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Dry-matter intake level and its effects on follicle growth and circulating progesterone in Nelore (Bos indicus) and Holstein (Bos taurus) heifers
The aim of this study was to evaluate circulating progesterone concentration (P4) and ovarian follicular dynamics in Bos indicus and Bos taurus heifers under high (HDM; weight gain of 900g per d) and low (LDM; maintenance, NRC 2001) consumption of dry matter. Cycling Holstein (n=16) and Nelore (n=16) heifers were used in a 2x2 factorial arrangement (cross-over). The experimental diet was given during 32 d (15 d before and 17 d during the hormonal protocol). The animals were pre-synchronized with two applications of cloprostenol (0.53mg, i.m. PGF2α, Sincrocio®, Ourofino Agronegócio) 12 d apart and 18 and 12 h before device insertion. At onset of synchronization protocol (D0), heifers received a new intravaginal P4 device (CIDR®, Zoetis Brasil), 2mg of estradiol benzoate i.m.(BE, Sincrodiol®, Ourofino Agronegócio) and a dose of PGF2α. After 8 d, the P4 device was removed and 1mg of BE was administered 24 h later. Ultrasonographic exams were performed every 24 h during P4 device treatment (D0 to D8), and at every 12 h from P4 device removal to ovulation. Blood samples were collected daily from D0 to D10. The results were analyzed using PROC MIXED of SAS 9.2 and presented as mean ± standard error. An interaction (genetic group*d, p < 0.0001; diet*d, p = 0.03) was observed between genetic group, diet and d of the hormonal protocol on the diameter of the dominant follicle (DDF). The effect of diet on the DDF during hormonal protocol was observed as soon as two d after follicular wave emergence (D5 to D10 of the hormonal protocol, P < 0.05). However, the effect of genetic group was observed only towards the end of the protocol (D8 to D10, P < 0.05). Regardless of the diet, the DDF on D8 (P=0.04) and D10 (P=0.01) of the hormonal protocol were larger in Holstein (11.6±0.4 and 14.4±0.4) than Nelore (10.3±0.4 and 12.2±0.4) heifers. Independently from genetic group, the DDF on D8 (P<0.0001) and D10 (P=0.01) of the hormonal protocol was larger in heifers receiving to HDM (12.2±0.4 and 14.3±0.4) than LDM (9.6±0.4 and 12.2±0.4). Curiously, lowering DM intake caused a greater increase in circulating P4 in Nelore than in Holsteins (genetic group*diet*d, P = 0.05). In conclusion, heifer breed had a market effect in hormonal profile and follicle growth during synchronization programs, but increasing DM intake greatly influenced ovarian dynamics and circulating P4. Acknowledgements:FAPESP, CNPq
Keywords: Bos indicus, Bos taurus, progesterone