The value of recording body measurements in beef cattle

Abstract

English: Body size and shape are objectively described using body measurements in beef cattle. How these measures of size and shape relate to the functioning of the individual is of paramount importance to livestock producers. Changes in these parameters that lead to inefficient animals are never welcomed by farmers. Therefore, constant checks on the relationships between body measurements and performance traits are vital in selection programs. To estimate heritabilities and genetic correlations among body measurements and growth traits, data of 7 266 performance records of Bonsmara bull calves participating in on-farm growth tests (Phase D) were used. The data set was extracted from the Integrated Registration and Genetic Information System (INTERGIS) of South Africa. The data covered a 25-year period i.e. from 1972 - 1996. Data were recorded from 45 herds, with 439 sires and 5 180 dams involved. Traits analyzed were scrotal circumference (SC), body length (BL), shoulder height (SH), birth weight (BW), weaning weight (WW), final weight (FW) and average daily gain (ADG) from weaning to final test date. Multivariate REML methodology was used to estimate (co)variances and genetic components for different traits. In cases where there were more than one value for an estimate, the values were pooled, weighting each estimate by the inverse of its sampling variance. Different models were, however, fitted for each trait. The permanent environmental effect was found to be important for most of the post-weaning traits, but it could, however, not be considered in the multivariate runs. This was due to computational limitations imposed by the data set. A simple model considering only direct animal effect and random error was fitted for all post-weaning traits. Heritability estimates for body measurements ranged from medium for body length (0.27±0.05) to high for shoulder height (0.42±0.05) and scrotal circumference (0.46±0.06). Corresponding estimates for performance traits were: direct (0.31±0.05) and maternal birth weight (0.10±0.03), direct (0.29±0.05) and maternal weaning weight (0.04±0.02), average daily gain (0.19±0.04) and final weight (0.30±0.05). Generally, body measurements were favourably and positively correlated with performance traits (0.03 to 0.83). However, scrotal circumference was found to be genetically weakly correlated to maternal birth weight (-0.22±0.15) and average daily gain (0.1O±O.13). A close to zero genetic correlation was found between average daily gain and maternal weaning weight (0.03±0.17). These results suggest that selection for fast growing bulls may not influence maternal performance at weaning. Considering the favourable genetic correlations between body measurements and performance traits, it could be inferred that selection for body measurements is compatible with that of performance traits. However, a further study should be conducted to evaluate which of those traits considered in this study are of economic importance so that an appropriate selection index can be developed.

Afrikaans: Liggaamsgrootte en -vorm van vleisbeeste kan objektief beskryf word m.b.v. liggaamsmates. Die verband tussen hierdie mates en die funksionering van die dier is van groot belang vir produsente. Veranderinge in hierdie parameters wat lei tot oneffektiewe diere sal nie deur boere verwelkom word nie. Dit is dus nodig om die verband tussen liggaamsmates en produksie eienskappe te monitor in seleksieprogramme. Oorerfbaarhede en genetiese korrelasies tussen liggaamsmates en groei eienskappe is bepaal. Produksierekords van 7 266 Bonsmara bulkalwers, afkomstig van 45 kuddes, met 439 vaders en 5 180 moeders, wat in op-die-plaas groeitoetse (Fase D) deelgeneem het, is gebruik. Die data was afkomstig van die geïntegreerde registrasie en genetiese informasie sisteem (INTERCIS) van Suid-Afrika en strek oor 'n 25 jaar periode (1972 tot 1996). Eienskappe wat bestudeer is sluit in skrotumomvang (SC), liggaamslengte (BL), skouerhoogte (SH), geboortegewig (BW), speengewig (WW), finale gewig (FW) en gemiddelde daaglikse toename (ADC). Meereienskap REML metodologie is gebruik om (ko)variansie komponente te beraam vir die verskillende eienskappe. In gevalle waar daar meer as een beramer vir 'n komponent was, is die waardes gepoel en geweeg deur die invers van die variansie. Verskillende modelle is vir elke eienskap gepas. Volgens enkeleienskap analises was die permanente omgewings effek belangrik vir meeste van die na-speense eienskappe, maar dit kon nie in ag geneem word in die meereienskap lopies nie, weens rekenaarbeperkings veroorsaak deur die grootte van die datastel. 'n Eenvoudige model wat slegs die direkte effek en toevallige fout komponent in ag neem, is gepas vir alle na-speense eienskappe. Oorerftikhede vir liggaamsmates varieer van medium vir liggaamslengte (0.27±0.05) tot hoog vir skouerhoogte (0.42±0.05) en skrotumomvang (0.46±0.06). Ooreenstemmende beramers vir produksie eienskappe is: direkte (0.31±0.05) en maternale geboortegewig (0.10±0.03), direkte (0.29±0.05) en maternale speengewig (0.04±0.02), gemiddelde daaglikse toename (0.19±0.04) en finale gewig (0.30±0.05). Oor die algemeen is liggaamsmates gunstig en positief gekorreleer met produksie eienskappe (0.03 tot 0.83). Skrotumomvang was geneties laag gekorreleerd met maternale geboortegewig (-0.22±0.15) en gemiddelde daaglikse toename (0.10±0.13). 'n Genetiese korrelasie naby nul is tussen gemiddelde daaglikse toename en maternale speengewig (0.03±0.17) gevind. Hierdie resultate suggereer dat seleksie vir vinnig groeiende bulle waarskynlik nie 'n verandering in maternale prestasie by speen sal veroorsaak nie. Aangesien daar 'n gunstige genetiese korrelasie is tussen liggaamsmates en produksie eienskappe kan dit afgelei word dat seleksie vir liggaamsmates verenigbaar is met die van produksie eienskappe. Daar word dus aanbeveel dat 'n verdere studie onderneem word om die eienskappe wat ekonomies belangrik is, te bepaal en om 'n seleksie indeks te ontwikkel.