The objective of this presentation is to compare the production, survival and fertility of strains of Holstein-Friesian (HF) cows, Jersey cows, and their crosses reared under an intensive-seasonal-pastoral dairy farming system in New Zealand (NZ). Results from trials of Holstein-Friesian (HF) cows, which differed genetically for liveweight, conducted at Massey University (NZ) have shown that the high liveweight line had reduced fertility, as demonstrated by delayed puberty and reduced conception rate, compared to the low liveweight line. The high liveweight line had a greater proportion of overseas HF genetics than the low line suggesting there may be strain differences in fertility which may be expressed in reduced survival for the overseas HF strain. Similar results have been obtained at Dairy Research Corporation (NZ) by comparing NZ HF and Dutch HF strain under two feeding regimes: a total mixed ration feeding system and a rotational pasture grazing system. These results have motivated a major study by Livestock Improvement to investigate the production, survival and fertility of strains of HF cows, Jersey cows, and crosses between these breeds and strains within the HF breed. The data were collected on Livestock Improvement's Sire proving scheme herds. These commercial herds are spread evenly across NZ, have a breed representation similar to the national herd, have intensive data recording and have 75\% to 95\% of their cows artificial inseminated to unproven sires. The data consisted of104,862 first-lactation cows calving in seasons 1987 to 1999. The results from this study will be presented.