor to lamb mortality, largely because of the inclement conditions often prevailing at lambing. For this reason, thermogenesis has been studied extensively in neonatal lambs. Heat is produced in the neonatal lamb by shivering and non-shivering thermogenesis. The latter is heat generated by metabolism of brown adipose tissue (BAT) found largely in the thorax and peri-renal areas of the newborn lamb. Brown adipose tissue differs from normal adipose tissue in that it contains densely packed mitochondria, a high cytochrome c content and a vast vascular network. Heat is generated in BAT by uncoupling of the proton conductance mechanism from ATP production, resulting in heat production instead of stored energy. The ability of lambs to resist cooling differs among individuals and this is likely to be due to both genetic and phenotypic factors. The heritability of cold resistance is moderate-to-high and polymorphic gene markers associated with energy homeostasis and cold-related mortality have been identified. Additionally, several aspects of the phenotype of the lamb have been associated with cold resistance. Most relate to properties of the coat, skin and bodyweight, the latter being particularly important, presumably through effects on surface area to volume ratios and subsequent heat loss. The ability of the neonate to achieve the transition from intra- to extra-uterine life has been termed physiological maturity and is associated with the ability to activate appropriate neuro-endocrinological and behavioural changes that are consistent with homeostasis of energy metabolism. Ways to alter physiological maturity of the lamb, such as nutrition, pharmacology and genetic selection, have been identified, and while these show promising results with regards to thermoregulation, a key limitation of their application has been the lack of a repeatable, representative model of neonatal cold stress. An estimation of the non-shivering component potential of a lamb’s ability to thermoregulate can be derived from norepinephrine challenges, but more useful models of real-world cold stress are climate chambers or controlled water bath tests. Further use of repeatable test models such as these with appropriate neuroendocrine and metabolic metrics will identify key components and markers of physiological maturity associated with lamb thermogenesis and survival.
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- 2016
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8. The impact of selecting for increased ewe fat level on reproduction and its potential to reduce supplementary feeding in a commercial composite flock
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Wayne S. Pitchford, Michelle L. Hebart, F. D. Brien, and S F Walkom
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0301 basic medicine ,Integrated pest management ,media_common.quotation_subject ,Drought tolerance ,0402 animal and dairy science ,04 agricultural and veterinary sciences ,Biology ,040201 dairy & animal science ,Genetic correlation ,03 medical and health sciences ,030104 developmental biology ,Animal science ,Agronomy ,Grazing ,Environmental management system ,Animal Science and Zoology ,Flock ,Reproduction ,Genetic merit ,Food Science ,media_common - Abstract
In southern Australian grazing systems, energy availability typically exceeds energy requirements. Grazing systems are likely to have higher profitability if ewes can utilise this relatively cheap feed by gaining more condition (muscle and fat) and then mobilising it when feed is expensive. The present paper focusses on the importance of genetic merit for fat on the lifetime productivity of the ewe within a commercial operation. The analysis was carried out on a maternal composite stud flock in Holbrook, New South Wales. Ultrasound fat and muscle depth were measured on 2796 ewes as lambs at post-weaning and as adult ewes, to determine the genetic relationship between young and adult body composition. The hypothesis of the paper is that selection for increased fat at young age will improve body condition of adult ewes, which will lead to improved reproduction and potentially reduced requirements for supplementary feeding. Given that the difference in feed cost between times of abundance and shortage is likely to be larger, the system may become more profitable despite being less efficient (owing to increased feed intake). Our results indicated that selection for scanned post-weaning fat and muscle depth in lambs should lead to increased fat muscle and body condition in the breeding ewe because of strong genetic correlation estimates between the post-weaning and adult traits of 0.68–0.99. The influence of body composition traits on reproduction (number of lambs weaned) within the stud flock was weak. However, it is hypothesised that by genetically increasing post-weaning fat depth in ewes, producers could improve profitability by reducing the demands for supplementary feeding.
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- 2016
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9. Season and reproductive status rather than genetic factors influence change in ewe weight and fat over time. 4. Genetic relationships of ewe weight and fat score with fleece, reproduction and milk traits
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S. Hatcher, F. D. Brien, Michelle L. Hebart, N. M. Fogarty, S F Walkom, and Wayne S. Pitchford
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0301 basic medicine ,media_common.quotation_subject ,Sire ,Drought tolerance ,0402 animal and dairy science ,Production cycle ,04 agricultural and veterinary sciences ,Biology ,040201 dairy & animal science ,Breed ,03 medical and health sciences ,030104 developmental biology ,Animal science ,Agronomy ,Environmental management system ,Animal Science and Zoology ,Flock ,Reproduction ,Corriedale ,Food Science ,media_common - Abstract
The profitability of a sheep enterprise is greatly influenced by the ability of the ewe to produce a lamb annually. This paper examines the between- and within-breed association between the liveweight and fat score of the adult ewe and key fleece, reproduction and milk production traits. The study analysed the performance of 2846 first-cross Merino and Corriedale ewes from the maternal central progeny test (MCPT) over their first three production cycles. Breed (9 sire breeds) and within-breed (91 sires) correlations were calculated from bivariate correlations of adult liveweight and fat score with fleece, reproduction and milk production traits. The mean liveweight and fatness of the breeds were low to moderately negatively correlated with greasy fleece weight (–0.55 and –0.25, respectively) and moderate to strongly positively correlated with fibre diameter (0.88 and 0.41, respectively). However, the within-breed correlations were generally low to negligible. The genetic relationships between ewe fat score and reproductive traits at the breed and within-breed level was generally low to negligible and, in some cases, negative under production conditions where the ewes were well managed and averaged a fat score of 3.5 pre-joining and became too fat across the production cycle. Strong breed correlations between ewe fat score and milk fat concentration (0.88) suggest that selection of fatter sire breeds will lead to increased fat in their progenies’ milk, which was associated with larger lambs. The potential advantages of selecting for more fat to improve the maternal performance of the ewe seem to be limited in enterprises where the production system can easily be adjusted to restrict the influence of temporary and long-term feed deficiencies, as was achieved within the MCPT research flocks.
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- 2016
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10. Foreword to ‘Sheep Reproduction: Part 2’
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F. D. Brien
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Soil indicators ,Ecology ,Domestic sheep reproduction ,Animal Science and Zoology ,Biology ,Food Science - Published
- 2016
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11. Season and reproductive status rather than genetics factors influence change in ewe weight and fat over time. 3. Analysis of Merino ewes
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S. F. Walkom, F. D. Brien, M. L. Hebart, S. I. Mortimer, and W. S. Pitchford
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Animal Science and Zoology ,Food Science - Abstract
The profitability of southern Australian sheep production systems depends on the optimisation of stocking rates by meeting the nutritional demands of the breeding ewe while effectively utilising grown pasture. The aim of the study was to evaluate the genetic variation in liveweight and body condition of Merino ewes across their breeding life within a wool-based enterprise. The results were consistent with findings in crossbred ewes and showed that the genetic component of weight and body condition remained constant across the production cycle and age. The overall additive genetic effect accounted for 92% of the genetic variation in weight of Merino ewes bred across five production cycles. A genetic correlation of 0.85 suggested that ewes that were superior at maintaining their condition when rearing a single lamb would maintain this superiority when rearing multiple lambs. To improve weight and condition of Merino ewes during the ‘tough’ times, when nutrient requirements are not met by the pasture, selection can be made at any time and this will result in increased genetic condition at all times.
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- 2014
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12. Season and reproductive status rather than genetic factors influence change in ewe weight and fat over time 2. Spline analysis of crossbred ewes
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Wayne S. Pitchford, N. M. Fogarty, F. D. Brien, S F Walkom, S. Hatcher, and Michelle L. Hebart
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geography ,geography.geographical_feature_category ,business.industry ,Drought tolerance ,Biology ,Heritability ,Crossbreed ,Pasture ,Biotechnology ,Animal science ,Weight loss ,Genetic variation ,Environmental management system ,medicine ,Trait ,Animal Science and Zoology ,medicine.symptom ,business ,Food Science - Abstract
The success of slaughter lamb enterprises is heavily influenced by the ability of the breeding ewe to produce a lamb annually across variable environments. It has been shown that by maintaining heavier weight and condition across the annual production cycle producers can make significant improvements in maternal performance. This paper follows on from a previous analysis of crossbred ewes within the Maternal Central Progeny Test and examines the potential to select for reduced fluctuation in weight and fat across the production cycle. A cubic spline model was fitted to the weight and fat score data from the first three parities of 2688 first-cross ewes. The analysis partitioned the influence of environment, reproduction and genetic effects on the shape of the weight and fat score splines across three parities. Yearly and seasonal variation in feed supply and the demands of raising a lamb are the major influences on fluctuations in the weight and fat score of the breeding ewe. The genetic effects were constant across time with 98 and 92% of the genetic variation for weight and fat, respectively, associated with the spline’s intercept. In agreement with the findings of the first paper of the series it can be concluded that genetic lines do not re-rank for weight or fat score over time. The influence of sire breed on weight and fat score was constant across time with sire breeds fluctuating in parallel across time. As a result it is concluded that to avoid low fat reserves and the subsequent low fertility during the ‘tough’ periods, selection to improve ewe body condition could be made at any time and under any environmental conditions.
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- 2014
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13. Reproductive performance in the Sheep CRC Information Nucleus using artificial insemination across different sheep-production environments in southern Australia
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R. C. Dobos, M. R. McCaskill, Steven Harden, Darryl Savage, Ralph Behrendt, F. D. Brien, K. W. Hart, Alex Ball, G. Refshauge, K. G. Geenty, J. E. Hocking-Edwards, Geoffrey Hinch, Klint Gore, and J. H. J. van der Werf
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Lamb mortality ,business.industry ,Artificial insemination ,medicine.medical_treatment ,Sire ,Domestic sheep reproduction ,Semen ,Biology ,Crossbreed ,Breed ,Biotechnology ,Animal science ,Environmental management system ,medicine ,Animal Science and Zoology ,business ,reproductive and urinary physiology ,Food Science - Abstract
The present paper covers reproductive performance in an artificial-insemination (AI) program of the Sheep CRC Information Nucleus with 24 699 lambs born at eight locations in southern Australia across five lambings between 2007 and 2011. Results from AI with frozen semen compared well with industry standards for natural mating. Conception rates averaged 72%, and 1.45 lambs were born per ewe pregnant for Merino ewes and 1.67 for crossbreds. Lamb deaths averaged 21% for Merino ewes and 15% for crossbreds and 19%, 22% and 20% for lambs from ewes that were mated to terminal, Merino and maternal sire types, respectively. Net reproductive rates were 82% for Merino ewes and 102% for crossbreds. From 3198 necropsies across 4 years, dystocia and starvation-mismothering accounted for 72% of lamb deaths within 5 days of lambing. Major risk factors for lamb mortality were birth type (single, twin or higher order), birthweight and dam breed. Losses were higher for twin and triplet lambs than for singles and there was greater mortality at relatively lighter and heavier birthweights. We conclude that reproductive rate in this AI program compared favourably with natural mating. Lamb birthweight for optimum survival was in the 4–8-kg range. Crossbred ewes had greater reproductive efficiency than did Merinos.
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- 2014
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14. Season and reproductive status rather than genetics factors influence change in ewe weight and fat over time. 1. Analysis of crossbred ewes
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S. F. Walkom, F. D. Brien, M. L. Hebart, N. M. Fogarty, S. Hatcher, and W. S. Pitchford
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Animal Science and Zoology ,Food Science - Abstract
The Australian sheep industry has historically made rapid advances in the quality and quantity of meat and wool through genetic improvement, but unfortunately, maternal performance, i.e. number of lambs weaned, is well below desired levels. The aim of the present paper is to investigate the potential to select for increased weight and fat across the production cycle to improve maternal performance. The analysis explores the potential to improve the weight and fat score of breeding ewes during ‘tough’ periods (i.e. when nutrient requirements are not met by the pasture), preparing the breeding ewe for the upcoming mating without an increase in overall ewe size. The 2846 ewes within the maternal central progeny test were weighed and scored for fatness 12 times across three production cycles. Low to moderate heritability estimates for weight (0.04–0.23) and fat (0.02–0.06) changes across the production cycle provide little hope for selection against weight loss during tough periods. The analysis showed very strong genetic correlations between time-points across multiple production cycles for both weight (0.99–0.93) and fat score (0.88–0.98). The very strong correlations between measurements suggest that weight and fat score are genetically the same trait throughout the ewe’s adult life. With 74% and 77% of the genetic variation in weight and fat, respectively, constant across the production cycle, there is little opportunity to select against the natural fluctuations in weight and fat reserves. In conclusion, selection for increased fat can be made at any time and it will result in more fat during tough times.
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- 2014
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15. Foreword to ‘Sheep Reproduction’
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F. D. Brien
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Soil indicators ,Agronomy ,Domestic sheep reproduction ,Zoology ,Animal Science and Zoology ,Biology ,Food Science - Published
- 2014
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16. Lamb survival in Australian flocks: a review
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Geoffrey Hinch and F. D. Brien
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Soil indicators ,Ecology ,animal diseases ,Cold resistance ,Environmental management system ,Animal Science and Zoology ,Flock ,Biology ,Food Science ,Demography ,Predation ,Maternal behaviour - Abstract
Lamb survival is known to be a key component of reproductive efficiency in sheep flocks. It has been the subject of a large number of studies over the decades and this review provides an update and insights into the latest understanding of the extent and variability of lamb losses across Australia. The pattern of causes of lamb losses, including dystocia, starvation/exposure, mismothering and predation, are examined. Likewise the importance of birthweight in contributing to such losses is discussed as are strategies for improving lamb survival. The strategies examined include improved ewe nutrition, shelter provision and selection for cold resistance and improved maternal behaviour.
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- 2014
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17. A review of the genetic and epigenetic factors affecting lamb survival
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N. M. Fogarty, F. D. Brien, J. E. Hocking Edwards, Michelle L. Hebart, K. L. Plush, Steven Cloete, D. R. Miller, J. C. Greeff, Karen L. Kind, J. M. Kelly, D. O. Kleemann, and Stefan Hiendleder
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business.industry ,Confounding ,Linear model ,Heritability ,Quantitative trait locus ,Biology ,Biotechnology ,Genetic gain ,Genetic variation ,Animal Science and Zoology ,Threshold model ,business ,Selection (genetic algorithm) ,Food Science ,Demography - Abstract
Poor lamb survival pre-weaning is a major source of reproductive inefficiency in Australian sheep flocks. While nutrition and management options have been extensively researched and promoted to improve lamb survival, the present review focuses on the prospects for obtaining genetic gain and helps identify selection strategies for boosting such gains to improve overall reproductive efficiency in the Australian sheep industry. Estimated heritability for lamb survival using linear model analysis is low, although use of threshold models suggests that heritability could be higher, which, if true, could help explain the substantial genetic gains obtained in long-term selection experiments. Epigenetic mechanisms may hinder selection and quantitative trait-loci identification through confounding and/or masking genetic variances and co-variances. With sufficient information, these effects could be considered in genetic evaluations by identifying those components that are amenable to selection. Regarding indirect selection, finding effective criteria for improving lamb survival has proved elusive. Most measures of maternal behaviour, temperament and lambing difficulty researched are poorly correlated genetically with lamb survival. Of lamb behaviours and thermo-genic indicators studied, latency to bleat following handling by humans is moderately genetically correlated with lamb survival, as is neonatal rectal temperature. Industry application remains to be adequately explored for the more promising of these measures. Finally, in lieu of direct selection for lamb survival, there is merit in selecting for multiple-rearing ability or its equivalent, possibly with additional selection criteria for lamb survival and reproductive efficiency.
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- 2014
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18. Opportunities for genetic improvement of lamb survival
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F. D. Brien, D. H. Smith, K. G. Geenty, M. Robertson, J. C. Greeff, T. L. Bird-Gardiner, K. W. Hart, Michelle L. Hebart, G. Refshauge, Ralph Behrendt, J. E. Hocking Edwards, Geoffrey Hinch, J. H. J. van der Werf, and G. Gaunt
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Soil indicators ,Ecology ,animal diseases ,Philosophy ,parasitic diseases ,Animal Science and Zoology ,respiratory system ,Theology ,Food Science - Abstract
Data on lamb survival and associated traits involving records from 15 192 lambs, 6308 dams and 284 sires from the Sheep CRC’s Information Nucleus were studied. Lamb survival to 3 days of age and to weaning was 85 and 80%, respectively, and heritability (±s.e.) was 0.014 ± 0.010 and 0.010 ± 0.010, respectively. Of the 14 traits recorded at birth, time taken for the lamb to bleat, rectal temperature and crown–rump length had the highest genetic correlations with lamb survival to weaning (–0.43 ± 0.32, 0.56 ± 0.33 and –0.38 ± 0.36, respectively). Under selection for a multi-trait objective including net reproduction rate (but not lamb survival), survival was predicted to decline genetically by 0.25 lambs weaned per 100 lambs born.year, although this was reversed to a gain of 0.20 lambs weaned per 100 lambs born.year by including the trait in the breeding objective and using 50 half-sib and 50 progeny records per selection candidate. Accuracy of selection for lamb survival was improved to 0.735 with a selection index of lamb survival to weaning, lamb ease, birth coat score, time taken to bleat, rectal temperature and crown–rump length, with the addition of 50 half-sibs and 50 progeny records per candidate. Our results suggest that unless actively incorporated into breeding objectives, lamb survival may genetically decline; however, gains are possible with direct selection using half-sib and progeny records. The addition of indirect selection criteria for lamb survival can further improve accuracy, up to 93.4%, but requires further investigation.
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- 2010
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19. Across population genetic parameters for wool, growth, and reproduction traits in Australian Merino sheep. 1. Data structure and non-genetic effects
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S. I. Mortimer, Arthur R Gilmour, F. D. Brien, K. D. Atkins, J. H. J. van der Werf, N. M. Fogarty, J. C. Greeff, E. Safari, and Andrew Swan
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education.field_of_study ,Animal breeding ,business.industry ,media_common.quotation_subject ,Monogastric ,Population ,Population genetics ,Biology ,Biotechnology ,Animal science ,Wool ,Plant breeding ,Flock ,Reproduction ,General Agricultural and Biological Sciences ,business ,education ,media_common - Abstract
Accurate estimates of adjustment factors for systematic environmental effects are required for genetic evaluation systems. This study combined data from 7 research resource flocks across Australia to estimate genetic parameters and investigate the significance of various environmental factors for production traits in Australian Merino sheep. The flocks were maintained for several generations and represented contemporary Australian Merino fine, medium, and broad wool bloodlines over the past 30 years. Over 110 000 records were available for analysis for each of the major wool traits, with over 2700 sires and 25 000 dams. Univariate linear mixed animal models were used to analyse 6 wool, 4 growth, and 4 reproduction traits. This first paper outlines the data structure and the non-genetic effects of age of the animal, age of dam, birth-rearing type, sex, flock, bloodline, and year, which were significant with few exceptions for all production traits. Age of dam was not significant for reproduction traits and fleece yield. Generally, wool, growth, and reproduction traits need to be adjusted for age, birth-rearing type, and age of dam before the estimation of breeding values for pragmatic and operational reasons. Adjustment for animal age in wool traits needs to be applied for clean fleece weight (CFW), greasy fleece weight (GFW), and fibre diameter (FD) with inclusion of 2 age groups (2 years old and >2 years old), but for reproduction traits, inclusion of all age groups is more appropriate. For GFW, CFW, and hogget weight (HWT), adjustment for only 2 dam age groups of maiden and mature ewes seems sufficient, whereas for birth (BWT), weaning (WWT), and yearling (YWT) weights, adjustments need to be applied for all dam age groups. Adjustment for birth-rearing type (single-single, multiple-single, multiple-multiple) is appropriate for wool, growth, and reproduction traits. The implications of adjustment for non-genetic effects are discussed.
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- 2007
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20. Across population genetic parameters for wool, growth, and reproduction traits in Australian Merino sheep. 2. Estimates of heritability and variance components
- Author
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K. D. Atkins, S. I. Mortimer, J. C. Greeff, F. D. Brien, Arthur R Gilmour, E. Safari, J. H. J. van der Werf, N. M. Fogarty, and Andrew Swan
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Litter (animal) ,education.field_of_study ,Animal breeding ,business.industry ,media_common.quotation_subject ,Sire ,Population ,Maternal effect ,Heritability ,Biology ,Biotechnology ,Animal science ,Wool ,Reproduction ,General Agricultural and Biological Sciences ,business ,education ,media_common - Abstract
Precise estimates of genetic parameters are required for genetic evaluation systems. This study combined data from 7 research resource flocks across Australia to estimate variance components and genetic parameters for production traits in the Australian Merino sheep. The flocks were maintained for several generations and represented contemporary Australian Merino fine, medium, and broad wool bloodlines over the past 30 years. Over 110 000 records were available for analysis for each of the major wool traits, and 50 000 records for reproduction and growth traits with over 2700 sires and 25 000 dams. A linear mixed animal model was used to analyse 6 wool traits comprising clean fleece weight (CFW), greasy fleece weight (GFW), fibre diameter (FD), yield (YLD), coefficient of variation of fibre diameter (CVFD), and standard deviation of fibre diameter (SDFD), 4 growth traits comprising birth weight (BWT), weaning weight (WWT), yearling weight (YWT), and hogget weight (HWT), and 4 reproduction traits comprising fertility (FER), litter size (LS), lambs born per ewe joined (LB/EJ), and lambs weaned per ewe joined (LW/EJ). The range of direct heritability estimates for the wool traits was 0.42 ± 0.01 for CFW to 0.68 ± 0.01 for FD. For growth traits the range was 0.18 ± 0.01 for BWT to 0.38 ± 0.01 for HWT, and for reproduction traits 0.045 ± 0.01 for FER to 0.074 ± 0.01 for LS. Significant maternal effects were found for wool and growth, but not reproduction traits. There was significant covariance between direct and maternal genetic effects for all wool and growth traits except for YWT. The correlations between direct and maternal effects ranged from –0.60 ± 0.02 for GFW to –0.21 ± 0.10 for SDFD in the wool traits and from –0.21 ± 0.03 for WWT to 0.25 ± 0.08 for HWT in the growth traits. Litter effects were significant for all wool and growth traits and only for LS in reproduction traits. The mating sire was fitted in the models for reproduction traits and this variance component accounted for 21, 17, and 8% of the total phenotypic variation for FER, LB/EJ, and LW/EJ, respectively. The implications of additional significant variance components for the estimation of heritability are discussed.
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- 2007
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21. Influence of sire by year interactions on the direct-maternal genetic correlation for weaning weight of Western Australian Merino sheep
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K. Konstantinov and F. D. Brien
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business.industry ,Sire ,Context (language use) ,Variance (accounting) ,Biology ,Heritability ,Interaction ,Genetic correlation ,Biotechnology ,Correlation ,Statistics ,Weaning ,General Agricultural and Biological Sciences ,business - Abstract
The relationship between the direct-maternal genetic (co)variance σam and sire by year (SY) interactions for weaning weight in Merino sheep was examined through simulation and real data analyses. Weaning weight was simulated using models containing interaction and σam = 0 (S1), interaction and σam < 0 (S2), interaction and σam >�0 (S3), and without interaction and σam < 0 (S4). When S1 data were analysed ignoring interaction, a negative (co)variance was observed and direct and maternal variances were inflated. Analysis of S2 data ignoring σam resulted in deflated direct and maternal variances, inflated residual and interaction variances, and no change for the permanent environmental component. Ignoring the interaction effect in S3 data resulted again in a negative (co)variance component and highly biased genetic parameters. On application to weaning weight of Merino sheep, the model ignoring SY resulted in a direct-maternal genetic correlation of –0.43. The model using both (co)variance and interaction effects fit the data better (P < 0.001). The interaction variance represented 9.2% of the phenotypic variance but explained 86% of the (co)variance between direct and maternal genetic effects estimated ignoring SY.�A small (–0.096) but still negative estimate of the genetic correlation was obtained. The implication of these findings in the context of Central Test Sire Evaluation and Maternal Sire Central Progeny Test Schemes is discussed.
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- 2003
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22. Genetic parameters for visually assessed traits and their relationships to wool production and liveweight in Australian Merino sheep.
- Author
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S. I. Mortimer, D. L. Robinson, K. D. Atkins, F. D. Brien, A. A. Swan, P. J. Taylor, and N. M. Fogarty
- Abstract
Heritability was estimated for a range of visually assessed traits recorded on Merino sheep, together with the phenotypic and genetic correlations among the visually assessed traits and correlations of the visually assessed traits with measured wool production traits and liveweight. Data were derived from four research resource flocks, with a range of 12958 to 57128 records from animals with 478 to 1491 sires for the various traits. The estimates of heritability were high for the wool quality traits of handle, wool character and wool colour (0.33–0.34) and the conformation traits of face cover, neck wrinkle and body wrinkle (0.42–0.45), moderate for front leg structure (0.18) and low for back leg structure (0.13). Fleece rot score had low heritability (0.14), while classer grade was moderately heritable (0.20). Estimates of genetic correlations among the visually assessed wool quality traits were low to moderate in size and positive (0.17–0.47). Genetic correlation estimates among the assessed conformation traits were generally very low, except for the genetic correlations between scores for neck and body wrinkle (0.92±0.01) and front and back leg structure (0.31±0.09). Fleece rot score had low positive genetic correlations with neck and body wrinkle scores (0.18±0.05 and 0.15±0.05, respectively) and classer grade (0.26±0.06). Classer grade was slightly positively correlated with the wool quality traits (0.17–0.45) and leg structure traits (0.21–0.25). The genetic correlations among the visually assessed traits were generally neutral to favourable. The visually assessed wool quality traits had low to moderate favourable genetic correlations with mean and coefficient of variation of fibre diameter (0.19 –0.47), but negative correlations with clean wool yield (–0.26 to –0.37). Face cover was unfavourably correlated with staple length (–0.27±0.04) and liveweight (–0.23±0.02). Neck and body wrinkle scores were genetically associated with higher greasy (0.33–0.39) and clean fleece weights (0.19–0.22), greater coefficient of variation of fibre diameter (0.24–0.26) and fibre curvature (0.27–0.28), but with reduced yield (–0.26 to –0.28) and staple length (–0.34 to –0.41). Fleece rot score was genetically correlated with clean fleece weight (0.26±0.05) and coefficient of variation of fibre diameter (0.27±0.04). Classer grade was favourably correlated with greasy and clean fleece weights (–0.41 to –0.43), staple length (–0.29±0.04), liveweight (–0.36±0.03) and coefficient of variation of fibre diameter (0.27±0.03). Most genetic correlations between the visually assessed traits and the measured production traits and liveweight were close to zero and less than 0.2 in magnitude. This study provides accurate values for the parameter matrix required to incorporate visually assessed traits into breeding objectives and the genetic evaluation programs used in the Australian sheep industry, allowing the development of breeding objectives and indexes that optimally combine visually assessed performance and measured production in Merino sheep. [ABSTRACT FROM AUTHOR]
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- 2009
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23. Role of plasma progesterone concentration in early pregnancy of the ewe
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CS Cocks, Iain J. Clarke, F. D. Brien, and IA Cumming
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geography ,geography.geographical_feature_category ,Progesterone level ,biology ,media_common.quotation_subject ,Embryo Deaths ,Early pregnancy factor ,Pasture ,Animal science ,Agronomy ,biology.protein ,Environmental management system ,Hay ,Plasma progesterone ,General Agricultural and Biological Sciences ,Ovulation ,media_common - Abstract
Eighty-eight maiden and 125 mature Merino ewes were grazed on green irrigated pasture or given dry hay on a fallow area with or without a lupin grain supplement just before and during mating. Progesterone concentrations in peripheral plasma were measured at 12 d after coitus. Progesterone concentration was lower (2.27 vs 2.87 ng/ml, P < 0.001 ) when lupins were fed, and maiden ewes had higher progesterone concentrations than mature ewes (2.75 vs 2.36 ng/ml, P < 0.05). Pregnant ewes had higher progesterone concentrations than non-pregnant ewes (2.77 vs 2.36 ng/ml, P < 0.05), and ewes with two ovulations had higher progesterone concentrations than ewes with a single ovulation (3.13 vs 2.08 ng/ml, P < 0.001). There was an interaction between pasture type and lupin supplement, with lupins depressing progesterone level more on green irrigated pasture (lupins 2.11 ng/ml, no lupins 3.00 ng/ml, P < 0.05) than on dry pasture (lupins 2.45 ng/ml, no lupins 2.74 ng/ml, P < 0.05). The results confirm that a high plane of nutrition at mating lowers progesterone levels in plasma and suggest that this may be a factor in the increase in embryo deaths when ewes are fed lupin grain supplements.
- Published
- 1981
- Full Text
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