AbstractFor a study of the effects of origin in a temperate climate on the rate of development and performance in their first lactation, a group of Holstein heifers were selected from herds in New York State and moved to Puerto Rico. The heifers were seven months old upon arrival in Puerto Rico. The 36 imported heifers were kept at all times together with 14 Puerto Rico born heifers of similar age on heavily fertilized grass pastures with some supplementary feeding prior to parturition. During lactation, they consumed a 20% crude protein concentrate at the rate of about 1 kg per 3 kg of milk produced. Month of calving affected lactation yields significantly (P <.05), but age, origin, and the interaction effects were not significant. Group means were similar for length of lactation, age of calving and number of days from parturition to first estrus. The imported heifers averaged higher than the locally born in milk yield (4004 vs 3815 kg), in fat yield (140 vs 130 kg), and in fat percentage (3.47 vs 3.41). In body weight, the imported heifers averaged about 23 kg heavier than the heifers born locally. Approxi mately 43% of the difference in milk yield was attributed to differences in genetic potential. Coefficients of variation were 30 to 50% more than expected tor milk yield and for fat and breeding efficiency. This study showed that in determining the performance of imported cattle, origin effects per se are much less important than stage of pregnancy, age, feed supplied and health maladies. The results also showed th at Puerto Rico born hi-grade heifers, sired by selected progeny-tested Holstein sires from the United States, will perform as well, or nearly so, as heifers which can be purchased at reasonable prices in the United States.
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