Nicolas DiLorenzo

Two experiments were conducted to evaluate the effect of nonprotein nitrogen (NPN) supplementation on in vitro fermentation and animal performance using a backgrounding diet. In experiment 1, incubations were conducted on three separate days (replicates). Treatments were control (CTL, without NPN), urea (U), urea–biuret (UB), and urea–biuret–nitrate (UBN) mixtures. Except for control, treatments were isonitrogenous using 1% U inclusion as a reference. Ruminal fluid was collected from two Angus-crossbred steers fed a backgrounding diet plus 100 g of a UBN mixture for at least 35 d. The concentration of volatile fatty acids (VFA) and ammonia nitrogen (NH3–N), in vitro organic matter digestibility (IVOMD), and total gas and methane (CH4) production were determined at 24 h of incubation. In experiment 2, 72 Angus-crossbred yearling steers (303 ± 29 kg of body weight [BW]) were stratified by BW and randomly allocated in nine pens (eight animals/pen and three pens/treatment). Steers consumed a backgrounding diet formulated to match the diet used in the in vitro fermentation experiment. Treatments were U, UB, and UBN and were isonitrogenous using 1% U inclusion as a reference. Steers were adapted to the NPN supplementation for 17 d. Then, digestibility evaluation was performed after 13 d of full NPN supplementation for 4 d using 36 steers (12 steers/treatment). After that, steer performance was evaluated for 56 d (24 steers/treatment). In experiment 1, NPN supplementation increased the concentration of NH3–N and VFA (P < 0.01) without affecting the IVOMD (P = 0.48), total gas (P = 0.51), and CH4 production (P = 0.57). Additionally, in vitro fermentation parameters did not differ (P > 0.05) among NPN sources. In experiment 2, NPN supplementation did not change dry matter and nutrient intake (P > 0.05). However, UB and UBN showed lower (P < 0.05) nutrient digestibility than U, except for starch (P = 0.20). Dry matter intake (P = 0.28), average daily gain (P = 0.88), and gain:feed (P = 0.63) did not differ among steers receiving NPN mixtures. In conclusion, tested NPN mixtures have the potential to be included in the backgrounding diets without any apparent negative effects on animal performance and warrant further studies to evaluate other variables to fully assess the response of feeding these novel NPN mixtures.

During cell death, DNA is fragmented and reaches the bloodstream in the form of cell‐free DNA (cfDNA). Luteal cells must undergo an apoptotic process during structural luteolysis to begin a new oestrous cycle. We hypothesized that cfDNA concentrations would increase when inducing luteolysis by applying prostaglandin F 2α (PGF2α) analog to the cycling cow. Multiparous non‐pregnant and non‐lactating Angus cows ( Bos taurus ; n = 15) were synchronized using the 7‐day CoSynch + CIDR protocol. Ten days after oestrus was detected, two treatments were applied (PGF2α, n = 10; or Con, n = 5). Twice a day, grey mode and colour Doppler ultrasonography were used to calculate area (CL‐A) and luteal blood perfusion (LBP%). Additionally, we collected one blood sample for plasma progesterone (P4) and cfDNA concentrations for four consecutive days. Data analysis was performed using the GLM procedure of SAS. The luteolysis induction was demonstrated by a decrease in P4 concentrations ( p ≤ .01) and CL‐A ( p ≤ .01) in the PGF2α group after 12 h of the PGF2α injection. Reduction of LBP% ( p ≤ .01) in the PGF2α group after 36 h of the injection. The concentration of cfDNA showed a significant increase ( p = .05) after 48 h of the PGF2α application in the PGF2α group. In conclusion, cfDNA showed a significantly increased concentration after luteolysis induction, which can imply that cfDNA could be used as a luteolysis biomarker in plasma.