Modelling spring and autumn calving systems in beef herds of the Salado region of Argentina A.J. Romera a , J.C. Burges b, ⁎ , S.T. Morris c , J. Hodgson c , S.J.R. Woodward d a Whole Farm Modelling Team, Dexcel Ltd., Hamilton, New Zealand b Grupo de Sistemas Ganaderos, INTA, CC 276, (7620) Balcarce, Argentina c College of Sciences, Massey University, Palmerston North, New Zealand d Supply Chain Systems Group, Lincoln Ventures Limited, Hamilton, New Zealand Received 8 August 2006; received in revised form 11 June 2007; accepted 19 June 2007 Abstract Spring calving is recommended for beef herds in the Salado region of Argentina, but autumn calving is an alternative being used by some farmers. This study explored the biological and economic feasibility of autumn calving in cow–calf systems and their long-term performance compared with spring calving. Reproduction and calf performance data were collected from an autumn calving herd (1999–2005) and from a spring calving herd (1966–1995) at the INTA-Balcarce Research Station (37°45′ S; 58°18′ W). Similar data were obtained from a commercial farm which practiced both autumn and spring calving (1998–2003). These data showed that autumn calving is feasible in the region, provided that cows calve with a high condition score. This is a major difference with spring calving, where cows can normally gain weight during breeding. A climatically driven computer model was used to compare, at farm level, the effect of calving season across a range of combinations of weaning dates and stocking rates. Spring calving systems had greater production potential (15–20%) and profitability (17–28%) at high stocking rates. However, at low to moderate stocking rates, calving season had little effect on expected production and risk efficiency. This suggests that autumn calving could be a suitable alternative for the Salado region of Argentina. To exploit its potential, however, calf weaning age should be greater than with spring calving. © 2007 Elsevier B.V. All rights reserved. Keywords: Cow–calf farms; Calving season; Modelling 1. Introduction The Salado region of Argentina is a vast grassland area, mostly dedicated to cattle breeding (Soriano, 1992). Approximately 80% of calves born in the region are sold at weaning for finishing outside the region. Although comprehensive statistics are not available, it is known that a majority of farmers breed their cows for long periods, typically between 4 and 6 months in spring–summer, and that continuous bull presence is still very common (Natinzon, 2006). These practices persist despite many years of effort by INTA (National Institute of Agricultural Technology) and other institu- tions promoting the convenience of short breeding seasons (2–3 months) in spring (Carrillo, 1997). In general, the October–December period has been recommended as the most appropriate. An example of these efforts is the “Reserva 6” cow–calf demonstration farm at the INTA-Balcarce Research Station, which has been operating since 1966 (Stewart and Bravo, 1967). Breeding is a highly sensitive period, and should be scheduled at a time of plentiful forage supply (D'hour Available online at www.sciencedirect.com Livestock Science 115 (2008) 62 – 72 www.elsevier.com/locate/livsci ⁎ Corresponding author. Tel.: +54 2266 439100; fax: +54 2266 439101. E-mail address: jcburges@balcarce.inta.gov.ar (J.C. Burges). 1871-1413/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2007.06.013