Modelling the growth, feed intake and backfat deposition of different South African sheep breed types

Van der Merwe, Daniel Andre (2020-03)

Thesis (PhDAgric)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: In order to set up a decision support system which can be applied to the feedlot finishing of lambs, models relating to the growth and production of lambs need to be developed. This dissertation presents the details of studies to develop models to describe growth, feed intake, back-fat deposition and wool growth, as well as describe meat, wool and leather quality characteristics of lambs of different breeds. The breeds that were included in the various studies consisted of ewes and rams from Dohne Merino, Dormer, Dorper, Meatmaster, Merino, Namaqua Afrikaner, South African Mutton Merino (SAMM) and White Dorper sheep. In the respective studies, the lambs were reared under optimal growth conditions from birth up until one year of age when they were assumed to have attained a mature body weight. In the growth studies, growth was monitored on a weekly basis from birth, while intake studies commenced when lambs were weaned at ~90 days of age. Measurement of the backfat and longissimus muscle depths was performed using ultrasound scans every two weeks after lambs attained body weights of 20 kg. Wool growth of the lambs was measured using the midrib patch production technique on a monthly basis until lambs were shorn when they attained a mature body weight at one year of age. Appropriate non-linear regressions were fitted to the respective curves of each individual and parameter values were then analysed to test for differences between sexes and breeds. The Logistic, Gompertz and Von Bertalanffy functions were found to appropriately model the sigmoidal growth curves of the various production groups from birth until a mature live weight. On a standard feedlot diet (9.92 MJ ME/kg and 16% crude protein), daily intakes of the different breeds followed a curvilinear trend when plotted against body weight. This trend was modelled using a quadratic function. The peak dry matter intakes estimated from the model for the different breeds were 2203 g/day, 2007 g/day and 1958 g/day for Dormer, Dorper and SAMM breeds, respectively, observed at body weights between 60-70 kg. White Dorper (1879 g/day), Meatmaster (1780 g/day), Dohne Merino (1744 g/day,) and Merino (1560 g/day) lambs obtained peak intakes at ~58 kg body weight. While the quadratic model can be used to observe trends in intake, more accurate linear models can be obtained by modelling the intake expressed as a percentage of body weight against the body weight of the lambs. Similarly, the regressions of cumulative intake with body weight ensured for accurate predictions to be made. The wool producing breeds were assessed to determine wool production rates. Merino sheep were found to have the highest wool growth rates (12.9 g/day) and finest fibre diameter (<20 μm), while Dormer lambs had the lowest wool growth rates (8.5 g/day) and coarsest fibre diameters (>27 μm). Dual-purpose Dohne Merino and SAMM lambs did not differ in terms of wool growth rate (10.1 g/day), though fleeces from Dohne Merino sheep had finer fibre diameters than that of SAMM (21.0 μm and 23.3 μm, respectively; P ≤0.05). Fat deposition, measured using ultrasound scans, could be modelled with body weight (20-65 kg) of the lambs using the exponential function with moderate success. These models showed that early maturing breeds such as the White Dorper and Meatmaster deposit fat at an earlier stage and have greater subcutaneous fat depths at a given body weight than Dorper sheep, which in turn exhibits greater fat deposition than the Dohne Merino, Dormer and SAMM breeds. After modelling the subcutaneous fat depth of the lambs, the ideal slaughter weights of the different breeds could be determined in order to produce a premium lamb carcass in terms of fat cover classification. In a feedlot study where back-fat was monitored, lambs with a back-fat depth of ~4 mm were selected for slaughter and the point of slaughter was taken as the ideal marketing weight. Early maturing Namaqua Afrikaner and Meatmaster sheep had the lowest ideal slaughter weights (32 kg and 35 kg, respectively), followed by Dorper sheep (38 kg) and later maturing Merino, Dohne Merino, Dormer and SAMM breeds (43- 45 kg). Dormer lambs were found to have highest growth rates (438 g/day) and desirable feeding efficiencies (3.71 kg feed/ kg weight gain) in the feedlot; whereas Namaqua Afrikaner lambs exhibited slow growth rates (~169 g/day) with unfavourable feeding efficiencies (~7.08 kg feed/ kg weight gain). The characteristics of the premium lamb carcasses of the various breeds fell within the expectations outlined by the South African carcass classification system, with meat quality traits showing small differences and so indicating a relatively uniform meat product. While the quality characteristics of the different breeds did not vary greatly, the carcasses of fat-tailed breeds differed in composition and conformation to the other breeds, with a majority of the carcass fat being deposited surrounding the tail, with a less developed forequarter region. Sheepskins obtained from the sheep that were slaughtered at the end of growth studies were tanned and the leather characteristics evaluated. Hair type breeds (White Dorper, Meatmaster and Dorper), on average, produced sheepskin leather with a stronger tensile strength (15.23 N/mm2 vs. 9.31 N/mm2; P ≤0.05) and so could be shaved to a thinner, more pliable thickness (1.36 mm vs. 1.78 mm; P ≤0.05) than that of wool type breeds. Skins from hair type breeds also produced a more favourable nappa leather product, while skins from wool type breeds should possibly be used for wool-on leather products. The models and results obtained in the above studies can be used to run simulations of feedlot rearing situations of different sheep breeds and predict the possible outcomes. Ideal slaughter weights for the lambs, in terms of market specifications, or optimal profitability can then be determined to assist the producers in decision making. The results also indicate the product quality of meat, wool and leather from the different breeds, which can assist the producer as well as processor in deciding on the most appropriate marketing strategy for optimal profitability.

AFRIKAANSE OPSOMMING: Om 'n besluitnemingsondersteuningstelsel op te stel, wat toegepas kan word op die voerkraalafronding van lammers, moet modelle rakende die groei en produksie van lammers ontwikkel word. Hierdie proefskrif bevat die besonderhede van studies om modelle te ontwikkel om groei, voerinname, rugvetneerlegging en wolgroei, sowel as vleis-, wol- en leergehalte-eienskappe van lammers van verskillende rasse te beskryf. Die rasse wat by die verskeie studies ingesluit is, bestaan uit ooie en ramme van Dohne Merino, Dormer, Dorper, Meatmaster, Merino, Namaqua Afrikaner, Suid-Afrikaanse Vleismerino (SAVM) en Witdorper. In die onderskeie studies is die lammers grootgemaak onder optimale groeitoestande vanaf geboorte tot en met die ouderdom van een jaar, toe dit aanvaar word dat hulle 'n volwasse liggaamsmassa behaal het. In die groei studies is groei vanaf die geboorte weekliks gemonitor, terwyl innames studies begin het met lammers op ‘n ouderdom van ~90 dae. Die meting van rugvet en longissimus spier weefsel dieptes was uitgevoer met behulp van ultraklank skanderings is elke twee weke nadat lammers liggaams gewigte van 20 kg bereik het. Wolgroei van lammers is op 'n maandelikse basis gemonitor deur die midribkolproduksie-tegniek totdat die lammers geskeer is toe hul 'n volwasse liggaamsgewig bereik het op jaar oud ouderdom. Gepaste nie-lineêre regressies is op die onderskeie kurwes van elke individu gepas en parameter waardes is daarna ontleed om te toets vir verskille tussen geslagte en rasse. Die Logistic, Gompertz en Von Bertalanffy-funksies is gevind om die sigmoïedale groei kurwes van die verskillende produksiegroepe vanaf geboorte tot 'n volwasse lewende gewig toepaslik te modelleer. Op 'n standaard voerkraal-dieet (9,92 MJ ME / kg en 16% ruwe proteïen), het die daaglikse inname van die verskillende rasse 'n kurwilinieêre neiging gevolg wanneer dit teen liggaamsmassa geplot is. Hierdie neiging is gemodelleer met behulp van 'n kwadratiese funksie. Die hoogste droëmateriaal inname wat geskat is van die model vir die verskillende rasse was 2203 g/dag, 2007 g/dag en 1958 g/dag onderskeidelik vir Dormer, Dorper en SAVM rasse, waargeneem by liggaams gewigte tussen 60-70 kg. Witdorper (1879 g/dag), Meatmaster (1780 g/dag), Dohne Merino (1744 g/dag) en Merino (1560 g/dag) lammers het 'piek inname op ~58 kg liggaamsgewig verkry. Terwyl die kwadratiese model gebruik kan word om neigings in die inname waar te neem, kan meer akkurate lineêre modelle verkry word deur die inname te modelleer uitgedruk as 'n persentasie liggaamsgewig, teenoor die liggaamsgewig van die lammers. Soortgelyk het die regressies van kumulatiewe inname teenoor liggaamsmassa akkurate voorspellings verseker. Die wolproduserende rasse is geassesseer om die wolproduksie tempo te bepaal. Merino skape het die hoogste wolgroei tempo (12.9 g/dag) en die fynste veseldiktes (<20 μm) gehad, terwyl Dormer-lammers die laagste wolgroei tempo (8.5 g/dag) en die grofste veseldiktes (>27 μm) gehad het. Dubbeldoel Dohne Merino en SAVM lammers het nie verskil in terme van wolgroei tempo nie (10.1 g/dag), hoewel vagte van Dohne Merino skape fyner veseldiktes gehad het as dié van SAVM (21.0 μm en 23.3 μm; P ≤0.05). Vetneerlegging, gemeet met behulp van ultraklank-skanderings, kan met liggaamsgewig (20-65 kg) van die lammers gemodelleer word met die gebruik van die eksponensiële funksie met matige sukses. Hierdie modelle het getoon dat vroeëvolwassende rasse soos die Witdorper en Meatmaster vet op ‘n vroeër stadium neerlê en dikker onderhuidse vetdiktes op 'n gegewe liggaamsgewig het as Dorper skape, wat weer hoër vetneerlegging toon as die Dohne Merino, Dormer en SAVM rasse. Nadat die onderhuidse vetdiktes van die lammers gemodelleer kon word, kon die ideale slaggewigte van die verskillende rasse bepaal word om 'n premiegraad lamkarkas te lewer in terme van die vetbedekking. In 'n voerkraal studie waar rugvet gemonitor was, is lammers met 'n rugvetdikte van ~4 mm geselekteer om te slag en die slagpunt word as die ideale bemarkings gewig beskou. Vroeëvolwassende Namaqua Afrikaner en Meatmaster skape het die laagste ideale slaggewigte gehad (32 kg en 35 kg, onderskeidelik), gevolg deur Dorper skape (38 kg) en latervolwassende Merino, Dohne Merino, Dormer en SAVM (43-45 kg) rasse. Dormer lammers het die hoogste groeitempo (438 g/dag) en die mees gewenste voerdoeltreffendheid (3,71 kg voer/kg gewigstoename) in die voerkraal getoon; terwyl die Namakwa-Afrikaner lammers 'n stadige groeitempo (~169 g/dag) met ‘n ongunstige voerdoeltreffendheid (~7,08 kg voer/kg gewigstoename) vertoon het. Die eienskappe van die premiegraad lam karkasse van die verskillende rasse het verwagtinge soos uiteengesit deur die Suid Afrikaanse karkas klassifikasie stelsel bereik, met klein verskille in vleis kwaliteit eienskappe getoon en dus 'n relatiewe eenvormige vleis produk aan te dui. Terwyl die vleis kwaliteit eienskappe nie grootliks verskil het nie tussen die rasse, die karkasse van vetstert-rasse het egter verskil in samestelling en bouvorm van die ander rasse, met die meerderheid van die karkasvet wat rondom die stert neergelê is, en met 'n minder ontwikkelde voorkwart. Skaapvelle wat verkry is van die skape wat aan die einde van die groei studies geslag is, is gelooi en die leereienskappe is geëvalueer. Haartipe rasse (Witdorper, Meatmaster en Dorper) het op gemiddeld, skaapvel leer met 'n sterker treksterkte geproduseer (15.23 N / mm2 vs. 9.31 N/mm2; P ≤0.05) wat dus tot 'n dunner, meer soepel dikte geskeer kon word (1.36 mm teenoor 1.78 mm; P ≤0.05) as dié van wol rasse. Velle van haartipes lewer 'n meer gunstiger nappa-leerproduk, terwyl velle van wolrasse moontlik vir wol-aan-leer produkte gebruik moet word. Die modelle en resultate wat in die bogenoemde studies verkry is, kan gebruik word om simulasies van voerkraal-situasies van verskillende skaaprasse uit te voer en die moontlike uitkomste te voorspel. Ideale slaggewigte vir die lammers, in terme van die mark spesifikasies, of optimale winsgewendheid kan dan bepaal word om die produsente te help met die besluitneming. Die resultate dui ook op die produk kwaliteit van vleis, wol en leer van die verskillende rasse, wat die produsent sowel as die verwerker kan help om te besluit oor die geskikste bemarkingstrategie vir optimale winsgewendheid.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107870
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