Dorman has just completed a Kellogg Rural Leaders Programme at Lincoln University with some sponsorship coming from the NZ Holstein-Friesian Association.
Her research project took a critical look at what role TOP has in the national breeding objective, which is currently under review.
In particular Dorman investigated where longevity and survivability rank in the national breeding objective, how their economic values are calculated for inclusion in BW and compared this with her own calculations on how much an extra lactation is actually worth.
Dorman’s calculations place an extra 54c/day on longevity. This is over 10 times more than the 4.8c value attributed to residual survival by the NZ Animal Evaluation (NZAEL) calculations.
The difference can be partially explained by the fact Dorman’s longevity measure includes all causes of voluntary and involuntary culling such as fertility, high somatic cell count (SCC) and production traits whereas the residual survival breeding value, as NZAEL methodology defines it, measures only the traits not already included in BW.
Dorman’s concern is that if the traits related to residual survival equate to an economic value of 4.8c then other traits relating to longevity already in BW such as production, fertility and SCC would have an economic value of 49c, which seems excessive, she said.
Dorman also looked at the relationship between cow liveweight (LWT) and BW.
Weight discrimination
She concluded that heavier animals are being unfairly penalised as LWT is not necessarily an accurate indicator of productive efficiency, in particular feed conversion efficiency (FCE).
Her study was timely given the national breeding objective review. Animal Evaluation Unit manager Jeremy Bryant said her work was taken into account along with submissions from a wide range of groups during the consultation phase of the review.
Dorman, formally a Federated Farmers policy analyst and DairyNZ developer, now works for Environment Canterbury (ECan) in its extension services division helping farmers develop farm plans and be part of the audited self-management systems promoted by the council.
She and husband Hayden Dorman have recently stepped up to 50:50 sharemilking 800 Holstein-Friesian cows on a high-input farm owned by Federated Farmers Dairy chair Willy Leferink and his wife Jeanet, having worked as variable sharemilkers on the property for two years.
On top of that Dorman is vice-chair of Federated Farmers Dairy Mid-Canterbury and the Federation’s Sharemilkers section.
During her Kellogg study Dorman said it became clear very few people in NZ understood the national breeding objective and the models behind BW. She wants to see more effort put into explaining the system so more people can get involved and have meaningful input into how weightings and calculations are set.
When determining her economic value for longevity Dorman used comprehensive modelling that followed the same methodology used by Professor Dorian Garrick in the well-known Milk Production from Pasture publication when he set out to demonstrate the economic value of longevity.
However, unlike Garrick who used one year’s information for some cost and income inputs to the model, Dorman used 10-year average data collected from the DairyNZ Economic Survey, NZAEL and Beef and Lamb NZ to prepare a budget for two comparison farms – one a typical NZ farm and one a reduced-longevity herd.
In setting up the farm models she’s made a number of assumptions, including taking the herd structure and survival rates for the typical farm from NZ Dairy Statistics 2010/11.
She calculated milk yields based on that age structure and NZ Dairy Statistics milk yield figures for that year, using a replacement rate of 21% as used by NZAEL, using costs/cow and /ha fixed in the same proportions as the NZAEL model and setting feed requirements for both herds and their replacement heifers based on DairyNZ’s Facts and Figures data.
Dorman also carried out a sensitivity analysis to see how varying input costs and prices in the model might affect the outcome.
Improved longevity lifts profitability because of the influence it has on the herd’s age structure. A greater proportion of cows in the herd are at their productive optimum at five, six and seven years old, contributing to better productive efficiency.
Replacement costs
Improved longevity reduces replacement rate, decreasing the costs as fewer heifers need to be reared, she said.
Previous NZ studies have found 15-18% to be the optimum replacement rate but NZ averages are well above this. NZ studies have also shown that around half of all culls are sent off the farm because they are empty – a factor that needs more investigation if longevity and herd age structure is to be improved, she said.
Dorman argues further assessment should be carried out on increasing the weighting given to TOP in the national breeding objective. She points out that NZ farmers are increasingly moving towards systems that push production/cow and in so doing will be challenging cows’ productive physical traits much more, pressure going on the udder, frame, heart and lungs.
“With increasing production/cow in the NZ dairy herd we will be more reliant on selecting for a robust cow with strong functional conformation traits in order to maintain longevity and prevent early involuntary culling from the herd.”
NZ studies found that registered herd owners place more emphasis on TOP that relate to conformation of the animal while commercial farmers are more likely to cull cows because of traits such as slow milking or poor temperament.
Across all farms reviewed in NZ studies udder overall, udder support, dairy conformation and speed of milking were among the top five TOP accounting for true and functional longevity in NZ commercial herds with farmer opinion number one in that top five. Farmer opinion could also include physical attributes such as udder and overall conformation as assessed by the farmer.
Currently the NZ BW system puts 66% of the economic value weightings on production traits while 34% are on functionality/ health traits.
No weighting is given to type and conformation in their own right, Dorman said.
The merit index (MI) promoted by CRV Ambreed puts 41% of the weightings equally on production and functionality/health and 18% on type and conformation. World averages from indexes in seven other dairying countries put 46% of weightings on production, 25% on functionality/health and 22% on conformation.
And while some will argue that the BW index is designed to rank cows most suitable to provide profitable returns for a NZ system Dorman believes our cows aren’t so different that no weighting for conformation traits can be justified.
Function and profit
Conformation traits are important because they relate to functional properties of the cow, which in turn relate to profitability. There are strong economic reasons for placing emphasis on breeding a cow with the right physical attributes, and this can be done in conjunction with selecting for production, she said.
The problem is few cows relative to the national herd size are TOP-scored and Dorman believes the industry would benefit from having a larger, more representative subset of the national herd TOP-scored regularly to see if there is any real improvement in TOP such as conformation and udder related traits.
“The current national trends for improvement in conformation traits are only reflected by the less than 1% of the national herd that are TOP-scored, the majority of which are from pedigree herds,” Dorman said. “This doesn’t tell us what is happening in the general population.”
From her investigations Dorman’s concluded there are several pieces of information the NZ dairy industry is lacking in to make decisions about the inclusion of traits in the national breeding objectives.
The reasons for voluntary and involuntary culling are not well recorded, making it difficult to assess the specific reasons cows are leaving the herd and so what traits need improving to boost longevity, she said.
The most recent genetic evaluation for cow longevity was completed in 2007 and was used to determine the residual survival breeding value calculation.
Dorman said at the time of the study it was recognised that a full multiple trait approach including predictor traits and actual longevity data would have been better so she suggested further analysis using that approach should be carried out.
