The effect of Cactus-alfalfa mixed silage on sheep feed intake, nutrients digestibility, microbial protein synthesis, rumen and blood parameters

Drought have had adverse effects on the animal husbandry industry and has caused a decrease in livestock population and performance. In this regard, changing the cultivation pattern and replacing water-resistant species can be a suitable solution for this problem. However, due to low protein and dry matter (DM), animals fed exclusively with cactus pear may show weight loss, and digestive disorders such as diarrhea. Combining cactus, which is high in soluble sugars, with high fiber and raw protein ingredients could complement each other's weaknesses and form a balanced diet. Therefore, this study aimed to investigate the effect of feeding different levels of cactus-alfalfa mixed silage on nutrient digestibility, rumen fermentation, and blood parameters.

The silage was prepared from a homogeneous blender of 66% fresh spineless cactus (Opuntia ficus indica) and 34% alfalfa hay on a w/w basis using 220 L plastic gallons. The chemical composition and quality of the ensiled material were determined. The samples were taken to determine the chemical composition after ensiling on day 45. In this experiment, four Kermani male sheep were used in a change-over design with four periods of 21 days. Experimental treatments were based on increasing levels of cactus-alfalfa mixed silage (0, 10, 20, and 30% DM). During the week of sampling the amount of feed offered and leftovers were collected and weighed daily before the morning feeding to measure daily feed intake (on a DM basis) and digestibility of nutrients. On the last day of each period at 0, 2, 4, 6, and 8 h after morning feeding, rumen fluid was sampled from sheep (by esophagus tube and was filtered through three layers of cheesecloth) to determine pH, ammonia nitrogen (NH3-N), and volatile fatty acid (VFA). Blood samples were collected on the four days of each period and three h after morning feeding in 10 ml. To determine the amount of allantoin and microbial protein synthesis, the daily urine produced during 24 hours was collected.

The gas production volume (ml) was a significant difference among experimental diets (P<0.05). Fat and neutral detergent fiber (NDF) digestibility increased when animals were fed 30% cactus-alfalfa mixed silage than those fed 10% and 20% cactus-alfalfa mixed silage and control diet (P<0.05). Also, there was a quadratic effect on DM, organic matter (OM), and acid detergent fiber (ADF) digestibility by feeding different levels of cactus-alfalfa mixed silage (P<0.05). The highest concentration of ruminal NH3-N was observed by an experimental diet containing 30% cactus-alfalfa mixed silage in all sampling occasions (P<0.05). Feeding of 20% and 30% of cactus-alfalfa mixed silage than after treatments increased linearly ruminal propionic acid molar and decreased linearly acetic acid and acetate/propionate ratio (P<0.05). There was a significant effect on concentrations of triglyceride and urea-nitrogen by adding different levels of cactus-alfalfa mixed silage (P<0.05). Blood Urea nitrogen level in sheep-fed cactus-alfalfa mixed silage was significantly increased linearly (P<0.05).

The results of this study indicated that cactus-alfalfa mixed silage has appropriate nutritional value and its inclusion up to 30% on DM basis in the diets provided favorable conditions for ruminal function and digestibility. Therefore, it is recommended, cactus-alfalfa mixed silage could be included in livestock diet during drought or feedstuff shortage especially in arid and semi-arid regions.