A Growth Curve Analysis for Bulls Tested at Station

Abstract

SummaryData on 2712 bulls teatmi a t station were a n a l y d to study the effect of certain external variables on growth traita of bulls. Moat of the animals were Ayrshires (2136). Otherwise Finncattle bulls and Frisian bulls were involved. The testing covers the interval 60-386 days of age, although in part of the data the period is 30-365. Bulls were weighted every 30th day (between 1965 and 1970).or at the ages of 80 and 180 days, and thereafter every 30 days up to the age of 366 days (between 1971 and 1977). Also birth weight waa available for 1250 calves. Feeding and general treatment of bulls a t station waa aa uniform aa possible for all animals. Consequently it can be assumed that effecta of non-genetic factors on the growth traita of bulls are minimized.One of the objectives of this study waa to compare the growth curves for the three breeds. In our data measurementa a t certain time-pointa have dropped out during the c o m e of data collection.Therefore we study the influence. of deleting measurements. We also consider the problem of influential measurements a t both the deaign level and the inference level. Several types of growth curves are fitted to the data in order to find the most appropriate model.

Determinação dos parâmetros da curva de crescimento de animais da raça guzerá e seus cruzamentos alimentados a pasto, com e sem suplementação

“…Fonte: Liski (1987) Para a quarta função, os valores de b 1 , b 2 , b 3 são respectivamente 1,98; -0,0012 e -57,44; sendo que b 0 representa o peso no tempo zero, ou seja, peso ao nascer e e representa o erro aleatório não observável (Liski, 1987).…”

“…Seguindo uma linha de raciocínio parecida com Liski (1987), esse pesquisador propôs outros três modelos de funções de crescimento: ( 1�) um modelo linear intrínseco (Menchaca, 1991a), um modelo multiplicativo, idêntico ao primeiro, entretanto considerando variáveis ambientais na função (Menchaca, 1991b) Além desses dois parâmetros, um outro é utilizado para dividir a curva peso-idade em duas fases distintas de crescimento. A primeira chamada de "fase de crescimento acelerado" e a segunda de "fase de crescimento inibitório" (Brody, 1945) .…”