Poor thrift / Trace elements

how is poor thrift defined in young animals?

animals that are not meeting their daily weight gain targets.

why do livestock in NZ usually don't reach their genetic potential for daily weight gain?

because the quality of their nutrition is not sufficient to allow them to do so.

- the aim is for them to grow as fast as is reasonably possible within the constraints of what they are being fed.

what factors contribute to liveweight gain targets?

- species

- age

- breed

- sex (and if male, whether or not they still have their testicles)

- time of year

- what they are being fed (quantity and quality)

why are growth rates of young livestock important?

- farmers get paid per kilogram of live weight or carcass weight (the faster young livestock reach their sale weight the more profitable they will be)

- replacements need to reach a target live weight by first mating for reproductive and long-term performance

- future milk, velvet and wool production is associated with growth rates as a young animal.

how is poor thrift defined in adult livestock?

animals that are in poorer than expected, or poorer than ideal, BCS.

why is it important for adult livestock to have optimal BCS?

- animals with below-optimal BCS have reduced production, reproductive performance, pre-weaning growth of offspring and also have an increased risk of death.

- animals with above optimal BSC leads to feed wastage and doesn't increase production

what are the differential diagnoses for poor thrift affecting entire groups of livestock?

young animals:

- Undernutrition

- Internal parasites

- Trace element deficiencies

adult animals:

- Undernutrition

what are some differential diagnoses for poor thrift affecting individual animals

- infectious diseases (most common)

- tooth defects

how should we assess nutrition?

- gather thorough history

- ideally do environmental exam

- combine the farmer's assessment of the current feed quality and quantity with what you observe

- compare nutritional levels with target feeding levels based on species and life stage

- rule out other differential diagnoses

what are trace elements?

elements that are required by the body in very small quantities but are essential for normal function.

what are the quantities of trace elements in pasture/forage dependant on?

the quantities in the soil

what are the most limiting trace elements in NZ?

Selenium (Se), Cobalt (Co), Copper (Cu) and Iodine (I)

what is the the difference between primary and secondary TE deficiencies?

primary: there are inadequate TE concentrations in either the soil or the plant/s

secondary: there are adequate TE concentrations in soil or plants, but the animal is unable to absorb or utilise sufficient amounts due to other factors

clinically, when do we usually see TE deficiencies?

- in areas where the soil concentrations are inadequate and the supplementation programme has gone wrong

- in areas where soil TE concentrations are marginal, or where secondary deficiencies occur.

Which formulation of a Se or Cu supplement is likely to be highest risk for resulting in toxicity?

injectable, as it leads to rapid absorption into the circulation and therefore potentially toxic concentrations reaching the tissues.

what are the issues with using TE supplements unnecessarily?

- poor use of money

- Se and Cu can be toxic in overdose

- other TE not usually as detrimental

generally what farmers are most proactive type at testing for TE status and supplementing appropriately?

Dairy farmers - as it is relatively easy for them to monitor cow health and performance via how much milk they produce each day

- sheep/beef/deer farmers have many more stock classes and have less ability to closely monitor animal performance.

what situations would vets assess TE status of animals?

Reactive manner:

- during an investigation for a health issue where they suspect deficiency or toxicity

proactive manner:

- as part of preventative health planning to ensure TE sufficiency and their production is not limited by low TE concentrations

- to monitor the effectiveness of a supplementation programme

what is the aim for trace elements?

- aim for sufficiency

- farmers and vets should work together to be proactive and ensure that animals always have sufficient TE quantities to perform to their potential

what are the methods that vets can use to assess TE status of animals?

- blood or serum samples for Se and Co, as Se is not stored in the body, and only a limited amount of Co is stored

- sample of liver for Cu, Se and Co can also be measured from liver if necessary.

- need to sample enough animals to give a reasonable indication of the variation in TE within the population

- need to balance cost vs accuracy

how do we collect samples for TE assessment?

- take bloods

- liver biopsy from live cows

- liver collection from animals after slaughter

what type of deficiency is Se deficiency?

Primary deficiency and most NZ soils are low or marginal in Se.

why is it uncommon for severe Se deficiencies to occur in livestock and when do deficiencies occur?

Soil Se concentrations in NZ have been mapped and farmers in areas where deficiency is common are usually very aware of this

- subclinical or mild clinical effects can result in substantial cumulative economic losses.

what is selenium's mode of action?

it is a key component of glutathione peroxidase (GPx) which helps protect cells against damage from free radicals (antioxidant)

- also has a role in immune function and adequate levels are required for growth and good reproductive health

what are the risk factors associated with selenium deficiencies?

- livestock grazing areas where soil concentrations are inadequate or marginal and where there is an insufficient supplementation programme

- no known seasonal predilection

- Cattle and sheep are equally susceptible.

- also affects deer and goats.

the clinical signs associated with Se deficiency?

- poor thrift in young growing livestock, sometimes accompanied by diarrhoea.

- white muscle disease

- reduced milk production in dairy cows

- increase in retained fetal membranes (RFMs) in dairy cows

- early embryonic death in sheep

what is white muscle disease?

- skeletal and cardiac muscle are affected, resulting in reduced function of these muscles and eventually death

- low Se concentrations allows cellular damage from free radicals

- primarily affects neonates

how do we assess Se status of animals?

Serum Se - gives estimate of how much has been absorbed in the past day or so

Glutathione peroxidase (GPx) - incorporated into red blood cells during haematopoiesis reflects Se status over around 3 months.

Liver Se - of thats the sample that has been collected

what do vets suggest for animals under high physiological demand in terms of Se concentrations?

that they have Se concentrations well above the 'adequate' range to reduce the likelihood of Se-related clinical signs.

- toxic range is very high so not too significant.

what type of deficiency is Co deficiency?

a primary deficiency and some NZ soils are low or marginal in Co

- Volcanic-based soils are particularly low

why is it uncommon for severe Co deficiencies to occur in livestock and when do deficiencies occur?

Soil Co concentrations in NZ have been mapped and farmers in areas where deficiency is common are usually very aware of this

- subclinical or mild clinical effects can result in substantial cumulative economic losses.

what is cobalts mode of action?

- is an essential component of vitamin B12.

- When vitamin B12 is deficient, less propionic acid can be converted to glucose

- Propionic acid is the only direct source of glucose available to ruminants and is required for optimal growth of young animals.

- Vitamin B12 also has a role in red blood cell formation and protein synthesis

what are the risk factors associated with cobalt deficiencies?

- Sheep have a much higher requirement for Co than other livestock species.

- young growing sheep (as it primarily affects growth rates)

- pasture concentrations are generally at their lowest in spring and summer

- animals in areas with low pasture concentrations (volcanic-based soils)

what are the clinical signs associated Co with deficiency?

- poor thrift in young growing sheep.

- poor appetite

- Severe: poor wool quality and anaemia.

- Cobalt/vitamin B12 supplements are not a toxicity risk.

how do we assess Co deficiency?

- blood or liver samples

- collection of as many samples as possible would be ideal (reasonable amount of variation)

- for cost-effectiveness recommended that 10 are collected.

- if animals have been yarded >6 hours their vitamin B12 concentrations are elevated.

how can you accurately predict from Co/vitamin B12 test results?

- whether Co deficiency was likely impacting on growth rates and/or whether there will be a growth response to supplementation (reactive testing)

- whether Co/vitamin B12 concentrations are adequate/not limiting to production (proactive testing)

why is Cu the most complex trace element?

- Cu deficiency is usually a secondary deficiency rather than primary in NZ

- there are many factors that can impact on whether secondary deficiency occurs

- liver is the best sample to collect

- there is a lot of variation in Cu concentrations within a group of animals

- clinical signs of Cu deficiency are also indicative of undernutrition - could be either.

- the clinical signs of marginal deficiency are vague.

- Cu is toxic in overdose

what are the main factors that lead to a secondary Cu deficiency?

High concentrations of molybdenum (Mo), Iron (Fe) or Sulphur (S) in the soil/plant bind to Cu in the rumen so it is unable to be absorbed.

- In NZ, Mo is the most significant

why is there a lot of variation in Cu concentrations within a group of animals?

animals have genetic variation in their ability to store Cu

what is the role of Cu?

an essential component of many different enzymes, which have a wide range of roles within the body including:

- energy metabolism

- myelin formation

- elastin and collagen synthesis

- pigmentation

what are the major effects likely to occur with Cu deficiency?

- impacts on growth

- reduced nerve function

- decreased strength/structural integrity of bones and tendons

- reduced pigmentation, affecting the colouration of hair follicles.

what are the risk factors associated with copper (Cu) deficiencies?

- presence of high concentrations of Mo (or sometimes Fe or S) in the soil/plants.

- Cattle and deer are most likely to develop Cu deficiency

- Cu liver concentrations lowest in spring

Which livestock species is the least likely to be affected by Cu deficiency?

sheep, as most NZ sheep breeds are very good at storing Cu in the liver and Cu toxicity is probably more common than a deficiency

Which trace element/s can cause clinical signs related to toxicity?

selenium and copper

what are the clinical signs associated with copper deficiencies?

can result in a range of clinical signs due to its many roles within the body.

- poor thrift in young or adult animals (mainly cattle)

- swayback (mainly deer)

- bone are cartilage defects

- faded coat colour

- anaemia

- reduced milk yield in cattle (cattle)

- reduced reproductive performance (cattle)

what is swayback

- Cu deficiency-induced hypomyelination of the central nervous system

- leads to progressive incoordination/ataxia in the hind limbs which is more marked when the animal is stressed

- progresses to recumbency and then death.

- usually only seen in deer, > 9 months of age

how should we assess Cu status of animals?

- Liver samples should be taken (blood is only useful for deficiency causing clinical signs)

- large number of animals should be sampled (as large variation)

- Statistically recommended = 16

- pragmatically recommended = 10.

- Testing soil Mo, Fe and S can also be useful.

what does testing Cu status of a few animals run the risk of?

being unable to make sound decisions - leading to risking toxicity or deficiency

what should the decision to supplement Cu be based on?

a risk assessment, including consideration of whether liver Cu stores are likely to be depleting (i.e. over winter) or increasing.

Under what circumstances would measurement of serum or blood Cu concentrations be of value?

to diagnose deficiency - causing clinical signs.

For which TE/s are the reference ranges for laboratory testing not based on production responses to supplementation??

Copper.

why is it reasonably common to test liver Cu stores in autumn?

- it is known that Cu concentrations in animals deplete over the winter

- to ensure they are sufficient to last through the winter.

what Liver Cu concentrations are considered adequate to maintain animal performance?

- >95umol/kg (recognising the limitations of the reference range!)

- the rough rule of thumb is to aim for liver concentrations of >300umol/kg in autumn to ensure they don't drop below 95umol/kg by the end of winter.

what type of deficiency is Iodine deficiency?

- primary deficiency due to very low concentrations of I in the soil

- secondary deficiency due to goitrogens in some livestock feeds which interfere with I uptake in the thyroid gland

what is the role of iodine?

- used in the synthesis of thyroid hormones

- Thyroid hormones in the developing foetus are important for: energy metabolism, development of fetal brain, lungs, heart, wool/hair follicles, stimulation of production of fetal lung surfactant.

what are the risk factors associated with I deficiency?

- Goats and sheep are the most susceptible species

- most commonly seen when pregnant ewes or does graze on brassica crops over the winter

- It can sporadically occur in goats and sheep grazing pasture, particularly in areas with low soil I.

when are clinical signs of I deficiency seen?

NZ clinical signs are seen in spring as developing foetuses are affected.

what are clinical signs associated with I deficiency?

- goitre (enlarged thyroid glands)

- increased perinatal mortality rates.

- Dystocia may occur for newborns with severely enlarged thyroid glands due to the thickness of the their neck.

how do we assess I status of animals?

- conduct PMs of dead perinatal offspring.

- recommendation is to PM 15-20

- for each, weigh the lamb and the thyroid gland (compare as a ratio of thyroid : bodyweight)

- dams blood or urine I can be tested; only reflective of a few days, testing at a single point in time is unlikely to provide whether supplementation is needed.

what ratio of thyroid : bodyweight is considered significant?

- Ratios above 0.7g/kg are considered deficient

- those greater than 0.4g/kg are considered suggestive of deficiency.

- A total thyroid weight of >2g is considered to be clinical goitre.

what is the risk based approach to I deficiency prevention?

- if grazing on brassica crops during pregnancy; supplementation is recommended.

- If I deficiency has been diagnosed when dams were grazing pasture, this may or may not recur the following season.

- The decision on whether to supplement is based on a case by case basis in partnership with the farmer.

what are the categories of supplementation options?

- additives to fertiliser

- oral dosing (water or drenching)

- foliar spray or a slurry that can be added to pasture or supplementary feed

- injectable forms

- pour-on (Se only)

- slow-release rumen boluses

- mineral licks - popular with farmers but a very poor choice for reliable supplementation

For which TE is addition to fertiliser likely to be an ineffective method at significantly raising animal concentrations?

copper; as Cu deficiency is almost alwasy a secondary deficiency

Why are mineral licks a very poor choice for TE supplementation?

you can't tell if each animals is getting an adequate dose

what are main factors to consider when selecting which TE supplement is most appropriate?

- Length of time the supplement raises animal TE concentrations

- Route and ease of administration

- Price

- Whether the farmer applies fertiliser at a time that is strategic to also apply TE

- Toxicity risk

why should vets ook at the science behind TE supplement products before recommending their use?

- there are a lot of products on the market that contain TEs

- claims from manufacturers of some products efficacy are not backed up by evidence

- they may not have effect on animal production and health.

what TEs can be potentially toxic in overdose?

Selenium and copper

what situations does copper or selenium toxicity occur due to accidental overdose?

1. The animals are getting supplemented via multiple sources and are getting too much.

2. Wrong dose of a supplement is given

3. Malfunction of in-line water dispensers.