| Popis: |
Ten measures related to breeding efficiency were used for comparisons among pure Jerseys and Red Sindhis and crossbreds with ¾, ½, or ¼ 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 ± 14.1, and 717 ± 40.4 days for Jerseys, crosses of ¾, ½, or ¼ and Sindhi. The increase in age of puberty was additive but not entirely. The ¾ and ½ tended to excel parent breeds in rebreeding less than 145 days postpartum, but by 200 days percentages of conception were similar. Average heterosis in percent was 18.4 for age at puberty, .04 days from calving to first heat, 9.6 days first breeding to conception, 8.5 days open, 4.3 calving interval, and 1.9 in services for conception. The average for the latter five measures was 4.9%. Significant effects of breed and location in several cases may have been due to sampling variance. Percentages of nonbreeding heifers were similar for Jerseys and ¾ or ½ crosses (8.0%) but high in ¼ crosses (15.4%). Fewer crosses completed two gestations. Both in first and later parities, crosses, particularly ¼, had higher frequencies of reproductive disorders than Jerseys (6.8 versus 4.2). Crosses also had higher frequencies of dystocia or abortions than Jerseys. Percentages of lactations terminated for health, sterility, or death were similar among breed groups. The ¾ and ½ crosses averaged about 17 days shorter in calving interval, but the calving interval required for the ¾ to equal Jerseys in milk yield should have been 15 to 29 days shorter than observed. The ½ crosses would need intervals less than 285 days to be as productive as Jerseys. |
