اثر جایگزینی سیلاژ ذرت با کاکتوس بی‌خار بر مصرف خوراک، قابلیت هضم مواد مغذی، برخی متابولیت‌های خونی و رفتارهای تغذیه‌ای میش

Introduction: There is an increasing interest in the use of spineless cactus (Opuntia fícus-indica) as fodder for cows, goats, and sheep around the world especially in the arid and semi-arid regions. Cactus withstands water shortage, high temperature, and poor soil fertility, and thus adapted to the arid and semi-arid zones of the world. Cactus is useful not only because it can withstand drought, but also because its conversion efficiency is greater than C3 grasses and C4 broadleaves. Biomass generation per unit of water is on average about three times higher than for C4 plants and five times higher than for C3 plants.
The spineless cactus has low crude protein but it has high levels of non-fiber carbohydrates (Barbera et al 1995). High levels of fermentable energy could support rumen fermentation, thus increasing microbial protein synthesis, the production of volatile fatty acids, and the subsequent nutrients supply for the host animal. Data on spineless cactus nutritive value and digestibility is scarce. Furthermore, no data is available regarding the feeding behavior of individual ewes fed diets containing spineless cactus. The objective of this study was to investigate the effects of partial replacement of corn silage by spineless cactus on feed intake, nutrient digestibility, blood metabolite, and feeding behavior of ewes.
Material and methods: A total of 21 Arabian ewes (37.1±1 kg live weight) were used in a completely randomized design with three treatments for 30 days. Experimental diets included control, diets containing 10 and 20% spineless cactus. Ewes were housed individually in pens (1.3 m×1.5 m) in an open shed building and were allowed ad libitum access to feed and water throughout the trial. All diets contained 60% forage (wheat straw, corn silage, and spineless cactus) and 40% concentrate (60: 40; forage: concentrate). The chemical composition of the spineless cactus is presented in Table 1. The ingredients and chemical composition of the rations fed to ewes are shown in Table 2. The ewes were fed the total mixed rations ad libitum twice daily at 0800 h and 1600 h and had free access to fresh water at all times. Feed offered and refusal of each lamb were recorded daily. Digestibility was measured by the total collection of feces during a 5-d period. Samples of ruminal fluid were collected from each ewe 3 h post-feeding using a stomach tube attached to an Erlenmeyer flask and vacuum pump. The first 50 ml of collected rumen fluid was discarded to avoid saliva contamination. The remaining was filtered through four layers of cheesecloth. Rumen fluid pH was measured using a portable pH meter. Blood samples were taken from each lamb at the same time as ruminal fluid sampling by venipuncture of the jugular vein in 10-mL tubes treated with sodium heparin. Samples were centrifuged in a refrigerated centrifuge at 850 × g for 30 min within 30 min of sampling, and the plasma was frozen at −20 °C until used. Behavioral parameters were monitored by direct observations of all ewes over the total time (min) devoted to each monitored behavior. Ewes were observed every 5 min by scan sampling, and the observer recorded the event of the behaviors. Chewing behavior was divided into eating and ruminating. An observation was defined as eating when the animal had its head in the feed bunk or was chewing or swallowing food with its head over it. Ruminating included regurgitation, mastication, and swallowing of the bolus. Activity was recorded as drinking when the lamb had his mouth in the water bowl or was swallowing the water. Self-grooming was defined as non-stereotyped licking of the body or scratching with a hind limb. Social behavior was registered when a lamb was licking or nosing a neighboring animal with the muzzle or horning. Oral behaviors included the act of licking or biting the fixtures. Resting was recorded as occurring when no chewing behavior and no apparent activity were being performed.
Data were analyzed using a MIXED procedure of SAS 9.2 (SAS Institute, Inc., Cary, NC) based on the statistical model Yij = μ + Ti+eij, where Yij was the observation, μ the general mean, Ti the effect of treatments and eij the residual effect. Comparisons between treatments were completed with Tukey’s test. Treatment effects were declared significant at P≤0.05.
Results and discussion: The intake of dry matter, organic matter, and neutral detergent fiber were higher in the control group as compared with the 20% cactus group (P <0.05). The decrease in total DMI with the increase in the proportion of cactus may be explained by the high moisture content of cactus occupying a considerable volume in the rumen, leading subsequently to limited DMI (Gebremariam et al 2006). Also, forages with high ash contents have poor DMI due to their mineral effect on rumen microbes (Ben salem et al 1996).
In the diet containing 20% cactus, the apparent digestibility of organic matter was increased compared to the control (P <0.05). Ammonia nitrogen concentration, rumen pH, and protozoa population in the rumen showed a significant increase in the treatment containing 20% cactus compared to the control (P <0.05). The increase in ruminal pH with an increase in the proportion of cactus in the diet may be explained by its high content of minerals (Barbera et al 1995). An increase in rumen ammonia concentration with increased cactus inclusion rate could be attributed to the higher degradability of protein content in spineless cactus (Batista et al 2003). Blood cholesterol concentration was lower in the treatments containing 10% cactus (P <0.05). Time spent eating per gram of dry matter consumed was higher in cactus-fed sheep than in control. In the cactus-containing diets, the rate of feed intake and amount of feed consumed decreased compared to the control group (P <0.05). Sheep fed diet containing 20% cactus spent a shorter time ruminating compared to the control group.
Conclusion: The results of this study showed that using 20% spineless cactus in the diet replacing corn silage could decrease dry matter intake and rumination time and increase rumen pH. Spineless cactus inclusion in the diet increased organic matter digestibility. Spineless cactus is thus recommended as part of the ewes’ diet, up to 10 percent, in Iran's arid and semiarid regions.