F. A. S. Silva

Macrominerals and Trace Element Requirements for Beef Cattle

Eighty-seven Nellore animals were utilized in this study to estimate net requirements for the maintenance and growth of beef cattle as well as the retention coefficients of 13 minerals: macrominerals (Ca, P, Mg, K, Na, and S) and trace elements (Cu, Fe, Mn, Se, Zn, Co, and Cr). The net requirements for maintenance and the true retention coefficient were estimated by using the regression between apparent retention and intake for each mineral. The net requirement for maintenance (μg/kg BW) and retention coefficients (%) were 163 and 85 for Cu, 2,097 and 53 for Fe, 32.3 and 24 for Mn, 3.72 and 48 for Se, 669 and 0.80 for Zn, 18.4 and 86 for Co, and 22.9 and 78 for Cr. The dietary requirements of macrominerals (g/kg DMI) were 5.12 for Ca, 2.38 for P, 0.96 for Mg, 2.40 for K, 0.79 for Na, and 1.47 for S. This is the first study using Nellore cattle to estimate mineral requirements; considering that Nellore cattle are the most common breed in Brazil and that Brazil is a major beef producer globally, this knowledge can help producers to improve animal performance by supplying the correct amount of minerals.

Effect of different forage types and concentrate levels on energy conversion, enteric methane production, and animal performance of Holstein × Zebu heifers

The aim of this study was to evaluate the effect of diets containing corn silage (CS) or sugarcane (SC) with 300 or 500 g/kg of concentrate (on a DM basis) on energy conversion, enteric methane (CH4) production, and the animal performance of Holstein × Zebu heifers. An experiment was conducted while using comparative slaughter. Twenty Holstein × Zebu heifers with an average age of 12 ± 1.0 months and an average bodyweight of 218 ± 36.5 kg were used. Four heifers were assigned to a baseline group, whereas the remaining 16 heifers were distributed in a completely randomised design using a 2 × 2 factorial scheme (n = 4), with two types of roughage (CS or SC) and two levels of concentrate (300 or 500 g/kg) on a DM basis of the diet over the course of 112 days. For the evaluation of the apparent total-tract digestibility of diets and energy losses, a digestibility assay was performed by using the total collection of faeces and urine over three consecutive days. The enteric CH4 production was quantified by continuous analysis of regular samples of air excreted by the animals throughout the day. The greatest (P 0.05) by variables that were analysed in this study. However, the mean value that was observed in the present study was above those values proposed by the main evaluation systems of feedstuffs and nutrient requirements of ruminants. Therefore, we concluded that CS-based diets allow for better animal performance of Holstein × Zebu heifers in relation to SC-based diets. Also, the increased concentrate improves the performance of growing heifers. A greater inclusion of concentrate in SC-based diets can allow for a reduction of CH4 emissions per consumed unit and per gain unit. The mean suggested value for the ME : DE ratio based on this study is 0.86. However, more studies are necessary to validate this result.

Effects of day of gestation and feeding regimen in Holstein × Gyr cows: III. Placental adaptations and placentome gene expression

This study investigated the influence of day of gestation (DG) and feeding regimens (FR) on the expression of genes responsible for placenta development, nutrient transfer, and angiogenic factors in Holstein × Gyr cows. Forty pregnant multiparous Holstein × Gyr cows with an average initial body weight of 482±10.8kg and an initial age of 5±0.8 yr were allocated to 1 of 2 FR: ad libitum (AL; n=20) or maintenance level (ML; n=20). Maintenance level was considered to be 1.15% of body weight (dry matter basis) and met 100% of the net energy requirements and AL provided 190% of the total net energy requirements. Cows were slaughtered at 4 DG: 139, 199, 241, and 268d. After the cows were slaughtered, the placenta and uterus were separated and weighed. Caruncles and cotyledons were individually separated, counted, and weighed. Placenta expressed as kilograms and grams per kilogram of empty body weight (EBW) was heavier in ML- than in AL-fed cows at 268d of gestation. Placenta expressed as kilograms and grams per kilogram of EBW was the lightest at 139d of gestation, and the greatest mass was observed at 268d in ML-fed cows. However, in AL-fed cows, the heaviest placenta expressed as grams per kilogram of EBW was observed from 199d of gestation. Placentomes expressed as grams per kilogram of EBW were heavier in ML-fed cows during gestation, and the number of placentomes was greater in ML-fed cows at 268d of gestation. We observed that IGFR1 and IGFR2 were involved in placenta adaptations when ML was provided, as their expression in placentome cells was greater in ML-fed cows at 268d of gestation. The genes responsible for angiogenesis were also greater in ML-fed cows: VEGFA, GUCY1B3, HIFA, FGF2, and NOS3 were altered by FR and DG interaction and they were greater in ML-fed cows at 268d of gestation. In addition, VEGFB and ANGPT2 did not show interactions between FR and DG, but they were greater in ML-fed cows. Thus, we suggest that the placenta from an ML-fed cow develops adaptations to the reduced nutrient supply by altering its structure and gene expression, thereby developing mechanisms for potential increased nutrient transfer efficiency to the fetus.