There are some slight nutritional differences between the two as well. Due to its solely grass diet, New Zealand lamb has less fat than grain-fed or finished American lamb, per New Zealand Spring Lamb. It also has less calories for this reason, and is higher in omega-3 fatty acids. A 1988 study in the Journal of Food Composition and Analysis found there was no difference in protein content between American and New Zealand lamb, but U.S. lambs had less cholesterol, higher fat, and a lower moisture content of the two.
Per Taste Pure Nature, grass-fed red meat contains more vitamin A and E, and is a good source of iron, zinc, and vitamin B12. Although lower in fat, leaner New Zealand lamb may have you reaching for richer sauces and cooking fats, which may negate any difference.
The nutritional difference between the two is correlated to the animal’s diet. Any lamb, regardless of its home country, fed a 100 percent grass-fed diet with no grain-finishing, will offer the same differences.