Comparison of purine bases and 15N to quantify microbial nitrogen yield in beef cattle and the effects of day of gestation and feeding regimen in Holstein × Gyr cows

• Ano de defesa: 2015
• Autor(a) principal: Rotta, Polyana Pizzi
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Proteína microbiana (Nutrição animal); Digestibilidade; Bovino de leite - Nutrição; Vaca - Reprodução; Gravidez; Nutrição e Alimentação Animal
• Link de acesso: http://www.locus.ufv.br/handle/123456789/6457

Microbial nitrogen yield (MN) is of great importance to protein metabolism in ruminants. The quantification of its flow to the small intestine is therefore important in calculating the amount of digestible MN available to the animal. Thus, an experiment was designed to evaluate the use of microbial markers (MM), sampling sites (SS), and marker systems (MS) to estimate MN in bulls and to develop equations to correct MN estimates. The MM systems that were evaluated were 1) purine bases (PB) and 2) 15 N labeling. The SS that were evaluated were 1) reticulum, 2) omasum, and 3) abomasum, and the studied MS were 1) single, 2) double, and 3) triple. Eight crossbred (Holstein × Zebu) bulls (353 ± 36.9 kg of BW; 24 ± 1 mo) with ruminal and abomasal cannulas were utilized in this experiment. For PB, the greatest (P < 0.01) values of MN were observed for the digesta that were sampled from the reticulum and abomasum. In contrast, for 15 N, the greatest (P < 0.01) values were observed for digesta that were sampled in the omasum and abomasum. Microbial nitrogen yield was only different (P < 0.05) from those estimated using abomasum and 15N when using reticulum and 15N. Thus, the equation that was developed to correct the MN value was as follows: MN (g/d) = 27.93 ± 2.46 + 0.99 ± 0.09 × reticulum 15N. The triple MS exhibited the greatest (P < 0.01) value of MN when compared to the single and double MS. No interactions (P > 0.05) were observed between MS and MM or SS; thus, the equation that was established to correct the MN value used only the MS. In conclusion, we have demonstrated that there is no difference when using 15N to estimate MN yield if the omasum or abomasum are used. Therefore, the omasum can be used as an accurate SS to predict MN. The triple MS presented with greater values than the single and double MS. Thus, if single or double MS is used, the value must be corrected by the equation that was obtained by using the triple MS. Another study was conducted with the aim of investigating how the feeding regimen (FR) alters apparent total tract digestibility, performance, N balance, excretion of purine derivatives, fat deposition, maternal and fetal visceral organ mass, and the expression of genes that are responsible for placental development, nutrient transfer, and angiogenic factors in Holstein × Gyr cows at different days of gestation (DG). Forty-four pregnant multiparous Holstein × Gyr cows with an average initial body weight of 480 ± 10.1 kg and an initial age of 5 ± 0.5 years were allocated to 1 of 2 FR: ad libitum (AL; n = 20) and maintenance level (ML; n = 24). Maintenance level was considered to be 1.15% of body weight on a dry matter (DM) basis and met 100% of the energy requirements, while AL provided 190% of the total net energy requirements. Cows were individually fed a corn silage-concentrate based diet composed of 93% roughage and 7% concentrate (DM basis) as a total mixed ration. Pregnant cows were slaughtered at 4 DG: 139 (n = 11), 199 (n = 11), 241 (n = 11), and 268 d (n = 11). Overall, DM intake decreased as DG increased. The decrease that was observed in DM intake may be associated with the reduction in ruminal volume caused by the rapid increase in fetal size during late gestation. We observed an interaction for DM and organic matter apparent total tract digestibility between FR and DG; at 150, 178, and 206 d of gestation, ML-fed cows had greater DM and organic matter apparent total tract digestibility values than AL-fed cows. Rib fat thickness, mesentery, and kidney, pelvic, and heart fat were greater in AL- than in ML-fed cows at all DG, with the exception of rib fat thickness on d-139. Ad libitum-fed cows excreted more N in their feces and urine compared to ML-fed cows. Pregnant cows that were fed at maintenance had greater digestibility during some DG, excreted less N in feces and less N and urea in urine, and deposited less fat in the body. Mass of the heart, liver, and gastrointestinal tract were heavier in AL- than in ML-fed cows. Feeding regimen did not influence fetal body weight in this study. The majority of the visceral organ masses were similar in fetuses from cows that were fed AL and ML. This data indicates that maternal feed-restriction does not affect the development of most fetal organs and fetal development; however, some maternal organs are affected according to the FR that is provided. Mammary gland mass was heavier in AL- than in ML-fed cows, and the heaviest mass was observed at 268 d of gestation. The negative impact on mammary gland mass caused by the ML probably will not affect the subsequent lactation because the crude protein concentration in the mammary gland increased with this FR. However, we suggest that the AL diet should be provided in pregnant dry cows with caution since the amount of fat in the mammary gland increased at 268 d of gestation. Placenta was heavier in ML- than in AL-fed cows at 268 d of gestation; the lightest mass was observed at 139 d of gestation, and the heaviest mass was observed at 268 d in ML-fed cows. However, in AL-fed cows, the heaviest placenta was observed from 199 d of gestation. Placentomes were heavier in ML-fed cows during gestation, and the number of placentomes was greater in ML-fed cows at 268 d of gestation. We observed that IGFR1 and IGFR2 genes were involved in placental adaptations when ML was provided, as their expression in placentome cells were greater in ML-fed cows at 268 d of gestation. The genes that are responsible for angiogenesis were also greater in ML-fed cows. VEGFA, GUCYB3, HIFA, FGF2, and NOS3 were altered by FR and DG interaction and they were greater in ML-fed cows at 268 d of gestation. Also, VEGFB and ANGPT2 did not present an interaction between FR and DG, but they were greater in ML-fed cows. We recommend ML (1.15% of body weight with 93% of roughage) as a FR for pregnant dry cows; however, during the last month of gestation, AL seems to be the most appropriate FR to avoid loss of body weight; however if AL diets in pregnant dry cows were to be provided, it had to be with caution since the amount of fat in the mammary gland increased at 268 d of gestation. Moreover, we suggest that the placenta from ML-fed cows develop adaptations to the reduced nutrient supply by altering its structure and gene expression, thereby developing mechanisms for a potential increase in the nutrient transfer efficiency to the fetus.