Discipline: breeding; Keywords: automatic milk recording system, efficiency measures, milk yield, liveweight, Kleiber ratio, component value.
The efficiency of milk production of dairy cows has been a common point of discussion among dairy farmers, veterinarians, feed and breeding consultants. Whereas there are different ways of expression, it primarily should be a financial metric of the value of product(s) produced in relation to the production cost of all product(s). For dairy cows this mainly includes milk production income in relation to the feed cost to produce milk. For the lifetime efficiency the beef production income of cows should probably also be included. Most dairy farmers have a breeding programme towards the improvement of the genetic merit of their herds which may or may not include efficiency measures. Whereas sire selection affects the genetic progress in a dairy herd, evaluation of cows on their production performance should also be part of the programme. This is because daughters of carefully selected sires may produce less milk because of environmental effects on milk yield and the random combination of genes. For this the milk yield of cows should be recorded after first calving to identify poor performing animals to be culled. Culling poor performing cows should be done on an on-going basis as not removing them would have a negative effect on the future genetic merit of a dairy herd as well as the current herd income.
The availability of automatic milk recording system (AMRS) records provide the opportunity to determine suitable efficiency measures towards improving the overall genetic merit of dairy herds. Efficiency parameters may include the milk yield of cows, the 4% fat corrected milk (FCM) yield and component value (CV) based on the fat and protein yield of cows. Because of the availability of live weight records additional efficiency measures for cows may also be estimated. This includes the Alternative Kleiber ratio (KR), FCM divided by live weight (LW) and the farmer-popular trait of milk yield divided by live weight (MY/LW). The reason for including LW is related to maintenance requirements of dairy cows. However, improving the efficiency of cows is not simply by reducing cow size. This is because of the positive genetic correlation between milk yield and live weight. The value of these efficiency measures have recently been investigated by the authors cited below.
Lactation (305-day) records from seven dairy herds from pasture- and total mixed ration (TMR) -based production systems were available for the study. Efficiency measures as indicated above were estimated for each herd. For each efficiency measure the same selection strategy was applied. A selection threshold value was estimated to identify the bottom 20% of cows using the following equation:
Threshold value = Mean - (0.8416 x Standard deviation)
Within each efficiency measure (or selection strategy), cows were ranked from low to high. Cows producing at levels at and below the selection threshold value were marked for culling. The mean 305 day milk yield and live weight of cows identified to be culled and cows to be kept (remain) in the herd were estimated for each selection strategy. The milk yield and live weight of cows identified to remain in the herd were compared to the milk yield selection strategy.
Unfortunately, there was some doubt about the accuracy of milk composition data in some of the herds. Therefore by means of illustration, the results of one herd of about 700 cows in a pasture-based system, where there was no doubt, showed that selection strategies such as FCM and CV compared to milk yield, resulted in a reduction in the milk yield of cows remaining in the herd, i.e. from 5065 kg to 5051 (-14 kg) and 5049 kg (-16 kg) respectively. For this herd the level of agreement using FCM and CV was high, i.e. 0.90 and 0 89 respectively. High levels of agreement indicate that similar cows were selected for culling using the different selection strategies for efficiency. By including LW in the selection strategy, the milk yield and the LW of cows remaining in all herds were reduced. This is probably related to the general positive relationship between milk yield and live weight. This may further emphasize that simply culling large cows would not necessarily result in improving efficiency.
The lifetime performance of cows can be estimated and compared to the live weight of cows. Such records were available from the data sets used. Using the same data set as mentioned above, the mean lactation milk yield and live weight showed that the milk yield and live weight of the cows increased from first to seventh lactation, i.e. 6111 vs. 8013 kg and 538 vs. 600 kg respectively. Efficiency as estimated by milk yield divided by live weight increased from 11.4 to 13.4 kg for cows that have completed two to seven lactations. Using the lifetime performance of cows this efficiency measure increased even further, i.e. from 22.7 to 93.5 kg for cows that have completed second to seven lactations. This seems to indicate that lifetime milk yield reduces the effect of live weight.
C.J.C. Muller, H.H. Meissner & C J van Dijk, 2021. Developing efficiency measures for production parameters in dairy herds using automatic milk recording system data. FINAL PROJECT REPORT FOR MILKSA – February 2021