Received  22 June, 2017    Accepted  15 November, 2017

Nowadays, most available information on the degradative behaviour of feeds in ruminants is based on in situ incubation in the rumen, and it is adopted by many feed evaluation systems currently in use for ruminants.  However, the outcome of this technique might be affected by many factors such as sequence of nylon bags incubation in the rumen.  The objective of current study was to investigate effects of sequence of nylon bag incubation on degradative behavior of dry matter (DM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) in some feed ingredients commonly used in dairy rations, including alfalfa haylage, corn silage, corn grain and soybean meal.  Four multiparous Holstein lactating cows fitted with permanent ruminal cannulas were used.  The nylon bags containing feed samples either were placed in the rumen at once and removed at designated time intervals (all in-gradually out method; AG) or were placed in the rumen at designated time points and retrieved at once (gradually in-all out method; GA).  Fractional rate of degradation of potentially degradable fraction, lag time and effective rumen degradability (ED) of DM and CP were significantly higher in the AG compared to the GA method (P<0.05).  Fractional rates of DM and CP degradation was higher in alfalfa haylage samples incubated in the rumen using the AG method compared to that using the GA method (0.138 h^–1 vs. 0.073 h^–1 and 0.002 h^–1 vs. 0.1125 h^–1, for DM and CP, respectively; P<0.05).  Due to a higher fractional rate of degradation (K_d) of DM and CP, the ED of DM and CP at different fractional passage rates were higher in the AG than those in the GA method (P<0.05).  Potentially degradable fraction and lag time of NDF were higher in the AG method compared to the GA method (P<0.05).  Placing all bags in the rumen at once and removing them at designated time intervals compared with introduction of bags in reverse sequence and removing them all at once led to a lower undegradable fraction (U) of NDF in alfalfa (1.8% vs. 4.0%, respectively; P<0.05) and corn silage (3.3% vs. 6.7%, respectively; P<0.05) samples.  Potentially degradable fraction of ADF was significantly higher in the AG method compared with the GA method (P<0.05).  Bag incubation sequence had profound effects on kinetics of degradation of DM, CP and NDF in situ in the feed samples studied.  The effects were more evident in the forages (especially alfalfa haylage) than in the concentrate ingredients

Reducing dietary cation-anion difference (DCAD) has been proved an effective way to prevent milk fever in dairy cows. Based on the similar physiological gastro-intestinal tract anatomy and metabolic process between female goats and dairy cows, this study was conducted to evaluate the effects of varying DCAD on fluid acid-base status, plasma minerals concentration and anti-oxidative stress capacity of female goats. Urinary pH, plasma Ca, P and Mg; and anti-oxidative stress indices of total superoxide dismutase (T-SOD), hydrogen peroxide (H2O2), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA) were determined to evaluate the effect. Forty-eight Guizhou black female goats ((15±1.9) mon of old, (22.3±3.75) kg of BW) were randomly allocated to 4 blocks of 12 goats each and were fed 1 of 4 diets differed in DCAD level (calculated as Na+K-Cl-S, mEq kg-1 DM). Levels of DCAD were preliminarily designed to be control (+150 mEq kg-1 DM, CON), high DCAD (+300 mEq kg-1 DM, HD), low DCAD (0 mEq kg-1 DM, LD) and negative DCAD (-150 mEq kg-1 DM, ND), respectively. A commercial anionic salts (Animate) and sodium bicarbonate (NaHCO3) were supplemented to reduce and increase DCAD level, respectively. There was no difference in dry matter intake for 4 groups of goats. Urine pH was aggressively decreased (P<0.0001) with reduced DCAD and there was a strong association between DCAD and urine pH (R2=0.793, P<0.0001). Compared with CON and HD feeding of LD and ND resulted in greater (P<0.05) plasma Ca concentration. Plasma P level was increased (P<0.05) when anionic salts were supplemented. The DCAD alteration did not affected (P>0.05) plasma Mg level. There was no significant (P>0.05) difference in plasma GSH-Px activity and H2O2, but anionic salts supplementation in LD and ND significantly increased (P<0.05) plasma T-SOD activity and tended to reduce MDA (P<0.1) over HD and CON. Results from this study indicated that reducing DCAD could decrease urine pH and increase plasma Ca concentration of female goats. Additionally, reducing DCAD was helpful to enhance anti-oxidative stress capability of female goats.