## 7 The Potential for Further Beef \(\times\) Dairy Development in New Zealand and Globally  
The evidence to hand would appear to confirm the benefit of using _MSTN_ c.821(del11) homozygous terminal sires for mating to dairy cows, in the quest to obtain progeny with carcasses and meat that meets CAB criteria. These sires could be strategically mated to dairy cows that do not have the genetic merit to be bred from again to produce herd replacements (they have low breeding worth), but that still adds value to the production system with their dairy performance. Their herd counterparts that have genetic merit could then be mated to high genetic merit dairy sires to produce herd replacements, and possibly using sex-selected semen to maximise the number of female dairy-type progeny to select replacements from.  
In New Zealand, given that only approximately a quarter of dairy progeny end up as herd replacements [4], as nearly all males and half the females are ultimately culled [63], then potentially only the top half or less of the milking herd would be mated to elite dairy sires, while all the other cows would be mated to dairy sires. At a global level, with an estimated 270 million dairy cattle in the world, albeit many likely filling dual meat and milk production roles, scale-up of the use of beef genetics across dairy cows of lower genetic merit should not only allow the production of more high-quality beef, but also accrue GHG reductions.  
While care would need to be taken to ensure there is not an increase in calving difficulties, the contrast between the findings [27, 46] would suggest that greater effort needs to be made in dairy production to further improve the birthing performance of dairy cattle. In that respect, it was reported that dystoxia rates in dairy cattle internationally are generally <5%, apart from those in the United States, where they are higher [64], while, in contrast, it was reported that New Zealand beef farmers assisted 7% and 1.7% of two- and three-year-old primiparous heifers, respectively [65].  
In New Zealand specifically, if the size of the nearly wholly grass-based beef breeding herd (approximately 3.81 million; [66]) was reduced by 500,000 cows, with 90% of the cows producing calves (of which half were female, and perhaps half again of these were needed as replacements), then approximately 375,000 potential finisher beef cattle would be lost per annum. Assuming an average carcass weight of 350 kg at slaughter and a value of NZD 5 per kg of carcass, then a NZD 656 million loss in value may accrue annually.  
However, if half the 4.67 million dairy cows in New Zealand produced beef finishing cattle as a consequence of being mated to elite homozygous _MSTN_ c.821(del11) Angus bulls, with the same reproductive performance of 90% calves to cows mated, and all the beef calves being finished to 350 kg carcass, then potentially an additional 2.14 million carcasses would be produced, which at NZD 5 per kg would create NZD 3.754 billion of value, a considerable financial gain for the loss of 500,000 beef cows. While potentially more beef cattle could be removed from production, it needs to be acknowledged that these cows serve other purposes, such as grooming overgrown pasture and allowing for the rotational management of sheep to manage parasites. Equally, not all the extensive rangeland where New Zealand beef cattle are farmed is able to support beef finishing systems.  
One can only speculate as to what kind of a change to the system this might mean in the context of the global dairy industry.