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Impact of Numbers and Frequency of Weighings on Bovine Weight-Age Curve Parameters¹

University of Tennessee^,4, Knoxville 37916

Abstract

Estimates of mature weight (A) and maturing rate (K), determined by asymptotic regression, were studied to evaluate the effects of using quarterly weights taken in different seasons of the year for estimating growth curve parameters. Quarterly weights of 102 Angus cows were used to calculate eight sets of weight-age curves. Four sets of estimates were calculated from weights from birth to 5 yr of age (FIVE-YEAR curves) and four sets were calculated from all weights collected throughout the life of each cow (LIFETIME curves). Within each age group, one set of parameters was estimated from all weights up to the respective ages (FIVE-YEAR and LIFETIME). The other three sets, within each age, were based on quarterly weights from birth to 1 yr of age plus one weight/year taken during the summer, fall or winter. The symbols A and K were used with the following subscripts: 0 or 5 as a first digit to represent weight-age parameters estimated from all weights taken during the life of the cow and from weights taken before the cow was 5 yr old, respectively; and 0, 2, 3, or 4 as a second digit to represent all quarterly weights, summer, fall or winter weights, respectively. Mean estimates of mature weight were 496, 492, 492, 522, 483, 478, 487 and 508 kg for A₀₀, A₀₂, A₀₃, A₀₄, A₅₀, A₅₂, A₅₃, and A₅₄, respectively. Season of weighing affected both A and K. Coefficients of correlation among the estimates of mature weights were all positive and larger than .70. Coefficients of correlation among estimates of rate of maturing were larger than .50, except those involving the correlation of K₀₀ and FIVE-YEAR estimates. This study indicates that weight-age characteristics estimated from quarterly weights from birth to 1 yr of age and a single annual weight from 1 to 5 yr are adequate for estimating practical weight-age parameters at an early cow age. However, in FIVE-YEAR estimates, the effect of a cow's being nonpregnant at 2, 3 or 5 yr of age and, in LIFETIME estimates, any open year, especially the terminal year, may result in serious bias.

Key Words: Growth-Curve • Characteristics • Age • Bovine Growth

¹ Published with the approval of the Dean of the Univ. of Tennessee, Knoxville.

² Present address: Anim. Sci. Dept., Univ. of Missouri, Columbia 65201.

³ USDA, SEA, Univ. of Tennessee, Knoxville.

⁴ Dept. of Anim. Sci