Effects of foaling season on growth and development of Lusitano suckling foals raised on extensive grazing systems

Abstract

Most Lusitano stud farms in Portugal are based in extensive grazing systems. In these systems, mares and foals are bred outdoors throughout the year, being pasture an important part of their diets. However, grass production is highly dependent on Mediterranean climatic conditions, with hot and dry summers. Therefore, a field study was conducted in order to evaluate the effects of foaling season on growth and development of the Lusitano suckling foal. One hundred and eight foals from four stud farms (A, n=39; B, n=33; C, n=12; D, n=24) were monitored from birth to six months of age, throughout three (A and B) and two (C and D) years. Monthly, foals were weighed (BW) and withers height (WH), girth (G) and cannon circumference (CC) were measured. According to birth date, two main foaling seasons were considered: February-March and April-May. A mixed linear model allowing for repeated measures on time was used to assess the effect of foaling season, stud farm, gender and their interactions on body weight, withers height, girth and cannon circumference. Quadratic effect of time was included in the model. The effect of foaling season was significant for withers height and girth (P<0.05) with higher values for foals born in February-March. Differences between stud farms were observed (P<0.001) for BW, WH, G and CC, which are probably linked with feeding options and pasture quality. The effect of gender was only significant on CC (P<0.05) with lower values registered in fillies. In the present study, foals born in February-March seem to have better development performances compared with foals born in April-May. Since pasture production and quality usually decreases from the end of May, these results suggest that April-May foaling mares may need a supplement to dry pasture, in order to support milk production and to promote an adequate foals’ growth and development.