Genetic parameter estimates for pre-weaning growth traits in Dorper sheep

(South African J of Animal Science, 2000, 30, Supplement 1: 99-101

Genetic parameter estimates for the South African Mutton Merino breed

(South African J of Animal Science, 2000, 30, Supplement 1: 102-104

Genetic studies on the South African Mutton Merino: growth traits

Genetic parameters were estimated for 36-, 42-, 50-, 100- and 150-day weight in the South African Mutton Merino breed. The direct heritability estimates obtained were 0.270, 0.366, 0.278, 0.185 and 0.115 respectively. The maternal heritability estimates for the respective weights were 0.494, 0.249, 0.129, 0.091 and 0.080. The correlation between the animal effects (direct and maternal) varied between -1.000 for 36-day weight to -0.376 for 150-day weight. Very little selection progress was made over the period (1980-1999) in the breed. (South African Journal of Animal Science, 2000, 30(3): 172-177

The heritability of acceptability in South African Merino sheep

Selection for production and reproduction in South African Merino sheep is always combined with selection based on visual appraisal and will, in all probability, remain so for many years to come. Heritabilities for acceptability were estimated using a threshold model to analyse data from two parent Merino studs. Effects included in the analysis were sex, birth status, age of dam and year of birth. An acceptable animal was defined as one that was present in the stud at 18 months of age, implying that such an animal would either be retained or sold for breeding purposes. This provided one threshold and two classes (acceptable or not acceptable). Records from the two studs used comprised 3011 progeny of 31 sires and 6495 progeny of 70 sires. Error variance was taken as unity and heritability estimated as h2 = 4s 2s / 1 + s2s where s 2s is the sire variance. Heritability estimates were 0.210 and 0.448. The results suggest that selection improvement for acceptability is possible, and that breeding values for this trait should be supplied for AI sires. (South African Journal of Animal Science, 2001, 31(1): 13-14

Heritabilities of reproductive traits in a beef cattle herd using multitrait analysis

(South African J of Animal Science, 2000, 30, Supplement 1: 140-141

Heritability estimates derived from threshold analyses for reproduction and stayability traits in a beef cattle herd

The object of this study was to estimate heritabilities and sire breeding values for stayability and reproductive traits in a composite multibreed beef cattle herd using a threshold model. A GFCAT set of programmes was used to analyse reproductive data. Heritabilities and product-moment correlations between predicted breeding values for stayability at 36, 48, 60, 72 and 84 months of age, calving success and longevity were estimated. The estimated heritabilities on the underlying scale for these traits were 0.06, 0.10, 0.06, 0.03, 0.11, 0.03 and 0.08 respectively. Product-moment correlations between breeding values for stayability traits were low. The highest correlation of 0.22 was obtained between the ages of 36 and 48 months. Heritability estimates and correlations between traits appear to be of such a low magnitude that selection for these characteristics would result in limited genetic improvement, and also indicate that sires had little influence on the stayability, longevity or calving success of their daughters. (South African Journal of Animal Science, 2001, 31(1): 25-32

Relationship of ewe reproduction with subjectively assessed wool and conformation traits in the Elsenburg Merino flock

Subjectively assessed wool and conformation traits are widely used to select breeding ewes and rams in the sheep industry. Data from a Merino flock that is maintained at Elsenburg Research Farm were used to investigate animal model (co)variance components for ewe reproduction traits with subjectively assessed wool and conformation traits. Ewe reproduction traits were assessed at their first lambing opportunity at two years, or over a three-year period from their lambing opportunities at two to four years old. Relationships of ewe reproduction traits with subjectively measured wool and conformation traits were also investigated. All these traits were heritable, with a range from 0.16 ± 0.03 for topline (TOPL) to 0.64 ± 0.04 for woolly face score (WFS). Genetic correlations of number of lambs born (NLB1) with colour (COL), number of lambs weaned (NLW1) with COL and belly and points (BANDP) and total weight of lamb weaned (TWW1) with COL were negative and significant. Significant genetic correlations of ewe reproduction traits over three lambing opportunities were found between number of lambs born (NLB3) and WFS (0.23 ± 0.11) and between total weight weaned (TWW3) and face cover score (FCS) (-0.33 ± 0.16). Among these traits, the noteworthy favourable genetic correlation between total fold score (TOT) and NLB1 suggested that plainer ewes were more reproductive. This is important for the South African Merino industry as plainer sheep are more desirable because of their faster growth and higher lambing percentages and reduced chances of fly strike. Selection for improved ewe reproduction in Merino sheep thus would not result in marked unfavourable correlated responses in most of these subjective wool and conformation traits.Keywords: Correlations, heritabilit

Multi-trait genetic evaluation for horn traits of economic importance in the Cape buffalo (Syncerus caffer caffer)

The wildlife industry in South Africa has shown immense growth since the 1990s, which was brought about by the private game segment of the industry. In recent years, trophy quality Cape buffalo breeding animals have achieved extremely high prices. Much of the economic value of these animals can be attributed to horn size, which is important for breeding and hunting purposes. The main objective of the study was to estimate variance components for horn traits of economic importance as well as to develop guidelines for recording these traits. To date, no quantitative genetic analysis has been done for any traits in Cape buffalo. The total number of horn measurement records included in the evaluation was n = 945 for outer spread (BHSO), n = 470 for tip to tip (BHTSCI), n = 468 for left boss and n = 479 for right boss. For descriptive statistics, males and females were considered separately while age was divided into clusters of six months. A multi-trait animal model using Monte Carlo Markov Chains methods was used for the estimation of genetic parameters. Results suggest that it is not economically viable to measure horn spread and tip to tip of females after 48 months of age. Horns of the males continue to grow beyond 91 months of age. Boss records were unreliable owing to the applied measurement techniques for female and young animals. An inbreeding coefficient of 0.008 was calculated, suggesting adequate genetic diversity in the studied population. The heritability estimates of the horn traits were low, showing that extreme care has to be taken to develop effective selection programmes for the buffalo game industry using their horn genetic parameters. Further quantitative studies are required to support the results of the current study.Keywords: genetic correlation, genetic parameters, heritability, Monte Carlo Markov Chai

Evaluating horn traits of economic importance in sable antelope (Hippotragus niger niger)

Much of the economic value of wildlife can be attributed to horn size, which is an important trait for trophy hunters. The main objective of the study was to estimate genetic parameters for the economically important horn traits of sable antelope that are currently being measured in the South African industry. To date, no quantitative genetic analysis has been done for any traits in sable antelope. The total number of records included in the evaluation were n = 1713 for horn length (SHL), n = 1503 for circumference (SHC), n = 1486 for tip to tip (SHTT), n = 1505 for tip length (SHT), and n = 1447 for rings (SHR). Males and females were considered separately in six-month age clusters. A Markov chain Monte Carlo (MCMC) multi-trait analysis was used to estimate (co)variance parameters for the horn traits. The results indicate a sex effect for all the traits and suggest that it is not economically viable to measure horn length of either sex after 54 months old. The horns of females are on average 40% shorter compared with bulls at maturity. Continuous horn growth throughout the lifetime of sable is suggested by the formation of ring posts, but is often masked by horn attrition and inadequate measuring techniques. An inbreeding coefficient of 0.0043 suggests adequate genetic diversity in the studied population. Heritability estimates of horn traits varied from 0.085 to 0.52, while genetic correlations ranged from 0.1 to 0.6 with the highest correlation being found between horn length and tip to tip. Further studies are recommended to confirm these results.Keywords: Game, genetic evaluation, heritabilit

Relationships between production and product traits in subpopulations of Bonsmara and Nguni cattle

Ninety bull calves of five Bonsmara strains, viz. Edelheer (E), T-49 (T), Wesselsvlei (W), Roodebos (R) and Belmont Red (BR), and two Nguni sub-populations, viz. Bartlow (B) and non-Bartlow (NB), were fattened under intensive feeding conditions and serially slaughtered at four different slaughter weights. Phylogenetic relationships between the five Bonsmara strains and between the two Nguni subpopulations were determined by means of blood typing. Growth performance, carcass characteristics and meat quality characteristics were compared between the sub-populations of each breed. Genetic distances between the Bonsmara animals confirmed the existence of five genetic subpopulations with variation in genetic distances between them. The genetic distance between the two Nguni subpopulations was very small, indicating genetic similarity. Means for production and product characteristics were adjusted for mean subcutaneous fat percentage by means of analysis of covariance. T gained weight faster and more efficiently on a live and carcass weight basis than the other Bonsmara groups, while B gained carcass and muscle weight more efficiently than NB. T had proportionally more meat in the high-priced cuts of the carcass than W. Muscle of the W line had a higher ageing potential (measured as myofibrillar fragmentation; MFI) than T, resulting in higher tenderness scores for W. Similarly, B had higher MFI for muscle aged for one or seven days, coupled with more tender meat than NB. Pairwise correlations between growth and muscle characteristics indicated that fast growing animals tend to produce less tender meat. South African Journal of Animal Science, Vol 31, Issue 3, Oct – Dec (2001): pp.181-19