The influence of dietary energy concentration and feed intake level on feedlot steers 2. Feed intake, live mass-gain, gut fill, carcass gain and visual and physical carcass measurements

Abstract

A total of 108 medium frame weaner steers, divided into 9 groups of 12 each with mean group masses of 200 kg, were used to determine the effect of three  concentrate to roughage (C: R) ratios (80: 20, 55: 45, and 30: 70), fed at three feeding levels (ad libitum, 90% ad libitum and 80% ad libitum), on mass gain, dressing percentage and visual and physical carcass characteristics. Steers were slaughtered at a mean mass of 380 kg. Alimentary canal mass and contents, three subcutaneous fat thicknesses, carcass and buttock length, and cold carcass mass of each steer were measured. Carcasses were classified according to fatness and conformation scores into specific grades. Steers on the three feeding levels were respectively fed for 106, 114 and 174 days on the 80: 20 diet, 156, 161 and 191 days on the 55: 45 diet, and 197, 297 and 322 days on the 30: 70 diet. Contrary to expectation, OM intake decreased and then increased as the C: R ratio increased. Respective carcass gains were 792, 723 and 530; 579, 535 and 489; and 448,
329 and 285 g / d. A decrease in C: R ratio reduced both dressing percentage and carcass gain linearly, while a decrease in feeding level did not significantly influence dressing percentage, but it reduced carcass gain linearly. Subcutaneous fat thickness measurements at different sites were divergently influenced by main effects, but they tended to be reduced by a decrease in either C: R ratio or feeding level. Carcass fatness score decreased with a decrease in either C : R ratio (linear, non-linear) or feeding level (linear). Carcass fatness can be nutritionally  manipulated at the assumed target mass within the constraints of the South African beef carcass classification and grading system.

Nege groepe van 12 mediumraam-speenosse met 'n groepgemiddelde  aanvangsmassa van ongeveer 200 kg elk, is gebruik om die invloed van drie voedingspeile (ad libitum, 90% ad libitum and 80% ad libitum) op massatoename,
uitslagpersentasie sowel as visuele en fisiese karkaseienskappe by drie kragvoer-tot-ruvoer(K: R)-verhoudings (80: 20, 55: 45, en 30: 70) te ondersoek. Na slagting by 'n groepgemiddelde massa van ongeveer 380 kg is die  spysverteringskanaalmassa en -inhoud, drie onderhuidse vetdiktemates, karkas- en boudlengte asook koue karkasmassa van elke os bepaal. 'n Gradeerder het aan elke karkas 'n bouvorm- en vetheidskode asook 'n graad toegeken. Die voerperiodes vir die drie voedingspeile was onderskeidelik 106, 114 en 174 dae vir die 80:20-dieet, 156, 161 en 191 dae vir die 55: 45-dieet en 197, 297 en 322 dae vir die 30: 70-dieet. Droemateriaal-inname het teen die verwagting in konveks toegeneem met 'n toename in die K: R-verhouding. Karkasmassatoename (KGDT) was  onderskeidelik 792, 723 en 530; 579, 535 en 489; en 448, 329 en 285 g/ d. 'n Afname in die K: R-verhouding het beide die uitslagpersentasie en KGDT lineer verlaag, terwyl 'n daling in die voedingspeil geen invloed gehad het op die uitslagpersentasie nie, maar KGDT wel lineer verlaag het. Onderhuidse  vetdiktemate was differensieel deur hoofeffekte beinvloed, maar het geneig om met 'n verlaging in die K: R-verhouding sowel as voedingspeil te verminder.  Karkasvethede het verlaag met 'n dating in die K: R-verhouding (lineer, nie-lineer) of voedingspeil (lineer). Karkasvetheid by 'n bepalde teikenmassa kan deur voeding gemanipuleer word binne die beperkinge van die Suid-Afrikaanse beeskarkasklassifikasie-en graderingstelsel.

Keywords: Beef steers, dietary energy concentration, feeding level, mass gain,  visual and physical carcass measurements.