Yearly production trends and genetic and environmental influences in a genetically closed Brahman herd. 3. Monthly weigths up to eighteen months.

Abstract

Genetic and non-genetic effects were evaluated on the live weights between birth and the age of 18 months, of 1074 calves born between 1966-1974 in a Brahman herd registered in Venezuela, weighed at birth (PN) and then monthly (P1, ... P18). The calves were kept on Panicum maximum grass and supplemented at weaning (P7 or P8) until the next rainy season. The adjusted means for PN, P7, P8, P12, and P18 were 26.9 ± 0.3, 155.4 ± 1.6, 168.3 ± 1.6, 223.5 ± 1.8, and 291.0 ± 2.2 kg. The average daily gain fell from 719g in the first month to 396g in the ninth, then between 289 and 531g. The data of each weight were subjected to ANOVA, including in the model: year (A), month of birth (M), sex (S), father (P), mother's age (E), A×M interaction and calf age (B). When analyzing PN, E was substituted for the mother's lactation status in the previous year (L). A was important in P1 to P11 and P16 to P18; M in all but two pesos; S in all; and P in PN to P3 and P14 to P18. PN was significantly affected by L, while P2 to P10 were affected by E. B was significant in all weights and A×M in half of them (P<.05). Inheritance indices decreased from 0.52±0.13 for PN to zero for P6 and P7, then rose to 0.16 ± 0.07 for P18. The repetition coefficients were: PN, 0.26; P1 to P9, 0.20 to 0.26; P10 to P14, 0.15 to 0.19; P15 to P18, 0.11 to 0.14. The growth curve (18,586 individual weights) up to 18 months of age was described by a third degree polynomial equation and the curves of males and females progressively separated at greater age.