Efecto de la fecha de parto sobre características productivas y reproductivas de vacas charolais
DANIEL PÉREZ TORRES
ROBERTO GARCÍA ELIZONDO (Thesis Adviser)
RAMIRO LÓPEZ TRUJILLO (Thesis Adviser)
JESÚS MANUEL FUENTES RODRÍGUEZ (Thesis Adviser)
FERNANDO RUIZ ZÁRATE (Thesis Adviser)
Summary or description
"Con el propósito de probar que la fecha de parto incide sobre las características productivas y reproductivas postparto de vacas y becerros Charolais en agostaderos semiáridos del noreste de México, se analizaron 1665 registros de 583 vacas en dos años consecutivos. Los registros se agruparon, de acuerdo a la fecha de parto, en cuatro grupos de parición (G1, G2, G3 y G4) de 21 d consecutivos. En el análisis de varianza se utilizó un diseño experimental completamente al azar con diferente número de repeticiones (SAS, 1989) y covariables. No se encontró efecto (P>0.05) de la fecha del parto sobre el peso al nacer de la cría. El peso al destete de los becerros nacidos en el G1 de parición en el año actual fue superior (P<0.05) en 17, 27 y 41 kg, y en el año siguiente 9, 19 y 28 kg al de los nacidos en los grupos 2, 3 y 4. Las becerros que nacieron en el G4 tuvieron (P<0.05) mayor ganancias diaria de peso predestete en ambos años (actual: 57, 50 y 29 g y siguiente 35, 31 y 18 g) a los nacidos en los grupos de parición 1, 2 y 3; los nacidos en los grupos 1 y 2, tuvieron incrementos diarios de peso similares (P>0.05) en ambos años. Las vacas del G1 destetaron en dos años consecutivos 26, 46 y 69 kg más de becerro que las vacas de los grupos 2, 3 y 4. Los días al empadre y días a la preñez fueron inversos al grupo de parición, en tanto que los días abiertos presentaron una dependencia directa de estas 51 51 dos variables; las vacas del G1 (día juliano al parto 84) se preñaron 11, 25 y 41 d más pronto que las vacas de los grupos 2, 3 y 4. El día juliano al parto siguiente tuvo una tendencia similar a días al parto siguiente y ambos fueron inversos al intervalo entre partos; éste y los días al parto siguiente fueron directamente proporcionales al día juliano al parto siguiente. Se concluyó que, con apareamientos de 90 días en verano, las vacas que paren al inicio de primavera tienen mejor comportamiento productivo y reproductivo postparto"
The objective of this study was to evaluate the effect of calving date on productive traits (weights at birth and weaning, preweaning daily gain and total kilograms of calf weaned in two consecutives years) and reproductive postpartum: days to mating (DAE), days to pregnancy (DPA), days open (DAB), days to following calving (DPS) calving interval (IEP) and julian day at calving (DJP) following from Charolais cows managed in semiarid rangelands. Date from 1665 records were analyzed out of 583 Charolais cows calving and weaning in two consecutive years (current and subsequent) during the years 1977 and 2000 at The Angeles ranch, located in northeastern Mexico (250 04' N x x and 1000 58' W). The animals were grazed under extensive grazing conditions in 6,704 ha with native vegetation throughout the year. The rotational grazing system was rotational with 20 paddocks, where the animals were rotated during the year between paddocks to another, with a stocking rate of 15 to 20 ha per animal unit per year. The management of cows and calves in the different years was very similar. The breeding season was of 90 days (June, July and August) using a bull of the same breed for every 20 to 30 cows. The calfs were born in spring (March, April and May) and weaned in fall at seven months age on average. The cows were grouped according to actual calving date, into four groups (G1, G2, G3, and G4) of 21 consecutive days. The analysis of variance was done using a completely randomized design with different number of repetitions and covariates. There was no effect (P>0.05) of the calving date on birth weight of calves in both years, but for the covariates age of cow, sex of calf and year of calving in the current year, and only sex of the calf in the subsequent year. There was significant effect (P<0.05) of the calving date on weaning weight of calves in consecutive years. The covariates age of cow, sex of calf, year of calving and calf birth weight used to reduce experimental error had significant effect (P<0.05) on weaning weight (P<0.05) in both years, except age of the cow in the subsequent year. The weaning weight of calves born at beginning (G1) from the time of calving in the current year was higher (P <0.05) in 17, 27 and 41 kg, and in the subsequent year 9, 19 and 28 kg of those born in groups G2 a G4. The G1 cows weaned in two consecutive years 26, 46 and 69 kg more calf than cows in groups G2 a G4. Indicating that the calves that were born at the beginning in the current year had better growth performance than xi xi those born later. There was significant effect (P<0.05) from the calving date and the covariates age of cow, sex of calf, year of calving and birth weight on preweaning daily gain of calves in both years. The calves born at the end (G4) had increased preweaning daily weight gains in both years (current: 57, 50 and 29 g and subsequent 35, 31 and 18 g) to those born in the calving groups G1 a G3, although the magnitude of change was lower the subsequent year. Calves born in groups G1 and G2 had similar daily weight gains in both years. The calving date affected (P<0.05) all postpartum reproductive characteristics evaluated (DAE, DAP, DAB, DPS, IEP and DJP following). Covariates year of calving, age of cow and parity had significant effects (P<0.05) on the DAE, DAB and DJP following; the year of calving on DAP and DPS; and the age of cow and parity on IEP. Cows that calved at the start (G1) had higher DAE, DAB and IEP and lower DAP, DPS and DJP following that cow calving groups G2 a G4. An inverse relationship was observed for the DAE and DAB with the DAP, DPS and DJP following and directly of the DAE with DAB and IEP, and DAB with DAE and IEP. An inverse relationship of DAP and DPS with DAE, DAB and IEP and direct of DAP with the DPS and DJP following, and DPS with DAP and DJP following. In conclusion, the calving date had effect (P<0.05) on all productive traits except birth weight of calves and postpartum reproductive evaluated, having better productive and reproductive performance postpartum the cows that calved at the beginning of the calving season.
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