Chromosomal Anomalies and Infertility in Farm Animals: A Review

Veterinary cytogenetics is an area of genetics that deals with normal or abnormal chromosomes of animals. Chromosome abnormalities in cattle can cause significant adverse effects on fertility through failure of production of viable gametes or early embryonic death that consequently leads to great economic loss. Chromosomal aberrations can occur as numerical errors or structural rearrangements usually without causing phenotypic abnormalities on carrier animals. According to current knowledge on chromosomal abnormalities, Robertsonian translocation (ROB) that involves chromosome 1 and 29 represents the most common form of aberration found in cattle of various breeds. Other less commonly encountered abnormalities in cattle include reciprocal translocation, chimerism (including freemartins), mosaic and rarely sex chromosome aberrations. A similar trend in incidence of abnormalities has been observed in sheep and goats although systematic studies are limited. Centric fusion that involves different chromosomes but not specific to chromosome (1;29), is the most common abnormality, followed by chimerism, sex chromosome abnormalities, and rarely deletions and inversions. In swine, reciprocal translocations are the most common abnormalities with significant economic loss due to reduction in litter size by up to 50%. This is followed by chimerism for sex chromosomes. Unlike cattle, incidence of ROB (1,29) in pigs is very rare. In domestic buffaloes, sex chromosome abnormalities are the most common found associated with infertility due to extensive damage to sex adducts. Freemartinism is the most prevalent form of all sex chromosome abnormalities detected in buffalo. However, translocations are rare incidences in buffalo. Sound breeding programmes and successful cattle production depend on minimizing Yimer, N. and Rosnina, Y. 2 Pertanika J. Trop. Agric. Sci. 37 (1) 1 18 (2014) and preventing all kinds of possible causes of reproductive failure in both females and males. Unlike many other causes of reproductive failure, little attention appears to be given towards cytogenetic anomalies examination at the time of breed selection for genetic improvement, as well as during investigation of causes of reproductive failure in farm animals. This is especially true in the tropical regions where cytogenetic studies are limited and their significance is poorly understood. This review provides an overview and update on chromosomal anomalies, their effect on fertility of farm animals and screening methods, with subsequent aim of drawing the attention of concerned bodies to make an effort towards understanding the magnitude and significance of the problem in the tropics by applying feasible and available biotechnological tools pertinent to cytogenetics. This consequently would help to design possible strategies to prevent and control the propagation of chromosomal aberrations in farm animals in the tropics.