Compared to CS, the CP content of CA was higher by 6%, and its NDF was lower by 4%. Therefore, with increased mixing ratio of CA, the CP content of the mixtures increased and the NDF content decreased. Since woody plants have high lignin content ( Hacke et al.2001), the ADF and ADL contents of CA were higher than those of CS or their mixture. The MT1 in this study was close to meeting the CP requirement of goats (Zhou et al.2003); when 20% of CA was added to the CS, the CP content increased and the nutritional requirements were met to the goats.
Five diets were formulated to meet the animals’ mineral and vitamin requirements based on the Cornell-Penn-Miner recommendations (Xu et al.2009). It showed the MT1 was 6.37% DM which can meet the CP requirements (5.1% DM) of cashmere goats during the winter, and we can assess its utility as feed. As shown in Table 2, these diets were formulated as a general winter feed, but the energy and protein contents were insufficient to meet the nutritional requirements of the Mongolian goat (Xu et al.2006).
General, woody plants contain large amounts of ADF and ADL, which results in decreased nutrient uptake and digestibility for livestock (Carlquist et al.1985; Malisetty et al.2014) In the present study, the ADF and ADL contents of CA were higher than those of CS (Malhado et al.2013). In addition, with increased mixing ratio of CA, the DM intake decreased. The major reason for this is that that CA has higher fibre and lignin content, which results in reduced dietary energy, feed uptake, and digestibility. If the ADF and ADL content in the diet was increased, and the goats had full rumens, continuous feed intake would be inhibited(Domingue et al.1991). The high fibre content could influence digestibility and cause the goats to feel more full, and therefore reduce their intake(Xu et al.2009). The lignin content of CA, and its effect on the production performance of goats, is a major factor limiting its use in feed mixtures (Zhang et al.2009; Yang et al.2005).
The apparent digestibility of DM in MT2 and MT3 was lower than that in MT1, showing that the MT1 was a good mixing ratio which has a higher apparent digestibility of DM. When the mixing ratio of CA was over 20%, the high lignin resulted in low apparent digestibility of DM. Regarding production, the apparent digestibility of CP increases with an increase of dietary CP. This could be due to reasonable dietary protein levels being conducive to the reproduction of rumen microbes, enhancing the ability to break down fibres, and thereby increasing their digestion and absorption (McDonald et al.1981). Additionally, CA contains various vitamins, trace elements, fats, sugars, nucleic acids, and inorganic nutrients, such as potassium, calcium, and magnesium, all of which are conducive to the growth and reproduction of fibre-decomposing bacteria (Salem et al.2010). Generally, the activity of rumen microorganisms may be low when ruminant fed low CP feed. As a result, it is difficult to correctly evaluate the difference in digestibility and rumen fermentation. In the future, it is necessary to study the relationship between low CP content and rumen microorganism activity, digestibility or rumen fermentation.
The proportions of various sizes of pellets in goat rumen and faeces were assessed. Small particles were most abundant, with those < 3 mm in size accounting for > 90% of all particles for both CA and CS. There was no significant difference in particle size distribution among the different types of roughage (P > 0.05). The proportion of > 1.0 mm-sized particles in MT1 (11.96%) was higher than those in MT2 and MT3. The small-sized particles (0.1–1 mm) were most abundant in MT3 relative to the other treatments, while the large particles (1–5 mm) were most abundant in CS. The reason for this may be related to the lignin in the diet, the lower ADL content in MT1 affects digestible particle activities and nutrient digestion (Russell et al.1981). The ADL content in MT3 (22.82% of DM) was lower than that in CA (24.72% of DM), but higher than in the other treatments. Due to the difficulty in digesting ADL, it stayed in the rumen for a long period (Komfelt et al.2013). Particles are chewed by cashmere goats repeatedly, such that the number of particles and surface area of the cell walls are increased, in turn increasing the chance that bacteria can reach the fibre and colonise it (Tikam et al.2013). There were no significant effects of particle size on the pH of the gastrointestinal tract at the time of slaughter. Previous studies reported no effect of corn particle size on rumen pH, and that starch content varying from 28–46% does not affect pH (Traiyakun et al.2013).
Similarly, in the present study, differences in particle size did not greatly influence pH (Wang et al.2016). A higher proportion of 1.0 mm-sized particles indicates that the indigestible and degradable content of feed is higher (Polyorach et al.2014). Here we found the MT1 contained a higher proportion of > 1.0 mm-sized particles, which explains why the goats were able to refine the feed pellets via multiple ruminations and chewing, to increase the availability of surface microorganisms (Hodate et al.2004). Therefore, adding 20% CA was effective for improving feed digestibility.
Typically, grazing is prohibited from mid-March to mid-June, but it remains necessary to supply cashmere goats with proper nutrition at a low cost. Cashmere goats are most productive from the beginning of September to the end of December, and their productivity ceases in February. In this study, we were able to supply nutrients at, or slightly below, the level required to maintain the goats. Cashmere goats have a greater ability to digest high-fibre materials than do goat(Salah et al.2014). Our data showed that, even though the CA cannot meet the nutritional needs of cashmere goats, increasing the ratio of CA to CS is feasible for feeding cashmere goats. In the future, a longer-term experiment is needed to study changes in digestive metabolism, carcass health status, and production performance after long-term feeding of livestock with unconventional feed in the Inner Mongolian Plateau desert grassland.
The intake, rumen fermentation, and apparent digestibility of Aerbasi cashmere goats fed CS, CA, and a mixture of the two were studied in the Inner Mongolia plateau. With increased CA mixing ratio, the CP dietary content, intake amounts, and apparent digestibility of CP increased. The intake and apparent digestibility of DM, rumen ammonia, and VFA, and the proportion of > 1.0 mm-sized particles, were higher in MT1 than in MT2 and MT3, indicating that MT1 was a good option as goat feed.