Impact of blood plasma calcium on lifetime performance
The plasma calcium level around parturition has been shown to have a major effect on fertility. The economic impact of improving the calcium level at calving – obtained by supplementing the pre-partum animals with the product X-Zelit, as reported by Kerwin et al. (2018, 2019) – was simulated using the Simherd model.
Reproduction and yield
Supplementing X-Zelit (Vilofoss) in the late part of the dry period is known to increase fertility (Fig. 1) and milk yield (Fig. 2). Fig. 1 shows the proportion of cows not pregnant. Median time to pregnancy was 19 days earlier for cows fed X-Zelit.
This highly improved reproduction result corresponds to a study in New Zealand in which pasture-fed multiparous cows were supplemented with X-Zelit. The cows which were given X-Zelit became pregnant 7.5 days earlier in lactation compared to the control group. In this study, pregnancy was also assessed in relation to when seasonal insemination begins, and it was found that cows in the X-Zelit group became pregnant 13.8 days earlier in the season compared to the control group.
Also, in a trial conducted by Martinez et al. (2012), the normocalcaemic group had 15 fewer empty days compared to the hypocalcaemic group. In the same trial, the probability of a positive pregnancy in normocalcaemic cows was estimated to be 1.61 times higher than the probability in hypocalcaemic cows.
Long-term effect on reproduction
The positive effect on reproduction of X-Zelit supplementation was also visible around day 150 (Fig. 2) in the trial in Cornell. At this point, 30% of all cows in the control group are still not pregnant, while only 10% of the cows in the X-Zelit group have not yet become pregnant.
This corresponds to findings by Caixeta et al.(2017), who established about twice as many non-pregnant cows in the group of hypocalcaemic cows compared to the group of normocalcaemic cows at 120 days into lactation. A previous Danish trial did not establish any differences in reproduction between cows supplemented with or without X-Zelit. However, it was found that multiparous cows supplemented with X-Zelit in the dry period had fewer cullings through lactation compared to cows not supplemented.
On average, the milk yield was 0.8 ECM higher during the first four weeks, reaching +1.9 ECM and +1.5 ECM compared to control animals during week three and four, respectively.
The positive effects on yield and reproduction are probably caused by the improved plasma calcium levels (Fig. 3).
The serum calcium level was significantly improved in the X-Zelit supplemented group. On average, cows fed X-Zelit had Ca concentrations which were 0.4mmol/L larger than those in the control group during the first days in milk.
Differences in the Ca levels were also reflected in the percentage of multiparous cows being subclinical calcaemic.
Three times as many control cows had subclinical hypocalcaemia compared with the control animals.
Simulation of farm economy
The information about these figures was used in the economic simulation shown in Table 1. As a means of better understanding the impact of X-Zelit on the herd, the economic impact is illustrated as individual effects as well as a total response.
In the reproduction scenario, the culling rate is lower, since fewer cows are culled due to failure to conceive. As the reproduction is better, fewer heifers are needed for replacement and more heifers can be sold. The animals will increase the number of lactations by an average of 0.5, which results in a 5.356 ECM higher lifetime performance. Rolling Herd Average increases by 32kg only, because of an increase in the proportion of dry cows (+1%) and an increase (+7 per 100 cows) in the disease (lameness and mastitis) incidence rate, due to a higher proportion of old cows in the herd.
It is interesting to observe that, basically, the improved reproduction and improved milk yield have the same economic values (Table 2). Earlier calculations of economic impact of metabolic diseases focus on loss of milk yield, but this study demonstrates that the loss of reproductive performance of the animals might lead to costs at around the same level.
X-Zelit both improves the reproduction and milk yield, thus, considering these two factors only, the return of the cows will amount to +€110 per treatment.
X-Zelit improves reproduction and yield in dairy cows and, in turn, this increases the lifetime production of the animals. An economic analysis splitting up these two components concludes that the return of using X-Zelit on all multiparous cows will be +€110/treatment.