Supplement protein level affects performance and reproduction of grazing heifers.

Abstract:

M103
Supplement protein level affects performance and reproduction of grazing heifers.
A. F. Machado¹, V. C. L. Moraes¹, D. L. Souza Netto¹, P. V. F. Correa¹, S. E. F. Guimaraes¹, G. M. Santos², M. I. Marcondes*¹. ¹Universidade Federal de Vicosa Vicosa, MG, Brazil, ²Univicosa Vicosa, MG, Brazil.

Evaluations of the interaction between nutrition and reproduction of dairy heifers grazing intensively managed pasture are scarce. Thus, we aimed to evaluate performance, muscle development, oocyte quality and in vitro embryo production of grazing crossbred heifers fed increasing CP levels in the supplement. Eighteen pubertal crossbred heifers (Holstein x Gyr; initial BW of 350 � 8.0 kg) were used in a 90-d trial. Two supplements (12 and 24% CP, S12CP and S24CP) and control treatment (mineral mixture, MM) were randomly assigned to the heifers. Three ovarium pic-up were performed. DMI and CP intake were greater for supplemented (SUP) compared with MM. SUP heifers had greater ADG (P = 0.003) and rib eye area (P = 0.04) than MM, and carcass ultrasonography indicated a trend for greater rib eye area for S24CP comparing with S12CP (Table 1). Viable oocytes were not affected by supplementation strategy. However, cleavage and blastocyst rates were negatively affected by SUP (P < 0.05), and S12CP had lower blastocyst rate than S24CP (P = 0.012; Table 1). In summary, supplementation with concentrate containing 24% CP might be an appropriate strategy for satisfactory performance during the rainy season in tropical climates. In contrast, the in vitro embryo production was impaired with supplementation.Table 1. Performance and reproductive parameters of Holstein � Gyr heifers not supplemented (MM) or supplemented with concentrate containing 12% CP (S12CP) or 24% CP (S24CP) in a rotational grazing system

Item	MM	Supplement		SEM	P-value1
S12CP	S24CP	MM�SUP	S12CP� S24CP	PER
DMI, kg/d	7.36	8.04	8.58	0.307	0.014	0.220	0.091
CPI,2 kg/d	1.28	1.30	1.63	0.053	0.008	0.001	0.327
ADG, kg/d	0.39	0.60	0.69	0.059	0.003	0.381	—
Ribeye area, cm2	53.32	56.00	61.56	1.983	0.040	0.070	—
Viable oocytes, no	6.07	5.39	7.25	1.572	0.926	0.420	0.007
Cleavage rate, %	41.17	23.92	36.71	5.716	0.017	0.102	0.676
Blastocyst rate, %	27.91	3.02	17.23	3.924	0.001	0.012	0.816

¹SUP�MM = supplementation effect; S12CP�S24CP = effect of supplement protein level; PER = period effect.We observed no TR�PER interaction (P > 0.05).²CPI = crude protein intake.

Keywords: supplementation, oocyte quality, embryo production.