So NZ dairy cows should have less lameness but how much less? And it’s not just about averages what should the target level of lameness be for dairy farms in NZ?
To answer these questions it is important to understand two concepts – prevalence and incidence. Both of these are important to measure if we are looking to manage and control lameness. Prevalence is the proportion of cows that are lame now while incidence is the proportion of cows that are lame over a period of time, usually from one calving to the next.
To get an accurate measurement of incidence requires active monitoring of lameness. Simply relying on farmers’ records is totally insufficient as the proportion of lame cows which have good records is very low, and varies greatly between farms. So incidences based on records, which average about 5%, are likely to be gross underestimates. Farmer estimates of lameness (ie “how many lame cows have you had this year?”) are higher, averaging about 12%, but are still an underestimate. To measure incidence properly needs proactive collection recording of all lame cows, regardless of what treatment they had.
Several studies have reported lameness incidence in small numbers of herds but only one large scale prospective study has been carried out in NZ. This study was carried out in 43 herds on the east coast of the South Island. The mean annual incidence of lameness on those farms was 26%, and the incidence on individual farms ranged from 4% to 64%. The data from this study suggested farms with an incidence of more than 25% had a major lameness problem, and even on large South Island farms, a lameness incidence of less than 10% was achievable.
No similar studies have been done in the North Island, but data from farmer estimates of incidence suggested the difference in lameness incidence between the two islands was likely to be small. So, just like in the South Island, in the North Island more than 25% of cows lame over a year would indicate a significant lameness problem and a target of less than 10% lameness should be achievable. In small herds (less than 300) this target could be reduced to 7.5%, because the increase in farm staff per cow means implementing lameness herd programmes is often more achievable.
Measuring lameness prevalence allows active management of lameness throughout the year. However, lameness is a seasonal problem, with different levels at different times, so if you are benchmarking herds in a region then prevalence needs to be measured at the same time in all herds. In addition, multiple measurements of prevalence are needed to establish a herd’s lameness pattern. Nevertheless, strategically measuring prevalence at critical times, such as one month before starting mating, can greatly improve management without requiring significant staff time.
There are two measures of prevalence – 1) the proportion of cows in the herd at the moment that you have recorded as lame; 2) the proportion of cows with a DairyNZ lameness score of 2 or 3. The second figure is usually 4-5 times the first, and is a much better reflection of the true level of lameness in the herd, but it does need to be done systematically, not just as a quick glimpse while cows are being milked or are in the paddock.
On average, peak lameness prevalence (measured in October-November in the North Island and January-February in the South Island) is more than 7% on more than 50% of farms, with 4% being an achievable target (that is equivalent, on farms which don’t lameness-score, to no more than 1% of the herd lame at any one time).
