Date Published: May 23, 2018
Publisher: Springer Berlin Heidelberg
Author(s): Asmaa T. Y. Kishawy, Shimaa A. Amer, Ali Osman, Shafika A. M. Elsayed, Mohamed E. Abd El-Hack, Ayman A. Swelum, Hani Ba-Awadh, Islam M. Saadeldin.
The present study evaluated the impact of supplementing the rabbit diet with graded levels of whey powder and citric acid. The dietary treatments were as follows: T1, control diet (basal diet); T2, basal diet + 10 g/kg citric acid; T3, T2 + whey powder (7.5 g/kg); T4, T2 + whey powder (15 g/kg); and T5, T2 + whey powder (22.5 g/kg). Results, the T5 diet resulted in the best (P < 0.05) final body weight, body weight gain, feed conversion ratio, protein efficiency, relative growth rate, and dressed weight. The best (P < 0.05) digestion coefficients were associated with the T4 and T5 diets. Rabbits fed diets supplemented with citric acid alone or with addition of graded levels of whey powder showed significantly lower (P < 0.05) intestinal pH than those fed the T1 diet. The T4 and T5 diets resulted in greater CP and ash in the thigh muscle compared with the T1 and T2 diets. Calcium content in the femur bone was higher (P < 0.05) in the T5 group followed by T4 and T3. The wall of different parts of the small intestine improved in the T4 and T5 groups, showing the greatest increase in the small intestinal villi, intestinal glands, and amount of goblet cells. In conclusion, addition of whey powder (1.5, and 2.25%) increased the growth performance, nutrient digestibility and crude protein content of the thigh muscle, and improved the gut health of growing rabbits and the best level was 2.25% whey powder. Citric acid addition had no positive effect on growth performance, nutrient digestibility, crude protein content of the thigh muscle, and the gut health.
Shortage of feed materials with high nutritive value for animal feed has motivated most nutritionists to search for new low-cost and nutritious materials. Whey is a by-product of cheese manufacturing that has high nutritional value and could be used in animal feeding (Rastad 2008). Whey protein is of high biological value containing a reasonable amount of essential amino acids, which rapidly increase plasma amino acids level to improve protein function in the body (Hayes and Cribb 2008). In particular, whey protein contains branched-chain amino acids, especially leucine, which act as modulators in muscle protein metabolism and as key regulators in the initiation translation pathway of muscle protein (Norton and Layman 2006). Whey powder contains approximately 65% lactose that will enhance the growth of lactic acid bacteria (natural probiotics) in the intestinal tract of the animal. In addition, the presence of β-lacto globulin and α-lactalbumin in whey proteins can enhance the immune system of animals and prolong their survival (Shariatmadari and Forbes 2005). Whey protein concentrate has a growth-promoting action in broiler chicks and induces favorable changes in intestinal tract metabolism (Szczurek et al. 2013). Whey powder also contains some traces of organic acids such as lactic acid and citric acid (Tsakali 2010).
The availability of low-cost raw materials for animal feed with high feed efficiency is a major target of nutritionists and animal producers. Whey is a by-product of the cheese industry, which is economical and has a high nutritive value (Fallah 2016). There are limited researches on application of whey on rabbit diets. Our results revealed that addition of citric acid (1%) to the basal diet didn’t cause significant improvement in the growth performance compared with the control group. Addition of whey powder (1.5, and 2.25%) to the basal diet along with citric acid led to significant improvement in BW, BWG, FCR, PER and RGR and the level 2.25% whey powder is better than 1.5%. This improvement in growth performance may be attributed to significant increase in the digestibility of crude protein, fat, crude fiber as well as well-developed intestinal glands and an increase in the number of goblet cells in groups T4 and T5 due to the higher contents of whey, which contain peptides and amino acids. Gilbert et al. (2008) reported that nutrient digestibility in broiler chicken improved because of an increase in the number of peptides, amino acids, and glucose transporters, as well as promoted enzyme production. These findings are in agreement with the data of (Fallah 2016), who reported that supplementation of a chicken diet with different levels of dried whey and protexin probiotic improved the body weight of chickens at 42 days. A similar result was also obtained by Majewska et al. (2009) who found that the addition of undiluted fresh acid whey and lactic acid to drinking liquid twice a week for 4 h improved broiler chicken performance. Malik et al. (2015) further supported these results in that the addition of whey protein at 2, 4, and 6% to broiler feed was found to improve their FCR. These consistent improvements in FCR, body weight, and total gain may be related to the higher digestibility of whey protein and reasonable essential amino acid content of whey protein (Hoffman and Falvo 2004).