No abstract

The study aims to determine the environmental and genetic components for the reproductive performance of a Tunisian local goat population to set up the basis for the future improvement of this important component of efficient production. The reproductive traits considered were kidding interval (KI) and litter size at birth (LSB). Records of 462 kiddings belonging to 185 dams and 11 sires were collected over a period of 22 years in the caprine herd of the Arid Areas Institute of Médenine. Significance of environmental effects was tested with ANOVA techniques. Genetic parameters were estimated using restricted maximum likelihood fitting an animal mixed model. Mean KI and LSB were 13.85 ± 5.20 months and 1.33 ± 0.49 kids, respectively. The effect of parity number and the interaction between year and month of kidding were significant for LSB and KI. Trait LSB increased with parity number up to the fifth parity while KI decreased with parity number indicating that young females show compromised reproductive performance probably because of growth requirements and scarcity of food resources. A detrimental effect for kiddings occurring during winter (matings in summer) was observed from estimates of the year by month of kidding effect. Heritability estimates for KI and LSB were 0.13 and 0.08, respectively. A moderate repeatability estimate of 0.31 was obtained for LSB while 0.17 was obtained for KI. The low estimates of heritability obtained for reproductive traits indicated that accurate selection based on the doe’s own performance will require large amounts of data. However, the estimated genetic variability was substantial, providing the grounds for the genetic improvement of the reproductive parameters in this population.

To provide the local goat population with an adequate breeding scheme under an arid environment, this study aimed to evaluate the use of alternative models attempting to dissect the additive genetic (AG) and permanent environmental (PE) components of direct and maternal effects on weights of kids up to weaning. Records of 903 local kids over a period of 16 years were used in this study. Data were split into four groups corresponding to four periods along weight recording. Periods 1/2/3/4 contained weights in an interval with upper-lower limits of 1-20/25-60/65-120/125-150 days of age. Models including or ignoring maternal genetic or permanent environmental effects were fitted for all traits. For all periods, the best models were those including the AG component for both direct and maternal effects and the direct PE effect. Heritability estimates of both the direct and maternal effects ranged from low (0.02 for maternal heritability in P1) to moderate (0.17 for direct and maternal heritability in P2 and P3). Period 1 showed the lowest values for heritability of both direct and maternal effects, with also the largest estimate of the ratio of residual to total variance (around 0.2) compared with the other periods, with decreasing ratios as age increased (from 0.13 for P2 to 0.07 for P4). Both direct and maternal estimated breeding values (EBVs) showed high correlations for models fitting direct AG and PE (DGP) effects. For direct EBVs (DEBVs), correlations were above 0.99, indicating that the same animals are expected to be selected under any model that includes those components, regardless of the maternal effects included. For maternal EBVs, correlations were also high, but slightly lower than for the DEBVs between models including DGP effects and maternal genetic effects. Overall, our recommendation for genetic evaluations of direct and maternal effects in this population raised in extensive and harsh conditions is to use weight records preferably collected during the period of high milk production of dams, for which direct and maternal effects are expected to show full expression. Complete pedigrees and several generations of dam-progeny recording are needed to obtain a proper separation of environmental and genetic components.

2020) Impact of simplified methods of growth recording on genetic parameter estimates of Tunisian local goat population under a low input production system,