Fatores genéticos e de ambiente que influenciam características reprodutivas em fêmeas da raça nelore.

Abstract

With the objective of to evaluate genetics and environmental effects over the variation of reprodution features, it was analyzed 475 observations of Calving Interval (CI), 558 of Gestation Length (GL) and 401 of Real Fertility (RF) of Nelore cows reared in Santa inês, State of Maranhão, Northeast of Brasil, in pasture regime with food supplement in dry season. The observations were taken between 1980 and 1994. The statistical analysis were acomplished using mixed linear models (SAS, Statistical Analysis System, 1990, and HARVEY, 1990) which included the Bull's etfects (aleatory effects), month and year of the least and the actual calving, orden of cow's parturition and offspring's sex (fixed) to CI and RF. For GL the model included calf weight. In CI, the orden of cow's parturition interfered (p<0,01 ) and the Buli (p< 0,01), while Gestation Length was affected by the BulI (p<0,01), month of calving (p<0,01 ) and calf weight (p<0,05 ). The "Real Fertility" was affected by the Bull (p<0,01 ), the orden of cow's parturition (p<0,01), and the offsprings sex (p<0,05). The estimated mean for minimum square, and their respective standard error (SE) and variation coeficient (VC) were: About CI, 433,84 ± 88,20 days, VC of 20,33%. Gestation Length, 295,49 ± 6,89, VC of 2,33%. Real Fertility, 184,69 ± 37,09 kg, with VC of 20,08%. The estimated heritability over genetic correlation between paternal half sisters were equal to 0,32 ± 0,15; 0,49 ± 0,19, and 0,26 ± 0,12, respectively for Calvin Interval, Real Fertility, and Gestation Length.