title: Modeling of crossbred cattle growth, comparison  between cubic and piecewise random regression models.
abstract: Two analyses, cubic and piecewise random regression,  were conducted to model growth of crossbred cattle from birth to about two  years of age, investigating the ability of a piecewise procedure to fit growth  traits without the complications of the cubic model. During a four-year period  (1994-1997) of the Australian "Southern Crossbreeding Project", mature Hereford  cows (N = 581) were mated to 97 sires of Angus, Belgian Blue, Hereford, Jersey,  Limousin, South Devon, and Wagyu breeds, resulting in 1141 steers and heifers  born over four years. Data included 13 (for steers) and eight (for heifers)  live body weight measurements, made approximately every 50 days from birth  until slaughter. The mixed model included fixed effects of sex, sire breed, age  (linear, quadratic and cubic), and their interactions between sex and sire  breed with age. Random effects were sire, dam, management (birth location,  year, post-weaning groups), and permanent environmental effects and for each of  these when possible, their interactions with linear, quadratic and cubic growth.  In both models, body weights of all breeds increased over pre-weaning period,  held fairly steady (slightly flattening) over the dry season then increased  again towards the end of the feedlot period. The number of estimated parameters  for the cubic model was 22 while for the piecewise model it was 32. It was  concluded that the piecewise model was very similar to the cubic model in the  fit to the data; with the piecewise model being marginally better. The  piecewise model seems to fit the data better at the end of the growth period.
authors.affiliation: Department of Animal Science, Zabol University, Zabol, Iran. president@imamreza.ac.ir
authors.forename: H R
authors.initials: HR
authors.lastname: Mirzaei
authors.forename: W S
authors.initials: WS
authors.lastname: Pitchford
authors.forename: A P
authors.initials: AP
authors.lastname: Verbyla
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D001835:Body Weight; D001947:Breeding; D002417:Cattle / Q000235:genetics / Q000254:growth & development*; D003433:Crosses, Genetic; D006824:Hybridization, Genetic; D008954:Models, Biological; D012044:Regression Analysis