Caracterização produtiva e reprodutiva das raças Merina Branca e Merina Preta em Portugal

Mestrado em Engenharia Agronómica - Agro-Pecuária - Instituto Superior de AgronomiaIn this study, growth and reproductive records from two Portuguese breeds of sheep - Merino Branco (MB) and Merino Preto (MP) were analyzed by linear model methodologies to assess the importance of systematic environmental factors on these traits. Data were gathered from flocks registered in the Herd Books owned by the Portuguese Merino Breeders Association from 1995 to 2008. Growth traits evaluated were adjusted weights at 30 (PA30), 60 (PA60) and 90 (PA90) days of age and average daily weight gains from birth to 30 (GMD30), 60 (GMD60) and 90 (GMD90) days of age. A total of 36029 weighing records were used for MB and 16098 records for MP. To evaluate prolificacy, 29008 and 12827 records were analyzed for MB and MP, respectively. Separated statistical analyses were performed for each breed. Growth data were analyzed as a trait of the lamb and models included the fixed effects of sex, type of birth, age of dam, season of birth and the interactions sex * type of birth, year of birth * breeder, age of dam * type of birth and type of birth * season of birth and ewe and residual as random effects. Prolificacy was evaluated as a repeated trait of the ewe and the model contained the fixed effects of season of birth of the ewe, lambing season, age of ewe at lambing and the interactions year of lambing * breeder and age of ewe at lambing * lambing season and the residual as random effect. Adjusted weights for MB single born lambs were 11,12±0,03 Kg for PA30, 17,74±0,06 Kg for PA60 and 24,20±0,09 Kg PA90. Corresponding weights for MP were 11,17±0,04 Kg for PA30, 17,40±0,08 Kg for PA60 and 23,42±0,13 Kg PA90, respectively. MB twin lambs weighted 1,85 Kg, 2,71 Kg and 3,16 Kg less than singles (p <0,001), for PA30, PA60 and PA90, respectively. On average, single born MP lambs were 14% heavier than twins and, as observed for MP lambs, differences increased with age. Males were significantly heavier than females (p < 0,001). Observed differences were 0,4 Kg for PA30, 0,7 Kg for PA60 and 1,0 Kg for PA90 in the MB breed and 0,5 Kg for PA30, 0,9 Kg for PA60 and 1,3 Kg for PA90 for MP. For both breeds, ewes of intermediate ages (4 and 5 years old) had in general heavier lambs than younger or older ewes (p < 0,001). Lambs born in the Fall were lighter as compared to those born in Winter (p < 0,001) (11% for MB and 13% for MP). Average daily gains for MB singles were 220±0,001 gr/day for GMD30, GMD60 and GMD90, respectively. Corresponding values for MP were 230±0,001 gr/day, 220±0,001 gr/day and 210±0,001 gr/day. In both breeds, differences between singles and twins (p < 0,001) ranged from 20 to 30 gr/day for all growth intervals. Males grew faster than the females (p < 0,001), with differences of 8 gr/day for GMD30 and 10 gr/day for GMD60 and GMD90 in the MB. For MP larger differences were observed between sexes (10 gr/day for GMD30 and GMD60 and 20 gr/day for GMD90). As for fixed age weights, a quadratic effect of age of dam was also observed for all weight gains in the two breeds. Consistently higher weight gains were obtained in lambs born in Winter than in the Fall (range 20 to 50 gr/day). Prolificacy was low for both breeds (average 1,10 lambs/ewe lambing). For MB, most of the variation was due to the interactions year of lambing * breeder and age (P<0,001) of ewe at lambing * lambing season (P<0,001) reflecting probably large management differences. In the MP breed,besides these effects, age of ewe at lambing was significant (p< 0,001). Four year old and older ewes showed higher prolificacies (range 1,14 to 1,16) than younger ewes (range 1,06 to 1,10). The results of this study show that the same environmental factors affect growth performance in both breeds. Growth rate is slower than typical meat sheep breeds, but having in perspective that animals are raised in extensive grazing conditions, the growth potential shown by both breeds is reasonable. In terms of reproduction, prolificacy is rather low, showing however an increase with increasing age. The combined results of growth and reproductive performance reveal that these genotypes show great longevity and adaptability to local production systems.------------------------------Procedeu-se à análise, pelo método dos quadrados mínimos, de alguns efeitos ambientais sistemáticos sobre caracteres produtivos e reprodutivos de ovinos das raças Portuguesas Merina Branca e Merina Preta. Os dados foram recolhidos nos efectivos dos criadores inscritos na ANCORME, entre 1995-2008. Os pesos ajustados aos 30, 60 e 90 dias para os borregos da raça MB e nascidos de partos simples foram 11,12±0,03 Kg; 17,74±0,06 Kg; 24,20±0,09 Kg, respectivamente e 11,17±0,04 Kg; 17,40±0,08; 23,42±0,13 Kg para borregos MP. Para as duas raças em estudo, os machos superiorizaram-se significativamente (P <0,001) às fêmeas e borregos nascidos no Inverno foram sempre mais pesados (P