Abstract #W261

# W261
IGF-1 concentrations during early pregnancy in suckled Nellore beef cows.
Rogerio F. G. Peres*1, Ky G. Pohler3, Hugo B. Graff2, Adnan D. P. Rodrigues1, Michael F. Smith3, Duane H. Keisler3, Jose L. M. Vasconcelos1, 1Departamento de Produção Animal, Faculdade de Medicina Veterinária e Zootecnia-UNESP, Botucatu, São Paulo, Brazil, 2Agropecuária Fazenda Brasil, Barra do Garças, Mato Grosso, Brazil, 3Department of Animal Sciences, University of Missouri, Columbia, MO.

The objective of this experiment was to evaluate temporal changes in serum IGF-1 concentrations in Nellore postpartum cows and its effect on the pregnancy rates to TAI. Cows (n = 1208) from 2 farms with different grass quality (Farm1 = high quality forage; n = 931, BCS 2.81 ± 0.01; Farm2 = low quality forage; n = 277, BCS 2.97 ± 0.03) with 53 ± 6.2 d postpartum were supplemented with mineral premix (110 g/cow/day) throughout the study. Cows underwent an estrous synchronization protocol with TAI. Blood was sampled on D-11 (first day of protocol), D0 (TAI), and D30 (pregnancy diagnosis) and analyzed for IGF-1 concentrations (all cows). Concentrations of IGF-1 on Days −11, 0 and 30 were analyzed using PROC MIXED including farm, BCS, pregnancy status on D30 and cow within pasture as a random effect. PROC GLM was used to evaluate IGF-1 concentrations effect on pregnancy rates. The pregnancies to TAI were 48.2% (449/931) and 45.5% (126/277) for Farm1 and 2, respectively. IGF-1 concentrations were greater (P < 0.05) in all days in Farm1 compared with Farm2 (P < 0.05). IGF-1 concentrations decreased during the study on Farm1 (D-11: 145.0 ± 2.4a, D0: 125.2 ± 2.9b and D30: 98.6 ± 1,8c ng/mL, P < 0.05). On farm 2 the IGF-1 concentrations were greater on D-11 compared with D0 and D30 (D-11: 73.0 ± 1.5a, D0: 65.1 ± 1.5b, D30: 63.0 ± 1.4b ng/mL, P < 0.05). There was a linear negative association of IGF-1 concentrations on pregnancy rates (P < 0.05). There was no difference in IGF-1 concentrations on D-11 and D0 between pregnant and open cows. Cows in Farm1 that became pregnant (96.0 ± 1.9a ng/mL) had less IGF-1 concentrations on D30 compared with nonpregnant cows (102.4 ± 1.9b ng/mL). In Farm 2 pregnant (60.0 ± 1.7b ng/mL) cows tended (P < 0.06) to have less IGF-1 concentration than nonpregnant cows (63.7 ± 1.5b ng/mL). These data show that Nellore cows have a decrease in IGF-1 concentrations within 30 d of the first insemination and pregnant cows had less IGF-1 concentration on D30 compared with nonpregnant cows. Although the farm with better quality forage had cows with increased IGF-1 concentrations compared with cows in the farm with low quality forage, in both farms pregnant cows had a decrease in IGF-1 after TAI. Further research is needed to understand mechanisms by which less IGF-1 is associated with pregnancy in beef cows. FAPESP Project #2014/03209–0.