Elena Bichi

Effect of the inclusion of quebracho tannins in a diet rich in linoleic acid on milk fatty acid composition in dairy ewes

Despite controversy surrounding the ability of tannins to modulate the fatty acid (FA) profile of ruminant-derived products, reports on this issue are still very limited for dairy sheep. This study was conducted to examine the effect of the inclusion of quebracho tannins in a diet rich in linoleic acid on ewe performance and milk FA composition. Thirty-six lactating ewes were distributed into 6 lots and allocated to 2 treatments (3 lots/treatment): control or quebracho. All sheep received a total mixed ration based on alfalfa hay and a concentrate (forage:concentrate ratio of 40:60) supplemented with 20 g of sunflower oil/kg of dry matter plus 0 (control diet) or 20 g of an extract of quebracho tannins/kg of dry matter (QUE diet). Milk production and composition were analyzed on d 0, 3, 6, 9, 12, 15, 18, 21, 24, and 27 on treatments, and milk FA profile on d 0, 3, 6, 12, 18, and 27. On d 27, samples of rumen fluid were collected for pH, and lactate, ammonia, and volatile FA concentration analysis. Feeding the QUE diet had no apparent effect on animal performance and hardly modified ruminal fermentation characteristics, except for a reduction in the molar proportions of minor volatile FA. Dietary tannins increased the milk concentration of several 18:1 and 18:2 isomers and decreased that of branched-chain FA. Some of these changes were relatively constant throughout the experiment (e.g., cis-12 18:1 and trans-9,cis-12 18:2), whereas others varied over time (e.g., trans-10 18:1, which increased gradually with the QUE diet). Significant differences between treatments in trans-11 18:1 and cis-9,trans-11 conjugated linoleic acid were only observed on d 3. Overall, addition of quebracho tannins to a diet rich in linoleic acid did not prove useful to beneficially modify milk FA composition, especially over the long term.

Milk fat depression induced by dietary marine algae in dairy ewes: persistency of milk fatty acid composition and animal performance responses.

Addition of marine algae (MA) to the diet of dairy ruminants has proven to be an effective strategy to enhance the milk content of some bioactive lipids, but it has also been associated with the syndrome of milk fat depression. Little is known, however, about the persistency of the response to dietary MA in sheep. Based on previous experiments with dairy ewes fed sunflower oil plus MA, it was hypothesized that the response might be mediated by time-dependent adaptations of the rumen microbiota, which could be evaluated indirectly through milk fatty acid (FA) profiles. Animal performance and milk FA composition in response to MA in the diet were studied using 36 Assaf ewes distributed in 6 lots and allocated to 2 treatments (3 lots/treatment) consisting of a total mixed ration (40:60 forage:concentrate ratio) supplemented with 25 g of sunflower oil (SO)/kg of dry matter plus 0 (SO; control diet) or 8 g of MA/kg of dry matter (SOMA diet). Milk production and composition, including FA profile, were analyzed on d 0, 6, 12, 18, 24, 34, 44, and 54 of treatment. Diet supplementation with MA did not affect milk yield but did decrease milk fat content. Differences in the latter were detected from d 18 onward and reached -17% at the end of the experiment (i.e., on d 54). Compared with the control diet, the SOMA diet caused a reduction in milk 18:0 and its desaturation product (cis-9 18:1) that lasted for the whole experimental period. This decrease, together with the progressive increase in some putative fat synthesis inhibitors, especially trans-10 18:1, was related to the persistency of milk fat depression in lactating ewes fed MA. Additionally, inclusion of MA in the diet enhanced the milk content of trans-11 18:1, cis-9,trans-11 18:2, and C20-22 n-3 polyunsaturated FA, mainly 22:6 n-3. Overall, the persistency of the responses observed suggests that the ruminal microbiota did not adapt to the dietary supply of very long chain n-3 polyunsaturated fatty acids.

Inhibition of ∆9-desaturase activity with sterculic acid: Effect on the endogenous synthesis of cis-9 18:1 and cis-9 trans-11 18:2 in dairy sheep

This study was conducted in lactating ewes to examine the involvement of ∆(9)-desaturase in mammary lipogenesis, especially in the endogenous synthesis of cis-9, trans-11 18:2 and cis-9 18:1, because no information on this matter was available for dairy sheep. With this aim, 6 Assaf ewes were monitored in a 15-d experiment, which included a 5-d pretreatment period, a 5-d treatment period, and a 5-d posttreatment period. During the treatment period, ewes received 0.5 g/d of sterculic acid (a cyclopropene fatty acid that inhibits ∆(9)-desaturase), delivered intravenously in 4 equal doses at 6-h intervals. Animals were fed pasture to supply mainly α-linolenic acid and minimize the amount of milk cis-9, trans-11 18:2 of ruminal origin. Sterculic acid administration was calculated to inhibit ∆(9)-desaturase by 70% based on the milk content of cis-9 14:1. This inhibition resulted in decreases in the milk content of the enzyme products (e.g., cis-9 10:1, cis-9 14:1, cis-9 16:1, cis-9 18:1, and cis-9, trans-11 18:2) and increases in its substrates (e.g., 14:0, 18:0, and trans-11 18:1), as well as in reductions in the desaturase indexes. Some other milk fatty acids, further to previously reported products or substrates of ∆(9)-desaturase (e.g., cis-15 18:1 and cis-9, cis-15 18:2, or trans-11, trans-15 18:2, and cis-9, trans-11, trans-15 18:3), were also affected by sterculic acid administration. Endogenous synthesis was the major source of cis-9 18:1 and cis-9, trans-11 18:2, accounting for 63 and 74% of its content in milk fat, respectively. To our knowledge, the present study provides the first estimates of endogenous synthesis of these 2 bioactive fatty acids in ovine milk fat.