Thursday, 29 September 2016 11:55

Body condition scoring service shaping up better

Written by  Pam Tipa
Chris Leach, DairyNZ. Chris Leach, DairyNZ.

Body condition score (BCS) will increasingly be adopted as a measure in welfare assurance schemes, so scoring must be accurate throughout the BCS range, say DairyNZ’s Chris Leach and Jacqueline McGowan.

The National Body Condition Score Assessor Certification Programme, backed by DairyNZ and the Ministry for Primary Industries, was launched in 2012. This is to ensure the dairy sector has access to trained, competent rural professionals who maintain calibration to the DairyNZ BSC national reference standards, say Leach and McGowan in a paper for the NZ Veterinary Association.

The programme ensures delivery of training, initial and ongoing assessment, and BCS assessment activity levels necessary to achieve and retain calibration. It certifies those achieving the set requirements and agreeing to provide service; they must agree to a code of practice and become certified BCS assessors.

Accurate BCS assessment is essential when farmers use it to support decision-making or when the BCS is a criterion in animal welfare assessments.

Farmers are encouraged to do their own BCS assessments, but many do not due to lack of time or confidence, the paper says.

Equally, in corporate farm structures, grazing arrangements and herd sales, a BCS assessment provided by a certified BCS assessor holds more weight than unvalidated assessments.

The Code of Welfare for Dairy Cattle stipulates a minimum BCS of 3.0. Farmers can be prosecuted under the Animal Welfare Act 1999 if they have cows thinner than this and fail to take action. Since 0.5 of a BCS unit could mean the difference between compliance and noncompliance, any operator scoring cows at the lower end of the range needs to be certain of accuracy.

Accurate BCS assessment is also essential to farmers for decision-making. For example, cows may be dried off to give them time to regain body condition lost during lactation before calving.

When using the BCS dry-off rules for cows in a low input system, incorrectly estimating a cow’s BCS by 0.5 could lead to premature dry off and missing out on another 30 days in milk. Alternatively, cows may calve thinner than the recommended optimum.

Although affected by milk price, the value of increasing BCS at calving from 4.5 to 5.0 is conservatively estimated at $60/cow (InCalf), through increased milk production and better reproductive performance.

The positive relationship between calving BCS and milk production continues above BCS 5.5 but the risk of metabolic disease increases significantly.

Peripartum health is very sensitive to calving BCS. For example, the risk of ketosis is doubled in cows that calve at a BCS >6, compared with cows that calve at a BCS 5.5.

In a recent DairyNZ study, 40% of cows that calved at a BCS of 5.5 had β-hydroxybutyrate concentrations greater than 1.4mmol/L postpartum whereas none of the cows calving at 4.5 exceeded this threshold. In the same study, although all cows underwent an inflammatory response around calving time, cows that calved at BCS 4.5 appeared to recover faster than cows calving at either BCS 3.5 or 5.5.

As farmers move toward winter crops such as fodder beet and put more value on achieving BCS targets, it is essential that accurate BCS is provided at the top end of the scale as well as the lower end to guard against metabolic disease.

Given that subtle changes in the BCS at calving can have significant effects on subsequent productivity and health, particularly when BCS is greater than 5.0, it is important that farmers make management decisions based on accurate BCS.

Despite evidence of the importance of BCS management for productivity and welfare, it is a subjective measure that requires practitioners to be trained and perform regular calibration.

Although rural professionals (RPs), particularly vets, consider themselves well able to assist their clients to score their herds, farmers have little confidence.

DairyNZ began to develop a BCS certification scheme in 2011. Initially, this was a one day training course aimed at improving the scoring capability of attendees (vets and other RPs), so that they could score a group of cows to within 0.2 of the trainer-derived mean for the group. However, most RPs believed they were fully competent and therefore did not need to attend training.

In autumn 2012, a BCS operator test scheme was piloted, which assessed individuals for their ability to score a group of cows (i.e. mean and range) as well as their ability to score individual animals. A ‘gold standard’ team provides the model scores against which assessors are tested.

In the first two rounds of testing, only 69% of newly trained practitioners passed (i.e. were within 0.2 BSC above or below the model). There was also a marked difference between regions. For example, in the first round, candidates in Northland scored an average of 0.21 above the model, but candidates in Waikato scored an average of 0.26 below the model, i.e. there was a difference between those two regions of almost 0.5 BCS.

The general consensus was that annual retesting was appropriate because of international evidence of the need for calibration to reduce drift, i.e. that accuracy of BCS declines with time since training. However, participants in the BCS programme frequently state that annual onfarm retesting is excessive.

Results from the NZ BCS certification assessments suggest that the scoring of most assessors changes relative to the DairyNZ reference standard from one assessment to the next. Additionally, assessors tend to under-score cows with high BCS and over-score cows with low BCS.

Even for candidates who had passed, and had an acceptable difference from the gold standard overall, scores were biased toward the herd average, and the range of scores allocated to the same cow by different assessors was more variable at the extremes of BCS. This highlighted the importance of re-calibration and re-testing to maintain high scoring accuracy among certified assessors, and the need to expose them to unfamiliar BCS scores in between on-farm assessments.

At the launch of the DairyNZ BCS certification scheme, the gold standard team consisted of five DairyNZ animal husbandry extension specialists. To facilitate greater flexibility, RPs with a history of BCS accuracy were invited during 2015 to join the gold standard team.

Once certified to the gold standard, these additional trainers have been helping to run training and assessment days in their regions. Every six months the whole team reconvenes to repeat BCS calibrations and for reassessment.

The calibration consists of hands-on scoring of a range of cows in a vet race, openly discussing all eight points of each cow, using the DairyNZ BCS Made Easy field guide, and scoring 80 cows in a paddock.

Most of the gold standard candidates also spend time scoring alongside one of the DairyNZ team in the months beforehand.

For the gold standard assessment each candidate scores a whole herd of 300-600 cows during milking, followed by hands-on scoring of 15–20 cows in a vet race.

The candidates’ scores are then compared with the modal score generated by a group of gold standard scorers (minimum n=5), who have been accepted to this standard for at least 12 months. To pass the gold standard, a candidate must achieve 75% agreement in a range of criteria, whereas regular certification requires 50% agreement. There are currently 12 gold standard scorers in the team – five DairyNZ extension specialists and seven contracted assessors.

 

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