Effect of Herbage Allowance on Forage Mass, Insulin and IGF-1 Concentrations during the Gestation and Lactation of Primiparous Beef Cows Grazing Campos

Our objective was to evaluate the effects of two herbage allowance (HA) on forage mass (FM), Insulin and IGF-1 concentrations of primiparous beef cows. Thirty two spring calving cows were allocated to a completely randomized block design of two blocks and two HA from -150 to 185 days postpartum (DPP). Treatments (ratio between FM and stocking rate) 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. Put-and-take was employed to adjust HA and FM was measured seasonally via the comparative yield method. Blood samples were collected –90 (autumn), -50, -20 (winter), 20, 50 (spring), 85, 185 DPP (summer). Forage mass, Insulin, IGF-I were analyzed using mixed models and means were compared using Tukey. High HA had greater FM than low (P = 0.04; Table 1) and was not affected by HAxDPP (P = 0.35). The FM decreased slightly in winter and then increased 3-fold in summer. Insulin was affected by DPP (P < 0.001; Table 1) but not by HA (P = 0.31) and HAxDPP (P = 0.21). Insulin decreased until 20 DPP, increased at 50 DPP and decreased again. Insulin increased 2-fold from 85 until 180 DPP. Seasonal changes in Insulin concentrations can be explained by forage intake associated to FM. The IGF-1 were greater in high than low HA at -90 but no other differences were identified (HAxDPP P < 0.007; Table 1). The IGF-1 decreased from -90 to -20 DPP, then increased to 50 DPP and remained constant until 185 DPP. Forage mass differences between treatments at -90 DPP and the low cow energy requirements could explain the improvement in IGF-1 in high HA. Herbage allowance affected the energy metabolism of primiparous beef cows grazing Campos.

Table 1. Insulin, IGF-1 and FM for high and low HA. L.s.m. ± s.e. are presented.

	Insulin µUI/ml				IGF-1 (ng/mL)				FM (kgDM/hectare)
DPP	High	Low	s.e.		High	Low	s.e.		High	Low	s.e.
-90	15.8bc	11.7bc	1.4		132.6a	89.3bd	8.4		983b	672bc	106
-50	11.5cd	11.5cd	1.4		103.1b	77.1bd	8.4
-20	13.2bc	12.9bc	1.4		70.5de	52.5e	8.4		613c	464c	106
20	8.5d	7.9d	1.4		57.5de	59.3ce	8.5
50	16.5ab	15.9ab	1.5		99bc	92.7ad	8.7		962b	796b	106
85	8d	8.8d	1.4		97.2bc	88.4bd	8.1
185	21a	16.8a	1.5		104.4b	89.8bd	8.8		2499a	2088a	106

^{a, b, c, d, e} different superscripts differ at P<0.05