Trade-offs between selection of crude protein and tannins in growing lambs.

Tannins are phenolic compounds that provide benefits to ruminants due to their protein-binding affinities and antioxidant properties. However, tannins may also have negative orosensorial and postingestive effects that decrease feed intake. This study explored how lambs trade-off the ingestion of crude protein (CP) with the ingestion of potentially beneficial and toxic condensed and hydrolyzable tannins, and the ensuing impacts on diet digestibility, animal performance, and blood parameters. Thirty-two lambs were housed in individual pens for 8 weeks and had access to two isoenergetic diets that varied in the concentration of CP (High-HP or Low-LP) and the presence of a mix of condensed and hydrolyzable tannins (4% DM). Animals were assigned to 4 treatment groups (N=8 lambs/group) and received a simultaneous offer of: HP and LP (Control); HP and LP+tannins (HP-LP+); HP+tannins and LP (HP+LP-); and both HP and LP with tannins (HP+LP+). All lambs preferred HP over LP and they avoided tannins in the diets (P < 0.001). Dry matter and CP intake were the lowest in HP+LP- (P < 0.0001), and DMD did not differ between Control and the other groups (P > 0.05), but it was greater for HP-LP+ (P < 0.0001). Crude protein digestibility was greater for groups without tannins in HP (P < 0.0001), but ADG did not differ among treatments (P > 0.05). No differences between Control and HP+LP+ were found in plasma antioxidant activity, total phenolic concentration, or haptoglobin concentration (P > 0.05). Intake of tannins was HP+LP+ > HP+LP- > HP-LP+ (P < 0.0001), and fecal excretion of nitrogen (N) was HP+LP+ > HP-LP+ = HP+LP- > Control (P < 0.05). In addition, intake of tannins with both diets reduced blood urea nitrogen (BUN) concentration relative to Control (P < 0.05), thus suggesting a shift in the partitioning of N excretion from urine to feces. In summary, lambs prioritized selection of HP over LP, regardless of the presence of a tannin extract in either or both diets. Nevertheless, lambs modulated their tannin consumption as a function of the specific diet where the tannin extract was added, with increasing levels of intake as tannins were present in just LP, then in just HP, and finally in both diets. Dietary tannins did not constrain ADG and resulted in a shift in the partitioning of N excretion from urine to feces. Such shifts have been found to result in reduced production of environmental pollutants such as ammonia, nitrous oxide, and nitrates.

The effect of plant bioactive compounds on lamb performance, intake, gastrointestinal parasite burdens, and lipid peroxidation in muscle.

Plant extracts have been widely used in animal production systems due to the benefits promoted by their bioactive components, mainly through their antioxidant effects and positive effects on animal growth, health, and meat quality. We determined whether bioactive compounds (BC) from grape (Vitis vinifera), olive (Olea europaea), and pomegranate (Punica granatum) have beneficial effects on lamb growth while controlling gastrointestinal parasitism and reducing skeletal lipid peroxidation in muscle. Fourteen lambs (4 to 5 mo of age) were housed in individual pens and assigned to two treatment groups (seven animals/group), where they received: 1) a basal diet of beet pulp:soybean meal (90:10) (CONTROL) and 2) the same diet, but containing 0.3% of BC extracted from grape, olive, and pomegranate (BNP). After 21 d of consuming their respective rations (period 1), all lambs were dosed with 10,000 L3 stage larvae of Haemonchus contortus. Intake, production, and physiological parameters were determined before infection (period 1), after oral dosage with L3 (period 2), and during early (period 3) and later (period 4) developmental stages of infection. Groups of animals did not differ in their ration intake or average daily gain, either before or after the infection, or in their parasitic burdens estimated through fecal egg counts (P > 0.05). Lambs under BNP showed greater feed efficiency before infection (P < 0.001), but the pattern reversed after infection. In addition, the inclusion of plant bioactives to the diet did not have an effect (P > 0.05) on blood or lipid peroxidation in muscle or on hemogram, serum concentration of haptoglobin, and immunoglobulin E. These results could be explained by low dietary doses and constrained absorption or ruminal inactivation of these compounds. Changes in feed efficiencies suggest a negative interaction between BC in the diet and parasitism, which warrants further research.

Self-selection of plant bioactive compounds by sheep in response to challenge infection with Haemonchus contortus.

Plant bioactives can potentially benefit herbivores through their effects on health and nutrition. The objective of this study was to determine the importance of polyphenols and terpenes on the ability of lambs to self-select these compounds when challenged by a parasitic infection and the subsequent impact on their health and productivity. Thirty-five lambs were housed in individual pens and assigned to five treatment groups (7 animals/group), where they received: 1) A basal diet of beet pulp:soybean meal (90:10) (CONTROL); 2) The same diet, but containing 0.3% of bioactive natural plant compounds extracted from grape, olive and pomegranate (BNP); 3) A simultaneous offer of the diets offered to the Control and BNP groups (Choice-Parasitized; CHP-1); 4) The Control diet, and when lambs developed a parasitic infection, the choice described for CHP-1 (CHP-2); and 5) The same choice as CHP-1, but animals did not experience a parasitic burden (Choice-Non-Parasitized; CHNP). Lambs, except CHNP, were dosed with 10,000 L3 stage larvae of Haemonchus contortus. Infected lambs under choice treatments (CHP-1 and CHP-2) modified their feeding behavior in relation to the CHNP group as they increased their preference for the feed containing polyphenols and terpenes, interpreted as a behavior aimed at increasing the likelihood of encountering medicinal compounds and nutrients in the environment that restore health. This change in behavior corresponded with an improvement in feed conversion efficiency. However, an increased preference for the diet with added plant bioactives did not have an effect on parasitic burdens, hematological parameters, blood oxidation, or serum concentration of IgE.