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Análise de fatores ambientais que influenciam o intervalo entre partos em bovinos mertolengos
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Este estudo teve como objetivos analisar os principais efeitos ambientais que influenciam o intervalo entre partos (IP) em bovinos da raça Mertolenga, particularmente o efeito do tipo de cobrição (época de cobrição definida versus época de cobrição contínua).
Utilizaram-se 46613 registos de IP’s de 8452 fêmeas Mertolengas, recolhidos entre 2000 e 2019 em 27 explorações. Os registos foram submetidos a diversas análises preliminares, através do PROC MEANS e do PROC FREQ do programa SAS® e, posteriormente, com um modelo misto, através do PROC MIXED do mesmo programa que incluiu os efeitos fixos do criador*ano de parto, tipo de cobrição (definida e contínua), sexo e raça do vitelo e como covariáveis os efeitos lineares e quadráticos da idade ao parto (IDP) e da idade ao primeiro parto (Id1P); a fêmea (vaca) foi considerada como efeito aleatório.
Observam-se valores médios da Id1P de 35,5±9,0 meses, da IDP de 87,9±41,7 meses e para IP de 436,5±128,2 dias.
Os resultados da análise de variância do IP indicaram que há diferenças significativas entre fêmeas (p<0,01) e que todos os fatores ambientais incluídos no modelo (criador*ano de parto, tipo de cobrição, sexo e raça do vitelo, idade ao parto e ao primeiro parto) têm um efeito significativo (p<0,01) nos valores de IP.
Observaram-se grandes diferenças nos valores de IP entre explorações e anos de parto e, que as explorações que optam por época de cobrição contínua, em média, têm IP mais baixos (≈430 dias) do que as explorações que utilizam épocas de cobrições definidas (≈438 dias). Há diferenças significativas entre fêmeas paridas na primavera/verão (438,753±1,325/ 439,833±1,286) e fêmeas paridas no outono/inverno (449,529±1,217/447,391±1,163). Vacas que parem vitelas, em média, têm IP’s inferiores (437,534±0,897) aos das vacas que parem vitelos (443,534±0,901) e vacas que parem vitelos Mertolengos puros, em média, têm IP’s inferiores (422,156±0,833) aos de vacas que parem vitelos cruzados (445,156±1,190).
A idade ao parto e idade ao primeiro parto têm um efeito quadrático no IP registando-se valores mais baixos quando as fêmeas têm aproximadamente 8,5 anos e quando parem pela 1ª vez com cerca de 36,9 meses.
Pelo impacto que o IP tem na produtividade das explorações de bovinos de carne é importante conhecer fatores que o influenciam, de forma a permitir a correção de aspetos relacionados com o maneio das explorações e, em termos de seleção, ter em consideração os efeitos não genéticos que contribuem para a variabilidade observada no IP.
The aim of this study was to analyze the main environmental factors influencing the calving interval (CI) in Mertolenga cattle, particularly the effect of the type of breeding (fixed breeding season versus continuous breeding). A total of 46613 CI records were collected, from 2000 to 2019, regarding 8452 Mertolenga cows in 27 farms. The records were first subjected to PRO® MEANS and PROC FREQ SAS® programs and subsequently to PROC MIXED SAS® mixed model. Variables included fixed effects of the breeder, year of delivery, type of breeding (fixed and continuous), calf sex and breed. Linear and quadratic effects of age of calving and age at first calving were co-variables and the female (cow) was considered a random effect. Mean age at first calving was found at 35,5±9,0 months, mean age at calving at 87,9±41,7 months and CI at 436,5±128,2 days. The results of the analysis of variance of CI indicated that there are significant differences between females (p <0,01), considering that all environmental factors included in the model (breeder, year of calving, type of calving, sex and calf breed, age at calving and age at first calving) have a significant effect (p <0,01) on CI values. Large differences in CI values were observed between farms and years of calving and that breeders that chose continuous breeding have a lower CI averages (≈430 days) in comparison to defined seasons (38438 days). There are significant differences between calving females in spring / summer (438,753±1,325/439,833±1,286) and calving females in autumn/winter (449,529±1,217/447,391±1,163). Cows that give birth to female calves, on average, have lower CIs (437,534±0,897) than calves that give birth to male calves (443,534±0,901). Cows giving birth to pure Mertolenga calves have lower CIs (422,156±0,833) than those giving birth to cross calves (445,156±1,190). Age at calving and age at first calving have a quadratic effect on CI with lower values when females are approximately 8,5 years old and when they first calve at about 36,9 months. Due to the impact that the CI has on the productivity of beef cattle farms, it is important to acknowledge influencing factors, allowing for possible improvements in farm management. As far as cow selection is concerned, understanding and considering non-genetic factors influencing CI would be extremely beneficial.
The aim of this study was to analyze the main environmental factors influencing the calving interval (CI) in Mertolenga cattle, particularly the effect of the type of breeding (fixed breeding season versus continuous breeding). A total of 46613 CI records were collected, from 2000 to 2019, regarding 8452 Mertolenga cows in 27 farms. The records were first subjected to PRO® MEANS and PROC FREQ SAS® programs and subsequently to PROC MIXED SAS® mixed model. Variables included fixed effects of the breeder, year of delivery, type of breeding (fixed and continuous), calf sex and breed. Linear and quadratic effects of age of calving and age at first calving were co-variables and the female (cow) was considered a random effect. Mean age at first calving was found at 35,5±9,0 months, mean age at calving at 87,9±41,7 months and CI at 436,5±128,2 days. The results of the analysis of variance of CI indicated that there are significant differences between females (p <0,01), considering that all environmental factors included in the model (breeder, year of calving, type of calving, sex and calf breed, age at calving and age at first calving) have a significant effect (p <0,01) on CI values. Large differences in CI values were observed between farms and years of calving and that breeders that chose continuous breeding have a lower CI averages (≈430 days) in comparison to defined seasons (38438 days). There are significant differences between calving females in spring / summer (438,753±1,325/439,833±1,286) and calving females in autumn/winter (449,529±1,217/447,391±1,163). Cows that give birth to female calves, on average, have lower CIs (437,534±0,897) than calves that give birth to male calves (443,534±0,901). Cows giving birth to pure Mertolenga calves have lower CIs (422,156±0,833) than those giving birth to cross calves (445,156±1,190). Age at calving and age at first calving have a quadratic effect on CI with lower values when females are approximately 8,5 years old and when they first calve at about 36,9 months. Due to the impact that the CI has on the productivity of beef cattle farms, it is important to acknowledge influencing factors, allowing for possible improvements in farm management. As far as cow selection is concerned, understanding and considering non-genetic factors influencing CI would be extremely beneficial.
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Autóctone Bovinos de carne Fertilidade Reprodução Tipo de cobrição Native breed Beef cattle Fertility, Reproduction, Breeding type