Effects of protein sources for milk replacers on growth performance and serum biochemical indexes of suckling calves

摘要

Abstract This study investigated the effects of protein sources for milk replacers on growth performance and serum biochemical indexes of suckling calves. Fifty Chinese Holstein bull calves with similar BW and age were randomly allocated to 5 groups (1 control and 4 treatments) of 10 calves in each group. Five types of milk replacers were designed to have the same level of energy and protein. The protein source?for milk replacers of the control group was full milk protein (MP). The protein source?of milk replacers of the 4 treatment groups was composed of MP and one vegetable protein (VP) (30 and 70% of total protein). The 4 types of VP were soybean protein concentrate (SP), hydrolyzed wheat protein (WP), peanut protein concentrate (PP), and rice protein isolate (RP). Results of the experiment showed: 1) there was no significant difference on average daily gain (ADG) and feed:gain ratio (F:G) among the MP, SP and RP groups ( P >?0.05), whereas the ADG and F:G of the WP and PP groups were significantly lower compared with the MP group ( P ?0.05). Thereby the 4 VP milk replacers had no adverse effects on body size of calves; 3) all groups showed no significant difference in the serum contents of urea nitrogen, total protein, albumin, globulin, β-hydroxybutyrate, growth hormone, insulin-like growth factor-1, and the ratio of albumin to globulin (A:G) ( P >?0.05). In conclusion, SP or RP (accounts for 70% of the total protein) as calf milk replacers could substitute MP, whereas wheat gluten and PP had a significant adverse effect on growth performance in this experiment. Keywords Calf ; Growth performance ; Milk replacer ; Milk protein replacement ; Serum biochemical parameters ; Vegetable protein prs.rt("abs_end"); 1. Introduction Using milk replacers to feed early-weaned calves is an effective way to raise replacement cattle in modern dairy industry ( Heinrichs, 1993 ). Protein is one of the most important nutrients in milk replacers, and choosing appropriate protein sources becomes an important factor affecting feedstuff quality and animal production costs ( Erickson et?al., 1989 ). Protein sources usually used as milk replacers fall into two types: milk protein (MP) and non-milk protein. Milk protein is an excellent protein source as a milk replacer because it has balanced amino acid constituents, a low level of anti-nutritional factors, and a high digestibility value. However, China has a relative shortage of MP source as a result of a high demand for dairy products, which keeps MP price high. Research has showed soybean protein as a protein source for milk replacers to be comparable to MP on growth performance of suckling calves ( Lalles et?al., 1995 , Tomkins et?al., 1994a and Tomkins et?al., 1994b . Furthermore, the nutritional value of vegetable proteins (VP) from wheat, peanut and rice is similar to that of soybean protein, and China produces considerable amounts of these crops. Thus, exploring the potential of these VP will open up novel sources of milk replacers. Studies on protein sources for milk replacers in the past focused mainly on adding low levels of soybean protein (replacement level lower than 50% crude protein). Using high levels of VP as milk replacers (replacement level higher than 50%) has rarely been reported. This study tested 4 types of VP as main protein sources of milk replacers with the main essential amino acids in relative balance. Growth performance and serum biochemical indexes of suckling calves were studied. 2. Materials and methods 2.1. Experimental animals The experiment was conducted at Zhuochen Livestock Co. Ltd., Beijing. Fifty Holstein bull calves (21?±?6?d, 46?±?6?kg) with similar age and BW were selected and randomly allocated to 5 groups of 10 calves per group. 2.2. Experiment design and diets In this experiment, a single-factor completely randomized design was used to study the effects of different VP sources on calves. These VP sources were soybean protein concentrate (SP), hydrolyzed wheat protein (WP), peanut protein concentrate (PP), and rice protein isolate (RP). Five milk replacers were formulated using 30% MP and 70% VP. The milk replacers used in this experiment had the same CP (22%), GE (19.66?MJ/kg), Lys (1.84%), and Lys:Met:Thr:Trp ratio (100:29.5:65:20.5). The amino acid levels of the milk replacers were adjusted by adding crystalline amino acids to the basal ration. Calves in the controlled group (MP) were fed a full MP milk replacer. Calves in treatment groups were fed 4 types of VP milk replacers, which were derived from SP (CP?=?65.2%), WP (CP?=?77.8%), PP (CP?=?54.7%) and RP (CP?=?82.0%). All calves in this experiment were fed the same starter up to 42 days of age. The nutrient levels and composition of milk replacers and starter in this experiment are shown in Table?1 and Table 2 . Table?1. Nutrient composition (%) of milk replacers (air dry matter basis). 1 Item Milk replacers MP SP WP PP RP DM 96.26 95.50 95.75 95.46 96.36 CP 22.71