Genetic variability of milk fatty acids.

The milk fatty acid (FA) profile is far from the optimal fat composition in regards to human health. The natural sources of variation, such as feeding or genetics, could be used to increase the concentrations of unsaturated fatty acids. The impact of feeding is well described. However, genetic effects on the milk FA composition begin to be extensively studied. This paper summarizes the available information about the genetic variability of FAs. The greatest breed differences in FA composition are observed between Holstein and Jersey milk. Milk fat of the latter breed contains higher concentrations of saturated FAs, especially short-chain FAs. The variation of the delta-9 desaturase activity estimated from specific FA ratios could explain partly these breed differences. The choice of a specific breed seems to be a possibility to improve the nutritional quality of milk fat. Generally, the proportions of FAs in milk are more heritable than the proportions of these same FAs in fat. Heritability estimates range from 0.00 to 0.54. The presence of some single nucleotide polymorphisms could explain partly the observed individual genetic variability. The polymorphisms detected on SCD1 and DGAT1 genes influence the milk FA composition. The SCD1 V allele increases the unsaturation of C16 and C18. The DGAT1 A allele is related to the unsaturation of C18. So, a combination of the molecular and quantitative approaches should be used to develop tools helping farmers in the selection of their animals to improve the nutritional quality of the produced milk fat

A suplementação com ácido linoléico conjugado reduziu a gordura corporal em ratos Wistar Conjugated linoleic acid suplementation decreased the body fat in Wistar rats

O ácido linoléico conjugado, um conjunto de isômeros geométricos e de posição do ácido linoléico, vem sendo muito estudado devido ao seu efeito sobre a composição corporal, promovendo redução da massa gorda. O objetivo deste trabalho foi avaliar o efeito da suplementação com ácido linoléico conjugado sobre a composição corporal de ratos Wistar saudáveis em crescimento. Um total de 40 ratos, divididos em quatro grupos, foram suplementados diariamente durante três semanas com AdvantEdge® ácido linoléico conjugado (EAS TM) nas concentrações 1,0%, 2,0% e 4,0% sobre o consumo diário de dieta, constituindo, respectivamente, os grupos AE1, AE2 e AE4, e com ácido linoléico na concentração de 2% sobre o consumo diário de dieta, constituindo o grupo-controle. Os animais foram suplementados por meio de entubação orogástrica. Para a avaliação da composição corporal centesimal foi removido o conteúdo intestinal para obtenção da carcaça vazia. Em seguida, a carcaça foi congelada em nitrogênio líquido, fatiada, liofilizada, moída e armazenada a -25&deg;C, até o momento das determinações de umidade, cinzas, proteína bruta e gordura. O grupo AE1 apresentou maior consumo de dieta e ganho de peso, mas não diferiu quanto à eficiência alimentar dos demais grupos (p< 0,05). Em relação à composição corporal, constatou-se redução dos teores de gordura corporal dos grupos AE2 (11,2%) e AE4 (11,6%), quando comparados ao teor do grupo-controle (13,9%). A suplementação com ácido linoléico conjugado nas concentrações de 2,0% e 4,0% sobre o consumo diário de dieta promoveu redução de gordura corporal de 18,0% nos ratos Wistar.<br>Conjugated linoleic acid, a group of positional and geometric isomers of linoleic acid, has been greatly investigated due to its effect on body composition, mainly the reduction of body fat. The purpose of this study was to evaluate the effect of conjugated linoleic acid supplementation on the body composition of healthy, growing Wistar rats. Forty male Wistar rats were divided into 4 groups and supplemented daily for 3 weeks with AdvantEdge® conjugated linoleic acid (EAS TM) at concentrations of 1.0%, 2.0% and 4.0% of the daily feed intake, corresponding to groups AE1, AE2 and AE4, and with linoleic acid at 2.0% (control) corresponding to group C. The animals were supplemented via a stomach tube. For the body composition analyses, the gut contents were removed to obtain the empty carcass weight. The carcasses were then frozen in liquid nitrogen, chopped, dried, ground and stored at -25ºC, until analyzed for water, ash, protein and fat. The AE1 group showed higher feed intake and weight gain, but did not differ in food efficiency from the other groups (p< 0.05). In terms of body composition, body fat reduced in groups AE2 (11.2%) and AE4 (11.6%), as compared to the control (13.9%). Conjugated linoleic acid supplementation at a rate of 2.0% and 4.0% with respect to the daily feed intake, decreased body fat by 18.0% in Wistar rats

Caloric stress alters fat characteristics and Hsp70 expression in milk somatic cells of lactating beef cows

Selection for higher production rate in cattle inhabiting challenging habitats may be considered disadvantageous because of possible deleterious effects on immunity and reproduction and, consequently, on calf crop percentage. In Israel, free-grazing high productive beef cows experience reduction in nutritional quality of forage during up to 8 months of the year. As milk production by dams dictates calf performance, dam’s nutritional needs and rebreeding rates, the aim of the present study was to test how lactating beef cows deal with combined caloric and protein stress both at the productive and self protective levels. For this purpose, we studied the effect of long-term caloric stress on milk characteristics and gene expression of stress and milk components producing proteins. Lactating dams responded to caloric stress by decreased body weight, milk, and milk protein production. To compensate for total energy loses in milk, they produced milk of higher fat concentration and shifted the proportions of its fatty acids towards long and unsaturated ones. This was reflected by increased mRNA transcription of the fatty acid binding protein. Prolonged low-energy diet promoted cell-specific heat shock protein (Hsp) response; whereas significant increase of Hsp90 but unchanged levels of Hsp70 proteins were observed in white blood cells, the expression of Hsp70 in milk somatic cells was markedly attenuated, in parallel with a marked increase of αs1-casein expression. At the mammary gland level, these results may indicate a decrease in turnover of proteins and a shift to an exclusive expression of milk components producing factors. Similar responses to caloric stress were revealed also in ketotic dairy cows. Ketosis promoted a shift towards long and unsaturated fatty acids and an increased expression of αs1-casein in milk somatic cells. These findings may reflect an evolutionary-preserved mechanism in lactating cows for coping with caloric restriction. Overall, our results provide an index to test suitability of beef cattle breeds to inadequate caloric demands