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Three ruminally fistulated Xuanhan steers weighting 312.5 (±23.85) kg were used to determine the kinetics of ruminal degradation of nutrients using in situ nylon bag technique, and a modified 3-step in vitro procedure was adopted to estimate intestinal digestibility of 16-h rumen undegradable protein (RUP) of maize cob (MC), distillers grains (DG), spent mushroom substrate (SMS), starch residue of sweet potato (SRSP), citrus pulp (CPP), and rice straw (RS). Samples were incubated for 0, 2, 6, 16, 24, 36, 48 and 72 h. Additional samples were incubated for 16 h in the rumen, and the residues from these bags were transferred to the nitrogen-free polyester bags for determination of intestinal digestibility in vitro. The highest DM disappearance at 6-h incubation was in SRSP (P 0.07) on CP disappearance between DG and MC at all the time points except for 16 and 24 h. NDF and ADF disappearance for SRSP was significantly higher (P < 0.01) than other roughages at all the time points except for ADF at 72 h. The lowest NDF and ADF disappearance was in DG at all the time points (P < 0.01) except 2 and 6 h. The effective degradability (ED) of DM was the highest in CPP (P < 0.01) and the lowest in MC and RS (P < 0.01). The highest and lowest ED of CP was in DG and in RS (P < 0.01), respectively. The ED of NDF was the highest in SRSP (P < 0.01), followed by CPP and RS, and the lowest in DG (P < 0.01). The ED of ADF was the highest in SRSP and CPP (P < 0.05), and the lowest in DG (P < 0.01). For MC, DG SMS, SRSP, CPP, and RS, the intestinal digestibility of RUP was 95.28%, 37.23%, 38.72%, 48.06%, 54.49%, and 37.88%, respectively, and the content of intestinal digestible crude protein (IDCP) was 23.65, 83.63, 35.63, 15.03, 25.60, and 12.03 g/kg, respectively. Distillers grain was considered to be of good quality for the greatest content of IDCP. Although not readily degraded in rumen, CP in MC may be digested well in small intestine.

Nitrogen excretion from sheep production systems is an important source of nitrate, ammonia, and nitrous oxide responsible for groundwater pollution and global warming. The present study aimed to identify key parameters influencing N utilization efficiency and develop prediction equations for manure N, feces N, and urine N outputs in sheep. Data used were collected from 82 sheep offered fresh perennial ryegrass () as the sole diet in 6 metabolism experiments (data from non-grass-only diets were not used). Sheep were from breeds of Highlander, Texel, Scottish Blackface, and Swaledale at the age of 5 to 18 mo and weighing from 24.5 to 62.7 kg. Herbage was harvested daily from 6 swards of contrasting harvest dates (May to December), offering wide variation in feed value to cover the range that would be offered in most practical farm situations. Before the commencement of each study, the experimental sward was harvested at a residual height of 4 cm and allowed to grow for 2 to 4 wk to target an average pregrazing sward height in a range of 8 to 15 cm depending on the time of year. Sheep were housed in individual pens for 14 d and then transferred to individual metabolism crates for 4 d with feed intake and feces and urine outputs measured. Data were analyzed using the linear mixed model procedure to develop prediction equations for feces N, urine N, and manure N outputs using N intake, herbage chemical composition, and digestibility with effects of sex, breed, and experimental periods removed. Nitrogen intake was the best single predictor for N output in feces, urine, and manure, and the value for prediction of manure N output was greater than those for feces N and urine N (0.86 vs. 0.70 and 0.77, respectively; < 0.001). Animal BW and herbage DM, ether extract, NDF, ADF, water soluble carbohydrate, and DE concentrations and N digestibility were also used to predict N outputs because N intake may not be available in commercial practice. The prediction equations for N utilization efficiency indicated that increasing feeding level and ME concentration and reducing N concentration could improve N utilization efficiency and shift N excretion into feces rather than urine ( < 0.001). The equations developed in the current study provide an approach for sheep producers to quantify N excretion against production and, consequently, to develop their own mitigation strategies to reduce the environmental impact of sheep production systems.

Forty-eight lowland lambs were used in a completely randomized design (23-d period) with a factorial arrangement of treatments: 2 breeds (Highlander vs. Texel) × 3 sexes (female vs. intact male vs. wether) × 2 diets (fresh grass vs. fresh grass plus 0.5 kg/d pelleted concentrate). Animals ( = 48) were approximately 5 mo old and 36 ± 5.0 kg BW at the commencement of the study with 4 lambs for each breed-sex-diet combination. Fresh grass was harvested daily from the first regrowth of perennial ryegrass sward and offered ad libitum with a similar growth stage throughout the experiment. The animals were individually housed in pens and fed experimental diets for 19 d before being transferred to individual calorimeter chambers for a further 4 d with feed intake, fecal and urine outputs, and methane (CH) emissions measured. Lambs offered 0.5 kg/d concentrate had greater DM and energy (i.e., GE, DE and ME) intake, BW, and CH production (g/d) and greater N intake, fecal and manure N outputs, and fecal N per N intake than those given only fresh grass ( 0.05). The results reflected that high-quality forages may play a role similar to concentrate in mitigation of enteric CH emissions. The effects of sex and breed on rumen function require further investigation to understand relationships with CH emissions and N excretion in sheep.

Three ruminally fistulated Xuanhan steers weighting 312.5 (±23.85) kg were used to determine the kinetics of ruminal degradation of nutrients using in situ nylon bag technique, and a modified 3-step in vitro procedure was adopted to estimate intestinal digestibility of 16-h rumen undegradable protein (RUP) of maize cob (MC), distillers grains (DG), spent mushroom substrate (SMS), starch residue of sweet potato (SRSP), citrus pulp (CPP), and rice straw (RS). Samples were incubated for 0, 2, 6, 16, 24, 36, 48 and 72 h. Additional samples were incubated for 16 h in the rumen, and the residues from these bags were transferred to the nitrogen-free polyester bags for determination of intestinal digestibility in vitro. The highest DM disappearance at 6-h incubation was in SRSP (P < 0.01), and that at 36, 48, and 72 h was in CPP (P < 0.01). The lowest DM disappearance at 2- and 6-h incubation was in RS and SMS (P < 0.01), and that at 36, 48, and 72 h incubation was in RS, MC, and DG (P < 0.01). The lowest and greatest CP disappearance was in RS and DG, respectively, at all the incubation times (P < 0.01). There was no difference (P > 0.07) on CP disappearance between DG and MC at all the time points except for 16 and 24 h. NDF and ADF disappearance for SRSP was significantly higher (P < 0.01) than other roughages at all the time points except for ADF at 72 h. The lowest NDF and ADF disappearance was in DG at all the time points (P < 0.01) except 2 and 6 h. The effective degradability (ED) of DM was the highest in CPP (P < 0.01) and the lowest in MC and RS (P < 0.01). The highest and lowest ED of CP was in DG and in RS (P < 0.01), respectively. The ED of NDF was the highest in SRSP (P < 0.01), followed by CPP and RS, and the lowest in DG (P < 0.01). The ED of ADF was the highest in SRSP and CPP (P < 0.05), and the lowest in DG (P < 0.01). For MC, DG SMS, SRSP, CPP, and RS, the intestinal digestibility of RUP was 95.28%, 37.23%, 38.72%, 48.06%, 54.49%, and 37.88%, respectively, and the content of intestinal digestible crude protein (IDCP) was 23.65, 83.63, 35.63, 15.03, 25.60, and 12.03 g/kg, respectively. Distillers grain was considered to be of good quality for the greatest content of IDCP. Although not readily degraded in rumen, CP in MC may be digested well in small intestine.

To better utilize native pasture at the high altitude region, three-consecutive-year feeding experiments and a total of seven metabolism trials were conducted to evaluate the impact of three forage stages of maturity on the chemical composition, nutrient digestibility, and energy metabolism of native forage in Tibetan sheep on the Qinghai–Tibetan Plateau (QTP). Forages were harvested from June to July, August to October, and November to December of 2011 to 2013, corresponding to the vegetative, bloom, and senescent stages of the annual forages. Twenty male Tibetan sheep were selected for each study and fed native forage ad libitum. The digestibility of DM, OM, CP, NDF, ADF, DE, DE/GE, and ME/GE were greatest (P < 0.01) from the vegetative stage, intermediate (P < 0.01) from the bloom stage, and least (P < 0.01) from the senescent stage. Nutrient digestibility and energy parameters correlated positively (linear, 0.422 to 0.778; quadratic, 0.568 to 0.815; P < 0.01) with the CP content of forage but correlated negatively with the content of NDF (linear, 0.343 to 0.689; quadratic, 0.444 to 0.777; P ≤ 0.02), ADF (linear, 0.563 to 0.766; quadratic, 0.582 to 0.770; P < 0.01), and ether extract (EE, linear, 0.283 to 0.574; quadratic, 0.366 to 0.718; P ≤ 0.04) of forage. For each predicted variable, the prediction of DMI expressed as grams per kilogram of BW (g/kg BW·d) yielded a greater R(2) value (0.677 to 0.761 vs. 0.616 to 0.711) compared with the equations of DMI expressed as g/kg metabolic BW by step-wise regression. The results suggest that parameters of forage CP, NDF, and ADF content were most closely related to nutrient digestibility. Contrary to previous studies, in this study, ADF content had a greater linear relationship (0.766 vs. 0.563 to 0.732) with OM digestibility than the other parameters of nutrient digestibility. The quadratic relationship between forage CP content and CP digestibility indicates that when forage CP content exceeds the peak point (9.7% DM in the present study), increasing forage CP content could decrease CP digestibility when Tibetan sheep were offered native forage alone on the QTP. Additionally, using the forage CP, EE, NDF, and ADF content to predict DMI (g/kg BW·d) yielded the best fit equation for Tibetan sheep living in the northeast portion of the QTP.

Twenty 5-mo-old Holstein cattle (10 steers and 10 heifers) were selected from a dairy herd for a 28 d study of enteric methane emissions and energy utilization. The cattle were offered a completely mixed diet with grass silage and concentrates (0.45 and 0.55, DM basis, respectively). They were housed as a single group in cubicle accommodation for the fi rst 20 d, transferred to metabolism units for 3 d, and subsequently housed in indirect open-circuit respiration calorimeter chambers for next 5 d with measurements of feed intake, feces and urine outputs, and gaseous exchange. There were no signifi cant differences (P > 0.05) between the 2 groups in terms of animal performance (feed intake, BW, or BW gain), energy metabolism (energy intake, energy outputs, or energy use effi ciency), or methane emission rates (total methane emissions expressed on feed intake or energy intake basis). Therefore, the data from the 2 groups were pooled to develop a range of relationships between inputs and outputs. The regression of energy balance or heat production against ME intake (r 2 = 0.85; P < 0.001) indicated a NE m of 0.57MJ/kg BW 0.75 , which is greater than reported for adult dairy cattle. The methane energy output was found to be 0.068 of GE intake when the intercept was omitted from the linear equation (r 2 = 0.73; P < 0.001), which is greater than the commonly accepted value (0.065) for adult cattle used for development of methane emission inventories for dairy and beef production systems. These data can add useful information, as there is little information available on measurements of maintenance energy requirement or methane emissions in young stock (6 mo old) of the current high-yielding dairy cattle. The use of these data can potentially improve the accuracy of prediction of energy requirement and methane emissions for dairy and beef production systems in these dietary conditions.