Francis Enjalbert

Although fat content in usual ruminant diets is very low, fat supplements can be given to farm ruminants to modulate rumen activity or the fatty acid (FA) profile of meat and milk. Unsaturated FAs, which are dominant in common fat sources for ruminants, have negative effects on microbial growth, especially protozoa and fibrolytic bacteria. In turn, the rumen microbiota detoxifies unsaturated FAs (UFAs) through a biohydrogenation (BH) process, transforming dietary UFAs with cis geometrical double-bonds into mainly trans UFAs and, finally, into saturated FAs. Culture studies have provided a large amount of data regarding bacterial species and strains that are affected by UFAs or involved in lipolysis or BH, with a major focus on the Butyrivibrio genus. More recent data using molecular approaches to rumen microbiota extend and challenge these data, but further research will be necessary to improve our understanding of fat and rumen microbiota interactions.

Le profil des acides gras du lait de vache est important pour le consommateur, le lait et les produits laitiers contribuant fortement aux apports de matières grasses, et le profil des acides gras alimentaires ayant un impact important sur la santé. Les acides gras du lait de vache proviennent seulement en partie de la ration, et la digestion ruminale modifie profondément le profil des acides gras de la ration. Ces particularités physiologiques conditionnent les stratégies permettant de moduler le profil des acides gras du lait en modifiant la ration des vaches. Les principaux choix alimentaires ayant un impact sur le profil des acides gras du lait sont le choix du fourrage (herbe ou fourrages conservés) et l'addition de matières grasses, le plus souvent sous forme de graines oléagineuses. Les choix alimentaires permettant de maîtriser les proportions d'acides gras insaturés, d'acides gras n-3 ou d'acides gras trans sont présentés dans cet article.

Establishment of ruminal bacterial community in dairy calves. Rumen bacterial community was analysed on 6 calves bred according to commercial practices from day one to weaning at day 83 of age, using 454 16S rRNA-based pyrosequencing. Samples taken at day 1 did not produce amplicons. Analysis of data revealed a three-stage implantation process with a progressive but important shift of composition. At day 2, the bacterial community was mainly composed of Proteobacteria (70%) and Bacteroidetes (14%), and Pasteurellaceae was the dominant family (58%). The bacterial community abruptly changed between days 2 and 3, and until day 12, dominant genera were Bacteroides (21%), Prevotella (11%), Fusobacterium (5%) and Streptococcus (4%). From 15 to 83 days, when solid food intake rapidly increased, Prevotella became dominant (42%) and many genera strongly decreased or were no longer detected. A limited number of bacteria genera correlated with feed intake, rumen volatile fatty acids and enzymatic activities. The ruminal bacterial community is established before intake of solid food, but solid food arrival in turn shapes this community. This study provides insight into the establishment of calves' rumen bacterial community and suggests a strong effect of diet.

To provide a comprehensive examination of the bacterial diversity in the rumen content of cows fed different diets, high-throughput 16S rRNA gene-bas

The greater cane rat is a recently domesticated monogastric herbivore, and the importance of the caecum in the functioning of its digestive tract has frequently been mentioned. However, no data are available on caecal fermentative activity of this animal and research on the digestive physiology was only performed in adult animals. The present work was initiated to describe some parameters of the digestive tract anatomy and to study caecal fermentation of the growing cane rat. Thirty 40-day-old weaned cane rats were used in this experiment. Six of them were immediately euthanased and 12 were housed in a collective pen for gastrointestinal tract (GIT) parameters measurements. Twelve others were kept in individual cages to record growth and food intake. Captive cane rats received a pelleted diet containing 12.5% of crude protein and 16.7% of lignocellulose. Six of the 12 collectively housed animals were euthanased on day 82 and a further six on day 103. The growth rate increased with age (P < 0.01) with a linear growth curve (P < 0.001) while the feed intake (g/kg body weight) did not vary (P > 0.05). The caecum represented the largest compartment of the digestive tract constituting more than 40% of total GIT contents. Acetate was the most abundant short-chain fatty acid with more than 70% of the total, followed by propionate (less than 25%) and butyrate (around 5%). Short-chain fatty acid profiles varied with age: when age increased, the acetate proportion increased (P < 0.01), the propionate proportion decreased (P < 0.001) and the butyrate proportion remained unchanged (P > 0.05). The propionate/butyrate ratio showed a decrease with an increase in age (P = 0.05). Ammonia concentrations did not vary with age (P > 0.05). It is concluded that the caecum is an important site of fermentation in the growing cane rat.

Summary: Two lactating dairy cows fitted with a rumen cannula received successively diets containing 0%, 20%, 34% and again 0% of wheat on a dry matter basis. After 5, 10 and 11 days, ruminal pH was measured between 8:00 and 16:00 hours, and milk was analysed for fat content and fatty acid profile. Diets with 20% and 34% wheat induced a marginal and a severe subacute ruminal acidosis respectively. After 11 days, diets with wheat strongly reduced the milk yield and milk fat content, increased the proportions of C8:0 to C13:0 even‐ or odd‐chain fatty acids, C18:2 n‐6 and C18:3 n‐3 fatty acids but decreased the proportions of C18:0 and cis‐9 C18:1 fatty acids. Wheat also increased the proportions of trans‐5 to trans‐10 C18:1, the latter exhibiting a 10‐fold increase with 34% of wheat compared with value during the initial 0% wheat period. There was also an increase of trans‐10, cis‐12 C18:2 fatty acid and a decrease of trans‐11 to trans‐16 C18:1 fatty acids. The evolution during adaptation or after return to a 0% wheat diet was rapid for pH but much slower for the fatty acid profile. The mean ruminal pH was closely related to milk fat content, the proportion of odd‐chain fatty acids (linear relationship) and the ratio of trans‐10 C18:1/trans‐11 C18:1 (nonlinear relationship). Such changes in fatty acid profile suggested a possible use for non‐invasive diagnosis of subacute ruminal acidosis.

Summary: A retrospective study using analysis of plasma copper and zinc, and erythrocyte glutathione peroxidase from 2 080 dairy and beef cow herds was conducted to evaluate the relationship between trace‐element status and production, reproduction and health in cows and their calves. Classification of the herd status as deficient, marginal, low‐adequate or high‐adequate was based on the lower tercile of individual values. Odds ratios for each disorder in herds were calculated by multivariable stepwise logistic regression. Inadequate copper status was not associated with adult disorders, but was an important risk factor for poor calf performance or health. Selenium deficient status was associated with most studied disorders in cows, and both deficient and marginal herd status were strongly associated with poor health of calves, particularly with increased risks of myopathy and infectious diseases. Zinc insufficiency was strongly associated with low milk production and impaired locomotion in dairy herds, and was also associated with diarrhoea and poor growth in calves. Because a low‐adequate status increased the risk of many disorders in adults and calves, we propose to classify herds as deficient and marginal when the lower terciles of plasma zinc concentration are below 12 and between 12 and 14 μmol/l respectively.

The extent and/or intermediates of ruminal biohydrogenation (BH) of fatty acids (FA) were investigated in vitro and in situ using a raw, pre-conditioned or extruded blend of linseed and wheat bran (70:30). The duration of in vitro incubations were 2, 4, 8, 16 and 24 h, with 5 replicates. In situ studies used 3 dry ruminally fistulated Holstein cows in a 3 × 3 Latin square design, with 3 weeks adaptation to the linseed form. The diet contained 20% (DM basis) of the linseed based blend. The duration of in situ incubations were 2, 4, 8, 16, 24 and 48 h. BH was much slower in situ than in vitro, resulting in a much lower effective disappearance of C18:2 and C18:3. Moreover, the in situ technique suggested that the technological pre-treatment of linseed did not affect C18:2 and C18:3 rate of BH, whereas reduced rates were observed in vitro. After 8 h of in vitro incubation and onwards, proportions of cis-9,trans-11C18:2 were the highest with extruded linseed. The BH of FA from linseed resulted in the appearance of great proportions of trans-10+11 to trans-16C18:1 intermediates. Extrusion increased the proportions of trans-10+11C18:1 both in vitro and in situ and proportions or trans-C18:1 were higher in situ than in vitro. Compared to previous in vivo results with the same material, the in situ method provided poor estimates of BH rates and intermediates

The extent and intermediates of ruminal biohydrogenation (BH) of fatty acids (FA) from a blend of linseed and wheat bran (70:30) were investigated in the rumen fluid, rumen particle phase and duodenal flow. The blend was ground through a 3 mm screen and used raw or extruded, or was ground through a 6 mm screen and preconditioned. Three dry Holstein cows fitted with ruminal and duodenal cannulas were used in a 3 × 3 Latin square design, with 18 days adaptation. The diet contained 20% (DM basis) of the linseed based blend. Twelve samples taken over 3 days were composited for analysis of rumen fluid, rumen particle phase and duodenal flow. The BH of FA from linseed resulted in the appearance of a great number of C18:1 intermediates, among which trans-10+11 to trans-16C18:1 were the most abundant. The proportion of cis-9,trans-11C18:2 was low. Preconditioning coarsely ground linseed resulted in a lower extent of C18:2 and C18:3 BH, and lower proportions of trans-12 to trans-16C18:1 intermediates than extrusion or a lack of processing of finely ground linseed. On the contrary, extrusion did not affect the extent of BH and had no significant effect on the proportions of trans-C18:1 intermediates, but increased the proportion of cis-9,trans-11C18:2 in both rumen phases. Different digesta types resulted in different estimates of BH. The extent of BH and the proportions of trans-C18:1 intermediates were lower in the rumen particle phase and higher in the rumen fluid than in the duodenum. Moreover, interactions between digesta type and treatment of linseed were observed