This study was conducted to evaluate the development of the mammary gland in Holstein heifers subjected to different dietary metabolisable protein (MP): metabolisable energy (ME) ratios. Twenty-five Holstein heifers (initial body weight (BW) 213±13·5 kg and initial average age 7·8±0·5 months) were divided into five treatments. The treatments were designed to provide MP:ME ratios equal to 33, 38, 43, 48, and 53 g of MP per Mcal of ME. All diets were formulated to have the same energy content (2·6 Mcal ME/kg dry matter). Actual MP:ME ratios were 36·2, 40·2, 46·2, 47·1, and 50·8 g MP/Mcal ME. The experiment was conducted in a randomised block design, while considering initial BW as a blocking factor to evaluate pre- and post-pubertal periods. Block effect was not observed for all variables evaluated; hence it was considered that the diets had the same influence both on pre- and post-pubertal phases. Dry matter and nutrient intake did not change between treatments, excepting protein intake and digestibility. Serum concentrations of insulin-like growth factor 1 increased linearly across treatments. Changes in the pixel brightness of mammary gland ultrasound images, which are associated with lipid content, were significantly influenced by MP:ME ratios in the diet of heifers that were subjected to accelerated growth rates. It is not recommended to use diets of less than 38 g MP/Mcal ME in diets to heifers allowed to gain more than 1 kg/d.

BackgroundDue to high neutral lipids accumulation in the cytoplasm, in vitro-produced embryos from Bos primigenius indicus and their crosses are more sensitive to chilling and cryopreservation than those from Bos primigenius taurus. The objective of the present study was to evaluate the effects of trans-10, cis-12 conjugated linoleic acid (CLA) on the development and cryotolerance of crossbred Bos primigenius taurus x Bos primigenius indicus embryos produced in vitro, and cultured in the presence of fetal calf serum. Bovine zygotes (n = 1,692) were randomly assigned to one of the following treatment groups: 1) Control, zygotes cultured in Charles Rosenkrans 2 amino acid (CR2aa) medium (n = 815) or 2) CLA, zygotes cultured in CR2aa medium supplemented with 100 μmol/L of trans-10, cis-12 CLA (n = 877). Embryo development (cleavage and blastocyst rates evaluated at days 3 and 8 of culture, respectively), lipid content at morula stage (day 5) and blastocyst cryotolerance (re-expansion and hatching rates, evaluated 24 and 72 h post-thawing, respectively) were compared between groups. Additionally, selected mRNA transcripts were measured by Real–Time PCR in blastocyst stage.ResultsThe CLA treatment had no effect on cleavage and blastocyst rates, or on mRNA levels for genes related to cellular stress and apoptosis. On the other hand, abundance of mRNA for the 1-acylglycerol-3-phosphate 0-acyltransferase-encoding gene (AGPAT), which is involved in triglycerides synthesis, and consequently neutral lipid content, were reduced by CLA treatment. A significant increase was observed in the re-expansion rate of embryos cultured with trans-10, cis-12 CLA when compared to control (56.3 vs. 34.4%, respectively, P = 0.002). However, this difference was not observed in the hatching rate (16.5 vs. 14.0%, respectively, P = 0.62).ConclusionsThe supplementation with trans-10, cis-12 CLA isomer in culture medium reduced the lipid content of in vitro produced bovine embryos by reducing the gene expression of 1-acylglycerol 3-phosphate 0-acyltransferase (AGPAT) enzyme. However, a possible improvement in embryo cryotolerance in response to CLA, as suggested by increased blastocyst re-expansion rate, was not confirmed by hatching rates.

To determine the effects of maternal nutrition on modifications of foetal development of the skeletal muscle and possible increase in the potential of skeletal muscle growth in cattle, gestating cows were either fed 190% NRC recommendations (overnourished; ON) or 100% NRC recommendation (control; CO). Interaction between maternal nutrition (MN) and the foetal sex (FS) was also investigated. Foetuses were necropsied at four different time points throughout gestation (139, 199, 241 and 268 days of gestation) to assess the mRNA expression of myogenic, adipogenic and fibrogenic markers in skeletal muscle. Phenotypic indicators of the development of skeletal muscle fibres, intramuscular lipogenesis and collagen development were also evaluated. Modifications in mRNA expression of skeletal muscle of foetuses were observed in function of MN and FS despite the lack of effect of MN and FS on foetal weight at necropsy. Maternal ON increased the mRNA expression of the myogenic marker Cadherin-associated protein, beta 1 (CTNNB1) and adipogenic markers Peroxissome proliferator-activated receptor gamma (PPARG) and Zinc finger protein 423 (ZNF423) at midgestation. However, no differences on foetal skeletal muscle development were observed between treatments at late gestation indicating that a compensatory development may have occurred on CO foetuses making the effect of MN on skeletal muscle development not significant at late gestation. Moreover, our data have shown an evidence of sexual dimorphism during foetal stage with a greater skeletal muscle development in male than in female foetuses. In conclusion, providing a higher nutritional level to pregnant cows changes the trajectory of the development of skeletal muscle during midgestation, but apparently does not change the potential of post-natal growth of muscle mass of the offspring, as no differences in skeletal muscle development were observed in late gestation.

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The pellucid zone (PZ) is a protective embryonic cells barrier against chemical, physical or biological substances. This put, usual transfection methods are not efficient for mammal oocytes and embryos as they are exclusively for somatic cells. Carbon nanotubes have emerged as a new method for gene delivery, and they can be an alternative for embryos transfection, however its ability to cross the PZ and mediated gene transfer is unknown. Our data confirm that multiwall carbon nanotubes (MWNTs) can cross the PZ and delivery of pDNA into in vitro-fertilized bovine embryos. The degeneration rate and the expression of genes associated to cell viability were not affected in embryos exposed to MWNTs. Those embryos, however, had lower cell number and higher apoptotic cell index, but this did not impair the embryonic development. This study shows the potential utility of the MWNT for the development of new method for delivery of DNA into bovine embryos.

The aim of this study was to determine the effect of increasing total solids (TS) in the liquid diet during the preweaning phase on mammary gland development in dairy heifers. The increase in TS was obtained with the addition of milk replacer powder to whole milk. Crossbreed Holstein-Gyr heifers (n = 60) were distributed in 4 treatments with different TS concentrations: 13.5% (n = 15), 16.1% (n = 15), 18.2% (n = 15), and 20.4% (n = 15). The liquid diets were provided from 5 to 55 d of age. From 56 to 59 d of age, the total amount of liquid feed was reduced by half. Heifers were weaned at 60 d and monitored until 90 d of age. Ultrasound mammary gland evaluations were performed weekly between 5 to 11 wk of age, using a B-mode ultrasound equipped with microconvex transducer at a frequency of 6 MHz. In those same weeks, the manual palpation of mammary parenchyma (PAR) was performed. Increased TS concentration of liquid diet during the preweaning period increased body weight of heifers, but did not alter PAR growth and the deposition of adipose tissue in the mammary gland evaluated by ultrasonography. The oval-shaped structure of PAR was altered after 2 mo of age. In the evaluated period, PAR growth was isometric with respect to the body growth rate. Palpation scoring of PAR had a strong correlation with the ultrasound evaluation of the PAR.

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