Supplementation plans for development of Nellore heifers, effects of creep-feeding on the lactating dam and dietary strategies for Nellore cows in the last third of gestation

• Ano de defesa: 2016
• Autor(a) principal: Silva, Aline Gomes da
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Nutrição animal; Bovino - Reprodução; Ciências Agrárias; Zootecnia; Nutrição e Alimentação Animal
• Link de acesso: http://www.locus.ufv.br/handle/123456789/7974

Reproduction is the single most important economic component in any beef production system and the low offtake rate observed in the Brazilian herd reflects the low fertility rate of cows and the late age at puberty of replacement heifers. In order to provide more information about nutritional strategies to better develop Nellore heifers and to improve dams’ performance, two studies were conducted and the results are here presented in three papers. In the first paper, fifty Nellore heifers with 131.8 ± 9.9 kg average body weight (BW) and 138 ± 19 d of age were supplemented from 4 to 14 months to evaluate the effects of high (H) and low (L) supplementation levels pre and post-weaning on performance, endocrine, metabolic and reproductive responses of heifers. Heifers were distributed in five supplementation plans: HH – animals received 6 g/kg of BW pre and post-weaning; HL – animals received 6 g/kg of BW of supplement pre-weaning and 3 g/kg of BW post-weaning; LH – animals received 3 g/kg of BW pre-weaning and 6 g/kg of BW post-weaning; LL – animals received 3 g/kg of BW pre and post-weaning; and CC – control, no supplement was fed. Interactions between level fed pre and post-weaning were not significant for any performance variables evaluated (P > 0.10). Level of supplement fed pre-weaning did not affect any of the performance variables evaluated at the end of the experiment (P > 0.10). There was a significant effect of supplementation and level of supplementation offered post-weaning on average daily gain (ADG) in the post-weaning phase and final BW (P < 0.05). Overall ADG was also affected only by supplementation and level of supplement fed post-weaning (P < 0.05) with animals receiving 6 g/kg of BW post-weaning gaining more. Follicular diameter was greater for animals receiving 6 g/kg of BW post-weaning (P < 0.05). Growth hormone tended to be higher for heifers receiving 6 g/kg of BW pre-weaning (P < 0.10) and in the post-weaning phase, growth hormone was lower for heifers receiving supplementation (P < 0.05). No difference in insulin levels was observed in the pre-weaning phase (P > 0.10) and insulin levels post-weaning were affected only by level of supplementation offered in that phase (P < 0.05). Most metabolites were not affected by pre-weaning treatment (P > 0.10). There was no difference in total cholesterol, HDL and LDL levels among treatments pre-weaning (P > 0.10). All metabolites related to fat metabolism reduced after weaning but only LDL was significantly different among treatments (P < 0.05). There was a positive effect of level of supplementation post-weaning on serum total protein concentration (P < 0.05). Supplementation increased albumin levels (P < 0.05) and animals receiving high amount of supplement had higher albumin levels as well (P < 0.05). There was no significant difference in globulins concentrations (P > 0.10). In summary, performance, endocrine, metabolic and reproductive variables evaluated were improved by level of supplement fed post-weaning, with heifers receiving 6 g/kg of BW having greater responses, independently of level received pre-weaning. The same fifty pairs used in the study described for the previous paper were used in the second paper to evaluate the effects of high and low supplementation levels for Nellore heifer calves on performance, milk production and metabolic prolife of their dams. The same treatments evaluated during the pre-weaning phase of the previous paper were also here evaluated: 0 – control, no supplement was fed to calves; 3 - calves received supplement in the amount of 3 g/kg of BW; 6 - calves received supplement in the amount of 6 g/kg of BW. There was no significant effect level of supplementation offered to offspring on cow BW, BCS and subcutaneous fat thickness (P > 0.10). Level of supplementation of heifer calves did not significantly affect milk production corrected to 4% of fat (P > 0.10). Fat, protein, lactose and total solids of the milk also did not differ among supplementation strategies (P > 0.10). Level of supplement fed to calves had no effect on cows’ glucose, total cholesterol, HDL, LDL, triglycerides, total protein and albumin levels (P > 0.10). In conclusion, creep-feeding calves in the amounts of 3 or 6 g/kg of BW daily has no major impact on dams’ performance. In the second study, presented in the third paper, two experiments were conducted aiming to evaluate the effects of supplementation strategies for beef cows on the last third of gestation. In Experiment 1, to evaluate performance and reproductive responses, thirty-five pregnant Nellore cows were assigned to a completely randomized design with 4 treatments: control, which received no supplement; supplementation for the last 30 d of gestation (30d; 3.0 kg/d); supplementation for the last 60 d of gestation (60d; 1.5 kg/d); or supplementation for the last 90 d of gestation (90d; 1.0 kg/d). All supplemented treatments received the same total amount of supplement (20% of crude protein) throughout the experiment, 90 kg. Experiment 2 was delineated aiming to evaluate the effects of the amounts fed for cows in Experiment 1 on intake and metabolism. Four multiparous pregnant Nellore cows were assigned to a 4 × 4 Latin square design, with 4 experimental periods of 15 d each. There was a linear effect of days of supplementation on calving body weight (BW; P < 0.05) and a quadratic effect on BW change from parturition to d 31 post-calving (P < 0.05), with cows on the 60d strategy loosing less BW. No difference was found in offspring birth BW (P > 0.10). The 60d strategy tended to have higher pregnancy rate in the first fixed time artificial insemination (FTAI; P < 0.10), but there was no difference in the overall pregnancy rates (P > 0.10). Level of supplementation did not affect forage intake or neutral detergent fiber digestibility (P > 0.10). Nitrogen excreted through urine tended to increase linearly with level of supplementation (P < 0.10). We conclude that providing 1.5 kg of supplement during the last 60 d of gestation improves cow reproductive performance in the following breeding season with no negative effect on forage intake.