Phenotypic characterization, correlations between body weight and linear body measurements and regression equations for prediction of live weight in different sheep breeds of botswana

Abstract

The study was conducted to phenotypically characterize and establish relationships between body weight and linear body measurements, and to develop prediction equations for body weight using linear body measurements for Tswana, Dorper, Damara, Meat-master, and Karakul sheep breeds kept under the ranch management system of Botswana. Qualitative and quantitative data were collected from a total of five hundred and ninety-five (595) adult sheep comprising of the Damara (44 females and 35 males), Dorper (105 females and 72 males), Karakul (126 females and 9 males), Meat-master (98 females and 58 males) and Tswana (33 females and 15 males) sheep breeds. The sheep populations at the study site determined the sampling size since almost all adult animals participated in the study. The dentition procedure was used to determine the age of the animals and only those with one pair of permanent incisors (1PPI) and above participated in the study. A total of ninety four animals (Damara: 20, Dorper: 30, Karakul: 16, and Meat-master: 28) were randomly sampled for the development of prediction equations fo live weight using linear body measurements in the four sheep breeds. Damara and Meat-master were characterized by brown coat color and straight long fat and moderate tails, respectively. Dorper and Karakul breeds have plain coat color pattern with Dorper having black head and white body while Karakul have black coat color. A patchy coat color pattern with predominantly white color characterized Tswana sheep. Breed and sex significantly influenced body weight and most linear body measurements, with males being heavier across all the breeds than females. Meat-master rams were the heaviest (73.8±1.60 kg), followed by Karakul (70.2±4.65 kg), Dorper (68.9±1.52 kg), Damara (55.5±1.98 kg), and lastly, Tswana (49.3±5.70 kg), while Dorper ewes were the heaviest (59.0±1.12 kg), followed by Meat-master (57.5±1.15 kg), Karakul (52.4±1.02 kg), Damara (51.7±1.72 kg) and lastly, Tswana (39.2±1.98 kg). Meatmaster, Dorper, and Karakul rams had significantly higher body length, heart girth, head width and ear width than their indigenous counterparts (Tswana and Damara). There were no significant differences between Damara and Tswana rams in body weight, heart girth, ear width and rump width. There was sexual dimorphism, with body weight and most linear body measurements favoring males (rams and castrates) as compared to females in almost all the breeds. There were strong, positive correlation coefficients between body weight and heart girth in Tswana, Dorper, Damara, Meat-master, and Karakul sheep breeds, irrespective of sex with males ii having higher correlation coefficients than females. Body length in males across the breeds had a much higher correlation coefficient with body weight compared to height at withers. Linear body measurements like heart girth, body length, height at withers, neck length, cannon bone length, cannon bone circumference and scrotal circumference in males were used to estimate the body weight of Dorper, Damara, Meat-master and Karakul sheep breeds. The following equations were therefore found fit to accurately estimate body weight of Dorper females y = -102.29+0.26HG – 0.77HW+0.34BL+4.71NL+3.61CBL and males y = -20.13+0.71HG+1.09HW – 2.05NL, Karakul females y = -107.08+0.58HG+0.69HW+5.58CBL and males y = - 137.20+1.60HG+0.41BL+0.61SC, Meat-master females y = -102.11+1.02HG+1.00BL – 1.71CBL+0.75NL and males y = 16.45+0.42HG+0.79HW+0.34SC – 2.05NL, and Damara females y = 77.80 – 0.48HG – 3.12HW – 8.38BL – 6.06NL+25.44CBL+66.26CBC and males y = -1063.34+8.02HG+0.86HW+4.64BL, where y is the body weight and HG, HW, BL, NL, CBL, CBC, SC are heart girth, height at withers, body length, neck length, cannon bone length, cannon bone circumference and scrotal circumference, respectively. Heart girth accounted for more variability in the prediction model for all the breeds, both males and females, except for Damara males. Heart girth and body length explained more variability in the model used to predict the body weight of Damara males, which means these traits can be used as selection criteria for body weight. The addition of more independent variables increases the accuracy of the prediction equation.