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Ten measures related to breeding efficiency were used for comparisons among pure Jerseys and Red Sindhis and crossbreds with 3/4, Vz, or 1/4 European dairy inheritance (Brown Swiss, Holstein, or Jersey) at two locations. Jerseys and crossbreds were common to both herds with Sindhis only at Jeanerette. Means for age at puberty (first estrus after 12 mo) were 425 + 4.2, 434 + 6.9, 459 + 6.9, 504 + 14

A BST R ACTEffects of herd, year, age, season, and their interactions on milk yield, lactation length, and reproductive efficiency for purebred and high grade Holsteins were determined by analysis of variance of 17,255 lactation records from 48 herds in Mexico. Herds differed in all traits. Herd average n,itk Add ranged from 2620 to 7670 kg. V,.::'.':;, ages, and seasons were import:mr :'c, milk yield, but these varixbles had little influence on lactation length, days open, days dry, and calving interval. Most two-, three-, and four-way imeractions for milk yield and days in milk were of importance. Main effects and interactions accounted for 37% of total variance in milk yield. Total variance for milk was 1,344,364 kg 2. From variance component analysis, percentages of total variance in milk yield attributed to herd, sire, cow, and error effects were 23.8, 2.2, 33.9, and 40.0. Phenotypic correlations among milk yield, days dry, days open, lactation length, and calving interval were positive but significant only for milk and lactation length. Lactation length accounted for about 34% of the variation in milk while days dry, days open, and calving interval contributed less than 4%. For milk yield the estimate of heritability within herd was 11.9% and repeatability 45.1%. Effects of herd, year, -tge, and season on the performance of Holsteins in Mexico do not differ markedly from temperate areas.

Variance components were estimated for herd, sire, and cow effects with a three-way nested model, using unadjusted and adjusted records for age and seasonal difference from 62 herds on DHIA recording in Puerto Rico. The cows calved from 1967 to 1973. They were high grade and purebred Holsteins imported from Canada or the United States or progeny of bulls and semen from the two countries. The percentages of the total variance for milk yield were 18.7, 4.9, and 40.8% for herd, sire, and cow, respectively. The percentages for fat yield were similar. These, plus the component for lactation length and days open, were in the range reported from temperate regions. The variance components of fat percent were similar to that of temperate regions for herd ( 14.9%) and cow (54.1%), but the sire component was negative, indicating factors yet unidentified that influenced this trait. Total variances for milk and fat yields indicated sufficient variability to permit selection. Estimates of heritability and repeatability for milk yield, fat yield, fat percent, lactation length, and days open computed from the sire and cow variance components were consistent with those reported from the temperate regions. The estimates indicate there was no loss of genotypic variance in the tropical environment. It appears that genotype exerts as much influence on production in Puerto Rico as elsewhere.