Effect of diet type on performance and metabolic traits of Peruvian local and introduced cow types kept at 200 and 3600Â m of altitude

Twelve Brown Swiss (BS) and 12 Peruvian Criollo cows (CR, a local Peruvian cow type adapted to altitude and harsh environment), both Bos taurus and adapted to altitudes  > 3500 m a.s.l. (above sea level), were kept at 200 and 3600 m a.s.l. and assigned to three dietary treatments, respectively. The experimental design was a 2 (cow types) × 3 (diets) × 2 (sites) factorial arrangement (total n = 72). The diets used represented the quality of typical highland dry-season forage (DS), highland rainy-season forage (RS) and a diet with optimized nutrient composition (OC). Contents (g/kg dry matter) of crude protein clearly increased from diet DS to RS and OC (from 42 to 81 and 131) and neutral detergent fiber contents decreased with increasing diet quality (from 734 to 580 and 512 for DS, RS and OC, respectively). The CR consumed less dry matter than the BS (P < 0.001) (g/day and kg BW0.75; 65 and 68, 117 and 136, 130 and 158, for CR and BS receiving diets DS, RS and OC, respectively). Both, dry matter intake and energy-corrected milk (ECM) yield increased with diet quality (P < 0.05); the latter nearly doubled for both cow types when switching from diet DS to OC. A similar increase was found for daily ECM yield expressed in g/kg BW0.75 (34 and 46, 57 and 76, 63 and 91, for CR and BS fed diets DS, RS and OC, respectively). Especially in CR the major part of this increase was already found when replacing DS by RS (cow type × diet interaction, P < 0.001), indicating that CR cows had approached their genetic production limit with diet OC. The low intake with diet DS resulted in an energy deficit characterized by a massive mobilization of body reserves in both cow types. In intake, performance and metabolic traits there were no clear indications that the CR cows tolerated the low-quality diet better than the BS cows. Both cow types also showed similar performances at the two sites, and high altitude did not seem to cause any extra maintenance energy requirements but was found to increase milk fat content (P < 0.05). These results lead to the conclusion that the metabolic responses to under-nutrition and hypoxia were similar for the two cow types.