Results and Discussion Effect of Herbage Allowance on Forage Mass, Insulin and IGF-1 Concentrations during the Gestation and Lactation of Primiparous Beef Cows Grazing Campos Martín Claramunt1 and Pablo Soca2 517 Centro universitario de la Regional Este 1 and Facultad de Agronomía 2, Universidad de la República, Uruguay. martinclaramunt@gmail.com Increase the herbage allowance (HA) from 2.5 to 4 increased the reproductive response, calf weight at weaning and biological efficiency of primiparous beef cows grazing Campos grasslands. Our objective was to evaluate the effects of 2 HA on forage mass, insulin and IGF-1 concentrations during gestation-lactation of primiparous beef cows as signals of forage intake, energy balance and metabolic memory. A sample of 32 (n = 16 per treatment) spring calving primiparous Hereford beef cows selected from 80 cows belonging to HA experiment was selected. Two (High vs Low) HA treatments (forage Dry Matter/kg liveweight) fluctuated throughout the seasons: autumn (middle gestation) 5 and 3, winter (late gestation) 3 and 3, spring (early lactation) and summer (late lactation) 4 and 2 kg DM/kg liveweight for high and low HA, respectively. Forage mass was greater in High than Low HA (P = 0.04) and was not affected by HA x days post partum (DPP). Insulin was not affected by HA and this suggests low differences in forage energy intake. Insulin concentrations decreased at 20 DPP (early spring) and increased at the end of summer (180 DPP) associated with greater forage mass and forage energy intake. IGF-1 was greater (P<0.05) in High than Low HA at -90 DPP but no other differences were identified. IGF-1 nadir occurred later in High than Low HA; then, both increased to 50 DPP and remained constant until 185 DPP. Herbage allowance improved IGF-1 levels during autumn despite the reduced differences in forage mass and probably in energy intake. Nutritional plane during autumn could be a lasting metabolic signal associated with greater reproductive response and biological efficiency of primiparous beef cows grazing Campos grasslands Introduction Material and Methods Results and Discussion Conclusion References Click Headings to View More Information

Introduction Beef cows primarily graze Campos grassland at high stocking rates Low productive and reproductive response (Weaning rate 64% and Calf BW at weaning 140 kg) . Even lower records in primiparous cows Increase the Herbage allowance (HA) from 2.5 to 4 kg of forage dry matter / kg bodyweight in multiparous and primiparous beef cows grazing Campos grasslands increased (Do Carmo et al. 2016): reproductive response calf weight at weaning biological efficiency An increase in HA could increase insulin and IGF-1 indicating an improvement in energy intake and energy balance, respectively. Insulin and IGF-1 are associated with a shorter anoestrus postpartum and pregnancy rates, and could explain the effect of HA on reproductive response and efficiency (Hess et al. 2005) Campos We hipothesize that an increase in HA increases the concentration of insulin and IGF-1 of primiparous beef cows

Material and Methods 32 (8 per treatment*block) spring calving cows were selected from 80 cows belonging to a completely randomized block design experiment of two blocks (spatial replica) and two HA from -150 (autumn) to 185 (summer) days postpartum (DPP) (Claramunt et al. 2017 Click here to view more information). Treatments (ratio between forage mass and stocking rate; Aiken 2016) fluctuated throughout seasons: autumn 5 and 3, winter 3 and 3, spring and summer 4 and 2 kg forage DM/kg liveweight for high and low HA, respectively (Fig. 1). Put-and-take was employed to adjust HA and forage mass was measured seasonally via the comparative yield method. Blood samples were collected –90 (autumn end), -50, -20 (winter), 20, 50 (spring), 85 and 185 DPP (summer) (Fig.1). Insulin and IGF-1 were determined by IRMA and RIA with comercial kits Forage mass, Insulin and IGF-I were analyzed using mixed models. Means were compared using Tukey. Fig. 1. Treatments, management and blood samples design

Results and Discussion HA P = 0.04 DPP P <.0001 HAxDPP P = 0.35 HA P = 0.31 DPP <.0001 HAxDPP P = 0.21 HA P = 0.01 DPP <.0001 HAxDPP P = 0.0007 Figures. Forage mass, Insulin and IGF-1 concentrations for High and Low Herbage allowance. Values are l.s.m. ± s.e. Forage mass was greater in High than Low HA. Summer forage mass was greater than autumn, winter and spring. Insulin was not affected by HA and this suggests low differences in forage energy intake. Insulin concentrations decreased at 20 DPP (early spring) and increased at the end of summer (180 DPP) associated with greater forage mass and forage energy intake (Da Trindade et al. 2016). IGF-1 was greater (P<0.05) in High than Low HA at -90 DPP but no other differences were identified. IGF-1 nadir occurred later in High than Low HA; then, both increased to 50 DPP and remained constant until 185 DPP. The high energy requirement during final gestation/winter (-90 to 0 DPP) and lactation (spring-summer) probably explained that High HA improved IGF-1 only during autumn. This improvement in IGF-1 occurred despite the reduced differences in forage mass and insulin between HA.

Conclusion Herbage allowance improved IGF-1 levels during autumn despite the reduced differences in forage mass and probably in energy intake. Autumn is a key season to improve the nutritional plane of the cow in this ecosystem. Prepartum IGF-1 levels could be a lasting metabolic signal associated with greater reproductive response and biological efficiency of primiparous beef cows grazing Campos grasslands

References Aiken GE (2016) Invited review: grazing management options in meeting objectives of grazing experiments. The Professional Animal Scientist 32, 1–9. doi:10.15232/pas.2015-01406 Claramunt, M., Fernández-Foren, A., & Soca, P. Effect of herbage allowance on productive and reproductive responses of primiparous beef cows grazing on Campos grassland. Animal Production Science. https://doi.org/10.1071/AN16601. Da Trindade, J. K., Neves, F. P., Pinto, C. E., Bremm, C., Mezzalira, J. C., Nadin, L. B., ... & Carvalho, P. C. (2016). Daily forage intake by cattle on natural grassland: response to forage allowance and sward structure. Rangeland ecology & management, 69(1), 59-67. Do Carmo, M. Claramunt, M. Carriquiry, Soca P (2016) Animal energetics in extensive grazing systems: rationality and results of research models to improve energy efficiency of beef cow-calf grazing Campos systems. Journal of Animal Science 94(S6):84–92 Hess, B. W., Lake, S. L., Scholljegerdes, E. J., Weston, T. R., Nayigihugu, V., Molle, J. D. C., & Moss, G. E. (2005). Nutritional controls of beef cow reproduction. Journal of Animal Science, 83(13_suppl), E90-E106.