In Bos taurus cattle, antimullerian hormone (AMH) has been demonstrated to have a high degree of correlation with ovarian antral follicle count and the number of healthy follicles and oocytes. To document the correlation between the plasma concentration of AMH and follicular number in Bos indicus and Bos taurus heifers, Nelore (Bos indicus, n = 16) and Holstein heifers (Bos taurus, n = 16) had their ovarian follicular waves synchronized. After synchronization, ovarian antral follicular population (AFP) was evaluated three times at 60-day (d) intervals (T-120 d, 120 days before plasma AMH determination; T-60 d, 60 days before; and T0, at the time of plasma AMH determination). The plasma AMH concentration was positively correlated with the number of ovarian follicles on the day of the follicular wave emergence in Bos indicus (Nelore) and Bos taurus (Holstein) heifers at each evaluation time (p < 0.05). The AFP was higher in Bos indicus (Nelore) than in Bos taurus (Holstein) heifers (p < 0.05). Similarly, the AMH concentration was higher in Bos indicus (Nelore) than in Bos taurus (Holstein) heifers (p < 0.0001). When heifers were classified as to present high or low AFP according to the mean of the AFP within each genetic group, high-AFP heifers presented a greater (p < 0.0001) AMH concentration than low-AFP heifers, regardless of the genetic group. In conclusion, the AFP is positively correlated with plasma AMH concentration in both Bos indicus (Nelore) and Bos taurus (Holstein) heifers. Furthermore, Bos indicus (Nelore) heifers presented both greater plasma AMH concentrations and AFP than Bos taurus (Holstein) heifers.

Feed additives and fat sources have been used to meet high productive dairy cow energy requirements. This study aimed to evaluate dietary chitosan and soybean oil effects on mid-lactation dairy cow intake, digestibility, metabolism and productive performance. Twenty-four Holstein cows (134.7 ± 53.1 days in milk, 36.14 ± 5.32 kg/day of milk yield, and 581.2 ± 73.6 kg of body weight, Mean ± SD) were used in a replicated 4×4 Latin square design with 21-d periods, with 14 d of adaptation and 7 d for data collection. The treatment arrangement was a 2×2 factorial design with two levels of chitosan (0 and 4 g/kg of dietary dry matter-DM) and two levels of soybean oil (0 and 33 g/kg of dietary DM). Chitosan decreased intake only in diets without oil (P < 0.05). Regardless of fat addition, chitosan increased DM and CP digestibility (P < 0.05). Soybean oil and chitosan increased total serum cholesterol (P < 0.05). Chitosan diet had higher urea plasma concentration than control diet (CON) (P < 0.05). Over all, soybean oil increased propionate and decreased acetate ruminal molar proportion, and therefore decreased acetate:propionate ratio (P < 0.05). Chitosan decreased milk yield, nitrogen use and feed conversion efficiencies in oil-diets (P < 0.05). Soybean oil decreased short and medium milk fatty acids concentration (P < 0.05). Chitosan had no effect on long-chain milk fatty acids in diets with soybean oil (P > 0.05). However, in free oil-diets, chitosan increased milk polyunsaturated fatty acids concentration, nitrogen and energy efficiency. Chitosan addition in free-fat diets improved feed efficiency, increased milk unsaturated fatty acids concentration and association with soybean oil negatively affect animal performance.

Our objective was to evaluate the effects of providing increasing levels of chitosan on nutrient digestibility, ruminal fermentation, blood parameters, nitrogen utilisation, microbial protein synthesis, and milk yield and composition of lactating dairy cows. Eight rumen-fistulated Holstein cows [average days in lactation = 215 ± 60.9; and average bodyweight (BW) = 641 ± 41.1 kg] were assigned into a replicated 4 × 4 Latin square design, with 21-day evaluation periods. Cows were assigned to be provided with four levels of chitosan, placed into the rumen through the fistula, as follows: (1) Control: with no provision of chitosan; (2) 75 mg/kg BW; (3) 150 mg/kg BW; and (4) 225 mg/kg BW. Chitosan had no effect on dry matter intake (P > 0.73); however, chitosan increased (P = 0.05) crude protein digestibility. Propionate concentration was increased (P = 0.02), and butyrate, isobutyrate, isovalerate and acetate : propionate ratio were decreased (P ≤ 0.04) by chitosan. Chitosan had no effect (P > 0.25) on acetate, pH and NH3 ruminal concentration. Glucose, urea, and hepatic enzyme concentrations in the blood were similar (P > 0.30) among treatments. Nitrogen balance was not affected, but chitosan increased milk nitrogen (P = 0.02). Microbial protein synthesis was not affected by chitosan (P > 0.44). Chitosan increased (P = 0.02) milk yield, fat-corrected milk, protein and lactose production. Chitosan changes ruminal fermentation and improves milk yield of lactating dairy cows; therefore, we conclude that chitosan can be used as a rumen modulator instead of ionophores in diets for dairy cows.

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Exogenous fibrolytic enzymes (EFE) can increase ruminal digestion of neutral detergent fiber (NDF) and improve its fermentation for cattle. Twenty-four multiparous Holstein cows (33.72 ± 7.63 kg milk/d and 176 ± 82.27 days in milk-DIM, at the start of the experiment) were used in a replicated 4 × 4 Latin square experimental design. Increasing doses of a commercial product was used to evaluate the effect of xylanase activity (100 units per gram of product) on intake and total-tract digestion of nutrients, sorting index, chewing time, milk yield and composition, N use, and ruminal fermentation. Treatments consisted of 0, 8, 16 or 24 g/d per cow of EFE product mixed into the concentrate. Corn silage was used as forage source. The basal diet had a forage-to-concentrate ratio of 50:50 (dry matter basis). Even though EFE supplementation had a positive linear effect on dry matter and NDF intake, it had no impact on total-tract digestion of nutrients. Moreover, this enzyme promoted a linear increase of the intake of feed with larger particle size (>19 mm) and quadratically affected rumination and chewing activity (hours), reaching the highest values at intermediate doses (8 g/d and 16 g/d). Treatments had no effect on milk yield and composition; however, the N use efficiency was linearly decreased by EFE, reducing thus the ability to synthesize milk and quadratically decreasing N retention. No treatment effect was found on ruminal pH, whereas a negative quadratic effect on ruminal NH 3-N concentration was significant. Regarding ruminal parameters, this enzyme supplementation provided linear increased in acetate, propionate, butyrate, and total short-chain fatty acids synthesis. As result, EFE supplementation improved DM and NDF intake, increasing the time spent chewing and ruminating, leading to a greater total short-chain fatty acids production in rumen. Nonetheless, EFE did not improve milk yield and composition of mid-lactating dairy cows.