Past exam Q's Flashcards
Define fecundity and ovulation rate.
Fecundity is the number of offspring delivered at birth/the ability to produce offspring in large numbers (physiological ability to produce).
Ovulation rate - number of ova released at each oestrus, major determinant of lambing rate. Controlled by genetics, nutrition and environment.
Briefly describe what is meant by the term ‘flushing’ in relation to ovulation rate.
Flushing is when ewes experience a 9 day flushing on live pasture or grain (220-450g/d) just prior to mating. Proven to increase ovulation rate by up to 22%. Quality of response is related to quantity of live pasture.
Works better on thin and mature ewes either early or late in the breeding season.
Describe the condition known as pregnancy toxaemia, including the metabolic causes.
Ketosis. Common condition caused by abnormal metabolism of carbs. and VFA’s. Occurs in late preg (last 6wks) on dry, poor quality pasture (<1000-1500kg DM/ha), in twin bearing ewes and during cold, stressful periods.
Metabolic disorder occuring when energy requirements are not being met. Foetal demands for glucose exceed ewes ability to supply and maintain her own levels (twin lamb disease). Appetite is supressed in late preg. so decreased nutrient intake, decreased insulin, liver breaks down fat to produce ketone bodies (high levels of these are toxic).
Adverse effects on lamb productivity.
Briefly discuss how good nutritional management can be used to prevent pregnancy toxaemia.
2 major strategies;
1) Avoid grazing ewes on pasture when rapid weight loss is likely in late preg., or supplement to avoid rapid weight loss.
2) Avoid getting ewes to fat (>3.5-4) or too thin (<2-2.5) in late pregnancy; grain can be supplied as CHO source to maintain energy and health, protein must be balanced for rumen microbes to make optimal use of available carbs.
Prevents or lessens the extent to which ewes exist in negative energy balance prior to and just after parturition. Essential in prevention of preg tox.
Ideally, producers will assess BCS at breeding and again mid gestation - avoid deterioration in overall flock condition, identify thin ewes and supply extra feed.
Ionophores can prevent subclinical ketosis - improve feed efficiency by changing microbial profiles in the rumen and the VFA profile.
Sheep have short gestation period; foetal demand greatest in last 2mths pregnancy, 80% of growth occurs during last 6wks.
Metabolic rate increases 50% in late preg, feed can exceed digestive capacity due to presence of foetus/es and so grain should be considered in stead of roughage to meet requirements (not as much space required and high energy).
A commercial merino producer retains ewes for 5 years (1.5-5.5yo) and weans 100% lambs from his 1000 head flock, 50% of which you can assume to be females. Given his breeding objective focuses on fleece weight and fibre diameter, would you recommend he use objective measurement to aid in selection of his replacements? Why/why not? If his weaning % was 60% would your recommendation change?
Breeder may opt to grade weaned stock objectively to get indication of which individual sheep meet production aims.
Fleece weight and fibre diameter are both traits measurable using ASBV’s however he shouldn’t rely solely on these as they are simple comparisons against individuals that aren’t 100% accurate and the trait may not have high heritability.
As he is weaning 100% and only retaining 200 females out of 500 he can afford to use objective measurements as it will allow selection of the most genetically superior stock and increase the rate of genetic gain for the flock.
If changed to 60% weaning there would only by 300 ewes from which to select 200 replacements - serious problems with weaning rates, significantly smaller population of lambs to select, don’t rely on objective measurements as smaller margin for error (simple mistake can cause large change). Better to focus on weaning % as this is a driver of profitability.
‘Nutrition of the pregnant ewe is critical to the newborn lambs chance of survival’. Discuss this statement with respect to the influence of nutrition throughout the various stages of pregnancy on lamb birthweight in both adult and maiden ewes, including any recommended condition score targets for lambing ewes.
Nutrition of the ewe during pregnancy influences the lifetime performance of progeny. Poor nutrition delays lactogenesis which can affect colostrum production.
Effects on birth weight, fat reserves, and colostrum production depend on level of restriction.
Between 50-90d can affect placental weight depending on ewe BCS and age. Restriction in last trimester (last 6wks); thin ewes may eat more but will partition energy to maternal live weight rather than foetus. Fat ewes will loose weight but foetus won’t be affected.
Ideal BCS in late gestation is 3 - 80% of growth occurs in last 6wks, higher glucose demand, ewes energy requirement 50-100% above maintenance.
Under/over nutrition can cause preg tox, depressed lamb birth weights, dystocia, lack of vigour in new borns and slower growth rates.
‘Nutrition of the pregnant ewe is critical to the newborn lambs chance of survival’. Discuss this statement with respect to the effect of lamb birth weight on the chances of survival of both single and twin lambs.
High birth weight is a very desirable trait to an extent as they are more developed and able to survive better.
Single lambs usually have greater birthweights than twins, however, even at the same weight, twins have lower chances of survival as energy from the mother needs to be shared.
If the birth weight becomes to great (>4.5-5kg) then survival rates start to decline due to dystocia and inability to meet large requirements straight after birth.
Males have shown to have decreased survival rate, particularly as a twin.
Low birth weights often occur in undernourished twinning ewes.
THINK GRAPH - SURVIVAL RATE VS BIRTH WEIGHT
Briefly describe what wether trials are. Briefly discuss how a commercial wool producer can use information from wether trials in choosing a bloodline.
A wether trial is a bloodline comparison that allows evaluation of flocks and indicates how well a particular bloodline is performing between flocks and other bloodlines.
Bloodline performance varies widely - eg. fibre diameter (+2.0 to -3.5 microns) 20% difference between best and worst.
Aims of trials usually a combination of; comparing traits of commercial importance, encouraging increased productivity, assists breeders in determining how their flock compares with other flocks, assists in ID of superior bloodlines by across comparison analysis, provides a forum for an exchange of ideas amongst wool professionals.
Useful tool to demonstrate that large production differences exist between sheep that in other respects look similar (highlights the importance of genetics).
Allows commercial wool producers to choose a bloodline by not only looking at bloodline comparison but also by looking where the bloodlines are intended to head. Allows producer to; set breeding objective, consider current bloodline performance and where it is heading, constraints of bloodlines (price, availability, distance).
Briefly describe what CTSE is.
Central Test Sire Evaluation.
Compares the breeding performance of a sire by evaluating its progeny.
Progeny performance is expressed relative to the progeny of other elite CTSE sires.
It is designed to assess the sires breeding performance for a large number of traits important to breeders, therefore assisting selection of sires suitable to a large range of breeding objectives.
Locations across Aus have annual matings of 10-16 sires, all mated to equal number of ewes to ensure the difference between the progeny can be attributed to the sire and not the ewes. Approx 50 ewes of similar breeding to the sires under evaluation are mated to each sire to obtain 25 or more progeny, 15-20 progeny can be expected to provide a satisfactory estimate of a sires breeding value.
Briefly describe how results fro one CTSE site can be related to other sites.
At least 1 link sire is mated for each 7 sires entered at a site. A link sire is a sire already mated in a CTSE site of that wool type (medium/fine) and has 25 progeny at that site that have been evaluated at least once.
Act as genetic connections between years and sites that allow the direct comparison of all the sires listed within the 2 groups.
Progeny are performance assessed at 10-16month (1st) and 17-24months (2nd). This involves fleece testing and visual assessment by 2 sheep classers.
Define repeatability.
Repeatability is the average proportion of differences likely to be repeated in later records. Value can only be determined from traits that manifest multiple times in an animals lifetime-performance at one point in time compared to performance at another point in time.
Generally it represents the upper level of heritability.
Calculated by taking the sum of genetic variance and permanent environment variance, and dividing by the phenotypic variance.
Explain why the repeatability of a trait can vary with the age of the animal when the trait is measured and the implications this has for selection.
Traits with high heritability also have high repeatability.
Almost as efficient to select sheep for production based on the earliest adult records as on the average of 2 records. The slight loss in efficiency as sheep get older is compensated by a higher gain each year because of early selection and the early disposal of surplus sheep.
Repeatability of a trait can vary with age of the animal when the trait is measured - weaning environment plays a massive role in phenotypes whereas it does not play this role in older sheep.
What are some characteristics that are highly repeatable in older sheep?
Greasy and clean fleece weight Yield Fibre diameter Staple length Body weight
Selection of bloodline is an important choice in Merino enterprises compared to lamb enterprises. Discuss why this is the case.
Merino enterprises need to consider micron premium as it is an indicator of the economic advantage of reducing fibre diameter (high premium has more influence on diameter, low more emphasis on fleece weight).
Merino enterprises are not terminal and there are many different traits (fleece weight, fibre diameter, staple strength, body weight) that can be selected for and that producers may choose to focus on. Therefore, selection of bloodline is important as it must adequately meet the set breeding objectives for the particular enterprise, increasing profitability.
Lamb enterprises, on the other hand, are terminal enterprises with only one main objective; high carcass weight. Crossbreeding to increase hybrid vigour and reproductive longevity through heterosis are common and terminal sires are used for the purpose of producing a market lamb.
2 different selection programs in use by the Australian sheep industry depending on enterprise aims; MerinoSelect ASBV’s and Lambplan ASBV’s, highlights the very different aims and practices of the two industries.
Describe the relationship between stocking rate and production/head and between stocking rate and productio/unit area of land.
Graph
As stocking rate increases, $ per lamb decreases
