Effect of using potato crop residues in supplementary feeding on the economic traits of pregnant ewes

Introduction: Large parts of Iran have a dry and semi-arid climate, which is why opportunities for fodder production in the country are limited. Providing feed from agricultural by-products, including potato vines, can be considered a suitable option to compensate for the limitations of traditional feed (e.g. alfalfa). Ardabil province has about 15-20% of the country's potato cultivation area, and with the annual production of about 800 thousand tons of potato tubers, it ranks second in the country. Therefore, there is great potential in this province to produce by-products related to potatoes. The present study was conducted to investigate the possibility and effect of replacing potato vines with regular forage in the diet of pregnant sheep (during the last 45 days of pregnancy). Materials and methods: In the first step of this research, the chemical compositions of alfalfa hay and potato vine including dry matter, organic matter, ash, crude protein, crude fat, neutral detergent fiber (NDF), and acid detergent fiber (ADF) were determined. In the next phase, 210 pregnant Moghani sheep were randomly assigned to seven treatments with three replicates and 10 sheep per replicate. In addition to the control treatment (pasture feeding), six treatments with different levels of potato vine (zero, 16, and 32%) were used in two food forms, mash and complete block. The mentioned diets were given to the animals in the last 45 days of pregnancy in the amount of 500 grams during the night feeding time. It should be noted that lactating ewes were not subjected to any treatment after lambing and the effect of an additional feeding period on milk production was examined after three months of lambing. Results and discussion: According to the results obtained, the percentage of dry matter, crude protein, crude fat, gross energy, and ADF in potato vine was not significantly different from alfalfa feed, but the NDF percentage in potato vine was lower than alfalfa and its ash content was more than alfalfa (P<0.05). No significant difference was observed in the amount of dry matter digestibility (DMD) and dry organic matter digestibility (DOMD) between the potato vine and alfalfa hay. Ewe weight gain during the supplementary feeding period was influenced by different treatments (P<0.05). A similar pattern was observed for other traits such as ewe weight after lambing, birth weight of lambs, weight gain before weaning, and, weaning weight of lambs. In the current study, the examined traits in sheep that were fed with complete block showed better performance compared to sheep fed with mash. In this feeding method, animals are not able to choose due to the uniform composition of food, which leads to a uniform effect on the rumen and thus reduces the fluctuation in ammonia release for more efficient use of non-protein nitrogen. Complete block feeding is an efficient method to increase voluntary feed intake in ruminants. It also improves nutrient utilization by stabilizing fermentation in the rumen. The increase in birth and weaning weight in lambs whose mothers were fed complete block diets showed that the use of supplementary feeding in the last weeks of gestation of ewes, when carried out appropriately, leads to improvement in fetal growth and proper development of the mammary gland, and increase in birth weight of the lamb and milk production. The different treatments have a significant impact on the amount of milk production so that the average daily milk production throughout the lactation period was lowest in the control treatment (without using any nutritional supplements) and highest in the block feeding treatment at 16% Potato vine. The results showed that using the complete block produced a higher profit compared to the mash. Conclusions: Based on the results of the present research, the use of 16% potato vine as a replacement for part of the usual fodder in the form of a complete feed block resulted in profitability in the nomadic sheep farming system. Given the cheap price and availability compared to alfalfa fodder and wheat straw, especially in drought conditions and poor pastures, its consumption is economical.