Growth efficiency-related traits are of economic importance for genetically improving of small ruminants especially in tropics with pastures of low quality and quantity. Data on body weights of Raeini Cashmere goat collected from 1979 to 2012 in Raeini breeding station, Kerman province, south-eastern part of Iran were used for estimating the genetic parameters of average daily gain from birth to weaning (ADG1), average daily gain from weaning to six months of age (ADG2), average daily gain from birth to six months of age (ADG3), Kleiber ratio from birth to weaning (KR1), Kleiber ratio from weaning to six months of age (KR2), Kleiber ratio from birth to six months of age (KR3), growth efficiency from birth to weaning (GE1), growth efficiency from weaning to six months of age (GE2) and growth efficiency from birth to six months of age (GE3). The numbers of final edited records were related to 2817, 2541 and 2701 kids for the traits considered from birth to weaning, from weaning to six months of age and from birth to six months of ages periods, respectively. Direct heritability estimates for ADG1, ADG2, ADG3, KR1, KR2, KR3, GE1, GE2 and GE3 were 0.08, 0.03, 0.06, 0.19, 0.03, 0.07, 0.07, 0.09 and 0.08, respectively. Maternal heritability estimates for ADG1, KR1 and GE1 were 0.09, 0.11 and 0.10, respectively. Genetic correlations between traits were ranged from -0.95 for ADG3-KR1 to 0.99 for ADG1-KR1, ADG2-KR2, ADG3-KR3 and KR1-GE1. Phenotypic correlations were positive and high for traits measured in the same period i.e. among ADG1, KR1 and GE1, among ADG2, KR2 and GE2 and among ADG3, KR3 and GE3; ranged from 0.77 for ADG2-GE2 to 0.96 for ADG3-KR3. The obtained results revealed little additive genetic variation in growth rate or efficiency related traits of Raeini Cashmere goat, implying little opportunity for genetic improvement of these traits in this breed through selection. تفاصيل المقالة

In the present study, records on 22872 first-parity Holsteins collected from 131 herds by the Animal Breeding and Improvement Center of Iran from 1995 to 2014 were considered to estimate genetic and phenotypic relationships between calving difficulty (CD) and the lactation curve traits, including initial milk yield (Ap), ascending (Bp) and descending (Cp) slope of the lactation curves, peak milk yield (Ym), days to attain peak yield (Tm) and milk persistency (Pers) under recursive mixed models (RMMs) and standard mixed models (SMMs). Recursive mixed models (RMMs) were applied by fitting CD as a covariate for any of the studied lactation curve traits while considering genetic relationships between CD and these traits. The obtained results denoted a statistically significant non-zero magnitude of the causal relationships of CD with Ap and Bp, while the former influencing the latter. The causal effects of CD on Ap and were -0.351 kg and 0.005, respectively. Direct genetic correlations between CD and the studied traits under RMMs and standard mixed models (SMMs) were not statistically different from zero, except for the correlations of CD with Tm; indicating that genes associated with difficult births also increase peak days in milk. Comparison of both models by the deviance information criterion (DIC) demonstrated the plausibility of RMMs over SMMs for studying the relationships of CD with Ap and Bp while SMMs performed better for estimating the relationships of CD with Cp, Ym, Tm and Pers. تفاصيل المقالة