Effects of age on haematological parameters have been documented in various breeds of horses (Hernández et al.
2008; Satue et al.
2009). Grondin and Dewitt (
2010) and Sgorbini et al. (
2013) reported that newborn foals have high PCV, RBC and Hb because erythrocytes are of foetal origin. Thus, the involvement of the liver and spleen in erythropoiesis and probably due to the transfusion of placental blood to the foal at birth may result in increased erythrocytic values. The high values of PCV, haemoglobin concentration and erythrocyte count observed in foals may also occur as a result of functional changes in haematopoiesis and high water content in foals or due to haemoconcentration because foals depend mainly on milk. Sgorbini et al. (
2013), Muñoz et al. (
2012) and Grondin and Dewitt (
2010) observed that PCV, Hb and erythrocyte count decreased significantly after the first 48 h of life, probably as a result of haemodilution, physiological destruction of erythrocytes by the spleen and decreased erythropoietin production secondary to increased blood oxygenation by lungs after birth. Muñoz et al. (
2012) also reported higher PCV, RBC and Hb in Spanish foals than those in adult Spanish horses. There is an increase in erythrocyte counts, PCV and Hb in donkeys as they get older (Etana et al.
2011). A reduction of erythrocyte count with a compensatory increase in MCV and MCH in older Carthusian pregnant mares and Spanish purebred mares have been reported (Hernández et al.
2008). Satue et al. (
2009), observed increased MCH, MCV and MCHC in adult horses. In a study conducted on working donkeys, the RBC, Hb, MCV, MCHV, PCV and MCH are higher in adult donkeys than in young ones (Etana et al.
2011). According to Folch et al. (
1997), young donkeys had significantly lower values of MCV and MCH as well as higher counts of leucocytes, segmented neutrophils, immature neutrophils and eosinophils than older animals. PCV and Hb increase with age in working horses (Pritchard et al.
2009). MCV in foals less than 1 year is significantly lower than that of the adult horses. Lippizan foals aged between 4 months and below have higher erythrocyte count and PCV than stallions and mares of the same breed (Cebulj-Kadunc et al.
2002). Brommer et al. (
2001) reported an increase in neutrophil and lymphocyte counts during the first months of life. Uluisik et al. (
2013) observed significant difference in RBC, PCV and MCV in horses of different ages. Adult working donkeys have higher PCV, RBC, Hb, MCV, MCHC and MCH than young donkeys (Lemma and Moges
2009). Old pregnant Andalusian mares have lower total leucocyte and lymphocyte counts, compared to younger ones (Satue et al.
2009). In addition, higher leucocyte count in younger animals when compared to adult was observed in Kathiawari horses in India (Gupta et al.
2002). The decrease in leucocyte count in healthy, aged horses may be related to age-associated decrease in immunocompetency (Mcfarlane et al.
2001).